Highly active V-TiO2 for photocatalytic degradation of methyl orange

Two kinds of vanadium-doped TiO₂ powders photocatalysts were prepared by sol-gel method in even doping and uneven doping modes, and were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of TiO₂ photocatalysts doped by vanadium evenly with lower dopant level up to 0.002 mol.% is better than that of undoped TiO₂, while with higher dopant level the activity is worse. TiO₂ photocatalysts doped by vanadium unevenly with a p-n junction semiconductor structure, was shown to have a much higher photocatalytic destruction rate than that of TiO₂ photocatalysts doped by vanadium evenly and undoped TiO₂, which is ascribed mainly to the electrostatic-field-driven electron-hole separation in TiO₂ particles doped by vanadium unevenly.     

Spin asymmetry and s-electron itinerancy in Co/X (X=Co,Cu, V and Ta) multilayers: their dependence on the electronegativity of non-magnetic layers

The electronic structure and magnetic properties of the Co at the Co/X (X=Co, Cu, V and Ta) interfaces have been studied by first-principle discrete variational method. We have found that the spin asymmetry and the s-electron itinerancy of the Co interface layer in the Co/X systems are strongly dependent on the electronegativity of the non-magnetic layers. A large difference in the electronegativity between the non-magnetic and Co layers is unfavorable both for s-electron itinerancy and for the spin exchange split of DOS at the Fermi level. Further study on charge density has revealed that a bond is formed across the Co/V and Co/Ta interfaces.     

Photoluminescence and transport in selectively doped p-GaAs/AlGaAs quantum wells: manifestation of the upper Hubbard band

By selective doping (Be) of the well and barrier regions of GaAs/Al_0.3Ga_0.7As structures we have realized the situation where the upper Hubbard band (A⁺ centers) has been occupied by holes in the equilibrium. We studied the temperature behavior of the Hall effect, variable range hopping (VRH) conductivity and the photoluminescence (PL) spectra of the corresponding structures. The experimental data demonstrated that the binding energy of the A⁺ states significantly increases with respect to 3D case and strongly depends on the well width (9 nm, 15 nm). The localization radii of the A⁺ states estimated from the transport data are of the order of the well widths.     

Chemical states of dodecanethiolate-passivated Au nanoparticles: synchrotron-radiation photoelectron spectroscopy

We have carried out a photoemission study using synchrotron radiation of dodecanethiolate (DT)-passivated Au nanoparticles supported on the highly oriented pyrolytic graphite substrates. From detailed line-shape analyses of Au 4f core-level photoemission spectra of DT-passivated Au nanoparticles, it was found that Au 4f core-level spectra consist of two components. We attribute these components to the inner Au atoms and surface Au atoms bonded to surface dodecanethiolates. From these results, we discuss the chemical states of the present DT-passivated Au nanoparticles.     

Study on the mechanisms of photoinduced carriers separation and recombination for Fe-TiO2 photocatalysts

The iron(III)-ion doped TiO₂ (Fe³⁺-TiO₂) with different doping Fe³⁺ content were prepared via a sol-gel method. The as-prepared Fe³⁺-TiO₂ nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe³⁺-TiO₂ catalysts with different Fe³⁺ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe³⁺-TiO₂ was revealed: that is, the Fe³⁺ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti ≤ 0.03 mol%); while Fe³⁺ dopant content exceeds 0.03 mol%, Fe₂O₃ became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe₂O₃ with TiO₂ leads to that the photoinduced electrons and holes of TiO₂ transfer to Fe₂O₃ and recombine quickly, which is unfavorable to the photocatalytic reaction.     

Adsorption of gold on hydrogen terminated Si(0 0 1): Formation of chain structure

Possible formation of stable Au atomic wire on the hydrogen terminated Si(0 0 1): 3×1 surface is investigated under the density functional formalism. The hydrogen terminated Si(0 0 1): 3×1 surface is patterned in two different ways by removing selective hydrogen atoms from the surface. The adsorption of Au on such surfaces is studied at different sub-monolayer coverages. At 4/9 monolayer (ML) coverage, zigzag continuous Au chains are found to be stable on the patterned hydrogen terminated Si(0 0 1): 3×1 surface. The reason for the stability of the wire structures at 4/9 ML coverage is explained. It is to be noted that beyond 4/9 ML coverage, the additional Au atoms may introduce clusters on the surface. The continuous atomic gold chains on the substrate may be useful for the fabrication of atomic scale devices.     

Injection of holes at indium tin oxide/dendrimer interface: An explanation with new theory of thermionic emission at metal/organic interfaces

The traditional theory of thermionic emission at metal/inorganic crystalline semiconductor interfaces is no longer applicable for the interface between a metal and an organic semiconductor. Under the assumption of thermalization of hot carriers in the organic semiconductor near the interface, a theory for thermionic emission of charge carriers at metal/organic semiconductor interfaces is developed. This theory is used to explain the experimental result from Samuel group [J.P.J. Markham, D.W. Samuel, S.-C. Lo, P.L. Burn, M. Weiter, H. Baessler, J. Appl. Phys. 95 (2004) 438] for the injection of holes from indium tin oxide into the dendrimer based on fac-tris(2-phenylpyridyl) iridium(III).     

The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface potential step and BCS-BEC crossover

The chemical potential μ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for μ for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between μ and the energy per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional many-body system with delta function interactions, exhibiting a BCS-BEC crossover. It is shown that in the BCS regime the chemical potential can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit.     

Calculation of photoemission characteristics for a semiconductor model with s-like valence band and p-like conduction band

The dependence of the quantum yield and photocurrent density on Light frequency is theoretically studied for various orientations of the emission surface for the semiconductor model with simple cubic lattice and s-like valence band and p-like conduction band, and it is assumed that electron photoexcitation occurs due to indirect optical transitions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 100–104, August, 1977.     

The surface of TiO2 gate of 2DEG-FET in contact with electrolytes for bio sensing use

In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO₂ thin films (13-17 nm) prepared with the sol-gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO₂ thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO₂/2DEG-FETs in this study exhibit a high sensitivity (410 mV/mM) for H₂O₂ detection. TiO₂ surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces.     

Revisiting Laughlin’s Hamiltonian for the chiral spin liquid

It is demonstrated that finding a parent Hamiltonian for the chiral spin liquid remains an open problem. The one existing solution in the literature [Ann. Phys. 191 (1989) 163] is shown to fail both numerically and analytically, due to a non-commutativity of certain lattice sums.     

Selective floating gate non‐volatile paper memory transistor

Here we report the performance of a selective floating gate (V_GS) n‐type non‐volatile memory paper field‐effect transistor. The paper dielectric exhibits a spontaneous polarization of about 1 mCm^–2 and GIZO and IZO amorphous oxides are used respectively as the channel and the gate layers. The drain and source regions are based in continuous conductive thin films that promote the integration of fibres coated with the active semiconductor. The floating memory transistor writes, reads and erases the stored information with retention times above 14500 h, and is selective (for V_GS > 5 ± 0.1 V). That is, to erase stored information a symmetric pulse to the one used to write must be utilized, allowing to store in the same space different information. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semiconductor–metal–semiconductor transition: valence band photoemission study of Ag/Si(1 1 1) surfaces

The , and 6×6 phases of Ag/Si(1 1 1) have been studied by angle-resolved photoemission and low-energy electron diffraction. The Ag/Si(1 1 1) surface has an intrinsic semiconducting character with two fully occupied, dispersing surface state bands. We find that only one of the additional surface bands on the surface is metallic in contrast to the two metallic bands discussed in the literature. On the 6×6 surface, the partially occupied surface band of the surface seems to be absent, resulting in a gap of about 0.2 eV with respect to the Fermi-level.     

Surface reaction mechanism of Y2O3 atomic layer deposition on the hydroxylated Si(1 0 0)-2 × 1: A density functional theory study

The surface reaction mechanism of Y₂O₃ atomic layer deposition (ALD) on the hydroxylated silicon surface is investigated by using density functional theory. The ALD process is designed into two half-reactions, i.e., Cp₃Y (Cp = cyclopentadienyl) and H₂O half-reactions. For the Cp₃Y half-reaction, the chemisorbed complex is formed along with the change of metal-Cp bonding from Y-C(π) to Y-C₁(σ). For the H₂O half-reactions, the chemisorbed energies are increased with the relief of steric congestion around yttrium metal center. In addition, Gibbs free energy calculations show that it is thermodynamically favorable for the Cp₃Y half-reactions. By comparing with the reaction of H₂O with {Si}-(O₂)YCp, it is thermodynamically more favorable and kinetically less favorable for the reactions of H₂O with {Si}-OYCp₂ as well as with {Si}-OYCp(OH).     

Small angle neutron scattering at very high time resolution: Principle and simulations of ‘TISANE’

The time resolution of SANS experiments is generally limited by frame overlap to some ms. We report on a new time-resolved stroboscopic SANS method, called TISANE, offering μs time resolution without a major sacrifice in intensity by making use of very large frame overlap. We may explore a new field in neutron scattering and complement the emerging field of time resolved small angle X-ray scattering. Here we discuss the principle of TISANE, its mathematical treatment and its limitations.     

Structural, optical properties and band gap alignments of ZrOxNy thin films on Si (1 0 0) by radio frequency sputtering at different deposition temperatures

ZrO_xN_y thin films have been prepared by radio frequency magnetron sputtering at various substrate temperatures. The effect of substrate temperature on structural, optical properties and energy-band alignments of as-deposited ZrO_xN_y thin films are investigated. Atomic force microscopy results indicate the decreased root-mean-square (rms) values with substrate temperature. Fourier transform infrared spectroscopy spectra indicate that an interfacial layer has been formed between Si substrate and ZrO_xN_y thin films during deposition. X-ray photoelectron spectroscopy and spectroscopy ellipsometry (SE) results indicate the increased nitrogen incorporation in ZrO_xN_y thin films and therefore, the decreased optical band gap (E_g) values as a result of the increased valence-band maximum and lowered conduction-band minimum.     

Reply to: “Comment on: ‘From classical to modern ether-drift experiments: the narrow window for a preferred frame’ [Phys. Lett. A 333 (2004) 355]” [Phys. Lett A 361 (2007) 509]

We present some arguments that should induce to re-consider from a new perspective the interference experiments in moving media (Michelson–Morley, Fizeau, …). These considerations are useful to understand and appreciate the experimental test recently proposed by Guerra and de Abreu.     

A unified model for metal/organic interfaces: IDIS, ‘pillow’ effect and molecular permanent dipoles

A unified model, embodying the induced density of interface states (IDIS) model, the reduction of the metal work function due to the adsorbed molecules (‘pillow’ effect) and molecular permanent dipoles, is presented for describing the barrier formation at metal/organic interfaces. While the IDIS model and ‘pillow’ effect have been described in previous approaches, in this paper we show how to introduce molecular permanent dipoles in the interface barrier formation. Examples for Au or Al/organic interfaces are discussed, which show the validity of our results and the generality of our formalism.     

Linearly and circular dichroism in a semiconductor with a complex valence band with allowance for four-photon absorption of light

This paper presents a theoretical study of the linear and circular dichroism of multiphoton absorption of light in semiconductors with a complex valence band. Matrix elements of optical transitions between subbands of the valence bands of a p-GaAs semiconductor are calculated. Transitions connected with both nonsimultaneous absorption of single photons and simultaneous absorption of two photons are taken into account. An expression for the temperature dependence of the coefficient of multiphoton absorption of polarized radiation with allowance for transitions between subbands of heavy and light holes is obtained.