411 research outputs found
Local Phonon Density of States in an Elastic Substrate
The local, eigenfunction-weighted acoustic phonon density of states (DOS)
tensor is calculated for a model substrate consisting of a semi-infinite
isotropic elastic continuum with a stress-free surface. On the surface, the
local DOS is proportional to the square of the frequency, as for the
three-dimensional Debye model, but with a constant of proportionality that is
considerably enhanced compared to the Debye value, a consequence of the
Rayleigh surface modes. The local DOS tensor at the surface is also
anisotropic, as expected. Inside the substrate the local DOS is both spatially
anisotropic and non-quadratic in frequency. However, at large depths, the local
DOS approaches the isotropic Debye value. The results are applied to a Si
substrate.Comment: 7 pages, 2 figures, RevTe
Dynamic and Static Transmission Electron Microscopy Studies on Structural Evaluation of Au nano islands on Si (100) Surface
Transmission electron microscopy (TEM) study on morphological changes in gold
nanostructures deposited on Si (100) upon annealing under different vacuum
conditions has been reported. Au thin films of thickness ~2.0 nm were deposited
under high vacuum condition (with the native oxide at the interface of Au and
Si) using thermal evaporation. In-situ, high temperature (from room temperature
(RT) to 850\degreeC) real time TEM measurements showed the evaluation of gold
nanoparticles into rectangular/square shaped gold silicide structures. This has
been attributed to selective thermal decomposition of native oxide layer.
Ex-situ annealing in low vacuum (10-2 mbar) at 850\degreeC showed no growth of
nano-gold silicide structures. Under low vacuum annealing conditions, the
creation of oxide could be dominating compared to the decomposition of oxide
layers resulting in the formation of barrier layer between Au and Si.Comment: 15 pages, 4 figure
Preparation of BaTiO3 nanotube arrays, CoFe2O4 nanoparticles and their composite
Multiferroic nanocomposites which possess both ferroelectric and ferromagnetic properties are attracting much attention because of their scientific interest and significant technological promise in the novel multifunctional devices. Gas-phase syntheses have been typically used to fabricate multiferroic nanocomposites [1]; however, high production cost has been hindering further expansion of the research field. In this research, the components of multiferroic nanocomposites are fabricated by anodization and hydrothermal treatment which were then used to fabricate multiferroic nanocomposites through electrophoretic deposition (EPD) as cheaper alternatives to the costly gas-phase processes.
TiO2 nanotubes arrays were firstly formed on Ti metal foils by anodization in an electrolyte containing ethylene glycol, dimethyl sulfoxide, ammonium fluoride and water. Then, BaTiO3 nanotube arrays were obtained by hydrothermal treatment of TiO2 nanotube arrays using Ba-containing aqueous solution. The morphologies and crystal structure of BaTiO3 nanotube arrays were analyzed by a scanning electron microscope (SEM) and an X-ray diffractometer (XRD).
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Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting
In layered polar semiconductor BiTeI, giant Rashba-type spin-split band
dispersions show up due to the crystal structure asymmetry and the strong
spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band
structures of BiTeI using the bulk-sensitive -dependent soft x-ray angle
resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is
shown to be well reproducible by the first-principles calculations, with huge
spin splittings of meV at the conduction-band-minimum and
valence-band-maximum located in the plane. It provides the first
direct experimental evidence of the 3D Rashba-type spin splitting in a bulk
compound.Comment: 9 pages, 4 figure
Whole-genome sequencing of Theileria parva strains provides insight into parasite migration and diversification in the african continent
The disease caused by the apicomplexan protozoan parasite Theileria parva, known as East Coast fever or Corridor disease, is one of the most serious cattle diseases in Eastern, Central, and Southern Africa. We performed whole-genome sequencing of nine T. parva strains, including one of the vaccine strains (Kiambu 5), field isolates from Zambia, Uganda, Tanzania, or Rwanda, and two buffalo-derived strains. Comparison with the reference Muguga genome sequence revealed 34 814–121 545 single nucleotide polymorphisms (SNPs) that were more abundant in buffalo-derived strains. High-resolution phylogenetic trees were constructed with selected informative SNPs that allowed the investigation of possible complex recombination events among ancestors of the extant strains. We further analysed the dN/dS ratio (non-synonymous substitutions per non-synonymous site divided by synonymous substitutions per synonymous site) for 4011 coding genes to estimate potential selective pressure. Genes under possible positive selection were identified that may, in turn, assist in the identification of immunogenic proteins or vaccine candidates. This study elucidated the phylogeny of T. parva strains based on genome-wide SNPs analysis with prediction of possible past recombination events, providing insight into the migration, diversification, and evolution of this parasite species in the African continent
Temperature-Dependence of Magnetically-Active Charge Excitations in Magnetite across the Verwey Transition
We have studied the electronic structure of bulk single crystals and
epitaxial films of magnetite FeO. Fe core-level spectra show clear
differences between hard x-ray (HAX-) and soft x-ray (SX-) photoemission
spectroscopy (PES), indicative of surface effects. The bulk-sensitive spectra
exhibit temperature ()-dependent charge excitations across the Verwey
transition at =122 K, which is missing in the surface-sensitive spectra.
An extended impurity Anderson model full-multiplet analysis reveals roles of
the three distinct Fe-species (A-Fe, B-Fe, B-Fe) below
for the Fe spectra, and its dependent evolution. The Fe
HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic
phase of magnetized 100-nm-thick films. The model calculations also reproduce
the MCD and identify the magnetically distinct sites associated with the charge
excitations. Valence band HAXPES shows finite density of states at for
the polaronic metal with remnant order above , and a clear gap formation
below . The results indicate that the Verwey transition is driven by
changes in the strongly correlated and magnetically active B-Fe and
B-Fe electronic states, consistent with resistivity and bulk-sensitive
optical spectra.Comment: 5 pages, 4 figures Accepted in Physical Review Letter
Evidence for a correlated insulator to antiferromagnetic metal transition in CrN
We investigate the electronic structure of Chromium Nitride (CrN) across the
first-order magneto-structural transition at T_N ~ 286 K. Resonant
photoemission spectroscopy shows a gap in the 3d partial density of states at
the Fermi level and an On-site Coulomb energy U ~ 4.5 eV, indicating strong
electron-electron correlations. Bulk-sensitive high resolution (6 meV) laser
photoemission reveals a clear Fermi edge indicating an antiferromagnetic metal
below T_N. Hard x-ray Cr 2p core-level spectra show T-dependent changes across
T_N which originate from screening due to coherent states as substantiated by
cluster model calculations using the experimentally observed U. The electrical
resistivity confirms an insulator above T_N (E_g ~ 70 meV) which becomes a
disordered metal below T_N. The results indicate CrN transforms from a
correlated insulator to an antiferromagnetic metal, coupled to the
magneto-structural transition.Comment: Submitted to Physical Review Letters (February 2010) 11 pages, 3
figures in the main text, 1 Supplementary Informatio
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