WO1983003165A1 - Polymeric films - Google Patents

Polymeric films Download PDF

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Publication number
WO1983003165A1
WO1983003165A1 PCT/GB1983/000065 GB8300065W WO8303165A1 WO 1983003165 A1 WO1983003165 A1 WO 1983003165A1 GB 8300065 W GB8300065 W GB 8300065W WO 8303165 A1 WO8303165 A1 WO 8303165A1
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Prior art keywords
process according
substrate
polymer
preformed
coated
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PCT/GB1983/000065
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French (fr)
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Research Development Corporation National
Original Assignee
Winter, Christopher, Simon
Tredgold, Richard, Harfield
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Application filed by Winter, Christopher, Simon, Tredgold, Richard, Harfield filed Critical Winter, Christopher, Simon
Priority to JP83500897A priority Critical patent/JPS59500339A/en
Publication of WO1983003165A1 publication Critical patent/WO1983003165A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02109—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates
    • H01L21/02112—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer
    • H01L21/02118—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer carbon based polymeric organic or inorganic material, e.g. polyimides, poly cyclobutene or PVC
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/18—Processes for applying liquids or other fluent materials performed by dipping
    • B05D1/20—Processes for applying liquids or other fluent materials performed by dipping substances to be applied floating on a fluid
    • B05D1/202—Langmuir Blodgett films (LB films)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/0226—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process
    • H01L21/02282—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating
    • H01L21/02285—Langmuir-Blodgett techniques
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/28008—Making conductor-insulator-semiconductor electrodes
    • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
    • H01L21/28158—Making the insulator
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/28008—Making conductor-insulator-semiconductor electrodes
    • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
    • H01L21/28158—Making the insulator
    • H01L21/28167—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
    • H01L29/51—Insulating materials associated therewith
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/701—Langmuir Blodgett films
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having a potential-jump barrier or a surface barrier
    • H10K10/20—Organic diodes
    • H10K10/23—Schottky diodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having a potential-jump barrier or a surface barrier
    • H10K10/40—Organic transistors
    • H10K10/46—Field-effect transistors, e.g. organic thin-film transistors [OTFT]
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
    • H10K71/40—Thermal treatment, e.g. annealing in the presence of a solvent vapour
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/10—Organic polymers or oligomers

Definitions

  • This invention relates to polymeric films; more particularly, this invention relates to very thin, highly ordered polymeric films on a substrate; to their preparation, for example, by the
  • L-B Langmuir-Blodgett
  • amphiphilic organic molecules for example soaps such as neutral or acid calcium stearate
  • a substrate for example glass
  • L-B technique J. Am. Chem. Soc. 56, 495 (1934) and 57, 1007 (1935)
  • Polymeric films may be formed in situ by the L-B technique by utilising, as amphiphilic organic molecule, an unsaturated ester of a fatty acid such as vinyl stearate which is subsequently radiation polymerised, for example by exposure to a -source such as 60 Co. (J. Polym. Sci. Al 10, 2061 (1972)).
  • This invention seeks to provide thin ordered polymeric films of improved mechanical and thermal stabilities.
  • a process for the preparation of an ordered polymeric film on a substrate which process comprises:
  • polymeric film is, from
  • X-ray analysis crystalline and, in the case where steps (i) and (ii) above are repeated, has a layered structure.
  • amphiphilic is meant herein that the preformed polymer comprises both hydrophobic and hydrophilic pendant groups.
  • the reservoir comprises a monomolecular layer of the preformed polymer formed at a fluid phase interface.
  • the monomolecular layer is maintained at a constant surface pressure.
  • the fluid phase interface is suitably one between a liquid (the subphase) and a gas, vapour or liquid.
  • the subphase may be any liquid which is immiscible with, and which will support, the monomolecular layer of the preformed polymer.
  • the liquid is preferably an aqueous medium and the gas is air.
  • the reservoir comprises a solution of the preformed polymer.
  • the solution comprises an organic solvent, for example chloroform.
  • the preformed polymer is suitably an organic polymer and, desirably, an organic addition polymer.
  • the polymer is thermoplastic and derived from one or more vinyl, vinylene or vinylidene monomers and, for convenience, it is especially preferred that it is a vinyl polymer. it is found to be undesirable to use preformed polymers of too high a molecular weight because the polymer chains become too entangled to give a sufficiently ordered product.
  • the molecular weight of the preferred polymer does not exceed that represented by a polymer chain comprising 200 monomer units; desirably less than that represented by a polymer chain comprising 100 monomer units; especially less than that represented by a polymer chain comprising 50 monomer units.
  • Suitable hydrophobic groups include hydrophobic heterocyclic groups and unsubstituted or mono- or poly- halo-or hydrocarbyloxy- substituted hydrocarbyi(oxy) groups.
  • hydrocarbyl(oxy) is meant herein hydrocarbyl or hydrocarbyloxy. Examples include aryl and aralkyl groups such as phenyl or benzyl and alkyl(oxy) groups such as C 40 to C 4 , preferably C 20 to C 10 , alkyl(oxy) groups such as n-octadecyloxy and n-hexadecyl. It is an important feature of this invention that comparatively short hydrophobic groups may be used, for example phenyl. This is to ensure that, where desired, resulting monomolecular preformed polymeric films may be thin enough to permit quantum mechanical tunnelling.
  • hydrophobic groups in the preformed polymer these may be the same or different.
  • hydrophilic groups include hydroxyl; poly(ethyleneoxy); pyridyl; N-pyrrolidyl; carboxyl, and precursors which are hydrolysable thereto, for example cyano-, amido-, imido, acid anhydride and acyl chloride.
  • hydrophilic groups in the preformed polymer these may be the same or different.
  • a mixture of preformed polymers may be utilised. While it is, in general, preferred that each hydrophobic group, or each hydrophilic group, in the or each type of preformed polymer are, for greater ordering, the same (especially each hydrophobic group) it has now been found that one or both may be chemically modified in order to tailor electronic parameters to requirements (especially each hydrophilic group). It is also preferred that, for greater ordering, the preformed polymer is an alternating copolymer.
  • preformed polymer which have given satisfactory results include copolymers of an unsaturated acid anhydride, such as maleic anhydride, with a substituted or unsub stituted styrene; a C 12 to C 22 alk-1-ene; or a C 10 to C 20 vinyl ether.
  • preformed polymer include poly (n-octadecyl vinyl ether/maleic anhydride); poly(styrene/maleic anhydride) and poly(octadecene-l/maleic anhydride).
  • MIS diodes prepared therefrom displayed Schottky barrier heights from 1.1 to 1.5 eV, depending on the mole fraction of anhydride remaining. This is believed to be the first use of an L-B film to produce a MIS device with a Schottky barrier height that can be tailored to requirements.
  • the preformed polymer is suitably incorporated as a monomolecular layer at the fluid phase interface by dissolving it in a volatile organic solvent, for example, a volatile hydrocarbon such as hexane, a volatile carboxylic ester, or a volatile halogenated hydrocarbon such as chloroform.
  • a volatile organic solvent for example, a volatile hydrocarbon such as hexane, a volatile carboxylic ester, or a volatile halogenated hydrocarbon such as chloroform.
  • This solution is then added to the subphase in an amount calculated in known manner (essentially by determining the effective area per molecule from the absorption isotherm and then determining the quantity of solution required to given a monomolecular layer over a known area) to leave, on evaporation, a monomolecular layer. It is preferred that the monomolecular layer is equilibrated for 15 minutes to 4 hours, preferably, 1 to
  • a constant surface pressure typically of 20 to 50, preferably 30 to 45, mNm -1 , by means of an adjustable boom, suitably of polyethylene tetrafluoride (PTFE) tape, which confines the monomolecular layer.
  • PTFE polyethylene tetrafluoride
  • the process of the present invention is applicable to a wide variety of substrates, preferably inorganic and metallic substrates, including glasses such as aluminosilicate glasses, optical materials of appropriate refractive index and surface smoothness, for example fused quartz, metals such as aluminium, chromium, nickel, brass, steel, cast iron, silver, platinum or gold, metal oxide layers on aluminium or tin, plastics such as polystyrene, poly(ethylene terephthalate), cellulose acetate or polypropylene plastics and, in accordance with one particularly preferred aspect of this invention, semiconducting materials, for example silicon single crystals; amorphous silicon; III-V compounds such as BN, BP, AlSb, GaN, GaP, GaSb, GaAs, InP, InSb, InAs, preferably GaP, GaAs and InP; II-VI compounds such as CdS, CdSe, CdTe, ZnO and ZnS, preferably CdS and CdTe;
  • the substrate may be superconducting material, for example a superconducting metal, or a superconducting alloy thereof, of Groups IIIA, IVA, VA, VIIA, VIII, IIB, IIIB or IVB of the Periodic Table, such as Nd, Ti, Zr, Hf, Th, V, Nb, Ta, Rh, Ru, Os, Zn, Cd, Hg, Al, Ga, In, Tl, Sn, Pb, preferably Nd, Nb, and Sn including the compound Nb 3 Sn.
  • the substrate may need preparation in known manner prior to coating; for example, silicon may need to be etched and it may need to have a thin coating of oxide formed thereon.
  • the substrate is advanced though the reservoir of preformed polymer in known manner, for example by being coupled to a simple variable speed motor, typically at a speed of 0.5 to 50, preferably 1 to 10, mm.min -1 .
  • the substrate may, depending (it is believed) on whether it is wetted on only one or both the advancing and recovering operations accrete one (X-mode) or two (Y-mode) ordered polymeric films. The advancing and recovering operations may be repeated, if desired, to build up thicker ordered films.
  • Monomolecular preformed polymeric films prepared in accordance with this invention may have a thickness less than 50 ⁇ , preferably no greater than 20 ⁇ , especially no greater than 10 ⁇ . Where the evisaged use does not depend on quantum mechanical tunnelling it may be desirable to prepare thicker, multilayer preformed polymeric films; for example, in optical devices a thickness of 1 mm to l ⁇ may be required.
  • the coated susbstrate When the final recovering operation has been effected it is desirable to dry the coated susbstrate, suitably overnight, in helium or nitrogen.
  • An electrode for example 50 ⁇ to 1000 ⁇ of Au, can then be evaporated thereon at a temperature from ambient temperature to -100°C. It is then desirable to give the dried coated substrate onto which coating an electrode has been evaporated (that is, a device in accordance with the invention) an annealing treatment in which it is maintained, typically for 1 to 24 hours, for example 2 to 4 hours, at a temperature from ambient temperature to 200°C, preferably above 50°C, typically from 100° to 180°C, such as 150°C which is believed to enhance the ordering of the polymeric film.
  • Semiconducting devices in accordance with this invention include MIS devices wherein (with reference to Figure 1 of the accompanying drawings) a semiconductor substrate 1 is provided with a contiguous ordered preformed polymeric film 2 on the other surface of which an electrode 3 is deposited.
  • MIS devices wherein (with reference to Figure 1 of the accompanying drawings) a semiconductor substrate 1 is provided with a contiguous ordered preformed polymeric film 2 on the other surface of which an electrode 3 is deposited.
  • Examples of the use of such devices include Schottky barrier MIS diodes, Schottky barrier tunnel diodes, and Schottky barrier MIS capacitors (which differ essentially by comprising progressively thicker preformed polymeric films).
  • Specific examples include solar cell and electroluminescent devices (which are both Schottky barrier MIS diodes).
  • FETs wherein (with reference to Figure 2 of the accompanying drawings) a semiconducting substate 4 is provided with source and drain electrodes 5 and 6 and a contiguous ordered preformed polymeric film 7 interposed between the electrodes as a gate insulator and carrying a gate electrode 8.
  • the insulator 7 is of a suitable nature (namely, that it is capable of reversible or irreversible binding of substances which, when bound, alter the electrical properties of the FET) the FET can give a detector response, inter alia, to gases, ions, and organic molecules including immunogens.
  • MIM devices in accordance with this invention include tunnel junctions such as Josephson junctions wherein (with reference to Figure 3 of the accompanying drawings) a superconducting substrate 9 is provided with a contiguous ordered preformed polymeric film 10 on the other surface of which a further superconducting layer 11 is deposited.
  • the interposed film 10 must be less than 50 ⁇ . At temperatures of about 3°K superconducting current may pass through the device by a tunnelling mechanism dissipating no device power and enabling their use as ultra high speed devices, for example in computer memories.
  • Figure 4 is a schematic side elevation of the Langmuir trough apparatus used in this invention.
  • Figures 5 to 7, inclusive, are schematic plans of the trough of Figure 4 showing detail of the constant perimeter design.
  • Two moveable, wax-coated brass barrier supports 3 and 4 are each supported by two pairs of PFTE diabolo-shaped wheels 5 which seat on two stainless steel rods 6 which are aligned generally parallel at the sides of the trough; and are each lockable onto two rubber drive belts 7 and 8 which are aligned generally parallel and in a vertical plane at either side of the trough.
  • Each moveable barrier support carries two pairs of PTFE capstans 9, 10, 9' and 10' which project downwardly into the trough.
  • a moveable, wax-coated brass bridge 14, spanning the trough, is mounted on parallel rails 15 which run at either side of the trough and carries an axially aligned micrometer screw 16 linked to a substrate holder 17.
  • a Cl balance head 18 supports a surface pressure sensor 19. The apparatus described above, with the exception of the balance head which is mounted thereon, is enclosed in an anodised aluminium glove box (not shown) having a perspex window.
  • the tank Before use, the tank is subject to a thorough cleansing regime: it is first washed with concentrated nitric acid, next with chloroform, then ethanol and finally rinsed with distilled water. The tape barrier and the capstans are wiped with isopropyl alcohol and assembled. 2.51 of fresh, premixed subphase (see the following Example for formulation details) are than poured into the tank and the pH is adjusted by addition of small amounts of hydrochloric acid or sodium hydroxide. The surface of the subphase bounded by the barrier is next sucked clean with a micropipette- terminated filter pump (not shown)and a film is spread with a micropipette (Finipipette).
  • the process is repeated until no discernable change between adjacent clean subphase readings is observed on the balance when the barrier supports are rapidly mutually reciprocated.
  • the Langmuir film is then carefully spread on the subphase using about 200 - 400 1 of a solution of preformed polymer (see the following Examples for formulation details) by a micropipette; and left for a period from 30 minutes to 4 hours to equilibriate.
  • the film is slowly compressed and expanded twice or three times. in use, the film is slowly compressed by moving the barrier supports 3 and 4 together by actuation of drive belts 7 and 8 by means of a Maxon 2332.908 DC motor with attached series 69 gearbox (1:400 ratio) (both not shown).
  • the surface pressure of the film is continuously monitored by the balance 18 and the output is fed into a differential feedback circuit (not shown) linked to the motor which is then driven to maintain a constant surface pressure.
  • the substrate holder 17 is moved down through the film by driving the micrometer screw 16 with a Maxon 2325.913 DC motor with attached series 27 gearbox (1:500) (both not shown) to give a substrate speed of 1 to 25 mm min -1 , generally 4 mm min -1 . After immersion, the substrate is then driven up through the film.
  • each monolayer is first dried for 4 hours before repeating the above sequence.
  • the final film is stored for a period from 1 to 5 days under dry nitrogen in a dissicator before top electrode evaporation.
  • the barrier support movement may be monitored by measuring the resistance of a 10-turn potentiometer (Phillips DM2517E multimeter) linked to the geared drive (both not shown) of the drive belts 7 and 8. From the change in reading per turn of the micrometer screw 16, the deposition ratio (DR) can be calculated where:
  • EXAMPLE Metal substrates were prepared in the following manner: "Chance Select" microscope slides (70 mm x 26 mm x 2 mm) were used as a base for thin, evaporated metal films. They were initially inspected for scatches, imperfections, grease or dust and discarded if necessary. They were then wiped clean, with a fibre-free tissue soaked in methanol, and sonicated in chloroform prior to overnight storage in isopropyl alcohol (IPA). Some slides were flame-smoothed, a process which gives a smoother surface, and recleaned. Before use the stored slides were boiled in IPA and then in distilled, deionized Millipore filtered water.
  • IPA isopropyl alcohol
  • the metal evaporations were next carried out in an Edward's Model 306 Vacuum System, using a standard oil diffusion pump and nitrogen trap. The system was capable of achieving a pressure of 2 x 10 -7 Torr, but the evaporations were routinely carried out at 10 -1 Torr. Prior to evaporation the sample was concealed behind a mask and the source preheated above the evaporation temperature to drive off any organic contaminant. The sample was then exposed and the rate of deposition and final film thickness monitored on an Edwards Quartz Crystal Film Thickness Monitor. Aluminium evaporations were normally carried out at 15 cm from tungsten wires at rates of ⁇ 0.5 nm s -1 to give a final film thickness of 30 nm.
  • the aluminium On exposure to air the aluminium rapidly oxidised to a depth of about 2.5 nm. Tin was more difficult to use; when evaporated slowly the film was heavily stressed and developed surface spikes. Films less than 100 nm thick exhibited considerable series resistance, attributed to the grain boundaries in the film. Good films were obtained by evaporating at rates > 10 nm s -1 at 10 cm range from tantalum or molybdenum boats. After a few evaporations the tin alloyed with the metal boat and the evaporation rate fell markedly - it was necessary to use new boats every 2-3 evaporations. 200 nm thick films were produced, which often appeared a milky-white colour. Oxidation in air proceeded rapidly to a depth of about 2.3 nm.
  • Cleanliness of evaporator was important in achieving consistently good quality films.
  • the evaporator was regularly cleaned with sodium hydroxide to remove the metal films deposited on the inside of the chamber during evaporations.
  • Semiconductor substrates were prepared in the following manner:
  • the substrate comprised single crystal n + -GaP slices which were ⁇ 100> oriented and polished on one side (ex Cambridge Instruments Ltd.).
  • the sulphur dopant concentration was 3.5 to
  • the slices were precleaned in boiling chloroform and sonicated in isopropanol before etching in a two-stage procedure: (i) 3 minutes in H 2 SO 4 :H 2 O 2 :H 2 O in the volume ratio 4:1:1; (ii) 1 minute in H 2 O 2 :H 2 O in the volume ratio 1:20 containing 2 g of NaOH per
  • a glass Langmuir trough having dimensions and filiments as hereinbefore described was filled with 2,500 ml of distilled deionised Millipore filtered water containing 2.5 x 10 -4 M aqueous
  • Poly(octadecene-l/maleic anhydride) films were allowed to equili briate only for 30 minutes to minimise hydrolysis; partial hydrolysis was effected by equilibriating for 5 hours; and the free acid was prepared ab initio by reactions with 1M NaOH followed by precipitation with HCl. (The latter was spread as a solution in ethyl acetate; there was no need to equilibriate longer than 30 minutes.)
  • MIS metal/ insulator/semiconductor
  • Figure 8 is a graph of bias voltage (mV) versus current
  • Figure 9 is a graph of bias voltage (V) versus log e J(A cm -2 );
  • Figure 10 is a Fowler plot; and Figure 11 is a graph of bias voltage (V) versus reciprocal
  • the preformed polymer films produced in accordance with this invention have improved mechanical and thermal stability; devices comprising them can be baked to 200°C and not only remain intact but also have greatly improved properties; for example, electrical resistance can be increased by up to 10 3 X.
  • Schottky barrier heights of devices of this invention can be precisely tailored to requirements.
  • the process offer means of imparting insulator films onto semiconductors, such as GaP and GaAs, which are not readily or usefully oxidised.

Abstract

A process for the preparation of an ordered polymeric film on a substrate, which process comprises: (i) providing a reservoir of the amphiphilic preformed polymer; (ii) advancing the polymeric film receiving substrate into or onto the reservoir at least once; and (iii) recovering the substrate coated with the polymeric film.

Description

POLYMERIC FILMS
This invention relates to polymeric films; more particularly, this invention relates to very thin, highly ordered polymeric films on a substrate; to their preparation, for example, by the
Langmuir-Blodgett (L-B) technique; and to semiconductor, super- conductor and optical devices utilising them.
It is known that successive monomolecular layers of amphiphilic organic molecules, for example soaps such as neutral or acid calcium stearate, may be deposited on a substrate, for example glass, by the L-B technique (J. Am. Chem. Soc. 56, 495 (1934) and 57, 1007 (1935)). Polymeric films may be formed in situ by the L-B technique by utilising, as amphiphilic organic molecule, an unsaturated ester of a fatty acid such as vinyl stearate which is subsequently radiation polymerised, for example by exposure to a -source such as 60Co. (J. Polym. Sci. Al 10, 2061 (1972)). More recently, this technique has been used with qualified success in the laboratory to provide gate insulators in field effect transistors and to increase the efficiency of photodiodes in solar cells. However, the mechanical and thermal stabilities of the films hitherto produced have been poor and have prevented their practical commercialisation.
This invention seeks to provide thin ordered polymeric films of improved mechanical and thermal stabilities.
According, therefore, to one aspect of this invention there is provided a process for the preparation of an ordered polymeric film on a substrate, which process comprises:
(i) providing a reservoir of the amphiphilic preformed polymer;
(ii) advan ing the polymeric film receiving substrate into or onto the reservoir at least once; and (iϋ) recovering the substrate coated with the polymeric film.
By "ordered" is meant herein that the polymeric film is, from
X-ray analysis, crystalline and, in the case where steps (i) and (ii) above are repeated, has a layered structure. By "amphiphilic" is meant herein that the preformed polymer comprises both hydrophobic and hydrophilic pendant groups.
In accordance with one embodiment of the invention, the reservoir comprises a monomolecular layer of the preformed polymer formed at a fluid phase interface. Preferably, the monomolecular layer is maintained at a constant surface pressure. The fluid phase interface is suitably one between a liquid (the subphase) and a gas, vapour or liquid. The subphase may be any liquid which is immiscible with, and which will support, the monomolecular layer of the preformed polymer. For convenience the liquid is preferably an aqueous medium and the gas is air.
In accordance with a further embodiment of the invention, the reservoir comprises a solution of the preformed polymer. Suitably, the solution comprises an organic solvent, for example chloroform. The preformed polymer is suitably an organic polymer and, desirably, an organic addition polymer. Preferably, the polymer is thermoplastic and derived from one or more vinyl, vinylene or vinylidene monomers and, for convenience, it is especially preferred that it is a vinyl polymer. it is found to be undesirable to use preformed polymers of too high a molecular weight because the polymer chains become too entangled to give a sufficiently ordered product. Preferably, the molecular weight of the preferred polymer does not exceed that represented by a polymer chain comprising 200 monomer units; desirably less than that represented by a polymer chain comprising 100 monomer units; especially less than that represented by a polymer chain comprising 50 monomer units.
Suitable hydrophobic groups include hydrophobic heterocyclic groups and unsubstituted or mono- or poly- halo-or hydrocarbyloxy- substituted hydrocarbyi(oxy) groups. By "hydrocarbyl(oxy)" is meant herein hydrocarbyl or hydrocarbyloxy. Examples include aryl and aralkyl groups such as phenyl or benzyl and alkyl(oxy) groups such as C40 to C4, preferably C20 to C10, alkyl(oxy) groups such as n-octadecyloxy and n-hexadecyl. It is an important feature of this invention that comparatively short hydrophobic groups may be used, for example phenyl. This is to ensure that, where desired, resulting monomolecular preformed polymeric films may be thin enough to permit quantum mechanical tunnelling.
Where there is a plurality of hydrophobic groups in the preformed polymer these may be the same or different. Suitably hydrophilic groups include hydroxyl; poly(ethyleneoxy); pyridyl; N-pyrrolidyl; carboxyl, and precursors which are hydrolysable thereto, for example cyano-, amido-, imido, acid anhydride and acyl chloride.
Where there is a plurality of hydrophilic groups in the preformed polymer these may be the same or different. A mixture of preformed polymers may be utilised. While it is, in general, preferred that each hydrophobic group, or each hydrophilic group, in the or each type of preformed polymer are, for greater ordering, the same (especially each hydrophobic group) it has now been found that one or both may be chemically modified in order to tailor electronic parameters to requirements (especially each hydrophilic group). It is also preferred that, for greater ordering, the preformed polymer is an alternating copolymer. Specific classes of preformed polymer which have given satisfactory results include copolymers of an unsaturated acid anhydride, such as maleic anhydride, with a substituted or unsub stituted styrene; a C12 to C22 alk-1-ene; or a C10 to C20 vinyl ether. Specific example of preformed polymer include poly (n-octadecyl vinyl ether/maleic anhydride); poly(styrene/maleic anhydride) and poly(octadecene-l/maleic anhydride). As mentioned above, these may be chemically modified, for example by lysis of the anhydride ring with water, alcohols (for example methanol, ethanol or benzyl alcohol) or phenols. MIS diodes prepared therefrom displayed Schottky barrier heights from 1.1 to 1.5 eV, depending on the mole fraction of anhydride remaining. This is believed to be the first use of an L-B film to produce a MIS device with a Schottky barrier height that can be tailored to requirements. In accordance with the first embodiment of the invention, the preformed polymer is suitably incorporated as a monomolecular layer at the fluid phase interface by dissolving it in a volatile organic solvent, for example, a volatile hydrocarbon such as hexane, a volatile carboxylic ester, or a volatile halogenated hydrocarbon such as chloroform. This solution is then added to the subphase in an amount calculated in known manner (essentially by determining the effective area per molecule from the absorption isotherm and then determining the quantity of solution required to given a monomolecular layer over a known area) to leave, on evaporation, a monomolecular layer. It is preferred that the monomolecular layer is equilibrated for 15 minutes to 4 hours, preferably, 1 to
3 hours, at 20° to 40°C, typically 30°C. It is then subjected, prior to advancing the substrate through it, to a constant surface pressure, typically of 20 to 50, preferably 30 to 45, mNm-1, by means of an adjustable boom, suitably of polyethylene tetrafluoride (PTFE) tape, which confines the monomolecular layer.
The process of the present invention is applicable to a wide variety of substrates, preferably inorganic and metallic substrates, including glasses such as aluminosilicate glasses, optical materials of appropriate refractive index and surface smoothness, for example fused quartz, metals such as aluminium, chromium, nickel, brass, steel, cast iron, silver, platinum or gold, metal oxide layers on aluminium or tin, plastics such as polystyrene, poly(ethylene terephthalate), cellulose acetate or polypropylene plastics and, in accordance with one particularly preferred aspect of this invention, semiconducting materials, for example silicon single crystals; amorphous silicon; III-V compounds such as BN, BP, AlSb, GaN, GaP, GaSb, GaAs, InP, InSb, InAs, preferably GaP, GaAs and InP; II-VI compounds such as CdS, CdSe, CdTe, ZnO and ZnS, preferably CdS and CdTe; and IV-VI compounds such as PbS and PbTe. In accordance with another particularly preferred aspect of this invention the substrate may be superconducting material, for example a superconducting metal, or a superconducting alloy thereof, of Groups IIIA, IVA, VA, VIIA, VIII, IIB, IIIB or IVB of the Periodic Table, such as Nd, Ti, Zr, Hf, Th, V, Nb, Ta, Rh, Ru, Os, Zn, Cd, Hg, Al, Ga, In, Tl, Sn, Pb, preferably Nd, Nb, and Sn including the compound Nb3Sn. The substrate may need preparation in known manner prior to coating; for example, silicon may need to be etched and it may need to have a thin coating of oxide formed thereon.
The substrate is advanced though the reservoir of preformed polymer in known manner, for example by being coupled to a simple variable speed motor, typically at a speed of 0.5 to 50, preferably 1 to 10, mm.min-1. The substrate may, depending (it is believed) on whether it is wetted on only one or both the advancing and recovering operations accrete one (X-mode) or two (Y-mode) ordered polymeric films. The advancing and recovering operations may be repeated, if desired, to build up thicker ordered films.
Monomolecular preformed polymeric films prepared in accordance with this invention may have a thickness less than 50Å, preferably no greater than 20Å, especially no greater than 10Å. Where the evisaged use does not depend on quantum mechanical tunnelling it may be desirable to prepare thicker, multilayer preformed polymeric films; for example, in optical devices a thickness of 1 mm to lμ may be required.
When the final recovering operation has been effected it is desirable to dry the coated susbstrate, suitably overnight, in helium or nitrogen.
An electrode, for example 50Å to 1000Å of Au, can then be evaporated thereon at a temperature from ambient temperature to -100°C. It is then desirable to give the dried coated substrate onto which coating an electrode has been evaporated (that is, a device in accordance with the invention) an annealing treatment in which it is maintained, typically for 1 to 24 hours, for example 2 to 4 hours, at a temperature from ambient temperature to 200°C, preferably above 50°C, typically from 100° to 180°C, such as 150°C which is believed to enhance the ordering of the polymeric film.
Semiconducting devices in accordance with this invention include MIS devices wherein (with reference to Figure 1 of the accompanying drawings) a semiconductor substrate 1 is provided with a contiguous ordered preformed polymeric film 2 on the other surface of which an electrode 3 is deposited. Examples of the use of such devices include Schottky barrier MIS diodes, Schottky barrier tunnel diodes, and Schottky barrier MIS capacitors (which differ essentially by comprising progressively thicker preformed polymeric films). Specific examples include solar cell and electroluminescent devices (which are both Schottky barrier MIS diodes).
Other semiconducting devices in accordance with this invention include FETs wherein (with reference to Figure 2 of the accompanying drawings) a semiconducting substate 4 is provided with source and drain electrodes 5 and 6 and a contiguous ordered preformed polymeric film 7 interposed between the electrodes as a gate insulator and carrying a gate electrode 8. Where the insulator 7 is of a suitable nature (namely, that it is capable of reversible or irreversible binding of substances which, when bound, alter the electrical properties of the FET) the FET can give a detector response, inter alia, to gases, ions, and organic molecules including immunogens.
MIM devices in accordance with this invention include tunnel junctions such as Josephson junctions wherein (with reference to Figure 3 of the accompanying drawings) a superconducting substrate 9 is provided with a contiguous ordered preformed polymeric film 10 on the other surface of which a further superconducting layer 11 is deposited. The interposed film 10 must be less than 50Å. At temperatures of about 3°K superconducting current may pass through the device by a tunnelling mechanism dissipating no device power and enabling their use as ultra high speed devices, for example in computer memories.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 4 is a schematic side elevation of the Langmuir trough apparatus used in this invention;
Figures 5 to 7, inclusive, are schematic plans of the trough of Figure 4 showing detail of the constant perimeter design.
In the drawings, a semi-cylindrical glass trough 1, 50 cm in length x 15 cm in diameter, is positioned in a hollow semi- cylindrical copper jacket 2 through which water flows to maintain a constant temperature measured with a Jenway 6000 pH meter used as a temperature sensor (not shown); water is also positioned contiguous to both trough and jacket to ensure their good thermal contact. Two moveable, wax-coated brass barrier supports 3 and 4 are each supported by two pairs of PFTE diabolo-shaped wheels 5 which seat on two stainless steel rods 6 which are aligned generally parallel at the sides of the trough; and are each lockable onto two rubber drive belts 7 and 8 which are aligned generally parallel and in a vertical plane at either side of the trough. Each moveable barrier support carries two pairs of PTFE capstans 9, 10, 9' and 10' which project downwardly into the trough. A fixed barrier support 11, positioned at one end of the trough, also carries two PTFE capstans 12 and 12' and an endless PTFE tape barrier 13 is wound around the ten capstans as shown in Figures 5 to 7 to give a maximum working area of about 195 cm2. A moveable, wax-coated brass bridge 14, spanning the trough, is mounted on parallel rails 15 which run at either side of the trough and carries an axially aligned micrometer screw 16 linked to a substrate holder 17. A Cl balance head 18 supports a surface pressure sensor 19. The apparatus described above, with the exception of the balance head which is mounted thereon, is enclosed in an anodised aluminium glove box (not shown) having a perspex window.
Before use, the tank is subject to a thorough cleansing regime: it is first washed with concentrated nitric acid, next with chloroform, then ethanol and finally rinsed with distilled water. The tape barrier and the capstans are wiped with isopropyl alcohol and assembled. 2.51 of fresh, premixed subphase (see the following Example for formulation details) are than poured into the tank and the pH is adjusted by addition of small amounts of hydrochloric acid or sodium hydroxide. The surface of the subphase bounded by the barrier is next sucked clean with a micropipette- terminated filter pump (not shown)and a film is spread with a micropipette (Finipipette). The process is repeated until no discernable change between adjacent clean subphase readings is observed on the balance when the barrier supports are rapidly mutually reciprocated. The Langmuir film is then carefully spread on the subphase using about 200 - 400 1 of a solution of preformed polymer (see the following Examples for formulation details) by a micropipette; and left for a period from 30 minutes to 4 hours to equilibriate. Finally, the film is slowly compressed and expanded twice or three times. in use, the film is slowly compressed by moving the barrier supports 3 and 4 together by actuation of drive belts 7 and 8 by means of a Maxon 2332.908 DC motor with attached series 69 gearbox (1:400 ratio) (both not shown). The surface pressure of the film is continuously monitored by the balance 18 and the output is fed into a differential feedback circuit (not shown) linked to the motor which is then driven to maintain a constant surface pressure.
The substrate holder 17 is moved down through the film by driving the micrometer screw 16 with a Maxon 2325.913 DC motor with attached series 27 gearbox (1:500) (both not shown) to give a substrate speed of 1 to 25 mm min-1, generally 4 mm min-1. After immersion, the substrate is then driven up through the film.
If multilayers are required each monolayer is first dried for 4 hours before repeating the above sequence. The final film is stored for a period from 1 to 5 days under dry nitrogen in a dissicator before top electrode evaporation.
The barrier support movement may be monitored by measuring the resistance of a 10-turn potentiometer (Phillips DM2517E multimeter) linked to the geared drive (both not shown) of the drive belts 7 and 8. From the change in reading per turn of the micrometer screw 16, the deposition ratio (DR) can be calculated where:
DR = Area of substrate moved through interface
Area of film removed from interface In practice, it is a necessary (but not always sufficient) condition that DR lies between 0.98 and 1.02 for good quality film formation. The following Example illustrates the invention.
EXAMPLE Metal substrates were prepared in the following manner: "Chance Select" microscope slides (70 mm x 26 mm x 2 mm) were used as a base for thin, evaporated metal films. They were initially inspected for scatches, imperfections, grease or dust and discarded if necessary. They were then wiped clean, with a fibre-free tissue soaked in methanol, and sonicated in chloroform prior to overnight storage in isopropyl alcohol (IPA). Some slides were flame-smoothed, a process which gives a smoother surface, and recleaned. Before use the stored slides were boiled in IPA and then in distilled, deionized Millipore filtered water. The metal evaporations were next carried out in an Edward's Model 306 Vacuum System, using a standard oil diffusion pump and nitrogen trap. The system was capable of achieving a pressure of 2 x 10-7 Torr, but the evaporations were routinely carried out at 10-1 Torr. Prior to evaporation the sample was concealed behind a mask and the source preheated above the evaporation temperature to drive off any organic contaminant. The sample was then exposed and the rate of deposition and final film thickness monitored on an Edwards Quartz Crystal Film Thickness Monitor. Aluminium evaporations were normally carried out at 15 cm from tungsten wires at rates of < 0.5 nm s-1 to give a final film thickness of 30 nm. The filaments broke on repeated use and new elements were made for each evaporation. On exposure to air the aluminium rapidly oxidised to a depth of about 2.5 nm. Tin was more difficult to use; when evaporated slowly the film was heavily stressed and developed surface spikes. Films less than 100 nm thick exhibited considerable series resistance, attributed to the grain boundaries in the film. Good films were obtained by evaporating at rates > 10 nm s-1 at 10 cm range from tantalum or molybdenum boats. After a few evaporations the tin alloyed with the metal boat and the evaporation rate fell markedly - it was necessary to use new boats every 2-3 evaporations. 200 nm thick films were produced, which often appeared a milky-white colour. Oxidation in air proceeded rapidly to a depth of about 2.3 nm.
Cleanliness of evaporator was important in achieving consistently good quality films. The evaporator was regularly cleaned with sodium hydroxide to remove the metal films deposited on the inside of the chamber during evaporations. Semiconductor substrates were prepared in the following manner:
The substrate comprised single crystal n+-GaP slices which were <100> oriented and polished on one side (ex Cambridge Instruments Ltd.). The sulphur dopant concentration was 3.5 to
10.0 x 1017 cm-3 and the resultant mobility was 99 - 120 cm2V-1S-1.
The slices were precleaned in boiling chloroform and sonicated in isopropanol before etching in a two-stage procedure: (i) 3 minutes in H2SO4:H2O2:H2O in the volume ratio 4:1:1; (ii) 1 minute in H2O2:H2O in the volume ratio 1:20 containing 2 g of NaOH per
100 ml of solution. After each etch the slice was next throughly rinsed in distilled deionized Millipore filtered water. Ohmic contacts were made to the samples by the method of Tredgold and Jones (Proc. Inst. Elect. Eng., Part 1, 128 (1981) 202), and the slice was then re-etched before film deposition. The etch was chosen to give a uniform surface oxide layer and a low level of organic contaminants.
A glass Langmuir trough having dimensions and filiments as hereinbefore described was filled with 2,500 ml of distilled deionised Millipore filtered water containing 2.5 x 10-4M aqueous
Cd Cl2 at pH=5.6 and maintained at 35°C.
500 μl of a solution of 0.1 mg ml-1 of poly(n-octadecyl vinyl ether/maleic anhydride) (ex Polysciences Ltd.) in chloroform were next spread on the aqueous surface in the trough to form a monolayer. The film was left for 2 hours partially to hydrolyse the anhydride groups and to equilibriate. The film was then slowly compressed and expanded two or three times before the substrate was driven through the expanded film. The film was next compressed very slowly to 32 mNm-1; kept under this constant surface pressure for 20 minutes; and the substrate driven upwards at a rate of 4 mm min-1 through the liquid-air interface. Deposition was continuously monitored and the resulting deposition ratio lay between 0.98 and 1.02.
Other preformed polymers which were utilised in the same amounts are poly(styrene/maleic anhydride); poly(octadecene-l/ maleic anhydride); and lysis products of the latter. These latter were then partially and completely hydrolysed products; and the methyl and benzyl partial esters (the latter having only been applied to an aluminium/aluminium oxide substrate). Poly(octadecene-l/maleic anhydride) films were allowed to equili briate only for 30 minutes to minimise hydrolysis; partial hydrolysis was effected by equilibriating for 5 hours; and the free acid was prepared ab initio by reactions with 1M NaOH followed by precipitation with HCl. (The latter was spread as a solution in ethyl acetate; there was no need to equilibriate longer than 30 minutes.)
Before top electrode evaporation the samples were dried overnight in dry nitrogen; circular gold electrodes 1.5 mm in diameter and 5 nm thick were evaporated onto the sample at rates of less than 0.5 nm min-1 at 10-5 Torr. The resulting metal/ insulator/semiconductor (MIS) devices were studied using a Hewlett Packard 4275A LCR Bridge (capacitance-voltage (C-V)), Keithley 602 and 600B electrometers (current-voltage and photomeasurements) and a Bausch-Lomb monochromator (33-86-02).
The results of this study are discussed with reference to the accompanying drawings, in which:
Figure 8 is a graph of bias voltage (mV) versus current
(A, log scale); Figure 9 is a graph of bias voltage (V) versus logeJ(A cm-2);
Figure 10 is a Fowler plot; and Figure 11 is a graph of bias voltage (V) versus reciprocal
(capacitance)2 (nF)-2.
In Figure 8, points denoted by open circles were derived from a device prepared from an Al/Al2O3 substrate coated with polymer I (see Table below) which has previously been stored for 1 day at 293ºK; points denoted by open squares were derived from similar devices which has previously been annealed by baking for 4 hours at 403 ºK; points denoted by filled circles were derived from a device prepared from an Al/Al2O3 substrate coated with polymer II which had previously been stored for 1 day at 293 ºK; points denoted by filled squares were derived from similar devices which had previously been annealed by baking for 4 hours at 413ºK. It is important to note that, in the annealed samples, the currents are graphically depicted x 500.
It may readily be seen, therefore, that annealing is most beneficial in increasing the resistivity of devices in accordance with this invention.
Figure imgf000014_0001
In Figure 9, 10 and 11 independent plots derived from a GaP substrate coated with polymer III (modified and unmodified) show conclusively the tailoring effect of modifying the polymer on Schottky barrier (derived directly from the Fowler plot intercept). In Figure 9 the open squares were derived from a GaP/Au device; the open circles were derived from devices prepared from the methyl partial ester of polymer III; the filled circles were derived from devices prepared from polymer III. In Figure 10 the filled circles were derived from devices prepared by hydrolysing polymer III by equilibriating the film for 6 hours at 30°C; the open circles were derived from devices prepared from polymer III; the open squares were derived from devices prepared from the methyl partial ester of polymer III. In Figure 11 the notation is the same as in Figure 10 with the filled squares being derived from devices prepared from GaP/Au.
The preformed polymer films produced in accordance with this invention have improved mechanical and thermal stability; devices comprising them can be baked to 200°C and not only remain intact but also have greatly improved properties; for example, electrical resistance can be increased by up to 103X. Schottky barrier heights of devices of this invention can be precisely tailored to requirements. Moreover, the process offer means of imparting insulator films onto semiconductors, such as GaP and GaAs, which are not readily or usefully oxidised.

Claims

1. A process for the preparation of an ordered polymeric film on a substrate, which process comprises:
(i) providing a reservoir of the amphiphilic preformed polymer; (ii) advancing the polymeric film receiving substrate into or onto the reservoir at least once; and (iii) recovering the substrate coated with the polymeric film.
2. A process according to Claim 1 wherein the reservoir comprises a monomolecular layer of the preformed polymer formed at a fluid phase interface.
3. A process according to Claim 2 wherein the monomolecular layer is maintained at a constant surface pressure.
4. A process according to Claim 2 or 3 wherein the fluid phase interface is an air/aqueous medium interface.
5. A process according to Claim 1 wherein the reservoir comprises a solution of the preformed polymer.
6. A process according to Claim 5 wherein the solution comprises an organic solvent.
7. A process according to any preceding claim wherein the polymer is an organic polymer.
8. A process according to Claim 7 wherein the polymer is a vinyl polymer.
9. A process according to any preceding claim wherein the hydrophobic groups comprise phenyl or C10 to C20 alkyl(oxy) groups.
10. A process according to any preceding claim wherein the hydrophilic groups comprise carboxyl groups or precursors which are hydrolysable thereto.
11. A process according to any of Claims 8, 9 or 10 wherein the preformed vinyl polymer is a copolymer of an unsaturated acid anhydride with styrene, a C12 to C22 alk-l-ene or a C10 to C20 vinyl ether.
12. A process according to any of Claims 8 to 11 wherein the preformed vinyl polymer is an alternating copolymer.
13. A process according to any preceding claim wherein the substrate comprises a semiconducting material.
14. A process according to Claim 9 wherein the semiconducting material comprises silicon, a III-V compound or a II-VI compound.
15. A process according to any preceding claim wherein the substrate comprises a superconducting material.
16. A process according to Claim 15 wherein the superconducting material comprises Nd, Nb, or Sn, or a compound thereof.
17. A process according to any preceding claim wherein the substrate is advanced through the reservoir of preformed polymer at a speed of 0.5 to 50 mm min
18. A process according to any preceding claim wherein conditions are such that the substrate is coated in the X-mode.
19. A process according to any of Claims 1 to 17 wherein condi tions are such that the substrate is coated in the Y-mode.
20. A process according to any preceding claim wherein the advancing and recovering operation are repeated.
21. A process according to any preceding claim wherein, after the final recovery operation, the coated substrate is dried.
22. A substrate coated with an amphiphilic preformed polymeric film whenever prepared by a process according to any preceding claim.
23. A coated substrate according to Claim 22 which comprises a semiconducting or a superconducting material.
24. A device comprising a coated substrate according to Claim 23 onto the polymeric surface of which an electrode has been evaporated.
25. A device according to Claim 24 which is annealed.
26. A device according to Claim 25 wherein the annealing is effected at a temperature above 50°C.
27. A coated substrate or device according to any of Claims 22 to 25 wherein the thickness of the coating is no greater than 20Å.
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US5079179A (en) * 1987-10-09 1992-01-07 Hughes Aircraft Company Process of making GaAs electrical circuit devices with Langmuir-Blodgett insulator layer
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EP0374866A3 (en) * 1988-12-22 1991-04-03 Hoechst Aktiengesellschaft Amphiphilic monomers with a mixed-chain structure and polymers and film from at least one monomolecular layer therefrom
US5116925A (en) * 1989-04-12 1992-05-26 Hoechst Aktiengesellschaft Amphiphilic monomers and polymers and film comprising at least one unimolecular layer thereof
EP0503420A1 (en) * 1991-03-15 1992-09-16 Hoechst Aktiengesellschaft Amphiphilic polymers with silane units and film with at least one monomolecular layer of such a polymer
US5256749A (en) * 1991-03-15 1993-10-26 Hoechst Aktiengesellschaft Amphiphilic polymers containing silane units and film comprising at least one monomolecular layer produced therefrom
US20110139601A1 (en) * 2008-04-24 2011-06-16 First Green Park Pty Ltd Solar stills
US20170331042A1 (en) * 2016-05-12 2017-11-16 Korea Research Institute Of Chemical Technology Composition for Insulator of Thin Film Transistor, Insulator and Organic Thin Film Transistor Prepared Thereby
US10158078B2 (en) * 2016-05-12 2018-12-18 Korea Research Institute Of Chemical Technology Composition for insulator of thin film transistor, insulator and organic thin film transistor prepared thereby

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GB2121315A (en) 1983-12-21
EP0114851A1 (en) 1984-08-08
GB8306026D0 (en) 1983-04-07
JPS59500339A (en) 1984-03-01
GB2117669A (en) 1983-10-19
GB2121315B (en) 1985-08-29

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