Undoped and Nd3+-doped TiO2 nanoparticles were synthesized by chemical vapor deposition in order to tailor the band gap of TiO2. The doping reduced the band gap. The band gap was measured by ultraviolet-visible light absorption experiments and by near-edge x-ray absorption fine structure. The maximum band gap reduction was 0.55 eV for 1.5 at. % Nd-doped TiO2 nanoparticles. Density functional theory calculations using the generalized gradient approximation with the linearized augmented plane wave method were used to interpret the band gap narrowing. The band gap narrowing was primarily attributed to the substitutional Nd3+ ions which introduced electron states into the band gap of TiO2 to form the new lowest unoccupied molecular orbital.

We present the findings of the superconductivity in the silicon nanostructures prepared by short time diffusion of boron after preliminary oxidation of the n-type Si (100) surface. These Si-based nanostructures represent the p-type high mobility silicon quantum well (Si-QW) confined by the δ-barriers heavily doped with boron. The ESR studies show that the δ-barriers appear to consist of the trigonal dipole centers, B +-B-, which are caused by the negative-U reconstruction of the shallow boron acceptors, 2B 0 → B + + B-. The temperature and magnetic field dependencies of the resistance, thermo-emf, specific heat and magnetic susceptibility demonstrate that the high temperature superconductivity observed seems to result from the transfer of the small hole bipolarons through these negative-U dipole centers of boron at the Si-QW-δ-barrier interfaces. The value of the superconductor energy gap obtained is in a good agreement with the data derived from the oscillations of the conductance in normal state and of the zero-resistance supercurrent in superconductor state as a function of the bias voltage. These oscillations appear to be correlated by on-and off-resonance tuning the two-dimensional subbands of holes with the Fermi energy in the superconductor δ-barriers. Finally, the proximity effect in the S-Si-QW-S structure is revealed by the findings of the multiple Andreev reflection (MAR) processes and the quantiza-tion of the supercurrent.

The thermal stability of anatase TiO2 nanoparticles, produced by flame synthesis, is investigated in the current study. Phase-pure anatase particles of ∼4 nm in size can be reproducibly synthesized by using a tubular burner and rotating sampler. Transmission electron microscopy (TEM), glancing incidence X-ray diffraction (XRD), and near-edge X-ray absorption fine structure (NEXAFS) were utilized to characterize the particles before and after annealing to various temperatures. TEM investigations reveal a primary particle size of ∼4 nm with standard deviations around 1 nm. XRD and selected area electron diffraction (SAED) indicate that TiO2 nanoparticles are phase-pure anatase. Our results indicate that the particles remain kinetically trapped upon annealing up to 773 K in air for 2 h. At 973 K, increases in average size, rutile content, and particle shape are observed, consistent with recent reports in the literature. NEXAFS measurements indicate that the O K-edge features of the nanoparticles show similarities to those of surfaces of bulk TiO2.

The decomposition and dehydrogenation of cyclohexene (c-C 6 H 10 ) are used as probe reactions to compare the surface reactivities of clean and carbide-modified W(111). The reaction mechanisms have been studied using temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS), and near-edge X-ray absorption fine structure (NEXAFS). On the clean W(111) surface, cyclohexene molecules decompose to produce hydrogen, atomic carbon and cyclohexane. In contrast, on the carbide-modified W(111) surface, cyclohexene undergoes primarily dehydrogenation to form benzene and hydrogen. The selectivity to the production of gas-phase benzene on C/W(111) is similar to that observed on the Pt(111) surface. † Part of the special issue "John T. Yates, Jr. Festschrift".

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