Radiant energy – Electron energy analysis
Reexamination Certificate
1998-07-21
2002-07-16
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Electron energy analysis
C250S307000
Reexamination Certificate
active
06420701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and a method for preparing a thin film containing a material having a crystal structure and exhibiting an absorption in ultraviolet region, in particular a carbon thin film containing graphite as principal ingredient. More particularly, it relates to an apparatus for preparing carbon thin film that is provided with means for analyzing the state of carbon thin film incorporated into a micro-area of 1 &mgr;m and less square and a method of preparing a carbon thin film comprised of feeding back the result of the analysis of the state of carbon and reflecting it to the carbon thin film preparing conditions.
2. Related Background Art
Graphite is an allotrope of carbon, having structure consisting of hexagonal reticular planes with the sp
2
hybridized orbital and showing the following specific physical properties. While it shows a semimetallic electroconductivity, a thermal conductivity three times as high as that of copper, a very high elasticity and also a very high mechanical strength within the reticular planes of carbon, its electric and thermal conductivities fall remarkably across the layers of its multilayer structure. Thus, it is exceptionally anisotropic if viewed along the reticular planes and a direction perpendicular to the planes.
A variety of different models have been proposed for the layered structure of reticular planes of carbon. For example, Franklin defines a turbostratic structure where reticular planes are randomly laid one on the other and a graphite crystal structure where reticular planes are arranged in a coordinated manner and says that each distance separating the reticular planes is 0.344 nm for the turbostratic structure and 0.335 nm for the graphite crystal (R. E. Franklin, Proc. Roy. Soc., A209, 196(1951)).
Because of the remarkable physical properties of graphite due to its particular structural feature including a high thermal resistance and a high chemical resistance, it finds a wide variety of industrial applications including refractory materials, materials of atomic furnaces and heat-emitting bodies. Additionally, highly-crystallized graphite shows excellent spectral and reflective characteristics for X-rays and neutron rays and hence are advantageously used for monochromators and filters.
Recently, a graphite intercalation compound obtained by utilizing interlayer spaces of graphite has been attracting attention and lithium ion cells prepared by utilizing a graphite intercalation compound are currently popular as small and high-performance secondary cells that find various practical applications. Other applications of the graphite include materials to be used for electronic circuits such as resistor coating film, adsorptive materials utilizing the porous structure of the graphite and electron emitting materials. Particularly, materials listed above and produced in recent years are of high quality, finely processed and thin. In response, there is a demand for techniques that can effectively analyze the structure, more specifically the average crystallite size, of the graphite used in a very fine area on the surface of a product comprising such a material.
The structure of graphite is typically defined in terms of the size of crystallites (crystallite size), using either the crystallite size Lc as observed along a direction perpendicular to the hexagonal reticular plane or the crystallite size La as observed along a direction parallel to the hexagonal reticular plane.
For the purpose of the present invention, the term “crystallite” refers to a unitary crystal (microcrystal) that is a constituting member of polycrystal or a unitary crystal (microcrystal) that is observed in a noncrystalline substance. As far as this specification is concerned, the crystallite size of graphite refers to Lc as observed along a direction perpendicular to the hexagonal reticular plane.
It is known that graphite materials having different average crystallite sizes show physical properties that are remarkably different from each other, including the specific resistance, the thermal conductivity and the bending strength. For example, the specific resistance, the thermal conductivity and the bending strength will be respectively about 50×10
−4
&OHgr;cm, about 3 kcal/mhr° C. and about 900 kgf/cm
2
for glassy carbon with an Lc of 10 nm, about 40×10
−4
&OHgr;cm, about 7 kcal/mhr° C. and about 1100 kgf/cm
2
for glassy carbon with an Lc of 20 nm and about 10×10
−4
&OHgr;cm, about 120 kcal/mhr° C. and about 200 kgf/cm
2
for artificial graphite. Clearly, graphite materials having different average crystallite sizes show physical properties that are remarkably different from each other. Therefore, in analyzing physical properties of a graphite material, it is indispensable to know the average crystallite size of the material. Conventionally, graphite, thin film containing graphite in particular, is produced by means of a thermal CVD, where a gaseous hydrocarbon compound is introduced onto a hot substrate to thermally decompose the gaseous compound and causes carbon in the decomposition product to precipitate in a vapor phase or a plasma CVD, where plasma is introduced into a reaction space to activate and decompose a gaseous hydrocarbon compound and causes carbon in the decomposition product to precipitate at relatively low temperature. Alternatively, graphite may be produced by heat treating a filmy polymeric compound. Known specific techniques for producing graphite include the one (as disclosed in Japanese Patent Publication No. 6-102531) with which a hydrocarbon compound such as methane is thermally decomposed by means of hot plasma to produce scale like film having a turbostratic crystal structure (the average crystallite size (Lc) is between that of graphite single crystal and that of amorphous carbon), the one (as disclosed in Japanese Patent Application Laid-Open No. 6-220638) with which a carbon coat is formed at relatively low temperature between 350 and 450° C. by applying the catalytic function of nickel oxide to a hot CVD (so that nickel oxide may be carried on the surface of a substrate) and the one (as disclosed in Japanese Patent Application Laid-Open No. 5-17115) with which graphite film is prepared by laying a number of polymeric films that have been subjected to a preliminary oxidation treatment process into a multilayer structure, which is then pressed and heat-treated. Otherwise, there are also known techniques including the one (as disclosed in Japanese Patent Application Laid-Open No. 5-43213) with which a film of a polyimide compound having a fluorene molecular structure is pinched between a pair of graphite plates and baked to produce graphite and the one (as disclosed in Japanese Patent Application Laid-Open No. 5-78194) with which molten carbon on a metal column is made to precipitate on crystal seeds of graphite. There is also known a method of producing ultra-fine particles of graphite by vaporizing carbon through arc-discharge and subsequently cooling and solidifying the vaporized carbon (Japanese Patent Application Laid-Open No. 7-206416).
Known techniques for analyzing various graphite materials for determining the structure (crystal structure) include X-ray diffraction method, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, high resolution electron energy loss spectroscopy, transmission-type electron energy loss spectroscopy and low energy electron diffraction method (see, for example, S. Aizawa, “Hyoumen Kagaku (Surface Science)”, Vol. 11, No. 7, 398 (1990)).
X-ray diffraction method is a technique for determining the structure of a graphite material, using a diffraction pattern obtained by irradiating the specimen with X-rays and a computation model. With this technique, the distance between hexagonal reticular planes of the specimen is estimated on the basis of the diffraction peak, and the average crystallite size Lc as determine
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