Cold nanoindentation of germanium

Abstract

Diamond cubic Ge is subjected to high pressures via nanoindentation at temperatures between À45 C and 20 C. The residual impressions are studied using ex-situ Raman microspectroscopy and cross-sectional transmission electron microscopy. The deformation mechanism at 20 C is predominately via the generation of crystalline defects. However, when the temperature is lowered, the analysis of residual indentation impressions provides evidence for deformation by phase transformation and formation of additional phases such as r8-Ge, hd-Ge, and amorphous Ge. Furthermore, these results show that at 0 C and below, dc-Ge will reliably phase transform via nanoindentation.

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

“…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.…”

“…For both testing modes, pop-in events marked by arrows in Figure 2 are observed during the loading process under various loading/unloading rates. This event was reported as a result of slip generation in dc-Ge sample and/or phase transformation to (β-Sn)-Ge [10,14]. In addition to the pop-in event during loading, unloading also showed some specific deformation events, i.e., pop-out and elbow as illustrated in Figure 3.…”

“…Compared with the main peak of pristine dc-Ge at 301 cm −1 , the corresponding peaks obtained from the indents show a little higher wavenumber as a result of compressive stress [14,23]. Furthermore, a broad component below 290 cm −1 corresponding to a-Ge and some peaks around 203, 225, and 247 cm −1 corresponding to r8-Ge phases [6,9,10,14] are observed. Bc8-Ge also shows very similar peaks to those of r8-Ge [6,11] and thus, it is difficult to distinguish these two phases from Raman data [9].…”

“…In addition to the pop-in event during loading, unloading also showed some specific deformation events, i.e., pop-out and elbow as illustrated in Figure 3. The correlation between these events and phase transformation has been established for indentation of Si [23][24][25][26][27][28] and cold indentation of Ge [10]. At room temperature, ultra-fast indentation of dc-Ge also triggered these phenomena [8], but the correspondence of these events with phase transformation was not clearly addressed.…”

“…Previous studies reported that diamond cubic Ge (dc-Ge) transforms to metallic (β-Sn)-Ge at a pressure of~10 GPa [1][2][3][4]. When the pressure releases, this metallic phase transforms to various metastable structures depending on the experimental conditions, such as simple tetragonal phase (st12-Ge) [5][6][7][8], rhombohedral phase (r8-Ge) [6,7,9,10], body centered cubic phase (bc8-Ge) [5,6,11], as well as amorphous Ge (a-Ge) and dc-Ge as end phases [8,11]. Another phase of hexagonal diamond Ge (hd-Ge) is also confirmed by compression of a-Ge [9,12,13].…”