National Institute Of Materials Physics - Romania

The electronic structure of alpha-Sn (001) thin films strained compressively in-plane was studied both experimentally and theoretically. A new topological surface state (TSS) located entirely within the gapless projected bulk bands is revealed by ab initio-based tight-binding calculations as well as directly accessed by soft x-ray angle-resolved photoemission. The topological character of this state, which is a surface resonance, is confirmed by unravelling the band inversion and by calculating the topological invariants. In agreement with experiment, electronic structure calculations show the maximum density of states in the subsurface region, while the already established TSS near the Fermi level is strongly localized at the surface. Such varied behavior is explained by the differences in orbital composition between the specific TSS and its associated bulk states, i.e., their hybridization, respectively.

N-Containing graphenes obtained either by simultaneous amination and reduction of graphene oxide or by pyrolysis of chitosan under an inert atmosphere have been found to act as catalysts for the selective wet oxidation of glucose to succinic acid. Selectivity values over 60% at complete glucose conversion have been achieved by performing the reaction at 160 degrees C and 18 atm O-2 pressure for 20 h. This activity has been attributed to graphenic-type N atoms on graphene. The active N-containing graphene catalysts were used four times without observing a decrease in conversion and selectivity of the process. A mechanism having tartaric and fumaric acids as key intermediates is proposed.

The electronic structure of the SiO2/SiC (0001) interface, buried below SiO2 layers with a thickness from 2 to 4 nm, was explored using soft X-ray angle-resolved photoemission spectroscopy with photon energies between 350 and 1000 eV. The measurements have detected the characteristic k-dispersive energy bands of bulk Silicon Carbide (SiC) below the SiO2 layer without any sign of additional dispersive states, up to an estimated instrumental sensitivity of approximate to 5 x 10(9) cm 2 eV. This experimental result supports the physical picture that the large density of interface traps observed in macroscopic measurements results from dangling bonds randomized by the SiO2 rather than from Shockley-Tamm surface derived states extending into the bulk SiC. Published by AIP Publishing.

We report the structural, electronic and magnetic investigation using extended X-ray absorption fine structure spectroscopy (EXAFS), photoelectron microscopy, spin-resolved photoemission and magneto-optical Kerr effect on the properties of MnGe systems obtained by molecular beam epitaxy deposition of manganese on Ge(001) wafers annealed on temperatures between 50 and 450 C. Magnetic ordering can be achieved when the substrate temperature is higher than 250 C, when the manganese tends to diffuse into the Ge matrix and segregate in MnGe-like compounds, as proved by EXAFS. High spatial resolution photoelectron spectroscopy reveals Mn inhomogeneities in the 5-10 m range, even though Mn is found mostly in the same chemical state all over the surface.

The present work investigates the photocatalytical abatement of trichlorethylene (TCE) under simulated solar irradiation (AM 1.5). The employed catalytic materials, Au and Pd-Au nanoparticles supported on TiO2, were prepared by incipient wetness and by deposition-precipitation methods. It is found out that TCE is converted efficiently (>80%) to CI- and CO2 over all scrutinized catalysts. Typically, the metal addition enhances to some extent the photooxidation activity of TiO2 via photogenerated center dot OH radicals, electrons, and holes. The photocatalytic abatement of TCE over the same catalytic materials was examined in the presence of small amount of methanol. The idea was to convert TCE to Cl- and C-2 (ethane and ethylene) over Au and Pd-Au/TiO2 catalysts by the H-2 generated photocatalytically in situ. The experimental results evidenced that, over Pd-Au/TiO2 catalysts, hydrodechlorination (HDC) and photomineralization reactions of TCE occurs simultaneously. In contrast, Au/TiO2 is inactive to catalyze the hydrogenation of TCE. The results of TCE abatement by combined photooxidation/HDC reactions in presence of methanol are corroborated with H-2 photocatalytic generation results, over the same catalytic materials, from water/methanol mixture. A reaction mechanism is advanced in light of experimental results. The photo generated center dot OH radicals, electrons, and holes participate in a complex reaction pathway to formation of oxygenated organic intermediates, Cl-, CO2, and H-2. (C) 2016 Elsevier Inc. All rights reserved.

TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe-N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe-N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

Electrochemical impedance spectroscopy (EIS), X-ray spectroscopy (XPS), and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) interaction with the L-cysteine-thiolate covered p- and n-GaAs(100) electrodes in H2SO4 solution. The potential-induced reversible proton transfer found to occur within the L-cysteine-thiolate layer in the simple acid solution during the cathodic as well as the anodic potential scans at the p-doped semiconductor electrode and only in the anodic scan at the n-doped one is suppressed in both cases. XPS data revealed that the anionic surfactant has a complex interaction with the L-cysteine-thiolate covered GaAs(100) electrodes, which implicates both electrostatic and chemical forces. The SO42 head group interacts electrostatically with the NH3+ group of the cysteine-thiolate but it is also chemically involved in a chemisorption bond with the available Ga atoms. The amount of Ga-bound SDS species is much more pronounced at the L-cysteine-thiolate/p-GaAs(100) than at the L-cysteine thiolate/n-doped GaAs(100) electrodes meaning that cysteine-thiolate is mainly formed at As sites in the first case and at Ga sites in the latter one. This outcome strengthens the previous conclusions concerning the role of the dopant in determining the bonding way of the L-cysteine on GaAs(100) surfaces. (C) 2016 Elsevier Ltd. All rights reserved.

A multi-component reaction involving metal ion, amines and formaldehyde has been used for a series of decaaza bismacrocyclic complexes M2L(CH3COO)(4)center dot nH(2)O [(1) M: Ni, n = 2.5; (2) M:Cu, n = 1; (3) M:Zn, n = 10; L:1,3-bis(N,N-1,3,6,9,12-pentaazacyclotridecane)-benzene] preparation. Elemental analyses, ESI-MS, IR, UV-Vis-NIR, NMR and EPR spectra, magnetic susceptibility at room temperature, molar conductivities, as well as thermogravimetric analysis, provided data concerning complexes features. The macrocyclic ligand behaves as bischelate, resulting in either a square planar or an octahedral stereochemistry. The in vitro screening of the antimicrobial activity was performed against both reference and clinical isolates multi-drug-resistant strains. The overall antimicrobial potency of complexes was enhanced in comparison with the free ligand, against both planktonic and biofilm-embedded pathogenic strains. Complexes exhibit no cytotoxicity on the HCT 8 tumour cells. Thermogravimetric curves (TG, DTG and DTA) evidenced in air processes as water elimination, acetate into carbonate transformation as well as oxidative degradation of the bismacrocyclic ligand. The powder X-ray diffraction data indicate MO (M: Ni, Cu, Zn) as final product.

The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO2. High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 degrees C) and by optimizing the ratios between reactants. The calcined tubular SiO2 is characterized by intense and broad absorption band centered at approximate to 320 nm, spanning from deep UV to green. The formation of Si3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320-380 nm. The photocatalytic generation of H-2 and CO2 from water-methanol mixture under solar (AM 1.5) and visible (lambda > 390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO2 are highlighted by employing [Ru(bpy)(3)]Cl-2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields. (C) 2016 Elsevier B.V. All rights reserved.