We investigated Raman vibrational modes in silicon-germanium-tin layers grown epitaxially on germanium/silicon virtual substrates using reduced pressure chemical vapor deposition. Several excitation wavelengths were utilized to accurately analyze Raman shifts in ternary layers with uniform silicon and tin content in 4–19 and 2–12 at. % ranges, respectively. The excitation using a 633 nm laser was found to be optimal leading to a clear detection and an unambiguous identification of all first order modes in the alloy. The influence of both strain and composition on these modes is discussed. The strain in the layers is evaluated from Raman shifts and reciprocal space mapping data and the obtained results are discussed in the light of recent theoretical calculations.

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Sn-containing group IV semiconductors provide a rich playground to independently engineer the band structure and lattice parameter with a potential impact of a variety of silicon-based electronic and optoelectronic devices. The introduction of these metastable alloys in device fabrication raises a number of concerns regarding the possible degradation of their composition and structural properties during different processing steps. With this perspective, in this work we present detailed in situ and ex situ investigations of the thermal behavior of both Sn-rich binary and ternary alloys. We used low energy electron microscopy and photoelectron emission electron microscopy to examine in real time the evolution of surface structure and composition during thermal annealing. These in situ studies are augmented using several ex situ characterization techniques. These investigations unraveled unprecedented details about the phase separation in these two systems. Particularly, in Ge0.84Si0.04Sn0.12 annealing above 410 °C leads to the formation of randomly distributed Sn-rich particles which grow as the annealing temperature increases. Additionally, the binary alloy Ge0.88Sn0.12 seems to be relatively more stable as compared to the ternary alloy with the same Sn content. The Sn-rich particles in the former system are not randomly distributed, but they are found to follow a well defined pattern on the surface along the <110> direction. The mechanisms and regimes involved in the phase separation are also briefly presented.

This paper presents a simple and effective approach to increase the normal zone propagation velocity (NZPV) in (RE)BaCuO thin films grown on a flexible metallic substrate. The concept is an extension of the current-flow-diverter concept already known in the literature. The key idea behind the novel approach is to use a specific geometry of the silver thermal stabilizer that surrounds the superconducting tape. More specifically, a very thin layer of silver stabilizer is deposited on top of the superconductor layer, typically less than 100nm, while the remaining stabilizer (still silver) is deposited on the substrate side. Normal zone propagation velocities up to 170cm s −1 at 77K have been measured experimentally for the first time with this novel architecture, corresponding to a stabilizer thickness of 20nm on top of the superconductor layer. This is at least one order of magnitude faster than the NZPV speeds measured on commercial 2G HTS tapes. Our results clearly demonstrate that a very thin stabilizer on top of the superconductor layer leads to high normal zone propagation velocities. The experimental values are in good agreement with predictions realized by finite element simulations. Furthermore, the propagation of the normal zone during the quench was recorded in situ and in real time using a high-speed camera. Due to high Joule losses generated on both edges of the tape sample, a 'Ushaped' profile could be observed at the boundaries between the superconducting and the normal zones, which matches very closely the profiles predicted by the simulations. The most direct application of this new HTS tape architecture is in high field magnets, since faster quench propagation allows easier detection and protection, which is likely to accelerate substantially the development of HTS magnets used as high-field MRI/NMR systems, etc.