Transitions of Boron Carbide to B-C-N Thin Film
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Transitions of Boron Carbide to B-C-N Thin Film Ruqiang Bao, Zijie Yan, and Douglas B Chrisey Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. ABSTRACT Boron carbon nitride (B-C-N) thin films are attractive due to their potential as hard coatings and as semiconductors with varying band gap. Both B-C-N (BC0.24N0.24) thin films and boron carbide (B4C) thin films were deposited by radio-frequency magnetron sputtering at room temperature. Also, the transition of boron carbide to B-C-N was studied by bombarding the boron carbide thin film by ~1 uA/cm2 4 keV N+ ions. The results show that the UV-Vis transmittance of B-C-N thin films is better than that of amorphous boron carbide and both B-C and B-N bonds exist in our B-C-N thin films. The nitrogen in our B-C-N thin films bonded with boron causes the XPS B 1s core level to shift 2 eV from that in the B4C boron carbide thin film. Ion bombardment shows that the N+ ion primarily reacts with boron to form B-N and this reaction causes the environmental change of carbon in the thin film and then the XPS C 1s core level to shift to 283.5 eV from 282.8 eV. INTRODUCTION Boron carbon nitride (B-C-N) thin films are interesting as a novel material system for studying disparate properties ranging from hard coatings [1] to a semiconductor of varying band gap [2]. Their electrical, mechanical, and optical properties can be adjusted by varying B, C, and N stoichiometry and bonding. The preparation of B-C-N films has been achieved by a large variety of deposition methods, such as radio frequency (RF) [3-6] and DC magnetron sputtering [7], ion beam assisted deposition [8], ECWR plasma assisted deposition [9], pulsed laser deposition [10], RF/MW PECVD [11], RF-inductively coupled plasma CVD [12] and conventional CVD [13]. Among the available deposition techniques, RF sputtering process is one of the most suitable methods to deposit compounds on any substrate [5]. By controlling the stoichiometry of boron, carbon, and nitrogen, amorphous B-C-N thin film properties can be easily explored with RF magnetron sputtering. The stoichiometry can be controlled in RF sputtering by choosing experimental parameters that eliminate impurities such as hydrogen, which is usually present in the films deposited by chemical vapor deposition [11]. The boron carbide (B4C) target is the most flexible choice to be used to deposit various stoichiometries of amorphous B-C-N (a-B-C-N) thin films by RF magnetron sputtering because we can vary the argon and nitrogen gas mixture, which is used as the plasma gas source. Moreover, there is no hydrogen introduced, which is more typical by using boron nitride as a target [6]. However, it is not clear how the structure and chemistry evolve from boron carbide (B4C) with icosahedral bonding to boron-carbon-nitrogen bonding. In order to study the transition from boron carbide to boron-carbon-nitrogen, a B4C target and argon-nitrogen gas mixtures were used to deposit aB-C-N thin films whereas amorphous boron c
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