Alloy Thin Films from Discrete Metallaborane Clusters
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ALLOY THIN FILMS FROM DISCRETE METALLABORANE CLUSTERS
T. P. FEHLNER*, M. M.AMINI*, M. V.ZELLER**t, W. F. STICKLE***, 0. A. PRINGLE , G. J. LONG , F. P. FEHLNER *Chemistry Department and **College of Engineering, University of Notre
Dame, Notre Dame, IN46556 Physical Electronic Laboratories, Perkin-Elmer, Mountain View, CA 94043 Departments of Physics and Chemistry, University of Missouri-Rolla, Rolla, MO 65401 R.D.&E. Division, Corning Glass Works, Corning, NY 14831 tPresently at NASA Lewis Research Center, Cleveland, OH 44135
ABSTRACT The ferraborane HFe 4 (CO) 1 2 BH2 sublimes at 50 °C and decomposes by loss of H2 and CO on various substrate surfaces at 160-180 °C to yield films having metallic appearances with typical thicknesses of 4000A. These films are amorphous by X-ray, conduct electricity and adhere well to glass, metal and silicon substrates. The composition was determined by ESCA and Auger spectroscopies. The films exhibit highly uniform composition and the Fe/B ratio is 4 showing that film stoichiometry is defined by the cluster core. The ESCA chemical shifts show the presence of boride and metallic iron. At present the bulk film contains a high level of oxygen in the form of iron and boron oxides. No ax-iron is present by X-ray or Mossbauer spectroscopies. Some carbon and hydrogen (SIMS) are present. Mossbauer spectra show the presence of magnetic iron similar to that exhibited by authentic Fe 8 0 B 2 0 samples but the films also contain substantial paramagnetic iron.
INTRODUCTION Although the Metal Organic Chemical Vapor Deposition techniques have been utilized for a long period of time [1], inorganic and organometallic chemists only recently have become involved in Mat. Res. Soc. Symp. Proc. Vol. 131. 61989 Materials Research Society
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synthesizing new molecular precursors for known materials [2-4]. Ease in handling and predefined, precise stoichiometry has made the preparation of advanced materials from organometallic precursors by MOCVD a fast growing area of research. Among new advanced materials, metallic glasses have a special position because of their properties such as hardness, strength, ease of magnetization [5] corrosion resistance [6] catalytic activity [7] and conductivity [8]. Metal borides were prepared for the first time by electrochemical deposition [9] and because of applications in the ceramic and electronic industries they are now prepared on a large scale by rapid quenching and melt-spining methods. Recently titanium, zirconium, and hafnium boride have been prepared from metal borohydrides [10,11] by CVD methods. We have explored the utility of ferraboranes in the preparation of iron-boride thin films and we report below the utilization of HFe 4 (CO) 1 2 BH 2 to prepare metal boron films of the composition Fe 8 0 B2 0 .
EXPERIMENTAL The HFe 4 (CO) 12 BH2 was prepared according to our procedures with purification by column chromatography followed by sublimation [12]. To prepare a film, the ferraborane was sublimed at 50 °C in a low pressure CVD reactor. The substrates ( g
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