Pulsed laser deposition of carbon nitride thin films in nitrogen gas ambient
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Pulsed laser deposition of carbon nitride thin films in nitrogen gas ambient Masayuki Okoshi,a) Hiroshi Kumagai, and Koichi Toyoda Laser Science Research Group, The Institute of Physical and Chemical Research, (Riken), 2-1 Hirosawa, Wako, Saitama 351-01, Japan (Received 21 July 1996; accepted 14 March 1997)
Carbon nitride thin films have been successfully deposited by ablating a graphite target (99.999%) in nitrogen gas ambient using the second (532 nm) or third (355 nm) harmonic of a Q-switched Nd : YAG laser. Carbon nitride films consisting of approximately 40% nitrogen were obtained at 7.5 3 1023 Pa of nitrogen gas pressure using the third harmonic laser. The C–N chemical bond in the films was observed by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Ellipsometric studies revealed that the refractive index of the fabricated films decreased with increasing nitrogen concentration. I. INTRODUCTION
Since the prediction by Liu and Cohen, by means of an empirical model and ab initio calculation, of the bulk moduli of covalent solids,1 carbon nitride has attracted much attention because it can theoretically be harder than diamond. Therefore, it has been extensively studied and fabricated experimentally in recent years. Carbon nitride films fabricated at low temperature can be used in various applications including precision instruments and aerospace, because they prevent serious abrasion of metal components by providing a hard coating. They have generally been fabricated by chemical vapor deposition (CVD) methods such as plasma-induced deposition in a gas mixture of methane and nitrogen2,3 and thermal decomposition of C –N–H organics.4 Sputtering of a graphite target in nitrogen gas ambient5,6 and the ion beam assisted deposition (IBAD) method7 have also been employed in order to reduce an amount of impurity C–H or N–H chemical bonds in the films. Synthesis of carbon nitride films by the laser ablation of graphite using the second harmonic of a Q-switched Nd : YAG laser under atomic or ionic nitrogen beam bombardment has also been reported.8,9 Recently, pulsed laser deposition (PLD) of nitride films such as TiN in nitrogen gas ambient has been studied because nitrogen molecules can be decomposed in an ablation plume.10 If carbon nitride films are also fabricated in nitrogen gas ambient without a nitrogen beam bombardment, the scheme becomes more interesting because it is simpler. We have carried out PLD using a graphite target in nitrogen gas ambient with the second (532 nm) or third (355 nm) harmonic of a Q-switched Nd : YAG laser. It a)
Present address: Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Tenpaku, Toyohashi 441, Japan.
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J. Mater. Res., Vol. 12, No. 12, Dec 1997
is generally known that a chemical compound of carbon and nitrogen is a gaseous cyanogen. Therefore, nitrogen atoms are easily removed from the films as cyanogens during a fabrication process of carbon nitride films. In th
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