CN1981356A - Field emission device containing heterodiamond - Google Patents

Abstract

The present invention discloses a novel Field Emission Device (FED) containing heterodiamondoids. In one embodiment of the invention, the hetero-diamond-like heteroatoms comprise electron-donating species (e.g., nitrogen) as a component of a cathode or electron-emitting element of the field emission device.

Description

Field Emission Devices Containing Heterogeneous Diamond

Background of the invention

field of invention

Embodiments of the present invention generally relate to new uses of heterodiamondoids and heterodiamondoid-containing materials in field emission devices. Specifically, the heteroatoms of the heterodiamondoids of embodiments of the present invention are electron donor species, and the field emission device (FED) contains a cold cathode that emits electrons.

current technology

Carbonaceous materials have many possible uses in microelectronics. As an element, carbon has many different structures, some crystalline, some amorphous, some with regions of both forms, but each form has a unique and potentially useful set of properties.

S. Prawer provides a review of the structure-property relationship of carbon in the chapter titled "The Wonderful World of Carbon" in Physics of Novel Materials (world Scientific, Singapore, 1999), pp.205-234 . Prawer suggested that the two most important parameters that can be used to predict the properties of carbonaceous materials are: first, the ratio of sp ² to sp ³ bonds in a material, and second, the microstructure, including the crystallographic Size, that is, the size of its individual grains.

Carbon has an electronic structure of 1s ² 2s ² 2p ² , in which the outer 2s and 2p electrons have the ability to hybridize according to two different processes. The so-called sp ³ hybridization includes four identical σ bonds arranged in a tetrahedral manner. The so-called sp ² hybridization consists of three triangular (also planar) σ bonds, the unhybridized p-electrons occupying the π orbitals of the bonds oriented perpendicular to the plane of the σ bonds. The "extreme" crystalline forms are diamond and graphite. In diamond, the carbon atoms are ^sp3 hybridized and bonded tetrahedrally. Graphite consists of planar "sheets" of ^sp2 hybridized atoms, where the sheets interact weakly through vertically oriented π bonds. Carbon also exists in other forms, including an amorphous form called "diamond-like carbon," and highly symmetrical spherical and rod-shaped structures called "fullerenes" and "nanotubes," respectively.

Diamond is a special material because it scores the highest (or lowest, depending on one's point of view) in many different classes of properties. Not only is it the hardest known material, it also has the highest thermal conductivity of any material at room temperature. It has excellent optical transparency from the infrared to the ultraviolet, has the highest refractive index of any transparent material, and is an excellent electrical insulator because of its wide bandgap. It also has high electrical breakdown strength, and high electron and hole mobility. If diamond has a drawback as a material for microelectronics, it is that, while diamond can be efficiently doped with boron to make p-type semiconductors, efforts to make n-type semiconductors by implanting electron-donating elements such as phosphorus into diamond (according to the present invention known) is far from successful.

Attempts to synthesize diamond films using chemical vapor deposition (CVD) techniques date back to about the early 1980s. The result of these attempts has been the emergence of new forms of carbon that are largely amorphous in nature but contain a high degree of ^sp hybridization and thus exhibit many of the properties of diamond. To describe such films, the term "diamond-like carbon" (DLC) was coined, although this term is not precisely defined in the literature. In "The Wonderful World of Carbon", Prawer states that since most diamond-like materials display a mixture of bond types, the proportion of carbon atoms that are quadruple coordinated (or sp ³ hybridized) is the stated A measure of the "diamond-like" content of a material. Unhybridized p-electrons associated with sp ^{hybridization} form pi-bonds in these materials, where the pi-bonded electrons are predominantly delocalized. This leads to increased electrical conductivity of materials with sp ² bonds such as graphite. In contrast, sp ^{hybridization} leads to the extremely hard, electrically insulating and transparent diamond properties. The hydrogen content of a diamond-like material is directly related to the types of bonds it has. In diamond-like materials, the band gap becomes larger and the hardness often decreases as the hydrogen content increases. Not surprisingly, loss of hydrogen from diamond-like carbon films leads to increased electrical conductivity and loss of other diamond-like properties.

Nevertheless, it is generally accepted that the term "diamond-like carbon" can be used to describe two different classes of amorphous carbon films, one denoted "a:CH" because hydrogen originates at the surface of the film The second hydrogen-free variant is called "ta-C" because most of the carbon atoms are tetrahedrally coordinated with sp ³ hybridization. The remaining carbon atoms of ta-C are essentially sp ^hybridized surface atoms. In a:CH, the dangling bonds can relax to the sp ² (graphite) configuration. The role of hydrogen in a:CH is to prevent untermianted carbon atoms from relaxing into a graphitic structure. The greater the sp ³ content, the more "diamond-like" the properties of the material, such as thermal conductivity and electrical resistance.

In his review article, Prawer states that tetrahedral amorphous carbon (ta-C) is a random network that exhibits order localized to one or two nearest neighbors within short distances rather than over long distances. state. There may be random carbon networks that may contain 3, 4, 5 and 6 membered carbon rings. Typically, the maximum sp ^content of ta-C films is about 80 to 90%. Those carbon atoms that are sp ² bonded tend to gather into small clusters, which prevent the formation of dangling bonds. The performance of ta-C mainly depends on the fraction of atoms with sp ³ or diamond-like configuration. Unlike CVD diamond, there is no hydrogen in ta-C to passivate the surface and prevent the formation of graphite-like structures. The fact that the formation of graphitic regions was not observed is due to the presence of isolated sp ² bonding pairs and the compressive stresses developed within the bulk of the material.

The microstructure of the diamond and/or diamond-like material further determines its properties to a certain extent, since the microstructure affects the content of bond types. As in "Microstructure and grain boundaries of ultrananocrystalline diamond films (microstructure and grain boundaries of ultrananocrystalline diamond films)" by D.M.Gruen, in Properties, Growth and Applications of Diamond (diamond properties, growth and applications), edited by As discussed in M.H.Nazare and A.J.Neves (Inspec, London, 2001), pp.307-312, recent efforts have been made to synthesize diamonds with crystallite sizes in the "nano" range rather than the "micro" range , the resulting grain boundary chemistry may differ significantly from that observed in the bulk. Nanocrystalline diamond films have grain sizes in the range of 3 to 5 nanometers, and it has been reported that nearly 10% of the carbon atoms in nanocrystalline diamond films are located on grain boundaries.

In the Gruen chapter, nanocrystalline diamond grain boundaries are reported to be high energy, high angle twisted grain boundaries where the carbon atoms are predominantly π-bonded. There may also be sp ² bonded dimers, and segments with sp ³ hybridized dangling bonds. Nanocrystalline diamond is apparently conductive, and it appears that grain boundaries are responsible for the conductivity. According to the authors, nanocrystalline materials are essentially new types of diamond films whose properties are primarily determined by the bonding of carbon within the grain boundaries.

MS Dresslehaus et al. discuss in the chapter titled "Nanotechnology and Carbon materials (nanotechnology and carbon materials)" in Nanotechnology (Nanotechnology) (Springer-Verlag, New York, 1999).pp.285-329. Another allotrope of carbon from fullerenes (and their counterparts, carbon nanotubes). Although only recently discovered, these materials already play a potential role in microelectronic applications. Fullerenes have an even number of carbon atoms arranged in the form of closed hollow cages in which carbon-carbon bonds on the surfaces of the cages define a polyhedral structure. The most abundant fullerenes are _C60 molecules, although _C70 and _C80 fullerenes are also possible. Each carbon atom in C ₆₀ fullerene adopts sp ² hybridization to form a triangle bond with three other carbon atoms.

Dresslehaus describes _C60 fullerenes as "rolled up" graphine sheets (where the term "graphite" refers to a single layer of crystalline graphite) forming closed shells. Twenty of the 32 faces on a regular truncated icosahedron are hexagonal, and the remaining 12 are pentagonal. Each carbon atom in C ₆₀ fullerene is in an equal lattice position, although the three bonds extending from each atom are not equal. The four valence electrons of each carbon atom are contained in covalent bonds, so two of the three bonds on the perimeter of the pentagon are electron-poor single bonds, while the one between the two hexagons The bonds are electron-rich double bonds. Fullerenes such as _C60 are also stabilized by the Kekule structure of alternating single and double bonds along the hexagonal surface.

Dresslehaus et al. further teach that, electronically speaking, the _C60 fullerene molecule has 60 π-electrons, one π-electron state per carbon atom. Since the highest occupied molecular orbital is fully occupied while the lowest unoccupied molecular orbital is completely empty, _C60 fullerenes are considered to be semiconductors with very high resistivity. When aggregated into a solid, fullerene molecules display weak van der Waals cohesive interactions with each other.

The following table summarizes some properties of diamond, DLC (both ta-C and a:C-H), graphite and fullerene:

performance Diamond ta-C a: C-H Graphite C ₆₀ Fullerene C-C bond length (nm) 0.154 ≈0.152 0.141 Pentagon: 0.146 Hexagon: 0.140 Density (g/cm ³ ) 3.51 ＞3 0.9-2.2 2.27 1.72 Hardness (Gpa) 100 ＞40 ＜60 soft Vander Waals Thermal conductivity (W/mK) 2000 100-700 10 0.4 Bandgap (eV) 5.45 ≈3 0.8-4.0 Metallicity 1.7 Resistivity (Ωcm) >10 ¹⁶ 10 ¹⁰ 10 ² -10 ¹² 10 ^-3 -1 >10 ⁸ Refractive index 2.4 2-3 1.8-2.4 - -

The data in this table are from page 290 of the above-cited Dresslehaus et al. document, page 221 of the above-cited Prawer document, A. Erdemir et al. in "Tribology of Diamond, Diamond-Like Carbon, and Related Films," in Modern Tribology Handbook , Vol. Two, B. Bhushan, Ed. (CRC Press, Boca Raton, 2001) 891 pages chapter, and W. Kulisch, "Deposition of Diamond-Like Superhard Materials" (Springer Verlag, New York, 1999) 28 pages to compile .

One form of carbon that is not widely discussed in the literature is "diamondoids". Diamondoids are bridged ring cycloalkanes, including adamantane, diamantane (diamantane), triamantane (triamantane) and adamantane (tricyclic [3.3.1.1 ^3,7 ] decane) tetramer, pentamer , hexamer, heptamer, octamer, nonamer, decamer, etc. (adamantane has the stoichiometric formula C ₁₀ H ₁₆ ), wherein individual adamantane units are face-fused to form larger structures. These adamantane units are essentially diamond-like subunits. Said compounds have a "diamond-like" topology, since their arrangement of carbon atoms can be superimposed on segments of the FCC (face centered cubic) diamond lattice.

Diamond-like carbons are a very unusual form of carbon because although they are hydrocarbons with molecular sizes typically in the range of about 0.2 to 20 nm (averaged in all directions), they simultaneously exhibit the electronic properties of ultrananocrystalline diamond. As hydrocarbons, they can self-assemble into van der Waals solids, possibly in repeating arrays of individual diamondoids assembled in specific orientations. The solidity results from cohesive dispersive forces between adjacent _CHx groups, which are more commonly found in n-alkanes.

In diamond nanocrystallites, the carbon atoms are completely sp ³ hybridized, but due to the small size of diamondoids, only a small fraction of the carbon atoms are exclusively bonded to other carbon atoms. Most have at least one hydrogen closest to the adjacent carbon. Thus, most of the carbon atoms of diamondoid occupy surface sites (or near surface sites), resulting in electronic states that are energetically distinct from bulk energy states. Therefore, diamond-like carbons can be expected to have unusual electronic properties.

As far as the inventors know, adamantanes, substituted adamantanes and possibly diamantanes are the only readily available diamondoids. Certain diamantanes, substituted diamantanes, ternamantanes and substituted rimamantanes have been investigated and only one diamantane has been synthesized. The remaining diamondoids are provided for the first time by the present inventors and disclosed in their co-pending U.S. provisional patent applications 60/262842, filed January 19, 2001; 60/300148, filed June 21, 2001; 60/307063, filed July 20, 2001; 60/312563, filed August 15, 2001; 60/317546, filed September 5, 2001; 60/323883, filed September 20, 2001 60/334929, filed December 4, 2001; and 60/334938, filed December 4, 2001, which are hereby incorporated by reference in their entirety. Applicants also incorporate by reference their non-provisional applications, filed December 12, 2001 sharing these titles, in their entireties. The diamondoids that are the subject of these co-pending applications have not been available for study in the past, and to the best of the inventors' knowledge, they have never before been used as cathodes for emitting electrons in field emission devices.

Brief description of the invention

Embodiments of the present invention generally relate to novel uses of heterodiamondoids and heterodiamondoid-containing materials in field emission devices. Specifically, the heteroatoms of the heterodiamondoids of the embodiments of the present invention are electron-donating species, and the field emission device (FED) contains a cathode that emits electrons. As used herein, the term "heterodiamondoid" refers to a diamondoid that contains heteroatoms that typically take substitutional positions in the crystal lattice of the diamond crystal structure. Heteroatoms are atoms other than carbon and, according to embodiments of the present invention, may be nitrogen, phosphorus, boron, aluminum, lithium, and arsenic. "Substituted" means that a heteroatom replaces the carbon host in the diamond lattice.

Exemplary methods of preparing n-type materials from heterodiamondoid compounds include CVD techniques, polymerization techniques, crystallization of heterodiamondoids themselves or heterodiamondoids together with other materials, and the use of diamondoids and/or heterodiamondoids at the molecular level. diamond.

According to embodiments of the present invention, heterodiamondoid or heterodiamondoid-containing materials are used as cathode filaments in field emission devices suitable for use in, among other things, flat panel displays. The unique properties of heteroatom-containing diamondoids make this possible. These properties include electron-donating species that donate electrons to the conduction band of the filament material, the negative electron affinity of the hydrogenated diamond surface, and the small size and predictable structure typical of heterodiamondoid compounds. Heterodiamondoids can be derivatized or underivatized, and can be derived from lower diamondoids (adamantane, diamantane, and triamantane), higher diamondoids (tetraadamantane and higher) and/or their derivatives. combination. The filament material (where the term "filament" is used interchangeably with the term "cathode") may be in film or fiber form. The heterodiamondoid-containing material is selected from the group consisting of heterodiamondoid-containing polymers, heterodiamondoid-containing CVD films and heterodiamondoid-containing molecular crystals. In an embodiment of the invention, the cathode has an electron affinity of less than about 3 eV, and the electron affinity can be negative.

Brief description of the drawings

Figure 1 is an overview of an embodiment of the present invention illustrating the isolation of diamondoids from petroleum, the synthesis of heterodiamondoids, the preparation of n-type materials therefrom, and the subsequent fabrication of field emission devices (FEDs) based on said heterodiamondoid-containing materials. )A step of;

Figure 2 shows an exemplary process flow for isolating diamond-like carbon from petroleum;

Figure 3 illustrates the relationship of diamondoids to the diamond lattice and enumerates many available diamondoids by stoichiometry;

Figures 4A-B illustrate exemplary locations of electron-donating heteroatoms on the carbon atom lattice sites of two exemplary diamondoids;

Figure 5A-B illustrates an exemplary route for the synthetic preparation of nitrogen-containing heterodiamondoids;

Figure 6 illustrates an exemplary processing reactor in which n-type heterodiamondoid materials can be produced using chemical vapor deposition (CVD) techniques;

7A-C illustrate an exemplary method by which heterodiamondoids can be used to introduce dopant impurity atoms into grown diamond films;

Figure 8 is an exemplary reaction scheme for the synthesis of polymers from heterodiamondoids;

Figures 9A-N show exemplary linking groups that can be conductive and can be used to link heterodiamondoids to make n-type materials;

Figure 10 shows an exemplary n-type material prepared from heterodiamondoids linked by polyaniline oligomers;

Figure 11 shows how [1(2,3)4]pentamantane stacks to form molecular crystals;

Figure 12 shows how individual heterodiamondoids are coupled at the molecular level to form n-type heterodiamondoid clusters, where such clusters may also contain p-type heterodiamondoids; and

13 is a schematic cross-sectional view of an exemplary field emission device in which a single heterodiamondoid or a heterodiamondoid-containing material can be used as the cathode filament component of the device.

Detailed Description of the Invention

The present disclosure will be organized as follows: First, a definition of diamondoid and heterodiamondoid will be given, followed by a description of how diamondoid is isolated from petroleum feedstock. Then, an exemplary method for the synthesis of electron-donating heterodiamondoids is given, followed by how to prepare n-type heterodiamondoid materials from electron-donating heterodiamondoids. After this, the properties of n-type diamond will be briefly discussed, and how these properties are envisioned to be relevant to field emission devices containing heterodiamondoids. The disclosure will conclude with examples of the actual synthesis of certain nitrogen-containing heterodiamondoids.

Definition of Miscellaneous Diamond

The term "diamondoid" refers to substituted and unsubstituted cage compounds of the adamantane series. "Lower diamondoids" are defined as adamantanes, diamantanes and triamantanes, including substituted and unsubstituted compounds thereof. "Advanced diamondoids" are defined to include tetramantane, pentamantane, hexamantane, heptamantane, octamantane, nonamantane, decamantane, undecamantane, etc., including all their isomers and stereoisomers. The compounds have a "diamond-like" topology, meaning that their arrangement of carbon atoms superimposes on segments of the FCC diamond lattice. The substituted diamondoids comprise 1 to 10, preferably 1 to 4 independently selected alkyl substituents.

Adamantane chemistry has been reviewed by Fort, Jr. et al. in "Adamantane: Consequences of the Diamondoid Structure", Chem. Rev. vol. 64, pp. 277-300 (1964). Adamantane is the smallest member of the diamondoid family and can be viewed as a clathrate crystalline subunit. Diamantane contains two subunits, triamantane contains three subunits, tetraamantane contains four subunits, and so on. Although adamantane, diamantane, and triamantane have only one isomeric form, there are four different tetramantane isomers (two of which represent an enantiomeric pair), i.e., the arrangement of the four adamantane Four different possible ways of an alkane subunit. The number of possible isomers increases non-linearly with each higher member of the diamondoid series, ie, pentamantane, hexamantane, heptamantane, octamantane, nonamantane, decamantane, etc.

Commercially available adamantanes have been extensively studied. The studies address several areas such as thermodynamic stability, functionalization and performance of adamantane-containing materials. For example, the following patents discuss materials comprising adamantane subunits: U.S. Patent 3,457,318 teaches the preparation of polymers from alkenyl adamantanes; U.S. Patent 3,832,332 teaches polyamide polymers formed from alkyladamantane diamines; U.S. Patent 5,017,734 discusses the formation of thermally stable resins from adamantane derivatives; and U.S. Patent 6,235,851 reports the synthesis and polymerization of various adamantane derivatives.

In contrast, diamondoid tetraamantanes and higher adamantanes have received less attention in the scientific literature. McKervey et al. in "Synthetic Approaches to Large Diamondoid Hydrocarbons", Tetrahedron, vol. 36, pp. 971-992 (1980) reported the synthesis of trans-tetramantane in low yields using a laborious multi-step process. As far as the inventors know, this is the only advanced diamondoid that has been synthesized so far. Based on mass spectrometry studies, Lin et al. proposed the existence (but not separated) of tetramantane, pentamantane and hexamantane in deep oil formations, reported in "Natural Occurrence of Tetramantane (C ₂₂ H ₂₈ ), Pentamantane (C ₂₆ H ₃₂ ) and Hexamantane (C ₃₀ H ₃₆ ) in a Deep Petroleum Reservoir", Fuel, vol.74(10), pp.1512-1521 (1995). Chen et al. in US Pat. No. 5,414,189 discuss the possible presence of tetramantane and pentamantane in the bottoms material after distillation of a diamond-like feedstock.

The four tetramantane structures are the two enantiomers of iso-tetramantane [1(2)3], trans-tetramantane [121] and ortho-skew-tetramantane [123] , the nomenclature of these diamondoids in parentheses follows the rules established by Balaban et al. in "Systematic Classification and Nomenclature of Diamond Hydrocarbons-I", Tetrahedron vol. 34, pp. 3599-3606 (1978). All four tetramantanes have _the molecular formula _C22H28 (molecular weight 292). There are 10 possible pentamantanes, nine with the formula _C26H32 (molecular weight 344), and of these nine there are three pairs generally represented by [12(1)3], _[ 1234], [1213] Enantiomers, nine enantiomeric pentamantanes are represented by [12(3)4], [1(2,3)4], [1212]. There is also a pentamantane represented by the molecular formula C ₂₅ H ₃₀ (molecular weight 330) [1231].

There are thirty-nine possible structures of hexamantanes, twenty-eight of which have the molecular formula C ₃₀ H ₃₆ (molecular weight 396), and of these twenty-eight six are symmetrical; ten hexamantanes have the molecular formula C ₂₉ H ₃₄ (molecular weight 382), the remaining hexamantane [12312] has the molecular formula C ₂₆ H ₃₀ (molecular weight 342).

Heptamantane has been postulated to exist in 160 possible structures, 85 of which have the molecular formula _C34H40 (molecular weight 448), and of these ₈₅ , seven are achiral and have no enantiomers. Of the remaining heptamantanes, 67 have the formula C ₃₃ H ₃₈ (molecular weight 434), six have the formula C ₃₂ H ₃₆ (molecular weight 420), and the remaining two have the formula C ₃₀ H ₃₄ (molecular weight 394).

Octamantane has 8 adamantane subunits and exists in 5 different molecular weights. Of the octamantanes, 18 have the molecular formula C ₃₄ H ₃₈ (molecular weight 446). Octamantane also has the molecular formulas C ₃₈ H ₄₄ (molecular weight 500); C ₃₇ H ₄₂ (molecular weight 486); C ₃₆ H ₄₀ (molecular weight 472), and C ₃₃ H ₃₆ (molecular weight 432).

Nonamantanes exist in six families of different molecular weights with the following molecular formulas: C ₄₂ H ₄₈ (MW 552), C ₄₁ H ₄₆ (MW 538), C ₄₀ H ₄₄ (MW 524), C ₃₈ H ₄₂ (MW 498) , C ₃₇ H ₄₀ (MW 484) and C ₃₄ H ₃₆ (MW 444).

Decadamantane exists in seven families of different molecular weights. Among the decamantanes, there is a decamantane having the molecular formula C ₃₅ H ₃₆ (molecular weight 456), which is structurally compact compared to other decamantanes. Other decamantanes have molecular formulas: C ₄₆ H ₅₂ (MW 604); C ₄₅ H ₅₀ (MW 590); C ₄₄ H ₄₈ (MW 576); C ₄₂ H ₄₆ (MW 550); C ₄₁ H ₄₄ (MW 550); 536); and C ₃₈ H ₄₀ (molecular weight 496).

Undecademantane exists in eight families of different molecular weights. Among the undecademantanes, there are two undecademantanes having the molecular formula C ₃₉ H ₄₀ (molecular weight 508), which are structurally compact compared with other undecademantanes. The other undecadamantanes have the formula _C41H42 (MW 534); _C42H44 (MW 548 _{); C45H48 (MW 588); C46H50 ( MW 602 ) ; C48H52 (} MW 628); C ₄₉ H ₅₄ (molecular weight 642); and C ₅₀ H ₅₆ (molecular weight 656).

As used herein, the term "heterodiamondoid" refers to a diamondoid that contains heteroatoms that typically take substitutional positions in the crystal lattice of the diamond crystal structure. Heteroatoms are atoms other than carbon and may be nitrogen, phosphorus, boron, aluminum, lithium, and arsenic according to embodiments of the present invention. "Substitutedly located" means that a heteroatom replaces a carbon host atom in the diamond lattice. Although most heteroatoms are substituted, in some cases they can also be found at interstitial positions. Like diamond analogs, heterodiamondoids can be functionalized or derivatized; such compounds can be referred to as substituted heterodiamondoids. In this disclosure, n-type diamondoid generally refers to n-type heterodiamondoid, but in some cases the n-type material may comprise heteroatom-free diamondoid.

Although heteroadamantane (heteroadamantane) and heterodiamantane compounds have been reported in the literature, to the best of the inventors' knowledge, no heterotriamantane or higher compounds have been synthesized before, and there is no report of the use of compounds including heteroadamantane or heterodiadamantane compounds, such as n-type materials as components of field emission devices, as in the case of the cathode of said devices. The present inventors contemplate the use of 1) heteroadamantanes and heterodiamantanes, or 2) heterotriamantanes, or 3) heterotetramantanes and higher compounds as possible materials for cathodes of field emission devices; however , n-type materials containing heterodiamondoids derived from tetramantane and higher compounds are expected to have advantages due to higher carbon-hydrogen ratios (where more carbons are in the quaternary position, where the carbons in the quaternary position are only mixed with other carbons Bond). There may also be mechanical advantages.

Figure 2 shows, in schematic form, a process flow diagram in which diamond-like carbon can be extracted from petroleum feedstocks, and Figure 3 lists the various diamond-like isomers that can be obtained according to embodiments of the present invention.

Isolation of diamond-like carbon from petroleum feedstocks

Feedstocks containing recoverable amounts of advanced diamondoid include, for example, natural gas condensates and refinery streams from cracking, distillation, coking processes, and the like. Particularly preferred feedstocks are derived from the Norphlet Formation in the Gulf of Mexico and the LeDuc Formation in Canada.

These feedstocks contain a large proportion of lower diamondoid (often as much as about two-thirds) and lower but significant amounts of higher diamondoid (often as much as about 0.3 to 0.5 wt%). Processing of these feedstocks to remove non-diamondoids and to separate higher and lower diamondoids (if desired) can be done using, by way of example only, size separation techniques such as membranes, molecular sieves, etc., evaporation and atmospheric or reduced pressure. Thermal separators, extractors, electrostatic separators, crystallization, chromatography, wellhead separators, etc.

A preferred separation method generally involves distillation of the feedstock. This removes low boiling non-diamond-like components. This also allows for the removal or separation of lower and higher diamondoid components having boiling points less than the boiling point of the higher diamondoid selected for separation. In both cases, the lower fraction will be enriched in low-grade DLC and low-boiling non-DLC materials. Distillation can be performed to provide several fractions in the temperature range of interest to provide the initial isolation of the identified higher diamondoids. Fractions enriched in higher diamondoids or diamondoids of interest are retained and may require further purification. Other methods for removing contaminants and further purifying the DLC-rich fraction may also include the following non-limiting examples: size separation techniques, evaporation at atmospheric or reduced pressure, sublimation, crystallization, chromatography, wellhead separators, flash Steam, fixed bed and fluidized bed reactors, decompression, etc.

Removal of non-diamondoids may also include a heat treatment step before or after distillation. The thermal treatment step may comprise a hydrotreating step, a hydrocracking step, a hydroprocessing step or a pyrolysis step. Thermal treatment is an effective method for removing hydrocarbonaceous non-diamond-like components from a feedstock, and pyrolysis, as one embodiment thereof, is by heating the feedstock to at least about 390°C under vacuum conditions or in an inert atmosphere temperature, most preferably to a temperature of about 410 to 450°C. Pyrolysis is conducted at a temperature high enough and for a time sufficient to thermally degrade at least about 10% by weight of the non-diamond-like components present in the feedstock prior to pyrolysis. More preferably at least about 50 wt%, more preferably at least 90 wt% of said non-diamondoid is degraded by heat.

Although pyrolysis is preferred in one embodiment, it is not always necessary to perform pyrolysis to facilitate recovery, isolation or purification of diamondoids. For given certain starting materials, other separation methods can result in diamondoid concentrations high enough that direct purification methods such as chromatography including preparative gas chromatography and high performance liquid chromatography, crystallization, fractional sublimation Can be used to isolate diamond-like carbon.

Even after distillation or pyrolysis/distillation, further purification of the material may be required to provide selected diamondoids suitable for use in compositions employed in the present invention. Such purification techniques include chromatography, crystallization, thermal diffusion techniques, zone refining, progressive recrystallization, size separation, and the like. For example, in one method, the recovered feedstock is subjected to the following additional steps: 1) gravity column chromatography using silver nitrate impregnated silica gel; 2) two-column preparative capillary gas chromatography to separate diamondoids; and/or or 3) crystallization to provide highly concentrated diamond-like crystals.

An alternative approach is to use single or multi-column liquid chromatography, including high performance liquid chromatography, to isolate the diamondoid of interest. As above, multiple columns with different selectivities can be used. Further processing using these methods allows finer separations, which can lead to substantially pure components.

In U.S. Provisional Patent Application 60/262842, filed January 19, 2001; U.S. Provisional Patent Application 60/300148, filed June 21, 2001; and U.S. Provisional Patent Application 60/307063, filed July 2001 20, and co-pending application entitled "Processes for concentrating higher diamondoids" by B. Carlson et al., assigned to the assignee of the present application, set forth detailed methods for processing raw materials to obtain advanced diamond-like carbon compositions. These applications are hereby incorporated by reference in their entirety.

Figure 2 shows, in schematic form, a process flow diagram in which diamond-like carbon can be extracted from petroleum feedstocks, and Figure 3 lists the various diamond-like isomers that can be obtained according to embodiments of the present invention.

Synthesis of heterogeneous diamond

As used herein, the term "heterodiamondoid" refers to a diamondoid that contains heteroatoms that typically take substitutional positions in the crystal lattice of the diamond crystal structure. Heteroatoms are atoms other than carbon and may be nitrogen, phosphorus, boron, aluminum, lithium, and arsenic according to embodiments of the present invention. "Substitutedly located" means that a heteroatom replaces a carbon host atom in the diamond lattice. Although most heteroatoms are substituted, in some cases they can also be found at interstitial positions.

Figure 4 illustrates an exemplary heterodiamondoid, indicating the types of carbon sites in which heteroatoms may be substituted. In the exemplary diamondoid of FIG. 4, these positions are labeled C-2 and C-3. The term "diamondoid" is used herein in a generic sense, including diamondoids with and without heteroatom substitution. As disclosed above, the heteroatom may be an electron donating element such as N, P or As, or a hole donating element such as B or Al. In this disclosure, the emphasis will be on nitrogen-containing heterodiamondoids, since the properties of the electron-donating nitrogen atoms are the focus of the field emission devices of the present invention.

Exemplary synthetic methods of such heterodiamondoids are discussed below. While certain heteroadamantane and heterodiamantane compounds have been synthesized in the past, and this may suggest a starting point for the synthesis of heterodiamondoids with more than two or more fused adamantane subunits, those skilled in the art can It is understood that the complexity of the individual reactions and the overall synthetic route increases with the number of adamantane subunits. For example, protecting groups may have to be employed, or it may become more difficult to dissolve the reactants, or the reaction conditions may be substantially different from those used for similar reactions of adamantanes. However, it may be instructive to discuss the chemistry based on the synthesis of heterodiamondoids using adamantane or diamantane as substrates since, to the best of the inventors' knowledge, these were the only systems for which data were available prior to this application.

Azaadamantane compounds have been synthesized in the past. For example, in the article "Synthesis of adamantane derivatives. 39. Synthesis and acidolysis of 2-azidoadamantanes. A facile route to 4-azahomoadamant-4-enes," by T. Sasaki et al., Heterocycles, Vol.7, No.1, p.315 (1977). These authors report the synthesis of 1-azidoadamantane and 3-hydroxy-4-azahomoadamantane from 1-hydroxyadamantane. The procedure involves the replacement of hydroxyl groups with azide functional groups by carbocation formation, followed by acidolysis of the azide product.

In a related synthetic route, Sasaki et al. were able to subject adamantanone to Schmidt reaction conditions, yielding 4-keto-3-azahomoadamantane as the rearrangement product. For details related to the Schmidt reaction, see T. sasaki et al., "Synthesis of Adamantane Derivatives. XII. The Schmidt Reaction of Adamantane-2-one," J.Org.Chem.Vol.35, No.12, p.4109 (1970 ).

Alternatively, 1-hydroxy-2-azadamantanes can be synthesized from 1,3-dibromoadamantanes as described by A. Gagneux et al. in "1-Substituted 2-heteroadamantanes," Tetrahedron Letters No. 17, pp. 1365-1368 as reported in (1969). This is a multi-step process in which the dibromo starting material is first heated to form a methyl ketone which then undergoes ozonation to form a diketone. The diketone is heated with four equivalents of hydroxylamine to generate a 1:1 mixture of cis and trans dioximes; this mixture is hydrogenated to the compound 1-amino-2-azadamantane dihydrochloride. Finally, nitrous acid converts the dihydrochloride to the heteroadamantane 1-hydroxy-2-azaadamantane.

Alternatively, 2-azaadamantane compounds can be synthesized from bicyclo[3.3.1]nonane-3,7-dione, as described by JG Henkel and WCFayth in "Neighboring group effects in the β-halo amines. Synthesis and solvolytic reactivity of the anti- 4-substituted 2-azaadamantyl system," reported in J. Org. Chem. Vol. 46, No. 24, pp. 4953-4959 (1981). The diketone can be converted to an intermediate by reductive amination (but using ammonium acetate and sodium cyanoborohydride in higher yields), which can be converted to another intermediate using thionyl chloride. Dehalogenation of this second intermediate to 2-azaadamantane was achieved in good yield using _LiAlH4 in DME.

S.Eguchi et al. reported in "A novel route to the 2-aza-adamantylsystem via photochemical ring contraction of epoxy4-azahomoadamantanes," J.Chem.Soc.Chem.Commun., p.1147 (1984) and the present invention The synthetic route used in is in principle related to a synthetic route. In this method, 2-hydroxyadamantane is reacted with a NaN _- based reagent system to generate azahomoadamantane, which is then oxidized by m-chloroperbenzoic acid (m-CPBA) to generate epoxy 4-azahomoadamantane Adamantane. The epoxide is then irradiated in a photochemical ring reduction reaction to generate the N-acyl-2-aza-adamantane.

An exemplary reaction scheme for the synthesis of nitrogen-containing heteroisotetramantanes is illustrated in Figure 5A. Those skilled in the art will appreciate that due to the differences in size, solubility and reactivity between tetramantane and adamantane, the reaction conditions for the scheme depicted in Figure 5A will differ significantly from those employed by Eguchi. A second route that can be used to synthesize nitrogen-containing heterodiamondoids is illustrated in Figure 5B.

In another embodiment of the present invention, by changing the route described in "Synthesis of 1-phosphaadamantane," Tetrahedron Vol.39, No.24, pp.4225-4228 (1983) by J.J.Meeuwissen et al. Phosphorous heterodiamondoids. This route is expected to enable the synthesis of heterodiamondoids containing both nitrogen and phosphorus atoms substituted in the diamondoid structure, with the advantage of having two different types of electron-donating heteroatoms in the same structure.

After preparing heterodiamondoids from diamondoids that do not have impurity atoms contained therein, the resulting heterodiamondoids can be functionalized to produce electron donating materials according to embodiments of the present invention. Alternatively, diamondoids (without impurity atoms) can be functionalized first and then converted to the heteroatom form.

Additional information on the synthesis of heterodiamondoids is provided in U.S. Patent Application Serial No. 10/622,130, filed July 16, 2003, entitled "Heterodiamondoids," which is incorporated by reference The full text is incorporated here.

Preparation of n-type heterogeneous diamond-like materials

An overview of an exemplary method for preparing n-type materials from heterodiamondoid molecules is illustrated in FIG. 1 . These methods include CVD techniques, polymerization techniques, crystallization of heterodiamondoids by themselves or with other materials, and the use of diamondoids and/or heterodiamondoids at the molecular level. The term "material preparation" as used herein refers to a method of obtaining heterodiamondoid after synthesizing it from a diamondoid raw material and making it into an n-type diamondoid-containing material.

In a first embodiment, the heterodiamondoid is injected into a reactor carrying out a conventional CVD process such that the heterodiamondoid is added to and becomes part of the extended diamond structure, and The heteroatoms are substituted on diamond lattice sites and behave like dopants in commonly prepared doped diamonds. In a second embodiment, the heterodiamondoids may be derivatized (or functionalized) with functional groups capable of undergoing polymerization reactions, and in a variation, the functional groups linking two adjacent heterodiamondoids are electrically semiconductor. In a third embodiment, the n-type material comprises only heterodiamondoids in a body of heterodiamondoid crystals, wherein individual heterodiamondoids in the crystal are held together by van der Waals (London) forces. Finally, in a fourth embodiment, a single heterodiamondoid can be used as part of the cathode of a field emission device.

In a first embodiment, the n-type diamond-like material is prepared using chemical vapor deposition (CVD) techniques. Using conventional CVD techniques, heterodiamondoids can be used as carbon precursors and as a source of self-contained dopants that have been sp ³ hybridized in the diamond lattice. In a new approach, the application of heterodiamondoids can be used to nucleate diamond films using conventional CVD techniques, including thermal CVD, laser CVD, plasma-enhanced or plasma-assisted CVD, electron beam CVD, etc.

The general method of synthesizing diamond by plasma-enhanced chemical vapor deposition (PECVD) techniques is well known in the art and dates back to the early 1980's or so. While it is not necessary to discuss the specific details of these methods as they relate to the present invention, one point should be mentioned in particular as it relates to the role played by hydrogen in the synthesis of diamond by the "general" plasma-CVD technique.

In A. Erdemir et al. in "Tribology of Diamond, Diamond-Like Carbon, and Related Films," in Modern Tribology handbook, Vol. Two, B. Bhushan, Ed. (CRC Press, Boca Raton, 2001) pp.871-908 In a method for the synthesis of diamond films discussed in , a modified microwave CVD reactor was used to deposit nanocrystalline diamond films using C ₆₀ fullerene or methane, gaseous carbon precursors. To introduce the _C60 fullerene precursor into the reactor, a device known as a "quartz transpirator" is attached to the reactor, wherein this device essentially The fullerene-containing soot is heated to a temperature of about 550 to 600° C. to sublimate the C ₆₀ fullerenes into the gas phase.

It is conceivable that a similar setup could be used to sublimate heterodiamondoids into the gas phase so that they can be introduced into a CVD reactor. An exemplary reactor, generally designated 600 , is illustrated in FIG. 6 . The reactor 600 comprises a reactor wall 601 delimiting an operating space 602 . A gas inlet tube 603 is used to introduce a process gas comprising methane, hydrogen and optionally an inert gas such as argon into the operating volume 602 . A DLC-containing gas can be volatilized and injected into the reactor 600 using a DLC sublimation or volatilization device 604 similar to the quartz evaporator discussed above. The volatilizer 604 may include means for introducing a carrier gas such as hydrogen, nitrogen, argon or an inert gas such as a rare gas other than argon, and it may contain other carbon precursor gases such as methane, ethane or ethylene.

Like conventional CVD reactors, reactor 600 may have an exhaust outlet 605 for removing process gases from the operating volume 602; for coupling energy into the operating volume 602 (and from the process A gas-triggered plasma) energy source; a filament 607 for converting molecular hydrogen into monatomic hydrogen; a susceptor 608 for growing a diamond-like film 609 thereon; for rotating the susceptor 608 means 610 for increasing the sp hybridization uniformity of the diamond-like-containing film ⁶⁰⁹ ; and for regulating and controlling the flow of gas via the inlet 603, the amount of energy coupled into the operating volume 602 from the source 606, injected into the operating volume 602 The amount of diamond-like carbon, the amount of process gas discharged via the exhaust port 405, the atomization of hydrogen by the filament 607 and the control system 611 of the device 610 of the rotating base 608. In an exemplary embodiment, plasma energy source 606 includes an induction coil such that energy is coupled into the process gas in operating volume 602 to generate plasma 612 .

According to an embodiment of the present invention, the heterodiamondoid precursor may be injected into the reactor 600 through a volatilizer 604, which is used to volatilize the diamondoid. A carrier gas, such as methane or argon, may be used to assist in the transfer of DLC entrained in the carrier gas into the operating volume 602 . Implantation of such heterodiamondoids provides a method by which impurity atoms can be inserted into diamond films without resorting to crystal damaging techniques such as ion implantation. Alternatively, the heterodiamondoid can be introduced into the reactor by simply placing the heterodiamondoid on the substrate on which the film is to be deposited, prior to inserting the substrate into the reactor.

It is conceivable that in some embodiments, the injected methane gas provides the majority of the carbon material present in films produced by CVD methods, and that the heterodiamondoid fraction in the input gas affects growth rate, crystallographic orientation and possibly grain structure, but more importantly, the heterodiamondoid moiety in the input gas provides the heteroatom impurities that will eventually serve as electron donors in n-type diamond or diamond-like films. This approach is schematically illustrated in Figures 7A-7C.

Referring to FIG. 7A , a substrate 700 on which a conventional CVD diamond film 701 is grown is placed in a CVD reactor 600 . This diamond film 701 comprises tetrahedrally bonded carbon atoms represented by the intersection of two straight lines in FIGS. The capped surface, as indicated by reference numeral 703 . The hydrogen-passivated surface 703 of the diamond film 701 is important. Hydrogen participates in the process of diamond synthesis by the PECVD technique by stabilizing the sp ^bond features on the surface of the grown diamond. As discussed in the references cited above, A. Erdemir et al. teach that hydrogen also controls the size of the initial crystal nuclei, the dissolution of carbon and the generation of condensable carbon groups in the gas phase, from the attachment to the growth of the diamond film Hydrogen abstraction by hydrocarbons on the surface, generation of vacancies into which sp ³ -bonded carbon precursors can insert. Hydrogen etches away most of the double-bonded or ^sp2- bonded carbon from the surface of the grown diamond film, thereby preventing the formation of graphite and/or amorphous carbon. Hydrogen also etches away smaller diamond grains and inhibits nucleation. Thus, in the presence of sufficient hydrogen, CVD-grown diamond films result in diamond coatings predominantly with large grains with highly faceted surfaces.

Referring again to FIG. 7A , heterodiamondoid 704 is injected into the CVD reactor in gas phase via vaporizer 604 described above. Schematically, a heterodiamondoid 704 has tetrahedrally bonded carbon atoms 702 at the intersections of the lines, and hydrogen passivated surfaces 703 at the endpoints of the lines, as previously described. Heterodiamondoid 704 also has heteroatoms 705 substituted in its lattice structure, which can be electron donors or acceptors.

As shown in FIG. 7B , during the deposition process, heterodiamondoid 704 is deposited on the surface of CVD diamond film 701 . The carbon atoms of the heterodiamondoid 704 become tetrahedrally coordinated (bonded) with the carbon atoms of the film 701 , and a continuous diamond lattice structure is formed along the interface between the newly produced heterodiamondoid 704 and the diamond film 701 .

The result is a diamond film 707 with impurity atoms (which may be electron donors or acceptors) substituted at lattice sites within the diamond crystal structure, as shown in Figure 7C. Since the heterodiamondoid has been introduced into the growing diamond film, its heteroatoms have been incorporated into the growing film, and the heteroatoms retain their sp ³ hybridization characteristics through the deposition process. Advantages of embodiments of the present invention include insertion of impurity atoms into the diamond lattice without having to resort to crystal-damaging implantation techniques.

As a function of the total weight of the CVD film (wherein the weight of the heterodiamondoid functional groups is included in the heterodiamondoid fraction), in one embodiment the weight of the heterodiamondoid and substituted heterodiamondoids can range from about 1 ppm to 1% by weight In the range. In another embodiment, heterodiamondoids and substituted heterodiamondoids are present in an amount from about 10 ppm to 1% by weight. In yet another embodiment, the proportion of heterodiamondoid and substituted heterodiamondoid in the CVD film is from about 100 ppm to 0.01% by weight relative to the total weight of the film.

In an alternative embodiment, heterodiamondoids can be assembled into n-type materials by polymerization. To this end, the heterodiamondoid must be derivatized (or functionalized) prior to polymerization, and methods for forming diamondoid derivatives and techniques for polymerizing derivatized diamondoids have been described in Shenggao Liu, Jeremy E. Dahl and Robert M. .Carlson's U.S. Patent Application Serial No. 10/046486, filed January 16, 2002, entitled "Polymerizable Higher Diamondoid Derivatives," which is hereby incorporated by reference in its entirety.

In order to prepare polymer films containing heterodiamondoid components as part of the polymer backbone or as pendant or branched chains of said backbone, a derivatized heterodiamondoid molecule is first synthesized, i.e., with hydrogen substituted for the original heterodiamondoids with at least one functional group. As discussed in that application, there are two main reaction sequences that can be used to derivatize heterodiamondoids: nucleophilic ( _SN 1 -type) and electrophilic ( _SE 2-type) substitution reactions.

_SN1 -type reactions involve the generation of heterodiamondoid carbocations, which subsequently react with various nucleophiles. Since the tertiary (bridgehead) carbons of heterodiamondoids are considered to be more reactive than secondary carbons under S _N1 reaction conditions, substitution on tertiary carbons is favored.

S _E 2-type reactions involve electrophilic substitution via the CH bond of a pentacoordinated carbocation intermediate. Of the two main reaction routes available for the functionalization of heterodiamondoids, _SN1 -type reactions can be more broadly employed to generate various heterodiamondoid derivatives. Mono- and polybrominated heterodiamondoids are some of the most versatile intermediates for functionalizing heterodiamondoids. These intermediates are used, for example, in Koch-Haaf, Ritter and Friedel-Crafts alkylation and arylation reactions. While direct bromination of heterodiamondoids on bridgehead (tertiary) carbons is advantageous, brominated derivatives can also be substituted on secondary carbons. In the latter case, the free radical route is often employed when synthesis on secondary carbons is generally desired.

While the above-described reaction routes may be preferred in certain embodiments of the invention, of course many other reaction routes can be used to functionalize heterodiamondoids. These reaction sequences can be used to produce derivatized heterodiamondoids with various functional groups, so that the derivatives can include heterodiamondoids halogenated with elements other than bromine (such as fluorine), alkylated diamondoids, nitrated diamondoid, hydroxylated diamondoid, carboxylated diamondoid, vinylated (ethenylated) diamondoid and aminated diamondoid. See Table 2 of the co-pending application "Polymerizable Higher Diamondoid Derivatives" for a list of exemplary substituents that can be attached to heterodiamondoids.

Polymers can be formed by subjecting heterodiamondoids and derivatives of heterodiamondoids having substituents capable of undergoing polymerization to appropriate reaction conditions. The polymer may be a homopolymer or a heteropolymer, and the polymerizable diamondoid and/or heterodiamondoid derivatives may be copolymerized with non-diamondoid, diamondoid and/or heterodiamondoid-containing monomers . Polymerization is generally carried out using one of the following methods: free radical polymerization, cationic or anionic polymerization, and polycondensation. Procedures for initiating free radical, cationic, anionic polymerization and polycondensation reactions are well known in the art.

Free-radical polymerization can occur spontaneously upon absorption of sufficient amounts of heat, ultraviolet light, or high-energy radiation. Usually, however, this polymerization process is enhanced by small amounts of free radical initiators such as peroxides, aza compounds, Lewis acids, and organometallic reagents. Free radical polymerization can use underivatized or derivatized heterodiamondoid monomers. As a result of the polymerization reaction, covalent bonds are formed between the diamondoid, non-diamondoid and heterodiamondoid monomers such that the diamondoid or heterodiamondoid become part of the polymer backbone. In another embodiment, functional group-containing substituents on the diamondoid or heterodiamondoid can be polymerized such that the diamondoid or heterodiamondoid is ultimately attached to the backbone as pendant groups. Diamond-like and heterodiamondoids with more than one functional group are capable of cross-linking polymeric chains together.

For cationic polymerization, cationic catalysts can be used to promote the reaction. Suitable catalysts are Lewis acid catalysts such as boron trifluoride and aluminum trichloride. These polymerization reactions are usually carried out in solution at low temperatures.

In anionic polymerization, derivatized diamondoid or heterodiamondoid monomers are usually subjected to the action of strong nucleophiles. Such nucleophiles include, but are not limited to, Grignard reagents and other organometallic compounds. Removal of water and oxygen from the reaction medium often promotes anionic polymerization.

Polycondensation reactions occur when the functional groups of one diamondoid or heterodiamondoid couple with those of another; for example, the amine group of one diamondoid or heterodiamondoid reacts with the carboxylic acid group of another to form an amide chain. In other words, when the functional group of the first diamond-like or heterodiamondoid is a suitable nucleophile such as alcohol, amine or thiol group, and the functional group of the second diamond-like or heterodiamondoid is a suitable electrophile such as carboxyl When acid or epoxy groups are present, one diamondoid or heterodiamondoid can be condensed with another diamondoid or heterodiamondoid. Examples of heterodiamondoid-containing polymers that may be formed via polycondensation reactions include polyesters, polyamides, and polyethers.

In one embodiment of the invention, a synthesis technique for polymerization of heterodiamondoids involves a two-step synthesis. The first step involves oxidation to form at least one ketone functional group at the secondary carbon (methylene) position of the heterodiamondoid. The heterodiamondoids can be directly oxidized using reagents such as concentrated sulfuric acid to generate ketone heterodiamondoids. In other cases, it may be desirable to convert the hydrocarbon to an alcohol, which is then oxidized to the desired ketone. Alternatively, heterodiamondoids can first be halogenated (e.g. with N-chlorosuccinimide, NCS) and the resulting halogenated diamondoid reacted with a base (such as _KHCO3 or _NaHCO3 in the presence of dimethylsulfoxide) . Those skilled in the art will appreciate that it may be necessary to protect the heteroatoms in the heterodiamondoid prior to performing the oxidation step.

The second step involves coupling two or more ketone heterodiamondoids to produce the desired polymer of heterodiamondoids. Coupling of diamondoids by ketone chemistry is known in the art and one method known as the McMurry coupling method has been disclosed in US Patent 4,225,734. Alternatively, coupling can also be performed by reacting keto-heterodiamondoids in the presence of _TiCl3 , Na and 1,4-dioxane. In addition, diamond-like (adamantane) polymers are described in Canadian Patent No. 2100654. Those skilled in the art can understand that due to the existence of a large number of oxidation and coupling reaction conditions, many kinds of keto-heterodiamondoids can be prepared in various configurations, positions and stereo configurations.

In an alternative embodiment, it is desirable to perform a series of oxidation/coupling steps to maximize the yield of the heterodiamondoid polymer. For example, a three-step procedure may be useful when the desired polymeric heterodiamondoid contains intercalated bridgehead carbons. The procedure involves chlorination of the intermediate-coupled polymeric heterodiamondoid with a reagent of choice such as NCS. This produces a chlorinated derivative with newly introduced chlorine on the methylene group adjacent to the double bond (or double bonds) present in the intermediate. The chlorine derivatives can be converted to the desired ketones by substitution of the chlorine with a hydroxyl group and further oxidation with a reagent such as sodium bicarbonate in dimethylsulfoxide (DMSO). Additional oxidations, including further treatment with pyridinium chlorochromate (PCC), can be performed to increase the yield of ketones.

Polymerization reactions between heterodiamondoid monomers are schematically illustrated in Figure 8A. The heterodiamondoid 800 is oxidized to keto-heterodiamondoid 801 using sulfuric acid. The specific diamondoid shown at 801 is tetraadamantane, but any diamondoid described above may be used. Again, the symbol "X" represents a heteroatom substituently located on a diamond-like lattice site. In this case, the keto group is attached at position 802.

As shown in step 802, two heterodiamondoids 801 can be coupled using McMurry's reagent. According to an embodiment of the present invention, the coupling between two adjacent heterodiamondoids can be realized between any two carbon atoms of the core structure of each heterodiamondoid, and in this exemplary case, the Coupling is achieved between carbon 803 of diamondoid 806 and carbon 804 of heterodiamondoid 806 . It will be apparent to those skilled in the art that the method can be continued; for example, the heterodiamondoid pair shown generally at 807 can be functionalized with keto groups on heterodiamondoids 805 and 806, respectively, to generate intermediate 808, wherein Two intermediates 808 can be coupled to form a complex 809 . In this way, each heterodiamondoid 800 can be used to construct a polymer to produce n-type materials. This material is expected to be conductive due to the π-bonds between adjacent heterodiamondoid monomers.

In an alternative embodiment, a conductive polymer "linker" can be used to couple individual heterodiamondoid molecules, resulting in an n-type heterodiamondoid material. Herein, a linker is defined as a short polymer segment comprising one to ten monomeric segments of a larger polymer. The linkers of the present invention may comprise conductive polymers such that electrical conductivity is established between adjacent heterodiamondoids in the overall bulk material. Polymers with conjugated π-electron backbones are able to exhibit these electrical properties. Conductive polymers are known and are described in the section entitled "Electrically Conductive Polymers" in JE Farmer and RRChance, High Performance Polymers and Composites, JI Kroschwitx, Ed. (Wiley, New York, 1991), pp. 174 to 219 technologies for these materials. The electrical conductivity of many of these polymers is described in this section and compared to metals, semiconductors, and insulators. A typical semiconducting polymer is p-polyphenylene sulfide, which has a conductivity as high as 10 ³ Siemens/cm ² (these units are the same as Ω ^-1 cm ^-1 ) and as low as 10 ^-15 (which is as insulating as nylon) . Polyacetylene is more conductive, with the highest conductivity at 10 ³ Ω ⁻¹ cm ⁻¹ and the lowest at about 10 ⁻⁹ Ω ⁻¹ cm ⁻¹ .

According to embodiments of the present invention, heterodiamondoids can be electrically linked using oligomers of the polymers discussed above to form bulk n-type materials. In this case, oligomer refers to a polymerization of about 2 to 20 monomers. Thus, oligomers can be considered as short polymers. In this case, the purpose of oligomers and/or linkers is to electrically connect several heterodiamondoids into a three-dimensional structure, making it possible to realize bulk materials with p-type or n-type conductivity.

Conductive polymers are generally discussed by J.E. Frommer and R.R. Chance in the chapter entitled "Electrically Conductive Polymers" in High Performance Polymers and Composites, J.I. Kroschwitz, Ed. (Wiley, New York, 1991), pp. 174 to 219 things. For the synthesis of conventional conductive polymers, it is important to introduce moieties with long π-electron conjugation. The monomers commonly used to synthesize such polymers are aromatic, or contain multiple carbon-carbon double bonds, which are retained in the final polymer backbone. Alternatively, conjugation can also be achieved in a subsequent step of converting the initial polymer product into a conjugated polymer. For example, the polymerization of acetylene produces a product of conjugated ethylene units, while the polymerization of benzene produces a chain of covalently linked aromatic units.

A catalog of exemplary oligomers (linkers) that can be used to connect heterodiamondoids in a conductive manner is illustrated in Figures 9A-N. Typical linkers that have been shown to be conductive are polyacetylene in Figure 9A, polythiophene in Figure 9E and poly(p-phenylene vinylene) in Figure 9F. A conductive linker highlighted as an example in the following discussion is polyaniline, the oligomers of which are depicted in Figure 9N.

A schematic diagram of heterodiamondoid polymers generated with polyaniline linkers is depicted in FIG. 10 . The polymers of Figure 10 are exemplary only, as the conductive linker groups between adjacent heterodiamondoids are polyaniline functional groups, but of course the linker groups can be any conductive polymer, many of which Contains conductive diene systems. In FIG. 10 , heterodiamondoid 1001 is connected to heterodiamondoid 1002 through a short segment 1003 of polyaniline oligomer. The same linker is also used for the connection of 1004 to heterodiamondoid 1005 in the same linear chain.

The polymer shown generally at 1000 may also contain crosslinks linking linear chains 1006 and 1007 . This produces a three-dimensional cross-linked polymer that is electrically conductive in a three-dimensional sense. Cross-link chains 1008 can be used to link adjacent linear chains 1006 and 1007 . This creates a conductive, three-dimensional matrix containing diamondoid. Each heterodiamondoid 1001 and 1002 contains within its structure a heteroatom that is either an electron donor or an electron acceptor. Overall, the preparation of n-type heterodiamond-like materials is achieved.

A third approach to making n-type materials is to crystallize heterodiamondoids into a solid, where the individual heterodiamondoids making up the solid are held together by van der Waals forces (also known as London forces or dispersion forces). Molecules held together in this manner have been discussed by J.S.Moore and S.Lee in "Crafting Molecular Based Solids," Chemistry and Industry, July, 1994, pp.556-559, and are known in the prior art as as a "molecular solid". According to these authors, in contrast to extended solid or ionic crystals, the preferred arrangement of molecules in molecular crystals is presumably the one that minimizes the total free energy, and thus the fabrication of molecular crystals is governed by thermodynamic reasons, distinct from synthetic processes. An example of a molecular crystal comprising pentamantane [1(2,3)4] will be discussed below.

In an exemplary embodiment, molecular crystals comprising pentamantane [1(2,3)4] are formed by the chromatographic and crystallographic techniques described above. Aggregates of these diamondoids stack to form actual crystals in the sense that the lattice basis can be defined. In this embodiment, [1(2,3)4]pentamantane was found to stack in an orthorhombic crystal system with space group Pnma, with unit cell dimensions a = 11.4786, b = 12.6418, and c = 12.5169, respectively eh. To obtain the diffraction data, pentamantane crystals were tested in a Bruker SMART 1000 diffractometer using radiation at a wavelength of 0.71073 Angstroms, the crystals being maintained at a temperature of 90K.

The unit cell of the pentamantane molecular crystal is schematically shown in FIG. 11 . This figure illustrates the general manner in which diamondoids can be stacked so as to be useful in embodiments of the present invention. These molecular crystals display well-defined exocrystal planes and are transparent to visible radiation.

Referring to FIG. 11 , the stacking of [1(2,3)4]pentamantane is illustrated as a perspective view of two unit cells 1102 and 1103 . Each unit cell of the crystal contains four pentamantane molecules, wherein the molecules are arranged such that there is a central cavity or pore per unit cell. In certain embodiments of the invention, cavities 1106 created by stacking of pentamantane cells can accommodate small impurities, or can be enlarged to accommodate transition element metals such as gold. The purpose of including these impurities may be to increase electrical conductivity.

An important feature of the stack of [1(2,3)4]pentamantanes illustrated in Figure 11 is that p or n- type of diamond-like material. In other words, no functionalization is required to polymerize or link individual diamondoid molecules, and in such embodiments no expensive deposition equipment is required. Since these crystals are mechanically soft and easily compressible, held together by van der Waals forces, an external "mold" may be required to support the n-type electron donating material. The mold may include, for example, regions of sp ² hybridized carbon material.

In another embodiment, a heterodiamondoid (or a small cluster of several heterodiamondoids) is envisaged to function as a quantum device at the molecular level, for example in a single electron emitter. Single electron devices are known and single electron transistors have been discussed in the prior art. See, eg, U.S. Patent 6,335,245 to Park et al., and Quantum Semiconductor Devices and Technologies, T.P Pearsall, ed. (Kluwer, Boston, 2000), pp.8-12. Park discloses that efforts to reduce the size of devices in the semiconductor industry drive the number of electrons present in a channel (e.g., the conduction channel between the source and drain of a transistor) by 2010 From about 300 in 2020 to no more than 30 in 2020. As the number of electrons required to operate a device is reduced, statistical changes in electron behavior become more interesting. Thus, although single-electron transistors have been conceived, there are still many difficulties to overcome in terms of their implementation, including the ability to fabricate them using today's lithographic techniques. Pearsall reviewed several types of single-electron transistors, including metal, semiconductor, carbon nanotube, and superconducting single-electron transistors.

One example of a heterodiamondoid contemplated for use in a single electron emitter is illustrated in FIG. 12 . Referring to Figure 12, an n-type heterodiamondoid comprising a tetraadamantane 1201 with a nitrogen heteroatom is coupled to a similar tetraadamantane 1202 via a carbon-carbon double bond 1208, as discussed in the polymer section above. In this composite, the number of heterodiamondoid molecules can range from about 1 to 10,000. The electron emitters contemplated by this embodiment are not limited to n-type materials. In other words, the emitter (anode of the FED) may also comprise p-type material. The p-type material acts as an electron acceptor, and it is desirable that the number of electron donating elements is greater than the number of electron accepting elements so that the material is electron donating overall. In some cases, it is envisioned to include electron-accepting elements in the emitter material to improve control over the number and distribution of electrons actually emitted. Thus, in FIG. 12 , a p-type tetramantane 1203 with a boron heteroatom can be coupled to a similar tetramantane 1204 via a carbon-carbon double bond 1209 . Of course, diamond-like carbons that do not contain any heteroatoms (not shown in Figure 12) may also be present in the clusters.

At the molecular level, n-type diamond-like complex 1205 can couple with p-type diamond-like complex 1206 to form complex 1207 . This molecular complex can be used as a single-electron emitter.

The heterodiamondoids of the present invention provide enhanced reliability, controllability and reproducibility not possible with prior art methods.

Properties of n-type diamond

Currently, known impurity atoms for doping diamond include boron and nitrogen. Boron is a p-type dopant with an activation energy of 0.37 eV. Nitrogen is an n-type impurity which can be called a deep donor because it has an energy level of 1.7 eV from the bottom of the conduction band. Since boron and nitrogen are adjacent to carbon on the same row in the periodic table, these atoms have similar sizes and thus they can be easily incorporated into the crystal if size alone is considered. R. Kalish and C.Uzan-Saguy in Properties, Growth and Applications of Diamond, edited by M.H.Nazare and A.J.Neves (Inspec, London, 2001), pp.321-330 titled "Doping of diamond using ion implantation The properties of boron and nitrogen doped diamonds, especially as they relate to ion implantation, have been discussed in Section B3.1 of .

In the past, p-type diamond materials have been more successfully developed than n-type materials. Satisfactory doping of diamond with nitrogen has proven elusive, although some success has been achieved recently with hot-filament CVD methods. Phosphorus has recently been demonstrated by CVD methods to have a donor state in the diamond bandgap with a reported activation energy of about 0.46 to 0.6 eV.

Boron-containing diamonds occur naturally (referred to as type IIb natural diamonds) and their electronic properties have been extensively studied. These studies reveal that the activation level of the boron acceptor is located at 0.37 eV above the valence band. More recently, p-type diamond doped with boron has been prepared using both high pressure high temperature (HPHT) and chemical vapor deposition (CVD) techniques. The best p-type diamond material produced to date is apparently produced by CVD epitaxial growth on <100> diamond faces. These materials are reported to give a carrier mobility of 1800 cm ² V ⁻¹ s ⁻¹ and a carrier concentration of about 2.3×10 ¹⁴ cm ⁻³ at room temperature. Presumably, the success in preparing boron-doped p-type diamond is due to the small size of the boron atom, which allows it to easily fit into the diamond lattice. Once within the lattice, it occupies the predominance of a substitution site (as opposed to a void site) where it acts as an electron acceptor on an electron.

Kalish and Uzan-Saguy summarize the main points about p-type diamond, pointing out that boron is the best studied p-type dopant in diamond. Boron-doped materials demonstrate hole mobilities as high as 600 cm ² /Vs, and compensation ratios below 5%. The optimum annealing profile has been found to be high temperature annealing at temperatures greater than 1400°C.

In contrast to p-type diamond, n-type diamond is more difficult to manufacture. Of the possible substitutional donors for diamond, only nitrogen and phosphorus appear to be able to enter the crystal to contribute to its electrical properties. These two elements can be introduced into diamond during CVD growth. In addition, group I elements occupying interstitial sites, such as sodium and lithium, are expected to act as donors with activation energies of 0.1 and 0.3 eV, respectively. The formation energy for bonding nitrogen into the carbon lattice is predicted to be negative at -3.4eV, in contrast to the predicted high positive formation energies for phosphorus (10.4eV), lithium (5.5eV) and sodium (15.3eV) on the contrary. This indicates the low solubility of these elements in diamond, with the exception of nitrogen.

Like boron, nitrogen is also present substitutively in natural diamond (type Ib diamond), where the impurity has an activation energy of 1.7 eV. Due to this high ionization energy, diamond containing nitrogen impurities is electrically insulating at room temperature, and thus these materials cannot be studied by conventional electrical measurement techniques. Using implantation techniques similar to those used for boron, about 50% of the implanted nitrogen was found to be in substitution sites after annealing, but the nature of the deep levels makes this type of material unsuitable for use at room temperature.

Phosphorus has been predicted to function as a shallow donor in diamond, with an activation energy of 0.1 eV. But recently, phosphorus-doped diamond has been grown by CVD techniques, and Hall effect measurements have shown that phosphorus creates a donor level with an ionization energy about 0.5eV below the bottom of the conduction band. The mobility of carriers in this material has been found to be about 30 to 180 cm ² V ⁻¹ s ⁻¹ , and typical room temperature carrier concentrations have been found to be about 10 ¹³ to 10 ¹⁴ cm ⁻³ . In other words, phosphorus has been found to occupy the substituted site about 70% of the time after annealing at 1200°C.

While this appears to be an attractive approach to prepare n-type diamond, the authors state that no n-type electrical activity of ion-implanted phosphorus in diamond has been found. The reason is presumed to be the large size of the phosphorus atoms relative to the size of the diamond lattice. This disproportion causes strain in the diamond lattice, which seems to attract and create electrically inactive defects.

Attempts have also been made to prepare n-type diamond by lithium implantation. In one study, n-type conductivity was confirmed by thermal probe measurements with an activation energy of 0.23 eV. Another study found an activation energy of 0.22eV. In yet another study, about 40% of the implanted lithium was found to occupy interstitial lattice sites and 17% to occupy substitutional sites, but no significant n-type electrical signal was found in this case. It is speculated that the substituted Li acts as an acceptor and the interstitial Li acts as a donor, with a possible compensation between these two effects resulting in no electroactivity.

C. Johnston et al. in Properties, Growth and Applications of Diamond, edited by MHNazare and AJNeves (Inspec, London, 2001), pp.337-344 in section B3.3 titled "Boron doping and characterization of diamond" gives Further discussion of boron doped diamond. These authors state that boron is known from studies on natural diamond to act as an acceptor with an energy level of 0.368 eV above the edge of the valence band. There are basically three approaches to achieve boron doping of diamond, these methods include 1) in situ introduction of boron into diamond during growth, 2) externally by ion implantation, and 3) high temperature diffusion. A disadvantage of the above method is that the introduction of boron may depend on the structure of the diamond film or the orientation of the substrate on which the diamond is deposited. In one study, the probability of boron incorporation into as-grown diamond films with <111> orientation was up to an order of magnitude greater than that into films with <100> orientation. The introduction of dopants into the grown diamond film also depends on the morphology of the deposited material. For example, the average crystallite size decreases by an order of magnitude when the boron concentration increases from about 10 ¹⁶ to 10 ²¹ cm ⁻³ .

As discussed above, n-type diamond is more difficult to produce than p-type diamond by ion implantation, but the introduction of nitrogen and phosphorus into diamond using CVD methods has recently proven to be more successful. This technique has been performed by GZCao in Section B3.4 titled "Nitrogen and phosphorus doping in CVDdiamond" in Properties, Growth and Applications of Diamond, edited by MHNazare and AJNeves (Inspec, London, 2001), pp.345-347 discussed. The authors state that due to its unique physical properties, diamond holds promise for high-power, high-frequency, and high-temperature electronic applications. These properties include high carrier mobility of 0.16 m ² /Vs, high thermal conductivity up to about 1.5×10 ⁴ W/mK, and wide bandgap energy of 5.5 eV. P-type conductivity has been demonstrated both in naturally occurring type lib diamond and in p-type diamond synthesized by high pressure high temperature (HPHT) techniques or by chemical vapor deposition CVD techniques. To generate n-type diamond, nitrogen and phosphorus are considered as possible donor elements.

Nitrogen is the most prevalent impurity in naturally occurring diamond and can be easily introduced into CVD diamond using _N2 or _NH3 as precursors. Hot wire CVD is the preferred method. A typical concentration is 6×10 ¹⁹ atoms/cm ³ . However, the rate of introduction of nitrogen into a growing diamond film depends on the orientation of the growing film, and the growth rate of the film depends on the amount of nitrogen in the feed gas. For example, the (100) plane introduces the highest concentration of nitrogen into diamond, followed by the (111) plane, and the (100) plane introduces the smallest amount of nitrogen. However, the addition of nitrogen to the feed gas resulted in the greatest improvement in the growth of the (100) plane, followed by the (111) plane, with the smallest improvement in the (110) plane.

Cao reiterated that phosphorus is a promising donor candidate for n-type semiconducting diamond films. Models show that phosphorus can behave as a shallow donor in diamond, with an energy level 0.2 eV from the bottom of the conduction band. However, phosphorus has a large positive formation energy (10.4eV) and thus has a low equilibrium solubility in diamond. This is due in part to the large size of phosphorus relative to carbon; for example, phosphorus has a radius of 1.10 Angstroms relative to carbon's 0.77 Angstrom radius.

In early phosphorus doping studies, only low concentrations of phosphorus doping were achievable, but it was found that phosphorus concentrations could be increased in the presence of other impurities such as boron. Unfortunately, n-type conduction cannot be obtained due to the donor-acceptor compensation effects discussed above.

Recap: The properties of doped diamond depend on the nature of the dopant. Boron-doped diamond has an acceptor energy level 0.368eV above the valence band, which can be regarded as a shallow energy level, and thus holes can be excited from energy states within the bandgap to the top of the valence band with lower energy . However, nitrogen is a deep donor (deep donor) whose energy level is 1.7eV from the bottom of the conduction band, so a large energy is required to lift electrons from the donor energy state in the conduction band to the bottom of the conduction band. Thus, when n-type diamond is doped with diamond, it is not conductive at room temperature because these temperatures do not provide sufficient energy to excite electrons from their energy states within the bandgap to the conduction band. Phosphorus is modeled as a shallow donor with energy states 0.2eV from the conduction band edge, making phosphorus a potential candidate for use as an n-type dopant, while lithium is another possibility.

It should be noted that in some cases the hydrogenated surface of diamond can impart p-type conductivity to the crystal. K. Bobrov et al. discuss this in "Atomic-scale imaging of insulating diamond through resonant electron injection," Nature, Vol.413, pp.616-619 (2001). The study demonstrates that "insulating" diamond surfaces can be imaged using scanning tunneling microscopy to study electronic properties at the atomic scale. (100) The hydrogenated surface of a single crystal of diamond can be imaged with STM under negative sample bias. Hydrogen-free diamond surfaces are insulating.

Embodiments of the present invention bypass the difficulties of the prior art by synthesizing heterodiamondoids such that impurity electron donor atoms are included in the diamond lattice structure prior to fabrication of the n-type semiconductor material. Such n-type heterodiamondoid materials can be used in devices such as field emission devices.

field emission device

According to embodiments of the present invention, heterodiamondoid or heterodiamondoid-containing materials are used as cold cathode filaments in field emission devices suitable for use in flat panel displays, among other applications. The unique properties of heteroatom-containing diamondoids make this possible. These properties include the negative electron affinity of the hydrogenated diamond surface, and the small size of the typical higher diamond-like molecules. The latter provide surprising electronic features in the sense that the diamond material at the diamond-like center comprises diamond single crystals of high purity, with significantly different electronic states at the diamond-like surface. These surface states allow conduction band electrons to have very long diffusion lengths. Electron donor heteroatoms, such as nitrogen, donate electrons to the conduction band of the material to facilitate electron emission from the cathode.

In the chapter titled "Novel Cold Cathode Materials" in Vacuum Micro-electronics (Wiley, New York, 2001), pp.247-287 written by W.Zhu et al. Current requirements for field emitter arrays, and the performance expected to be provided by improved field emission cathodes. Probably the most difficult problem with conventional field emission cathodes is the high voltage that must be applied across the device in order to extract electrons from the filament. Zhu et al. report that typical control voltages for microtip field emitter arrays are about 50-100 volts due to the high work function of the materials that typically make up the field emission cathode. Diamond in general, and hydrogenated diamond surfaces in particular, offer a unique solution to this problem due to the fact that diamond surfaces exhibit a negative electron affinity.

The electron affinity of a material is a function of the state of electrons at the surface of the material. When a diamond surface is passivated with hydrogen, that is, each carbon atom on the surface is ^sp hybridized, i.e. bonded to a hydrogen atom, the electron affinity of the hydrogenated diamond surface can become negative . A remarkable consequence of a surface with a negative electron affinity is that the energy barrier for electrons trying to exit the material is energetically favorable and in a "downhill" direction. Diamond is the only known material that has a negative electron affinity in air.

In more specific terms, a material has a negative electron affinity χ, where χ is defined as the energy required to excite an electron from an electronic state at the conduction band minimum to the vacuum level. For most semiconductors, the minimum value of the conduction band is below the minimum value of the vacuum level, so that the electron affinity of the material is positive. Electrons in the conduction band of such materials are bound to the semiconductor by an energy equal to the electron affinity, and this energy must be provided to the semiconductor to excite electrons from the surface of the material.

It should be noted that field emission cathodes comprising diamond filaments may suffer from an inherent property: while electrons in the conduction band can be easily emitted into the vacuum level, excitation of electrons from the valence band to the conduction band makes them available Field emission can be problematic. This is because of the wide bandgap of diamond. Under normal circumstances, few electrons are able to traverse the band gap, in other words, move from an electronic state in the valence band to an electronic state in the conduction band. Therefore, diamond is generally considered unable to sustain electron emission because of its insulating properties. To reiterate, while electrons can easily escape from the hydrogenated diamond film surface into vacuum due to the negative electron affinity of the surface, the problem is that there is no readily available mechanism by which electrons can be excited from the bulk to electronic surface states.

There are several ways to solve this problem. Electron emission from diamond surfaces has been observed with either: 1) a high defect density, such as a large content of elemental nitrogen, or 2) an unusual microstructure, including vapor-deposited islands or films with nanocrystalline morphology. They also demonstrate quantum mechanically tunneling. It is known in the art that diamond material with small grain size and high defect density generally emits electrons more readily than diamond material with large crystal size and low defect concentration. Prominent emission properties observed in ultrafine diamond powders containing crystallites with sizes in the range of 1 to 20 nm have been reported (see Zhu above). Electron emission has been found to originate from sites associated with defect structures in diamond, rather than sharp features associated with the surface, and compared to conventional silicon or metal microtip emitters, diamond emitters Shows lower threshold field, improved emission stability and intensity and vacuum environment.

According to an embodiment of the present invention, the field emission cathode comprises heterodiamondoid, derivatized heterodiamondoid, polymerized heterodiamondoid, and all or any other diamondoid-containing materials discussed in previous sections of this specification. According to a further embodiment of the present invention, the heteroatoms in said heterodiamondoid are electron donating species such as nitrogen.

An exemplary heterodiamondoid-containing field emission cathode is illustrated in FIG. 13 . Referring to Figure 13, a field emission device, shown generally at 1300, includes a heterodiamondoid-containing filament 1301 serving as a cathode for the device 1300, and a faceplate 1302 on which a phosphorescent coating 1303 has been deposited. The anode of the device may be a conductive layer 1304 behind the phosphorescent coating 1303 or an electrode 1305 adjacent to the filament 1301 . During operation, a voltage from a power supply 1306 is applied between the filament electrode 1307 and the anode, ie, electrode 1304 or 1305 of the device. Typical operating voltages (ie, the potential difference between cathode and anode) are less than about 10 volts. This is what allows the cathode to operate in a so-called "cold" configuration. For diamond-like surfaces, a typical electron affinity is expected to be less than about 3 eV, and in other embodiments it can be negative. Electron affinities of less than about 3 eV are considered "low positive".

While diamond material is generally considered to be electrically insulating, the heterodiamond filament (or cathode) 1301 contains electron-donating heteroatoms 1310, which can be any group V (IUPAC symbol) or group VI element, such as N, P, As or O, S, Se. These electron-donating elements donate one electron (in the case of group V) or two electrons (in the case of group VI) to the conduction band of the material constituting the heterodiamondoid-containing cathode. Additionally, the cathode may be small enough in two dimensions to allow electrons to tunnel (in the quantum mechanical sense) from the filament electrode 1307 onto the opposite surface of the heterodiamondoid, which may be the surface 1308 or the tip 1309. Those skilled in the art will appreciate that it is not necessary for the heterodiamondoid filament 1301 to have an apex or tip 1309 since the surface of the diamondoid is hydrogenated and ^sp3 hybridized. In an alternative embodiment, the surface of cathode 1301 may comprise a heterodiamondoid-containing material that is at least partially derivatized such that the surface includes both ^sp2 and ^sp3 hybridization. In embodiments of the invention, the electron affinity of the cathode is less than about 3 eV, and may be negative.

For a heterodiamondoid-containing component, whether the heterodiamondoid-containing component is a product of a CVD reaction, a polymer, a molecular crystal, or a cluster of individual heterodiamondoids, the heterodiamondoid content of the cathode 1301 can be from about 1 to 100% by weight. Additionally, the form of the heterodiamondoid-containing material may include fiber or film form. The surface of the heterodiamondoid-containing material may comprise substantially sp ³ hybridized carbon atoms, but the surface may also be derivatized or co-crystallized such that the surface comprises both sp ² and sp ³ hybridized carbon.

A contemplated advantage of this embodiment of the invention is that greater resolution of the device can be achieved relative to conventional field emission devices due to the greater number of emittable electrons typical of heterodiamondoids. Small size, and more reproducible and uniform structures achievable with heterodiamondoids.

Example

The following examples demonstrate methods for the synthesis of heterodiamondoids and polymeric heterodiamondoids containing nitrogen and boron according to embodiments of the present invention. They are intended as examples and should not be considered as limitations of the invention claimed below.

Examples 1-3 describe methods that can be used to prepare nitrogen-containing heterodiamondoids, such as azadiamondoids. Example 4 discloses an exemplary method for preparing polymers from heterodiamondoids, including polymers comprising heterodiamondoids coupled through double bonds between carbons in the diamondoid lattice sites. Example 1 illustrates the preparation of azatetramantanes from a feedstock containing a mixture of tetramantanes including certain alkyltetramantanes and other impurities. Other feedstocks containing different diamondoids such as triamantane, or tetramantane and higher diamondoids can also be used and result in similar heterodiamondoid mixtures.

Example 1

Preparation of azatetramantane from a mixture containing tetramantane isomers

In the following examples, a mixture of azatetramantanes was prepared from a starting material containing a mixture of the three tetramantane isomers, i.e. iso-tetramantane, trans-tetramantane, and ortho-cross-tetramantane .

The first step in this exemplary synthesis involves photohydroxylation of the tetramantane-containing starting material. The starting materials can be obtained by the methods described in U.S. Patent Application 10/052636, filed January 17, 2002, which is hereby incorporated by reference in its entirety. A fraction is obtained that contains at least one tetramantane isomer, which fraction may include substituted tetramantanes such as alkyltetramantanes, as well as hydrocarbon impurities. Gas chromatography/mass spectrometry (GC/MS) analysis of the composition of this fraction indicated a tetramantane mixture.

A solution of 200 mg of the above tetramantane-containing starting material in 6.1 g of dichloromethane was mixed with a solution of 1.03 g (13.5 mmol) of peracetic acid in ethyl acetate, 4.22 g. Under vigorous stirring, the solution was irradiated with 100 watts of UV light. Gas production was seen from the start. During the irradiation period of about 21 hours, the temperature was maintained at 40-45°C. The solution was then concentrated to near dryness, treated twice successively with 10 mL each of toluene, and evaporated to dryness. The product was then characterized by GC/MS, showing the presence of the hydroxylated tetramantane isomer.

In an alternative embodiment, the tetramantane starting material can be oxidized directly according to the procedure of McKervey et al. (see J. Chem. Soc., Perkin Trans. 1, 1972, 2691). The crude product mixture was then characterized by GC/MS, showing the presence of isotetramantanone. The oxidized starting material prepared by direct oxidation (wherein the product contains tetramantanone) was then reduced at low temperature with lithium aluminum hydride in diethyl ether. After the reaction was complete, the reaction mixture was worked up by adding saturated _{aqueous Na2SO4} at low temperature to decompose excess lithium aluminum hydride. Decantation from the precipitated salt gave a dry diethyl ether solution which was then evaporated to give the crude product. The crude product can be characterized by GC/MS, indicating the presence of the hydroxylated tetramantane isomer.

In a next step, azahomo tetramantane-ene can be prepared from the above hydroxylated tetramantane or from photooxidized tetramantane. To a stirred and ice-cooled mixture of 98% methanesulfonic acid (1.5ml) and dichloromethane (3.5ml) was added solid sodium azide (1.52g, 8.0mmol). To this mixture was added the hydroxylated tetramantane prepared above. To this resulting mixture was gradually added sodium azide (1.04 g, 16 mmol) in small amounts over about 0.5 h. Stirring was continued at 20-25°C for about 8 hours, then the mixture was poured into ice water (about 10 ml). The aqueous layer was separated, washed with _CH2Cl2 (3ml), basified with 50% aqueous KOH-ice, and extracted with _CH2Cl2 ( _10ml x ₄ ). The combined extracts were dried over _Na2SO4 and the solvent was removed to give _the product as a brown oil. The product was characterized by GC/MS, indicating the presence of the azahomotetraadamantene isomer.

In the next step, epoxy azahomotetramantane was prepared from the azahomotetramantane by the following procedure. The above mixture was treated with m-CPBA (1.1 equiv) in _{CH2Cl2 - NaHCO3} at a temperature of about 20 °C for 12 hours _, and the reaction mixture was then worked up by extraction with _CH2Cl2 to give A crude product which was characterized by GC/MS indicated the presence of epoxyazahomotetramantane.

In the next step, N-formyl azatetramantane was prepared from the epoxyazahomotetramantane mixture by irradiating the epoxyazatetramantane mixture in cyclohexane for about 0.5 h using a high-intensity Hg lamp. mixture. The reaction was carried out under an argon atmosphere. In general, if the reaction is allowed to proceed for only a short time, simpler reaction products are obtained; longer reaction times give complex mixtures. The initial product was characterized by GS/MS, showing a mixture of N-formylazatetramantanes.

In the final step, the azatetramantane was prepared from the N-formylazatetramantane described above by mixing the N-formylazatetramantane with 10 mL of 15% hydrochloric acid. The resulting mixture was heated to boiling for about 24 hours. After cooling, typical workup of the mixture afforded a product characterized by GS/MS, indicating the presence of the azatetramantane.

Example 2

Preparation of azaiso-tetramantane from iso-tetramantane

In this example, azaisotetramantane was prepared from a single tetramantane isomer, isotetramantane, as shown in Figures 5A-B. As in the case of mixtures of tetramantanes, this synthetic route also starts from photohydroxylation or chemical oxidation/reduction of isotetramantanes to hydroxylated compound 2a, as shown in Figure 5A.

A solution of 3.7 mmol of isotetramantane in 6.1 g of dichloromethane was mixed with a solution of 1.03 g (13.5 mmol) of peracetic acid in ethyl acetate, 4.22 g. Under vigorous stirring, the solution was irradiated with 100 watts of UV light, and gas evolution was observed at the beginning of the irradiation process. During the irradiation time of about 21 hours, the temperature was maintained at 40-45°C. The solution was then concentrated to near dryness, treated twice successively with 10 mL each of toluene, and evaporated to dryness. The crude product containing a mixture of isotetramantanes hydroxylated at C-2 and C-3 was not purified, but the mixture was used directly in the reaction involving the oxidation of hydroxylated compound 2a to ketone compound 1 .

The photohydroxylated isotetramantane moiety containing a mixture of C-2 and C-3 hydroxylated isotetramantane was dissolved in acetone. The oxidized components go into solution, but not all of the unreacted isotetramantane is able to be dissolved. A solution of chromic acid and sulfuric acid was then added dropwise until excess acid was present, and the reaction mixture was stirred overnight. The acetone solution was decanted from the precipitated chromium sulfate and unreacted isotetramantane and dried over sodium sulfate. Unreacted isotetramantane was recovered by dissolving the chromium salt in water followed by filtration. Evaporation of the acetone solution gave a white solid. The crude solid was chromatographed on alumina using conventional procedures, where it could be eluted initially with 1:1 (v/v) benzene/petroleum ether, followed by diethyl ether or a mixture of diethyl ether and methanol (95: 5 v/v) to collect unreacted isotetramantane first and then the ketone compound 1. Further purification by recrystallization from cyclohexane yielded substantially pure product 1 .

Alternatively, isotetramantane can be directly oxidized to the ketone compound 1 following the procedure of McKervey et al. (see J. Chem. Soc., Perkin Trans. 1, 1972, 2691). After the oxidation step, the ketone compound 1 can be reduced to the C-2 hydroxylated isotetramantane 2a by treating the ketone compound 1 with excess lithium aluminum hydride in diethyl ether at low temperature. After the reaction was complete, the reaction mixture was worked up by adding saturated aqueous _Na2SO4 at _low temperature to decompose excess hydride. Decantation from the precipitated salt gave a dry diethyl ether solution which was then evaporated to give crude monohydroxylated isotetramantane substituted on the secondary carbon. This compound may be referred to as C-2 tetraamantanol. Further recrystallization from cyclohexane gave essentially pure product.

Alternatively, a 0.8 M solution of methyllithium in diethyl ether (2.8 mL, 2.24 mmol), C-2 methylhydroxyisotetramantane 2b can be prepared from said ketone compound 1. Stirring was continued for about 2 hours at -78°C and for a further 1 hour at room temperature. Then, saturated ammonium chloride solution (1 mL) was added, and the mixture was extracted with diethyl ether (2 x 30 mL). The organic layer was dried over sodium sulfate and concentrated to give the product 2b, which was subsequently purified by chromatography or recrystallization.

In the next step, azahomo-tetraadamantene 3 was prepared from hydroxylated compound 2. To a stirred and ice-cooled mixture of 98% methanesulfonic acid (15ml) and dichloromethane (10ml) was added solid sodium azide (1.52g, 8.0mmol) followed by the above C-2 hydroxylated Compound 2a or 2b (6 mmol). To the resulting mixture was gradually added sodium azide (1.04 g, 16 mmol) in small amounts over about 0.5 h. After addition of sodium azide, stirring was continued for about 8 hours at about 20-25°C. The mixture was then poured into ice water (about 10ml). The aqueous layer was separated, washed with _CH2Cl2 (3ml), basified with 50% aqueous KOH-ice, and extracted with _CH2Cl2 ( _10ml x ₄ ). The combined extracts were dried ( _Na2SO4 ) and the solvent was removed to give a brown oil which was chromatographed to give essentially pure sample ₃ (3a or 3b).

In the next step, epoxy azahomo-tetramantane 4 was prepared from azahomo-tetramantene 3 . A mixture of azahomo-tetraadamantene 3 (3a or 3b) and m-CPBA (1.1 equiv) in _{CH2Cl2 - NaHCO3} was stored at 5-20 °C, followed by the usual work-up and short Separation by column chromatography gives epoxy azahomo-tetramantane 4 (4a or 4b).

In the next step, N-acyl azaisotetramantane 4b was prepared from epoxy azaisotetramantane 4b by irradiating epoxy azaisotetramantane 4b in cyclohexane using a UV lamp for about 0.5 h 5b. The irradiation was passed through a quartz filter and the reaction was performed under an argon atmosphere. In general, when the reaction is allowed to proceed for only a short time, a single product is formed; longer reaction times give complex product mixtures. Products can be separated by chromatographic techniques.

Similarly, N-formylazais-tetramantane 5a can be prepared from epoxyazahomo-tetramantane 4a.

In the next step, the N-acylazaiso-tetramantane 5b (5 mmol) and 2 g of powdered sodium hydroxide in 20 mL of diethylene glycol were heated to reflux for about 5 hours, from N-acylazaiso-tetramantane Preparation of azaiso-tetramantane 6 from tetramantane 5b. After cooling, the mixture was poured into 50 mL of water and extracted with ether. The ether extract was dried with potassium hydroxide. The product azaiso-tetramantane 6 was obtained after distilling off the ether. The hydrochloride salt is usually prepared for analysis. Thus, the salt is isolated as a crystalline compound by passing dry hydrogen chloride through an ethereal solution of the amine. The salt can be purified by dissolving in ethanol and precipitating with anhydrous ether. Typically, the solution is left undisturbed for several days to achieve complete crystallization.

Alternatively, azaisotetramantane 6 can be prepared from N-formylazaiso-tetramantane 5a by mixing N-formylazaiso-tetramantane 5a (2.3 mmol) with 10 mL of 15% hydrochloric acid. The resulting mixture was heated to boiling for about 24 hours. After the mixture was cooled, the precipitate was filtered and recrystallized in isopropanol to give the product azaiso-tetramantane 6.

Example 3

Preparation of azaiso-tetramantane 6 products by fragmentation of ketone compound 1 to unsaturated carboxylic acid 7

An alternative synthetic route for the preparation of the product azaiso-tetramantane 6 is illustrated in Figure 5B. Referring to Fig. 5B, according to the method of McKervey et al. (Synth. Commun., 1973, 3, 435), the iso-tetramantananone 1 prepared above can be fragmented into unsaturated carboxylic acid 7 by irregular Schmidt reaction. This synthesis is expected to be similar to that reported in the literature for adamantane and diamantane (see, e.g., Sasaki et al., J. Org. Chem., 1970, 35, 4109; and Fort, Jr. et al., J. Org. Chem., 1981, 46(7), 1388).

Compound 8 can be prepared from carboxylic acid 7 in the next step. To 4.6 mmol of carboxylic acid 7 was added 12 mL of glacial acetic acid and 3.67 g (4.48 mmol) of anhydrous sodium acetate. The mixture was stirred and heated to about 70°C. Lead(IV) acetate (3.0 g, 6.0 mmol, 90% pure, 4% acetic acid) was added in 3 portions over 30 minutes. Stirring was continued at 70°C for 45 minutes. The mixture was then cooled to room temperature and diluted with 20 mL of water. The resulting suspension was stirred with 20 mL of ether and a few drops of hydrazine hydrate were added to dissolve the precipitated lead dioxide. Then the ether layer was separated, washed several times with water, once with saturated sodium bicarbonate, and dried over anhydrous sodium sulfate. Removal of ether gave an oily substance from which a mixture of two isomers (exo- and endo-) of compound 8 was obtained. Further purification and separation of the stereoisomers (exo- and endo-) can be achieved by distillation under vacuum.

Compound 9 (exo- or endo-) can then be prepared from compound 8 (exo- or endo-) by adding 0.13 g (3.4 mmol) of lithium aluminum hydride to a solution of compound 8 (0.862 mmol) in 5 mL of anhydrous diethyl ether Mode-). The mixture was refluxed with stirring for about 24 hours. Excess lithium aluminum hydride was destroyed by adding water dropwise, and the precipitated lithium hydroxide and aluminum hydroxide were dissolved in excess 10% hydrochloric acid. The ether layer was separated, washed with water, dried over anhydrous sodium sulfate, and evaporated to give Compound 9 (if the starting material is a mixture of Exo-8 and Inner-8, Compound 9 is Exo-9 and Inner -9 isomer mixture). Further purification can be achieved by recrystallization of the product from methanol-water.

Compound 10 was then prepared from the exo- and endo mixture of compound 9. A solution of a mixture of alcohol 9 (1.05 mmol) in 5 mL of acetone was stirred at 25 °C in an Erlenmeyer flask. To this solution was added dropwise 8N chromic acid until the orange color persisted; the temperature was maintained at 25°C. The orange solution was then stirred for about 3 additional hours at 25°C. Most of the acetone was removed and 5 mL of water was added to the residue. The aqueous mixture was extracted twice with diethyl ether, and the combined extracts were washed with saturated sodium bicarbonate, dried over anhydrous sodium sulfate, and evaporated to give crude compound 10. Sublimation in a steam bath afforded essentially pure 10.

In an alternative embodiment, compound 10 can be prepared from individual compound 9 isomers rather than a mixture of exo- and endo-9 isomers. For example, compound 10 can be prepared from Exo-9 by stirring a solution of Exo-9 (1.05 mmol) in 5 mL of acetone in an Erlenmeyer flask at 25°C. To this solution was added dropwise 8N chromic acid until the orange color persisted, keeping the temperature at about 25°C. The orange solution was then stirred at 25°C for about 3 hours. Most of the acetone was removed and 5 mL of water was added to the residue. The aqueous mixture was extracted twice with diethyl ether, and the combined extracts were washed with saturated sodium bicarbonate, dried over anhydrous sodium sulfate, and evaporated to give crude compound 10. Sublimation in a steam bath afforded essentially pure 10.

In another alternative embodiment, compound 10 can be prepared directly from carboxylic acid 7 without going through intermediate compounds 8 and 9. For this purpose, a solution of carboxylic acid 7 (4.59 mmol) in 15 mL of dry THF was stirred under dry argon and cooled to 0°C. Under argon atmosphere, a solution of 1.5 g (13.76 mmol) lithium diisopropylamide in 25 mL dry THF was added to the solution of 7 via syringe at a rate such that the temperature did not rise above about 10 °C. The resulting solution of the dianion of 7 was stirred at 0°C for about 3 hours. The solution was then cooled to about -78°C with a dry ice-acetone bath, and dry oxygen was slowly bubbled through the solution for about 3 hours or more. A mixture of about 10 mL THF and 1 mL water was added to the reaction mixture, which was then allowed to warm to room temperature and stirred overnight. The solution was concentrated in vacuo to about 10 mL, poured into excess 10% HCl, and extracted with ether. The ether layer was washed with 5% NaOH to remove unreacted 7, which could be recovered by acidifying the basic wash. The ether layer was dried over anhydrous sulfate and stripped to yield crude 10. Sublimation in a steam bath at 3-5 torr afforded essentially pure product.

Referring again to Figure 5B, compound 11 can be prepared from compound 10 as follows. To a solution of compound 10 (1.6 mmol) in a (1:1) mixture of pyridine and 95% ethanol was added 250 mg (3.6 mmol) of hydroxylamine hydrochloride, and the mixture was stirred at reflux for about 3 days. Most of the solvent was evaporated in an air stream, and the residue was dissolved in 25 mL of water. The ethereal extract of the aqueous solution was washed with 10% HCl to extract the oxime 11. Oxime 11 was precipitated by neutralizing the acid wash with 10% sodium hydroxide, which was filtered off and recrystallized in ethanol-water.

In the final step, azaiso-tetramantane 6 was prepared from compound 11 by adding dropwise compound 11 (0.98 mmol) in 25 mL of anhydrous ether. The mixture was stirred at reflux for about 2 days. The excess lithium aluminum hydride was destroyed with water, and the precipitated lithium hydroxide and aluminum hydroxide were dissolved in an excess of 25% sodium hydroxide. The resulting basic solution was extracted twice with ether, and the combined extracts were washed with 10% HCl. Neutralization of the acidic washes with 10% sodium hydroxide precipitated product 6, which was extracted back into fresh diethyl ether. The ether solution was dried over anhydrous sodium sulfate and stripped. The crude product was purified by repeated sublimation under vacuum in a steam bath.

Example 4

Preparation of polymeric heterodiamondoids coupled by double bonds between carbons located at diamond lattice sites

This example describes an exemplary method that can be used to prepare polymeric heterodiamondoids coupled by double bonds between carbon atoms of adjacent heterodiamondoids located at diamond lattice sites. In this example, polymeric heterodiamondoids can be prepared in many different configurations, including cyclic, linear and zigzag polymers, depending on the position of the carbon atoms within the diamondoid itself. Those skilled in the art will understand that an essentially unlimited number of configurations can be prepared using the method of this embodiment, but a specific oxidation reaction will be described below, and a coupling reaction will be described in Example 9.

Heterodiamondoid ketones (keto-heterodiamondoids) were prepared by adding 10 mmol of heterodiamondoids to 100 mL of 96% sulfuric acid. The reaction mixture was then heated at about 75°C for about 5 hours with vigorous stirring. Stirring was continued for about 1 hour at room temperature. The black reaction mixture was poured onto ice and subjected to steam distillation. The steam distillate was extracted with ether, and the combined ether extracts were washed with water and dried over _MgSO4 . Ether was evaporated to give a crude product mixture. Chromatography on alumina separates unreacted heterodiamondoids, yielding a ketone fraction (eluted with petroleum ether or other suitable solvent) and a by-product alcohol fraction (eluted with diethyl ether or other suitable solvent) ). The yield of the ketone (mixture of different positions and stereoisomers) is generally about 20%. Those skilled in the art will appreciate that certain heteroatoms in the heterodiamondoid may need to be protected prior to undergoing the oxidation/coupling reactions described herein.

By-product alcohols from oxidation with strong oxidizing agents such as _H2SO4 or from mild oxidations such _as oxidation with tert-butyl hydroperoxide to direct oxidation products can _be converted to ketones by treatment with _H2SO4 as described below . The alcohol, dissolved in 96% _H2SO4 , was stirred vigorously at 75 °C for about 4.5 hours in _a loosely corked flask with occasional shaking. After about 5 hours, the reaction was quenched and worked up as described above. Overall ketone yields are typically about 30%.

Example 5

Preparation of keto compounds in which the keto group introduced into a double-bond-coupled heterodiamondoid is highly selectively located on a methylene group adjacent to the double bond linking the diamondoid

To a solution of 1 mmol double bond coupled heterodiamondoid in 20 mL _CH2Cl2 , 1.05 mmol ₍ 140 mg) NCS was added. The reaction mixture _was stirred at room temperature for about 1 hour, diluted with _CH2Cl2 , and washed twice with water. The organic layer was dried over _MgSO4 and evaporated. Chlorinated products (mixtures of different positions or stereoisomers) were prepared. The intermediate chloride is converted to a mixture of the corresponding alcohol and ketone by heating the intermediate chloride in a solution of sodium bicarbonate in DMSO to about 100°C for several hours. The reaction mixture was partitioned between hexane and water, and the hexane layer was evaporated to give a product mixture. Conversion of the remaining alcohol to the ketone was achieved by refluxing with a 0.15 mol solution of PCC for about 2 hours under stirring conditions. The ketone was isolated by adding a large excess of ether to the cooled mixture and washing all solids with additional ether. Passing the ether solution through a short pad of Florisil and evaporating the ether gives ketone products with different positions or stereoisomers, which can be isolated and used in subsequent coupling reactions.

High selectivity for the introduction of ketones to positions adjacent to the double bond can also be achieved by selective bromination as follows: To a solution of 3 mmol of double bond-coupled heterodiamondoids in ₄₀ mL of _CHCl , add 6.6 mmol (1.175 g) N-bromosuccinimide (NBS). The reaction mixture was refluxed and stirred for about 12 hours. The reaction _mixture was diluted with _CH2Cl2 and washed twice with water and _{saturated Na2S2O3 solution} . The organic layer was dried over _MgSO4 and evaporated. The yield of the brominated product was about 90%. Conversion of this intermediate to the ketone product was achieved using the same procedure as above.

Example 6

Preparation of Diketones of Heterodiamondoids

Heterodiamondoid diketones can be prepared by more intense oxidation than the above examples (Examples 4 and 5), using strong oxidizing agents such as _{H2SO4 or CrO3} / _Ac2O , but heterodiamondoids are preferably prepared by serial oxidation. Diketones of diamondoids. Monoketones or hydroxyketones are formed first, followed by further oxidation or rearrangement-oxidation, depending on the intermediates involved. Monoketones are generally treated with a solution of _CrO3 in acetic anhydride at near room temperature for about 2 days. The reaction was quenched with dilute aqueous caustic (NaOH) and the product was isolated by extraction with diethyl ether. The product diketone is then isolated and used in a coupling reaction.

Example 7

Preparation of adjacent ketones on the same heterodiamondoid face

A particularly useful oxidation procedure for the preparation of adjacent ketones on _the same DLC surface is the selective oxidation of intermediate ketones with _SeO2 / _H2O2 to lactones, which are then reconstituted with strong acids. Alignment of hydroxyketones and oxidation of the hydroxyketones to the desired diketones. For example, monoketodiamondoid was treated with a 1.5 molar excess of _SeO2 in 30% _H2O2 at _about 60°C for several hours at elevated temperature. The mixed lactone products were isolated by diluting the reaction solution with water, extracting with hexane and removing the hexane by evaporation. The lactone was hydrolyzed and rearranged by _heating with 50% _H2SO4 . Again, the product was isolated as described above and further converted to a mixture of positional diketone isomers, which were isolated and used in further coupling reactions.

Example 8

Preparation of Mixed Keto-Heterodiamondoids

In certain embodiments, it may be desirable to prepare double bonded polymeric heterodiamondoids from mixtures of heterodiamondoids via coupling reactions of heterodiamondoid ketones. Thus _, mixtures _{containing heterodiamondoids} ( _{heterotetramantane} , heteropentamantane, etc.) to prepare a mixture of ketones. The procedure described above was used to achieve isolation of the product ketone and to prepare mixed polymeric heterodiamondoids by the coupling reaction described in the next example.

Example 9

Preparation of polymeric heterodiamondoids by coupling ketone derivatives of heterodiamondoids

Polymeric heterodiamondoids can be prepared by coupling ketone derivatives of heterodiamondoids using several procedures. A very useful procedure is the McMurray coupling reaction described below. The preparation of reagent (M) (containing Mg, K, or Na reducing agent, with Na being the most preferred reducing agent) can be performed by weighing 20 mmol of _TiCl3 into a three-necked flask in a glove box. Then 60 mL of dry solvent (eg THF) is added. To the stirred slurry was added the required amount (typically about 30 to 100 mmol) of Grignard magnesium via a Schlenk tube under an argon atmosphere. The mixture was refluxed for about 3 hours, during which time all the Mg had reacted and the color of the mixture had changed from purple through blue, green and brown to black. A comparable amount of freshly cut and hexane washed K can be used in place of Mg. The reduction was complete after a reflux time of about 12 hours.

To prepare reagent (M) with _LiAlH4 reducing reagent, the _TiCl3 /THF mixture was cooled to about 0 °C and the required amount (typically 15 to 50 mmol) of _LiAlH4 was added in small portions to maintain the resistance to the vigorous reaction ( Precipitation of H ₂ ) control. After the addition was complete, the reaction mixture was stirred at 0 °C for about 0.5 hours. If hydrogenation as a side reaction should be minimized, the black suspension of (M) was refluxed for another hour.

The coupling reaction is carried out by adding the required amount of ketone (typically 10 to 20 mmol of keto groups) to the cold black suspension of (M). A rapid release of _H2 was observed, especially when _LiAlH4 was used as reducing agent. After the addition is complete, the mixture is stirred at room temperature for 6 to 20 hours, depending on the particular diamondoid being coupled. During the reaction, a slight flow of argon was maintained. Experiments have shown that the above reaction times are sufficient to obtain complete coupling. The reaction was then quenched by adding 40 mL of 2N hydrochloric acid, and the reaction mixture was extracted three times with 10 mL of CHCl ₃ . The combined organic layers were dried over _MgSO4 and the solvent was evaporated to obtain polymerized heteroadvanced diamondoids in about 80% yield. Purification of the product can be achieved by column chromatography on _Al2O3 eluting with a suitable solvent such as petroleum ether and recrystallization from _a suitable solvent.

Using this procedure, the intermediate ketones can be coupled in high yields to produce dimers. Mixed dimers result if two different keto-diamondoids are co-coupled. In addition, higher-order polymeric product forms are formed upon coupling of multi-substituted heterodiamondoids, such as linear rigid rod polymers, which have lower solubility and higher melting points than the corresponding Z-shaped polymers.

Under special conditions such as highly dilute coupling conditions (ketodiamondoid concentration <0.01 mol/liter), ring polymeric heteroadvanced diamondoids can be formed from said diketones which allow ring closure. In these cyclizations tetramers are generally preferred, but cyclic trimers are also formed in specific cases. Those skilled in the art will appreciate that under such coupling conditions, polymeric heterodiamondoids can be prepared from different keto-heterodiamondoids, their different positional isomers and stereoisomers.

Two-dimensional sheet-like polymers can be formed from heterodiamondoids with more than two ketone groups. Such precursors can be formed by extended oxidation of the parent heterodiamondoid or by the series of oxidation/couplings described in the above examples. Cyclic tetramers are particularly useful as intermediates for the preparation of two-dimensional sheet polymers by an additional oxidation/coupling series as described in the preceding examples.

Besides polymerization using McMurray coupling reactions, other methods of forming double bonds between heterodiamondoids are applicable. Another very useful procedure also uses ketones as intermediates. This method involves the condensation of heterodiamondoid (G) ketones with hydrazine to form azides (G=NN=G), to which _H2S is added to form bisdiamondoid thiadiazolidines (bisdiamondoids). thiadiazolidine), oxidation of this intermediate to bidiamondoid thiadiazine, and final elimination of N and S heteroatoms to prepare the desired coupling product (G=G). This procedure is useful because it allows one to systematically prepare mixed coupled DLC polymers by the sequential reaction of one heterodiamondoid and then another heterodiamondoid with hydrazine to form mixed azides. It is also easier to remove by-products from coupled heterodiamondoids.

The following is an example of heterodiamondoid coupling via this route. To form the azide, a solution of hydrazine hydrate (98%, 1.30 g, 26 mmol) in 15 mL of tert-butanol was added dropwise to heterodiamondoid ketone (35 mmol) in 60 mL of A stirred reflux solution of tert-butanol. After the addition was complete, the solution was refluxed for about 12 hours and then allowed to stand at room temperature for about 24 hours. Removal of the solvent gave a crystalline material, to which 200 mL of water was added. The aqueous mixture was extracted with diethyl ether (4 x 100 mL). The combined ether extracts were washed with brine, dried ( _MgSO4 ), and the azide product was recrystallized.

To form thiadiazolidine, hydrogen sulfide was bubbled through a solution of the above azine compound (41.1 mmol) and 5 mg p-toluenesulfonic acid in 300 mL of 1:3 acetone:benzene at room temperature. The conversion was complete after about 12 hours. Evaporation of the solvent yielded >90% of the thiadiazolidine. This material was used in subsequent steps without further purification.

To prepare the thiadiazine, to a suspension of CaCO ₃ (20.7 g, 0.21 mol) in 300 mL benzene at 0° C. was added lead tetraacetate (20.7 g, 46.7 mmol) in portions. The mixture was stirred for about 20 minutes. The above mixture of thiadiazolidine (35.9 mmol) and 300 mL of benzene was added dropwise with stirring over a period of about 1.5 hours. After the addition was complete, the mixture was stirred at room temperature for about 8 hours. After adding 400 mL of water, a brown precipitate formed which was removed by filtration. The aqueous layer was separated, saturated with NaCl, and extracted with ether. The organic fractions were combined, washed with brine, dried over _MgSO4 , and concentrated to give thiadiazine as a yellow residue in about 90% yield. This material was used in the subsequent step without further purification.

To couple heterodiamondoids, a homogeneous mixture of thiadiazine (3.32 mmol) and triphenylphosphine (2.04 g, 7.79 mmol) was heated at 125-130° C. for about 12 hours under a nitrogen atmosphere. Column chromatography of the residue on silica gel using a suitable solvent gave the desired coupled product in about 70% yield.

All publications, patents and patent applications cited in this application are herein incorporated by reference in their entirety to the same extent as if the disclosure of each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.

Numerous modifications will readily occur to those skilled in the art from the above-disclosed exemplary embodiments of the invention. Accordingly, the present invention should be construed to include all structures and methods falling within the scope of the appended claims.

Claims (23)

1. field emission device with negative electrode, wherein said negative electrode comprises Heterodiamondoid.

2. the field emission device of claim 1, wherein said Heterodiamondoid is the part of Heterodiamondoid-containing material.

3. the field emission device of claim 1, wherein said Heterodiamondoid comprises the Heterodiamondoid of derivatization.

4. the field emission device of claim 1, wherein said Heterodiamondoid comprises the Heterodiamondoid of underivatized.

5. the field emission device of claim 1, wherein said Heterodiamondoid comprises and contains heteroatomic rudimentary diamond like carbon.

6. the field emission device of claim 1, wherein said Heterodiamondoid comprises and contains heteroatomic senior diamond like carbon.

7. the field emission device of claim 6, wherein said to contain heteroatomic senior diamond like carbon synthetic by the diamond like carbon that is selected from down group: four adamantane, five adamantane, six adamantane, seven adamantane, eight adamantane, nine adamantane, ten adamantane and 11 adamantane.

8. the field emission device of claim 2, the material of wherein said Heterodiamondoid-containing is a film.

9. the field emission device of claim 2, the material of wherein said Heterodiamondoid-containing is a fiber.

10. the field emission device of claim 2, the material of wherein said Heterodiamondoid-containing is selected from down group: the CVD film of the polymer of Heterodiamondoid-containing, Heterodiamondoid-containing and the molecular crystal of Heterodiamondoid-containing.

11. the field emission device of claim 10, wherein for the polymer of Heterodiamondoid-containing, the Heterodiamondoid content of described negative electrode is about 1 to 100wt%.

12. the field emission device of claim 10, wherein for the CVD film of Heterodiamondoid-containing, the Heterodiamondoid content of described negative electrode is about 1 to 100wt%.

13. the field emission device of claim 10, wherein for the molecular crystal of Heterodiamondoid-containing, the Heterodiamondoid content of described negative electrode is about 1 to 100wt%.

14. the field emission device of claim 11, the electron affinity of wherein said negative electrode is born.

15. the field emission device of claim 12, the electron affinity of wherein said negative electrode is born.

16. the field emission device of claim 13, the electron affinity of wherein said negative electrode is born.

17. the field emission device of claim 11, the electron affinity of wherein said negative electrode is less than about 3.0eV.

18. the field emission device of claim 12, the electron affinity of wherein said negative electrode is less than about 3.0eV.

19. the field emission device of claim 13, the electron affinity of wherein said negative electrode is less than about 3.0eV.

20. the field emission device of claim 2 further comprises the anode of the contiguous described negative electrode in position, and is used for providing between described anode and negative electrode the power supply of electrical potential difference.

21. each field emission device of claim 20 wherein is applied to electrical potential difference between described anode and the negative electrode less than about 10 volts.

22. each field emission device of claim 2, the surface of the material of wherein said Heterodiamondoid-containing comprises sp basically ³The carbon atom of hydridization.

23. each field emission device of claim 3, the surface of the material of wherein said Heterodiamondoid-containing is by derivatization, so that described surface comprises sp simultaneously ²And sp ³The carbon of hydridization.

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