GB1572181A - Device comprising a thin film of organic materila - Google Patents

Description

(54) DEVICE COMPRISING A THIN FILM OF ORGANIC MATERIAL (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to composite devices comprising thin film components.

Many devices, particularly electrical, electrochemical or photochemical devices, comprise one or more very thin films or layers of material, for example of insulating material, of thickness usually not exceeding 5000A and often not exceeding 100A. It is often important or at least desirable that such films are free from imperfections such as, for example, discontinuities or regions of uneven thickness. Conventional techniques for the preparation of such films have usually involved deposition from vapour or the use of thermally grown oxide films.

The present invention provides an electronic, electrical, electrochemical or photochemical device comprising a thin film of organic material, which film is prepared by a process which comprises forming a monomolecular layer of the organic material upon the surface of a suitable supporting liquid and repeatedly passing a substrate through the layer so that a film comprising a plurality of monomolecular layers of the organic material is deposited upon the surface of the substrate.

Such films if carefully prepared show a high degree of molecular orientation and relative freedom from discontinuities.

The deposited film of organic material may be employed as such, but it will often be found desirable to extend its applicability by, say, interlaying with other materials to modify its properties. The number of monomolecular layers may also be varied. For example, for thin film transistor (TFT) applications we may deposit a large number of layers (film thicknesses typically between 100A and 5000A), whereas for hot electron tunnelling applications a much smaller number of layers, would be more appropriate (film thicknesses usually less than 100A).

The process for the deposition of monomolecular layers is known, but for convenience is described in outline below.

The supporting subphase liquid is preferably one which is inert to the organic material, that is, it does not react chemically with the material of the monomolecular layer or of the substrate under the conditions employed in the process of the invention, (although on occasion it may be desirable to include materials which do not act disadvantageously with the film), nor will it usually be a solvent for the organic material although some solubility is not necessarily detrimental so long as the film is not thereby destroyed or its formation prevented. The liquid may be organic or inorganic; usually we prefer to use water, although the presence of certain inorganic ions may improve the stability of the organic layer.

Formation of the monomolecular layer of the organic material on the surface of the supporting liquid is most conveniently effected by applying to the surface of the liquid an appropriate volume of a solution of the organic material in a volatile solvent which is immiscible with the supporting liquid under the process conditions employed. The concentration of the organic material in the solution is selected such that the evaporation of the solvent leaves behind a layer of the desired thickness on the surface of the supporting liquid.

Transfer of the organic material to the substrate, is effected by dipping the substrate into the supporting liquid and withdrawing it again, so that a coherent film of organic material adheres to the surface of the substrate. Provision of means for maintaining the integrity of the film on the liquid is necessary and this means can comprise a sweep or paddle, preferably responsive to a microbalance which constantly measures the pressure of the film upon the supporting liquid. This feature of maintaining pressure upon the film is important for the production of an aligned continuous film upon the substrate.

The method described lends itself particularly to 'doping', either by incorporating the dopant as an 'impurity' at a suitable concentration in the film of organic material on the supporting liquid, by deposition of the dopant as a separate layer, or by interleaving with the organic material (usually referred to as the host material).

Suitable dopants include for example colorants intended to alter the colour of radiation emitted from an electroluminescent device comprising a film according to the invention.

Examples of devices obtained using such a technique include a device comprising alternate layers of a photoconductor and sensitiser, alternate p-type and n-type layers or alternate semiconductor/insulator layers. For example, Esaki structures, known as superlattices, require the use of very thin components-each layer usually being of the order of 40A thick.

The devices of the invention find many applications, depending upon the precise configuration employed and circumstances of use. For example: A. Electroluminescent devices Electroluminescent devices may be prepared which comprise a film of a suitable electroluminescent material applied as described. As examples of suitable organic film materials we would mention particularly anthracene, pyrene and perylene derivatives.

In such an application, the device may comprise a film of a suitable anthracene or other derivative (as described above), the film, and preferably each side of the film, being in electrical contact with two separate electrodes. Preparation of such a device may, for example, comprise the formation upon a suitable substrate of a first layer of an electrode material, deposition of a film (preferably of the order of lOOO-lOOOOA thick) of the derivative upon the conducting material, or upon a portion thereof, and subsequent deposition of a second layer of an electrode material to the film derivative. The arrangement of the first and second electrodes will be such, of course that they are not in physical contact one with the other.

One electrode material for such an application as described above may be for example any appropriate electron-injecting material, e.g. Awl203 on Al3, or other suitable material alone or in suitable admixture, a second electrode material being any appropriate positive-hole injecting-material e.g. Au, Pt, CuOlI (I diffused into CuO), Se/Te alloy, or mixtures thereof. The use of organic positive-hole injecting materials is not excluded as electrode, as neither is the use of transparent~SnO2 (with or without dopants) or any other suitable conducting material, coated on any suitable substrate, e.g. glass.

B. Photoconductors Further devices of the invention include improved photoconductive and photovoltaic systems in which deposition of molecularly ordered material may be an important factor in optimising performance.

The photoconductive gain of a semi-conductor is given by t/td where t is the lifetime of the charge carrier and td is the time taken for it to drift through the sample under the influence of an applied voltage. Consequently, for a large gain, td should be small, which in turn requires the sample thickness to be small. Thin films deposited as described above are particularly advantageous in this context.

Photovoltaic devices are well-known and rely upon the formation of a barrier at the interface between two materials e.g. pn junctions or M-I-S tunnel diodes for their effectiveness. When electron-hole pairs are created by light incidence, the electrons and holes are swept to opposite sides of the junction; for maximum efficiency it is desirable that the total resistance of the structure is low and thin films of a semiconductor and/or tunnel insulator obtained as described are particularly advantageous in this application.

C. Superconductors The superconducting state in metals and alloys occurs as a result of an attractive interaction between electrons which is brought about by the conduction electron polarising ions in the crystal lattice. The transition to the superconducting state occurs at temperatures lower than 25"K for all known materials. Devices according to the present invention may comprise two dimensional multilayer structures of suitable materials which display the phenomenon of superconductivity including, optionally, superconductivity at a temperature above 25"K. The structures are illustrated diagrammatically in Figures 6 and 7 in the attached drawings and comprise essentially a layer of a polarisable dielectric material in contact with a layer of a conducting material; said layers preferably are bounded by insulating material, as shown in the diagrams. The conducting layer comprises a two dimensional close packed array of electronically conducting organic molecules; the insulating layer is composed of hydrocarbon chains.

An example of a polarisable dielectric material is a 4,4'-quinolinium cyanine dye, the hydrocarbon chain (for example C,8H37) attached to the dye acting as an insulator. The conducting layer is formed from molecules of 7,7',8,8'tetracyanoquinodimethane (TCNQ) or its anionic salt or some intermediate structure carrying a partial negative charge.

The preferred orientation of the polarisable molecule with respect to the conducting layer is one in which one end of the molecule is in close contact with this layer (within 5A). The other end of the molecule should be remote from the conducting layer.

In molecules such as that of a cyanine dye suitable for use as the polarisable material, the balance of hydrophobic (long alkyl chain) and hydrophilic (quinolinium salt) groups enables the molecule to be deposited as an oriented thin film using the dipping technique described (conveniently referred to as the Langmuir trough technique). Mixed mono-layers and multilayers of dyes with nonpolarisable molecules (e.g. salts of long-chain fatty acids) can also be employed.

The following types of materials are particularly suitable for use according to this aspect of the invention: 1. Cyanine dyes 2. Dimethylamino styryl dyes 3. Merocyanine dyes 4. Triphenylmethane dyes 5. Heterocyclic salts 6. Radical ion systems These materials must of course be suitably modified by incorporation of a hydrocarbon chain to confer surface activity so that the Langmuir Trough technique can be used for fabrication, where the properties of the material are not already suitable.

By use of the Langmuir deposition technique the molecule can be manipulated to give a very close packed monolayer which the long axis of a cyanine dye for example is perpendicular to the plane of the interface between the two phases. The distance between the planes of this molecule is then of the order of 3-SA. Mixed mono-layers may also be formed in which the cyanine is mixed with inactive i.e.

non-polarisable molecules, e.g. salts of long chain fatty acids e.g. stearic, arachidic, etc.

D. Electrical devices The invention provides also improved electrical devices that may be classified as diodes or transistors. Some of these rely on a structure in which a relatively thick insulating film is sandwiched between a metal and a semiconductor. In these structures the reactance/capacitance can be varied in a controlled manner using a bias voltage. If the insulating film is made sufficiently thin (of the order of loA to I 00A) quantum tunnelling can occur and this ract may be made use of in a variety of electrical devices. Another application of the invention involves devices having layers with specific properties.

The invention will now be described in more detail in relation to specific devices, some of which may be novel per se and do not necessarily involve the use of the specific film deposition technique already described, although it may be preferred. fleference is made to the attached Figures which are diagrammatic and not to scale.

In the first class of devices we include the varactor, the gate controlled diode, the IGFET and the thin film transistor.

(i) Veractor This is a device whose reactance/capacitance can be varied in a controlled manner using a bias voltage. Such devices comprise essentially a metal-insulatorsemi-conductor structure. The advantages of employing an insulating film deposited using the Langmuir process are that a higher capacitance may be obtainable due to the possibility of obtaining a very thin, large area film, lower operating voltages due to the thin insulating layer, and improved reproducibility and reliability of the device.

(ii) Gate Controlled Diode (Figure 1) This comprises an n+ highly doped semiconductor region formed on a p-type semiconductor substrate (or the equivalent structure on an n-type semiconductor).

The insulator, which is advantageously deposited using the Langmuir process produces an M-I-S type arrangement in which the p-n junction characteristics are modulated by the applied field across the M--ZZ-S annular structure.

(iii) Field Effect Transistors The basic principle common to all types of unipolar transistors is the control by a gate electrode of current flow between a source and a drain electrode. The common feature of these transistor devices is that an insulating layer located between a metal gate electrode and an active semiconductor layer essentially forms a capacitor. A change in the voltage applied across the structure changes the conductance of the surface channel through which the source-drain current flows.

Thus, the conductance of the channel is modulated by the gate bias voltage.

The fabrication of thin layer devices, and particularly the fabrication of transistors which rely for their operability upon the accurate spacing of their components, depends upon the accuracy with which the various components may be deposited. For example, to avoid undesirable capacitative effects it is important that in a thin film transistor the gate electrode is laid down in register with the channel between the source and drain electrodes. (Sections of typical transistor configurations are shown diagrammatically in the attached drawings and are described in more detail below. The diagrams are, of course, very greatly magnified-many of the thin-film components of transistors are of the order of only thousandths of a millimetre in thickness). It is well known that a difficulty associated with the fabrication of thin film transistors is the preparation of an insulating layer which is free from imperfections and we have found that the film deposition technique already described facilitates the preparation of satisfactory insulating layers for this purpose and films may be deposited to form a multilayer insulating component of appropriate thickness for the intended purpose.

(a) Insulated gate field effect transistor (Figure 2) This comprises two n+ highly donor-doped electrodes formed on a p-type semiconductor substrate or vice versa. The electrodes serve as source and drain electrodes. The insulator, which is advantageously deposited using the Langmuir process, is reasonably thick, of the order of 500 to 2000A, although thicknesses not within this range may be acceptable with the use of an appropriate gate voltage-lower voltages and hence thinner insulating layers (down to say, 100A being more convenient in some applications.

In such devices only a small current can flow from the source to drain electrode unless a sufficiently large bias voltage is applied to the gate electrode, in which case the conductance of the source-drain channel increases many-fold.

(b) Thin film transistor (Figure 3) The Figure shows in diagrammatic form a typical thin film transistor. The mode of operation is essentially similar to that of the insulated gate field effect transistor. except that a thin semiconductor film is used deposited on an insulating substrate. The source and drain electrodes are usually metallic. A relatively thick insulator layer (ca. lOOOA) is usual in such devices, but using the Langmuir process it is possible to deposit thin defect-free layers which are effective down to about 150A (thicknesses less than this are undesirable because tunnelling may occur).

Thus, we may employ insulator thicknesses between 100 and 5000A, preferably between 200 and 2000A and more preferably between 250A and IOOOA the insulator thickness gate voltage, of course, being compatible. For example using an insulator layer 500A thick the gate voltage may be, say, 0.5v instead of the more usual lv.

The semiconductor film also may be deposited by the Langmuir process.

In the second class of devices we include those that require control of the interfacial barrier height between a metal and a semiconductor to enable charge transport to occur across the interface by tunneling.

(iv) Electroluminescent devices If an insulating film is deposited between a metal electrode and an electroluminescent material (e.g. ZnS, GaN, GaP, anthracene), and a voltage applied across the device; some voltage drop occurs across the insulating film thus shifting the Fermi level of the metal relative to that of the semiconductor. The electrons, upon application of a suitable voltage, can tunnel into the semi-conductor from the electrode and the electrons recombine radiatively with holes in the semiconductor. Such devices may very conveniently be obtained by deposition of the insulator material by the Langmuir process.

(v) Gun effect Many devices such as the Gunn effect oscillator work most efficiently when a barrier (typically about 0.3 eV high) is present at the metal/semi-conductor interface. This cannot always be achieved using a metal contact alone owing to the presence of surface or interface states. Thus, the principle described in (iv) above is used in a Gunn effect device to lower or raise the Fermi level of the semiconductor relative to that of the metal. Again, suitable devices may be prepared by deposition of an insulating barrier by the Langmuir process.

(vi) Hot electron transistors These consist essentially of a metaVinsulator/metal/insulator/metal sandwich.

Electron tunneling occurs through the insulator layers, which therefore need to be between 10 and lOOA thick. Use of the Langmuir deposition process in the preparation of such layers is advantageous.

(vii) Floating gate field effect transistor (Figure 5) These devices are very similar to those shown in Figures 2 and 3, with the addition of a further metal insulator combination. Upon application of a positive bias, electrons tunnel through the additional very thin (up to IOTA, usually 25 to IOOA) insulator and form an accumulation of electrons in the Floating Gate. When the field is removed these charges remain on the gate with the result that there is created a 'permanent' high conductance region in the semi-conductor. The device therefore has a memory. Insulator 1 will usually be of the order of lOOOA thick (as in a conventional TFT).

As examples of the invention requiring thin layers with specific properties we include the integrated thin-film transistor and the phototransistor.

(viii) Integrated thin film transistor (Figure 4) It has been observed that films of many organic materials e.g. anthracene and its derivatives, deposited as hereinbefore described, display a large anisotropy of conductivity parallel and perpendicular to the plane of the layers. For fields of the order 106 V/m we have measured in a twenty layer Cd C4 anthracene propionate film an anisotropy of 104. Integrated devices based on this fact and exemplified by that illustrated diagrammatically in Figure 4, may comprise a film of an appropriate organic material displaying anisotropy and capable of acting as described, having on one surface a plurality of source-drain electrodes, the other surface being in contact with a metal gate electrode.

Separation of the source/drain electrodes may be as small as l,u (with suitably low currents), and the thickness of the film may be 100 to 5000A, preferably 200 to IOOOA thick.

In such a device the film acts both as the semiconductor and the insulator layer-when no gate voltage is applied reasonable conductivity exists between the source and drain electrodes; application of a gate voltage either enhances or reduces the conductance of the channel.

(ix) Photo-thin film transistor This device is essentially similar to the preceding device, except that the metal gate is replaced by a suitable photoconductor which forms a p-n junction with the film. Light falling upon the p-n junction generates a photo-voltage which produces a change in the conductance of the source-drain channel. Such a device could function for example, as a light detector.

Alternative arrangements are similar to that of Figure 3, but having a photoconductor deposited between the gate electrode and the insulator so that light falling on the photoconductor renders it more conducting, resulting in a voltage drop across the insulator which produces a change in conductance of the source-drain channel; or having a photosensitive material (e.g. a dye) located between the gate and insulator or incorporated in the insulator as dopant. Light falling on the photosensitive material causes charge carriers to be injected into the dielectric under the influence of the gate voltage where they affect the source-drain channel conductance.

We also include in this section transistors relying on special thin films (in place of or overlaying the insulating film) that are sensitive to pressure, temperature, certain chemicals and gases.

It will be apparent that the successful operation of many of the devices mentioned depends upon the accurate laying down of the film upon the substrate, not only so that a coherent film is obtained over a relatively large area, but also so that the actual area over which the film is laid down can be controlled.

It will also be apparent that many of the devices described comprise essentially a film of an organic material having properties appropriate to an intended function of the device, the film conveniently deposited using the Langmuir process, and the film usually being in electrical contact with at least one, often two and sometimes three or more electrode materials. In addition to this basic structure many devices according to the invention will comprise in addition a substrate and other structural or functional components.

Examples of materials which may find application for use as a thin film insulator are fatty acids and their salts, e.g. stearic (and particularly its Cd, Ba and Ca salts); arachidic (and particularly its Cd, Ba and Ca salts); orthophenanthroline; suitably modified dyes; cholesterol; chlorophyll and TCNQ.

Usually long chain molecules are employed but short chain molecules are not excluded.

Examples of materials suitable as source and drain electrodes are metal elements, alloys and metal oxides and salts, e.g. Au, Al, In, Ag; high conductivity semiconductors, e.g. Te, and conducting organic materials e.g. bisbenzthiazole azine disulphonic acid. Similar materials may be used as gate electrodes components.

Insulating substrates may be any of a wide range of materials, e.g. mica, glass, sapphire, cleaved crystals, high thermal conductivity plastics.

The material of the active layer may comprise any of a wide range of semiconductor materials, including CdS, CdSe, GaAs, Si, PbS, InAs, InSb, InP, Te, phthalocyanine, violanthrene, porphyrins, and derivatives of anthracene, of tetracene, of naphthalene, of pyreiie and of perylene. In some cases it may be convenient to oxidise or treat the surface of the active layer to facilitate efficient transfer of the Langmuir film.

As examples of organic materials which may be incorporated in the devices of the invention, dependent upon the material having appropriate properties which may be determined by simple trial in the light hereof, we would mention particularly those materials having a planar delocalised system of 7r electrons which may be cyclic or acyclic. For preparation of the film using the Langmuir process the material should usually have both hydrophilic and hydrophobic properties, conveniently resulting from the presence in the molecule of suitable groupings.

Typical hydrophobic groups include hydrocarbon groups which are usually linear alkyl groups but which may be branched alkyl or linear polyacene chains or aromatic rings.

Where the hydrophobic group is a hydrocarbon chain it is often desirable that the organic material does not comprise a hydrophobic chain more than 10 carbon atoms in length (i.e. straight chain length) and preferably comprises no hydrophobic group greater than from 3 to 8 carbon atoms in chain length; preferably any such chain will be linear. Longer hydrophobic chains are not excluded.

A compound comprising a plurality of both hydrophobic and hydrophilic groups may be employed, but the "hydrophobic/hydrophilic balance" should be retained, for example so that the compound does not dissolve or disperse in the subphase liquid so that it does not form a film thereon and also such that it does not become so overwhelmingly hydrophobic that the film is unstable.

Usually, therefore, the organic compound will have the structure: R-C-X where R is a hydrophobic group, X is a hydrophilic group and C is a cyclic or acyclic structure having a planar delocalised system of -electrons, although where C itself has marked hydrophobic or hydrophilic properties R or X as appropriate may be absent. Preferably C is a cyclic structure, and it may comprise substituents in addition to R and X, for example H, halogen, quinoid oxygen, doubly bound sulphur, nitro, dimethylamino, acyl and oxyamino. One or more of such substituents may function as metal ligands.

Alternative arrangements of constituents may be C - R - X or C - X - R.

Where C is cyclic it may comprise one or more rings, which may be homoor heterocyclic, and which may include metal atoms.

As examples of classes of organic compound which may be employed as a film component in the described manner we would mention the following. (In the formulae R is preferably a normal alkyl chain of length not greater than 10, more preferably 3-8, carbon atoms although longer chain lengths e.g. up to about 18 carbon atoms are possible and n may be O or an integer not greater than 12 and preferably I to 3).

Homocyclic compounds

Heterocyclic compounds

eN YNyMe < NIMe Sk ;N+3R BF4 R BF R R1 A (CH2)nX (64) (65) (66) (67) R R p R R-Q i"-0 R < 3NOle MeNCO SNMeHeNNM2 H MeN (68) (69) (70) p p RN > NMe MeN 1NNMe N NMe BF7 (71) (72) (73) Transition Metal Complexes C6H5 S"'NiS S\NiAI I p/\ N N 06h5 Hg (74) (75) (76) Cl Go 0000 0o0o0 00M OCOR 3J (77) (78) o 502NHR 1 GO S02NHR 0 NH N ; < 502NOR 0 (79) (80) The precise location of the substituents indicated may not be important, and additional substituents may be incorporated into the above molecules, consistent with the resulting material being capable of forming a monomolecular layer upon a suitable liquid and of being deposited in a suitably integral form upon a substrate to give a film having desired properties.

Mononuclear heterocyclic compounds, we have found, can be formed into Langmuir f lms only with great difficulty and are preferably avoided.

The invention is illustrated by the following Examples.

Example 1.

Thin film transistor A film of cadmium sulphide 10z1 thick was formed upon one surface of a thoroughly cleaned quartz disc substrate 2.5 cm diameter subphase consisting of ultra pure water at pH 4.5 containing 2.5 x 10-4M barium chloride and carrying a monomolecular layer of the cadmium salt of 9-butyl-l0anthryl propionic acid (applied as a I mg/ml solution in chloroform). Dipping was effected at 19--210C, at a rate of 3.7 mm/min and a surface pressure of 15 + I dynes/cm. 20 Layers of the anthracene derivative were picked up by dipping.

Two gold electrodes, each 7 x 2 mm and 500A thick and 25y apart were applied to the surface of the film so obtained and electrical contact with the electrodes made via silver paste.

The surface conductivity of the film was observed in the dark and during irradiation with white light. The current/voltage curve shown in Figure 9 was obtained.

Example 5.

One surface of a glass slip, cleaned as in Example 4 but omitting the treatment with NaOH, was coated by evaporation with a 500A thick layer of aluminium. The slip was dipped as described in Example 4 except that the Langmuir film was the barium salt of 9-butyl-l0-anthryl propionic acid. 467 Layers were applied to the slip. A pattern of aluminium dots, each 2.5 mm in diameter and 300 thick, was deposited from vapour through a mask onto the anthracene film so obtained.

Application of a current of 40 v, DC or AC, (Au&commat;, Al) produced an emission of blue light.

Attention is drawn to copending application 34264/75 (Serial No. 1,572,182) in which is claimed a method of preparing an electrical, electrochemical or photochemical device comprising a sheet or film of organic material, said sheet or film having a high degree of molecular orientation, upon a substrate, the method comprising forming a monomolecular layer of an organic material having a planar delocalised system of 'v-electrons upon the surface of a suitable liquid and repeatedly passing a substrate through the layer so that a film comprising a plurality of monomolecular layers is formed upon a surface of the substrate.

WHAT WE CLAIM IS:- 1. An electronic, electrical, electrochemical or photochemical device comprising a substrate in association with a thin film of an organic material, which film is prepared by a process which comprises forming a monomolecular layer of the organic material upon the surface of a suitable supporting liquid and repeatedly passing the substrate through the layer so that a film comprising a plurality of monomolecular layers of the organic material is deposited upon the surface of the substrate.

2. A device according to claim 1 in which the film is from 10 to l0000A thick.

3. A device according to claim 1 or 2 in which the film is in electrical contact with at least one electrode material.

4. A device according to any of the preceding claims in which the film is an insulator.

5. A device according to any of claims 1 to 3 in which the film is a semiconductor.

6. A device according to any of the preceding claims in which the organic material of the film comprises a cyclic or acyclic organic compound having a planar delocalised system of or-electrons.

7. A device according to any one of the preceding claims in which the organic material has the structure R-C-X where R is a hydrophobic group, X is a hydrophilic group and C is a cyclic or acyclic structure having a planar delocalised system of 7r-electrons.

9. A device according to claim 1 and substantially as hereinbefore described.

10. A device according to claim 1 and substantially as hereinbefore described with reference to any one of the examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   subphase consisting of ultra pure water at pH 4.5 containing 2.5 x 10-4M barium chloride and carrying a monomolecular layer of the cadmium salt of 9-butyl-l0anthryl propionic acid (applied as a I mg/ml solution in chloroform). Dipping was effected at 19--210C, at a rate of 3.7 mm/min and a surface pressure of 15 + I dynes/cm. 20 Layers of the anthracene derivative were picked up by dipping.

   Two gold electrodes, each 7 x 2 mm and 500A thick and 25y apart were applied to the surface of the film so obtained and electrical contact with the electrodes made via silver paste.

   The surface conductivity of the film was observed in the dark and during irradiation with white light. The current/voltage curve shown in Figure 9 was obtained.

   Example 5.

   One surface of a glass slip, cleaned as in Example 4 but omitting the treatment with NaOH, was coated by evaporation with a 500A thick layer of aluminium. The slip was dipped as described in Example 4 except that the Langmuir film was the barium salt of 9-butyl-l0-anthryl propionic acid. 467 Layers were applied to the slip. A pattern of aluminium dots, each 2.5 mm in diameter and 300 thick, was deposited from vapour through a mask onto the anthracene film so obtained.

   Application of a current of 40 v, DC or AC, (Au&commat;, Al) produced an emission of blue light.

   Attention is drawn to copending application 34264/75 (Serial No. 1,572,182) in which is claimed a method of preparing an electrical, electrochemical or photochemical device comprising a sheet or film of organic material, said sheet or film having a high degree of molecular orientation, upon a substrate, the method comprising forming a monomolecular layer of an organic material having a planar delocalised system of 'v-electrons upon the surface of a suitable liquid and repeatedly passing a substrate through the layer so that a film comprising a plurality of monomolecular layers is formed upon a surface of the substrate.

   WHAT WE CLAIM IS:-

   1. An electronic, electrical, electrochemical or photochemical device comprising a substrate in association with a thin film of an organic material, which film is prepared by a process which comprises forming a monomolecular layer of the organic material upon the surface of a suitable supporting liquid and repeatedly passing the substrate through the layer so that a film comprising a plurality of monomolecular layers of the organic material is deposited upon the surface of the substrate.

   2. A device according to claim 1 in which the film is from 10 to l0000A thick.

   3. A device according to claim 1 or 2 in which the film is in electrical contact with at least one electrode material.

   4. A device according to any of the preceding claims in which the film is an insulator.

   5. A device according to any of claims 1 to 3 in which the film is a semiconductor.

   6. A device according to any of the preceding claims in which the organic material of the film comprises a cyclic or acyclic organic compound having a planar delocalised system of or-electrons.

   7. A device according to any one of the preceding claims in which the organic material has the structure R-C-X where R is a hydrophobic group, X is a hydrophilic group and C is a cyclic or acyclic structure having a planar delocalised system of 7r-electrons.

   9. A device according to claim 1 and substantially as hereinbefore described.

   10. A device according to claim 1 and substantially as hereinbefore described with reference to any one of the examples.