N. Stojilovic

Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3

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.

Erbia-modified electrospun titania nanofibres for selective infrared emitters

Tetraisopropyl titanate (TPT) was mixed with a solution of polyvinylpyrrolidone (PVP) and the solution electrospun into nanofibres. Thermal annealing at 900 °C was used to pyrolyse the PVP, leaving nanofibres of rutile-phase titania. Erbium (III) oxide particles were also added into the solution before electrospinning, and selectively modified the near-infrared optical properties of the titania nanofibres as verified by both absorption and emission spectra. We thereby demonstrate the production of high-temperature optically functionalized nanostructures that can be used in a thermophotovoltaic energy conversion system.

Comparative dissolution of electrospun Al2O3 nanofibres in artificial human lung fluids

Sub-micron sized alumina fibres were fabricated by electrospinning and calcination of a polymer template fibre. In the calcination step, different controlled temperature heating cycles were conducted to obtain fibres of different crystalline structures. Their biodurabilities were tested at pH 7.4 with lung airway epithelial lining fluid or serum ultrafiltrate (SUF) and at pH 4.5 with macrophage phagolysosomal simulant fluid (PSF). Potential to generate free radicals was tested in vitro. Through the variation in the soak temperature from 650 °C to 950 °C (experiments S650-S950), the heating protocol affected the morphological characteristics, crystal structure, surface area, and density of the alumina fibres while their dissolution half-times were not significantly affected in SUF or PSF. Fibre samples formed at different heating ramp rates (experiments R93-R600) showed significant variation in the dissolution rates with the highest ramp rate corresponding to the highest dissolution rate. Thus, by increasing the calcination temperature ramp rate the alumina fibres may be produced that have reduced biodurability and lower inflammogenic potential. The fibres with the highest dissolution rated had the least aluminium content. The solubility half-times of the alumina fibres were shortest for fibres calcined at the fastest temperature ramp rate (though soak temperature did not have an effect). The ramp rates also affected the aluminium content of the fibres suggesting that the content may affect the structural strength of the fibres and control the dissolution.

Temperature programmed desorption study of C6H12∕Zr(0001)

Temperature programmed desorption (TPD) has been used to investigate the behavior of cyclohexane (C6H12) on Zr(0001) and the effects of 500eV electron bombardment on its desorption characteristics. Following adsorption at 150K, molecular desorption above 600K suggests exceptionally strong interaction between C6H12 and Zr(0001). These high-temperature desorption features shift to higher temperatures with increasing exposure. Electron bombardment alters TPD profiles and results in small quantities of H2 desorption from C6H12∕Zr(0001) at about 310K.

Organic molecules on zirconium surfaces

In this work, the behavior of Zr(0001) exposed to benzene (C6H6) and deuterated methanol (CD3OD) is discussed. Relatively simple surface kinetics for the C6H6/Zr(0001) and CD3OD/Zr(0001) systems are observed, with only molecular desorption detected in thermal desorption experiments. We attribute this to the presence of a passivating layer of carbon formed by the initial decomposition of these species on the reactive Zr(0001) surface. Following adsorption at 150 K, benzene desorbs at about 715 K, whereas methanol desorbs near 600 K. An increase in adsorption temperature of 20 K for C6H6 and of 10 K for CD3OD lowers desorption yields significantly. An increase in surface oxygen is observed by Auger electron spectroscopy (AES) after exposure to benzene, possibly due to surface-carbon/subsurface-oxygen exchange. AES indicates that carbon stays in the near-surface region after thermal desorption, but that oxygen diffuses into the bulk in both cases.

Effect of carbon doping on electronic transitions in Mn5Ge3

Mn5Ge3 is a ferromagnetic compound with high Curie temperature (Tc = 293 K), high spin polarization, and a good lattice match to germanium. Doping Mn5Ge3 with carbon increases Tc above room temperature and makes these compounds promising candidates for spin injectors for potential spintronics applications. The resistivity and magnetic susceptibility measurements show anisotropic behavior of these compounds. Optical spectroscopy is employed to measure near-normal reflectance of Mn5Ge3C0.89 in the frequency range from far-infrared to ultraviolet at three different temperatures (10, 200, and 300 K), and results are compared with those on pure Mn5Ge3. Both Mn5Ge3 and Mn5Ge3C0.89 have weak temperature dependence of the optical properties in the 10–300 K range, and both have similar electrodynamics responses with similar temperature trends. However, important differences in the region of interband transitions, indicating the electronic nature of the increased ferromagnetic stability of carbon doped compound, ar...

Influence of Exposure Conditions on Bacterial Adhesion to Zirconium Alloys

In this paper we combine surface analytical techniques (X-ray photoelectron spectroscopy, X-ray diffraction, infrared reflection absorption spectroscopy, optical and electron microscopy) with viable counts and statistical ANOVA methods to determine the propensity for biological adhesion on zirconium alloy surfaces. We compare the adhesion of laboratory and clinical strains of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa to Zircaloy-2 and Zircadyne-705 materials. Thermal oxidation of the alloys prior to exposure to biological species is also investigated. We present data for 72-h incubation of bacteria and alloys in both shaken and stationary environments. The results of our statistical analysis and experimental observations are relevant to the use of zirconium-based materials for biomedical applications.

Fano q-reversal in topological insulator Bi2Se3

We studied the magneto-optical response of a canonical topological insulator Bi2Se3 with the goal of addressing a controversial issue of electron-phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron-phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm(-1) phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.

Fano {\it q} reversal in topological insulator Bi

We studied the magneto-optical response of a canonical topological insulator Bi2Se3 with the goal of addressing a controversial issue of electron-phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron-phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm(-1) phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.

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We investigate the interaction of sulfur dioxide (SO2) with Zircaloy-4 (Zry-4) surfaces after adsorption at 300K. A shift in the Zr(MNN) feature toward lower energies of about 3eV is observed following saturation exposures, indicating oxidation of Zr by dissociated oxygen. Temperature programed desorption experiments indicate irreversible adsorption. Relatively short Ar-ion sputtering removes sulfur from the near-surface region without significantly affecting the oxygen Auger signal. Annealing of the SO2∕Zry-4 system results in dissolution of oxygen into the bulk, leaving sulfur in the near-surface region.