Phase transformation pathways in amorphous germanium under indentation pressure

Abstract

Nanoindentation-induced phase transformations have been studied in amorphous Ge thin films. These films initially tend to deform via plastic flow of the amorphous phase under load but at a critical pressure a sudden phase transformation occurs. This transformation, to a soft metallic (b-Sn-like)-Ge phase confined under the indenter, is signified by a "pop-in" event on loading. Following "pop-in," the indentation tests fall into two distinct types of behavior. In one case, the rate of deformation with increasing load after "pop-in" increases, and the observed end-phase following complete unloading is observed to be predominately diamond-cubic Ge. In the other case, the deformation rate (slope of the loading curve) remains the same as that before "pop-in," and the end phases following unloading are found to contain predominantly unstable r8 and more stable hexagonal Ge phases. The different transformation pathways for these two cases are shown to be related to the probability that the soft (b-Sn-like)-Ge phase volume, which suddenly forms at the transformation pressure, is either unconstrained by the indenter tip (the first case) or totally constrained under the indenter tip (in the latter case). V C 2014 AIP Publishing LLC.

Comparative Study of Phase Transformation in Single-Crystal Germanium during Single and Cyclic Nanoindentation

“…Hence, the dominant cause of the observed pop-in events is expected to be defect nucleation rather than phase transformation. There is another possibility for the cause of pop-in events by phase transformation to intermediate (β-Sn)-Ge then ending up as dc-Ge, which was reported in indentation on a-Ge [14][15][16][17]. However, it is impossible to distinguish this possibility in our experiment because the end phase is the same as the initial phase.…”

“…To ensure that the residual phases were minimally affected by further phase transformation at room temperature [5,11,13], the measurement of residual phases in indents was performed within three hours after indentation. In previous studies, some specific deformation responses, for example pop-in, pop-out, and elbow have been reported in indentation studies of Si [20][21][22][23][24][25][26][27][28] and Ge [8,10,11,[14][15][16]23]. In this study, the effects of experimental parameters on these deformation responses were statistically analyzed as well as phase transformation process during both single and cyclic indentation.…”

Nanoindentation of Silicon and Germanium

“…The experimental peak positions for r8-Ge, hd-Ge, and dc-Ge are also indicated. Reprinted with permission from Deshmukh et al (2014). Copyright (2014), American Institute of Physics.…”

“…While the SAD pattern of "type I" indexed to hd-Ge, the "type II" SADP indexed to dc-Ge. Reprinted with permission from Deshmukh et al (2014). Copyright (2014), American Institute of Physics.…”

“…The recent work of Deshmukh et al (2014) has revealed distinctly different transformation pathways in a-Ge depending on the indentation loading/ unloading conditions and the morphology of the initial metallic (β-Sn)-Ge formed under the indenter during loading. This work is summarized below.…”