Line Narrowing in Photoemission by Coincidence Spectroscopy (original) (raw)
Related papers
2011
We present the Auger Photoelectron Coincidence Spectroscopy (APECS) measurements of Ag (100) and Cu (100) over a full range of emitted energies from 0 eV to 81eV. The measurements were successful in separating the low energy Auger lines from a large background, due to loss processes unrelated to the Auger transition. The measurements reveal a well formed Auger peak at 60 eV for Cu and an Auger peak at 40 eV for Ag accompanied by a low energy tail (LET). The LET extends to 0 eV with a broad maximum at 6eV and 10 eV in the case of Cu and Ag respectively. The integrated intensity of the LET in Cu (100) and Ag (100) were 6 and 2 times larger than that of the Auger peak itself. The origin of this LET is discussed in terms of extrinsic mechanisms in which electrons from the peak lose energy as they propagate to the sample surface, as well as intrinsic mechanisms in which multi-electron Auger processes distribute the energy gained by the filling of the core-hole to multiple valence electrons.
The capability of the recently observed dichroic effect in angle-resolved Auger-photoelectron coincidence spectroscopy ͑DEAR-APECS͒ to disentangle individual multiplet terms has been exploited to study the lineshape of the M 3 M 45 M 45 Auger spectrum measured in coincidence with the 3p 3/2 photoelectrons from the Cu͑111͒ surface. The relevant multiplet structure of the two hole final state is determined with an unprecedented sensitivity, including a reliable experimental estimation of the energy of the 1 D multiplet term. Spectroscopic data for the 3p photoemission feature are also given and energy conservation applied to the photoelectron-Auger-electron pair has been successfully used in order to quantitatively explain energy shifts in coincidence spectra. Multiple-scattering calculations prove that the DEAR-APECS effect is not destroyed by diffraction effects and a simple model which combines atomic angular distributions and electron-diffraction modulations is provided in order to obtain a detailed understanding of the multiplet energy and intensity distributions in Auger spectra.
Asymmetric broadening of the Cu 2p3/2 photoelectron line
Surface Science, 2000
ABSTRACT The 2p photoelectron spectra in Cu give rise to the L23VV Auger spectra. This is known to be complex, displaying both quasi-atomic-like features as well as features that reflect the band structure of the material. In this work we have used Auger photoelectron coincidence spectroscopy (APECS) to study the 2p3/2 photoelectron line in coincidence with the L23VV.
Auger photoelectron coincidence spectroscopy (APECS), in which the Auger spectra are measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band (VB) photoelectrons. However the APECS method alone cannot eliminate the background due to valence band photoemission processes in which the initial photon energy is shared by two or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method to determine the contributions from these background processes and apply this method in the case of copper M 3 VV Auger spectrum obtained in coincidence with the 3p 3/2 photoemission peak. A beam of 200 eV photons was incident on a Cu(1 0 0) sample and a series of coincidence measurements were performed using a spectrometer equipped with two cylindrical mirror analyzers (CMAs). One CMA was set at series of fixed energies that ranged between the energy of the core and the VB peaks. The other CMA was scanned over a range corresponding to electrons leaving the surface between 0 eV and 70 eV. The set of measured spectra were then fit to a parameterized function which was extrapolated to determine the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. The extrapolated background was subtracted from the APECS spectrum to obtain the spectrum of electrons emitted solely as the result of the Auger process. A comparison of the coincidence spectrum with the same spectrum with background removed shows that in the case of Cu M 3 VV the background due to the inelastic scattering of VB electrons is negligible in the region of the Auger peak but is more than half the total signal down in the low energy tail of the Auger peak.
Final state interaction observed in M 2,3 VV Auger profile of Cu(110)
Journal of Physics: Condensed Matter, 2009
We have measured the M 2,3 VV Auger spectra of Cu(110) and studied the final state interaction following the Cu 3p core electron excitation. We have observed that the kinetic energy of the M 2,3 VV Auger electron shifts to an energy higher than that of the normal Auger electrons near the Cu 3p threshold, and it converges to the constant kinetic energy of the normal Auger electrons as the excitation energy increases above the Cu 3p threshold. In the excitation energy dependence of the kinetic energies of the M 2,3 VV Auger electrons, we observed step features at the excitation energies corresponding to the 3p core electron excitations to the L 1 and X 1 van Hove singularities in the valence states. The kinetic energy shifts of the M 2,3 VV Auger electrons are reasonably understood by considering the localization of the two-hole Auger final state and the hybridization between Cu 3d states and other valence states.
Physical Review B, 2011
Positron-annihilation-induced Auger electron spectroscopy (PAES) was used to obtain Cu and Au Auger spectra that are free of primary-beam-induced backgrounds by impinging the positrons at an energy below the secondary-electron-emission threshold. The removal of the core electron via annihilation in the PAES process resulted in the elimination of postcollision effects. The spectra indicate that there is an intense low-energy tail (LET) associated with the Auger peak that extends all the way to 0 eV. The LET is interpreted as indicative of processes in which filling of the core hole by a valence electron results in the ejection of two or more valence electrons which share the energy of the conventional core-valence-valence Auger electron.
Auger photoelectron coincidence spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 1999
Auger photoelectron coincidence spectroscopy (APECS) is a technique that provides us with unique information and a chance to gain insight into the significance of processes in the Auger spectra of atoms in solids. Hence it is a great aid in our understanding of the Auger process in atoms where electron correlations are strong. Despite the first demonstration of the technique more than 20 years ago, there are still very few working experiments. The reasons why, and the ways forward are discussed.
Emission-Depth-Selective Auger Photoelectron Coincidence Spectroscopy
Physical Review Letters, 2005
The collision statistics of the energy dissipation of Auger and photoelectrons emitted from an amorphized Si(100) surface is studied by measuring the Si 2p photoelectron line as well as the first plasmon loss peak in coincidence with the Si-LVV Auger transition and the associated first plasmon loss. The Si 2p plasmon intensity decreases when measured in coincidence with the Si-LVV peak. If measured in coincidence with the Si-LVV plasmon the decrease is significantly smaller. The results agree quantitatively with calculations accounting for surface, volume, and intrinsic losses as well as elastic scattering in a random medium. In this way one can determine the average emission depth of individual electrons by means of Auger photoelectron coincidence spectroscopy, which therefore constitutes a unique tool to investigate interfaces at the nanoscale level.
Angle-scanned photoemission spectrum from Cu(100): theory vs experiment
Surface Science, 2001
We have carried out simulations of the angle-scanned photoemission spectrum of Cu(1 0 0) within the framework of the one-step model at the He I energy of 21.2 eV for unpolarized photons. Comparison with the corresponding measurements reveals dierences with respect to the theoretical predictions of our state-of-the-art computations. The main discrepancy is associated with the details of the Shockley type surface state, localized around the X symmetry point on Cu(1 0 0), which are not well described within our model. However, re®nement of the potential in the surface region yields a good level of accord with the experimental results.
Near-Threshold Nonlinear Photoemission From Cu(100)
2021
Photocathodes that have a low mean transverse energy (MTE) are crucial to the development of compact X-ray Free Electron Lasers (XFEL) and ultrafast electron diffraction (UED) experiments. For FELs, low MTE cathodes result in a lower requirement for electron energy when lasing at a defined energy, and for a defined electron energy result in lasing at higher energy. For UED experiments, low MTE cathodes give a longer coherence length, allowing measurements on larger unit cell materials. A record low MTE of 5 meV has been recently demonstrated from a Cu (100) surface when measured near the photoemission threshold and cooled down to 30 K with liquid Helium [*]. For UED and XFEL applications that require a high charge density, the low quantum efficiency of Cu (100) near threshold necessitates the use of a high laser fluence to achieve the desired charge density [**]. At high laser fluences the MTE is limited by nonlinear effects, and therefore it is necessary to investigate near photoem...