JPS5999401A - Silicon carbide mirror - Google Patents

Abstract

PURPOSE:To obtain a mirror with high reflectance suitable especially for high energy by forming a beta-form silicon carbide surface by a chemical vapor deposition method while providing specified crystallizability and size. CONSTITUTION:This silicon carbide mirror has a beta-form silicon carbide surface formed by a chemical vapor deposition method. The half-value width of the (200) faces of silicon carbide crystals in the polished surface under X-ray diffraction is <=0.40 deg.. Silicon carbide crystals obtd. by the deposition method have close relation with the reflectance when conditions during manufacture are changed in several ways, and the reflectance is practically in proportion to the crystallizability and size of the obtd. silicon carbide crystals. The crystallizability and size can be measured by X-ray diffraction, and relation represented by the equation (where beta is half-value width, theta is Bragg angle, lambda is the wavelengths of characteristic X-rays, epsilon is the size of crystallite, and eta is the effective strain of the lattice) is established.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mirror that has a high reflectance and is particularly suitable for high energy beams.

Generally, mirrors are made by forming an aluminum or silver film on the back surface of an ordinary plate glass, and then applying paint or the like to make it aesthetically pleasing. Mirrors like this cannot be used in special atmospheres because the glass has poor corrosion resistance and heat resistance. On the other hand, although many ceramic materials such as silicon carbide have high corrosion and heat resistance, they generally have low reflectance and cannot be used as high-precision mirrors in many cases. It is preferable to polish the mirror to a smooth surface, but conventional silicon carbide has not been suitable for use as a mirror in terms of pores, crystallinity, size, etc.

Regarding silicon carbide, which is suitable as a material, the present inventors have
As a result of considering favorable conditions as a father and mirror,
This invention was made.

Conventional silicon carbide is manufactured using the Kake-Radbreath method and the self-sintering method.

It is manufactured by a CVD method or the like, and in particular, when a hot press method or a self-sintering method is used, there are many impurities and pores, making it unsuitable as a mirror.

Also, even when using the CVD method, no reflectance of 60% or more has been observed. This is based on the discovery that silicon carbide crystals are fine and have poor crystallinity, which is the reason why the reflectance cannot be improved.

In the present invention, it has been revealed that silicon carbide crystals obtained by chemical vapor deposition (CVD) have a close relationship with reflectance when the manufacturing conditions are varied. That is, this reflectance is approximately proportional to the crystallinity and size of the obtained silicon carbide crystal. Crystallinity, size is X
It can be measured by line diffraction and is related by the following formula.

β・possible θ/λ=1/ε+η・ground θ/λ where β is the half-width, θ is the Bragg angle, λ is the wavelength of the characteristic X-ray, ε is the crystallite size, and η is the effective strain of the lattice. be.

It was also found that the smaller the value of the half width β, the better the reflectance and the better the similar characteristics. Further, the deposited surface was polished and etched to clarify the crystal shape on the polished surface, and the largest diameter of each particle was measured to determine the area occupied by particles of 20 μm or more.

Comparing the results with the reflectance, it was found that the area of large crystal particles (20μ or more) was 2
What accounts for 0% or more is reflection. Examples of the present invention will be explained below.

Example 1 Four types of silicon carbide films were formed on the surface of a carbon plate that had been subjected to high purity treatment by the CVD method under different conditions. This surface was polished to a mirror finish under the same polishing conditions. Using an X-ray diffractometer, these mirror surfaces were converted into Cw- by α-rays (2 (1(1)
As a result of determining the half width of the diffraction line of the surface, a mirror exhibiting crystallinity as shown in FIG. 1 was obtained. The results of determining the reflectance of each visible light beam are shown in Table 1.

Table 1 As a result, it became clear that the reflectance of a sample having a half-value width exceeding 0.4 (1) decreases rapidly.

Example 2 Six types of silicon carbide films were formed on the surface of a high-purity-treated carbon plate by CVD under different conditions. This surface was polished to a mirror finish under the same polishing conditions. When we measured the maximum size of the crystal grains on those mirror surfaces and determined the area of the grains with a diameter of 2F1μ or more, the areas were 5%, 9%,
They were 15%, 20%, 25%, and 30%. Table 2 shows the results of determining the reflectance by visible light for each of these.
Shown below.

Table 2 As a result, it became clear that when the area ratio of particles of 20μ or more was less than 20%, the reflectance decreased significantly. In the above examples, the reflectance of visible light was measured, but the reflectance of each wavelength such as infrared rays and X-rays showed the same tendency as that of visible light. Also, C
The conditions of the VD method and the crystal size do not necessarily match.
At least a relatively small half-width does not mean that the atoms in the crystal are arranged well, and the crystallinity seems to have a good effect on workability during polishing. Although silicon carbide was formed on the surface of high-purity carbon, the base material is not necessarily limited to carbon, and may be other materials such as silicon carbide or alumina.

[Brief explanation of the drawing]

FIG. 1 shows an X-ray diffraction pattern of a silicon carbide mirror. Inventor: Hideo Nagataka Inventor: Kari 1) Akio Inventor: Matsuo
Excellent

Claims (2)

[Claims] (1) Silicon carbide crystals on the polished and polished surface of β-type silicon carbide formed by chemical vapor deposition
200) A silicon carbide mirror characterized in that the mid-half value of the X-ray diffraction plane is 0.40 degrees or less. (2) The silicon carbide mirror according to claim 1, wherein the area ratio of crystals having a maximum crystal boundary of 20 μ or more on the polished surface is 20% or more.