Tiberiu Arion - Academia.edu (original) (raw)
Papers by Tiberiu Arion
Journal of Electron Spectroscopy and Related Phenomena, 2015
The creation of slow electrons due to Interatomic Coulombic Decay of 2s vacancies in Ne clusters ... more The creation of slow electrons due to Interatomic Coulombic Decay of 2s vacancies in Ne clusters is quantitatively compared to the slow electron yield by intracluster electron impact ionization. Using electron-electron coincidence spectroscopy, both channels can be separated experimentally. Two cluster size distributions, corresponding to two and five to six filled solvation shells, are probed.
Applied Physics Letters, 2015
Applied Physics Letters, 2015
We report the site-specific probing of charge-transfer dynamics in a prototype system for organic... more We report the site-specific probing of charge-transfer dynamics in a prototype system for organic photovoltaics (OPV) by picosecond time-resolved X-ray photoelectron spectroscopy. A layered system consisting of approximately two monolayers of C60 deposited on top of a thin film of Copper-Phthalocyanine (CuPC) is excited by an optical pump pulse and the induced electronic dynamics are probed with 590 eV X-ray pulses. Charge transfer from the electron donor (CuPC) to the acceptor (C60) and subsequent charge carrier dynamics are monitored by recording the time-dependent C 1s core level photoemission spectrum of the system. The arrival of electrons in the C60 layer is readily observed as a completely reversible, transient shift of the C60 associated C 1s core level, while the C 1s level of the CuPC remains unchanged. The capability to probe charge transfer and recombination dynamics in OPV assemblies directly in the time domain and from the perspective of well-defined domains is expected to open additional pathways to better understand and optimize the performance of this emerging technology.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2014
In a molecular Auger spectrum information on the decaying state is implicitly ensemble-averaged. ... more In a molecular Auger spectrum information on the decaying state is implicitly ensemble-averaged. For a repulsive core-ionized state, for example, contributions from all parts of its potential curve are superimposed in the Auger spectrum. Using carbon tetrafluoride (CF 4 , tetrafluoromethane), we demonstrate for the first time that these contributions can be disentangled by recording photoelectron-Auger electron coincidence spectra with high energy resolution. For the F K-VV spectrum of CF 4 , there are significant differences in the Auger decay at different intermediate state (single core hole) geometries. With the help of calculations, we show that these differences result primarily from zero-point-fluctuations in the neutral molecular ground state, but are amplified by the nuclear dynamics during Auger decay.
The Review of scientific instruments, 2012
In this article, a newly constructed electron spectrometer of the magnetic bottle type is describ... more In this article, a newly constructed electron spectrometer of the magnetic bottle type is described. The instrument is part of an apparatus for measuring the electron spectra of free clusters using synchrotron radiation. Argon and helium outer valence photoelectron spectra have been recorded in order to investigate the characteristic features of the spectrometer. The energy resolution (E/ΔE) has been found to be ∼30. Using electrostatic retardation of the electrons, it can be increased to at least 110. The transmission as a function of kinetic energy is flat, and is not impaired much by retardation with up to 80% of the initial kinetic energy. We have measured a detection efficiency of most probably 0.6(-0.1) (+0.05), but at least of 0.4. Results from testing the alignment of the magnet, and from trajectory simulations, are also discussed.
Ion beams allow to investigate mass selected cluster species, such as (H 2 O) 2 H + , and are ess... more Ion beams allow to investigate mass selected cluster species, such as (H 2 O) 2 H + , and are essential for experiments on ions for which a neutral isonuclear system is inexistent, such as HeH + . As ion beams have a density which is inevitably orders of magnitudes lower than the one of neutral gas jets, numerous experiments on photon induced processes are only viable at a free electron laser. Examples are photoelectron spectroscopy and momentum spectroscopy of nuclear fragments. We use the Trapped Ion Facility at FLASH (TIFF) [1] to investigate the dynamics of photofragmentation after ionization with the FLASH beam. In 2009, we have added an extension of TIFF towards the PG2 platform, which allows to probe the same ion beam in a second centre of interaction ( . Here, we have placed a magnetic bottle electron spectrometer to record electron spectra from photoionization of the ion beam. Using ten shifts of FLASH beamtime in 2009, we have determined the photofragmentation patterns of the smallest protonated water clusters, (H 2 O) 2,3 H + (see separate report), and have demonstrated the feasibility of electron spectroscopy on a beam of Ne + ions. In a magnetic bottle spectrometer, an anisotropic magnetic field is used to bend electrons around a set of magnetic field lines, which guide them towards the detector. This spectrometer achieves electron detection from a large solid angle (up to 4π sR) and with good to moderate energy resolution. Momentum information is lost though. The instrument used in 2009 is similar to an earlier design [2], but incorporates some modifications for the use at FLASH. Most importantly, the length of the drift tube has been shortened to 60 cm. The strong magnetic field at the point of interaction is produced by permanent magnets and further concentrated by a conical iron tip. For the set-up at FLASH, a holder was constructed which allows to remove the magnets from the interaction chamber during baking. Figure 1: Sketch of the TIFF extension (TIFF Jr.), and the magnetic bottle type electron spectrometer as used at FLASH. shows the electron spectrum recorded from a free Ne + ion beam in the magnetic bottle spectrometer. As the signal (at a chamber background pressure of 6 × 10 −10 mbar) was dominated by outer valence ionization of the residual gas, a spectrum with ion beam switched off was
Physical Review Letters, 2011
Electron-electron coincidence spectra of Ar-Kr clusters after photoionization have been measured.... more Electron-electron coincidence spectra of Ar-Kr clusters after photoionization have been measured. An electron with the kinetic energy range from 0 to approximately 1 eV is found in coincidence with the Ar 3s cluster photoelectron. The low kinetic energy electron can be attributed to an Ar þ Kr þ þ Kr þ final state which forms after electron transfer mediated decay. This autoionization mechanism results from a concerted transition involving three different atoms in a van der Waals cluster; it was predicted theoretically, but hitherto not observed.
Physical Review Letters, 2010
Photofragmentation of the protonated water dimer H+(H2O)_{2}, a fundamental system both in aqueou... more Photofragmentation of the protonated water dimer H+(H2O)_{2}, a fundamental system both in aqueous solutions and gas-phase water clusters, has been studied at 13.8 nm using the Free Electron Laser FLASH in Hamburg. In a crossed-beam experiment using time-resolved, single-molecule fragment imaging, the two-body breakup into H2O++H3O+ was found as a prominent fragmentation channel with a kinetic energy release of up to 10 eV. This channel was observed with at least a similar yield as events with stronger fragmentation, producing protons together with neutral fragments and showing an absolute cross section of (0.5 ± 0.2) × 10(-18) cm2.
Physical Review B, 2010
The 3p valence region of argon clusters has been investigated with photoemission near the photoio... more The 3p valence region of argon clusters has been investigated with photoemission near the photoionization threshold. A strong feature between 14.6 and 15.3 eV binding energy shows a photon-energy dependence indicative of electronic-energy band dispersion. A similar feature at approximately the same binding energy and with a similar dispersion occurs in photoemission spectra of both the ordered and disordered solids. The effect is already fully developed for scaling-law mean cluster sizes ͗N͘ of approximately 200 atoms, thus showing an early onset of bulklike electronic properties.
Physical Review A, 2013
ABSTRACT The photofragmentation of the water cation H2O+ through dicationic states has been studi... more ABSTRACT The photofragmentation of the water cation H2O+ through dicationic states has been studied at 35.0±0.2 nm (35.4±0.3 eV) and 21.8±0.2 nm (56.8±0.5 eV) with a crossed ion-photon beams experiment at the free electron laser FLASH. The dissociation of the dications is found to be similar at the two wavelengths and to proceed into O0+2H+, OH++H+, and O++H2+, with determined ratios σOH++H+/σO++H2+=4.2±0.3 and σOH++H+/σO0+2H+>0.7. The measured kinetic-energy releases for these processes are consistent with three-body breakup (O0+2H+) occurring mainly through the 2 3 A′′ and 2 1 A′′ states of H2O2+ and two-body breakup (OH++H+) occurring through X 3 A′′, 1 3 A′, and 1 1 A′′ states of H2O2+, as predicted in a recent theoretical study [ Gervais et al. J. Chem. Phys. 131 024302 (2009)]. In addition to the kinetic-energy releases, we also report on fragment correlation in the three-body channel where the two protons carry the major part of the released momentum.
Physical Review A, 2011
We present high-resolution photoelectron-Auger electron coincidence spectra of methane (CH 4 ).
Nature Physics, 2010
Low-energy electrons are the most abundant product of ionizing radiation in condensed matter. The... more Low-energy electrons are the most abundant product of ionizing radiation in condensed matter. The origin of these electrons is most commonly understood to be secondary electrons 1 ionized from core or valence levels by incident radiation and slowed by multiple ...
Journal of Electron Spectroscopy and Related Phenomena, 2011
Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion i... more Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion in the photon energy range from threshold up to 28 eV. Measurements were performed both at high resolution with a hemispherical electrostatic energy analyser and at low resolution with a magnetic bottle device. The latter experiments were performed for various mean cluster sizes. In addition to the ≈ 1.5 eV broad 3p-derived valence band seen in previous work, there is a sharper feature at ≈ 15 eV binding energy. Surprisingly for nonoriented clusters, this peak shifts smoothly in binding energy over the narrow photon energy range 15.5 -17.7 eV, indicating energy band dispersion. The onset of this bulk band-like behaviour could be determined from the cluster size dependence.
Journal of Electron Spectroscopy and Related Phenomena, 2012
Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of... more Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of Auger decay processes with different core-ionized intermediate states. In this paper we describe an investigation into the Auger decay of the O 2 molecule, with the purpose of bringing new insight into the dynamics of the core hole decay mechanism. Using a novel experimental approach to measuring such coincidence spectra we report the highest resolution Auger spectrum of O 2 recorded hitherto. In our approach, we have combined the advantages of these coincidence spectra with the high resolution and excellent signal-to-noise ratios of non-coincident Auger spectra and a state-of-the-art fit analysis. In this way we have derived information about the potential energy curves of the final states W 3 u , B 3 g , and B' 3 u and concluded that the corresponding Auger transitions are formed to a large part by strongly overlapping vibrational progressions. The present findings are compared to earlier results reported in the literature confirming some theoretical predictions.
Journal of Electron Spectroscopy and Related Phenomena, 2011
Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Au... more Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Auger decay following the photoionization of core or inner valence levels in atoms, molecules or clusters. Moreover, the technique provides valuable insight into the dynamics of core hole decay. This paper serves the dual purpose of demonstrating the additional information obtained by this technique compared to Auger spectroscopy alone as well as of describing the new IPP/FHI apparatus at the BESSY II synchrotron radiation source. The distinguishing feature of the latter is the capability to record both the photoelectron and Auger electron with good energy and angle resolution, for which purpose a large hemispherical electrostatic analyser is combined with several linear time-of-flight spectrometers. Results are reported for the K-shell photoionization of oxygen (O 2 ) and the subsequent K-VV Auger decay. Calculations in the literature for non-coincident O 2 Auger spectra are found to be in moderately good agreement with the new data.
Journal of Electron Spectroscopy and Related Phenomena, 2013
ABSTRACT We report the development and present status of the iDEEAA (Instrument for Direct Electr... more ABSTRACT We report the development and present status of the iDEEAA (Instrument for Direct Electron Energy and Angular Analysis) experimental end station for time- and angle-resolved X-ray photoelectron spectroscopy. The setup is based on multidimensional detection of photoelectrons by means of both time-of-flight (TOF) and/or electrostatic analyzers. The instrument offers the possibility to record simultaneously and independently photoelectron and Auger electron spectra. Samples can be either gases or solids. The system can operate with multiple photon sources, such as laboratory-based table-top laser extreme ultraviolet (EUV) sources, monochromatic Helium discharge lamp and soft X-ray synchrotron pulses. We demonstrate the performance of the setup by carrying out electron–electron coincidence experiments on CH4 and by mapping the band structure of Bi2Se3 using photons of the BESSY II electron storage ring.
The Journal of Chemical Physics, 2011
We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A welldefin... more We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A welldefined feature ranging from 9 to 12 eV in kinetic energy is observed in coincidence with the Ne 2s photoelectrons. It derives from an ICD process, in which an initial Ne 2s vacancy is filled by a Ne 2p electron and an electron is emitted from a 4p level on a neighboring Kr atom. We have studied the dependence of the effect on photon energy, cluster composition, and cluster size. Interestingly, the ICD electron energy increases slightly and grows a shoulder on going from 2% to 5% Kr in the coexpansion process, which we interpret in terms of surface versus bulk effects.
The Journal of Chemical Physics, 2013
The angular distribution of photoelectrons emitted from water clusters has been measured by linea... more The angular distribution of photoelectrons emitted from water clusters has been measured by linearly polarized synchrotron radiation of 40 and 60 eV photon energy. Results are given for the three outermost valence orbitals. The emission patterns are found more isotropic than for isolated molecules. While a simple scattering model is able to explain most of the deviation from molecular behavior, some of our data also suggest an intrinsic change of the angular distribution parameter. The angular distribution function was mapped by rotating the axis of linear polarization of the synchrotron radiation. [http://dx.
Journal of Applied Physics, 2014
ABSTRACT
Journal of Electron Spectroscopy and Related Phenomena, 2015
The creation of slow electrons due to Interatomic Coulombic Decay of 2s vacancies in Ne clusters ... more The creation of slow electrons due to Interatomic Coulombic Decay of 2s vacancies in Ne clusters is quantitatively compared to the slow electron yield by intracluster electron impact ionization. Using electron-electron coincidence spectroscopy, both channels can be separated experimentally. Two cluster size distributions, corresponding to two and five to six filled solvation shells, are probed.
Applied Physics Letters, 2015
Applied Physics Letters, 2015
We report the site-specific probing of charge-transfer dynamics in a prototype system for organic... more We report the site-specific probing of charge-transfer dynamics in a prototype system for organic photovoltaics (OPV) by picosecond time-resolved X-ray photoelectron spectroscopy. A layered system consisting of approximately two monolayers of C60 deposited on top of a thin film of Copper-Phthalocyanine (CuPC) is excited by an optical pump pulse and the induced electronic dynamics are probed with 590 eV X-ray pulses. Charge transfer from the electron donor (CuPC) to the acceptor (C60) and subsequent charge carrier dynamics are monitored by recording the time-dependent C 1s core level photoemission spectrum of the system. The arrival of electrons in the C60 layer is readily observed as a completely reversible, transient shift of the C60 associated C 1s core level, while the C 1s level of the CuPC remains unchanged. The capability to probe charge transfer and recombination dynamics in OPV assemblies directly in the time domain and from the perspective of well-defined domains is expected to open additional pathways to better understand and optimize the performance of this emerging technology.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2014
In a molecular Auger spectrum information on the decaying state is implicitly ensemble-averaged. ... more In a molecular Auger spectrum information on the decaying state is implicitly ensemble-averaged. For a repulsive core-ionized state, for example, contributions from all parts of its potential curve are superimposed in the Auger spectrum. Using carbon tetrafluoride (CF 4 , tetrafluoromethane), we demonstrate for the first time that these contributions can be disentangled by recording photoelectron-Auger electron coincidence spectra with high energy resolution. For the F K-VV spectrum of CF 4 , there are significant differences in the Auger decay at different intermediate state (single core hole) geometries. With the help of calculations, we show that these differences result primarily from zero-point-fluctuations in the neutral molecular ground state, but are amplified by the nuclear dynamics during Auger decay.
The Review of scientific instruments, 2012
In this article, a newly constructed electron spectrometer of the magnetic bottle type is describ... more In this article, a newly constructed electron spectrometer of the magnetic bottle type is described. The instrument is part of an apparatus for measuring the electron spectra of free clusters using synchrotron radiation. Argon and helium outer valence photoelectron spectra have been recorded in order to investigate the characteristic features of the spectrometer. The energy resolution (E/ΔE) has been found to be ∼30. Using electrostatic retardation of the electrons, it can be increased to at least 110. The transmission as a function of kinetic energy is flat, and is not impaired much by retardation with up to 80% of the initial kinetic energy. We have measured a detection efficiency of most probably 0.6(-0.1) (+0.05), but at least of 0.4. Results from testing the alignment of the magnet, and from trajectory simulations, are also discussed.
Ion beams allow to investigate mass selected cluster species, such as (H 2 O) 2 H + , and are ess... more Ion beams allow to investigate mass selected cluster species, such as (H 2 O) 2 H + , and are essential for experiments on ions for which a neutral isonuclear system is inexistent, such as HeH + . As ion beams have a density which is inevitably orders of magnitudes lower than the one of neutral gas jets, numerous experiments on photon induced processes are only viable at a free electron laser. Examples are photoelectron spectroscopy and momentum spectroscopy of nuclear fragments. We use the Trapped Ion Facility at FLASH (TIFF) [1] to investigate the dynamics of photofragmentation after ionization with the FLASH beam. In 2009, we have added an extension of TIFF towards the PG2 platform, which allows to probe the same ion beam in a second centre of interaction ( . Here, we have placed a magnetic bottle electron spectrometer to record electron spectra from photoionization of the ion beam. Using ten shifts of FLASH beamtime in 2009, we have determined the photofragmentation patterns of the smallest protonated water clusters, (H 2 O) 2,3 H + (see separate report), and have demonstrated the feasibility of electron spectroscopy on a beam of Ne + ions. In a magnetic bottle spectrometer, an anisotropic magnetic field is used to bend electrons around a set of magnetic field lines, which guide them towards the detector. This spectrometer achieves electron detection from a large solid angle (up to 4π sR) and with good to moderate energy resolution. Momentum information is lost though. The instrument used in 2009 is similar to an earlier design [2], but incorporates some modifications for the use at FLASH. Most importantly, the length of the drift tube has been shortened to 60 cm. The strong magnetic field at the point of interaction is produced by permanent magnets and further concentrated by a conical iron tip. For the set-up at FLASH, a holder was constructed which allows to remove the magnets from the interaction chamber during baking. Figure 1: Sketch of the TIFF extension (TIFF Jr.), and the magnetic bottle type electron spectrometer as used at FLASH. shows the electron spectrum recorded from a free Ne + ion beam in the magnetic bottle spectrometer. As the signal (at a chamber background pressure of 6 × 10 −10 mbar) was dominated by outer valence ionization of the residual gas, a spectrum with ion beam switched off was
Physical Review Letters, 2011
Electron-electron coincidence spectra of Ar-Kr clusters after photoionization have been measured.... more Electron-electron coincidence spectra of Ar-Kr clusters after photoionization have been measured. An electron with the kinetic energy range from 0 to approximately 1 eV is found in coincidence with the Ar 3s cluster photoelectron. The low kinetic energy electron can be attributed to an Ar þ Kr þ þ Kr þ final state which forms after electron transfer mediated decay. This autoionization mechanism results from a concerted transition involving three different atoms in a van der Waals cluster; it was predicted theoretically, but hitherto not observed.
Physical Review Letters, 2010
Photofragmentation of the protonated water dimer H+(H2O)_{2}, a fundamental system both in aqueou... more Photofragmentation of the protonated water dimer H+(H2O)_{2}, a fundamental system both in aqueous solutions and gas-phase water clusters, has been studied at 13.8 nm using the Free Electron Laser FLASH in Hamburg. In a crossed-beam experiment using time-resolved, single-molecule fragment imaging, the two-body breakup into H2O++H3O+ was found as a prominent fragmentation channel with a kinetic energy release of up to 10 eV. This channel was observed with at least a similar yield as events with stronger fragmentation, producing protons together with neutral fragments and showing an absolute cross section of (0.5 ± 0.2) × 10(-18) cm2.
Physical Review B, 2010
The 3p valence region of argon clusters has been investigated with photoemission near the photoio... more The 3p valence region of argon clusters has been investigated with photoemission near the photoionization threshold. A strong feature between 14.6 and 15.3 eV binding energy shows a photon-energy dependence indicative of electronic-energy band dispersion. A similar feature at approximately the same binding energy and with a similar dispersion occurs in photoemission spectra of both the ordered and disordered solids. The effect is already fully developed for scaling-law mean cluster sizes ͗N͘ of approximately 200 atoms, thus showing an early onset of bulklike electronic properties.
Physical Review A, 2013
ABSTRACT The photofragmentation of the water cation H2O+ through dicationic states has been studi... more ABSTRACT The photofragmentation of the water cation H2O+ through dicationic states has been studied at 35.0±0.2 nm (35.4±0.3 eV) and 21.8±0.2 nm (56.8±0.5 eV) with a crossed ion-photon beams experiment at the free electron laser FLASH. The dissociation of the dications is found to be similar at the two wavelengths and to proceed into O0+2H+, OH++H+, and O++H2+, with determined ratios σOH++H+/σO++H2+=4.2±0.3 and σOH++H+/σO0+2H+>0.7. The measured kinetic-energy releases for these processes are consistent with three-body breakup (O0+2H+) occurring mainly through the 2 3 A′′ and 2 1 A′′ states of H2O2+ and two-body breakup (OH++H+) occurring through X 3 A′′, 1 3 A′, and 1 1 A′′ states of H2O2+, as predicted in a recent theoretical study [ Gervais et al. J. Chem. Phys. 131 024302 (2009)]. In addition to the kinetic-energy releases, we also report on fragment correlation in the three-body channel where the two protons carry the major part of the released momentum.
Physical Review A, 2011
We present high-resolution photoelectron-Auger electron coincidence spectra of methane (CH 4 ).
Nature Physics, 2010
Low-energy electrons are the most abundant product of ionizing radiation in condensed matter. The... more Low-energy electrons are the most abundant product of ionizing radiation in condensed matter. The origin of these electrons is most commonly understood to be secondary electrons 1 ionized from core or valence levels by incident radiation and slowed by multiple ...
Journal of Electron Spectroscopy and Related Phenomena, 2011
Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion i... more Using photoemission we have investigated free argon clusters from a supersonic nozzle expansion in the photon energy range from threshold up to 28 eV. Measurements were performed both at high resolution with a hemispherical electrostatic energy analyser and at low resolution with a magnetic bottle device. The latter experiments were performed for various mean cluster sizes. In addition to the ≈ 1.5 eV broad 3p-derived valence band seen in previous work, there is a sharper feature at ≈ 15 eV binding energy. Surprisingly for nonoriented clusters, this peak shifts smoothly in binding energy over the narrow photon energy range 15.5 -17.7 eV, indicating energy band dispersion. The onset of this bulk band-like behaviour could be determined from the cluster size dependence.
Journal of Electron Spectroscopy and Related Phenomena, 2012
Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of... more Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of Auger decay processes with different core-ionized intermediate states. In this paper we describe an investigation into the Auger decay of the O 2 molecule, with the purpose of bringing new insight into the dynamics of the core hole decay mechanism. Using a novel experimental approach to measuring such coincidence spectra we report the highest resolution Auger spectrum of O 2 recorded hitherto. In our approach, we have combined the advantages of these coincidence spectra with the high resolution and excellent signal-to-noise ratios of non-coincident Auger spectra and a state-of-the-art fit analysis. In this way we have derived information about the potential energy curves of the final states W 3 u , B 3 g , and B' 3 u and concluded that the corresponding Auger transitions are formed to a large part by strongly overlapping vibrational progressions. The present findings are compared to earlier results reported in the literature confirming some theoretical predictions.
Journal of Electron Spectroscopy and Related Phenomena, 2011
Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Au... more Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Auger decay following the photoionization of core or inner valence levels in atoms, molecules or clusters. Moreover, the technique provides valuable insight into the dynamics of core hole decay. This paper serves the dual purpose of demonstrating the additional information obtained by this technique compared to Auger spectroscopy alone as well as of describing the new IPP/FHI apparatus at the BESSY II synchrotron radiation source. The distinguishing feature of the latter is the capability to record both the photoelectron and Auger electron with good energy and angle resolution, for which purpose a large hemispherical electrostatic analyser is combined with several linear time-of-flight spectrometers. Results are reported for the K-shell photoionization of oxygen (O 2 ) and the subsequent K-VV Auger decay. Calculations in the literature for non-coincident O 2 Auger spectra are found to be in moderately good agreement with the new data.
Journal of Electron Spectroscopy and Related Phenomena, 2013
ABSTRACT We report the development and present status of the iDEEAA (Instrument for Direct Electr... more ABSTRACT We report the development and present status of the iDEEAA (Instrument for Direct Electron Energy and Angular Analysis) experimental end station for time- and angle-resolved X-ray photoelectron spectroscopy. The setup is based on multidimensional detection of photoelectrons by means of both time-of-flight (TOF) and/or electrostatic analyzers. The instrument offers the possibility to record simultaneously and independently photoelectron and Auger electron spectra. Samples can be either gases or solids. The system can operate with multiple photon sources, such as laboratory-based table-top laser extreme ultraviolet (EUV) sources, monochromatic Helium discharge lamp and soft X-ray synchrotron pulses. We demonstrate the performance of the setup by carrying out electron–electron coincidence experiments on CH4 and by mapping the band structure of Bi2Se3 using photons of the BESSY II electron storage ring.
The Journal of Chemical Physics, 2011
We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A welldefin... more We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A welldefined feature ranging from 9 to 12 eV in kinetic energy is observed in coincidence with the Ne 2s photoelectrons. It derives from an ICD process, in which an initial Ne 2s vacancy is filled by a Ne 2p electron and an electron is emitted from a 4p level on a neighboring Kr atom. We have studied the dependence of the effect on photon energy, cluster composition, and cluster size. Interestingly, the ICD electron energy increases slightly and grows a shoulder on going from 2% to 5% Kr in the coexpansion process, which we interpret in terms of surface versus bulk effects.
The Journal of Chemical Physics, 2013
The angular distribution of photoelectrons emitted from water clusters has been measured by linea... more The angular distribution of photoelectrons emitted from water clusters has been measured by linearly polarized synchrotron radiation of 40 and 60 eV photon energy. Results are given for the three outermost valence orbitals. The emission patterns are found more isotropic than for isolated molecules. While a simple scattering model is able to explain most of the deviation from molecular behavior, some of our data also suggest an intrinsic change of the angular distribution parameter. The angular distribution function was mapped by rotating the axis of linear polarization of the synchrotron radiation. [http://dx.
Journal of Applied Physics, 2014
ABSTRACT