Enhancing the phase stability of ceramics under radiation via multilayer engineering

In metallic systems, increasing the density of interfaces has been shown to be a promising strategy for annealing defects introduced during irradiation. The role of interfaces during irradiation of ceramics is more unclear because of the complex defect energy landscape that exists in these materials. Here, we report the effects of interfaces on radiation-induced phase transformation and chemical composition changes in SiC-Ti3SiC2-TiCx multilayer materials based on combined transmission electron microscopy (TEM) analysis and first-principles calculations. We found that the undesirable phase transformation of Ti3SiC2 is substantially enhanced near the SiC/Ti3SiC2 interface, and it is suppressed near the Ti3SiC2/TiC interface. The results have been explained by ab initio calculations of trends in defect segregation to the above interfaces. Our finding suggests that the phase stability of Ti3SiC2 under irradiation can be improved by adding TiCx, and it demonstrates that, in ceramics, interfaces are not necessarily beneficial to radiation resistance.

Investigation of phase transformations of iron nanoparticles during thermal annealing

Structural properties and phase composition of nanoparticles based on iron oxide were studied. Mossbauer spectroscopy, X-ray diffraction, and scanning electron microscopy were used for the analysis of phase transformations. According to XRD and Mossbauer spectroscopy data, an increase in the annealing temperature, as well as the subsequent phase transformations of magnetite into maghemite and then to hematite, indicate an improvement in the structure and a decrease in microdistortions in the lattice as a result of annealing defects and vacancies. According to Mossbauer spectroscopy data at temperatures above 400°C, the lines of characteristic FeO, which are characteristic for disordered iron oxide, are observed, which also confirms the improvement of the crystal structure of nanoparticles.

MICRO-RAMAN STUDY OF SURFACE ALTERATIONS IN InGaAs AFTER THERMAL ANNEALING TREATMENTS

We present a micro-Raman study of alterations in InGaAs/InP epilayers after rapid thermal annealing. Defects consisting of protruding material with typical dimensions of a few microns can be observed on the surface of the annealed samples. Micro-Raman measurements on these defects show that they consist of In x Ga 1-x P alloys, suggesting that phosphorus diffusion from the InP substrate occurs during the RTA cycle. The defect-free region of the epilayer is also altered leading to the formation of an In 1-x Ga x As 1-y P y quaternary alloy.

Annealing of Metastable Recombination Centers in Hydrogenated Amorphous Silicon

ABSTRACTWe report results on the annealing behaviors of light- and deposition-induced metastable recombination centers, as measured by steady-state photoconductivity, in undoped hydrogenated amorphous silicon. The relaxation time inferred from the stretched-exponential time law reveals a thermally activated behavior, and the activation energies are nearly identical in both (Ea=1.1eV). This value is much less than that of the light-induced darkconductivity relaxation (Ea=1.7eV) measured simultaneously with photoconductivity. While in the deposition-induced case both activation energies of dark- and photoconductivity relaxation time are identical. These results support that there is more than one kind of defect created by light exposure, and at least, as considering activation energies for annealing defects, the light-induced recombination center differ from other metastable defects.