JPH0642330B2 - Organic conductive thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention can be obtained by changing the types and compositions of an organic donor (hereinafter abbreviated as D) and an organic acceptor (hereinafter abbreviated as A). The present invention relates to an organic conductive thin film having various conductivity.

[Conventional technology]

In the past, organic chemists, condensed matter physicists, and theoretical physicists have been pursuing research in search of low-molecular organic substances that give high conductivity. The study material mostly D _n A _m consist of a combination of stoichiometry or n: m has a consistent composition represented by a simple integer ratio, the bulk single crystal, filed polycrystalline It was Therefore, D-A complex crystals having a stoichiometrically uniform composition were the main subjects of study [eg, Molecular Crystals and Liquid Crystals].
Crystals (Molecular Crystals and Liquid Crysta
ls) 83-86 (1982)]. There are very few studies on thinning of these DA compounds, and tetrathiafulvalene (hereinafter abbreviated as TTF) -tetracyanoquinodimethane (hereinafter abbreviated as TCNQ) 1: 1 complex system [P. Applied Physics Letters, Vol. 24, p. 439 (1974)], P. Chaudrari et al., N-docosylpyridinium-TCNQ
1: 1 complex-iodine doping system [A. R. Morel Crystals and Liquid Crystals, Vol. 120, No. 31 by A.R. Teixier
There is only page 9 (1985).

Its conductivity is TTF-TCNQ thin film, room temperature conductivity σ _RT = 20
˜30 Scm ⁻¹ (film thickness 0.2 μm, single crystal orientation), N-docosylpyridinium-TCNQ-iodine system, σ _RT = 1
It is reported to be 0 ^-1 Scm ^-1 . However, the former is
This is a TTF-TCNQ 1: 1 complex prepared by vacuum deposition on rock salt cleaved in a vacuum, which is not realistic considering industrial application to electronic materials. In addition, the latter is prepared by the Langmuir Brodgett (LB) method, but with only the LB film containing the N-docosylpyridinium-TCNQ salt, σ _RT =
There is only 10 ^-5 Scm ^-1 , and the conductivity of σ _RT = 10 ^-1 Scm ^-1 can be obtained only by exposure to iodine vapor. However, this also has a fatal defect that it returns to its original conductivity in about 1 hour if left in the atmosphere. Organic conductive complexes that have been known or will be studied in the future are
From the viewpoint of application as a leading role of electronic materials such as i, Ge, and GaAs semiconductor industry, it is necessary to form a single crystal having a diameter of several inches and process it, or to form a thin film having a thickness of several Å to several μm. Most of the reported D-A type organic complexes are mechanically fragile, and the size of the single crystal is at most a few centimeters in length and a few millimeters in width. Almost difficult. On the other hand, if the D-A complex can be formed on a suitable solid substrate, it has a great merit in terms of workability. In addition, a DA complex system, for example, Hg
_If the band gap and conductivity can be controlled by controlling the composition of X, Y, and Z as in the case of the _X Cd _Y Te _Z system, the possibility of semiconductor-like application such as organic pn junction can be opened by thinning the film.

[Problems to be solved by the invention]

However, up to now, there has been no report on thinning of the film with controlled conductivity due to the composition of D _x A _1-x .

An object of the present invention is to provide organic thin films having various electroconductivity by changing the composition and components of substances D and A.

[Means for solving problems]

Briefly describing the present invention, the present invention relates to an organic conductive thin film, which is an amorphous thin film composed of D and A having an arbitrary average composition D _x A _1-x (x: average mole fraction). Is characterized by.

The main feature of the thin film of the present invention is that it is an amorphous organic conductive thin film having an average composition of D _x A _1-x . The conventional thin film is
It is a crystalline organic conductive bulk complex having a stoichiometrically uniform composition of D _{n Am} (n: m is a simple integer ratio).

D _n A _m type organic conductive crystals have so far been mainly composed of D solution and A
Diffusion method by contact of solution, solvent evaporation method of DA solution, D
-The slow cooling method of the A solution, the electrochemical redox method, and the sublimation method are known. However, with these methods, D _x A _1-x
Fabrication of type non-stoichiometric organic thin films is difficult. D _x A _1-x
In order to obtain a type organic thin film, application of the LB method was tried. In the conventional concept, it was believed that the substrate had to have a long chain alkyl group in order to obtain a good quality LB film. However, in the experiments conducted by the present inventors, it was possible to obtain unsubstituted or lightly substituted (methyl, ethylene, trimethylene, fluorine-containing) D and A, which have been known so far, without having a long-chain alkyl moiety. Also found that a good quality LB film (but not a monomolecular film) can be formed. Of course, a normal vacuum binary vapor deposition method (D and A are put in separate evaporation boats to control the temperature of the substrate, D boat, and A boat) can also give a D _x A _1-x thin film. It was confirmed. However, controlling x is more difficult than the LB method. Therefore,
The D _x A _1-x thin film was produced by the LB method. That is, D _x
It was prepared by developing the A _1-x mixed solution on the air-water surface and scooping it on a solid substrate.

Examples of D used in the present invention include, in addition to the above TTF, tetraselenafulvalene (TSF), tetramethyltetrathiafulvalene (TMTTF), tetramethyltetraselenafulvalene (TMTSF), hexamethylenetetrathiafulvalene ( HMTTF), hexamethylenetetraselenafulvalene (HMTSF), hexamethylenetetratellafulvalene (HMTTeF), bisethylenedithiatetrathiafulvalene (BEDT-TTF) and other derivatives of fulvalene skeleton,
Tetrathiatetracene (TTT), Tetraselenatetracene (TST), Tetrathiaanthracene (TTA), Tetraselenaanthracene (TSA), Tetrathianaphthalene (TT)
There are ace skeleton derivatives such as N).

In addition, examples of A used in the present invention are as described above.
In addition to TCNQ, dimethyl tetracyanoquinodimethane (DMTC
NQ), dicyanotetracyanoquinodimethane (DCTCNQ),
TCNQ derivatives such as tetrafluorotetracyanoquinodimethane (TFTCNQ), dichlorodicyanobenzoquinone (DD
There are benzoquinone derivatives such as Q) and tetrachlorobenzoquinone (TCQ).

〔Example〕

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example 1 (Production of Membrane) A uniformly mixed dilute solution having a composition of D _x A _1-x was spread on the water surface which was kept at a constant temperature. A thin film was formed on a solid substrate (SiO ₂ , CaF ₂ ) by the horizontal deposition method while controlling the surface 5-30 dyn / cm. The film thickness is about 250Å / stamp for TTF _X TCNQ _1-X system, about 80Å / stamp for TMTSF _X TCNQ _1-X system
Stamp, TTF _X TFTCNQ _1-X system, changed about 1000Å / stamp and D-A combination.

(Identification of film thickness) X-ray photoelectron spectroscopy (XPS) was performed to clarify whether D _x A _1-x (x: average mole fraction, charged mole fraction) is the actual membrane composition. The intensity ratio of N _1s , S _2p , Se _3d, etc. was confirmed to be almost the same as the charged composition.

Figure 1 shows the X-ray diffraction (XRD) pattern of the TTF _X TCNQ _1-X (X = 0.5) LB film, showing the relationship between 2Θ (CuKα) (degrees, horizontal axis) and intensity I (vertical axis). Is shown as a graph. d = 9.2
In addition to the weak broad reflection corresponding to 2Å (002) and d = 4.58Å (004), a very broad and strong amorphous reflection centered at d = 4Å was observed. The same applies to other compositions x. This means that TTF _X TC prepared by the LB method
It shows that the NQ _1-X thin film is substantially amorphous. Similarly, the other D-ALB films were also amorphous.

In Fig. 2, TTF _X TCNQ _1-X (x = 0, 0.33, 0.5
0) The optical absorption spectrum of the LB film was measured by the energy E
V, horizontal axis), wave number (10 ⁴ cm ^-1 , horizontal axis) and absorbance ABS
It is shown as a graph of the relationship with (vertical axis). x = 0.4 ~
In the range of 0.9, the absorption spectrum has a value in the literature [P.
Applied Physics Letters, Vol. 24, p. 439 (1974), C. Caudrali, et al. S. Physical Review Letters, Vol. 33, No. 1559, by Jacobsen, CS, etc.
Page (1974), J. Tanaka and others, Bulletin of the Chemical Society of Japan (Bull.Chem.So
c.Japan) 49: 2358 (1976)]. On the other hand, when x = 0.33,
An absorption attributed to the TCNQ cluster was observed at 2.84 eV. On the other hand, in the range of x = 0.33 to 0.9, TCNQν
_The charge mobility estimated from the absorption shift of _C≡N was 0.52, which was constant. This means that a thin film having an average composition x of TTF _X TCNQ _1-X is actually (TTF-TCNQ) _X or 1-X excess (TTF or TCNQ) _1-2X or 2X-1 (x0.5). 2 indicates that phase separation has occurred in the two phases.

(Electrical conductivity of D-ALB film) Fig. 3 shows the x dependence of the room temperature in-plane conductivity σ _RT of the TTF _X TCNQ _1-X LB film, the average mole fraction x (horizontal axis) and the room temperature conductivity. Shown as a graph of the relationship with σ _RT (Scm ^-1 , vertical axis). As is clear from FIG. 3, σ _RT greatly and specifically changes with x. In particular, σ _RT has a maximum around x = 0.45 and 0.55, which are slightly deviated from x = 0.5. Maximum conductivity is σ _RT = 1.5Scm when x = 0.55
^-1 . This value is σ _RT = 2 to 4 Scm ^-1 obtained in TTF-TCNQ polycrystalline pellets [G. Saito et al., Chemistry Letters, 1983, pp. 503].

FIG. 4 shows the x dependence of σ _RT in the TMTSF _X TCNQ _1-X LB film as a graph of the relationship between σ _RT (vertical axis) and x (horizontal axis) as in FIG. In the composition of x = 0.2 to 0.5, the maximum value of σ _RT = 1 to 2 × 10 ^-6 Scm ^-1 is shown, and TTF _X T
Although it is a little different from the CNQ _1-X system, σ _RT also changes with x, and its value is semiconducting. in this way,
The conductivity of the D _x A _1-x LB film greatly changes depending on the combination of D and A and the composition x.

Table 1 below shows σ _RT together with other D _x A _1-x (x = 0.5) LB films.

[Effects of the Invention] As described above, according to the present invention, a D _x A _1-x amorphous conductive thin film can be easily produced by the LB method, and its conductivity is
It can be greatly changed depending on the combination of DA and the average composition x. As a result, there is an advantage that the electric conductivity can be arbitrarily controlled over the range of σ _RT 10 ⁰ to 10 ^-12 Scm ^-1 . value of σ _RT 10 ⁰ Scm ^-1 is the D-A polycrystalline body sigma
_When viewed as _RT , it is substantially close to σ _RT of a polycrystalline organic conductor exhibiting a metallic state of dσ / dT0 (T: absolute temperature).
That is, the D _x A _1-x LB film can give various conductivity from almost a metallic state to a semiconductor close to an insulator. Therefore, in consideration of application as a semiconductor, for example, if a D _0.2 A _0.8 thin film and a D _0.8 A _0.2 thin film are laminated, a pn junction can be formed to show diode characteristics. Is. Also, as an antistatic film, σ _RT 10
If it is ^-1 Scm ^-1 , a sufficiently good effect is exhibited. In this case σ _RT
As a TTF _X TCNQ _1-X thin film system giving 10 ^-1 Scm ^-1 , x =
It is necessary to have a value of 0.35 to 0.70.

[Brief description of drawings]

Figure 1 is _{TTF X TCNQ 1-X (x} = 0.5) X -ray diffraction pattern diagram of the LB film, FIG. 2 _{TTF X TCNQ 1-X (x} = 0,0.3
3, 0.50) LB film optical absorption spectrum, Fig. 3 is a graph showing the x-dependence of σ _RT in TTF _X TCNQ _1-X LB film, and Fig. 4 is TMTSF _X TCNQ _1-X LB film. σ _RT x
It is a graph which shows dependence.

Claims (4)

[Claims] 1. An amorphous thin film comprising an arbitrary average composition D _x A _{1-x of} an organic donor and an organic acceptor (wherein D is an organic donor, A is an organic acceptor, and x is an average mole fraction). The organic conductive thin film is characterized by: 2. The organic donor is tetrathiafulvalene,
Tetraselenafulvalene, tetramethyltetrathiafulvalene, tetramethyltetraselenafulvalene, hexamethylenetetrathiafulvalene, hexamethylenetetraselenafulvalene, hexamethylenetetraterlafulvalene, bisethylenedithiatetrathiafulvalene Derivatives, tetrathiatetracene, tetraselenatetracene, tetrathiaanthracene, tetraselenaanthracene, acene skeleton derivatives such as tetrathianaphthalene, the organic acceptor, tetracyanoquinodimethane, dimethyltetracyanoquinodimethane,
The organic conductive thin film according to claim 1, which is a tetracyanoquinodimethane derivative such as dicyanotetracyanoquinodimethane or tetrafluorotetracyanoquinodimethane, or a benzoquinone derivative such as dichlorodicyanobenzoquinone or tetrachlorobenzoquinone. 3. The method according to claim 1, wherein the thin film is obtained by developing the D _x A _1-x mixed solution on an air-water surface and scouring it on a solid substrate. Organic conductive thin film. 4. In the D _x A _1-x thin film, D is tetrathiafulvalene, A is tetracyanoquinodimethane, and x
Has a value of 0.35 to 0.70 and an electric conductivity of 0.1.
The organic conductive thin film according to claim ^1, which has a S · cm ⁻¹ or more.