In Situ FT-IR Studies of Oxide and Oxynitride Sol-Gel-Derived Thin Films
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IN SITU FT-IR STUDIES OF OXIDE AND OXYNITRIDE SOL-GEL-DERIVED THIN FILMS*
DAVID M. HAALAND AND C. JEFFREY BRINKER Sandia National Laboratories, Albuquerque,
NM
87185
ABSTRACT A high-temperature infrared cell was developed to study the gel-to-glass conversion of sol-gel-derived thin films. FT-IR spectra of matched thin-film borosilicate sol-gel samples were taken as the samples were heated at 100C intervals to 700*C in either air or ammonia. The gels were converted to oxide and oxynitride glasses, respectively, by these heat treatments. The gel-to-glass conversion could be followed and compared for these two treatments by monitoring changes in the vibrational bands present in the spectra. Comparisons between the infrared spectra of NH3 -treated and air-treated films heated above 500eC reveal the appearance of new B-N bonds at the expense of B-O-Si bonds for the NH3 -fired films. These spectra also exhibit changes which may indicate the formation of Si-N bonds. Thus, ammonolysis reactions can result in thin-film oxynitride glass formation at relatively low temperatures.
INTRODUCTION Oxynitride glasses have been shown to exhibit greater fracture toughness and microhardness, higher glass-transition temperatures, better chemical durability and altered thermal-expansion properties relative to the corresponding oxide glasses [1-61. We have recently demonstrated that oxynitride glasses can be prepared without melting by heating porous gels in gaseous ammonia [6-8]. Fourier transform infrared spectroscopy (FT-IR) has been shown to be useful in identifying the mechanisms involved in the synthesis of the oxynitride glasses from silicate gels [6-7]. In these earlier studies, however, bulk gels were heated in ammonia and then disperses in a KBr matrix. Thus, the samples were exposed to the ambient atmosphere prior to analysis and only the relative infrared band intensities between samples could be compared. Using a high-temperature infrared cell designed for in-situ FT-IR studies, the infrared investigation of sol-gel-derived oxide and oxynitride glasses was extended to thin-film glasses. This new cell made possible the infrared study of thin-film glasses as a function of temperature and atmosphere without exposure to the ambient environment. In addition, by studying the various treatments of sol-gel samples of nearly identical initial composition and thickness, it was possible to monitor changes in absolute infrared band intensities with treatment atmosphere and temperature.
EXPERIMENTAL PROCEDURES Thin-film samples were prepared by spinning multiple coatings of a hydrolyzed solution of the binary composition 1 Si0 2 .1 B 2 0 3 (3 wt. % oxides) *This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under Contract Number DE-AC04-76DP00789. Mat. Rs. Soc. Syp. Proc. Vol.
32 (1984) Published by Elsevier Science Publishing Co., Inc.
268
onto polished 1 mm thick polycrystalline silicon substrates. The solution was prepared from Si(OC2 H5 ) 4 and B(OCH 3 ) 3 in an ethanol solvent and
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