<i>In situ</i>observation of the indentation-induced phase transformation of silicon thin films

Abstract

Indentation-induced phase transformation processes were studied by in situ Raman microspectroscopy of the deformed contact region of silicon on sapphire samples during contact loading and unloading. During loading, the formation of Si-II and another phase, indentified as the bct5 structure, was observed, thus providing experimental evidence for both the existence of the bct5 phase and the possibility of generating this phase under indentation conditions. The pressure dependence of the Raman phonon frequencies for the bct5 modes was determined. During unloading, the transformation of the bct5 phase into the metastable bc8 (Si-III) and r8 (Si-XII) structures was observed. The measurements indicated that bc8 can form simultaneously with the r8 structure in indentation tests rather than subsequently from r8 in a separate process as previously assumed.