Search results for "photoemission"
showing 10 items of 174 documents
IMAGING OF DICHROISM IN PHOTOEMISSION ELECTRON MICROSCOPY AT NONMAGNETIC MATERIALS USING CIRCULARLY POLARIZED SOFT X-RAYS
2002
A new approach for investigations of circular dichroism in the angular distribution of photoelectrons (CDAD) is presented. The image contrast using a photoemission line of a certain material is combined with imaging of the angular distribution pattern using a photoemission electron microscope (PEEM). CDAD can be used to investigate pure scattering information by means of the same instrument in microscopically selected regions on a surface. The experiment combines angle-resolved XPS imaging with the indirect mapping of the local environment of atoms by means of CDAD holography. In a conventional photoelectron diffraction or photoelectron holography experiment, it is necessary to move the sa…
Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides
2016
Using a second-order perturbative Green's functions approach we determined the normal state single-particle spectral function $A(\vec{k},\omega)$ employing a minimal effective model for iron-based superconductors. The microscopic model, used before to study magnetic fluctuations and superconducting properties, includes the two effective tight-binding bands proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and inter-orbital local electronic correlations, related to the Fe-3d orbitals. Here, we focus on the study of normal state electronic properties, in particular the temperature and doping dependence of the total density of states, $A(\omega)$, and of $A(\vec{k},\o…
A small spherical liquid: A DFT molecular dynamics study of WAu12
2009
The finite-temperature dynamics of WAu12, incorporating both electronic and structural effects, is studied using a density-functional-based Born-Oppenheimer molecular dynamics method. Molecular dynamics simulations for monomolecular WAu12 suggest a surface-melting-type behaviour of the angular degrees of freedom between 366 and 512 K. Thermally averaged electron density-of-states of WAu12 are compared to the experimental photoelectron spectra of WAu12(-).
Revealing the Electronic Structure and Optical Properties of CuFeO2 as a p-Type Oxide Semiconductor
2021
Delafossite CuFeO2 is a p-type oxide semiconductor with a band gap of ∼1.5 eV, which has attracted great interests for applications in solar energy harvesting and oxide electronics. However, there are still some discrepancies in the literature regarding its fundamental electronic structure and transport properties. In this paper, we use a synergistic combination of resonant photoemission spectroscopy and X-ray absorption spectroscopy to directly study the electronic structure of well-defined CuFeO2 epitaxial thin films. Our detailed study reveals that CuFeO2 has an indirect and d-d forbidden band gap of 1.5 eV. The top of the valence band (VB) of CuFeO2 mainly consists of occupied Fe 3d sta…
Electron-spectroscopic investigations on ternary HFS: CeT2X2
1997
Investigations of the electronic properties were carried out for ternary Ce-based heavy fermion systems. The well-ordered surfaces of HFS were prepared by MBE on W (110) with subsequent annealing. The layers are characterised by MEED, LEED, AES and XPS. For the electron-spectroscopic investigations, ARUPS and SPEELS were used. In the photoemission spectra, dispersion effects could be detected. By means of SPEELS, the dipole-forbidden Ce f-f transitions could be observed. The comparison of the energy loss spectra above and below the characteristic temperature T∗ reveals differences in the energy losses as well as in the asymmetries.
Phonon Driven Floquet Matter.
2018
The effect of electron–phonon coupling in materials can be interpreted as a dressing of the electronic structure by the lattice vibration, leading to vibrational replicas and hybridization of electronic states. In solids, a resonantly excited coherent phonon leads to a periodic oscillation of the atomic lattice in a crystal structure bringing the material into a nonequilibrium electronic configuration. Periodically oscillating quantum systems can be understood in terms of Floquet theory, which has a long tradition in the study of semiclassical light-matter interaction. Here, we show that the concepts of Floquet analysis can be applied to coherent lattice vibrations. This coupling leads to p…
Survival of Floquet–Bloch States in the Presence of Scattering
2021
Floquet theory has spawned many exciting possibilities for electronic structure control with light, with enormous potential for future applications. The experimental demonstration in solids, however, remains largely unrealized. In particular, the influence of scattering on the formation of Floquet-Bloch states remains poorly understood. Here we combine time- and angle-resolved photoemission spectroscopy with time-dependent density functional theory and a two-level model with relaxation to investigate the survival of Floquet-Bloch states in the presence of scattering. We find that Floquet-Bloch states will be destroyed if scattering-activated by electronic excitations-prevents the Bloch elec…
Internal photoemission in solar blind AlGaN Schottky barrier photodiodes
2005
We have analyzed the photoresponse of solar blind AlGaN Schottky barrier photodiodes below the alloy band gap energy, in the 3.5-4.5 eV range, and we show that it is dominated by internal photoemission. The n-type Schottky barrier height is shown to increase linearly with the band gap energy of the AlGaN alloy. The amplitude of the internal photoemission signal is about 20 times smaller than the value given by the Fowler theory based on a free electron model. We explain this result by taking into account the interband transitions and the ballistic transport of photoexcited electrons in the metal. This low value of internal photoemission allows us to achieve a spectral rejection ratio betwee…
Multidimensional photoemission spectroscopy—the space-charge limit
2018
New journal of physics 20(3), 033004 - (2018). doi:10.1088/1367-2630/aaa262
Ab Initio Simulation of Clusters: Relativistic Effects in Structure and Bonding of Noble Metal Nanoparticles
2005
Resolving the atomic and electronic structures of nanoclusters represents an important preliminary for their controlled use in future nanotechnologies. Here we show through the comparison of density-functional calculations with high-resolution photoelectron spectroscopy that 1.4 nm nanoparticles of silver (negatively charged clusters of 53 to 58 atoms) are icosahedral-based structures displaying a perfect icosahedral-induced electronic shell structure for Ag 55 − and slightly perturbed shell structures for the neighboring cluster sizes. At variance, 55-atom gold clusters exhibit several isomeric structures of low symmetry, with a largely diminished electronic shell structure. This surprisin…