Characterization of bond formation in SiC and Si 3 N 4 implanted with Ti, Fe, and Co
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´bastien Gautrot and Odile Kaı¨tasov Centre de Spectrome´trie Nucle´aire et de Spectrome´trie de Masse, Baˆt. 108, 91405 Orsay Cedex, France (Received 20 April 2000; accepted 6 November 2000)
Ti, Fe, and Co ions were implanted in two ceramics, SiC and Si3N4, to reach concentrations on the order of 10% over a depth of about 50–60 nm. X-ray absorption spectroscopy was performed at the K edge of the implanted ions to identify their local environment at the end of the implantation process. Ti was found to form Ti–C and Ti–N bonds whereas Co and Fe precipitated and formed clusters in Si3N4. CoSi was detected in SiC whereas, in the same matrix, Fe clusters coexist with FeSi. A coherent interpretation of these results is given in terms of the heat of reaction for all possible systems. We also successfully interpret in the same way some results found in literature in the case of implanted oxides.
I. INTRODUCTION
Use of ion implantation makes it possible to insert any ion into any matrix. This doping technique concerns a depth of about 100 to 500 nm, so it is used to improve surface properties of materials. The energy loss process of the incident ions along their paths results in structural modifications of the matrix; i.e., defects are created in the host lattice, and in some cases amorphization takes place. Hence, improved surface properties depend on two parameters: (i) the type of bonds formed at the end of the implantation process (bonds between the target atoms and implanted ions or between the implanted ions themselves), (ii) the resulting crystallographic disorder inside the doped matrix. In recent years ceramics have attracted attention as model systems of fundamental interest such superconductors with high critical temperatures1 or in technological applications such as substrates for electronics devices2 and optical waveguides.3 Several review articles have dealt with defects and amorphization under ion bombardment in nonmetallic compounds.4,5 An important aspect is also to understand the bond formation so the behavior can be predicted in various situations. Our
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J. Mater. Res., Vol. 16, No. 2, Feb 2001 Downloaded: 03 Apr 2015
aim here is to address the problem of compound formation during ion treatment of ceramics. Previous work has shown that implanted alkali metals form precipitates, e.g., Li, Na, K in MgO,6 whereas it is known that implanted Au forms Au3Mg in MgO.7 For low Fe concentrations implanted in TiO2 and SiO2, typically below 1016 at/cm2, Fe is bonded to O atoms in Fe2+ or Fe3+ states.8 For higher concentrations, above 1017 at/cm2, Fe precipitates start to form, with diameters of the order of 2 to 4 nm.9 In Ref. 10, the authors reported that part of Fe (about 40%) is in the metallic state whereas the rest (about 60%) is oxidized. More recently, implantations of Ti, Cu, Fe, Ni, and Er have been performed in AlN.11–13 The heat of formation appears to be the key parameter in predicting the
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