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In the light of growing importance of semiconductor nanocrystals for photonics, we report on the growth and characterization of annealed germanosilicate layers used for Ge nanocrystal formation. The films are grown using plasma enhanced chemical vapor deposition (PECVD) and post-annealed in nitrogen at temperatures between 600 and 1200°C for as long as 2h. Transmission electron microscopy (TEM), Raman scattering and photoluminescence spectroscopy (PL) has been used to characterize the samples both structurally and optically. Formation of Ge precipitates in the germanosilicate layers have been observed using Raman spectroscopy for a variety of PECVD growth parameters, annealing temperatures and times. Ge–Ge mode at ~300cm−1 is clearly observed at temperatures as low as 700°C for annealing durations for 45min. Raman results indicate that upon annealing for extended periods of time at temperatures above 900°C; nanocrystals of few tens of nanometers in diameter inside the oxide matrix and precipitation and interdiffusion of Ge, forming SiGe alloy at the silicon and oxide interface take place. Low temperature PL spectroscopy has been used to observe luminescence from these samples in the vicinity of 1550nm, an important wavelength for telecommunications. Observed luminescence quenches at 140K. The photoluminescence data displays three peaks closely interrelated at approximately 1490, 1530 and 1610nm. PL spectra persist even after removing the oxide layer indicating that the origin of the infrared luminescent centers are not related to the Ge nanocrystals in the oxide layer. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the Mo and Co on the magnetic properties and the characteristics of martensitic transformation of the Fe–Mn alloy have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, ɛ(h.c.p.) and α′(b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. The Mo or Co (5wt%) addition to the Fe-13%Mn alloy does not change coexistence of ɛ and α′ martensites between 10–15wt%Mn content. However, it stabilizes the parent phase leading to the depression of the transformation temperatures. In addition, Mössbauer spectra of the alloys reveal a paramagnetic character with a singlet for the γ(f.c.c.) austenite and ɛ martensite phases and a ferromagnetic character with a broad sextet for α′ martensite phase. The volume fractions of the phases change and the amount of α′ martensite increases significantly with the Mo or Co addition. Third element addition also influences internal magnetic field and particularly, the addition of the Mo considerably decreases the internal magnetic field in the Fe–Mn alloy. [Copyright &y& Elsevier]