WO2014150584A1

WO2014150584A1 - Functional inclusion of interlayer devices in multi-level graphene devices and methods for forming same

Info

Publication number: WO2014150584A1
Application number: PCT/US2014/023692
Authority: WO
Inventors: Mark Alan Davis
Original assignee: Solan LLC
Current assignee: Solan LLC
Priority date: 2013-03-15
Filing date: 2014-03-11
Publication date: 2014-09-25
Anticipated expiration: 2015-09-15

Abstract

Multi-level graphene devices and methods for forming such devices are provided. A first foundation material is deposited onto a substrate thereby forming a first foundation layer. Graphene is grown on the first foundation layer thereby forming a first graphene level having one or more graphene stacks at least one of which comprises a first graphene based nanostructure. An interlayer is formed on the first graphene level. A second foundation material is deposited onto the interlayer thereby forming a second foundation layer. Graphene is grown on the second foundation layer thereby forming a second graphene level. Like the first graphene level, the second graphene level includes one or more graphene stacks at least one of which comprises a second graphene based nanostructure.

Description

FUNCTIONAL INCLUSION OF INTERLAYER DEVICES IN MULTI-LEVEL GRAPHENE DEVICES AND METHODS FOR FORMING SAME

CROSS REFERENCE TO RELATED APPLICATION

[0001] This Application claims priority to United States Patent Application No. 61/793,653, filed March 15, 2013, entitled "Functional Inclusion of Interlayer Devices in Multi-level Graphene Devices and Methods for Forming Same," which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The disclosed embodiments are generally related to multi-level graphene devices and the methods by which such devices are made.

BACKGROUND

[0003] A thin layer of a material, typically nanometers thick, can exhibit properties for various promising applications that are substantially diminished in the bulk three-dimensional counterparts of the material. A graphene sheet and a thin graphitic layer comprising a plurality of graphene sheets are good examples. Compared to its bulk three-dimensional counterparts, graphene sheets and ultra-thin graphite layers have demonstrated a number of distinguishing chemical, mechanical, electronic and optical properties, including high carrier mobility, high Young's elastic modulus, and excellent thermoconductivity. Such materials are well suited for applications in electronic devices, super-strong composite materials, and energy generation and storage. As such, graphene-based structures (e.g., graphene quantum dots, graphene nanoribbons, graphene nanonetworks, graphene plasmonics, and graphene super-lattices) have wide ranging applications because of some of the distinguishing chemical, mechanical, electronic, and optical properties. For example, graphene can be used in electronics, composite materials, and for energy generation and storage.

[0004] Some of the properties of some graphene-based structures are dependent on the dimensions of and/or the number of defects, disruptions and boundary conditions in one or more graphene sheets forming a stack (i.e. layer or film). However, graphene-based structures are difficult to pattern and integrate with other elements or components. Conventional methods of manufacturing graphene -based structures include growing a substantially uniform graphene film and then patterning (e.g., by etching, oxidation, etc.) the graphene film to produce isolated graphene segments, such as graphene nanoribbons. However, patterning graphene can damage the desirable properties of graphene by introducing defects, especially along the edges of the resulting graphene segments.

SUMMARY

[0005] Various implementations of methods and devices that are within the scope of the appended claims each have several aspects, no single one of which is solely responsible for the attributes described herein. Without limiting the scope of the claims, some prominent features are described herein. After considering the discussion herein, and particularly the section entitled "Detailed Description," one will understand how aspects of various implementations are used to enable methods of manufacturing a graphene structures that are integrated with one or more functional interlay ers.

[0006] In some implementations, a functional interlayer is provided between two graphene stacks, between two layers of graphene stacks, and/or between two layers including patterned graphene stacks. In some implementations, a functional interlayer is one of a waveguide, a diffraction film, light and/or electromagnetic collector, thermal condenser, optical condenser, lenses, nanostructures, nanonetworks, absorbers, fractal patterns, electronic components (e.g. resisters, capacitors, inductors, etc.), electrical interconnects, thermal interconnect, filaments, OLED components, transmissive conductive oxides (e.g. indium tin oxide), a dielectric (e.g., a high K dielectric), and a flexible film.

[0007] The present disclosure advantageously provides systems methods for making graphene based thin films from layered materials and band gap devices formed without any requirement for patterning graphene. For instance, one aspect of the present disclosure provides a method for fabricating multilevel stacked graphene structures. The method includes optionally depositing a first foundation material onto a substrate thereby forming a first foundation layer. Graphene is formed using the first foundation layer or by other means thereby forming a first graphene level. The first graphene level comprises one or more graphene stacks. A graphene stacks in the first graphene level forms a first graphene based nanostructure. In one example, the first graphene based nanostructure has a dimension (e.g., height, length, width, perimeter, etc.) that is 100 microns or less, 10 microns or less, 1 micron or less, 500 nanometers or less, 100 nanometers or less, 50 nanometers or less, 25 nanometers or less, or between 2 and 25 nanometers.

[0008] The method further includes forming a first interlayer on the first graphene level. After forming the first interlayer, an optional second foundation material, which may be the same as or different than the optional first foundation material, is optionally deposited onto the first interlayer thereby forming a second foundation layer. Graphene is grown onto the second foundation layer using the optional second foundation material or by other means thereby forming a second graphene level. Like the first graphene level, the second graphene level includes one or more graphene stacks, with a respective graphene stack in the second graphene level including a second graphene based nanostructure. In one example, the second graphene based nanostructure has a dimension (e.g., height, length, width, perimeter, etc.) that is 100 microns or less, 10 microns or less, 1 micron or less, 500 nanometers or less, 100 nanometers or less, 50 nanometers or less, 25 nanometers or less, or between 2 and 25 nanometers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the present disclosure can be understood in greater detail, a more particular description may be had by reference to aspects of various implementations, some of which are illustrated in the appended drawings. The appended drawings, however, merely illustrate the more pertinent aspects of the present disclosure and are therefore not to be considered limiting, for the description may admit to other effective aspects and features.

[0010] FIG. 1A is a detailed graphical representation of an exemplary method for forming graphene on a substrate using foundation material, in accordance with some embodiments of the present disclosure.

[0011] FIG. IB is a detailed graphical representation of an exemplary method for forming multilevel stacked graphene structures, in accordance with some embodiments of the present disclosure.

[0012] FIG. 2 is a detailed graphical representation of an exemplary method for forming multilevel stacked graphene structures having backfilled interlayers, in accordance with some embodiments of the present disclosure. [0013] FIGS. 3A-3C depict detailed graphical representations of exemplary multilevel stacked graphene structures with variable dimensions and layouts, in accordance with some embodiments of the present disclosure.

[0014] FIG. 4 illustrates an exemplary multiple band gap device that is made using the methods of the present disclosure.

[0015] FIG. 5 illustrates an additional exemplary multiple band gap device that is made in accordance with an aspect of the present disclosure.

[0016] FIG. 6 depicts a schematic electrical diagram of a multiple band gap photovoltaic device, in accordance with some embodiments of the present disclosure.

[0017] FIG. 7 depicts a schematic electrical diagram of a multiple band gap photodetector, in accordance with some embodiments of the present disclosure.

[0018] FIG. 8 depicts a schematic electrical diagram of a multiple band gap light emitting diode, in accordance with some embodiments of the present disclosure.

[0019] FIGS. 9A-B depicts a schematic top view of semiconducting nanohole superlattices, in accordance with some embodiments of the present disclosure.

[0020] FIG. 10 depicts a schematic top view of a multiple band gap device comprising a nanohole superlattice, in accordance with some embodiments of the present disclosure.

[0021] In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. The dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

DETAILED DESCRIPTION

[0022] In some embodiments, graphite -based structures, e.g. graphene quantum dots, graphene nanoribbons (GNRs), graphene nanonetworks, graphene plasmonics and graphene super-lattices, exhibit many exceptional chemical, mechanical, electronic and optical properties, and are very desirable for use in electronic devices, composite materials, and energy generation and storage. Such graphite -based structures in general comprise a graphene layer, typically nanometers thick and having a characteristic dimension also in the nanometers range. For example, in order to obtain adequate band gaps for operation at room temperature, GNRs are required to have a width within a few nanometers due to the inverse relationship between the band gap and the width of the GNRs.

[0023] In some embodiments, various methods are provided for fabricating graphite-based structures while achieving desired size, specified geometries, and characterized electronic properties of the graphite -based structures. These methods include, but are not limited to, (1) the combination of e-beam lithography and oxygen plasma etching; (2) stripping of graphite that is sonochemically processed; and (3) bottom-up chemical synthesis, e.g., by cyclodehydrogenation of l ,4-diiodo-2,3,5,6-tetraphenylbenzene6, or 10, 10'-dibromo-9,9'- bianthryl, polyanthrylene oligomers self-assembled on Au(l l l), Ag(l l l) or silica substrates, to name a few examples.

[0024] In some embodiments, different pitch and duty cycle combinations in graphene devices are utilized to improve efficiency. In particular, in some embodiments, graphene sheets are stacked, with different pitch and critical dimensions, such that devices have multiple pass functionality. Similarly, in some embodiments, structures comprising multiple levels of graphene layers allow for more versatile and efficient band gap devices.

[0025] Embodiments of the present disclosure are described in the context of methods for fabricating thin films from layered materials and in the context of thin films made therefrom. In this specification and claims, layered materials refer to a material comprising a plurality of sheets, with each sheet having a substantially planar structure.

[0026] As used herein, the term "thin films" refers to a thin layer comprising one sheet (e.g, a sheet of graphene); it also refers to several, several tens, hundreds or thousands of such sheets. The thickness of the thin films can range from a nanometer to several micrometers, or to several tens of micrometers. Final thin films produced by some processes disclosed in this application have a thickness in nanometers, and preferably less than fifty nanometers. Similarly, as used herein, a "graphene layer" refers to several, several tens, several hundreds or several thousands of such sheets. As user herein a sheet is a sheet of graphene, which is a single sheet composed of sp -hybridized carbon.

[0027] As used herein, the term "stacks" refers to one or more layers of a material (e.g., one or more layers of graphene). Like "thin films," "stacks" can also refer to several, several tens, several hundreds or several thousands of layers of material. For example, a stack of graphene refers to one or more layers of graphene or graphene structures. As used herein, the term "graphene structures" is used interchangeably with "graphene." As used herein, the term "stacks" is interchangeable with the terms "graphene stacks" and "stacks of graphene."

[0028] As used herein, the terms "graphene based nanostructure" and "graphene nanostructure" are interchangeable and refer to any carbon based structure incorporating graphene. Examples of graphene based nanostructures include, but are not limited to, graphene nanoribbons, graphene nanonetworks, graphene poles/pillars, and graphene based nanohole superlattices.

[0029] As used herein, the term "level" refers to one or more graphene stacks for a given foundation layer or substrate. Thus, in some embodiments, a level of graphene contains multiple graphene stacks formed from a respective foundation layer or substrate. As sometimes used herein, "level" is shorthand for "graphene level" or "level of graphene."

[0030] As used herein, the term "substrate" refers to one layer or multiple layers. In some embodiments, a substrate is glass, Si, Si0₂, SiC, or another material. When referring to multiple layers, the term "substrate" is equivalent to and interchangeable with the term "substrate stack."

[0031] As used herein, the term "foundation material" refers to any material that is suitable for growing graphene. In some embodiments, foundation materials are catalytic metals, e.g., Pt, Au, Fe, Rh, Ti, Ir, Ru, Ni, or Cu. In some other embodiments, foundation materials are non-metal materials, such as Si, SiC, non-stoichiometric SiC (e.g., boron doped or otherwise), and other carbon enhanced materials. As used herein, the phrase "carbon enhanced" materials refers to any materials into which carbon has been added.

[0032] As used herein, the term "backfilled" refers to forming or depositing a layer of material without leaving any air gaps in between stacks of a level. In some embodiments, "backfilling" means to fully backfill all gaps in between portions of a given layer.

[0033] Those of ordinary skill in the art will realize that the following detailed description of the present application is illustrative only and is not intended to be in any way limiting. Other embodiments of the present application will readily suggest themselves to such skilled persons having benefit of this disclosure. Reference will now be made in detail to implementations of the present application as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.

[0034] In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

[0035] FIG. 1 A is a detailed graphical representation of an exemplary method for fabricating multilevel stacked graphene structures, in accordance with some embodiments of the present disclosure. In some implementations, a first graphene level is formed on a substrate, a first interlayer is formed on the first graphene level, and a second graphene level is formed on the first interlayer. In some embodiments, the methods or materials used to form the first and second graphene levels are different and, consequently, the characteristics (e.g., band gap, number of graphene sheets, etc.) of the first and second graphene levels differ. This is a highly advantageous architecture which gives rise to the ability to form any number of composite type graphene devices, including multi-functionality (each graphene level has a different function) and composite functionality (the combined properties of the graphene levels work to produce a common composite function). Generally speaking, each of the graphene levels can be formed by any of three general mechanisms (i) catalytic or precipitation from a metal, (ii) reverse epitaxial sublimation of silicon leaving carbon, and (iii) nucleation growth, typically on a non-metallic material. Throughout this description it will be appreciated that in some embodiments a foundation layer is deposited and then used to form graphene. However, the disclosure is not so limited. Methods that consume a portion of the substrate, such as reverse epitaxial sublimation of silicon leaving carbon often do not make use of a foundation layer. Thus, the use of such foundation layers herein should be considered optional, nonlimiting embodiments. [0036] In FIG. 1 A, which provides a detailed graphical representation of the aforementioned exemplary method for depositing graphene on a substrate and foundation material in accordance with some embodiments of the present disclosure, initial operation 200 demonstrates a clean substrate 220. In some embodiments, substrate 220 is a material that facilitates formation or deposition of one or more layers of a foundation material.

[0037] In some implementations, the substrate used in the present disclosure is glass, silicon, SiC, Si0₂, or SiC/Si. In some embodiments, the substrate is a solid substance in a form of a thin slice. In some embodiments, the substrate is planar. In some embodiments the substrate is flexible. In some embodiments the substrate is rigid. In various embodiments, the substrate is made of a dielectric material, a semiconducting material, a metallic material, or a combination of such materials. Exemplary dielectric materials include glass, silicon dioxide, neoceram, and sapphire. Exemplary semiconducting materials include silicon (Si), silicon carbide (SiC), germanium (Ge), boron nitride (BN), and molybdenum sulfide (MoS). Exemplary metallic materials comprise copper (Cu), nickel (Ni), platinum (Pt), gold (Au), cobalt (Co), ruthenium (Ru), palladium (Pd), titanium (Ti), silver (Ag), aluminum (Al), cadmium (Cd), iridium (Ir), combinations thereof, and alloys thereof. In some embodiments the substrate comprises Si, Si0₂, SiC, Cu, Ni, or other materials. In some embodiments, the substrate substantially comprises neoceram, borosilicate glass, germanium arsenide, a IV-V semiconductor material, a substantially metallic material, a high temperature glass, or a combination thereof.

[0038] In some embodiments, the substrate substantially comprises Si0₂ glass, soda lime glass, lead glass, doped Si0₂, aluminosilicate glass, borosilicate glass, dichroic glass, germanium/semiconductor glass, glass ceramic, silicate/fused silica, soda lime glass, quartz or chalcogenide/sulphide glass, fluoride glass, a glass-based phenolic, flint glass, or cereated glass.

[0039] In some embodiments, the substrate is a transition metal substrate. Examples of transition metal substrates include, but are not limited to iridium (Ir), ruthenium (Ru), platinum (Pt), cobalt (Co), nickel (Ni), and palladium (Pd). In some embodiments the transition metal substrate is crystalline. For instance, in some embodiments the substrate is Ir(l 11), Ru(OOOl), Pt(l 1 1), Co(0001), Ni(l 11), or Pd(l 11). In some embodiments where the substrate is a transition metal, graphene is grown by heating the transition metal substrate in the presence of carbon. Thus, in such embodiments, the carbon is considered the foundation material. In some embodiments, the transition metal substrate is overlayed on another substrate material, such as silicon, quartz, sapphire, or silica. In some embodiments, the transition metal substrate is overlayed on porous material, such as porous silicon, which is in turn overlayed on another layer, such as crystalline silicon. In such embodiments, the porous material acts as a barrier to prevent diffusion of the transition metal into the crystalline substrate.

[0040] In some embodiments, the substrate includes one layer. In alternative embodiments, the substrate includes a plurality of layers. In some embodiments, a substrate comprises a plurality of layers, each with a different material. In some embodiments, a layer of another substance is applied onto the substrate. In some embodiments, the substrate has crystallographic symmetry.

[0041] In some embodiments, the substrate is made of poly methyl methacrylate (PMMA), polyethylene terephthalate (PET), polyvinyl alcohol (PVA), or cellulose acetate (CA). In some embodiments, the substrate is made of a urethane polymer, an acrylic polymer, a fluoropolymer, polybenzamidazole, polymide, polytetrafluoroethylene, polyetheretherketone, polyamide-imide, glass-based phenolic, polystyrene, cross-linked polystyrene, polyester, polycarbonate, polyethylene, polyethylene, acrylonitrile-butadiene-styrene, polytetrafluoroethylene, polymethacrylate, nylon 6,6, cellulose acetate butyrate, cellulose acetate, rigid vinyl, plasticized vinyl, or polypropylene.

[0042] In operation 202, foundation material layer 230 is optionally deposited onto substrate 220 using any deposition method, in order to form foundation material layer 230. Foundation material layer 230 is any material that facilitates graphene growth through deposition. In one embodiment, foundation material layer 230 is a catalytic metal, e.g., Cu.

[0043] In some embodiments, the foundation material is a catalytic metal or any other material, as long as the material is conducive to growing or depositing graphene on the surface of the material. In some embodiments, the foundation material used is not a metal at all. For instance, in some embodiments, the foundation material comprises a carbon compound, such as silicon carbide. The foundation layer can be deposited onto the substrate via any standard microfabrication technology, e.g. sputtering, spin coating, or chemical vapor deposition. In some embodiments, no foundation material is deposited. For instance, in some embodiments, the substrate itself serves as the source material for graphene growth (e.g., in some embodiments the substrate itself is the foundation material). As an example, in some embodiments the substrate is silicon carbide and graphene is formed by epitaxial growth on the silicon carbide. In some embodiments, the graphene is grown epitaxially using a silicon carbide substrate and using near-atmoshoperic pressure with argon gas suppression.

[0044] In some embodiments, the foundation material layer 230 is etched such that the graphene layer grown, via operation 202, comprises a plurality of graphene stacks, separated by the etching process. Operations 204-210 represent a detailed implementation, e.g. photolithography, of an example etching process used to etch foundation material layer 230. As discussed above, other lithography methods, such as e-beam lithography, direct write, block copolymer, to name a few, can also be used in other embodiments of the present disclosure.

[0045] Operation 204 shows a layer of a photoresist 240 deposited onto the foundation material layer 230. After the foundation material layer 230 has been coated with resist layer 240, the next operation is alignment and exposure of the resist layer. Alignment and exposure is, as the name implies, a two-purpose photomasking operation. The first part of the alignment and exposure operation is the positioning or alignment of the required image on the material surface. The image is found on a mask. The second part is the encoding of the image in the resist layer from an exposing light or radiation source. In operation 206, a light (not shown) illuminates photoresist layer 240 through the mask (not shown), exposing portions of the foundation material 230 in accordance with the features of the mask. In some embodiments, apertures in the mask are arranged in such a way as to form a nanopattern from which a nanotemplate will be formed. In some embodiments, the nanotemplate defines the structure of the graphene nanostructure grown during the graphene growing operations of the methods described above.

[0046] After exposure through a mask, the pattern is coded as a latent image in resist as regions of exposed and unexposed resist. In some embodiments, the pattern is optionally developed in the resist by chemical dissolution of the unpolymerized resist regions. There are several methods in which a developer is applied to resist in order to develop the latent image. Such methods include, but are not limited to, immersion, spray development, and puddle development. Additionally and/or alternatively, in some implementations, lithography techniques including interference and/or holographic methods that do not necessarily require a mask can be used.

[0047] In operation 208, the exposed portions of foundation material layer 230 are etched away using a plasma etcher. A plasma etcher uses energized ions to chemically dissolve away either exposed or unexposed portions of the resist layer. The etching process can be any etching process that etches away only the exposed foundation material layer. It is important to note that the etching process should not affect the patterned photoresist layer 240, the portions of foundation material layer 230 that are directly under and covered by photoresist layer 240, or the substrate 220.

[0048] In operation 210, the remaining portions of the photoresist layer 240 are removed by any of a number of residual layer removal techniques.

[0049] In operation 212, the foundation layer 230 is used to form one or more layers of graphene 250 (also referred to herein as "graphene layers 250"). In some embodiments, the one or more layers of graphene 250 grown on foundation layer 230 form first graphene level 260, as depicted in Fig. 1 A. As mentioned above, in some implementations, foundation layer 230 is nonexistent, and thus first graphene level 260 simply comprises one or more layers of graphene 250. In some embodiments, first graphene level 260 comprises one or more stacks 261 of graphene structures, also called graphene stacks 261, where a respective stack 261 includes a first graphene based nanostructure, e.g., nanoribbon 300. In some embodiments, the first graphene based nanostructure is any carbon based structure incorporating graphene. In some embodiments, a graphene stack in the first graphene level comprises thin films for use in band gap devices. In some embodiments, the graphene layer can be formed using any standard deposition technique, e.g., chemical vapor deposition. The one or more layers of graphene 250 can be deposited in a variety of methods, e.g. chemical vapor deposition.

[0050] FIG. IB is a detailed graphical representation of an exemplary method for forming multilevel stacked graphene structures, in accordance with some embodiments of the present disclosure. The method depicted in Fig. IB is a continuation of the method depicted in Fig. 1A. Thus, the method begins with operation 212, as described with reference to Fig. 1A. In operation 214, first interlayer 270 is formed from a first interlayer material. In some embodiments, interlayer 270 is formed with one or more air gaps 231. In some embodiments, the interlayer is any layer of material deposited or formed on a graphene level to separate the graphene level from another graphene level.

[0051] In some implementations, the interlayer is deposited or formed such that at least one air gap exists between two different graphene stacks. In some implementations, the interlayer is deposited or formed such that at least one air gap exists between two different portions of a given substrate or foundation layer, each portion corresponding to different graphene stack. Such air gap can be horizontally juxtaposed or vertically juxtaposed under a separation sheet as used in MEM devices. A benefit of such air gaps is for manipulation of the index of refraction in optical devices. By definition air has an index of refraction of 1. Therefore apparent indices of graphene devices can be changed by addition of an air gap into such devices. A difference in n (index of refraction) is also a boundary or interface for wavelength manipulation. Thin graphene is also a transparent material such that transmission as well as absorptive diffraction properties can be exploited. Optionally, in some alternative embodiments, the interlayer is deposited or formed such that the gaps in between different graphene stacks, or different portions of the substrate or foundation layer corresponding to different graphene stacks, are completely backfilled with the interlayer material.

[0052] In some embodiments, the interlayer comprises glass, Si, SiC, Si0₂, S1₃N₄, HfO, TiO, or any other semiconductor dielectrics. In other embodiments, the interlayer is a functional film, e.g. a transparent conductive oxide, such as ITO (indium tin oxide) or any other derivatives of such. Still in other embodiments, the interlayer is a conductive material, e.g., aluminum, tungsten, or platinum. As used herein, the term "functional" describes materials with qualities that serve one or more functions, e.g., conductivity. For example, an interlayer comprising indium tin oxide (ITO) can be used as a top lead in a solar device because it is transparent and conductive. Thus, sunlight would pass through the ITO interlayer, strike the graphene nanostructures in the graphene level directly underneath the interlayer, and cause electrons to be pulled out by the ITO interlayer, resulting in a current. Advantageous uses of the interlayer in the disclosed graphene devices include, but are not limited to implementation of wavelength band filters, concentrators, interconnects, device functionality such as line buses, drains for photo voltaic, isolation material (dielectrics), lead to batteries, work functions between the metals for band gap enhancement, leads to other elements in the electronics package such as transistor or resistors, ability to integrate Schottky barrier or diode, to name a few. Moreover, in devices in which the first and second graphene levels have different sheet thickness (i.e., different numbers of graphene sheets), the interlayer can be used to leverage the first and second graphene levels to produce a desired composite effect. For instance, with each of the first and second graphene levels having different critical dimensions as required by final functionality, the interlayer can be used to accomplish wavelength tuning and broadband coverage (including increased efficiency by cascading photon capture).

[0053] In some implementations, a functional interlayer is one of a waveguide, a diffraction film, light and/or electromagnetic collector, thermal condenser, optical condenser, lenses, nanostructures, nanonetworks, absorbers, fractal patterns, electronic components (e.g. resisters, capacitors, inductors, etc.), electrical interconnects, thermal interconnect, filaments, OLED components, transmissive conductive oxides (e.g. Indium tin oxide), a dielectric (e.g., a high K dielectric), and a flexible film. In some implementations, a functional interlayer is any combination of one or more waveguides, diffraction films, light and/or electromagnetic collectors, thermal condensers, optical condensers, lenses, nanostructures, nanonetworks, absorbers, fractal patterns, electronic components (e.g. resisters, capacitors, inductors, etc.), electrical interconnects, thermal interconnect, filaments, OLED components, transmissive conductive oxides (e.g. Indium tin oxide), dielectrics (e.g., a high K dielectric), and/or flexible films.

[0054] In some embodiments, like the optional first foundation layer, the optional second foundation layer comprises any material suitable for growing or depositing graphene. In some embodiments, the second foundation material is the same material as the first foundation material. Hence, in some embodiments, the second foundation layer is the same material as the first foundation layer. In some embodiments, the second foundation material is different from the first foundation material. In some implementations, having different materials for different foundation layers allows for different functions or different methods of forming/depositing graphene. This is because the different foundation layer materials necessarily produce graphene levels having different physical properties. In some instances such differing graphene characteristics produces a desired composite characteristic for the device as a whole.

[0055] As depicted in Fig. IB, second foundation layer 232 is already etched. In some embodiments, second foundation layer 232 is etched (although not shown) with the same processes depicted in operations 204-210 of Fig. 1A. In other embodiments, second foundation layer 232 is etched using different processes, e.g., e-beam lithography. Similarly, one or more graphene layers 252 of second graphene level 262 can be grown in the same manner as or in a different manner from graphene layers 250 of first graphene level 260. In operation 222, operations 214, 216 and 218 are repeated to form second interlayer 272, third foundation layer 234, and third graphene level 264 comprising one or more graphene layers 254. As mentioned above, graphene layers 250, 252, and 254 can comprise the same amount of graphene layers and the same graphene structures, all different numbers of layers and types of graphene structures, or a combination of the number of graphene layers and the types of graphene structures.

[0056] In Fig. IB, each graphene level, 260, 262, and 264 comprises one or more graphene stacks 261, 263, and 265, respectively. The example illustrated in Fig. IB shows graphene stacks 261, 263, and 265 as having the same or similar dimensions. The example also shows the stacks in each level being aligned. However, in some embodiments, the number of stacks for each level varies, or the dimensions of a stack for a given level differs from the dimensions of a stack for another level, as illustrated in Figs. 3A-3C. Varying the dimensions of the stacks and the number of stacks per level allows for production of various devices having advantageous properties. That is, the graphene stacks are tailored by any combination of number of layers, width, length, thickness, domain, impurities, edge conditions (chair/zigzag), contiguous nature, band gap, defects, etc., to achieve desired functionality. Such parameters are modified and tuned for the wavelength physical condition. In some embodiments, each graphene level {e.g., 260, 262, 264) has a different electromagnetic spectral response. The shorter the width of a graphene stack 261, 263, 265, the higher the band gap. The narrower the pitch of a graphene stack 261, 263, 265, the tighter the packing. The duty cycle of the pitch accounts for 'empty' or non productive space. Theoretically, there are different ways to capture a 450nm wavelength (blue channel) it can be by a narrow ribbon, or multiple layers, or 'stripping' other wavelengths (Wave guide theory). There is also the case of redundancy, if one element (20 nm wide with 30 layers of graphene) can capture 20%, then five stacked layers of the same composition would have a theoretical capture of 100%. Efficiency calculations which also include transmission, opacity and diminishing power per layer can also be considered in order to design and optimize the physical characteristics of each graphene stack in each graphene level of the resultant device. [0057] As with the first graphene level, the second graphene level comprises one or more graphene stacks. A respective graphene stack in the second graphene level includes a second graphene based nanostructure. As described above, in some embodiments, the second graphene based nanostructure is any of a variety of graphene based nanostructures, such as nanoribbons or nanonetworks. As used herein, the term nanonetworks include isolated arrays of pillars and/or cavities. Such pillars and cavities are used in antenna arrays, biomed applications sensing, evanescence, etc. The ability to stack these structures using the methods disclosed herein provides for a diverse and highly versatile array of structures. Isome embodiments, the second graphene based nanostructure is different from the first graphene based nanostructure. In other embodiments, the second graphene based nanostructure is the same as the first graphene based nanostructure.

[0058] In some implementations, the method for growing or forming/depositing graphene on the second foundation layer to form the second graphene level is a different method from that for forming the first graphene level. Alternatively, in some embodiments, the method for forming the second graphene level is the same as the method for forming the first graphene level.

[0059] Having multiple levels of graphene in a structure provides several advantages. One advantage is that each level of graphene can be specifically designed for a specific function.

For example, one level can be designed to be responsive to a first wavelength range {e.g., one portion of the visible, infrared and/or ultraviolet spectrum), while another level is designed to be responsive to a second wavelength range {e.g., another portion of the visible, infrared and/or ultraviolet spectrum). By "responsive" it is meant that in varying respective embodiments, the level emits or absorbs light in the designated wavelength range. For example, in some embodiments a first level absorbs or emits blue light whereas a second level absorbs or emits red light. The ability to provide multiple functions in the same device allows for more versatile and efficient devices (such as solar devices), integration of broadband devices (EUV through IR), increased efficiency by the design of elements to capture maximum peak wavelength energy, generation of 'neighboring effects of different

'functionality of graphene (single and multiple layers), reduced resistivity by use of more sheets, band gap tune ability, workfunction definition, denser packing of device, shorter mean free paths, better capture of photons, cascade devices (sometimes called stair case devices) where photons or wavelengths are stripped from top to bottom, advantageous optical properties and electrical interactions (e.g., sensing and response to specific wavelength at each level). An important consideration for the above is integration of functionalities.

[0060] As described above, in some embodiments that make use of a foundation material for formation of both the first and second graphene level, the respective foundation layers can each be a catalytic metal material. More generally, the first and second graphene levels can generally be formed by the same or different processes selected from the group consisting of (i) catalytic or precipitation from a metal, (ii) reverse epitaxial sublimation of silicon leaving carbon, and (iii) nucleation growth (usually on a nonmetallic metal). In some embodiments, the foundation material layer is nanopatterned, thereby forming a nanotemplate before growing graphene. Nanopatterning of the foundation material layer can be achieved using standard lithography techniques, including depositing a layer of photoresist, nanopatterning by shining light onto the photoresist layer over a mask, and chemical etching exposed areas. It should be noted that any technique that results in the catalytic nanotemplate, e.g. e-beam lithography, can be used for nanopatterning a foundation material.

[0061] Fig. 2 is a detailed graphical representation of an exemplary method for forming multilevel stacked graphene structures having backfilled interlayers, in accordance with some embodiments of the present disclosure. Operations 215-221 are analogous to operations 214- 222 of Fig. IB, except that interlayers 271 and 273 fully backfill the recesses in between graphene stacks in graphene levels 260 and 262, respectively.

[0062] Figs. 3A-3B depict detailed graphical representations of exemplary multilevel stacked graphene structures 297, 298, and 299, with variable dimensions and layouts, in accordance with some embodiments of the present disclosure. As mentioned above, one advantage of having multiple levels of graphene is the ability to design each level differently. Structure 297 of Fig. 3 A, a variation of structure 292 in Fig. IB, is an example where stacks 265, 263, and 261 , of graphene levels 264, 262, and 260, vary in width across the different graphene levels. Structure 298 of Fig. 3B is a variation of structure 297, with the stacks of each level being arranged such that the stacks of each level are not vertically aligned with stacks from another level. Structure 299 of Fig. 3C illustrates yet another variation of structure 297, with each level containing a different number of stacks.

[0063] Fig. 3A represents an embodiment in which a center of each respective graphene stack in one graphene level aligns with a center of a corresponding graphene stack in another graphene level. Moreover, although not drawn, embodiments of the present disclosure encompass structures in which a leading edge 502 of each respective graphene stack in one graphene level aligns with a leading edge 502 of a corresponding graphene stack in another graphene level. Furthermore, although not drawn, embodiments of the present disclosure encompass structures in which a trailing edge of each respective graphene stack in one graphene level aligns with a trailing edge of a corresponding graphene stack in another graphene level.

[0064] Methods for producing multilayer and multilevel graphene structures have been described above. Examples of graphene nanostructures included in the multilayer and multilevel graphene structures, as well as examples of band gap devices that may incorporate the multilayer and multilevel graphene structures, will now be described.

[0065] Fig. 4 illustrates an exemplary embodiment 400 of a multiple band gap device arranged on a substrate 102 in accordance with the present disclosure. Instead of arranging nanoribbons or stacks in one row, exemplary embodiment 400 comprises a plurality of rows, with each row having a first common lead 406 and a second common lead 408. Graphene structures 404-i and 404-j represent either a single ribbon or a stack of graphite nanoribbons (GNR) 300. Graphene structures 404-i and 404-j are either identical or have different characteristics. Each row can be electrically connected in series or parallel for a desired output. As illustrated in Fig. 4, the layout of the ribbons can be assumed to be in parallel lines. However, for optical considerations the ribbons can also be laid down in an orthogonal arrangement for additive effects and non-additive areas. In one specific embodiment, solar cells for static tracking the complementary layers can be offset by a number of degrees with respect to each other (e.g., 30, 45, or 60 degrees). Some designs are also related to a radius of curvature for exposures (e.g., Fresnel lens configurations).

[0066] Fig. 5 illustrates an additional exemplary multiple band gap device 500 in accordance with an aspect of the present disclosure, where 504 represents either a single ribbon or a stack of GNR 300, and GNN 506 represents a nanohole superlattice or a vertical stack of multiple nanohole superlattices. Nanoribbons, nanohole superlattices or stacks (formed with either nanoribbons or nanohole superlattices) in exemplary embodiment 500 are nanopatterned and arranged into a plurality of clusters (000-1 , 000-2, 000-N) on substrate 102. Each cluster is spatially separated from each other, and has its own first lead 510 and second lead 512. With respect to structure and function, 000-1, 000-2, 000-N can represent embodiments for either nanoribbons or nanoholes superlattices. Exemplary embodiment 500 is a conglomerate that comprises a plurality of multiple band gap devices. Although not illustrated, similar arrangements of pillars or cavities are encompassed in the present disclosure. In some embodiments, the arrangement of clusters 000-N, such as those depicted in Figure 5, form a single first graphene level of a graphene device, such as level 260 of Figure 1A. In some embodiments, a different arrangement of clusters 000-N, such as those depicted in Figure 5, forms each graphene level in any of the multi-level graphene device such as the devices illustrates in Figures 1, 2, and 3.

[0067] In some embodiments, cluster 000-i has the same structure as cluster 000-j. In other embodiments, cluster 000-i has the same structure as cluster 000-j, but both of them are different from cluster 000-k. In yet other embodiments, cluster 000-i has the same structure as cluster 000-j, but nanoribbons or stacks of cluster 000-i have different characteristics than nanoribbons or stacks of cluster 000-j. In some embodiments, cluster 000-i is a device comprising a plurality of lateral spaced nanoribbons, whereas in other embodiments, cluster 000-i is a device comprising a plurality of vertically stacked nanoribbons. In some embodiments, cluster 000-i is a device comprising a plurality of lateral spaced nanohole superlattices, whereas in other embodiments, cluster 000-i is a device comprising a plurality of vertically stacked nanohole superlattices. In some embodiments, cluster 000-i is a device comprising one single nanohole superlattice, whereas in other embodiments, cluster 000-i is a device comprising one single stack formed by a plurality of vertically stacked nanohole superlattices.

[0068] In some embodiments, the plurality of multiple band gap devices, or clusters 000-1, 000-2, 000-N, is geometrically arranged in a planar array, preferably with each cluster parallel or near parallel to adjacent clusters. In some embodiments, however, some clusters are displaced or tilted as shown in Fig. 5. In other embodiments, one cluster is placed on top of another cluster in the plurality of clusters. Depending on the desired application, the plurality of multiple band gap devices, or clusters 000-1, 000-2, 000-N, are electrically connected in parallel, in series, or in combination of parallel and series.

[0069] In general, each device in the plurality of multiple band gap devices or each cluster in the plurality of clusters has a width that is between 1 μιη to 10 mm and a length that is between 1 μηι to 10 mm. In some embodiments, each cluster in the plurality of clusters has a width that is between 10 μιη to 1 mm and a length that is between 10 μιη to 1 mm. In some embodiments, each cluster in the plurality of clusters has a width that is between 50 μιη to 500 μιη and a length that is between 50 μιη to 500 μιη. Additionally and/or alternatively, in some implementations, an element can be as small as 5 nm, and a cluster of elements can include two or more elements, e.g., 2-100 elements. As such, in some implementations, cluster sizes are typically corresponding multiples of a constituent element size, e.g., 10 nm, 250 nm and 500 nm, and so forth.

[0070] In some instances, exemplary embodiments 400 and 500 respectively depicted in Figs. 4 and 5 comprise an optical splitter and can be used, for example, as photovoltaic devices or photodetectors.

[0071] Figs. 6-8 provide exemplary schematic electric diagrams for a multiple band gap device in accordance with the present disclosure. In Figs. 6-8, element 602 represents all the embodiments previously described, such as embodiments 400 and 500, and equivalents within the scope of the present disclosure. Through the first lead 604 and the second lead 606, embodiment 602 can be electrically connected to a selective external circuit, creating a multiple band gap photovoltaic device 600 (Fig. 6), a multiple band gap photodetector 700 (Fig. 7), or a multiple band gap LED 900 (Fig. 8).

[0072] A multiple band gap photovoltaic device 600 is created by connecting embodiment 602 to an external load, a schematic electrical diagram of which is illustrated in Fig. 7. Represented by the resistor 608, the load is an electricity generator, a water heater, a battery, or other appliances. In some embodiments, the load is an electrical grid when embodiment 602 is connected to a main electrical grid. In some embodiments, upon receiving incident sunlight, photovoltaic device 700 produces power at 50 W/m or higher without a solar concentrator. In some embodiments, photovoltaic device 700 includes a solar concentrator and the power output is higher. For example, using a lOOx solar concentrator, a power of 5000 W/m" is achieved in some embodiments.

[0073] Connecting embodiment 602 to an electrometer produces a multiple band gap photodetector 700, a schematic electrical diagram of which is illustrated in Fig. 7. The electrometer is any type of electrometer, including vibrating reed electrometers, valve electrometers, and solid-state electrometers, and measures either electric charge or electrical potential difference. By tuning and controlling the band gaps of embodiment 602, photodetector 700 is designed to measure infrared radiation, visible light, and/or ultraviolet radiation, in wavelength ranges anywhere between 10 nm and 100 μιη.

[0074] When embodiment 602 is connected to an external current, such as a battery, a multiple band gap LED 800 is generated. Fig. 8 provides a schematic electrical diagram of a multiple band LED 900 in accordance with the present disclosure. By tuning and controlling the band gaps of embodiment 602, the multiple band gap LED 800 can emit light in a wide wavelength spectrum in the range of between 10 nm to 100 μιη. In some embodiments, the multiple band LED 900 emits a hybrid light, such as a white light.

[0075] In addition, present photovoltaic device 600, photodetector 700, and LED 800 can be integrated into more complex electronic devices to facilitate desired applications. For instance, in some embodiments the photovoltaic device 600 is combined with the LED 800 for a variety of self-sustained solar lighting applications examples of which include outdoor lighting at night. During the daytime, the photovoltaic device 600 absorbs solar energy, converts solar energy into electricity and stores electricity, for example, in a battery. At night, stored electricity powers the LED 800 causing it to light.

[0076] In some embodiments the graphene based nanostructures in one more graphene levels is a semiconducting nanohole superlattice. Figs. 9A and 9B depict a semiconducting nanohole superlattice 930 with triangular nanoholes 932 and with rectangular nanoholes 934 respectively. Other shapes of nanoholes or combination of different shapes of nanoholes can be patterned. As used herein the term "semiconducting nanohole superlattice" refers to graphene having an array of nanoholes defined therein. In some embodiments, the nanohole superlattice comprises one sheet of graphene or multiple vertically stacked sheets of graphene. The array of nanoholes can be produced using any suitable fabrication known in the art. For example, in some embodiments, a nanohole superlattice structure is patterned with one or more nanohole arrays using conventional photolithography techniques. Effectively, a nanohole superlattice is a two-dimensional network of crossing nanoribbons, in which the size, shape, and density of the nanoholes define the shape and dimensions of the nanoribbons. Thus, nanohole superlattices have similar characteristics to nanoribbons. For example, while not intending to be bound by any particular theory, the tight-binding model indicates that band gaps of graphene nanohole superlattices increase linearly with the product of nanohole size and density. This is because the width of a nanoribbon in the two- dimensional network of crossing nanoribbons can be decreased by either increasing the sizes of nanoholes or increasing the number of nanoholes in one fixed unit. Other similar characteristics include larger mean free paths for charge carriers in nanohole superlattices and dependence or weak dependence of the work functions of nanohole superlattices on the size, shape, density of the nanoholes. These characteristics make it possible to design a device with nanohole superlattices in a similar way as nanoribbons. In addition to having similar characteristics, a nanohole superlattice in general has several advantages compared to an individual nanoribbon. For instance, a nanohole superlattice usually provides more surface area for absorbing or omitting light, and hence potentially higher efficiency for any device comprising such a nanohole superlattice. Furthermore, a nanohole superlattice tolerates defects better than an individual nanoribbon.

[0077] Fig. 10 depicts a schematic top view of a multiple band gap device comprising a nanohole superlattice 930 in accordance with an aspect of the present disclosure. As in embodiments comprising nanoribbons, the nanohole superlattice is disposed on a substrate 102. There are also two leads, the first lead 1006 and the second lead 1008, electrically contact two opposite edges of the nanohole superlattice. Patterned within the nanohole superlattice is an array of rectangular nanoholes 1034. By way of illustration, rectangular nanoholes 1034 depicted in FIG. 10 have different sizes and spacing, rendering the analogous nanoribbons within the nanohole superlattice 930 having different widths. Thus the nanohole superlattice 930 is expected to have multiple band gaps. Depending on the application and the desired band gap range, an array of nanoholes having different shapes, sizes, densities, or any combination thereof is used, or is distributed differently within the nanohole superlattice. In addition, in some embodiments, the nanohole superlattice is doped, in bulk or on edges, with different dopants or concentrations, to further tune the band gap range. Other parameters, such as the thickness of the nanohole superlattice, are varied as well to modify the band gap in some embodiments of the present disclosure.

[0078] In some embodiments, the one or more nanohole superlattices are arranged vertically by stacking one on top of another or arranged laterally by placing one next to another side by side. In some embodiments, the architecture of devices having nanohole superlattices is essentially the same as those described above when using nanoribbons, whether it is vertically stacked or lateral spaced. [0079] The present disclosure provides for the fabrication of any number of graphene levels on a substrate. In some instances, the graphene levels are interspersed with interlayers. Within each graphene level there exist graphene stacks that form graphene based nanostructures. In some embodiments, the graphene stacks in any given graphene level generally have the same number of sheets of graphene, although this is not an absolute requirement. In some embodiments, the graphene stacks in one graphene level differ in some physical property from the graphene stacks in another graphene level. This advantageously provides for the ability to generation a wide array of devices, include devices in which the graphene stacks in one graphene level perform one function (because of some physical property common to these graphene stacks) while the graphene stacks in another graphene level perform another function (because of some physical property common to these other graphene stacks). Numerous examples of the wide variety of physical properties that may be shared or may be varied amongst the graphene stacks and among the graphene levels have been disclosed herein. This diversity gives rise to the ability to design a wide variety of composite devices as disclosed herein. Moreover, this is all accomplished without any requirement to post process graphene once the graphene has been formed, which is a notoriously difficult process particularly in the nanoscale dimensions some of the disclosed dimension have.

Claims

What is claimed includes:

1. A structure comprising:

a substrate;

a first graphene level overlayed on the substrate, the first graphene level comprising one or more graphene stacks, wherein a first graphene stack in the first graphene level forms a first graphene based nanostructure;

a first interlayer overlayed on the first graphene level; and

a second graphene level overlayed on the first interlayer, wherein the second graphene level comprises one or more graphene stacks, and wherein a second graphene stack in the second graphene level forms a second graphene based nanostructure.

2. The structure of claim 1, wherein the first graphene stack and the second graphene stack differ in a characteristic dimension, pitch, band gap, or index of refraction.

3. The structure of claims 1 or 2, wherein the first graphene stack is not aligned with the second graphene stack.

4. The structure of any one of claims 1-3, wherein the first graphene level and the second graphene level each comprises a respective plurality of graphene stacks.

5. The structure of claim 4, wherein spacing between graphene stacks in the first graphene level is different from spacing between graphene stacks in the second graphene level.

6. The structure of any one of claims 1-5, further comprising:

a second interlayer overlayed on the second graphene level; and

a third graphene level overlayed on the second interlayer, wherein the third graphene level comprises at least a third graphene stack, wherein the third graphene stack includes a third graphene based nanostructure.

7. The structure of any one of claims 1-6, wherein the first graphene level includes a first foundation material comprising Ni, Cu, Pt, Au, Fe, Rh, Ru, Ti, Ir, Si, SiC, boron doped SiC, or any combination thereof.

8. The structure of any one of claims 1-7, wherein the second graphene level includes a second foundation material comprising Ni, Cu, Pt, Au, Fe, Rh, Ru, Ti, Ir, Si, SiC, boron doped SiC, or any combination thereof.

9. The structure of any one of claims 1-8, wherein the first or second graphene levels comprise a graphene nanoribbon, a graphene nano-network, a graphene pole, a graphene pillar, or a graphene based nanohole superlattice.

10. The structure of any one of claims 1-9, wherein the substrate comprises glass, silicon, SiC, Si0₂ or SiC/Si.

11. The structure of any one of claims 1-10, wherein the first interlayer comprises glass, Si, SiC, Si0₂, Si₃N₄, HfO, TiO, indium tin oxide, Al, W, or Pt.

12. The structure of any one of claims 1-8, wherein the first graphene level comprises a graphene based nanohole superlattice comprising a plurality of layers arranged on the substrate, the plurality of layers having an array of holes defined therein, and wherein the first graphene level is characterized by a band gap or a band gap range.

13. The structure of any one of claims 1-10, wherein the first interlayer is a transparent conductive oxide.

14. The structure of any one of claims 1-13, wherein the first graphene level and the second graphene level differ in a curvature, an edge shape, or a width.

15. The structure of any one of claims 1-14, wherein the first interlayer comprises at least one of waveguide, a diffraction film, an electromagnetic collector, a thermal condenser, an optical condenser, a lens, a nanostructure, a nanonetwork, an absorber, a fractal pattern, an electronic component, an electrical interconnect, a thermal interconnect, a filament, an OLED, a transmissive conductive oxide, a dielectric, and a flexible film.

16. A structure comprising :

a substrate;

a first graphene level, the first graphene level comprising a first plurality of graphene stacks, wherein each respective graphene stack in the first plurality of graphene stacks is (i) overlayed on the substrate and (ii) spatially separated from all other graphene stacks in the first plurality of graphene stacks;

a first interlayer overlayed on the first graphene level; and

a second graphene level, the second graphene level comprising a second plurality of graphene stacks, wherein each respective graphene stack in the second plurality of graphene stacks is (i) overlayed on the first interlayer and (ii) spatially separated from all other graphene stacks in the second plurality of graphene stacks.

17. The structure of claim 16, wherein

each respective graphene stack in the first plurality of graphene stacks has the same first thickness,

each respective graphene stack in the second plurality of graphene stacks has the same second thickness, and

the first thickness is other than the second thickness.

18. The structure of claim 16, wherein spatial separations between the plurality of graphene stacks in the first plurality of graphene stacks forms a plurality of spaces and the first interlayer backfills into the plurality of spaces.

19. The structure of claim 16, wherein spatial separations between the plurality of graphene stacks in the first plurality of graphene stacks forms a plurality of spaces and the first interlayer overlays these spaces thereby forming air gaps in the graphene structure.

20. The structure of any one of claims 16-19, wherein

a first graphene stack in the first plurality of graphene stacks is characterized by a first value for a physical property,

a second graphene stack in the second plurality of graphene stacks is characterized by a second value for a physical property, and

wherein the first value is other than the second value.

21. The structure of claim 20, wherein the physical property is a number of graphene layers, a width, a length, a thickness, an impurity concentration, an edge condition, a band gap, a defect, or an electromagnetic spectral response.

22. The structure of any one of claims 16-19, wherein the first plurality of graphene stacks is collectively characterized by a first value for a physical property,

the second plurality of graphene stacks is collectively characterized by a second value for a physical property, and

wherein the first value is other than the second value.

23. The structure of claim 22, wherein the physical property is a graphene stack packing density, a duty cycle, a pitch, an index of refraction, a band gap, or an electromagnetic spectral response.

24. The structure of any one of claims 16-23, wherein

the first plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged in parallel on the substrate, and

the second plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged in parallel on the first interlayer.

25. The structure of claim 24, wherein the spacing between graphene stacks in the first plurality of graphene stacks is different than the spacing between graphene stacks in the second plurality of graphene stacks.

26. The structure of any one of claims 16-25, wherein

the first plurality of graphene stacks are spaced apart from each other with a first spacing interval, and

the second plurality of graphene stacks are spaced apart from each other with a second spacing interval.

27. The structure of claim 26, wherein the first spacing interval is the same as the second spacing interval.

28. The structure of claim 26, wherein the first spacing interval is different than the second spacing interval.

29. The structure of any one of claims 16-25, wherein

the first plurality of graphene stacks are spaced apart from each other and are arranged at acute angles on the substrate with respect to each other, and the second plurality of graphene stacks are spaced apart from each other and are arranged at acute angles on the first interlayer with respect to each other.

30. The structure of any one of claims 16-23, wherein

the first plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged at acute angles on the substrate with respect to each other, and

the second plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged at acute angles on the first interlayer with respect to each other.

31. The structure of any one of claims 16-23, wherein

the first plurality of graphene stacks are nanoribbons that are spaced apart from each other with a first spacing, and

the second plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged so that each respective graphene stack in the second plurality of graphene stacks aligns with a corresponding graphene stack in the first plurality of graphene stacks.

32. The structure of any one of claims 16-22, wherein a center of each respective graphene stack in the second plurality of graphene stacks aligns with a center of a corresponding graphene stack in the first plurality of graphene stacks.

33. The structure of any one of claims 16-22, wherein a leading edge of each respective graphene stack in the second plurality of graphene stacks aligns with a leading edge of a corresponding graphene stack in the first plurality of graphene stacks.

34. The structure of any one of claims 16-22, wherein a trailing edge of each respective graphene stack in the second plurality of graphene stacks aligns with a trailing edge of a corresponding graphene stack in the first plurality of graphene stacks.

35. A structure comprising :

a substrate;

a first graphene level, the first graphene level comprising a first plurality of graphene stacks, wherein each respective graphene stack in the first plurality of graphene stacks is (i) overlayed on the substrate and (ii) spatially separated from all other graphene stacks in the first plurality of graphene stacks; and a second graphene level, the second graphene level comprising a second plurality of graphene stacks, wherein each respective graphene stack in the second plurality of graphene stacks is (i) overlayed on a corresponding graphene stack in the first plurality of graphene stacks and (ii) spatially separated from all other graphene stacks in the second plurality of graphene stacks.

36. The structure of claim 35, wherein

each graphene stack in the first plurality of graphene stacks has the same first thickness,

each graphene stack in the second plurality of graphene stacks has the same second thickness, and

the first thickness is other than the second thickness.

37. The structure of claim 35 or 36, wherein

wherein the first value is other than the second value.

38. The structure of claim 37, wherein the physical property is a number of graphene layers, a width, a length, a thickness, an impurity concentration, an edge condition, a band gap, a defect, or an electromagnetic spectral response.

39. The structure of any one of claims 35-38, wherein

the first plurality of graphene stacks is collectively characterized by a first value for a physical property,

the second plurality of graphene stacks is collectively characterized by a second value for a physical property,

wherein the first value is other than the second value.

40. The structure of claim 39, wherein the physical property is an index of refraction, a band gap, or an electromagnetic spectral response.

41. The structure of any one of claims 35-40, wherein the first plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged in parallel on the substrate.

42. The structure of any one of claims 35-41, wherein the spacing between graphene stacks in the first plurality of graphene stacks is different than the spacing between graphene stacks in the second plurality of graphene stacks.

43. The structure of any one of claims 35-40, wherein the first plurality of graphene stacks are nanoribbons that are spaced apart from each other and are arranged at acute angles on the substrate with respect to each other.

44. The structure of any one of claims 35-41, wherein a center of each respective graphene stack in the second plurality of graphene stacks aligns with a center of a corresponding graphene stack in the first plurality of graphene stacks.

45. The structure of any one of claims 35-41, wherein a leading edge of each respective graphene stack in the second plurality of graphene stacks aligns with a leading edge of a corresponding graphene stack in the first plurality of graphene stacks.

46. The structure of any one of claims 35-42, wherein a trailing edge of each respective graphene stack in the second plurality of graphene stacks aligns with a trailing edge of a corresponding graphene stack in the first plurality of graphene stacks.