Pressure-induced transformations in amorphous Si-Ge alloy

Abstract

The pressure behavior of an amorphous Si-rich SiGe alloy (a-SixGe1−x, x=0.75) has been investigated up to about 30 GPa, by a combination of Raman spectroscopy, x-ray absorption spectroscopy and x-ray diffraction measurements. The trends of microscopic structural properties and of the Raman-active phonon modes are presented in the whole pressure range. Nucleation of nanocrystalline alloy particles and metallization have been observed above 12 GPa, with a range of about 2 GPa of coexistence of amorphous and crystalline phases. Transformations from the amorphous tetrahedral, to the crystalline tetragonal (β-Sn) and to the simple hexagonal structures have been observed around 13.8 GPa and 21.8 GPa. The recovered sample upon depressurization, below about 4 GPa, shows a local structure similar to the as-deposited one. Inhomogeneities of the amorphous texture at the nanometric scale, probed by high resolution transmission electron microscopy, indicate that the recovered amorphous sample has a different ordering at this scale, and therefore the transformations can not be considered fully reversible. The role of disordered grain boundaries at high pressure and the possible presence of a high-density amorphous phase are discussed.

Single Hit Energy-resolved Laue Diffraction

“…Of particular interest is in-situ x-ray diffraction, which has been used to investigate the structure of materials in laser compression experiments. Techniques exist to probe both single and polycrystalline samples, with phase transitions and plasticity having been observed in a growing number of materials [12][13][14][15][16] . One such method is in-situ Laue diffraction.…”

Pressure-induced metallization and amorphization inVO2(A)nanorods

“…Among various physical properties, pressure-induced metallization (PIM) is one of the most important concerns in the study of amorphization since the first discovery of a density driven metallization in semiconducting amorphous silicon, which stimulated a surge of study in various amorphous tetrahedrally coordinated materials, including Ge [2,16], GaSb [17], other alloys like Si-Ge alloy [18], and even glassy SiO 2 , GeO 2 [19,20]. Up to now, most studies are limited on pressure-induced nonmetallic amorphous to metallic amorphous transition.…”

Revisiting Stabilities of Cubic Zincblende IV‐IV Materials From Density Functional Theory

“…[38,39] For Si 1Àx Ge x alloys, the grown of high quality materials is laborious to achieve with standard deposition techniques such as MBE or Chemical Vapor Deposition (CVD) due to the strain energy which emerge from the %4% lattice mismatch between Si and Ge, and to the segregation coefficients of Si and Ge, which vary with Ge composition and differ markedly from unity. Si-rich amorphous Si x Ge 1Àx (x ¼ 0.75) [40] was grown with MBE, where amorphous Si x Ge 1Àx (x ¼ 0.2, 0.4, 0.6 and 0.8) [41] was created by co-sputtering. For Si 1Àx Sn x alloys, a polycrystalline growth study has been conducted on amorphous Si 1Àx Sn x layers with Sn composition of 2-30%.…”