On the method of photoluminescence spectral intensity ratio imaging of silicon bricks: Advances and limitations J. Appl. Phys. 112, 063116 (2012) Measurement of net dopant concentration via dynamic photoluminescence J. Appl. Phys. 112, 063704 (2012) Luminescence and deep-level transient spectroscopy of grown dislocation-rich Si layers AIP Advances 2, 032152 (2012) The role of excess minority carriers in light induced degradation examined by photoluminescence imaging J. Appl. Phys. 112, 033703 (2012) Effect of hydrofluoric acid concentration on the evolution of photoluminescence characteristics in porous silicon nanowires prepared by Ag-assisted electroless etching method

Magnetically doped semiconducting topological insulators J. Appl. Phys. 112, 063912 (2012) Effect of the thickness of the MoO3 layers on optical properties of MoO3/Ag/MoO3 multilayer structures J. Appl. Phys. 112, 063505 (2012) Local conductivity and the role of vacancies around twin walls of (001)−BiFeO3 thin films We report on systematic study of photoluminescence properties of nanocrystalline titanium dioxide films consisting of predominantly anatase nanoparticles with diameters larger than 13 nm. We measured photoluminescence under two selected excitation wavelengths ͑325 nm/442 nm, i.e., above/below band gap excitation͒, under different values of ambient air pressure ͑5-10 5 Pa͒, and in the temperature interval 10-300 K. On basis of our results, we are able to distinguish two different processes leading to photoluminescence: the exciton recombination and the recombination of carriers in the energy states related to the surface of nanocrystals. We propose microscopic models describing well the effects of temperature and ambient conditions on photoluminescence of nanocrystalline titanium dioxide films.

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of X-ray diffraction experiments conducted at 300, 275 and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present X-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (∼ 290 K) and than to a triple CeCoAl superstructure at ∼ 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the γ → α transition in elementary Cerium, suggesting that similar physics, i.e. , a Kondo influenced transition and strong lattice vibrations might be the driving forces.

We have investigated the magnetic response of residual metal catalyst in the raw and super purified HiPco single wall carbon nanotubes (HiPco_raw and HiPco_SP SWCNTs). It has been shown that the residual metal catalyst is in the form of nanoparticles, even in the HiPco_SP SWCNTs that should contain a minimal amount of the metal. M€ ossbauer spectroscopy of the HiPco_raw SWCNTs proved the catalyst nanoparticles are in the form of Fe 3 C. Analysis of the synchrotron X-ray diffraction data provided an average diameter of nanoparticles about 1.9 nm. Magnetic studies by means of temperature dependence of magnetization, magnetization isotherms and susceptibility suggested that the nanoparticles obey the behavior of weakly interacting superparamagnetic systems in both samples. Further analysis of the data revealed a coreÀshell structure of the nanoparticles in the HiPco_raw nanotubes, with a magnetically oriented core and a paramagnetic shell, which is almost removed in the case of the HiPco_SP catalyst nanoparticles.

An anomalous behavior of the lattice parameters is reported for RTAl and R͑T , TЈ͒Al compounds, with R a rare-earth element and T and TЈ transition metals or Cu. In these compounds, which crystallize in the hexagonal ZrNiAl-type of structure, an abrupt transition in the temperature or composition dependence of the lattice constants a and c is observed with the common feature that values of the c / a ratio around 0.565-0.575 are generally not realized. Total-energy calculations based on density-functional theory show the occurrence of two close energy minima, which explains the observed structural instability and the associated transitions.