Synthesis of Crystalline Structures of CN x , Thin Films Deposited on Sapphire, Quartz and Alumina Substrates
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R. CIREASA*,
A. CRUNTEANU*,
C.S.
COJOCARU*,
I.MORJAN*, A. KUMAR**, F. VASILIU*** *National Institute for Lasers, Plasma and Radiation Physics, Lasers Department, P.O.Box MG-36, R-76 900 Bucharest, Romania "**Department of Electrical Engineering , University of South-Alabama, Mobile, AL 36688, U.S.A. ***National Institute for Materials Physics, Electron Microscopy Laboratory, P.O.Box MG-7, Bucharest, Romania ABSTRACT Carbon nitride films raise current interest for their potential applications as ultrahard materials. We report on the formation of crystalline CN structures in films deposited at 248 nm on different substrates (sapphire, quartz, alumina) using the laser-induced CVD method and a gas mixture containing ethylene/nitrous oxide and ammonia as carbon and nitrogen source, respectively. The structural and morphological properties of the films were characterized by different analytical techniques (SEM, TEM, TED and
XPS). INTRODUCTION Due to their potential ultra-high hardness, carbon nitride materials could be potential candidates for many technological applications. Liu and Cohen [1] predicted a very high elastic modulus for a covalent C3N4 compound, with a structure equivalent to Si3N 4. Laser-induced chemical vapor deposition (L-CVD) has been often employed as a reliable technique in materials engineering of surfaces and related areas [2]. In our previous works [3-6] we have first demonstrated the possibility to use the L-CVD method in order to produce CN, thin films using different substrates and radiation wavelengths, by induced reactions in carbon/nitrogen containing gas precursors. In this work we prepared CN, thin films by the L-CVD method employing a KrF laser (248 nm), a mixture of carbon/nitrogen gas precursors (ethylene/nitrous oxide/ammonia) and various substrates (such as sapphire, quartz and alumina). A comparison of the morphology and chemical composition of the films deposited on different substrates, as determined by several analytical techniques (SEM, TEM, TED, XPS) is discussed. EXERIMENT The experimental set-up for L-CVD has been described elsewhere [3]. Briefly, the cross-shaped glass reaction cell in which the gases and the substrates were introduced allowed to monitor gas composition by IR spectrometry. The focused UV laser radiation (X=248 nm, fr-2 Hz, 40 mJ/pulse) was directed perpendicular to the substrate. Different substrates (quartz plates, single-crystal sapphire, polished alumina) were used. In all the experiments the deposition of CNx films was performed by irradiating a mixture of
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Mat. Res. Soc. Symp. Proc. Vol. 555101999 Materials Research Society
ethylene/nitrous oxide/ammonia (C2H 4:N20:NH 3=l:2 8), at a total pressure of about 80 torr, with different number of laser pulses (from 500 to 20000 pulses). Different analytical methods (X-ray photoelectron spectroscopy - XXPS, scanning and transmission electron microscopy - SEM and TEM and transmission electron diffraction-TED [4]) were used in order to characterize the structural, chemical and morphological properties
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