Usually, SrTiO3 monodoped with Cr cations at the Ti4+ site hardly shows visible light photocatalytic activity. Revealing the origin of this issue is important for us to find an alternative approach to make SrTiO3 active under visible light irradiation. In this paper, two Cr-doped SrTiO3-(Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3-were synthesized by a conventional solid-state reaction method, and their photophysical and photocatalytic properties were studied comparatively. It was found that both (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 showed considerable absorption to visible light. However, their photocatalytic activities for H2 evolution from aqueous methanol solution under visible light irradiation were significantly different: the H2 evolution rate over (Sr0.95Cr0.05)TiO3 (approximately 21 micromol/h) was more than 100 times that over Sr(Ti0.95Cr0.05)O3 (approximately 0.2 micromol/h). X-ray photoelectron spectroscopy analysis results revealed that the Cr cations doped at the Sr2+ site were all trivalent state (Cr3+), while those doped at the Ti4+ site were mixed valent states (Cr3+ and Cr6+). The different photocatalytic activities of H2 evolution are supposed to closely relate to the different valent states of Cr doped at different sites (Sr2+ or Ti4+) in SrTiO3. Possible electronic structures of (Sr0.95Cr0.05)TiO3 and Sr(Ti0.95Cr0.05)O3 were proposed in relation to their photophysical and photocatalytic properties.

We have determined electron inelastic mean free paths (IMFPs) in C (graphite), Si, Cr, Fe, Cu, Zn, Ga, Mo, Ag, Ta, W, Pt and Au by elastic-peak electron spectroscopy (EPES) using Ni as a reference material for electron energies between 50 and 5000 eV. These IMFPs could be fitted by the simple Bethe equation for inelastic electron scattering in matter for energies from 100 to 5000 eV. The average root-mean-square (RMS) deviation in these fits was 9%. The IMFPs for Si, Cr, Fe, Cu, Ag, Ta, W, Pt and Au were in excellent agreement with the corresponding values calculated from optical data for energies between 100 and 5000 eV. While the RMS differences for graphite and Mo in these comparisons were large (27 and 17%, respectively), the average RMS difference for the other 11 elements was 11%. Similar comparisons were made between our IMFPs and values obtained from the TPP-2M predictive equation for energies between 100 and 5000 eV, and the average RMS difference for the 13 solids was 10.7%; in these comparisons, the RMS differences for Ta and W were relatively large (26% for each). A correction for surface-electronic excitations was calculated from a formula of Werner et al.; except for Si and Ga, the average correction was 5% for energies between 150 and 5000 eV. The satisfactory consistency between the IMFPs from our EPES experiments and the corresponding IMFPs computed from optical data indicates that the uncertainty of these IMFPs is about 11% for electron energies between 100 and 5000 eV. Similar comparisons with IMFPs from the EPES experiments of Werner et al. showed a consistency of 8% for energies between 200 and 5000 eV.

A Langmuir probe was used to determine the electron density, electron temperature, plasma potential and the electron energy probability function (EEPF) in O 2 /Ar plasma in a planar inductive discharge for a pressure range of 2-30 mTorr. The electron density increases with increased argon content and increases more steeply with increased argon content after the fractional argon flowrate has reached 50%. The measured dc plasma potential and the average electron energy gradually decrease with increased argon content. Mass spectroscopy indicates that the [O + 2 ]/[O + ] ratio increases with increased pressure and decreases with increased fractional argon flowrate. The measured values are compared to global model (volume averaged) calculations assuming a Maxwellian electron energy distribution.

A ternary silicide Ca(Al0.5,Si0.5)2 was prepared by Ar arc melting. Powder x-ray diffraction measurement indicates that it has the AlB2-type structure with lattice constants of a=4.1905(5) and c=4.3992(8) Å, where Si and Al atoms are arranged in the disordered honeycomb lattice and Ca atoms are intercalated between them. The silicide is isostructural with a superconductor MgB2. Electrical resistivity and dc magnetization measurements revealed that it is a superconductor with a TC of 7.7 K.

The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively-coupled radio frequency (RF, 13.56 MHz) Ar/CF 4 discharge over a pressure range 3-30 mTorr by changing the CF 4 content from 0 to 20%, while keeping the power injected into the plasma at about 50 W. EEDFs measured at a pressure lower than 10 mTorr are bi-Maxwellian distributions over the measured CF 4 content, while those at a pressure of 30 mTorr are Druyvesteyn ones in the presence of a small amount of CF 4 . The average electron energy slightly increases with CF 4 content, while the electron density decreases. The decrease in the electron density with addition of CF 4 is more prominent as the total pressure increases. Dependences of the electron density and the averaged electron energy on CF 4 content are predicted in the global model.