JP2914518B2 - Oriented conductive organic thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oriented conductive organic thin film.

[Industrial applications]

The oriented conductive organic thin film of the present invention can be used as a conductive material.

[Conventional technology and problems]

Until now, it has been known that a conductive material can be obtained by doping a conjugated polymer such as polyacetylene, polypyrrole, polythiophene, polyarylenevinylene, or polythienylenevinylene with an electron-donating molecule or an electron-accepting molecule. I have. It is also known that a charge transfer complex formed by a combination of an electron donating molecule such as tetrathiafulvalene and an electron accepting molecule such as tetracyanoquinodimethane has conductivity. These conductive materials have high conductivity but are difficult to form a thin film, and have problems in stability of the conductive materials due to oxidation in the air, addition reaction of dopants, and the like.

Attempts have been made to produce a thin film of the above-mentioned conductive material using the LB method as a thin film production method, but a thin film having high conductivity and excellent stability has not been obtained.

It is known that an oriented thin film can be obtained by vapor deposition of a condensed polycyclic aromatic compound [Z. Physik. Chem. 19 , 206 (19)
59)], but there is no example of obtaining a conductive thin film.

There is a demand for an organic thin film having excellent stability in the atmosphere and high electric conductivity.

[Means for solving the problem]

In view of such problems, the present inventors have conducted intensive studies to obtain an organic thin film having excellent stability and high conductivity, and as a result, have obtained the oriented conductive organic thin film of the present invention.

That is, in the present invention, a linear condensed polycyclic aromatic compound represented by the following formula (I) wherein x is 2 to 5 is doped with an electron-accepting molecule, and a (00n) diffraction surface (n is 1 or more) (Integer).

The linear condensed polycyclic aromatic compound used in the present invention will be described. Examples of the linear condensed polycyclic aromatic compound used in the present invention include naphthacene (x = 2) and pentacene (x =
3), hexacene (x = 4) and heptacene (x = 5).

Next, the electron accepting molecule used in the present invention will be described. Cl ₂ , Br ₂ , I ₂ , ICl, ICl ₃ , I
Br, halogen such as _{IF, PF 5, AsF 5,} SbF 5, BF 3, BCl 3,
Lewis acids such as BBr ₃ , SO ₃ , NOx, SO ₂ , HF, HCl, HNO ₃ ,
_{H 2 SO 4, HClO 4,} FSO 3 H, ClSO 3 H, CF 3 SO 3 H, CF 3 SO 3 H, acetic, organic acids such as formic acid, protonic acids such as amino acids, TC
Electron-accepting organic molecules such as NQ, chloranil, tetrafluorotetracyanoquinodimethane, tetracyanoethylene, dicyanochloroquinone, FeCl ₃ , FeOCl, TiCl ₄ , ZrC
_{l 4, HFCl 4, NbF 5} , NbCl 5, TaCl 5, MoCl 5, WF 5, WCL 6, U
Transition metal compounds such as F ₆ , LnCl ₃ , (Ln = lanthanoids such as La, Ce, Pr, Nd, Sm), Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , P
Electrolyte anions such as F ₆ ⁻ , AsF ₅ ⁻ , SbF ₆ ⁻ , BF ₄ ⁻ , FeCl ₄ ⁻ , and a sulfonate anion can be used.

When these electron accepting molecules coexist with the above-mentioned linear condensed polycyclic aromatic compound, electron transfer occurs from the latter, and the molecular structure of the latter electron accepting molecule changes.

Next, an example of a method for producing an oriented conductive organic thin film of the present invention will be described. The oriented conductive organic thin film of the present invention is a method for obtaining an oriented conductive thin film by doping an electron-accepting molecule into the above-mentioned method for producing a condensed polycyclic aromatic compound thin film, and producing the above-mentioned condensed polycyclic aromatic compound thin film. It can be produced by a method in which an electron-accepting molecule is sometimes doped to obtain a distributed conductive thin film.

In the former method of producing an oriented conductive thin film, first, a thin film of a linear condensed polycyclic aromatic compound is formed on a substrate by using a thin film forming method such as a vacuum evaporation method, an MBE method, a CVD method, or a sputtering method. At this time, ceramic materials such as quartz glass, calcium fluoride, sapphire, alumina, magnesia, sodium chloride, potassium chloride, aluminum nitride, boron nitride, and semiconductors such as silicon, germanium, ITO, GaAs, InSb, and GaN are used as substrate materials. Material, metal material such as gold, aluminum, silver, iron, stainless steel, Y-Ba
A superconducting material such as —Cu—O, Bi—Sr—Ca—Cu—O, or Nb, or an organic material such as polyester, polystyrene, polyethylene, polyacetylene, or polypyrrole can be used. Various forms of the substrate can be used depending on the purpose of use.

The substrate temperature at the time of film formation is not particularly limited, but at a low temperature such as liquid nitrogen temperature, the orientation of the film decreases. As the substrate temperature increases, the orientation of the film improves. However, the orientation of the thin film decreases when heated above the melting point of the condensed polycyclic aromatic compound. Therefore, the substrate temperature is usually −100 ° C. to 3
00 ° C. is preferred. A good oriented thin film can be obtained even when the substrate temperature is near room temperature. This orientation can be evaluated by a usual X-ray diffraction method. Here, since the (00n) plane (n is an integer of 1 or more) selectively appears, it is understood that the film is an oriented thin film. For example, when a vacuum evaporation method is used as a thin film forming method, the above-mentioned condensed polycyclic aromatic compound is heated and evaporated in an atmosphere at a pressure of 10 ⁻² Torr or less. The lower the pressure of this atmosphere is, desirably 10 ^-4 Torr or less, in order to obtain an oriented thin film. When using the MBE method, Knudsen cell as a condensation polycyclic aromatic vapor deposition source,
Either electron beam heating or gas cell can be used, and an oriented thin film can be obtained by a normal film forming method. Further, in the case of the CVD method, an oriented thin film can be obtained by supplying a condensed polycyclic aromatic vapor onto a substrate in a vacuum or in the presence of a carrier gas. In sputtering, a thin film can be formed by argon sputtering using the condensed polycyclic aromatic compound target. As described above, an oriented condensed polycyclic aromatic compound thin film is obtained, and the higher the orientation is, the more preferable it is to obtain an oriented conductive thin film having high conductivity.

Next, the obtained oriented thin film can be doped with an electron accepting molecule to form an oriented conductive thin film. As the doping method, any of gas phase doping using gaseous molecules (dopant), liquid phase doping in a dopant solution or liquid dopant, and solid phase doping in which a solid dopant is brought into contact with a thin film and diffused is used. It is possible. If necessary, the efficiency of doping can be improved by electrolysis.
This doping improves the orientation of the thin film as compared to a non-doped thin film. For example, in a pentacene vapor-deposited film, an increase in the diffraction intensity of the (00n) plane of the X-ray diffraction pattern due to iodine doping, and a decrease or disappearance of the diffraction intensity of the sub-peak due to disorder of the orientation are observed. This indicates that doping improves the orientation of molecules.

An example of the latter method, that is, a method of obtaining a conductive thin film by supplying an electron-accepting molecule into the thin film at the time of preparing the thin film of the above-mentioned condensed polycyclic aromatic compound, will be described. Obtaining an oriented conductive thin film by laminating a condensed polycyclic aromatic compound and a dopant (electron-accepting molecule) on a substrate from their respective evaporation sources using the above-mentioned thin film production methods such as vacuum evaporation and MBE. Can be. If necessary, a thin film in which a condensed polycyclic aromatic compound and a dopant molecule are alternately and regularly stacked, for example, a thin film in which one atomic layer is stacked, can be obtained by controlling the film forming speed during film formation and using shuttering. it can. In the CVD method, a vapor of a condensed polycyclic aromatic compound and a vapor of a dopant can be respectively supplied onto a substrate to obtain an oriented conductive thin film. In sputtering, a thin film can be obtained by sputtering a linear condensed polycyclic aromatic compound in the presence of argon and a dopant. Depending on the dopant, binary sputtering is also possible.
The substrate material described above can be used as the substrate material used here.

The thickness of the thin film of the present invention cannot be limited because it varies depending on the purpose of use, but it can be manufactured from 50 ° to the order of microns.

If necessary, diffusion of the dopant on the thin film of the present invention
A protective layer for preventing scattering and a layer of another material may be provided. Further, in order to obtain a functional material to which the thin film of the present invention is applied, the thin film of the present invention and a thin film of another material may be used as a multilayer laminated film.

The organic thin film containing the dopant molecule obtained above has excellent molecular orientation and high conductivity. The molecular orientation of the thin film can be evaluated by a structural analysis method such as the X-ray diffraction method and the electron beam diffraction method described above. The thin film of the present invention is (00
An n) plane (n is an integer of 1 or more) diffraction plane appears, and the lattice constant thereof corresponds to the long axis of the molecule. Therefore, the molecules of the condensed polycyclic aromatic compound have the long axis regularly in the direction perpendicular to the substrate surface. It can be seen that they are arranged.

The conductivity of the thin film of the present invention is a two-terminal method which is a usual method,
It can be evaluated by the four terminal method. The conductivity can be changed depending on the type and content of the dopant according to the purpose of use. The conductivity of the thin film of the present invention is 10 ^-13 S / cm to 1
00S / cm. Further, since the thin film of the present invention has high molecular orientation as described above, it has anisotropy in electric conductivity. That is, the conductivity anisotropy (σ = / σ⊥) in the direction parallel to and perpendicular to the substrate surface is 1 to 10 ⁴ .

Since the thin film of the present invention is very stable without any problem in stability due to oxidation and addition reaction of dopants even when left in the air for a long time, it can be applied to various fields such as electronics and optoelectronics as an electronic material. Is beneficial.

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

Example 1 Pentacene was vacuum-deposited to a thin thickness of 500 ° on a quartz glass substrate to produce a pentacene thin film. The substrate temperature was room temperature, the pressure was 2 × 10 ⁻⁵ Toor, and the evaporation source was resistance heating of a tungsten boat. When the structure of the thin film was measured by X-ray diffraction, a (00n) plane (n = 1 to 3) having a lattice constant of 15 ° was recognized. Next, the obtained thin film was doped in an iodine gas atmosphere (room temperature, under a pressure of 1 Torr) to produce an oriented conductive thin film.

When the structure of the thin film was measured by an X-ray diffraction method (CuK α ray), a diffraction plane of (00n) (n = 1 to 14) having a lattice constant of 19 ° was observed. The conductivity of the thin film was measured by a DC four terminal and found to be 70 S / cm.

Example 2 In the same manner as in Example 1, a pentacene thin film having a thickness of 1000 ° was formed on a polyester substrate. When the structure of the thin film was measured by an X-ray diffraction method, a (00n) plane (n = 1 to 3) having a lattice constant of 15 ° was recognized.

The obtained film was doped in a 5 Torr SO ₃ gas atmosphere to obtain an oriented conductive thin film.

When the structure of the thin film was measured by an X-ray diffraction method (CuKα ray), a diffraction plane of (00n) (n = 1 to 8) having a lattice constant of 18 ° was recognized. The conductivity of the thin film was measured by a DC four-probe method and found to be 6 S / cm.

Example 3 A pentacene thin film was formed on a magnesia substrate in the same manner as in Example 1. The thin film was immersed in a FeCl ₃ nitromethane solution (0.1 M) for 1 hour. The structure of the obtained thin film is represented by X
(00n) with a lattice constant of 20Å as measured by X-ray diffraction
Surfaces (n = 1 to 10) were observed. The conductivity of the thin film was measured by a DC four-terminal method, and was 1 S / cm.

Example 4 Using a quartz substrate partially provided with a gold thin film (300 °), pentacene was vacuum-deposited on the substrate to a thickness of 2000 ° to obtain a pentacene thin film. The substrate temperature is 30
In an atmosphere at a temperature of 4 ° C. and a pressure of 4 × 10 ⁻⁵ Torr, the deposition source was performed by resistance heating of a tungsten boat.

To obtain an oriented conductive thin film performs a doping ^- ClO ₄ by electrolysis in acetonitrile perchlorate tetramethylammonium (0.05 mM) of gold thin film of the thin film as an anode.

When the structure of the thin film was measured by an X-ray diffraction method (CuK α ray), a (00n) (n = 1 to 10) diffraction plane having a lattice constant of 18 ° was observed. The conductivity of the thin film was measured by a DC four-terminal method and found to be 10 S / cm.

Example 5 A pentacene-iodine thin film was formed on a quartz glass substrate partially covered with a gold thin film (thickness: 500 °). Using an MBE apparatus, pentacene was heated in a K cell under an atmosphere of a pressure of 10 ⁻⁵ Torr, and a 5000 ° pentacene-iodine thin film was formed on a substrate of iodine using a gas cell. Pentacene and iodine were each laminated in a monoatomic layer by controlling the temperature of the deposition source and the atmospheric pressure, which are the conditions for forming the thin film. The substrate temperature is 0 ° C.
Met.

When the structure of the thin film was measured by an X-ray diffraction method (CuK α ray), a diffraction plane of (00n) (n = 1 to 14) having a lattice constant of 19 ° was observed. Conductivity of the thin film in the direction of the substrate surface (σ =)
Was measured by a DC four-terminal method, and the conductivity was 80 S / cm.

A gold electrode (500 °) was provided on the thin film by a vacuum evaporation method to form a sandwich structure. After doping the film with this structure with iodine, the conductivity (σ⊥) in the direction perpendicular to the substrate surface of the pentacene-iodine thin film was measured by a DC two-terminal method.
The conductivity was 0.04 S / cm. From this, the anisotropy of conductivity (σ = / σ⊥) was 2000.

Example 6 A hexene thin film was formed by a vacuum deposition method using a silicon substrate (the film thickness was 2000 Å). The production conditions in this production were a pressure of 2 × 10 ⁻⁵ Torr, a substrate temperature of 50 ° C., and an evaporation source by resistance heating of a tungsten boat. Next, iodine doping was performed on the thin film obtained in the same manner as in Example 1.

When the structure of the thin film was measured by an X-ray diffraction method (CuK α ray), a (00n) (n = 1 to 16) diffraction plane having a lattice constant of 22 ° was observed. The conductivity of the thin film was measured by a DC four-probe method and found to be 60 S / cm.

Example 7 A heptacene thin film having a film thickness of 10 was formed on a polyethene film substrate.
Vacuum deposited at 00 °. The thin film was doped with SO ₃ gas (pressure 5 mTorr) in a vacuum vessel.

The film was formed under the conditions of a substrate temperature of 25 ° C. and a pressure of 1 × 10 ⁻⁵ Torr, and the deposition source was formed by resistance heating of a tungsten boat.

The structure of the obtained thin film was measured by an X-ray diffraction method (CuK α-ray) to find that the lattice constant was 25 ° (00n) (n = 1 to 15).
Was observed. The conductivity of the thin film was measured by a DC four-terminal method and found to be 40 S / cm.

Example 8 A 800-nm-thick naphthacene thin film was formed on a quartz glass substrate by a vacuum evaporation method. The substrate temperature was 40 ° C,
Under an atmosphere of a pressure of 5 × 10 ⁻⁵ Torr, the deposition source was formed by resistance heating of a tungsten boat. Then, the thin film was doped with AsF ₅ gas (pressure 5 mTorr) in a vacuum vessel.

The structure of the obtained thin film was measured by an X-ray diffraction method (CuK α ray).
The diffraction surface of 3) was recognized. The conductivity of the thin film was measured by a DC four-terminal method and found to be 1 × 10 ⁻³ S / cm.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction pattern of the pentacene thin film produced in Example 1, and FIG. 2 shows an X-ray diffraction pattern of the pentacene-iodine thin film produced in Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-77322 (JP, A) JP-A-60-166298 (JP, A) JP-A-63-94507 (JP, A) JP-A-1- 265404 (JP, A) JP-A-62-84120 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09K 3/00 H01B 1 / 12,5 / 14 G02F 1/35 CA (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. A linear condensed polycyclic aromatic compound represented by the following formula (I) wherein x is 2 to 5 is doped with an electron accepting molecule, and a (00n) diffraction surface (n is 1 or more) Orientated conductive organic thin film having the following formula: