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

Abstract

Single-crystal germanium is a semiconductor material which shows complicated phase transformation under high pressure. In this study, new insight into the phase transformation of diamond-cubic germanium (dc-Ge) was attempted by controlled cyclic nanoindentation combined with Raman spectroscopic analysis. Phase transformation from dc-Ge to rhombohedral phase (r8-Ge) was experimentally confirmed for both single and cyclic nanoindentation under high loading/unloading rates. However, compared to single indentation, double cyclic indentation with a low holding load between the cycles caused more frequent phase transformation events. Double cyclic indentation caused more stress in Ge than single indentation and increased the possibility of phase transformation. With increase in the holding load, the number of phase transformation events decreased and finally became less than that under single indentation. This phenomenon was possibly caused by defect nucleation and shear accumulation during the holding process, which were promoted by a high holding load. The defect nucleation suppressed the phase transformation from dc-Ge to r8-Ge, and shear accumulation led to another phase transformation pathway, respectively. A high holding load promoted these two phenomena, and thus decreased the possibility of phase transformation from dc-Ge to r8-Ge.

Hexagonal germanium formation at room temperature using controlled penetration depth nano-indentation

“…However, the Raman spectrum of indented Ge exhibits both a (dc-Ge) peak centered at ~301 cm −1 and an additional peak at ~202 cm −1 . This extra peak with other peaks position at 86 cm −1 , 94 cm −1 , 202 cm −1 , 225 cm −1 , and 249 cm −1 are identified to be linked to the presence of the r8 phase of Ge 24–27,43,44 . It was reported that unlike Si BC8 and R8 phases which coexist stably under ambient conditions, germanium phases R8 and BC8 are observed to transform to a hexagonal diamond phase under ambient pressure and temperature 23,43 .…”

Territorial distribution of germanium in the c5 coal seam on the territory of the “Pavlohradska” mine

“…Global demand for germanium is expected to grow to 320 -400 tons annually by 2030, and production could increase by about one-and-a-half times, according to the US Geological Survey [32]. The cost of germanium single crystals, depending on their quality characteristics, can reach 10 -15 thousand dollars per kilogram [33]. Meanwhile, approximately 100 tons of germanium are lost each year during coal mining in Donbas, which is about 45% of the known total annual production of this metal in the world.…”

Crack Propagation Behavior of Fused Silica during Cyclic Indentation under Incremental Loads

“…However, most previous indentation studies focused on individual indentations, thus the effects of incremental-load cyclic loading/unloading still remains unknown. In recent years, cyclic indentation has been attempted on brittle singlecrystalline materials such as silicon [16,17] and germanium [18,19], and it was demonstrated that multi-cyclic indentation induced completely different mechanical responses from that of individual indentations. For optical glasses, multi-cyclic indentation tests were performed by using Vickers indenters [20] and spherical indenters [21] to investigate fatigue properties, and the evolution of indentation-induced cracks during cyclic bending tests was also investigated [22].…”