Crystallization Studies of Glassy Te-Se-Br Thin Films
- PDF / 1,226,666 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 98 Downloads / 210 Views
CRYSTALLIZATION STUDIES OF GLASSY Te-Se-Br THIN FILMS J.L. ADAM*, C. ORTIZ*, J.R. SALEM* and X.I1. ZIIANG** *IBM Research division, Almaden Research Center, 650 ilarry Road, SAN JOSE, CA 95120-6099, U.S.A. **Laboratoire de Chimie Min6rale D, Unit6 associ~e au C.N.R.S. No. 254, Universit6 de Rennes I, Avenue du Gn&ral Leclerc, 35042 RENNES-Cedex, FRANCE
ABSTRACT We have studied the effect of laser irradiation on Te-Se-Br thin films. The major effects were found to be dominated by changes in composition because of the complete loss of Br and variable loss of Se. These losses are measured by EIDS and are reasonable in view of the temperatures obtained from a heat flow calculation. The remaining Te-Se material can be made crystalline under specific conditions of laser pulse length and laser power (which determine the cooling rate). We have been able to establish that the crystallization starts with surface filamentary growth exhibiting fractal network formation. With higher laser energy it tends to coalesce to form three dimensional crystals.
INTRODUCTION Recently, a totally new class of IR-transmitting glasses has been discovered. First based on two elements, Te and Cl, these materials have been found to vitrify in a number of binary and ternary systems of Te - Cl, Br or I - Se or S [1]. Because they transmit the 10.6gm line of the CO 2 laser, can be drawn into fibers [2], and can be deposited as thin-films [3], these materials have a tremendous potential for IR optical applications. In the present study, we report for the first time the structural changes induced by laser irradiation in these materials, specifically in a Te-Se-Br thin film. Amorphous and crystalline phases with different chemical compositions are studied.
EXPERIMENTAL METHODS The glasses used in this study have the following starting composition: Te 30Ses0 Br20 and were prepared using the method described in detail elsewhere [I]. The results of differential scanning calorimetry (D.S.C.) have shown no crystallization peaks indicating that this composition is very stable in the glassy state with little tendency to become an ordered material. 5Onm-thick films have been deposited by R.F. sputtering with a 0.11 nm s-' deposition rate on carbon-coated mica substrates at room temperature. Experimental parameters for the sputtering process may be found in Ref. [4]. As mentioned earlier [3], the sputtering of this type of material induces a loss of halogen. The composition has been analyzed by electron microprobe and was found to be Te•SesBr] 3 indicating loss of both Se and Br. A DSC scan of a bulk sample with a similar composition of our thin film shows that, contrary to the target, the thin films can exhibit a crystallization peak at 150°C. Thus, crystallization events may now be expected from this different composition. Irradiation was carried out by a Coherent 8W-argon laser beam at 514.5nm with 10 ,am FWHM diameter. The sample was mounted in a vacuum chamber where a pressure as low as 3x10-7 mmHg was routinely achieved. The experimental set-up is des
Data Loading...
