Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0=x=0.33) reveal that their density of states around the Fermi energy ( E(F)) is strongly reduced as x is increased. In particular, Fe2VAl ( x = 0.33) has a deep, well-developed pseudogap of 0.1-0.2 eV at E(F) and a small density ( approximately 5x10(20) cm(-3)) of carriers, which is highly unusual for intermetallic compounds. It is shown that the pseudogap results from the band structure of Fe2VAl, rather than from temperature-dependent correlation effects. Based on the present results, we propose a simple model that consistently explains both the semiconductorlike transport and the metallic photoemission results previously observed for Fe2VAl.
Optical reflectivity study has been made on the hexagonal (NiAs-type) Ni 1−δ S in order to probe its electronic properties, in particular those associated with the metal-nonmetal transition in this compound. Samples with δ=0.005 and 0.02 are studied, which have transition temperatures Tt=246 K and 161 K, respectively. A pronounced dip appears in the reflectivity spectra upon the transition, and the optical conductivity spectra show that the electronic structure below Tt is similar to that of a carrier-doped semiconductor with an energy gap of ∼ 0.15 eV. The optical spectra indicate that the gap becomes larger with decreasing temperature, and it becomes smaller as δ increases. It is also found that the overall spectrum including the violet region can be described based on a charge-transfer-type semiconductor, consistent with recent photoemission results. Keywords: D. optical properties, D. phase transitionsThe problem of the metal-nonmetal phase transition in the hexagonal NiS has been studied for three decades, but the transition mechanism is not completely understood yet. The high temperature (HT) phase above the transition temperature, T t ∼ 260 K, is a paramagnetic metal. Upon cooling through T t , the resistivity increases suddenly by a factor of ∼ 40, associated with slight increase in the lattice constants (0.3 % in a and 1 % in c) and the appearance of an antiferromagnetic order.1-3 T t is lowered sharply with increasing Ni vacancies, and the transition disappears when the vacancy content exceeds ∼ 4 %.4 Similar behavior is observed also with an applied pressure, and the transition is not observed at pressures above ∼ 2 GPa.5 These behaviors are summarized in the phase diagram of Fig. 1.The nature of the low-temperature (LT) phase below T t has been studied by many experiments. The resistivity (ρ) increases only slightly with cooling, with an activation energy of several meV.4 In contrast, an optical study by Barker and Remeika 6 clearly showed the presence of an energy gap of about 0.15 eV. Hall effect experiment by Ohtani 4 has shown that the majority carrier in the LT phase is the hole, and the density of holes is proportional to that of Ni vacancies, with ∼ 2 holes per Ni vacancy. Namely, the LT phase can be described as a p-type degenerate semiconductor, where the Ni vacancies act as acceptors. Effects of substituting other elements for Ni or S have been also studied in detail. 7,8 Recently, two high-resolution photoemission studies 9,10 have revealed a finite density of states (DOS) around the Fermi energy (E F ) in the LT phase, but they have given contrasting interpretations: Nakamura et al.9 have concluded that there is a small correlation-induced band gap with an unusually sharp band edge, and that the observed finite DOS at E F is due to thermal and instrumental broadenings of the edge. On the other hand, Sarma et al. 10 have concluded that the LT phase is an "anomalous metal".Various models have been proposed to account for the phase transition and the gap opening in NiS. At early stage, it wa...
The beamline BL7B at the UVSOR facility for solid-state spectroscopy has been opening for users after reconstruction. This beamline consists of a 3 m normal incidence monochromator and covers the spectral range from the vacuum ultraviolet to the infrared region. The optical configuration and the performance, such as photon number, purity and resolving power, are reported
Introduction: Proton beam radiotherapy is an advanced cancer treatment technique, which would reduce the effects of radiation on the surrounding healthy cells. The usage of radiosensitizers in this technique might further elevate the radiation dose towards the cancer cells. Material and methods: The present study investigated the production of intracellular reactive oxygen species (ROS) due to the presence of individual radiosensitizers, such as bismuth oxide nanoparticles (BiONPs), cisplatin (Cis) or baicalein-rich fraction (BRF) from Oroxylum indicum plant, as well as their combinations, such as BiONPs-Cis (BC), BiONPs-BRF (BB), or BiONPs-Cis-BRF (BCB), on HCT-116 colon cancer cells under proton beam radiotherapy. Results: It was found that the ROS in the presence of Cis at 3 Gy of radiation dose was the highest, followed by BC, BiONPs, BB, BRF, and BCB treatments. The properties of bismuth as a radical scavenger, as well as the BRF as a natural compound, might contribute to the lower intracellular ROS induction. The ROS in the presence of Cis and BC combination were also time-dependent and radiation dose-dependent. Conclusions: As the prospective alternatives to the Cis, the BC combination and individual BiONPs showed the capacities to be developed as radiosensitizers for proton beam therapy.
Interest in combining metallic nanoparticles, such as iron (SPIONs), gold (AuNPs) and bismuth oxide (BiONPs), with radiotherapy has increased due to the promising therapeutic advantages. While the underlying physical mechanisms of NP-enhanced radiotherapy have been extensively explored, only a few research works were motivated to quantify its contribution in an experimental dosimetry setting. This work aims to explore the feasibility of radiochromic films to measure the physical dose enhancement (DE) caused by the release of secondary electrons and photons during NP–radiotherapy interactions. A 10 mM each of SPIONs, AuNPs or BiONPs was loaded into zipper bags packed with GAFCHROMIC™ EBT3 films. The samples were exposed to a single radiation dose of 4.0 Gy with clinically relevant beams. Scanning was conducted using a flatbed scanner in red-component analysis for optimum sensitivity. Experimental dose enhancement factors (DEFExperimental) were then calculated using the ratio of absorbed doses (with/without NPs) converted from the films’ calibration curves. DEFExperimental for all NPs showed no significant physical DE beyond the uncertainty limits (p > 0.05). These results suggest that SPIONs, AuNPs and BiONPs might potentially enhance the dose in these clinical beams. However, changes in NPs concentration, as well as dosimeter sensitivity, are important to produce observable impact.
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