JP2864427B2 - Highly oriented organic thin film - Google Patents

Description

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

[Industrial applications]

The oriented organic thin film of the present invention can be used as an electronic material and an optoelectronic material.

[Conventional technology and problems]

At present, application of thin film organic materials to fields such as conductive materials, insulating materials, nonlinear optical materials, optical recording materials, display materials, and resist materials is being actively studied. In order to apply an organic thin film to the above fields, it is necessary to have excellent molecular orientation.

Until now, organic thin films have been prepared by LB method, vacuum deposition method, MBE method, plasma polymerization method, electrolytic polymerization method, coating method, and the like. However, the molecular orientation of the organic thin films obtained by these methods is not sufficient for application to the above-mentioned application fields. In particular, since a charge-transfer complex-based conductive material has a crystal axis anisotropy that is strong in its conductivity, a high molecular orientation is required for use as a highly conductive material or an anisotropic conductive material. When used as a nonlinear optical material,
It is known that the higher the molecular orientation, the better the nonlinear characteristics. As described above, in order to apply it to a functional organic thin material, it is required to improve its molecular orientation.

[Means for Solving the Problems] In view of such problems, the present inventors have conducted intensive studies to obtain an organic thin film having excellent molecular orientation, and as a result, have obtained an oriented organic thin film of the present invention. Reached.

That is, in the present invention, the number of fused benzene rings is 3 or more.
The present invention relates to a highly oriented organic thin film obtained by subjecting an organic thin film of a condensed polycyclic aromatic compound having a molecular weight of 13 or less to electron doping and subsequent undoping.

The fused polycyclic aromatic compound used in the present invention will be described. The condensed polycyclic aromatic compound used in the present invention is a condensed polycyclic aromatic compound having 3 to 13 condensed benzene units. Next, an example is shown. As condensed polycyclic aromatic compounds, anthracene (n = 3), naphthacene (n =
4), pentacene (n = 5), hexacene (n = 6),
Heptacene (n = 7), phenanthrene (n = 3), acenaphthene (n = 3), pyrene (n = 4), chrysene (n = 4), perylene (n = 5), coronene (n = 3)
7), Terylene (n = 8), Ovalene (n = 10), Quarterylene (n = 11), Circum anthracene (n = 13)
And hydrocarbon compounds such as derivatives thereof, trifenodioxazine (n = 5), trifenodithiazine (n
= 5), triphenodiselenazine (n = 5), hexacene-6,15-quinone (n = 6), etc.
Derivatives substituted with S, O, carbonyl and the like can be mentioned.

Next, the electron accepting molecule used in the present invention will be described. As electron-accepting molecules, halogens such as Cl ₂ , Br ₂ , ICl, ICl ₃ , IBr, IF, Lewis acids such as PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ , SO ₃ , HF, HCl, HNO ₃ , H ₂ SO ₄ , HClO ₄ , FSO ₃ H, ClSO ₃ H, C
F ₃ SO ₃ H, organic acids such as acetic acid and formic acid, protonic acids such as amino acids, FeCl ₃ , FeOCl, TiCl ₄ , ZrCl ₄ , HfCl ₄ , NbF ₅ , NbCl ₅ , T
aCl ₅ , MoCl ₅ , WF ₆ , WCl ₆ , UF ₆ , LnCl ₃ , (Ln = La, Ce, Pr, Nd, Sm
Transition metal compounds such as lanthanide) such as, Cl ^-, B
Electrolyte anions such as r ⁻ , I ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , AsF ₅ ⁻ , SbF ₆ ⁻ , BF ₄ , and sulfonate anion can be used.

Next, a method for producing the highly oriented organic thin film of the present invention will be described. The highly oriented organic thin film of the present invention is a highly oriented organic thin film obtained by doping an electron accepting molecule into the thin film after preparing the condensed polycyclic aromatic compound thin film and then performing dedoping of the electron accepting molecule. Can be made.

An example of production of a highly oriented organic thin film of the present invention will be described. As a method for producing a highly oriented organic thin film of the present invention, a method of obtaining a highly oriented organic thin film by subjecting a thin film of a condensed polycyclic aromatic compound prepared in advance to a doping treatment and an undoping treatment of an electron accepting molecule, A method of obtaining a highly oriented organic thin film by performing a dedoping treatment after the preparation of the aromatic compound / electron accepting molecular thin film can be given.

The former method for producing a highly oriented organic thin film will be described.
First, a thin film of the above-mentioned condensed polycyclic aromatic compound is prepared by a thin film forming method such as a vacuum evaporation method, an MBE method, a CVD method, and sputtering. The resulting film is obtained as a thin film on a substrate. At this time, ceramic materials such as quartz glass, calcium fluoride, sapphire, and alumina; semiconductor materials such as silicon, germanium, ITO, GaAs, InSb, and GaN; and metal materials such as gold, aluminum, silver, iron, and stainless steel , Y-Ba-Cu-O, Bi-Sr-Ca-Cu-
Superconductive materials such as O-based and Nd-based materials, organic materials such as polyester, polystyrene, polyethylene, polyacetylene, and polypyrrole can be used. Various forms of the substrate can be used depending on the purpose of use.

As a method for forming a thin film of the condensed aromatic ring compound, for example, when a vacuum evaporation method is used, the condensed polycyclic aromatic compound is heated and vapor-deposited 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 the MBE method is used, a Knudsen cell, an electron gun heating, or a gas cell can be used as a condensation polycyclic aromatic vapor deposition source, and a thin film can be obtained by an ordinary film forming method. Further CVD
In the case of the method, a thin film is obtained by supplying a condensed polycyclic aromatic vapor onto a substrate under vacuum or in the presence of a carrier gas. In the case of sputtering, a thin film is formed on a substrate by performing argon sputtering using a condensed polycyclic aromatic compound target. In this way, a condensed polycyclic aromatic compound thin film can be obtained, but is not limited to the above method.

Next, the obtained thin film is doped with electron-accepting molecules and then undoped to obtain an oriented 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.

Next, a highly oriented organic thin film can be obtained by subjecting the doped thin film to undoping. An example of this dedoping method will be described. In the doping process, a thin film doped with a dopant molecule having a high vapor pressure can be treated under a high vacuum to undope the dopant molecule from the thin film. At this time, if necessary, heating can be performed to accelerate dedoping. In a thin film from which a dopant can be extracted in a liquid phase, undoping can be performed by immersing in a solvent or a solution capable of dissolving the dopant to diffuse and remove the dopant. If necessary, an electric field opposite to that of the electrolytic dopant may be applied to the thin film to accelerate dedoping. Dedoping is performed as described above, but is not limited thereto.

Next, the latter method, that is, a method of producing a condensed polycyclic aromatic compound-electron accepting molecular thin film and then performing a dedoping treatment to obtain a highly oriented organic thin film will be described.

An example of a method for producing a condensed polycyclic aromatic compound-electron accepting molecular thin film will be described. A thin film is prepared by laminating a condensed polycyclic aromatic compound and an oxidizing molecule on a substrate from a vapor deposition source, respectively, using the above-described thin film preparation methods such as vacuum deposition and MBE. Since the obtained thin film is already doped with electron-accepting molecules, an oriented organic thin film can be prepared by dedoping this film. The method of undoping can be performed in the same manner as the former method.

If necessary, doping and undoping steps can be repeated to enhance the orientation.

The orientation of the thin film obtained after the undoping is improved as compared with the thin film before the doping. The orientation of the thin film can be evaluated by ordinary diffraction methods such as X-ray diffraction and electron diffraction. For example, in the X-ray diffraction method, an index indicating the high orientation of an organic thin film is an increase in the order n of the (OOn) plane (n is an integer of 1 or more) of the thin film and a decrease or disappearance of a subpeak other than the (OOn) plane. It is. In some cases, an increase in the diffraction intensity of the (OOn) diffraction plane is observed. From these facts, it is possible to evaluate the improvement of the orientation of the thin film by doping / undoping. Also, based on the lattice constant corresponding to the interlayer distance of the (OO1) plane of the X-ray diffraction pattern, whether the major axis of the condensed polycyclic aromatic compound is oriented in a direction perpendicular or horizontal to the substrate surface in the thin film Can be estimated. In general, the condensed polycyclic aromatic compound thin film tends to have its major axis easily oriented in a direction perpendicular to the substrate surface. We have found that doping and undoping of this thin film makes it more highly oriented. Although the cause of the improvement in the orientation is not clear, the doping of the electron-accepting molecules into the molecular phase of the condensed polycyclic aromatic compound by doping causes the arrangement of the condensed polycyclic aromatic molecules to be arranged by some kind of interaction. it is conceivable that. The dopant content after dedoping is not particularly limited because it differs depending on the film thickness, the dopant molecular species, the molecular species of the condensed polycyclic aromatic compound, the dedoping method, and the like. Further, when the content of the dopant is permitted depending on the application to be used, it can be used in a film in the course of undoping.

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, a protective layer, an electrode, and a layer of another material can be provided on the thin film of the present invention. 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 highly oriented organic thin film obtained above has excellent molecular orientation and is stable even when left in the air for a long time, so it can be applied to various fields such as electronics and optoelectronics as an electronic material. Is beneficial.

〔Example〕

 Hereinafter, the present invention will be described in more detail by way of examples.

Example 1 Pentacene was vacuum-deposited on a quartz glass substrate to a thickness of 2000 ° to form a pentacene thin film. As the manufacturing conditions, the substrate temperature was room temperature and the pressure was 10 ⁻⁵ Torr, and the deposition source was a resistance heating of a tungsten boat. When the structure of the obtained pentacene thin film was measured by an X-ray diffraction method, an (OOn) plane having a lattice constant of 15 ° (n = 1 to 3) and a (OOn) plane having a lattice constant of 14 ° (n = 1 to 3) were recognized. Was. Next, the obtained thin film is placed in an iodine gas atmosphere (room temperature, 2 Torr).
After the doping was performed, the thin film was dedoped by keeping the thin film at a temperature of 50 ° C. under an atmosphere of a pressure of 1 × 10 ⁻⁵ Torr for 10 hours.

When the structure of the obtained thin film was measured by an X-ray diffraction method, an (OOn) plane with a lattice constant of 15 ° (n = 1 to 4) was recognized, and the diffraction plane with a lattice constant of 14 ° disappeared.

Example 2 A pentacene thin film having a thickness of 1000 ° was formed on a polyester substrate in the same manner as in Example 1. When the structure of the obtained thin film was measured by the X-ray diffraction method, a diffraction plane having an interlayer distance of 28 ° and an interlayer distance of 14 to 15 ° was observed.

This pentacene thin film was doped under a 10 mTorr SO ₃ gas atmosphere to obtain an oriented conductive thin film. Subsequently, the thin film was dedoped while being kept at 90 ° C. in an atmosphere at a pressure of 10 ⁻⁵ Torr.

When the structure of the obtained thin film was evaluated by an X-ray diffraction method, an (OOn) plane (n = 1 to 4) having a lattice constant of 15 ° was recognized.
From these results, it was found that the orientation of the molecules in the pentacene thin film was improved by doping / undoping.

Example 3 Using a quartz substrate partially provided with a gold thin film (300 °), pentacene was vacuum-deposited to a thickness of 3000 ° on the substrate 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. The structure of the obtained thin film was measured by X-ray diffraction.
A diffraction peak at an interlayer distance of 14 ° was observed together with the plane (n = 1 to 3).

After doping with ClO ₄ ⁻ by performing electrolysis in a solution of tetramethylammonium perchlorate in acetonitrile (0.05 mM) using the gold thin film as an anode, immersion and washing with acetonitrile were repeated to perform dedoping.

When the structure of the thin film was measured by an X-ray diffraction method (CuKα ray), a diffraction plane of (OOn) (n = 1 to 4) with a lattice constant of 15 ° was recognized, and the diffraction peak at an interlayer distance of 14 ° disappeared.

Example 4 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. The substrate temperature was 10 ° C. Next, the thin film was dedoped while being kept at 60 ° C. in an atmosphere of a pressure of 10 ⁻⁴ Torr.

When the structure of the obtained thin film was evaluated by an X-ray diffraction method, an (OOn) plane (n = 1 to 5) having a lattice constant of 15 ° was recognized.

Example 5 Thickness of heptacene thin film on polyethylene film substrate
Vacuum deposited at 1000Å. The substrate temperature is 25
In an atmosphere at a temperature of 1 ° C. and a pressure of 1 × 10 ⁻⁵ Torr, the deposition was performed by resistance heating of a tungsten boat as a deposition source. The structure of the obtained thin film was evaluated by an X-ray diffraction method.
An n) plane (n = 1 to 3) diffraction plane was observed. After doping by introducing iodine gas (pressure 2 mTorr) into the thin film in a vacuum vessel, the thin film was left for 1 week in an atmosphere of pressure 1 × 10 ⁻⁶ Torr to perform dedoping. When the structure of the obtained thin film was evaluated by X-ray diffraction method, the (OOn) plane (n
= 1 to 6).

Example 6 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. The structure of this thin film was evaluated by X-ray diffraction.
Surfaces (n = 1 to 3) were observed. After doping by introducing a NOx gas (pressure 10 Torr) into this thin film in a vacuum vessel, dedoping was performed by maintaining the film under an atmosphere of pressure 4 × 10 ⁻⁶ Torr for 2 hours.

The structure of the obtained thin film was measured by an X-ray diffraction method (CuKα ray), and the (OOn) plane having a lattice constant of 12 ° (n = 1 to 1)
The diffraction surface of 4) was observed.

Example 7 A coronene thin film was formed on a quartz glass substrate by an evaporation method. The deposition was performed under a pressure of 4 × 10 ⁻⁵ Torr in an atmosphere at a substrate temperature of 20 ° C., and the deposition source was a tungsten boat by resistance heating. When the structure of this coronene thin film was evaluated by an X-ray diffraction method, an (OOn) plane (n = 1 to 4) having a lattice constant of 9.3 ° was observed.

After doping this thin film in a bromine gas atmosphere (pressure 100 Torr), dedoping was performed while maintaining the atmosphere at a pressure of 1 × 10 ⁻⁶ Torr. When the structure of the obtained thin film was evaluated by X-ray diffraction method, the (OOn) plane (n =
1 to 6) were observed.

Example 8 A quaterylene thin film was formed on a quartz glass substrate by an evaporation method. The deposition was performed under a pressure of 1 × 10 ⁻⁵ Torr in an atmosphere of a substrate temperature of 20 ° C., and the evaporation source was performed by resistance heating of a tungsten boat. The structure of the quarterylene thin film was evaluated by an X-ray diffraction method.
3) was seen.

After doping this thin film in a bromine gas atmosphere (pressure 2 Torr), dedoping was performed while maintaining the atmosphere at a pressure of 1 × 10 ⁻⁶ Torr. When the structure of the obtained thin film was evaluated by an X-ray diffraction method, a (OOn) plane (n = 1) having a lattice constant of 20 ° was obtained.
To 6) were observed.

Example 9 A trifenodithiazine thin film was formed on a quartz glass substrate by a vacuum evaporation method. The production conditions were as follows: the substrate temperature was 60 ° C. in an atmosphere of a pressure of 1 × 10 ⁻⁴ Torr, and the evaporation source was resistance heating of a tungsten boat. When the structure of this trifenodithiazine thin film was evaluated by X-ray diffraction, an (OOn) plane (n = 1, 2) having a lattice constant of 9 ° was found.

After doping this thin film in an iodine gas atmosphere (pressure 2 mTorr), dedoping was performed at a temperature of 80 ° C. in an atmosphere of pressure 1 × 10 ⁻⁶ Torr. When the structure of the obtained thin film was evaluated by an X-ray diffraction method, the (OOn) plane having a lattice constant of 10 ° (n = 1)
To 4) were observed.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction pattern of a pentacene thin film before doping produced in Example 1. FIG. 2 shows an X-ray diffraction pattern of the pentacene thin film after doping and undoping prepared in Example 1.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01B5 / 14 H01B5 / 14Z (56) References JP-A-61-77322 (JP, A) JP-A-60-166298 ( JP, A) Materials Technology, Vol. 3 (3) p143-150 (1985) Thin Sid Films, Vol. 175, p89-93 (1989) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09K 3/00 C08L 57/00 G02F 1/35 G03C 1/73 H01B 1/12 H01B 5/14 CA ( STN) REGISTRY (STN)

Claims (1)

(57) [Claims] An organic thin film of a condensed polycyclic aromatic compound in which the number of condensed benzene rings is 3 or more and 13 or less is subjected to doping with an electron accepting molecule and subsequent undoping, and a highly blendable organic thin film.