JPH01302203A - Infrared transmittable optical material - Google Patents

Abstract

PURPOSE:To obtain the IR transmittable material having high mechanical strength and excellent durability by forming a carbon film contg. a specific element to one face of a base material consisting of the IR transmittable material. CONSTITUTION:The carbon film 2 contg. hydrogen or group VII element is formed on at least one face of the base material 1 consisting or the IR transmittable material and is so formed that the concn. of the hydrogen or the group VII element is decreased continuously from the base material side to the front surface side. A diamond-like carbon film or plasma-polymerized carbon film is used as the carbon film 2. Since the concn. of the hydrogen or the group VII element is high on the base material side in such a manner, the carbon hardness is low and the internal stress is small. The adhesive property is thus enhanced. Conversely, the concn. is low on the front surface side and, therefore, the hardness is high and the internal stress is large. The mechanical strength is consequently high and the durability is improved. This material is thus used effectively for IR optical apparatus.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an infrared-transmissive optical material, which can be used as a window material for infrared optical instruments, such as infrared absorption measuring instruments, infrared detection elements, and infrared lasers. can.

[Background Art] In recent years, infrared optical devices that utilize infrared rays have been used in a wide range of fields such as communication, control, and measurement.

This type of infrared optical equipment is equipped with a window material that transmits infrared rays to guide the infrared rays to the sensor part. Conventionally, SiO! is generally used as the material for this infrared transmitting optical window material. , Zn Se, Ge, SI, polyethylene, etc. are used, and KBr, Na CIS, etc. are used as materials with excellent transparency over a wide range of infrared regions.
NaF, LiF.

Ca Fz, KC l, K! , Cs Br , Cs
Alkali halides such as T are used.

[Problem to be solved by the invention] The above-mentioned KBr, Na C I, Na F, Li
F.

Ca Fz, KC l. , K I, CsBr, Csl
Infrared-transmitting optical window materials made of alkali halides such as halogenated alkali have excellent infrared transmittance, but they do not have sufficient mechanical strength and are deliquescent, so they have poor environmental resistance and durability. There were drawbacks.

In order to solve these problems, an infrared transparent optical window material has been proposed in which a film of hard carbon, ie, diamond or diamond-like carbon, is formed on the surface of a conventional infrared transparent base material. However, with such a window material, the adhesion between the infrared transmitting base material and the hard carbon film was poor, and problems still remained in terms of durability, and the window material was not sufficiently durable for practical use.

An object of the present invention is to provide an infrared transmitting optical material having excellent mechanical strength, durability, and the like.

[Means for Solving the Problems 1] The infrared-transparent optical material according to the present invention comprises forming a carbon film containing hydrogen and/or a group (I) element on at least one surface of a base material made of an infrared-transparent substance. , the concentration of hydrogen and/or Group Ⅰ elements (fluorine, chlorine, bromine, etc.) is reduced continuously or stepwise from the base material side to the surface side.

One or more arbitrary types of elements may be included as the Group ■ element.0 If hydrogen and Group ■ elements are contained, the concentration of one of the hydrogens (or the Group ■ element) It also includes a case where only the concentration of the other group Ⅰ element (or hydrogen) is reduced continuously or stepwise while making the other group Ⅰ element (or hydrogen) uniform.

In this infrared-transparent optical material, the carbon film is a diamond-like carbon film (a carbon film containing a diamond structure) and/or a plasma-polymerized carbon film.

Examples of the infrared transparent substance used as the base material include -
Boat fishing Si Ox, Zn Se, Ge, Si
, polyethylene, etc., as well as KBr, which has excellent transmittance over a wide range of infrared regions.

Na C1, Na FSLi F, Ca F, , K
C.I.

K l5Cs Br , Cs I, A! ! S es
, KR3-5, KR3-6, and the like.

Examples of carbon sources for forming the carbon film include alkanes such as methane, ethane, propane, butane, pentane, and hexane, alkenes such as ethylene, propylene, butene, pentene, and butadiene, alkynes such as acetylene, and benzene. , aromatic hydrocarbons such as toluene, xylene, indene, naphthalene, and phenanthrene; cycloparaffins such as cyclopurpane and cyclohexene;
Examples include cycloolefins such as cyclopentene and cyclohexene, and ketones such as acetone and benzophenone. In addition, oxygen-containing carbon compounds such as carbon monoxide, carbon dioxide, and methyl alcohol, and nitrogen-containing carbon compounds such as methylamine, ethylamine, and aniline can also be used. These carbon sources may be used alone or in combination of two or more.

Particularly preferred among these are paraffin hydrocarbons such as methane, ethane and propane, ketones such as acetone and benzophenone, and oxygen-containing carbon compounds such as carbon oxide and methyl alcohol.

Group ■ element sources include C1x, Ft, B rz,
Only one type of HCI or the like or two or more types thereof can be used.

Or, the carbon source and the Group Ⅰ element source are contained in the same compound, for example, CClx F-x, CH, C1a-x
, CH'll Bra-x, CHX
F4-X, CFX Bra-++, CC
Iw Bra-K (x=0 to 4), etc. can also be used.

The composition ratio (atomic ratio) of the raw materials used is hydrogen/carbon of 1 or more, group (III) element/carbon of 1 or more, preferably 2 or more, (hydrogen + group (III) element)/carbon of 1 or more, preferably shall be 2 or more.

In addition, a carrier gas may be mixed with the raw material gas, and this carrier gas not only plays the role of a carrier for introducing the carbon source gas into the plasma reaction system, but also plays the role of stably generating and sustaining plasma. As such a carrier gas, argon gas, neon gas, helium gas, xenon gas, nitrogen gas, etc. can be used.

These may be used alone or in combination of two or more.

Among the carrier gases mentioned above, nitrogen gas, argon gas, etc. are particularly preferred.

Then, using a mixed gas such as the above-mentioned carbon Bi gas, hydrogen gas, and/or Group Ⅰ element source gas as a reaction gas, diamond-shaped A carbon film, a plasma polymerized carbon film, or both are formed on the surface of an infrared transparent substrate.

In addition, when using the RF plasma CVD method, the reaction pressure, that is, the pressure inside the reaction chamber, is usually 10 4 to 10' Torr, preferably 10 -' to 10'' T.

It is rr. If this reaction pressure is lower than 10-'Torr, the rate of carbon film formation may be significantly slowed down. On the other hand, if it is higher than 103, the carbon film may not be formed.

Further, the heating temperature of the base material made of an infrared transparent substance is usually room temperature to 600°C, preferably room temperature to 400°C. If this temperature is lower than room temperature, a carbon film may not be formed.

The formation of this diamond-like carbon film or plasma-polymerized carbon film can be controlled by changing the synthesis conditions (reaction pressure, etc.).

For example, if the reaction pressure is lowered, the concentration of hydrogen and/or group Ⅰ elements in the film to be synthesized will be lowered, making it easier to form a diamond-like carbon film.On the other hand, if the reaction pressure is increased, the concentration of hydrogen and/or Group Ⅰ elements in the film to be synthesized will be lower, and on the other hand, if the reaction pressure is increased, the concentration of hydrogen and/or Group III elements in the film to be synthesized will be lower. And/or the concentration of group (Ⅰ) elements becomes high, making it easy to form a plasma-polymerized carbon film.

When forming this carbon film, it is possible to change the concentration of hydrogen and/or Group Ⅰ elements in the carbon film by controlling the reaction pressure, gas composition, temperature, input power, etc. in the reactor. It is possible.

For example, as shown in FIG. 1, when forming the carbon film 2,
For example, by continuously decreasing the reaction pressure in the device, the concentration of hydrogen and/or group
A carbon film 2 is obtained which decreases continuously from the side to the surface. In addition, as shown in FIG. 2, when forming the carbon film 2, by reducing the reaction pressure in the apparatus in three steps, for example, the concentration of hydrogen and/or group A carbon film 2 is obtained consisting of layers 2A, 2B and 2C which are gradually reduced.

[Function] In the infrared-transmissive optical material according to the present invention, when the concentration of hydrogen and/or Group Ⅰ elements in the carbon film increases, the hardness of the carbon film decreases and the internal stress decreases; When the concentration of hydrogen and/or group Ⅰ elements becomes smaller, the hardness of the film becomes higher and the internal stress becomes larger. Therefore, by incorporating hydrogen and Group Ⅰ elements into the film and reducing them continuously or stepwise from the base material side to the surface side, the stress in the part that contacts the base material is reduced and the adhesion to the base material is improved. It is possible to improve durability and environmental resistance by increasing the hardness of the surface side portion.

"Example" - As shown in Figure 2, a base material made of KBr with a diameter of 40 mm and a thickness of 4 mm was used, and methane gas was added as a carbon source to 203CC11 and hydrogen gas as a carbon source. A carbon layer 2A with a thickness of 300 mm was first formed at a pressure of 0.70 Torr, and then at a pressure of 0.30 Torr. Form a carbon layer 2B with a thickness of 300 mm at the bottom, and finally apply a pressure of 0.10 Torr.
By forming a carbon layer 2C with a thickness of 900 densities under the conditions of
It was formed on both sides of the base material 1 to obtain an infrared transmitting optical material according to this example.

Regarding each of N2A to 2C constituting this carbon film 2,
The results of measuring the hydrogen concentration and Knoop hardness are shown in Table 1 below.
A to 2C were formed under the same conditions as in the above example. Further, the hydrogen concentration was calculated based on an infrared absorption spectrum.

Table 1 As shown in Fig. 2, a base material 1 made of KBr with a diameter of 40 mm and a thickness of 4 cm was used, and by high-frequency plasma CVD method, methane gas was added as a carbon source at 20 sec, hydrogen gas was added at 20 scc+e, and a group Using CF as a source, gas flowing at lQsccm, high frequency power of 120W, and substrate temperature of 150''C, a carbon layer 2A with a thickness of 500 mm was first formed under the condition of a pressure of 0.70 Torr, and then a pressure of Q , form carbon 1li2B with a thickness of 500 under the condition of 3Q Torr, and finally the pressure is 0.10 Torr.
By forming carbon N2C with a thickness of 1,000 people under the conditions of , the concentration of hydrogen decreased stepwise from the base material side to the surface side, and the film thickness of carbon II! 42 to K
It was formed on both sides of the Bri material 1 to obtain an infrared transmitting optical material according to this example.

Regarding each layer 2A to 2C constituting this carbon film 2,
The results of measuring hydrogen concentration, fluorine concentration, and Knoop hardness are shown in Table 2 below. These measurements were performed by forming these N2A to 2C on a Si base under the same conditions as in the above example.

Furthermore, the hydrogen concentration and fluorine concentration were calculated based on infrared absorption spectra.

Table 2 Using a base material made of KBr with a diameter of 40 mm and a thickness of 4 mm, 20 sec of methane gas and 20 scc of hydrogen gas were flowed as a carbon source by high-frequency plasma CVD method.
High frequency power is 120W, base material temperature is 100°C,
A carbon film having a thickness of 1500 mm was formed on both sides of the KBrl material under a pressure of 0.70 Torr to obtain an infrared transmitting optical material according to this comparative example.

1''■1i Using a base material made of KBr with a diameter of 40 mm and a thickness of 41111 mm, methane gas was flowed for 20 sec as a carbon source, hydrogen gas was flowed for 20 sec as a carbon source, high frequency power was 120 W, and the base material temperature was 100' using the high frequency plasma CVD method. C, the film thickness is 150 at a pressure of 0.10 Torr.
An infrared-transmissive optical material according to this comparative example was obtained by forming carbon films on both sides of a KBr base material.

Using a base material of JjL and KBr with a diameter of 40 mm and a thickness of 4 cm, 20 sec of methane gas as a carbon source, 20 sec of hydrogen gas as a source of group ① elements, and 103 CC- of gas as a source of group In this comparative example, a carbon film with a thickness of 2000 mm was formed on both sides of the KBr substrate under the following conditions: high frequency power of 120 W, substrate temperature of 15 o'c, and pressure of 0.70 Torr. Such an infrared-transparent optical material was obtained.

Using a substrate with a diameter of 40 mm and a thickness of 4 mm made of KBr, 203 CCIm of methane gas as a carbon source, 20 scca of hydrogen gas, and 10 seclI of CF gas as a group element source were flowed using the high-frequency plasma CVD method. ,
High frequency power is 120W, base material temperature is 150°C,
A carbon film having a thickness of 2000 mm was formed on both sides of a KBr base material under a pressure of 0.10 Torr to obtain an infrared transmitting optical material according to this comparative example.

The infrared transmitting optical materials according to Examples 1 and 2 and Comparative Examples 1 to 4 were tested for adhesion, infrared absorption, and environmental resistance. The adhesion test was conducted by measuring the peeling rate of Scotch Tape (trade name). Measurement of infrared transmittance was performed using an infrared spectrometer. In addition, the environmental resistance test was conducted in an atmosphere with a temperature of 40°C and a humidity of 70%.
This was done by measuring the decrease in infrared transmittance after leaving the sample for a day. The results of these measurements are shown in Table 3 below.

In Table 3, the infrared absorption rate characteristics are around 2900 am-'. In the overall evaluation in this table, O means good, Δ means average, and × means bad. In addition, Fig. 3 shows Example 1.
, shows the measurement results of the infrared transmittance of the infrared transmitting optical materials according to Comparative Example 1 and Comparative Example 2.

In this graph, curve A is a graph of the example, curve B is a graph of comparative example 1, and curve C is a graph of comparative example 2. The figure also shows the results of measuring the infrared transmittance of the KBr base material as a curve for reference.

Table 3 [Effects of the Invention] According to the present invention, an infrared transmitting optical material having excellent mechanical strength, environmental resistance, and durability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example, FIG. 2 is a cross-sectional view of another example, and FIG. 3 is a graph showing the measured infrared transmittance of the example and the comparative example. ]... Base material, 2... Carbon film. Applicant Idemitsu Petrochemical Co., Ltd.

Claims (2)

[Claims] (1) A carbon film containing hydrogen and/or a Group VII element is formed on at least one surface of a base material made of an infrared transparent substance, and the concentration of the hydrogen and/or Group VII element is adjusted to the base material side. An infrared transmitting optical material characterized in that the infrared rays transmittance decreases continuously or stepwise from the surface side. (2) A first characterized in that the carbon film is a diamond-like carbon film and/or a plasma polymerized carbon film.
An infrared transmitting optical material according to the claims.