Mechanical properties of tungsten following rhenium ion and helium plasma exposure

Mechanical properties of Tungsten (W) samples irradiated with 2 MeV Rhenium (Re) ions and helium (He) plasma were investigated using nanoindentation. It was found that there was an increase in hardness for all samples following separate irradiation with both Re ion and He plasma. A slight increase in hardness was obtained for combined exposures. A comparable increase in hardness was observed for a pure He plasma with a sample temperature of 473 K and 1273 K. Optical interferometry was employed to compare surface modification of the samples. Grazing incidence small angle x-ray scattering confirmed He nano-bubble formation of approximately 1 nm diameter in the higher temperature sample, which was not observed with samples at the lower temperaturesPK, CC and JB acknowledge support from the Future Fellowship Scheme of the Australian Research Council (FT120100289, FT100100825 and FT130101355). This research has also been supported by the Science and Industry Endowment Fund grant (PS034)

Electric Field- And Current-Induced Electroforming Modes in NbOx

Electroforming is used to initiate the memristive response in metal/oxide/metal devices by creating a filamentary conduction path in the oxide film. Here, we use a simple photoresist-based detection technique to map the spatial distribution of conductive filaments formed in Nb/NbOx/Pt devices, and correlate these with current-voltage characteristics and in situ thermoreflectance measurements to identify distinct modes of electroforming in low- and high-conductivity NbOx films. In low-conductivity films, the filaments are randomly distributed within the oxide film, consistent with a field-induced weakest-link mechanism, while in high-conductivity films they are concentrated in the center of the film. In the latter case, the current-voltage characteristics and in situ thermoreflectance imaging show that electroforming is associated with current bifurcation into regions of low and high current density. This is supported by finite element modeling of the current distribution and shown to be consistent with predictions of a simple core-shell model of the current distribution. These results clearly demonstrate two distinct modes of electroforming in the same material system and show that the dominant mode depends on the conductivity of the film, with field-induced electroforming dominant in low-conductivity films and current bifurcation-induced electroforming dominant in high-conductivity films.This work was partly funded by the Australian Research Council (ARC) and Varian Semiconductor Equipment/ Applied Materials through an ARC Linkage Project Grant: LP150100693

Depth profiling of ion-implanted samples by high-energy electron scattering

For heavy ions implanted in low-Z targets it is possible to determine the depth and concentration of introduced heavy impurities by studying the energy spectra of electrons scattered from the surface. Here, we demonstrate this for the case of 30 and 300 keV Au implantation in SiO2. For high-energy incoming electrons the elastic peak splits up in different components as the recoil losses depends on the mass of the scattering atom. Heavy impurities also affect the partial intensities and hence changes in the shape of the energy loss spectra are observed. These effects are reproduced by a simple model that uses sample composition, atomic elastic scattering cross sections and target dielectric function as input

Effect of substrate proximity on luminescence yield from Si nanocrystals

The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.QC 2010091

Oxygen diffusion in TiO 2 films studied by electron and ion Rutherford backscattering

The diffusivity of oxygen in thin, sputter-deposited TiO2 films, as can be used in RRAMs, is measured using electron and ion backscattering techniques. The as-grown sample consisted of two layers (Ti16O2 and Ti18O2) and was annealed between 500 °C and 900 °C. The depth profiles of 18O, as measured with both techniques, were similar. The extent of diffusion was much larger than expected from the literature data for O diffusion in single-crystal rutile, suggesting that defects in the sputter-deposited film play an essential role in the diffusion proces