48,208 research outputs found
Visible light driven photocatalysis mediated via ligand-to-metal charge transfer (LMCT): An alternative approach to solar activation of titania
Visible light harvesting or utilization through semiconductor photocatalysis is a key technology for solar chemical conversion processes. Although titania nanoparticles are popular as a base material of photocatalysis, the lack of visible light activity needs to be overcome. This mini-review is focused on an uncommon approach to visible light activation of titania: the ligand-to-metal charge transfer (LMCT) that takes place between TiO2 nanoparticles and surface adsorbates under visible light irradiation. We discuss a basic concept of photoinduced LMCT and the recent advances in LMCT-mediated visible light photocatalysis which has been applied in environmental remediation and solar energy conversion. Although the LMCT processes have been less investigated and limited in photocatalytic applications compared with other popular visible light activation methods such as impurity doping and dye sensitization, they provide lots of possibilities and flexibility in that a wide variety of organic or inorganic compounds can form surface complexes with TiO2 and introduce a new absorption band in the visible light region. The LMCT complexes may serve as a visible light sensitizer that initiates the photocatalytic conversion of various substrates or the self-degradation of the ligand complexes (usually pollutants) themselves. We summarized and discussed various LMCT photocatalytic systems and their characteristics. The LMCT-mediated activation of titania and other wide bandgap semiconductors has great potential to be developed as a more general method of solar energy utilization in photocatalytic systems. More systematic design and utilization of LMCT complexes on semiconductors are warranted to advance the solar-driven chemical conversion processes.open11144136Ysciescopu
A method to find quantum noiseless subsystems
We develop a structure theory for decoherence-free subspaces and noiseless
subsystems that applies to arbitrary (not necessarily unital) quantum
operations. The theory can be alternatively phrased in terms of the
superoperator perspective, or the algebraic noise commutant formalism. As an
application, we propose a method for finding all such subspaces and subsystems
for arbitrary quantum operations. We suggest that this work brings the
fundamental passive technique for error correction in quantum computing an
important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter
Origin of Electric Field Induced Magnetization in Multiferroic HoMnO3
We have performed polarized and unpolarized small angle neutron scattering
experiments on single crystals of HoMnO3 and have found that an increase in
magnetic scattering at low momentum transfers begins upon cooling through
temperatures close to the spin reorientation transition at TSR ~ 40 K. We
attribute the increase to an uncompensated magnetization arising within
antiferromagnetic domain walls. Polarized neutron scattering experiments
performed while applying an electric field show that the field suppresses
magnetic scattering below T ~ 50 K, indicating that the electric field affects
the magnetization via the antiferromagnetic domain walls rather than through a
change to the bulk magnetic order
Axial charges of octet and decuplet baryons
We present a study of axial charges of baryon ground and resonant states with
relativistic constituent quark models. In particular, the axial charges of
octet and decuplet , , , , , and
baryons are considered. The theoretical predictions are compared to existing
experimental data and results from other approaches, notably from lattice
quantum chromodynamics and chiral perturbation theory. The relevance of axial
charges with regard to -dressing and spontaneous chiral-symmetry breaking
is discussed
Calculating using HYP staggered fermions
We present preliminary results for calculated using HYP
staggered fermions in the quenched approximation. We compare different choices
of quenched penguin operators.Comment: 3 pages, 4 figures, Contribution to Lattice 2004 International
Symposiu
Composition dependence of electronic structure and optical properties of Hf1-xSixOy gate dielectrics
Copyright © 2008 American Institute of Physics. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditionsComposition-dependent electronic structure and optical properties of Hf1−xSixOy 0.1 x 0.6 gate
dielectrics on Si at 450 °C grown by UV-photo-induced chemical vapor deposition UV-CVD have
been investigated via x-ray photoemission spectroscopy and spectroscopy ellipsometry SE . By
means of the chemical shifts in the Hf 4f, Si 2p, and O 1s spectra, the Hf–O–Si bondings in the
as-deposited films have been confirmed. Analyses of composition-dependent band alignment of
Hf1−xSixOy / Si gate stacks have shown that the valence band VB offset Ev demonstrates little
change; however, the values of conduction band offset Ec increase with the increase in the silicon
atomic composition, resulting from the increase in the separation between oxygen 2p orbital VB
state and antibonding d states intermixed of Hf and Si. Analysis by SE, based on the Tauc–Lorentz
model, has indicated that decreases in the optical dielectric constant and increase in band gap have
been observed as a function of silicon contents. Changes in the complex dielectric functions and
band gap Eg related to the silicon concentration in the films are discussed systematically. From the
band offset and band gap viewpoint, these results suggest that Hf1−xSixOy films provide sufficient
tunneling barriers for electrons and holes, making them promising candidates as alternative gate
dielectrics.National Natural Science Foundation of China and Royal Society U.K
Low-velocity anisotropic Dirac fermions on the side surface of topological insulators
We report anisotropic Dirac-cone surface bands on a side-surface geometry of
the topological insulator BiSe revealed by first-principles
density-functional calculations. We find that the electron velocity in the
side-surface Dirac cone is anisotropically reduced from that in the
(111)-surface Dirac cone, and the velocity is not in parallel with the wave
vector {\bf k} except for {\bf k} in high-symmetry directions. The size of the
electron spin depends on the direction of {\bf k} due to anisotropic variation
of the noncollinearity of the electron state. Low-energy effective Hamiltonian
is proposed for side-surface Dirac fermions, and its implications are presented
including refractive transport phenomena occurring at the edges of tological
insulators where different surfaces meet.Comment: 4 pages, 2 columns, 4 figure
Causal structures and the classification of higher order quantum computations
Quantum operations are the most widely used tool in the theory of quantum
information processing, representing elementary transformations of quantum
states that are composed to form complex quantum circuits. The class of quantum
transformations can be extended by including transformations on quantum
operations, and transformations thereof, and so on up to the construction of a
potentially infinite hierarchy of transformations. In the last decade, a
sub-hierarchy, known as quantum combs, was exhaustively studied, and
characterised as the most general class of transformations that can be achieved
by quantum circuits with open slots hosting variable input elements, to form a
complete output quantum circuit. The theory of quantum combs proved to be
successful for the optimisation of information processing tasks otherwise
untreatable. In more recent years the study of maps from combs to combs has
increased, thanks to interesting examples showing how this next order of maps
requires entanglement of the causal order of operations with the state of a
control quantum system, or, even more radically, superpositions of alternate
causal orderings. Some of these non-circuital transformations are known to be
achievable and have even been achieved experimentally, and were proved to
provide some computational advantage in various information-processing tasks
with respect to quantum combs. Here we provide a formal language to form all
possible types of transformations, and use it to prove general structure
theorems for transformations in the hierarchy. We then provide a mathematical
characterisation of the set of maps from combs to combs, hinting at a route for
the complete characterisation of maps in the hierarchy. The classification is
strictly related to the way in which the maps manipulate the causal structure
of input circuits.Comment: 12 pages, revtex styl
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