Search results for "Spectroscopy"
showing 10 items of 10293 documents
Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals
2006
The pressure behavior of the absorption edge of PbWO4 was studied up to 15.3 GPa. It red-shifts at -71 meV/GPa below 6.1 GPa, but at 6.3 GPa the band-gap collapses from 3.5 eV to 2.75 eV. From 6.3 GPa to 11.1 GPa, the absorption edge moves with a pressure coefficient of -98 meV/GPa, undergoing additional changes at 12.2 GPa. The results are discussed in terms of the electronic structure of PbWO4 which attribute the behavior of the band-gap to changes in the local atomic structure. The changes observed at 6.3 GPa and 12.2 GPa are attributed to phase transitions.
Optical properties of Ge-oxygen defect center embedded in silica films
2007
The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick Ge-doped silica film on a pure silica substrate were investigated by looking at the emission spectra and time decay detected under synchrotron radiation excitation in the 10-300 K temperature range. This center exhibits two luminescence bands centered at 4.3eV and 3.2eV associated with its de-excitation from singlet (S1) and triplet (T1) states, respectively, that are linked by an intersystem crossing process. The comparison with results obtained from a bulk Ge-doped silica sample evidences that the efficiency of the intersystem crossing rate depends on the properties of the matrix embedding the Ge-oxygen defect ce…
Brownian reservoir computing realized using geometrically confined skyrmion dynamics
2022
AbstractReservoir computing (RC) has been considered as one of the key computational principles beyond von-Neumann computing. Magnetic skyrmions, topological particle-like spin textures in magnetic films are particularly promising for implementing RC, since they respond strongly nonlinearly to external stimuli and feature inherent multiscale dynamics. However, despite several theoretical proposals that exist for skyrmion reservoir computing, experimental realizations have been elusive until now. Here, we propose and experimentally demonstrate a conceptually new approach to skyrmion RC that leverages the thermally activated diffusive motion of skyrmions. By confining the electrically gated a…
Direct atomic layer deposition of ultrathin aluminium oxide on monolayer $MoS_2$ exfoliated on gold: the role of the substrate
2021
In this paper we demonstrated the thermal Atomic Layer Deposition (ALD) growth at 250 {\deg}C of highly homogeneous and ultra-thin ($\approx$ 3.6 nm) $Al_2O_3$ films with excellent insulating properties directly onto a monolayer (1L) $MoS_2$ membrane exfoliated on gold. Differently than in the case of 1L $MoS_2$ supported by a common insulating substrate ($Al_2O_3/Si$), a better nucleation process of the high-k film was observed on the 1L $MoS_2/Au$ system since the ALD early stages. Atomic force microscopy analyses showed a $\approx 50\%$ $Al_2O_3$ surface coverage just after 10 ALD cycles, its increasing up to $>90\%$ (after 40 cycles), and an uniform $\approx$ 3.6 nm film, after 80 cycle…
In Situ Study of Zinc Peroxide Decomposition to Zinc Oxide by X‐Ray Absorption Spectroscopy and Reverse Monte Carlo Simulations
2022
The authors wish to thank Dr. R. Kalendarev for the synthesis of ZnO2 sample. A.K. would like to thank the financial support of the ERDF Project No. 1.1.1.1/20/A/060. The experiment at the MAX IV synchrotron was performed within the project 20190823. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.
Controlling magnetism with light in zero orbital angular momentum antiferromagnet
2023
Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making them ideal candidates for future magnonic devices operating at THz frequencies. A major focus of current research is the investigation of optical methods for the efficient generation of coherent magnons in antiferromagnetic insulators. In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling enables spin dynamics through the resonant excitation of low-energy electric dipoles such as phonons and orbital resonances which interact with spins. However, in magnetic systems with zero orbital angular momentum, microscopic pathways for the resonant and low-energy optical excitation of coherent spin …
New Insights into the Structure of the Vapor/Water Interface from Large-Scale First-Principles Simulations
2015
We present extensive ab initio simulations of the molecular arrangements at the vapor/water interface, which provide valuable insights into the interface structure. In particular, the simulations address the controversy of whether there is a significant amount of nondonor configurations at this prototypical interface, using a novel Car-Parrinello-like ab initio molecular dynamics approach. The interface is modeled by a system of 384 water molecules for 125 ps in a two-dimensional periodic slab, the most extensive ab initio molecular dynamics simulation to date. In contrast to previous theoretical simulations and X-ray absorption spectroscopy, but consistent with sum-frequency generation exp…
Clean and ordered surfaces of CeNi 2 Ge 2 layers on W(110)
1997
Investigations of the geometric and electronic properties of ternary Ce-based heavy fermion systems CeT2X2 (T : Ni,Pd,Rh; X : Ge,Si) were carried out by means of electron spectroscopic methods. The main problem for these surface-sensitive techniques is the preparation of well-ordered and atomically clean surfaces. The ternary substance CeNi2Ge2 was grown on a W(110) substrate by MBE with subsequent annealing. A nearly layer-by-layer growth mode was detected using MEED. The annealed layers are ordered, but show small Ni2Ge crystalline islands. The composition was characterised by means of AES in dependence of the substrate as well as the annealing temperature. Electronic properties are inves…
Different Look at the Spin State ofCo3+Ions in aCoO5Pyramidal Coordination
2004
Using soft-x-ray absorption spectroscopy at the Co ${L}_{2,3}$ and O $K$ edges, we demonstrate that the ${\mathrm{Co}}^{3+}$ ions with the ${\mathrm{CoO}}_{5}$ pyramidal coordination in the layered ${\mathrm{Sr}}_{2}{\mathrm{CoO}}_{3}\mathrm{Cl}$ compound are unambiguously in the high spin state. Our result questions the reliability of the spin state assignments made so far for the recently synthesized layered cobalt perovskites and calls for a reexamination of the modeling for the complex and fascinating properties of these new materials.
Properties of Co/sub 2/YZ Heusler compounds
2005
Heusler compounds of Co/sub 2/XY composition (Co/sub 2/Cr/sub 0.6/Fe/sub 0.4/Al, Co/sub 2/FeSi) offer a variety of half-metallic ferromagnetic materials. These were prepared by arc melting and comprehensively characterized by means of X-ray diffraction ( XRD), Mossbauer spectroscopy, magnetic X-ray circular dichroism spectroscopy (MXCD), superconducting quantum interference device (SQUID) magnetometry, electron spectroscopy for chemical analysis (ESCA), extended X-ray absorption fine structure (EXAFS) and Auger electron spectroscopy (AES) depth profiling. Structural disorder phenomena, magnetic hysteresis, magnetic moments, magnetic transition temperatures and Curie temperature were obtaine…