Microstructural evolution and metastable phase formation in laser ablation-deposited films of Fe-rich Fe-Ge intermetallic compounds

Abstract

Thin films of Fe-rich Fe-18 at% Ge and Fe-25 at% Ge were deposited by a pulsed laser ablation technique on single crystal NaCl substrates at room temperature to study phase evolution using transmission electron microscopy. As-deposited films contain nano-scale clusters embedded in a featureless matrix. Quadrupole mass spectrometric observations of the laser-ablated plume show the presence of charged clusters. During in situ heating of the films, the fine-scale clusters grow and profuse crystallization to a bcc FeGe solid solution occurs. For Fe-25?at% Ge thin film, crystallized bcc grains undergo two ordering transitions, viz. bcc→ B2→ DO₃, during subsequent cooling to room temperature. However, in the case of Fe-18 at% Ge thin film, crystallization leads to formation of the disordered bcc phase. Growth morphologies of the crystals formed during heat treatment indicate faceted growth form, which has been explained by using Jackson's interface model.