Single and double Auger decays from vibrationally excited core-ionized N2 molecules are studied using multielectron coincidence spectroscopy. The high vibrational sublevels (ν ≥ 5) of the core-hole ...state are populated via autoionization following core-valence double excitation. The features of the Auger spectra vary significantly as the initial vibrational excitation increases, which reflects the vibrational wave functions in the core-hole state and the repulsive potential energy curves for Auger final states.
•A combination use of the efficient multielectron spectroscopy and the pulsed synchrotron light.•Single and double Auger decays from vibrationally excited core-ionized N2 molecules are studied.•The Auger structures appear to broaden with increasing initial vibrational excitation.
Nature of the arsenic oxide surface modification during the XPS analysis.
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•Arsenic oxide is photoreduced under standard XPS measurements.•Photoreduction involves oxygen desorption ...from the oxide surface.•Carbon contamination plays an important role in degradation.•Long X-ray exposures combined with long vacuum times should be avoided.
XPS is extensively used for the characterization of arsenic-containing compounds like As(V) oxides, which can be found on the surface of minerals and important functional materials such as semiconductors and catalysts. However, potential sample degradation could alter the results. In this study, we explore the nature and extent of As2O5.5/3H2O phase degradation under XPS measurements in order to assess the intrinsic impact of this spectroscopic technique on the collected data. A series of experiments were designed for unravelling the effect of several factors like X-ray.
irradiation time and intensity, vacuum time and charge compensation system. The influence of the structure and composition of the oxide was tested by taking the As2O5 phase as reference. Analyses were based on curve fitting of As3d, C1s and O1s high-resolution spectra, including survey quantification. Results show that degradation involves reduction of As(V) to As(III) species along with oxygen lost from the oxide lattice. As(V) photoreduction becomes extensive by repeating doses of X-ray irradiation; the photon beam intensity plays a major role in degradation, especially combined with the use of a dual flood gun as charge compensation system, while longer vacuum times also favor reduction. The dehydrated phase is more resistant to degradation likely due to a broader valence-band width. The presence of organic molecules from carbon contamination seems to play an important role in degradation. The possible underlying mechanism based on Auger decay of the initial core hole is considered. Minimal sample damage can be obtained by fixing the operating power and the vacuum and irradiation times at the least affordable values.
Optically Excited Lasing
In article number 2206613, Namyoung Ahn, Victor I. Klimov, and co‐workers demonstrate optically excited lasing in a fully functional colloidal quantum dot electroluminescent ...device with an integrated optical resonator prepared as a distributed feedback grating, representing an important milestone toward solution‐processable laser diodes. The colloidal quantum dots are cast from solution onto a grating and excited either electrically or optically to produce multicolor output. Image credit: Albin Guyot.
Laser diodes based on solution‐processable materials can benefit numerous technologies including integrated electronics and photonics, telecommunications, and medical diagnostics. An attractive ...system for implementing these devices is colloidal semiconductor quantum dots (QDs). The progress towards a QD laser diode has been hampered by rapid nonradiative Auger decay of optical‐gain‐active multicarrier states, fast device degradation at high current densities required for laser action, and unfavorable competition between optical gain and optical losses in a multicomponent device stack. Here we resolve some of these challenges and demonstrate optically excited lasing from fully functional high‐current density electroluminescent (EL) devices with an integrated optical resonator. This advance has become possible due to excellent optical gain properties of continuously graded QDs and a refined device architecture, which allows for highly efficient light amplification in a thin, EL‐active QD layer.
Dual‐function colloidal quantum dot (QD) devices that operate as a high‐current density light emitting diode and an optically excited laser are demonstrated. The device structure has been optimized to reduce optical losses and allow for efficient wave‐guiding within the active QD layer. This demonstration represents an important milestone toward the practical implementation of a colloidal QD laser diode.
•Energies, radiative and Auger decay rates for the 1s23lnl′ 1, 3S (n = 3–4) states are calculated.•The regular change of the Auger branching ratios and the total fluorescence yield along the Be-like ...ions is discussed.•The percentage contribution of leading configurations of states 1s23lnl′ 1S (n = 3–4) states is given.
Energies, radiative and Auger decay rates for the doubly-excited states 1s23lnl′ 1, 3S (n=3–4) of Be-like ions are calculated by the saddle-point variation and saddle-point complex-rotation methods. The configuration structure of the doubly-excited series is checked by the relative contribution to the normalization of the angular-spin components. Relativistic corrections and mass polarization effects are taken into account by the first-order perturbation theory. The partial Auger decay rates and the Auger branching ratios for these states are studied. The calculated Auger electron energies are compared with the high resolution electron spectroscopy. The total fluorescence yield of these doubly-excited states 1s23lnl′ 1, 3S in the Be-like ions are also analyzed along with the increase of atomic number Z.
Auger decay is a relaxation process of core-vacant states in atoms and molecules, in which one valence electron fills the core vacancy while a second one is emitted. These states pose a challenge to ...electronic-structure theory, because they are embedded in the ionisation continuum. Recently, we showed that molecular Auger decay can be described using complex-variable coupled-cluster (CC) methods and that partial widths and branching ratios can be computed based on a decomposition of the CC energy. Here, we introduce channel-specific core-valence projectors, dubbed Auger channel projectors, as a more general technique to evaluate partial widths from complex-variable treatments. We apply this new method to core-ionised states of neon, water, ammonia and methane using CC singles and doubles (CCSD), equation-of-motion ionisation potential CCSD and configuration interaction singles (CIS) wave functions. Even though a single CIS calculation can never describe all Auger decay channels at once, we show that a combination of CIS calculations based on different reference states is able to recover partial and total decay widths from CC calculations to an excellent degree.
Multiple electron processes occur widely in atoms, molecules, clusters, and condensed matters when they are interacting with energetic particles or intense laser fields. Direct multielectron ...processes (DMEP) are the most complicated among the general multiple electron processes and are the most difficult to describe theoretically. In this work, a unified and accurate theoretical formalism is proposed on the DMEP of atoms including the multiple auger decay and multiple ionization by an impact of a single electron or a single photon based on the atomic collision theory described by a correlated many-body Green's function. Such a practical treatment is made possible by taking consideration of the different coherence features of the atoms (matter waves) in the initial and final states. We first explain how the coherence characteristics of the ejected continuum electrons is largely destructed, by taking the electron impact direct double ionization process as an example. The direct double ionization process is completely different from the single ionization where the complete interference can be maintained. The detailed expressions are obtained for the energy correlations among the continuum electrons and energy resolved differential and integral cross sections according to the separation of knock-out (KO) and shake-off (SO) mechanisms for the electron impact direct double ionization, direct double and triple auger decay, and double and triple photoionization (TPI) processes. Extension to higher order DMEP than triple ionization is straight forward by adding contributions of the following KO and SO processes. The approach is applied to investigate the electron impact double ionization processes of C+, N+, and O+, the direct double and triple auger decay of the K-shell excited states of C+ 1 s 2 s 2 2 p 2 2 D and 2 P , and the double and TPI of lithium. Comparisons with the experimental and other theoretical investigations wherever available in the literature show that our theoretical formalism is accurate and effective in treating the atomic multielectron processes.
Electron correlation describes the interaction between electrons in a multi-electron system. It plays an important role in determining the speed of relaxation of atoms and molecules excited by ...XUV/X-ray pulses, such as the argon decay rate. Most research on electron correlation has centered on the role of correlation in stationary states. A time-resolved experimental study of electron correlation is a grand challenge due to the required temporal resolution and photon energy. In this research, we investigated Auger decay in argon using 200-attosecond X-ray pulses reaching the carbon K-edge. At such a high photon energy, ionization occurs not only from the outer most levels (3s and 3p), but also from the 2p core shells. We have measured a lifetime of 4.9 fs of L-shell vacancies of argon in pump–probe experiments with a home-built high-resolution time-of-flight spectrometer.
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