Topic
Photoemission spectroscopy
About: Photoemission spectroscopy is a research topic. Over the lifetime, 10821 publications have been published within this topic receiving 250888 citations. The topic is also known as: photoelectron spectroscopy & PES.
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TL;DR: First applications demonstrate the capabilities of the instrument to easily select the probe wavelength of choice, to obtain angle-resolved photoemission maps, and to trace ultrafast electron dynamics in an optically excited semiconductor (Ge).
Abstract: We present a laser-based apparatus suitable for visible pump/extreme UV (XUV) probe time-, energy-, and angle-resolved photoemission spectroscopy utilizing high-harmonic generation from a noble gas. Tunability in a wide range of energies (currently 20–36 eV) is achieved by using a time-delay compensated monochromator, which also preserves the ultrashort duration of the XUV pulses. Using an amplified laser system at 10 kHz repetition rate, approximately 109–1010 photons/s per harmonic are made available for photoelectron spectroscopy. Parallel energy and momentum detection is carried out in a hemispherical electron analyzer coupled with an imaging detector. First applications demonstrate the capabilities of the instrument to easily select the probe wavelength of choice, to obtain angle-resolved photoemission maps (GaAs and URu2Si2), and to trace ultrafast electron dynamics in an optically excited semiconductor (Ge).
75 citations
TL;DR: In this article, the electronic structure of phosphaethene (CH2=PH) was deduced from its photoelectron spectrum, which is the first known electronic structure for CH2 =PH.
Abstract: For the first time the electronic structure of phosphaethene (CH2=PH), the unstable parent compound in the phosphaalkene series, is deduced from its photoelectron spectrum.
75 citations
TL;DR: In this article, the authors present time-delayed two-color photoionization photoelectron spectra of aniline, 2-aminopyridine, and 3-amino-polycyclic acid (3-AMO) seeded in a cold molecular beam.
Abstract: We present time‐delayed two‐color photoionization photoelectron spectra of aniline, 2‐aminopyridine, and 3‐aminopyridine seeded in a cold molecular beam. The molecules are prepared in their S1 electronic states by a picosecond UV laser pulse and ionized by a time‐delayed 200 nm probe pulse. The photoelectron spectrum is observed with a time‐of‐flight spectrometer. All time‐delayed spectra reveal only one product of the nonradiative relaxation process. Careful considerations of electronic and vibrational overlap propensity rules for the ionization step lead to the conclusion that the dominant nonradiative decay mechanism in these molecules is the intersystem crossing to a bath of vibrationally excited levels of the T1 electronic state. Our observations reveal no admixtures of T2 or higher triplet levels. The pathway of the nonradiative electronic relaxation in 2‐aminopyridine is found to be independent of the initially prepared vibrational states up to 1000 cm−1 of vibrational energy. We find no evidence o...
75 citations
TL;DR: In this article, the effects of compositional, vibrational, long-range positional, and topographical disorders upon the angle-resolved photoemission spectra of tightly bound valence electrons are investigated.
Abstract: The effects of compositional, vibrational, long-range positional, and topographical disorders upon the angle-resolved photoemission spectra of tightly bound valence electrons are investigated. In order to take into account the strong potential sensed by the electron in the vicinity of the atomic core, an augmented-planewave final state is employed. With this final state, the interference between atoms in the optical ionization step is identical to that obtained with a plane-wave final state, but the atomic cross sections are those calculated from spherical, not plane waves. The angle-energy dependence of the photoemission spectra of crystalline alloys depends upon the degree of chemical ordering, the concentration, and the atomic photoionization cross sections of each element present. The primary effect of spatial disorder is to weaken $k$ conservation in the optical ionization step, particularly as the momentum of the final state increases. It is found that phonon disorder is not important in the ultraviolet-photoemission (UPS) regime, but it is sufficient to destroy almost totally $k$ conservation in the x-ray-photoemission (XPS) regime in most materials at room temperature. In this limit, the observed angle-resolved spectra ought to reveal the total density of states modulated by atomic-like photoionization cross sections. High-order phonon induced optical transitions might limit the energy resolution obtainable in the XPS regime to a few tenths of an electron volt. Surface roughness is shown to weaken the conservation of the component of the momentum parallel to the surface, possibly even in the XPS regime. Topographical disorder is important as long as refraction of the photoelectron at the surface remains large. It is argued that if the final electron states are very heavily mixed plane waves, then surface roughness and refraction are much more important than when the states are free-electron-like. Photoemission spectra of electrons directed along a crystallographic axis are shown to provide an important test for determining the validity of several recent models for the final electron state.
75 citations
TL;DR: In this paper, the electrostatic Madelung potential of 1-buthyl-3-alkylimidazolium ion with fluorine-containing anions (tetrafluoroboronate BF 4 -, hexafluorophosphate PF 6 - ) was studied by ultraviolet photoemission spectroscopy (UPS), IPES, and near-edge X-ray absorption fine structure (NEXAFS), and the calculated density of states with the observed spectra has revealed that the energies of the molecular orbitals of these
75 citations