Anomalous small angle x-ray scattering studies of amorphous metal-germanium alloys

Abstract

This dissertation addresses the issue of composition modulation in sputtered ,, amorpnous metal-germanium thin films with the aim of understanding the intermediate range structure of these films as a function of composition. The investigative tool used in this work is anomalous small-angle X-ray scattering (ASAXS).The primary focus of this investigation is the amorphous iron-germanium (a-FexGel00-x) system with particular emphasis on the semiconductor-rich regime. Brief excursions are made into the amorphous tungsten-germanium (a-WxGeloo.x) and the amorphous molybdenum-germanium (a-MoxGeloo. x) systems. All three systems exhibit an amorphous structure over a broad composition range extending from pure amorphous germanium to approximately 70 atomic percent metal when prepared as sputtered films. Across this composition range the structures change from the open, covalently bonded, IIi tetrahedral network of pure a-Ge to densely packed metals. The structural changes are accompanied by a semiconductor-metal transition in all three systems as well as a ferromagnetic transition in the a-FexGeloo,x system and a superconducting transition in the a-MoxGe 100-x_ystem.A long standing question, particularly in the a-FexGel00, x and the a-MoxGe_oo, x systems, has been whether the structural changes (and therefore the accompanying electrical and magnetic transitions) are accomplished by homogeneous alloy formation or phase separation. Several structural analysis tools have already been applied to this question with limited, and in some cases contradictory, results.

The Chemically-Specific Structure of an Amorphous Molybdenum Germanium Alloy by Anomalous X-ray Scattering

“…The average amorphous sample density was assumed to be 95% of the weighted average of the number densities for crystalline Ge and α-MoGe 2 [91]. The assumption that the amorphous density is 95% of the linear combination of the crystalline densities is widely used and has proven to be reasonable.…”