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

This dissertation addresses the issue of composition modulation in sputtered amorphous 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-Fe{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar}) system with particular emphasis on the semiconductor-rich regime. Brief excursions are made into the amorphous tungsten-germanium (a-W{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar}) and the amorphous molybdenum-germanium (a-Mo{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar}) 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, 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-Fe{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} system and a superconducting transition in the a-Mo{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} system.; A long standing question, particularly in the a-Fe{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} and the a-Mo{dollar}sb x{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} 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 application of ASAXS to this problem proves unambiguously that fine scale composition modulations, as distinct from the simple density fluctuations that arise from cracks and voids, are present in the a-Fe{dollar}sb{lcub}x{rcub}{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar}, a-W{dollar}sb{lcub}x{rcub}{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar}, and a-Mo{dollar}sb{lcub}x{rcub}{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} systems in the semiconductor-metal transition region. Furthermore, ASAXS shows that germanium is distributed uniformly through out each sample in the x {dollar}{dollar} 33 while the a-Mo{dollar}sb{lcub}x{rcub}{dollar}Ge{dollar}sb{lcub}100-x{rcub}{dollar} system is not. The ASAXS results are compared with two and three phase models.