5,782 research outputs found
Determining the energetics of vicinal perovskite oxide surfaces
The energetics of vicinal SrTiO(001) and DyScO(110), prototypical
perovskite vicinal surfaces, has been studied using topographic atomic force
microscopy imaging. The kink formation and strain relaxation energies are
extracted from a statistical analysis of the step meandering. Both perovskite
surfaces have very similar kink formation energies and exhibit a similar
triangular step undulation. Our experiments suggest that the energetics of
perovskite oxide surfaces is mainly governed by the local oxygen coordination.Comment: 16 pages, 4 figure
Theory of spin-orbit coupling in bilayer graphene
Theory of spin-orbit coupling in bilayer graphene is presented. The
electronic band structure of the AB bilayer in the presence of spin-orbit
coupling and a transverse electric field is calculated from first-principles
using the linearized augmented plane wave method implemented in the WIEN2k
code. The first-principles results around the K points are fitted to a
tight-binding model. The main conclusion is that the spin-orbit effects in
bilayer graphene derive essentially from the single-layer spin-orbit coupling
which comes almost solely from the d orbitals. The intrinsic spin-orbit
splitting (anticrossing) around the K points is about 24\mu eV for the
low-energy valence and conduction bands, which are closest to the Fermi level,
similarly as in the single layer graphene. An applied transverse electric field
breaks space inversion symmetry and leads to an extrinsic (also called
Bychkov-Rashba) spin-orbit splitting. This splitting is usually linearly
proportional to the electric field. The peculiarity of graphene bilayer is that
the low-energy bands remain split by 24\mu eV independently of the applied
external field. The electric field, instead, opens a semiconducting band gap
separating these low-energy bands. The remaining two high-energy bands are
spin-split in proportion to the electric field; the proportionality coefficient
is given by the second intrinsic spin-orbit coupling, whose value is 20\mu eV.
All the band-structure effects and their spin splittings can be explained by
our tight-binding model, in which the spin-orbit Hamiltonian is derived from
symmetry considerations. The magnitudes of intra- and interlayer
couplings---their values are similar to the single-layer graphene ones---are
determined by fitting to first-principles results.Comment: 16 pages, 13 figures, 5 tables, typos corrected, published versio
Imaging Pulsed Laser Deposition oxide growth by in-situ Atomic Force Microscopy
To visualize the topography of thin oxide films during growth, thereby
enabling to study its growth behavior quasi real-time, we have designed and
integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD)
vacuum setup. The AFM scanner and PLD target are integrated in a single support
frame, combined with a fast sample transfer method, such that in-situ
microscopy can be utilized after subsequent deposition pulses. The in-situ
microscope can be operated from room temperature (RT) up to 700C and at
(process) pressures ranging from the vacuum base pressure of 10 mbar up
to 1 mbar, typical PLD conditions for the growth of oxide films. The
performance of this instrument is demonstrated by resolving unit cell height
surface steps and surface topography under typical oxide PLD growth conditions.Comment: 8 pages, 8 figure
Electronic coupling between Bi nanolines and the Si(001) substrate: An experimental and theoretical study
Atomic nanolines are one dimensional systems realized by assembling many
atoms on a substrate into long arrays. The electronic properties of the
nanolines depend on those of the substrate. Here, we demonstrate that to fully
understand the electronic properties of Bi nanolines on clean Si(001) several
different contributions must be accounted for. Scanning tunneling microscopy
reveals a variety of different patterns along the nanolines as the imaging bias
is varied. We observe an electronic phase shift of the Bi dimers, associated
with imaging atomic p-orbitals, and an electronic coupling between the Bi
nanoline and neighbouring Si dimers, which influences the appearance of both.
Understanding the interplay between the Bi nanolines and Si substrate could
open a novel route to modifying the electronic properties of the nanolines.Comment: 6 pages (main), 2 pages (SI), accepted by Phys. Rev.
Measurement of Electron-Optical Parameters for High-Resolution Electron Microscopy Image Interpretation
A method is presented to measure various electron-optical parameters needed for high-resolution electron microscopy image interpretation with high accuracy. The method is based on the measurement of a series of beam-tilt induced image displacements. The displacements are calculated via cross-correlation of the images, and subsequently fitted to a third-order polynomal in the beam tilt. From two series of images (using the x and y beam tilt coils), the spherical aberration constant of the microscope can be measured, as well as the current values of defocus, beam tilt and astigmatism. The spherical aberration constant of three Philips microscopes is measured with a precision better than 1 %, apart from calibration errors.The misalignment in the reference image (i.e. without induced beam tilt) can be measured with an absolute accuracy of 0.05 mrad, while the accuracy in the measured defocus value is 5 nm (at a magnification of 250,000). A computer is used to direct the experiments via remote control of the microscope and perform fast image processing to calculate the cross-correlations
Attentional avoidance of high-fat food in unsuccessful dieters
Using the exogenous cueing task, this study examined whether restrained and disinhibited eaters differ in their orientation of attention towards and their difficulty to disengage from high versus low-fat food pictures in a relatively short (500 ms) and a long presentation format (1500 ms). Overall, participants in the 500 ms condition showed a tendency to direct attention away from high-fat food pictures compared to neutral pictures. No differential pattern was evident for the 1500 ms condition. Correlational analysis revealed that reduced engagement with high-fat food was particularly pronounced for disinhibited eaters. Although in the short term this seems an adaptive strategy, it may eventually become counterproductive, as it could hinder habituation and learning to cope with seductive characteristics of high-fat food. (C) 2010 Elsevier Ltd. All rights reserved
Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-layer- induced Octahedral Distortion
With reduced dimensionality, it is often easier to modify the properties of
ultra-thin films than their bulk counterparts. Strain engineering, usually
achieved by choosing appropriate substrates, has been proven effective in
controlling the properties of perovskite oxide films. An emerging alternative
route for developing new multifunctional perovskite is by modification of the
oxygen octahedral structure. Here we report the control of structural oxygen
octahedral rotation in ultra-thin perovskite SrRuO3 films by the deposition of
a SrTiO3 capping layer, which can be lithographically patterned to achieve
local control. Using a scanning Sagnac magnetic microscope, we show increase in
the Curie temperature of SrRuO3 due to the suppression octahedral rotations
revealed by the synchrotron x-ray diffraction. This capping-layer-based
technique may open new possibilities for developing functional oxide materials.Comment: Main-text 5 pages, SI 6 pages. To appear in Physical Review Letter
Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements
We report time-resolved Kerr effect measurements of magnetization dynamics in
ferromagnetic SrRuO3. We observe that the demagnetization time slows
substantially at temperatures within 15K of the Curie temperature, which is ~
150K. We analyze the data with a phenomenological model that relates the
demagnetization time to the spin flip time. In agreement with our observations
the model yields a demagnetization time that is inversely proportional to T-Tc.
We also make a direct comparison of the spin flip rate and the Gilbert damping
coefficient showing that their ratio very close to kBTc, indicating a common
origin for these phenomena
Effective calculation of LEED intensities using symmetry-adapted functions
The calculation of LEED intensities in a spherical-wave representation can be substantially simplified by symmetry relations. The wave field around each atom is expanded in symmetry-adapted functions where the local point symmetry of the atomic site applies. For overlayer systems with more than one atom per unit cell symmetry-adapted functions can be used when the division of the crystal into monoatomic subplanes is replaced by division into subplanes containing all symmetrically equivalent atomic positions
- …