Giant pop-ins and amorphization in germanium during indentation

Abstract

Thermal stability of metastable silicon phases produced by nanoindentationSudden excursions of unusually large magnitude ͑Ͼ1 m͒, "giant pop-ins," have been observed in the force-displacement curve for high load indentation of crystalline germanium ͑Ge͒. A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or "elbowing," observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered.

Dramatic Changes in Thermoelectric Power of Germanium under Pressure: Printing n–p Junctions by Applied Stress

“…These Raman spectra well agreed with those observed in previous works for a metastable polymorph of germanium, prepared either in diamond anvil cells60, or by a surface nanoindentation6162. In the literature, these spectra were attributed to a simple tetragonal lattice with 12 atoms per unit cell ( st12 , space group #96 – P 4 3 2 1 2) (also known as Ge-III)606162. Whereas, other papers reported different Raman spectra, e.g., a strong peak at near 200 cm −1 , and addressed them to another metastable polymorph with a body-centred cubic lattice with 8 atoms per unit cell ( bc8 , Ge-IV)63646566.…”

“…This pressure range covered the known phase transition from the original cubic-diamond-type lattice (Ge-I) to the metal phase with the β -Sn-type lattice (Ge-II) at about 10 GPa3031323334353637383940414243444546474849. As reported earlier, upon decompression, germanium can transform to one of its metastable polymorphs, instead of turning back to the cubic-diamond-type phase (Ge-I)555657585960616263646566. To verify the crystal lattice of the recovered from high pressure samples, we examined them by Raman and X-Ray diffraction studies (Fig.…”

Molecular dynamics simulations of nanoindentation of monocrystalline germanium

“…Gogotsi et al using Raman spectroscopy found a phase transformation to occur very rarely and irreproducibly [12]. Bradby et al found that shear deformation by mechanical twinning and dislocation slip is the dominant deformation mechanism of Ge during nanoindentation [13,14]. Oliver et al found that the deformation mechanism of Ge during nanoindentation depends critically on the film thickness [15] and loading rate [16].…”

A comprehensive model for the electrical nanocontact on germanium for scanning spreading resistance microscopy applications

“…As in the case of Si, Ge undergoes a phase transformation towards a metallic-like b-Sn phase if exposed to a large enough pressure, typically in the order of $10 GPa. [19][20][21][22] It has been shown that the SSRMcontact can be described as a nano-indentation, whereby in a small volume below the probe, a high pressure is developed which can exceed the pressure range required for the phase transformation. 11 Although the affected volume is extremely small (few nm), its effect can be visualized by monitoring the impact of the force applied to the tip on the measured (spreading) resistance, leading to the so-called resistanceforce curve.…”