JPH03182011A - Organic superconductor thin film and its manufacture - Google Patents

Abstract

PURPOSE:To form a superconductor thin film at low temperature and make the formation method suitable for forming conjunction and sensors by forming a molecular monolayer containing a donor on a conductive substrate and doping the monolayer with an acceptor by electrolytic process in forming of an organic superconductor thin film of a Langmuir-Brodgett film. CONSTITUTION:An ITO layer 2 is formed on a conductive substrate 3 of an ITO-coated glass, ITO-coated polyester, silicon wafer, etc., and a molecular mono-layer 1 containing donor molecule such as bis(ethylene dithiotetrathiafulvalene) tetramethyltetraselenofulvalene, etc., is formed on a prescribed region of the substrate by LB method and the rest part except the prescribed region of the substrate is doped with an acceptor such as halogens. Lewis acids, proton acids, transition metal halides, etc., by electrolytic process. In this method, a metal conductive organic thin film having a high conductivity, furthermore, an organic thin film having superconductive properties is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an organic thin film having superconductivity, and more particularly to an organic superconducting thin film using the Langmuir-Prodgett film (LB film) method and a method for producing the same.

[Conventional technology]

Organic thin films are manufactured by techniques such as LB peritoneal deposition, ICB (cluster ion beam evaporation), and MBE (molecular beam epitaxy). These organic thin film manufacturing methods can produce semiconductive or conductive organic thin films such as tetracyanoquinodimethane (TCNQ), tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ), metal phthalocyanine, fatty acids, etc. Insulating films have been created. Organic thin films with electrical conductivity can be applied to electronics, optoelectronic materials, energy conversion materials, etc. by utilizing their properties as electrical conductors or semiconductors. In particular, organic thin films with high conductivity and even superconductivity are expected to be applied to microwirings, strip lines, sensors, display elements, memories, switching elements, etc. By the way, as an organic conductive ultra-thin film technology using the LB peritoneal method, for example, iodine-doped phthalocyanine LB film (electrical conductivity 10-'S/cm) s long chain pyridinium tetracyanoquinodimethane (TCNQ) 1:1 complex LB
There are membranes (10-'S/cm), etc. Furthermore, a conductive ultra-thin film made of a charge transfer complex compound having a long-chain hydrocarbon group without performing secondary treatments such as iodine doping has also been proposed (Japanese Patent Laid-Open No. 163-205-1989).
issue). As described above, attempts have been made to create conductive organic ultra-thin films using the LB peritoneal method, but no organic thin film that exhibits metallic conductivity or metallic conductivity has yet been created. There are also no known organic ultrathin films that exhibit superconductivity. [Problems to be Solved by the Invention] An object of the present invention is to provide an organic thin film that exhibits high electrical conductivity or metallic conductivity, and furthermore, an organic thin film that exhibits superconductivity. As a result of intensive research to create an organic superconductor thin film, the present inventors discovered that donor molecules (electron donors)
They discovered that an organic thin film exhibiting superconductivity could be obtained by forming a monomolecular cumulative film of a monomolecular film-forming substance containing , and then doping with acceptors (electron acceptors) using an electrolytic method. Based on this, the present invention has been completed. [Means for Solving the Problems] Thus, according to the present invention, a monomolecular cumulative film of a monomolecular film-forming substance containing donor molecules is formed on a conductive substrate, and then an acceptor is doped by an electrolytic method. An organic superconducting thin film and a method for producing the same are provided. The present invention will be explained in detail below. The method for producing a conductive organic thin film of the present invention basically includes the following steps. (1) A monomolecular cumulative film is created on a conductive substrate by the LB method using a mixture of donor molecules and a monomolecular cumulative film forming substance. (2) Next, an acceptor is doped into the film by an electrolytic method to obtain an organic superconducting thin film. As the donor molecule used in the present invention, for example, bisethylene dithiotetrathiafulvalene (BEDT-TTF)
, tetramethyltetraselenofulvalene (TMTSF
), dimethyl (ethylenedithio) diselena dithiafulvalene (DMET), methylene dithiotetrathiafulvalene (MDT-TTFl), etc. Examples of the monomolecular film forming substance used in combination with donor molecules include, for example, valmitin. fatty acids such as stearic acid and alaxic acid; polymerizable fatty acids with double bonds and triple bonds such as ω-tricosenic acid, α-octadecyl acrylic acid, and diacetylene derivatives; electrolytically polymerizable monomers such as alkylvirol; Examples include polymeric substances such as methacrylic acid, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, polypeptide, and polyimide.The conductive substrate used in the present invention is not particularly limited, and includes, for example, ITO coated glass, IO coco glass, NESA
Examples include substrates made of glass, ITO-coated polyester film, metallized glass, silicon wafers (n-type, p-type), conductive polymer films and thin films, conductive LB films, carbon, graphite, and the like. Acceptors used in the present invention include halogens, Lewis acids, protonic acids, transition metal halides, and other dopants, such as 11IBr*-, Brx\B
F, -1IC12-, AuI=-1AuCji-1Au
Brx-1Hg*, 5tBrs, PFa-, Au(C
N)*-1NO,-1Cu(NC3)*-,Ag(NC
3) i-, Au(NC3)x-, CjO,-Cu (N
C3e) *-1Cu (NCO) *-, Au (CN) *
Examples include anions such as -1N03-1Re04\, but are not limited to these. In the present invention, 1. By the LB method, on a conductive substrate,
A monomolecular cumulative film consisting of a donor molecule and a monomolecular cumulative film forming substance is formed. In the LB method, a monomolecular film is usually formed on a water surface, this monomolecular film is transferred onto a solid substrate, and the monomolecular film is repeatedly transferred from the water surface to a fixed monomolecular layer. This is a method of creating a stacked cumulative film (LB film). Specifically, using an LB film production device (a commercially available product may be used),
The donor molecule and the monomolecule-forming substance are dissolved in a developing solvent such as chloroform, acetonitrile, or benzene, and the solution is dropped onto the water surface of the Langmuir Trough to be developed, and the solvent is vaporized. Next, a movable float or the like is used to control the surface area and surface pressure to form a monomolecular film, and then the monomolecular film is deposited on a conductive substrate by a known method such as a vertical adhesion method or a horizontal adhesion method. Repeated deposition forms a monomolecular cumulative film. The film thickness can be controlled by the number of times of accumulation. From a monomolecular film with a thickness of several 10 layers, a thin film with a thickness of several 100 to several 1000 layers can be easily obtained. In the present invention, an acceptor is doped by an electrochemical redox method (electrolysis method) using a conductive substrate on which an organic ultra-thin film of a monolayer-forming substance containing donor molecules is formed as an anode. By doping, a charge transfer complex formation reaction between donor molecules and acceptors occurs in the film, and an organic superconducting thin film can be obtained. Doping by electrolytic method can be performed by a conventional method using, for example, a known electrolytic crystal growth apparatus. However, the electrolytic solution used does not contain donor molecules but only contains acceptors. Furthermore, it is necessary to use a solvent in which donor molecules and monolayer-forming substances are not dissolved. As the solvent, alcohols such as methanol and ethanol, water, etc. are effective. The conditions for electrolytic doping are, for example, 20°C and 0.5°C.
Doping can be completed in 5 to 6 hours at 5 μA. The progress of doping can be seen from the fact that the initially colorless or pale yellow thin film changes to blackish brown. In the example of the present invention, a reactor shown in FIG. 3 was used, and a conductive substrate (10) on which a thin film was formed could be held on the anode side, and a platinum plate (11) was used on the cathode side. The electrolytic solution used is one in which the supporting electrolyte containing the anion is dissolved in a highly polar organic solvent solution that is not susceptible to oxidation and reduction. In the present invention, since doping is performed by an electrolytic method, the doping rate can be arbitrarily and accurately controlled by controlling the potential and the amount of electricity. When a polymerizable fatty acid or an electrolytically polymerizable monomer is used as the monomolecular film forming substance, the film strength and heat resistance can be improved by polymerizing the monomer after doping is completed. It is preferable to use a monomolecular film-forming substance that provides a conductive polymer, such as alkylpyrrole, since this improves the conductivity of the resulting organic superconducting thin film.

【Example】

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. [Example 1] As a conductive substrate, an ITO glass substrate (10 mm x 20
BE is applied onto the substrate using the following method.
A cumulative film consisting of a mixture of DT-TTF and a monomolecular film-forming substance was created. BEDT-TTF and alaxic acid were mixed into purified chloroform, and the molar ratio of BEDT-TTF and alaxic acid was l:
1 and dissolve it, and as a subphase C
dCn, 4X 10-'M, KHCO 5x10-@M
A monomolecular film was created in the Langmuir trough by a conventional method using water containing . This monomolecular film on the water surface was repeatedly transferred and accumulated on an ITO-coated glass substrate by a vertical dipping method to produce a cumulative film (LB film) with a film thickness of about 1000 cm (FIG. 1). Next, in the reactor (4) shown in FIG. 2, CuSCN70mg%KSCN126mg, 18
-Crown-6210 mg was dissolved in 100 mI2 of ethanol to prepare an electrolytic solution (5). Next, as shown in Fig. 3, an ITO-coated glass substrate (
1O) is immersed in the electrolyte, and a metal clip (9) is attached to the anode side.
), and a constant DC current of 10 ILA was passed between both electrodes in a thermostat (not shown) at a temperature of 20°C. In about 5 to 6 hours, the colorless to pale yellow thin film began to turn black, confirming that a charge transfer complex formation reaction was occurring. After the reaction was completed, the substrate was taken out, washed with ethanol, and dried. From the X-ray diffraction results of the obtained black thin film -(BEDT-
The presence of a peak assigned to TTF) ICU (NCS)* was confirmed. When the DC magnetic susceptibility of this thin film was measured, it showed a Meissner effect at about 8. Moreover, the electrical conductivity of this black thin film is 1×10-”3 at room temperature.
It was 7cm. [Effects of the Invention] According to the present invention, it is possible to provide an organic superconducting thin film consisting of a donor molecule doped with an acceptor and an LB film of a monomolecular film forming substance. This organic superconducting thin film, due to its low production temperature,
It is possible to fabricate and process thin films on various substrate materials, and it can be effectively used to create bonds, sensors, and devices. Applications are expected for electromagnetic shielding, magnetic shielding, microwiring, strip lines, sensors, display elements, memories, switching elements, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view and a plan view of an ITO-coated glass substrate coated with a BEDT-TTF/araxic acid monooxygen molecule cumulative film. FIG. 2 is a schematic diagram of a reaction vessel for preparing a solution containing electron acceptors, and FIG. 3 is a schematic diagram of an apparatus for doping electron acceptors by an electrolytic method. The symbols in FIGS. 1 to 3 are as follows. 1, BEDT-TTF/araxic acid monooxygen molecule cumulative film, ITO layer, 310. Glass substrate, 491
0 reactor, 590. Electrolyte, 619. Glass filter 711. Lead I! (Anode side), 7', Lead wire (Cathode side), 809. Terumo holder 931 made of polytetrafluoroethylene. Metal clip, Ol. BEDT-T Ding F/Conductive substrate having a monomolecular araxic acid cumulative film, l 0. . platinum electrode

Claims (2)

[Claims] (1) A method for producing an organic superconducting thin film, which comprises forming a monomolecular cumulative film of a monomolecular film-forming substance containing donor molecules on a conductive substrate, and then doping with an acceptor by an electrolytic method. (2) An organic superconducting thin film characterized in that a monomolecular cumulative film of a monomolecular film-forming substance containing donor molecules is formed on a conductive substrate, and then an acceptor is doped by an electrolytic method.