JP2918587B2 - Conductive organic thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel conductive organic thin film, particularly to a conductive organic thin film laminated on a solid substrate as a cumulative multilayer film.

[Conventional technology]

When an amphiphilic organic substance having a hydrophilic group and a hydrophobic group in one molecule is dissolved in an organic solvent such as chloroform and spread on a water surface, the solvent evaporates to form a film of the organic substance. When the area of the water surface on which the organic film is formed is narrowed by a frame (barrier), the amphiphilic molecule regularly turns the hydrophilic group part toward the water side and the hydrophobic group part toward the air side on the water surface in a certain area. A film having a thickness of one molecule aligned and oriented, that is, a monomolecular film is formed.

A film obtained by repeatedly transferring a monomolecular film from the water surface to a solid substrate is called a cumulative multilayer film (Langmuir-Blodgett film, LB film). The method of manufacturing a cumulative multilayer film in this manner is generally called an LB method. The laminate in which the accumulated multilayer film is laminated on the solid substrate includes various sensors, functional elements, display elements, storage and recording media, coating materials, liquid crystal alignment films, nonlinear optical elements, resists for ultra-fine patterns, switching elements, It can be applied to applications such as a target permeable membrane.

Conventional thin films or ultrathin films obtained by this method have good characteristics such as mechanical characteristics and electric characteristics by themselves, but are generally insufficient and few examples have been put to practical use.

Various attempts have been made to impart conductivity to the conductive LB film, for example, "Chemistry Letters", pp. 1667-1670 (1970).
According to (Reference 1), an LB film having a conductivity of 1 s / cm is obtained by using a charge transfer complex for a hydrophilic group, and “Tetrahedron Letters”, Vol. 27, No. 46, No. 5633-563.
Page 6 (1986) (Literature 2) discloses a polypyrrole LB film having a conductivity of 0.1 s / cm in which pyrrole is introduced into a hydrophilic group and polymerized. Furthermore, in the 6th Next-Generation Industrial Technology Symposium, Preliminary Collection of Highly Functional Polymer Materials, 185, 1988 (Reference 3), an LB film was prepared using diacetylenic acid having no aromatic ring, and after photopolymerization. It has been reported that the conductivity of polyacene LB films obtained by heat treatment or electron beam irradiation and intramolecular cyclization increases to the order of 1 × 1 ⁻³ s / cm when iodine is doped. One layer of the LB film mentioned here is almost 30
It is found to have a thickness of ~ 50mm.

Such LB films with relatively good conductivity are expected to be applied to electronic materials in the future, but LB films made by conventional methods generally have low conductivity and are not suitable for practical applications such as electrode materials. It is a serious problem.

For example, "Transactions of the Institute of Electrical Engineers of Japan", Vol. 106, No. 9, 1986-435
On page 441 (Reference 4), there is a report on a polyimide LB ultrathin film. An ultrathin film with a thickness of about 4 mm having excellent thermal and mechanical properties has been obtained, but the conductivity is extremely low and Conductivity of 20 layers and 50 layers is 8.00 × 10 ^-15 and 8.19 × 10 ^{-15 respectively}
(S / cm).

It is known that an aromatic heat-resistant polymer such as polyimide can be converted into a conductive pyropolymer by firing, but there is no example in which an LB film is used. By using the LB method, an ultrathin film can be formed and molecules can be highly aligned and aligned. Therefore, it is expected that a pyropolymer having the same characteristics as the cast film can be manufactured with lower energy than the cast film.

[Summary of the Invention]

The present inventors have conducted various studies and experiments with the aim of providing a conductive organic thin film that can solve the above-mentioned problems and improve the conductivity and can be put to practical use for electrode materials and the like. As a result, it has been found that heating a thin film of an organic molecule having an aromatic ring such as a polyimide described in the above-mentioned Document 4 to thermally decompose and polymerize it can significantly improve the conductivity, which was extremely low. It is a thing.

Therefore, the present invention relates to an organic molecule having an aromatic ring.
The present invention provides a conductive organic thin film obtained by heating a thin film produced by the method and thermally decomposing and polymerizing the thin film.

[Detailed description of the invention]

 The present invention will be described in detail below.

The organic molecule used in the present invention has an aromatic ring, and examples thereof include polyimide and polyparaphenylene vinylene. Among them, polyimide is preferable. An example of the molecular formula of this polyimide is as follows.

This organic molecule thin film is usually formed on a substrate by the LB method as described above. According to the LB method, in the case of polyimide, an ultrathin film such as 4 mm can be formed, and in that case, a good transparent electrode can be formed, which is effective. However, the present invention is not limited to such an ultrathin film and is usually obtained by this method. Any thickness is also included.

When the substrate is used only for the LB method, a slide glass or an aluminum vapor-deposited plate can be used. However, in the present invention, it is preferable to use a quartz glass plate, a silicon wafer, mica, or the like that can withstand a heat treatment performed later. By repeating the operation on the substrate, a laminate composed of one to 100 or more accumulated thin films can be formed. In the present invention, such a thin film may be a single layer or multiple layers, and the number is arbitrary.

The thus-obtained organic thin film of organic molecules having an aromatic ring is subjected to a heat treatment to thermally decompose and polymerize the organic molecules. Conditions such as temperature and time are determined to the extent necessary for causing thermal decomposition polymerization. In the case of polyimide, heating is performed at 700 ° C. or higher, at a temperature of about 1000 ° C. The time depends on the number or thickness of the thin film layers, but about 60 minutes is sufficient.

This heat treatment is performed in a high vacuum (about 1 × 10 ⁻⁵ torr) or in an atmosphere of an inert gas such as nitrogen or argon. Thus, the organic molecules are pyrolyzed and polymerized to form a pyropolymer.

The organic thin film thus obtained has, for example, a conductivity of more than 70 s / cm in a laminate of 50 layers, is an electrode material that is much higher than before heat treatment and has excellent stability.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 A cumulative multilayer film of polyimide was prepared according to the teaching of the above-mentioned reference 4.

First, polyamic acid (PAA) is synthesized by polymerizing pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (DDE) in N, N'-dimethylacetamide (DMAC). Benzene is added to this polyamic acid DMAC solution to make a solution of both solvents. This PAA solution is mixed with an N, N-dimethyl-n-hexadecylamine (C ₁₆ DMA) solution prepared in the same solvent and at the same concentration to prepare a polyamic acid derivative (PAAD) solution. In this PAAD molecule, the portion of the C ₁₆ DMA having a long chain becomes hydrophobic, enabling the formation of a monomolecular film.

A quartz glass plate is used as a substrate, and an organic molecular thin film is formed according to a vertical immersion method in which the quartz glass plate is put in and out of the surface of pure water. The temperature during film accumulation is about 20 ° C.

The following table summarizes the cumulative conditions of this polyamic acid derivative (PAAD).

This LB film of polyamic acid derivative is treated with acetic anhydride: pyridine:
It was immersed in a benzene (1: 1: 3 volume ratio) mixed solution at room temperature for about 12 hours, and imidization proceeded to form a polyimide LB film.

Thus, 51 layers of the polyimide LB film were formed on the quartz glass plate. The obtained LB film was dried under vacuum of 1 × 10 ⁻⁵ torr for 10
A heat treatment was performed at 00 ° C. for 60 minutes, followed by thermal decomposition polymerization to form a pyropolymer LB film.

The conductivity of the pyropolymer LB film was measured by a measuring system as shown in FIG. In the figure, 1 is vertical (l) 1.3cm,
It is a quartz substrate having a thickness (t) of 1 mm, on which an LB film 2 is formed. Two silver paste terminals 3 are provided on the substrate 1 with d = 0.5 cm apart from each other, and a copper wire 4 is connected thereto.
This measurement system was prepared, and the conductivity was measured using a normal digital voltmeter by a DC two-terminal method. When the thickness of the pyropolymer film according to the present invention was converted into 4Å per layer, the thickness was 51Å for the 51 layers and the conductivity was 74 s / cm for the 51 layers, which was extremely high. The conductivity of the pyropolymer LB film was extremely stable without change even after 42 days in the air.

Comparative Example 1 A quartz substrate, on which the polyimide LB film was not accumulated, was heat-treated under the same conditions as in Example 1, but was not conductive as in Example 1, and no new substance was formed by the heat treatment. It was confirmed that the LB film was a conductive thin film formed by heat treatment.

By the way, the conductivity of the polyimide LB film before the heat treatment according to the above example was measured using the measurement system of Example 1, and the result was measured by YHP4329 HIGH RESISTANCE METER.
1.89 × 10 ⁻⁸ s / cm or less.

As is clear from this, the organic thin film heat-treated according to the present invention has remarkably high conductivity, and can be favorably used for applications such as electrodes.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a system for measuring the conductivity of an organic thin film according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Quartz substrate, 2 ... Organic thin film, 3 ... Silver paste electrode, 4
... lead wire.

Claims (1)

(57) [Claims] 1. A conductive organic thin film obtained by subjecting a thin film produced by an LB method to an organic molecule containing an aromatic ring and subjecting it to thermal decomposition polymerization.