JP3393538B2 - Organic compound thin film and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic compound thin film and a method for manufacturing the same. More specifically, the present invention relates to an organic compound thin film mainly used in the field of optoelectronic devices such as a light emitting device, a light modulation device, an optical logic device, and an optical recording medium, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
A dry method and a wet method are used as a method for producing a highly oriented thin film or a single crystal organic compound thin film. Among such manufacturing methods, a vacuum method and a molecular beam epitaxial (MBE) method can be given as a dry method, and a solvent evaporation method, a melt method, a Langmuir-Blodgett method (LB method) can be given as a wet method. Is mentioned.

Among the wet methods, the solvent evaporation method or the melt method is generally used as a method for producing a bulk single crystal. These methods are methods for producing a single crystal thin film by sucking a solution or a melt into a gap between two flat glass plates by utilizing a capillary phenomenon and crystallizing the solution or the melt. However, since the above method is a wet method, there are many opportunities to mix impurities and it is difficult to precisely control the film thickness, so it is difficult to manufacture a thin film having a film thickness of nm order.

Next, in the LB method, the monomolecular film developed at the air-water interface is scooped and laminated on the substrate to obtain a desired number of layers (film thickness).
Is a method of obtaining a thin film of. The LB method is an excellent method for controlling the film thickness, but although there is a periodic structure in the direction perpendicular to the film surface, in most cases it is disordered in the film surface. The vacuum deposition method and the MBE method, which are dry methods, have few opportunities to mix impurities and have excellent controllability of the film thickness.
However, there are very limited combinations of materials and substrates that can control orientation and grow single crystals.

On the {001} plane of an alkali halide substrate such as KCl, a thin film can be formed by epitaxially growing many organic compounds represented by phthalocyanine compounds by using the vacuum deposition method and the MBE method. It has long been known that it can be done. The clean {001} surface of the alkali halide substrate has a very strong cation
Group atoms and extremely strongly anionic Group VII atoms are regularly arranged. The thin film can be grown on this substrate is
It is considered that the electrostatic force between the regularly-arranged substrate surface atoms and the molecules supplied on the substrate contributes to film formation during epitaxial growth.

However, the arrangement of atoms on the substrate surface is repeated four times (9
Since it is (0 °) symmetry, it is generally oriented in two planes that are perpendicular to each other and equivalent to each other, and a single crystal or biaxial orientation film (both in the direction perpendicular to the substrate surface and in the direction parallel to the substrate surface) It is difficult to put it into practical use because it is not a uniform polycrystalline film. As described above, in the conventional method for manufacturing an organic compound thin film, a single crystal having a quality necessary for practical use, 2
It is very difficult to manufacture an axially oriented crystal thin film. The present invention has been made in view of such circumstances,
It is an object to provide a method for producing a biaxially oriented or single crystal thin film.

[0007]

Thus, according to the present invention, an ionic crystal substrate having a plane orientation of {110} is used as a substrate, and a single crystal or biaxially oriented organic substrate is formed on the ionic crystal substrate. There is provided an organic compound thin film characterized in that a compound thin film is formed. Furthermore, according to the present invention, a single crystal or biaxially oriented thin film is formed by growing an organic compound on an ionic crystal substrate having a {110} orientation used as a substrate. A manufacturing method is provided.

The ionic crystal substrate used in the present invention includes fluorite type crystal structure, NaCl type crystal structure, and CsCl.
Either a crystal structure of inverted type or a crystal structure of inverted fluorite type can be used. As the compound having a fluorite crystal structure, a compound composed of a combination of elements of Group II and Group VII can be used, and as such a compound, CaF ₂ (lattice constant: 0.546 nm) and SrF ₂ (lattice constant: 0.580 nm
), BaF ₂ (lattice constant: 0.620 nm) and the like. In addition to that, CeO ₂ having a fluorite type crystal structure
(Lattice constant: 0.541nm), UO ₂ (Lattice constant: 0.547nm)
) And the like can be used as a compound having a NaCl type crystal structure, KCl (lattice constant: 0.629 nm),
NaCl (lattice constant: 0.564 nm), KBr (lattice constant:
0.660 nm) and the like.

Examples of compounds having a CsCl type crystal structure include CsCl (lattice constant: 0.412 nm) and TlCl (lattice constant: 0.384 nm). As a compound having an inverted fluorite crystal structure, Li ₂ O (lattice constant: 0.461 nm
), Na ₂ O (lattice constant: 0.556 nm), Li ₂ S (lattice constant: 0.571 nm), Na ₂ S (lattice constant: 0.654 nm)
), K ₂ S (lattice constant: 0.741 nm) and the like.

The above-mentioned ionic crystal substrate can form a plane having a {110} orientation by a known method. For example,
There are two types of forming methods. First, in the first method, each bulk single crystal is
It is possible to obtain a clean {110} plane by cutting out at 0 plane, polishing, removing the damaged layer by chemical etching or ion etching, and performing heat treatment in vacuum. In the second method, a substrate having a good lattice matching (for example,
For the {110} plane of CaF ₂ , {11} of silicon
It is possible to form a film by vapor phase epitaxial growth such as a vacuum vapor deposition method or a molecular beam epitaxy method.

Further, these compounds can be used as a mixed crystal. The mixed crystal can be formed by vapor phase epitaxial growth. As the mixed crystal compound, for example, (Ca _{X
· Sr 1-X) F 2} , (Sr X · Ba 1-X) F 2, (Na
_X · K _1-X ) Cl (0 ≦ x ≦ 1) can be used. In addition, when a compound having a fluorite type crystal structure is used for these mixed crystal compounds, the compound is 0.546
Since it has a lattice constant of 0.620 nm, it can be adjusted to the size of the lattice constant determined from the molecular arrangement of the organic compound to be grown.

The plane orientation of the crystal selected and formed as described above preferably has an orientation of plane index as simple as possible from the viewpoint of application. For example, the ion array on the CaF ₂ (110) plane has a two-fold (180 °) rotational symmetry as shown in FIG. 1, and the orientations are <110> and <-11 which are orthogonal to each other.
The ratio of the period of the 0> direction ion array is about 1: for negative ions.
It is 0.7, and it is about 1: 1.4 for positive ions, neither of which is an integer multiple. A biaxial orientation of an organic compound or a single crystal thin film can be grown on such a crystal plane by matching the lattice constant.

The above-mentioned ionic crystal substrate can be used as it is, but it can also be formed on a substrate such as a semiconductor. As the substrate material, any material can be used, whether inorganic or organic, crystalline or amorphous, as long as an ionic crystal substrate can be grown on it. As such a substrate, for example, various kinds of glass, quartz or amorphous SiO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , T
Oxides such as iO ₂ and MgO, amorphous Si, Ga
Semiconductor materials such as As and Al _1-X Ga _X As, polymer compounds such as polycarbonate, polystyrene and polymethylmethacrylate (PMMA), Al, Ti, Cu, A
Examples thereof include metals such as g, Au, W, and Mo, and organic semiconductors such as phthalocyanine porphyrin.

Next, the organic compound thin film of the present invention can be used as a nonlinear optical material, photoelectric conversion, optical recording material, light emitting material, conductive material and the like. For example, as an organic compound thin film that can be used for a nonlinear optical material, 4- (N, N-dimethylamino) -3-acetamidonitrobenzene (DA
N), merocyanine-pTS complex (MC), 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA), 2-methyl-4-nitroaniline (MNA), 3-methyl-4-methoxy-4. ′ -Nitrostilbene (MNONS), 4-nitro-4′-methylbenzylideneaniline (NMBA), 3,5-dimethyl-1- (4-nitrophenyl) -pyrazole (DMN)
P), N- (4′-nitrophenyl)-(L) -prolinol (NPP), 2- (N-prolinol) -5-nitropyridine (PNP), 2- (α-methylbenzylamino)- 5-nitropyridine (MBANP), 2-cyclooctylamino-5-nitropyridine (COAN)
P), 3-methyl-4-nitropyridine-1-oxide (POM), 4- (N, N-dimethylamino) benzylidene-4-nitroaniline (DBNA) and 1,6-di (N-carbazolyl)-. 2,4-dihexadiene (DC
HD) and the like.

As the organic compound thin film that can be used for photoelectric conversion and optical recording materials, metal-free phthalocyanines, various metals (Cu, Pb, Al, Sn, VO, TiO, etc.) phthalocyanines, various chlorinated metals (Cu). , Pb, Al,
Sn, VO, TiO, etc.) phthalocyanines, various fluorinated metals (Cu, Pb, Al, Sn, VO, TiO, etc.) phthalocyanines, naphthalocyanines and the like.

Next, as an organic compound thin film that can be used as a light emitting material, quinolinol type metal complexes such as perylene, phthaloperylene, aluminum quinoline and aluminum quinolinium complex, distyrylbenzenes, anthracene derivatives, anthracene derivatives, triazole derivatives and Examples include cyclopentadiene. Furthermore, examples of the organic compound thin film that can be used for the conductive material include charge transfer complexes represented by TTF-TCNQ complexes and the like.

As the combination of the substrate material and the organic compound thin film, DAN and KCl, DAN and BaF ₂ , MNA and KCl, DBNA and KCl, DCHD and KCl, DAN are available.
And (Sr.Ba) F _{2 and the} like. As a method for forming the organic compound thin film, a known method such as a vacuum vapor deposition method, recrystallization from a melt, or precipitation from a solution can be used.

For example, when the vapor deposition method is used, a thin film can be formed by heating and gasifying an organic compound material at a system pressure of 10 ^-2 Pa or less.
When recrystallizing from a melt, the substrate is immersed in a melt of an organic compound precisely controlled in the vicinity of the melting point and then slowly cooled,
A thin film of an organic compound is deposited on the substrate. At this time, the growth rate is controlled by the temperature decrease rate, and the film thickness is controlled by the growth time based on the previously measured relationship between the growth rate and the temperature decrease rate.

Further, in the case of precipitating from a solution, the substrate is immersed in a saturated solution of an organic compound whose temperature is precisely controlled,
The solution is gradually cooled to deposit a thin film of an organic compound on the substrate. At this time, the growth rate is controlled by the temperature decrease rate, and the film thickness is controlled by the growth time based on the previously measured relationship between the growth rate and the temperature decrease rate.

As a forming apparatus which can be used for forming the organic compound thin film of the present invention, a known apparatus can be used. For example, when a film is formed by a vacuum evaporation method, the apparatus shown in FIG. 2 is used. it can.

[0021]

As described above, in the method using the {001} plane of the I-VII group compound (alkali halide) substrate,
The 4-fold symmetry in the arrangement of cations and anions is responsible for the orientation in two directions orthogonal to each other. Therefore, in the present invention, since the compound single crystal having a strong ionicity capable of utilizing the strong electrostatic attraction of the cation and the anion and the symmetry of the atomic arrangement on the substrate surface is low, the two directions in different planes are different. Substrates having mutually different arrangement periods of atoms (ions) are used.

When an organic compound thin film is formed on such a substrate, biaxially oriented in one specific direction with respect to the substrate crystal by a combination of the crystal structure of the vapor deposition material and the period of the ion arrangement of the substrate. It is possible to form an alignment film or a single crystal film.

[0023]

EXAMPLES Examples of the present invention will be shown below. The present invention is not limited to the following materials, processes and conditions thereof.

Example 1 BaF₂The substrate 14 consisting of the (110) plane of
After washing with ethanol, ethanol, and pure water respectively,
It is moved to the analysis chamber 3 by the substrate transfer system 18 of the vacuum evaporation system shown.
After letting it, 10^-6It should be heated at 800 ° C in a vacuum of Pa level.
The surface cleaning treatment was performed by and. Analyze this board 14
Moved to chamber 3 and used low-energy electron diffraction equipment (LEED) 11
, Confirm that a clean surface is obtained, and grow.
Placed in chamber 2. The DAN of the raw material is the game above the K cell.
10 with the valve 9 closed. ^-Four50 ℃ under the vacuum of the table,
Heat treatment was performed for 2 hours or more. Then the gate valve 9
Open and open the K cell 12 with the bellows type linear movement mechanism 17.
It was introduced into the long chamber 2 and the distance between the substrate and the K cell 12 was set to 150 mm.
After that, the temperature of K cell 12 is heated to 65 ° C to sublimate the raw material.
The film thickness monitor 13 controls the film thickness to about 0.5 μm,
A thin film was formed on the substrate.

As a result of measuring this thin film with a transmission electron microscope, a scanning electron microscope and an X-ray diffractometer, as shown in FIG. 5, the <001> direction of DAN crystallites was aligned in the direction perpendicular to the substrate surface, and Field is observed, but crystallite b
It was found that the axial direction (axis parallel to the substrate) was a thin film that was oriented and grown in one direction of the substrate and was extremely close to a single crystal.

Example 2 The (Sr _0.1 .Ba _0.9 ) F ₂ substrate 14 was subjected to surface cleaning treatment in the same manner as in Example 1 on the (110) surface. Next, DAN having a film thickness of about 0.5 μm was formed on the substrate 14 in the same manner as in Example 1. As a result of measuring this thin film with a transmission electron microscope, a scanning electron microscope and an X-ray diffractometer, the <001> direction of the DAN crystallites was aligned in the direction perpendicular to the substrate surface as shown in FIG. 5, and grain boundaries were observed. However, it has been found that the b-axis direction of the crystallite is a thin film which is oriented and grown in one direction of the substrate and is extremely close to a single crystal.

Example 3 The (110) plane of the KCl substrate 14 was surface-cleaned as described in Example 1. However, the condition for forming a clean surface is that the heating temperature is 600 ° C and the heating time is 3
It was time. Next, a DAN having a film thickness of about 0.5 μm was used in Example 1.
It was formed on the substrate 14 in the same manner as. This thin film was measured by a transmission electron microscope, a scanning electron microscope and an X-ray diffractometer, and as a result, as shown in FIG.
Although the <001> directions of the AN crystallites were aligned and grain boundaries were observed, it was found that the thin film was a crystallite whose b-axis direction was oriented and grown in one direction of the substrate and was extremely close to a single crystal.

Comparative Example 1 KCl single crystal substrate 14 was cleaved along the (001) plane and immediately introduced into the apparatus. 10 ^-6 Pa to form a clean surface
It was heated at 800 ° C. for 2 hours in the vacuum of the table, and the clean surface was confirmed by the LEED pattern. Next, DAN with a film thickness of about 0.5 μm
Was formed on the substrate 14 in the same manner as in Example 1. As a result of measuring this thin film with a transmission electron microscope, a scanning electron microscope and an X-ray diffractometer, the <001> direction of the DAN crystallites was aligned in the direction perpendicular to the substrate surface as shown in FIG. Observed, a thin film was obtained in which the b-axis direction of the crystallite was oriented and grown in two directions of (110) and <−110> of the substrate which were orthogonal to each other.

Comparative Example 2 The (001) plane of the BaF ₂ single crystal substrate 14 was treated as shown in Example 1 to obtain a clean surface. Next, the film thickness is about 0.5μ
m of DAN was formed on the substrate 14 in the same manner as in Example 1. As a result of measuring this thin film with a transmission electron microscope, a scanning electron microscope and an X-ray diffractometer, the <001> direction of the DAN crystallites is aligned in the direction perpendicular to the substrate surface, but grain boundaries are observed and Then, it was not oriented in one direction.

[0030]

According to the thin film manufacturing method of the present invention, it has become possible to form a biaxially oriented or single crystal organic compound thin film, which has been difficult to obtain conventionally.

[Brief description of drawings]

FIG. 1 is a view showing an arrangement of atoms (ions) on the outermost surface of a (110) plane of CaF ₂ .

FIG. 2 is a top view and a cross-sectional view of an ultra-high vacuum vapor deposition apparatus used in an example of the present invention.

FIG. 3 is a mixed crystal ratio of (Ca _X · Sr _1-X ) F ₂ x (0 ≦ x
It is a figure which shows the relationship of <= 1) and the lattice constant a.

FIG. 4 is a mixed crystal ratio x (0 ≦ x of (Sr _X · Ba _{1 -X} ) F ₂
It is a figure which shows the relationship of <= 1) and the lattice constant a.

FIG. 5 is a schematic view showing the orientation direction of the crystallite of the present invention.

FIG. 6 is a schematic view showing the orientation direction of crystallites in a conventional method.

[Explanation of symbols]

1 exchange room 2 growth room 3 analysis room 4, 5 turbo molecular pump 6 ion pump 7,8,9 gate valve 10 Metal valve 11 Low-speed electron beam diffractometer (LEED) 12 K cell 13 Thickness monitor 14 board 15 Liquid nitrogen shroud 16 K cell part exhaust pipe 17 Bellows type linear movement mechanism 18 Substrate transfer system

Continuation of front page (56) Reference JP-A-5-188417 (JP, A) JP-A-2-197822 (JP, A) JP-A-3-197394 (JP, A) JP-A-3-197395 (JP , A) JP 3-197399 (JP, A) JP 4-97994 (JP, A) JP 4-104996 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) C30B 1/00-35/00 G02F 1/35 CA (STN) WPI / L (QUESTEL)

Claims (4)

(57) [Claims] 1. An organic compound thin film comprising a single crystal or biaxially oriented organic compound thin film formed on an ionic crystal substrate having a plane orientation of {110} as a substrate. 2. The ionic crystal substrate is a fluorite crystal structure,
The organic compound thin film according to claim 1, comprising an NaCl type crystal structure, a CsCl type crystal structure, or an inverted fluorite type crystal structure. 3. A method for producing an organic compound thin film, which comprises growing a single crystal or biaxially oriented thin film on an ionic crystal substrate having a {110} orientation used as a substrate. 4. A growth method of an organic compound thin film is a vapor deposition method,
The method for producing an organic compound thin film according to claim 3, which comprises a precipitation method from a melt or a recrystallization method from a solution.