CRYSTAL-TO-AMORPHOUS PHASE-TRANSITION INDUCED BY MECHANICAL ALLOYING IN THE GE-SI SYSTEM

We report on the crystal-to-amorphous phase transition induced by mechanical alloying in a mixture of germanium and silicon powders. Scanning electron micrographs show that some particles exhibit particularly smooth shapes. The X-ray diffraction patterns reveal the coexistence of a crystalline diamond Ge1-xSix solid solution and an amorphous phase. Neither silicon nor germanium crystalline phases have been detected. Some particles about 100 nm in diameter exhibit a pure amorphous structure (transmission electron microscopy bright field images and selected-area diffraction patterns). Differential thermal analysis confirms the existence of an amorphous Ge-Si phase by an exothermic crystallization peak on heating. The influences of the mechanical alloying conditions and of the initial composition on the end product have been investigated. The container contamination, which has been determined by scanning electron microscopy and energy-dispersive X-ray microanalyses, has been found not to exceed 0.4 at.% Fe (no significant chromium contamination has been detected).