Formation of Cr–germanide nanoparticles during growth of epitaxial Ge–Cr thin films

Microstructural evolution has been investigated as a function of substrate temperature in Ge–4 at.%Cr films grown by molecular beam epitaxy (MBE), by employing transmission electron microscopy (TEM); the TEM results have been correlated to the magnetic properties. Magnetometry measurements show that samples grown at substrate temperatures of 200 °C and above are paramagnetic. Significantly different microstructures have been shown to evolve, depending on the substrate temperature (<f>Ts</f>) during MBE growth. For <f>Ts=200</f> °C, the film consists of elongated rods, or “noodles” of the equilibrium Cr11Ge19 phase. For <f>Ts=400</f> °C, a nanodispersion of metastable Cr11Ge8 equiaxed precipitates form within the Ge-matrix. It is thus proposed that for <f>Ts=400</f> °C a supersaturated Ge–Cr solid-solution is initially formed from the vapor phase, followed by solid-state precipitation. At <f>Ts=200</f> °C, precipitation analogous to a cellular/discontinuous transformation results in the formation of cooperatively grown rod-like or noodle shaped microstructures. [Copyright &y& Elsevier]