JPH05249514A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To easily obtain a film having high nonlinearity by using amorphous carbon as the matrix of superfine particles of a metal, thereby enabling the incorporation of the superfine particles to be conducted at a high density into the thin film. CONSTITUTION:The film dispersed with the superfine particles is formed by dispersing the superfine particles of the fine crystalline metal into the matrix of the amorphous carbon, by which the value its X<3> (nonlinear sensitivity) is improved. Namely, the content of the superfine particles of the fine crystalline metal is increased by adopting the amorphous carbon as the matrix to be dispersed with these superfine particles. The metallic material constituting the superfine particles is preferably Ag and Au and more particularly the Au. Further, the grain sizes of the superfine particles are preferably in the range where the quantum size effect of electrons and excitons appear; for example, the grain sizes are confined to <=100Angstrom . The size control of the superfine particle are executable by, for example, heating a substrate at the time of the film formation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nonlinear susceptibility.

[Equation 1] The present invention relates to a nonlinear optical material having an improved value of. The nonlinear optical material of the present invention is used as a thin film in the fields of optical bistable elements, optical gate optical switches, wavelength conversion elements, and the like.

[0002]

2. Description of the Related Art Non-linear optical thin films have been conventionally used as transparent insulators (for example, amorphous Al ₂ O ₃ and amorphous SiO _2).
2 ) In which semiconductor ultrafine particles of 100 Å or less are dispersed is used. However, this non-linear optical thin film cannot provide sufficiently large X ³ . Although X ³ representing the nonlinearity of magnitude particle number proportional to the number density of fine particles it is preferably larger, when manufacturing by heating the substrate in the conventional RF sputtering method, etc., the particle density is the number atm% Was 15 atm% at the maximum. If a material having a larger X ³ can be obtained, the switching operation can be performed with weaker light, and the effect is great. The present invention improves this point.

[0003]

An object of the present invention is to provide a non-linear optical material having an improved X ³ value, characterized in that ultrafine particles of metal microcrystals contain amorphous carbon in a matrix.

[0004]

The present invention relates to a non-linear optical material exhibiting a so-called quantum size effect in which electrons and excitons exhibit zero-dimensional behavior due to a three-dimensional confinement effect.

Here, the non-linear optical effect is a phenomenon in which, when a substance is irradiated with light, the optical characteristics such as the absorption coefficient and the refractive index of the substance change according to the intensity of the light. Can be controlled, and an all-optical logic element that uses only light for input and output can be realized.

The quantum size effect means that the electrons and holes of semiconductor particles embedded in transparent glass in the visible light region are three-dimensionally confined by the deep potential created by the glass. If you think
In a small box, the wave pattern is limited to a specific one, so the electronic states become discrete and the vibration intensity and nonlinear susceptibility increase.

The quantum size effect of this fine particle-dispersed glass has recently been discovered (7 to 8 years ago) and has come to the forefront, and 100 Å in an insulating material such as glass.
The following semiconductor fine particles are dispersed.

These technical matters are described in, for example, [JAP
ANESE JOURNAL OFAPPLIED P
HYSICS, Volume 28, No. 10, 1928-193.
3] and "Optics, Vol. 19, No. 1 (1990, 1
Mon) 10-16 ”.

The ultrafine particle dispersion film of the present invention is obtained by dispersing ultrafine particles of microcrystalline metal in a matrix of amorphous carbon to improve the value of X ³ . That is, the present invention is characterized in that the content of the particles is increased by adopting amorphous carbon as the matrix in which the microcrystalline ultrafine metal particles are dispersed. In the present invention, the metal material constituting the ultrafine particles is not particularly limited as long as it is a material that can be made into ultrafine particles, but Ag, Au and particularly Au are preferable. further,
The particle size of the ultrafine particles can be adopted without particular limitation as long as it is within the range where the quantum size effect of electrons or excitons appears, but it is, for example, 100 Å or less. The size control of the ultrafine particles can be performed, for example, by heating the substrate during film formation. According to the present invention, the particle density can be 20 atm% or more.

Next, the hard carbon film used in the present invention will be described. An organic compound gas, particularly a hydrocarbon gas is used to form the hard carbon film. The phase state of these raw materials does not necessarily have to be a gas phase at room temperature and normal pressure, and can be in a liquid phase or a solid phase as long as it can be vaporized through melting, evaporation, sublimation, etc. by heating or decompression. Is. Examples of the hydrocarbon gas as the raw material gas include paraffin hydrocarbons such as CH ₄ , C ₂ H ₆ , C ₃ H ₈ and C ₄ H ₁₀ , olefin hydrocarbons such as C ₂ H ₄ and acetylene hydrocarbons. It is possible to use a gas containing at least all the hydrocarbons such as a diolefin hydrocarbon, and an aromatic hydrocarbon. In addition to hydrocarbons, compounds containing at least a carbon element such as alcohols, ketones, ethers, esters, CO and CO ₂ can be used.

As a method of forming a hard carbon film from a source gas in the present invention, a film formation active species is formed through a plasma state generated by a plasma method using direct current, low frequency, high frequency, or microwave. Although the method described above is preferable, the method of utilizing the magnetic field effect is more preferable because the deposition is performed under a low pressure for the purpose of increasing the area, improving the uniformity, and forming a film at a low temperature. Active species can also be formed by thermal decomposition at high temperature. Besides, it may be formed through an ionic state generated by an ionization vapor deposition method, an ion beam vapor deposition method, or the like, or may be formed from neutral particles generated by a vacuum vapor deposition method, a sputtering method, or the like. However, it may be formed by a combination thereof. An example of the deposition conditions of the hard carbon film thus produced is as follows in the case of the plasma CVD method. RF output: 0.1 to 50 W / cm ² Pressure: 10 ^{−3 to} 10 Torr Deposition temperature: Room temperature to 950 ° C.

This plasma state causes the source gas to decompose into radicals and ions and react with each other, so that amorphous and microcrystalline (crystal size) consisting of carbon atoms C and hydrogen atoms H are formed on the substrate. Is several 10Å to several μ
A hard carbon film containing at least one of m) is deposited. Table 1 shows various characteristics of the hard carbon film.

[Table 1] Note) Measurement method; Specific resistance (ρ): Determined from the IV characteristics of a coplanar cell. Optical bandgap (Egopt): The absorption coefficient (α) is obtained from the spectral characteristics, and is determined from the relationship of Equation 2.

[Equation 2] Amount of hydrogen in film [C (H)]: 29 from infrared absorption spectrum
The peak around 00 / cm is integrated and multiplied by the absorption cross section A to obtain the value. That is, [C (H)] = A · ∫α (ν) / ν · dν SP ³ / SP ² ratio: infrared absorption spectrum of SP ³ , SP ²
It is decomposed into the Gaussian functions respectively assigned to, and calculated from the area ratio. Vickers hardness (H): By micro Vickers meter. Refractive index (n): By ellipsometer. Defect density: According to ESR. The hard carbon film thus formed has Raman spectroscopy and IR.
As a result of analysis by the absorption method, it has been clarified that carbon atoms have mixed interatomic bonds forming SP ³ hybrid orbitals and SP ² hybrid orbitals. The ratio of SP ³ bond to SP ² bond can be roughly estimated by separating peaks in the IR spectrum. IR spectrum shows 2800-3150
Although the spectrum of many modes overlaps with cm ^-1 and is measured, the attribution of the peak corresponding to each wave number has been clarified, and the peak separation is performed by the Gaussian distribution, and the respective peak areas are calculated. If the ratio is calculated, SP ³ /
You can know SP ² . Further, it is known by X-ray and electron diffraction analysis that it is in an amorphous state (a-C: H) and / or in an amorphous state containing fine crystal grains of about 50Å to several μm. Generally, in the case of the plasma CVD method suitable for mass production, the smaller the RF output, the more the specific resistance value and hardness of the film increase, and the lower the pressure, the longer the life of active species. The area can be made uniform, and the specific resistance and hardness tend to increase.
Further, since the plasma density decreases at a low pressure, the method utilizing the magnetic field confinement effect is particularly effective for increasing the specific resistance. Furthermore, this method has a feature that a good quality hard carbon film can be similarly formed even under a relatively low temperature condition of room temperature to about 150 ° C.

Further, the hard carbon film is composed of a group III element, a group IV element, a group V element, an alkali metal element, an alkaline earth metal element and a nitrogen atom of the periodic table in addition to carbon atoms and hydrogen atoms. , An oxygen element, a chalcogen element, or a halogen atom may be included as a constituent element. Those in which a Group III element of the periodic table, a Group V element, an alkali metal element, an alkaline earth metal element, a nitrogen atom or an oxygen atom is introduced as one of the constituent elements is a non-doped hard carbon film. It is possible to make the thickness about 2 to 3 times larger than that of the above, and by this, it is possible to prevent the occurrence of pinholes at the time of manufacturing the element and to dramatically improve the mechanical strength of the element. Further, in the case of a nitrogen atom or an oxygen atom, the same effect as that in the case of the group IV element of the periodic table as described below can be obtained.
Similarly, the introduction of a Group IV element, a chalcogen element, or a halogen element of the periodic table dramatically improves the stability of the hard carbon film and also improves the hardness of the film. These effects are obtained because the active double bond existing in the hard carbon film is reduced in the case of the group IV element and the chalcogen element, and in the case of the halogen element, 1) to hydrogen. The extraction reaction promotes decomposition of the source gas to reduce dangling bonds in the film, and 2) during the film formation process, the halogen element X extracts hydrogen in the C—H bond and replaces it with the C—X bond. And enters the film to increase the binding energy (the binding energy between C-H and C-X is C-
This is because the distance between X is larger). In order to use these elements as the constituent elements of the film, in addition to hydrocarbon gas and hydrogen as the source gas, the periodic table II is used as a dopant in the film.
In order to contain a Group I element, a Group IV element, a Group V element, an alkali metal element, an alkaline earth metal element, a nitrogen atom, an oxygen atom, a chalcogen element or a halogen element,
Compounds (or molecules) containing these elements or atoms (hereinafter,
These are sometimes referred to as "other compounds"). Examples of the compound containing a Group III element of the periodic table include B (OC ₂ H ₅ ) ₃ , B ₂ H ₆ , BCl ₃ , and B.
_{Br 3, BF 3, Al (} O-i-C 3 H 7) 3, (CH 3) 3
_{Al, (C 2 H 5)} 3 Al, (i-C 4 H 9) 3 Al, AlC
_{l 3, Ga (O-i} -C 3 H 7) 3, (CH 3) 3 Ga, (C
_{2 H 5) 3 Ga, GaCl} 3, GaBr 3, (O-i-C 3 H
₇ ) ₃ In, (C ₂ H ₅ ) ₃ In and the like. Examples of the compound containing a Group IV element of the periodic table include Si ₂ H ₆ and (C
₂ H ₅ ) ₃ SiH, SiF ₄ , SiH ₂ Cl ₂ , SiCl ₄ ,
Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) ₄ , Si (OC ₃ H
₇ ) ₄ , GeCl ₄ , GeH ₄ , Ge (OC ₂ H ₅ ) ₄ , Ge
_{(C 2 H 5) 4,} (CH 3) 4 Sn, (C 2 H 5) 4 Sn, Sn
Cl ₄ etc. Examples of the compound containing a Group V element of the periodic table include PH ₃ , PF ₃ , PF ₅ , PCl ₂ F ₃ and PC.
l ₃ , PCl ₂ F, PBr ₃ , PO (OCH ₃ ) ₃ , P (C _{2
H 5) 3, POCl 3,} AsH 3, AsCl 3, AsBr 3,
_{AsF 3, AsF 5, AsCl 3} , SbH 3, SbF 3, S
bCl ₃ , Sb (OC ₂ H ₅ ) _{3 and the} like. As the compound containing an alkali metal atom, for example _{LiO-i-C 3 H 7} ,
_{NaO-i-C 3 H 7} , there is KO-i-C ₃ H ₇ or the like. Examples of the compound containing an alkaline earth metal atom include Ca
(OC ₂ H ₅ ) ₃ , Mg (OC ₂ H ₅ ) ₂ , (C ₂ H ₅ ) ₂ Mg
Etc. Examples of the compound containing a nitrogen atom include an inorganic compound such as nitrogen gas and ammonia, an organic compound having a functional group such as an amino group and a cyano group, and a heterocycle containing nitrogen. Examples of the compound containing an oxygen atom include oxygen gas, ozone, water (water vapor), hydrogen peroxide, carbon monoxide,
Inorganic compounds such as carbon dioxide, carbon suboxide, nitric oxide, nitrogen dioxide, dinitrogen trioxide, dinitrogen pentoxide, nitric oxide, hydroxyl group, aldehyde group, acyl group, ketone group, nitro group, nitroso group, sulfone Examples thereof include organic compounds having functional groups or bonds such as groups, ether bonds, ester bonds, peptide bonds, oxygen-containing heterocycles, and metal alkoxides. Examples of the compound containing a chalcogen element include H ₂ S, (CH ₃ ) (CH ₂ ) ₄ S (CH ₂ ) ₄ C
H ₃ , CH ₂ = CHCH ₂ SCH ₂ CH = CH ₂ , C ₂ H ₅ S
C ₂ H ₅ , C ₂ H ₅ SCH ₃ , thiophene, H ₂ Se, (C ₂
H ₅ ) ₂ Se, H ₂ Te and the like. Examples of compounds containing a halogen element include fluorine, chlorine, bromine, iodine, hydrogen fluoride, carbon fluoride, chlorine fluoride, bromine fluoride, iodine fluoride, hydrogen chloride, bromine chloride, iodine chloride and hydrogen bromide. Inorganic compounds such as iodine bromide and hydrogen iodide, and organic compounds such as alkyl halides, aryl halides, styrene halides, polymethylene halides and haloforms are used.

The substrate used in the present invention is not particularly limited in its material as long as it is transparent to visible light, and examples thereof include glass, quartz, and plastics such as polycarbonate and polyester.

The film forming method is also not particularly limited, and P
Both VD and CVD methods can be used, but the ion beam sputtering method, which has good crystallization, is preferable. The film thickness is not particularly limited, but 100 Å to 1 μm is suitable.

[0016]

【Example】

Example 1 A transparent thin film having a thickness of about 1500 Å was formed on a quartz substrate by the ion beam sputtering method under the following conditions. Three types of substrates were manufactured by changing the substrate temperature to room temperature, 100 ° C., and 250 ° C. Target Au Ionized gas Ar (50%) + CH ₄ (5
0%) Ion gun 4 mA x 9 KV Ion incidence angle 30 degrees Base pressure 6 x 10 ^-6 Torr Target-substrate distance 15 mm Three types of thin films prepared were examined by (X-ray diffraction method, TEM method) Approximately 25Å fine Au particles are
It was found that Au particles of about 35 Å existed in the film formed at 100 ° C and about 48 Å in the film formed at 250 ° C in the amorphous carbon film. In addition, a high energy shift (blue shift) was recognized from the measurement result of the optical absorption edge examined using a spectrophotometer at room temperature, and its size is proportional to the square of the average particle size of the fine particles, and the quantum size effect is Indicated.

Comparative Example 1 Using RF sputtering, as in Example 1, approximately 1580.
Å A transparent thin film was prepared. An Au chip was placed on the target SiO ₂ . Introduced gas Ar (99.999%) Introduced gas pressure 4 × 10 ⁻³ Torr Quartz substrate temperature 200 ° C. to 400 ° C. Base pressure 8 × 10 ⁻⁷ Torr Target-substrate distance 50 mm High frequency power 200 to 300 W As shown above Then, the glass substrate temperature and the high frequency power were changed to form three types of films. The average particle size of each sample was set to about 25, 35, 48 Å as in Example 1. X
From the line diffraction and the TEM method, the film was an amorphous film of SiOx and the above-mentioned particles of Au were present. From the measurement result of the optical absorption edge examined at room temperature, the same high energy raft as in Example 1 was recognized, but the shift amount was smaller than that in Example 1.

[0018]

[Effect] According to the present invention, by using amorphous carbon as a matrix of ultrafine metal particles, the fine particles can be contained in a high concentration in the thin film.
A film with large non-linearity can be easily obtained.

Claims (1)

[Claims] 1. A nonlinear optical material comprising an ultrafine particle-dispersed thin film, wherein ultrafine particles of metal microcrystals are contained in a film having amorphous carbon as a matrix.