We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined ...plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.
Effects of clinical X-ray irradiation on UHMWPE films Stojilovic, N.; Dordevic, S.V.; Stojadinovic, S.
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
11/2017, Letnik:
410
Journal Article
Recenzirano
Irradiation of biocompatible polymers is generally performed using 60Co gamma sources delivering high doses of radiation, ranging from kGy to MGy levels. This irradiation is typically employed for ...sterilization and/or crosslinking purposes. However, exposure to gamma rays may generate free radicals responsible for polymer degradation and, therefore, studies of the irradiation effects on these polymers are of great practical interest. In this study, ultra-high molecular weight polyethylene (UHMWPE) films were exposed to high-energy photons to doses comparable to those used in radiotherapy for patients with cancer. Specifically, three dose levels of 30, 60, and 120Gy were delivered utilizing linear accelerator X-rays (6MV) and irradiation effects were studied using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Ultraviolet–visible (UV–vis) spectroscopy. It was found that radiation doses up to 120Gy do not change the polymer crystallinity but affect its optical properties. In particular, the decrease in the optical band gap is observed in irradiated polymers.
Electrospinning of a sol-gel and polymer mixture is used to produce titania-alumina (TiO2–Al2O3) fibers with diameters ranging from 200 to 800 nm. These composite metal-oxide fibers were calcined at ...various temperatures and their morphology is studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decrease in the average diameter of the fibers with increasing temperature is observed. Powder X-ray diffraction (XRD) reveals that up to 800 °C the composite fibers have anatase titania structure whereas at 900 °C the fibers exhibit mixture of anatase and rutile phases. It is found that specific surface area decreases as a function of temperature in the 700–900 °C range. The change in phase (anatase-to-rutile) and the increase in crystallite size occur simultaneously. The presence of smaller amount of amorphous alumina in the primarily titania-based structure seems to play the role in stabilizing the anatase phase.
► Composite titania-alumina nanofibers were successfully prepared. ► Calcination changes morphology and increases the crystallite size. ► Delayed anatase-to-rutile transition was observed. ► The specific surface area of the fibers decreased above 700 Celsius.
This article presents an overview of the surface chemistry of zirconium, focusing on the relationship of what is known from model studies and how this connects to current and future applications of ...Zr-based materials. The discussion includes the synergistic nature of adsorbate interactions in this system, the role of impurities and alloying elements, and temperature-dependent surface–subsurface transport. Finally, some potential uses of zirconium and its alloys for biomedical and nanolithographic applications are presented.
Titania nanofibers were synthesized by electrospinning and characterized with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The nanofibers were annealed to ...773
K to achieve the anatase titania crystal structure, and to 1173
K to obtain the rutile phase. In order to create erbia-containing titania nanofibers, erbium (III) oxide particles were added to the pre-cursor solution before electrospinning. After pyrolysis the titania nanofibers supported and encapsulated the erbia particles. Temperature-dependent near-infrared emission spectra demonstrate that the erbia-containing nanofibers emit selectively in the range 6000–7000
cm
−1. Because of their large surface to volume ratios and narrow-band optical emission, these nanofibers can be used as selective emitters for thermophotovoltaic applications.
We investigate the adsorption of CO2 onto Zircaloy-4 (Zry-4) surfaces at 150, 300 and 600K using Auger electron spectroscopy (AES). Following CO2 adsorption at 150K the graphitic form of carbon is ...detected, whereas upon chemisorption at 300 and 600K we detect the carbidic phase. As the adsorption temperature is increased, the carbon Auger signal increases, whereas the oxygen signal decreases. Adsorption at all three temperatures results in a shift of the Zr Auger features, indicating surface oxidation. The effect of adsorbed CO2 on the Zr(MVV) and Zr(MNV) transitions depends on adsorption temperature and is less pronounced at higher temperatures. On the other hand, changes in the Zr(MNN) feature are similar for all three adsorption temperatures. The changes in the Zr Auger peak shapes and positions are attributed to oxygen from dissociated CO2, with the differences observed at various temperatures indicative of the diffusion of oxygen into the subsurface region.
Understanding and controlling the interaction of water with solid surfaces is relevant from both technological and fundamental viewpoints. Since Zircaloy-4 serves as a structural magerial exposed to ...hot water in nuclear reactors, understanding the oxidation by water is of applied interest, The interaction of H2O with Zircaloy-4 (Zry-4) is investigated using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) methods. Following adsorption of H2O at 150 K the Zr(MNV) and Zr(MNN) Auger features shift by -6.5 and 4.5 eV, respectively, indicating surface oxidation. Heating H2O/Zry-4 results in molecular desorption of water at both low and high temperatures. The low-temperature desorption is attributed to ice multilayers, whereas, three overlapping high-temperature features are presumably due to recombinative desorption. This high-temperature desorption begins before the surface oxide is dissolved, continues upon its removal, and is atypical for water/metal systems. Unexpectedly, no significant desorption of hydrogen is observed near 400 K, as is typically observed following O2 adsorption on Zr-based materials. However, we do observe that H2O adsorption on Zry-4 surfaces roughened by argon ion sputtering results in H2 desorption.
Non-woven fibers were produced by sol-gel and electrospinning methods, from a solution containing cerium nitrate, zinc acetate, titanium isopropoxide, polyvinylpyrrolidone, acetic acid, ethanol, and ...water. The fibers were calcined at various temperatures ranging from 300 to 900 °C and were characterized using Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, Energy Dispersive X-ray (EDX), Raman spectroscopy, Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Structural characterization revealed the fluorite nanocrystalline phase of ceria (CeO2) at all temperatures, the wurtzite zinc oxide (ZnO) phase in the 300–500 °C range, and a variety of zinc titanate phases (such as ZnTiO3, Zn2Ti3O8 and Zn2TiO4) at higher temperatures. Titania (TiO2) phases were not observed following calcination up to 900 °C. The average ceria nanocrystallite size increases with calcination temperature, as revealed by XRD and confirmed by the Phonon Confinement Model (PCM) of Raman spectra. The opposite trend is observed for the BET specific surface area of the nanofibers, where this value decreases with calcination temperatures above 400 °C. These nanofibers containing ceria and zinc titanates are potential candidates for photocatalytic applications.
•Composite metal-oxide nanofibers are produced from cerium, titanium, and zinc precursors using sol-gel and electrospinning methods.•Fluorite nanocrystalline phase of ceria dominates at all temperatures, the wurtzite zinc oxide phase forms in the 300–500 °C range.•Titania phases were not observed following calcination up to 900 °C.•The average ceria nanocrystallite size increases with calcination temperature, whereas the specific surface area has opposite trend above 400 °C.
In this Letter, we compare the effects of 500 eV electron bombardment on the thermal desorption of benzene (C
6H
6) and cyclohexane (C
6H
12) from Zr(0
0
0
1) surfaces. In both cases, unexpectedly ...high desorption temperatures above 600 K indicate strong adsorbate-substrate interaction. Two desorption states are observed for each molecule, presumably due to tilted and flat molecular orientations. Electron fluence does not significantly alter the amount of desorbing species, but for C
6H
12/Zr(0
0
0
1) results in small amounts of H
2 desorption near 310 K. Electron bombardment seems to affect the tilted species more than the flat-lying species.
