In situobservation 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.

Origin of a Nanoindentation Pop-in Event in Silicon Crystal

“…3b), the latter exhibits a relationship which does not result in any pop-in. These results led us to conclusion that the indentation deformation of silicon, although based solely on the extrusion of stressed material -as advocated by Bradby et al [13] and Gerbig et al [14,33] -is governed by two essentially different mechanisms M1 and M2.…”

“…While our MD-simulations involved cono-spherical indentation, the lion part of experiments employ pyramidal tips [15], which facilitate amorphization due to their sharpness and excessive stress-concentration near the edges. It is quite possible that the indentation deformation is dominated in such cases by the M2-mechanism, leading to frequently reported pop-in free loading path, e.g., [12,33,34].…”

Nanoindentation of Silicon and Germanium

“…2). Although such ex situ Raman can only report on the end phases present after indentation, Gerbig et al (2011) have recently carried out in situ Raman microscopy and reported the formation of r8/bc8 phases during slow unloading from the β-Sn metallic phase. Furthermore, their results suggested that the Raman signatures of these phases did not change further on complete unloading, which is consistent with our suggestion above that a metastable mixed r8/bc8 phase forms during unloading.…”

Effect of crystal orientation on the formation of bct-5 silicon

“…On loading, crystalline silicon-I transforms to metallic phases, Si-II [3] and bct-5 Si [4]. During a slow pressure release, the metallic Si-II phase transforms to BC8 (Si-III) [3][4][5][6][7] and R8 (Si-XII) [4,[8][9][10][11], but on a rapid pressure release it transforms to Si-VIII and Si-IX or a-Si [12]. Si-XIII and Si-IV phases form from Si-III and Si-XII in nanoindents located in the relatively thicker areas on the sample [13].…”