122 research outputs found
Far infrared properties of the rare-earth scandate DyScO3
We present reflectance measurements in the infrared region on a single
crystal the rare earth scandate DyScO3. Measurements performed between room
temperature and 10 K allow to determine the frequency of the infrared-active
phonons, never investigated experimentally, and to get information on their
temperature dependence. A comparison with the phonon peak frequency resulting
from ab-initio computations is also provided. We finally report detailed data
on the frequency dependence of the complex refractive index of DyScO3 in the
terahertz region, which is important in the analysis of terahertz measurements
on thin films deposited on DyScO3
Raman scattering of perovskite SmScO3 and NdScO3 single crystals
We report an investigation of perovskite-type SmScO3 and NdScO3 single
crystals by Raman scattering in various scattering configurations and at
different wavelengths. The reported Raman spectra, together with the phonon
mode assignment, set the basis for the use of Raman scattering for the
structural investigation of RE-scandates. Further to the phonon signature, a
fluorescence signal is observed for both scandates and is particularly intense
for NdScO3 when using a 488 or 514 nm excitation line. A comparison of Raman
spectra of RE-scandates with literature Raman data on orthorhombic perovskites
shows that the frequency of particular modes scales with the orthorhombic
distortion in terms of the rotation (or tilt) angle of the ScO6 octahedr
Raman scattering of perovskite DyScO3 and GdScO3 single crystals
We report an investigation of DyScO3 and GdScO3 single crystals by Raman
scattering in various scattering configurations and at various wavelengths. The
Raman spectra are well-defined and the reported spectral signature together
with the mode assignment sets the basis for the use of Raman scattering for the
investigation of RE-scandates. The observed positions of Raman modes for DyScO3
are for most bands in reasonable agreement with recent theoretical ab initio
predictions of the vibrational spectrum for the same material. Further to the
phonon signature, a luminescence signal is observed for both scandates. While
the luminescence is weak for DyScO3, it is very intense for GdScO3 when using a
488 or 514 nm excitation line, which in turn inhibits full analysis of the
phonon spectrum. We show that a meaningful phonon Raman analysis of GdScO3
samples can be done by using a 633 nm excitation
Temperature-dependent Raman scattering of DyScO3 and GdScO3 single crystals
We report a temperature-dependent Raman scattering investigation of DyScO3
and GdScO3 single crystals from room temperature up to 1200 {\deg}C. With
increasing temperature, all modes decrease monotonously in wavenumber without
anomaly, which attests the absence of a structural phase transition. The high
temperature spectral signature and extrapolation of band positions to higher
temperatures suggest a decreasing orthorhombic distortion towards the ideal
cubic structure. Our study indicates that this orthorhombic-to-cubic phase
transition is close to or higher than the melting point of both rare-earth
scandates (\approx 2100 {\deg}C), which might exclude the possibility of the
experimental observation of such a phase transition before melting. The
temperature-dependent shift of Raman phonons is also discussed in the context
of thermal expansion
Recommended from our members
Nanoimaging of Organic Charge Retention Effects: Implications for Nonvolatile Memory, Neuromorphic Computing, and High Dielectric Breakdown Devices
While a large variety of organic and molecular materials have been found to exhibit charge memory effects, the underlying mechanism is not well-understood, which hinders rational device design. Here, we study the charge retention mechanism of a nanoscale memory system, an organic monolayer on a silicon substrate, with Au nanoparticles on top serving as the electrical contact. Combining scanning probe imaging/manipulation and density functional simulations, we observe stable charge retention effects in the system and attributed it to polaron effects at the amine functional groups. Our findings can pave the way for applications in nonvolatile memory, neuromorphic computing, and high dielectric breakdown devices
A Rapid Dynamical Monte Carlo Algorithm for Glassy Systems
In this paper we present a dynamical Monte Carlo algorithm which is
applicable to systems satisfying a clustering condition: during the dynamical
evolution the system is mostly trapped in deep local minima (as happens in
glasses, pinning problems etc.). We compare the algorithm to the usual Monte
Carlo algorithm, using as an example the Bernasconi model. In this model, a
straightforward implementation of the algorithm gives an improvement of several
orders of magnitude in computational speed with respect to a recent, already
very efficient, implementation of the algorithm of Bortz, Kalos and Lebowitz.Comment: RevTex 7 pages + 4 figures (uuencoded) appended; LPS preprin
Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering
We report a Raman scattering investigation of columnar BiFeO3-CoFe2O4
(BFO-CFO) epitaxial thin film nanostructures, where BFO pillars are embedded in
a CFO matrix. The feasibility of a strain analysis is illustrated through an
investigation of two nanostructures with different BFO-CFO ratios. We show that
the CFO matrix presents the same strain state in both nanostructures, while the
strain state of the BFO pillars depends on the BFO/CFO ratio with an increasing
tensile strain along the out-of-plane direction with decreasing BFO content.
Our results demonstrate that Raman scattering allows monitoring strain states
in complex 3D multiferroic pillar/matrix composites.Comment: revised version submitted to Appl. Phys. Let
Phase transition close to room temperature in BiFeO3 thin films
BiFeO3 (BFO) multiferroic oxide has a complex phase diagram that can be
mapped by appropriately substrate-induced strain in epitaxial films. By using
Raman spectroscopy, we conclusively show that films of the so-called
supertetragonal T-BFO phase, stabilized under compressive strain, displays a
reversible temperature-induced phase transition at about 100\circ, thus close
to room temperature.Comment: accepted in J. Phys.: Condens. Matter (Fast Track Communication
Orientation and stability of a bi-functional aromatic organic molecular adsorbate on silicon
In this work we combine scanning tunneling microscopy, near-edge X-ray absorption fine structure spectroscopy, X-ray photoemission spectroscopy and density functional theory to resolve a long-standing confusion regarding the adsorption behaviour of benzonitrile on Si(001) at room temperature. We find that a trough-bridging structure is sufficient to explain adsorption at low coverages. At higher coverages when steric hindrance prevents the phenyl ring lying flat on the surface, the 2+2 cycloaddition structure dominates
- …