JPH0719925B2 - Conductive thin film - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a conductive thin film, and more specifically to a conductive thin film containing a charge transfer complex layer in the resulting thin film and having excellent conductivity and practicality. .

[Technical Background of the Invention and its Problems] Conductive compounds have the potential to replace metals, and the concept of charge transfer has been adopted in the research of conductive molecular materials today, and this charge transfer is frequently used. Sex has received a lot of attention. In particular, a charge transfer complex in which two kinds of molecules are bonded by the charge transfer force between an electron donor (hereinafter referred to as a donor) and an electron acceptor (hereinafter referred to as an acceptor) has properties such as conductivity and paramagnetism. ing. Therefore, the solid charge transfer complex has a possibility of becoming a new material, and most of the organic substances which have recently attracted attention as organic metals and organic superconductors are these complexes. Furthermore, a charge transfer complex having conductivity and rich in reaction products has been produced in other inorganic compounds.

However, the charge transfer complexes obtained so far are limited to those made for the purpose of studying physical properties, and most of them are single crystals. Most of the single crystals are small needle-like crystals, and even large ones are only about several mm × several mm × 10 several mm. Moreover, it takes a long time (on the order of a month) to obtain this crystal, which is not practical. Further, conventionally, a donor and an acceptor were dissolved in a solvent, and a charge transfer complex layer was formed on a substrate by a diffusion method, a slow cooling method, or an electrochemical method. However, in any method, the impurities contained in the solvent are mixed. I couldn't avoid it.

On the other hand, a conductive thin film formed by directly depositing a charge transfer complex has been reported, but a thin film of a charge transfer complex having sufficient film quality and orientation has not been obtained yet.

[Object of the Invention] An object of the present invention is to solve the above problems and provide a conductive thin film comprising a charge transfer complex having excellent conductivity and practicality.

[Summary of the Invention] The conductive thin film of the present invention is characterized in that a donor and an acceptor are alternately laminated in a thin film form, and a charge transfer complex layer is formed at least at a contact interface between the thin layers.

That is, according to the present invention, the donor and the acceptor constituting the charge transfer complex are alternately laminated directly on the substrate in a thin film form, and as a result, the charge transfer complex layer is directly formed on the substrate and the complex itself is formed. It was possible for the first time to orient the film so that conductivity was generated parallel to the surface of the complex layer. Further, the present invention relates to a conductive thin film capable of significantly improving the conductivity of the whole thin film by forming a large number of thin film charge transfer complex layers.

Hereinafter, the present invention will be described in more detail.

The acceptor according to the present invention may be organic or inorganic. Among these, as the acceptor of organic matter, for example, 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2
-Methyl-7,7,8,8-tetracyanoquinodimethane (MTCN
Q), 2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane (DMTCNQ), 2,5-diethyl-7,7,8,8-tetracyanoquinodimethane (DETCNQ), 2 -Methoxy-7,7,8,8-
Tetracyanoquinodimethane (MOTCNQ), 2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane (DMOTCNQ),
2-Methoxy-5-ethoxy-7,7,8,8-tetracyanoquinodimethane (MOEOTCNQ), 2-methoxydihydrodioxabenzo-7,7,8,8-tetracyanoquinodimethane (MOD
OTCNQ), 2-chloro-7,7,8,8-tetracyanoquinodimethane (CTCNQ), 2-bromo-7,7,8,8-tetracyanoquinodimethane (BTCNQ), 2,5-dibromo -7,7,8,8-Tetracyanoquinodimethane (DBTCNQ), 2,5-diiodo-7,
7,8,8-Tetracyanoquinodimethane (DITCNQ), 2-chloro-5-methyl-7,7,8,8-tetracyanoquinodimethane (CMTCNQ), 2-bromo-5-methyl-7, 7,8,8-Tetracyanoquinodimethane (BMTCNQ), 2-iodo-5-
Methyl-7,7,8,8-tetracyanoquinodimethane (IMTCN
Q), 11,11,12,12-tetracyano-2,6-naphthoquinodimethane (TNAP), 1,1,2,3,4,4-hexacyanobutadiene (HCB), sodium 13,13,14, 14-tetracyanodiphenoquinodimethane (NaTCNQ), tetracyanoethylene (TCNE), o-benzoquinone, p-benzoquinone, 2,6
-Naphthoquinone, diphenoquinone, tetracyanodiquinone (TCNDQ), p-fluoranyl, tetrachlorodiphenoquinone.

On the other hand, as the acceptor of the inorganic substance, for example, iodine (I ₂ ), bromine (Br ₂ ), chlorine (Cl ₂ ), ferric chloride (FeCl 2
₃ ), aluminum chloride (AlCl ₃ ), nickel chloride (NiCl
₂ ), antimony chloride (SbCl ₅ ), chromium oxide (CrO ₃ ),
Molybdenum oxide (MoO ₃ ), antimony pentafluoride (Sb
F _5), include pentafluoride arsenic (AsF _5).

The donor according to the present invention may be either an organic substance or an inorganic substance. Of these, examples of organic donors include tetrathiafulvalene (TTF), dimethyltetrathiafulvalene (DMTTF), tetramethylthiafulvalene (TMTTF), hexamethylenetetrathiafulvalene (HMTTF), diselenadithiafulvalene (DSDTF). ),
Dimethyl diselena dithiafulvalene (DMDSDTF), hexamethylene diselena dithiafulvalene (HMDSDTF), tetraselena fullvalene (TSF), tetramethyl tetraselena fullvalene (TMTSF), hexamethylene tetraselena fullvalene (HMTSF), tetra Selenotetracene (TS
T), quinoline (Q), N-methylquinolinium iodide (NMQ), acridine (Ad), N-methylphenazinium methylsulfate (NMP), 1,2-di (N-ethyl-4-) Pyridinium) ethyl iodide ((DEP
_{^{E) 2+ ▲ I 2- 2 ▼}} ) and the like.

On the other hand, as the inorganic donor, for example, lithium, sodium, potassium, rubidium, cesium, silver, copper,
Examples include nitric oxide and ammonia.

The conductive thin film of the present invention has a structure in which the above-mentioned donor and acceptor are alternately laminated in a thin film, but the combination of the donor and the acceptor is not limited to the case where both are organic substances or both are inorganic substances; It may consist of a combination. The structure of the thin film of the present invention in which donors and acceptors are alternately laminated is a charge transfer complex in which all the donor layers and the acceptor layers have disappeared because all the donor molecules and the acceptor molecules are bound to form a complex. A layered structure composed of only a layer (hereinafter referred to as a DA layer); a layered structure having a DA layer at a contact interface between a donor layer and an acceptor layer; and a layered structure composed of one of a donor layer and an acceptor layer and a DA layer ( There is only a layer of either donor or acceptor molecules that could not participate in the complex formation because either the donor or acceptor molecules were in too small an amount). In any case, in the above laminated structure, at least the charge transfer complex layer is formed at the interface of the thin film composed of the donor layer and the acceptor layer that are laminated. By forming a complex, the charge transfer complex layer may be formed over the entire stacked thin films.

The conductive thin film of the present invention can have a desired film thickness and a desired number of layers depending on how to set the time and the number of layers of the donor molecule or the acceptor molecule.

The number of times of stacking, that is, the number of stacks may be such that only one donor layer and one acceptor layer are formed (the number of stacks is 1), but a larger number may be stacked. At least, the charge transfer complex layer formed at the interface between the stacked layers has an orientation that generates a current in parallel with this interface, and thus the number of interfaces increases as the number of layers increases, and the thin film of the present invention is formed. Conductivity is improved.

The conductive thin film composed of the charge transfer complex of the present invention is usually formed on a substrate, but this substrate may be any one conventionally used for thin film formation, Preferably glass, metal (Au, Ag, Al,
Cu, etc.) are exemplified.

The conductive thin film of the present invention is obtained by alternately stacking a donor molecule and an acceptor molecule on a substrate in vacuum, whereby a charge transfer complex layer is directly formed on the substrate. Further, the same operation is repeated to continue the lamination to form a DA layer having multiple layers. Various methods can be adopted as a method for forming the conductive thin film. Examples of the method include a vacuum vapor deposition method, a sputtering method, an ion plating method and a cluster ion beam vapor deposition method, and the most preferable method is the vacuum vapor deposition method. According to this method, a thin film can be formed without decomposing the organic donor molecule and the organic acceptor molecule.

When forming the conductive thin film of the present invention by the vacuum vapor deposition method, the donor and the acceptor are alternately deposited in a vacuum. In this case, the type of the vaporized substance is changed by opening and closing a shutter provided between the vaporizing boat and the substrate. And controlling the film thickness of the deposited film. The film thickness is monitored by using a quartz oscillator film thickness meter provided near the substrate in the vacuum chamber. By opening and closing the shutter, the thickness of one layer can be controlled to a minimum of about 100Å.

The degree of vacuum during vapor deposition is usually 10 ⁻⁵ to 10 ⁻⁸ Torr. Also,
The substrate temperature during vapor deposition is usually in the range of room temperature or lower to the liquid nitrogen temperature. In addition, when the thickness of the donor layer or the acceptor layer is set to 400 Å, the time required for forming this layer is about 1 minute.

When the conductive thin film of the present invention is formed by the sputter method, a fine crystal powder of a donor substance or an acceptor substance hardened by pressing or the like or a crystal itself is used as a target. Back pressure during spattering is 10 ^-5 to 10 ^-8
Torr, the substrate temperature is from room temperature to liquid nitrogen temperature. Argon is used as the carrier gas.
The stacking control is performed by opening and closing a shutter provided on the target according to the display on the thin film monitor.

When the conductive thin film of the present invention is formed by the ion plating method, the donor substance and the acceptor substance are gasified (by heating or the like) and introduced into a vacuum chamber. The stacking is controlled by opening and closing the valve of the introduced gas.

When forming the conductive thin film of the present invention by the cluster ion beam vapor deposition method, two crucibles for a donor and an acceptor are provided, and lamination is performed by a shutter installed on them.

As described above, in the present invention, the structure of the thin film is an alternating laminated body of the donor layer and the acceptor tank, so that the charge transfer complex itself formed by the lamination has conductivity in parallel with the film surface of the DA layer. It is possible to orient as it occurs. Furthermore, by making the thickness of each layer in the thin film as thin as possible, a large number of charge transfer complex layers can be formed in a conductive thin film of a certain size, resulting in an increase in the ratio of the conductive layer in the entire thin film. The conductivity of the thin film as a whole can be significantly improved.

[Effects of the Invention] According to the conductive thin film of the present invention, the obtained thin film layer is such that the complex itself is oriented so that the current flows in parallel to the film surface. As a result, the orientation of the complex layer is remarkably improved, and the complex layer has excellent conductivity.
Furthermore, since a large number of conductive layers can be formed by alternately stacking donor layers and acceptor layers, a thin film having higher conductivity than before can be obtained, and the desired conductivity can be obtained by adjusting the number of layers and the time for lamination. It is possible to obtain a conductive thin film having the same.

Further, while the crystal of the conventional charge transfer complex is small and it takes a long time to form it, the conductive thin film comprising the charge transfer complex of the present invention can be formed into a desired size in a short time. Therefore, it is extremely practical and its practical value is extremely large.

Further, since the conventional conductive thin film is formed by dissolving the already formed charge transfer complex in a solvent and then depositing the complex itself, impurities in the solvent are likely to intervene. Since a charge transfer complex layer can be formed by alternately stacking a donor and an acceptor on a substrate directly without using a solvent, there is no risk of impurities intervening, and a high quality conductive thin film can be obtained.

Therefore, the conductive thin film comprising the charge transfer complex of the present invention can be widely used as a conductor for connection and the like, and its industrial value is great.

Hereinafter, the present invention will be described in more detail with reference to examples.

[Examples of the Invention] Example 1 Tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) were reprecipitated and purified using special grade acetonitrile. The purified TTF and TCNQ were filled in a tungsten boat installed in a vacuum chamber at 50 mg each. Cut the slide glass to a length of 15 mm, degrease and wash it with neutral detergent, acetone and trichlene, and gold comb type electrode (width 0.5 mm, length 10 mm, interval 2 mm, thickness 1000 Å)
Was vacuum-deposited on this slide glass. The above-mentioned slide glass with electrodes was held by a holder at a position 15 cm above the boat in the vacuum chamber. After evacuating until the degree of vacuum reached 10 ⁻⁶ Torr, the TCNQ boat was energized, the boat temperature was stabilized at 200 ° C., and then the shutter was opened to deposit TCNQ on the glass substrate. The film thickness was monitored by a crystal vibrating type film thickness meter which was previously calibrated by a stylus type film thickness meter. After the film thickness of TCNQ reached a predetermined value, the shutter was closed and the energization was stopped. Then TTF
After the boat was energized to stabilize the boat temperature at 120 ° C., the shutter was opened, TTF was vapor-deposited on TCNQ to reach a predetermined film thickness, and then the shutter was closed to stop energization. TCNQ and TT
Each film thickness of F was set to 400 Å, and the above vapor deposition operation was repeated three times.

During the above vapor deposition operation, the substrate temperature was kept at 100 K by flowing liquid nitrogen through a copper pipe welded to the substrate holder. The time required for the vapor deposition operation was about 20 minutes.

It was confirmed that TTF and TCNQ formed a charge transfer complex by measuring infrared and visible-ultraviolet absorption spectra of the formed 2500 Å-thick film.

Further, when X-ray diffraction of the above film was measured, no peak showing crystallinity appeared, and it was found that this thin film was amorphous.

Next, a constant current (10 μA) was applied in a cryostat using a gold electrode deposited in advance, and the conductivity (σ) was measured from room temperature to 80 K by the two-terminal method. The conductivity at room temperature was 5 Scm ^-1 , and at 80K it was 0.5 Scm ^-1 , showing semiconductor-like temperature dependence.

Example 2 Vacuum deposition was performed in the same manner as in Example 1 except that the substrate temperature was kept at room temperature. When the X-ray diffraction of the obtained film was measured, a diffraction peak corresponding to the (002) plane of the TTF / TCNQ complex single crystal was obtained, and the orientation of the complex in the interface direction was recognized. The conductivity σ is a 10Scm ^-1 at room temperature, a 1Scm ^-1 at 80K, improvement in conductivity due to crystallinity increase was observed.

Example 3 After performing vacuum deposition in the same manner as in Example 1 except that the substrate temperature was kept at room temperature using the electron donor (D) and the electron acceptor (A) shown in the table below, the conductivity σ at room temperature was obtained. Was measured.
The measurement results are shown in the table below. However, the temperature of the substrate was kept at room temperature.

Example 4 1 g each of TTF and TCNQ microcrystalline powders, each having a diameter of 50 mm
Spread it evenly on a 2 mm thick stainless steel (SUS 304) disc.
These were pressed with a vacuum press machine at a pressure of 10 kg / cm ² to prepare a sputtering target.

The above two targets were set in a sputtering apparatus, and a shutter for stacking control was provided at a position 20 mm above these targets.

As the substrate, the same glass plate with a comb-shaped electrode as in Example 1 was used. The substrate holder was cooled by circulating water to keep the substrate temperature at 18 ± 1 ° C.

After evacuation of the sputter vacuum chamber to 10 ^-6 Torr, a carrier gas, argon, was introduced into the vacuum chamber at a partial pressure of 10 ^-3 Torr. Then after opening the TCNQ target shutter, 1
Plasma was generated in the sputtering vacuum chamber with a high frequency of 3.56 MHz (output 10 W) to form a thin film of TCNQ on the substrate. The thickness of the formed thin film is ~ 50 in 1 minute of plasma discharge.
It was 0Å.

Next, close the TCNQ shutter, open the TTF shutter, and
A TTF thin film was formed on the TCNQ thin film under the same conditions as CNQ. The TTF layer was formed to a thickness of ~ 500Å by sputtering for 1.5 minutes. Then again TCNQ layer with film thickness 500Å, film thickness 500Å
And a TCNQ layer having a film thickness of 500Å were sequentially laminated to form a laminated film having a total thickness of 2500Å.

When the conductivity was measured using a gold electrode, σ = 8Scm ^-1
The value of was obtained.

Example 5 Graphite sputtering target (diameter 100 mm,
Using a carrier gas of argon, a graphite thin film having a thickness of 1000 Å was formed on a glass substrate by RF sputtering using a thickness of 5 mm). The glass substrate has a thickness of 2000Å
The gold comb-shaped electrode of 1 was formed by vapor deposition. The sputter was performed under the conditions of an argon gas pressure of 50 mmTorr, a sputtering power of 10 W and a sputtering time of 2 minutes. At this time, the substrate temperature was kept at 20 ° C.

Iodine gas was introduced into the sputtering apparatus using the gas introduction terminal. An iodine film having a thickness of 1000 Å was formed on the graphite sputtered film at a pressure of iodine of 100 mm Torr and a time of 10 minutes.

Again, a 1000 Å graphite film was formed on the iodine film by the RF sputtering method to form a thin film having a three-layer sandwich structure of graphite / iodine / graphite.

The conductivity (σ) of the above thin film was measured by the four-terminal method and found to be σ1.2 × 10 ³ Scm ⁻¹ (25 ° C.).

Continuation of the front page (56) References JP-A-54-27787 (JP, A) JP-A-57-83054 (JP, A) JP-A-54-18853 (JP, A)

Claims (1)

[Claims] 1. An electron donor and an electron acceptor are alternately laminated in a thin film form, and a charge transfer complex layer is formed at least at a contact interface between the thin films, and conductivity is parallel to the surface of the charge transfer complex layer. A conductive thin film which is oriented so as to occur.