scholarly journals Analysis of a measurement scheme for ultrafast hole dynamics by few femtosecond resolution X-ray pump–probe Auger spectroscopy

2014 ◽  
Vol 171 ◽  
pp. 93-111 ◽  
Author(s):  
Bridgette Cooper ◽  
Přemysl Kolorenč ◽  
Leszek J. Frasinski ◽  
Vitali Averbukh ◽  
Jon P. Marangos
Keyword(s):  
Auger Spectroscopy ◽  
X Rays ◽  
Core Hole ◽  
Pump Probe ◽  
X Ray ◽  
Molecular Systems ◽  
The Core ◽  
Probe Delay ◽  
Valence Region ◽  
Hole Migration

Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump–probe scheme uses X-rays with photon energy below the K edge of carbon (275–280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump–probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.

scholarly journals Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect

2019 ◽  
Vol 116 (11) ◽  
pp. 4877-4882 ◽  
Author(s):  
Denis Céolin ◽  
Ji-Cai Liu ◽  
Vinícius Vaz da Cruz ◽  
Hans Ågren ◽  
Loïc Journel ◽  
...  
Keyword(s):  
Delay Time ◽  
Doppler Effect ◽  
Auger Electron ◽  
Molecular Motion ◽  
General Point ◽  
Core Hole ◽  
Time Resolved ◽  
Pump Probe ◽  
X Ray ◽  
The Core

Observing and controlling molecular motion and in particular rotation are fundamental topics in physics and chemistry. To initiate ultrafast rotation, one needs a way to transfer a large angular momentum to the molecule. As a showcase, this was performed by hard X-ray C1s ionization of carbon monoxide accompanied by spinning up the molecule via the recoil “kick” of the emitted fast photoelectron. To visualize this molecular motion, we use the dynamical rotational Doppler effect and an X-ray “pump-probe” device offered by nature itself: the recoil-induced ultrafast rotation is probed by subsequent Auger electron emission. The time information in our experiment originates from the natural delay between the C1s photoionization initiating the rotation and the ejection of the Auger electron. From a more general point of view, time-resolved measurements can be performed in two ways: either to vary the “delay” time as in conventional time-resolved pump-probe spectroscopy and use the dynamics given by the system, or to keep constant delay time and manipulate the dynamics. Since in our experiment we cannot change the delay time given by the core-hole lifetime τ, we use the second option and control the rotational speed by changing the kinetic energy of the photoelectron. The recoil-induced rotational dynamics controlled in such a way is observed as a photon energy-dependent asymmetry of the Auger line shape, in full agreement with theory. This asymmetry is explained by a significant change of the molecular orientation during the core-hole lifetime, which is comparable with the rotational period.

CORE-HOLE EFFECT IN THE Ce L3 X-RAY ABSORPTION SPECTRA OF CeO2 AND CeFe2: NEW EXAMINATION BY USING RESONANT X-RAY EMISSION SPECTROSCOPY

2013 ◽  
Vol 27 (16) ◽  
pp. 1330012 ◽  
Author(s):  
A. KOTANI
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Theoretical Calculations ◽  
Emission Spectra ◽  
Core Hole ◽  
Final State ◽  
X Ray ◽  
The Core ◽  
X Ray Absorption ◽  
Hole Effect

We consider two different resonant X-ray emission spectra for Ce compounds: Ce 3d to 2p X-ray emission (denoted by 3d-RXES) and valence to 2p X-ray emission (v-RXES), both of which follow the Ce 2p to 5d resonant excitation. We propose that the comparison of the 3d- and v-RXES spectra is a new powerful method of directly detecting the core-hole effect in the final state of Ce L 3 X-ray absorption spectra (XAS). We applied this method to recent experimental RXES spectra for CeO 2 and CeFe 2, and showed unambiguously that the core-hole effect should be essential in the XAS of both materials. This result is confirmed by theoretical calculations, which reproduce well the experimental RXES and XAS spectra. We conclude that the ground state of CeO 2 is in the mixed state of 4f0 and [Formula: see text] configurations, where [Formula: see text] is a ligand hole, instead of a pure 4f0 configuration which was proposed recently by first-principles energy band calculations. Also, we conclude that the double peaks observed in L 3 XAS of CeFe 2 are caused by the 4f0 and 4f1 configurations, which are mixed in the ground state but separated in energy by the large core-hole potential in the final state of XAS.

scholarly journals X-ray Emission from Massive Stars at the Core of Very Young Clusters

2016 ◽  
Vol 12 (S329) ◽  
pp. 362-365
Author(s):  
Norbert S. Schulz
Keyword(s):  
Massive Stars ◽  
Stellar Winds ◽  
X Rays ◽  
Stellar Clusters ◽  
Orion Nebula ◽  
X Ray ◽  
The Core ◽  
Hot Plasma ◽  
Young Clusters ◽  
Massive Cluster

AbstractMost cores of very young stellar clusters contain one or more massive stars at various evolutionary stages. Observations of the Orion Nebula Cluster, Trumpler 37, NGC 2362, RCW38, NGC 3603 and many others provide the most comprehensive database to study stellar wind properties of these massive cluster stars in X-rays. In this presentation we review some of these observations and results and discuss them in the context of stellar winds and possible evolutionary implications. We argue that in very young clusters such as RCW38 and M17, shock heated remnants of a natal shell could serve as an alternate explanation to the colliding wind paradigm for the hot plasma components in the X-ray spectra.

COMPOSITION AND OPTICAL CHARACTERISTICS OF ELECTROCHEMICALLY-SYNTHESIZED GaAs NANOCRYSTALS

2004 ◽  
Vol 03 (03) ◽  
pp. 281-292 ◽  
Author(s):  
J. NAYAK ◽  
S. VARMA ◽  
D. PARAMANIK ◽  
S. N. SAHU
Keyword(s):  
Room Temperature ◽  
Low Cost ◽  
Energy Shift ◽  
Electrochemical Technique ◽  
X Rays ◽  
Emission Analysis ◽  
X Ray ◽  
The Core ◽  
Infrared Luminescence ◽  
Binding Energy Shift

The synthesis of the GaAs nanoparticles, having sizes 7 nm to 15 nm, by a low cost electrochemical technique has been reported. The absence of any foreign impurity has been confirmed by the Proton-Induced X-rays Emission analysis. Rutherford Backscattering measurement has been performed in order to estimate the thickness of the nanoparticle-generated thin film as a function of the electrolysis current density. The X-ray Photoelectron Spectroscopic study confirms the formation of GaAs and exhibits the binding energy shift of the core shell electrons as an implication of the nanostructure effect. Very weak infrared luminescence due to the radiative recombination of the impurity bound exciton has been detected from yttrium-doped GaAs nanocrystals, even at room temperature.

scholarly journals Spectral weight of resonant inelastic X-ray scattering in doped cuprates: Effect of core-hole lifetime

2018 ◽  
Vol 32 (17) ◽  
pp. 1840017 ◽  
Author(s):  
Takami Tohyama ◽  
Kenji Tsutsui
Keyword(s):  
Spectral Weight ◽  
Main Peak ◽  
Core Hole ◽  
X Ray ◽  
The Core ◽  
X Ray Scattering ◽  
Spin Flip ◽  
X Ray Absorption ◽  
Magnon Excitation ◽  
Ray Scattering

We examine the effect of core-hole lifetime on the spectral weight of resonant inelastic X-ray scattering (RIXS) in hole-doped cuprates. We calculate the spectral weight by using the exact diagonalization technique for a 4 × 4 doped Hubbard lattice and find that the spin-flip channel detecting single-magnon excitation is less sensitive to the core-hole lifetime while in the non-spin-flip channel the spectral weight is strongly dependent on the lifetime. In the latter, charge and two-magnon excitations predominately contribute to RIXS for short and long core-hole lifetimes, respectively. For a realistic value of the core-hole lifetime in cuprates, both the charge and two-magnon excitations are expected to contribute to the non-spin-flip channel in RIXS when the incident-photon energy is tuned to the main peak of X-ray absorption spectrum.

scholarly journals Finite lifetime broadening of calculated X-ray absorption spectra: possible artefacts close to the edge

2018 ◽  
Vol 25 (2) ◽  
pp. 523-528 ◽  
Author(s):  
Ondřej Šipr ◽  
Jiří Vackář ◽  
Ján Minár
Keyword(s):  
Absorption Spectra ◽  
Real Axis ◽  
Absorption Edge ◽  
Spectral Features ◽  
Core Hole ◽  
Energy Component ◽  
X Ray ◽  
The Core ◽  
X Ray Absorption ◽  
Small Imaginary Part

X-ray absorption spectra calculated within an effective one-electron approach have to be broadened to account for the finite lifetime of the core hole. For methods based on Green's function this can be achieved either by adding a small imaginary part to the energy or by convoluting the spectra on the real axis with a Lorentzian. By analyzing the FeK- andL2,3-edge spectra it is demonstrated that these procedures lead to identical results only for energies higher than a few core-level widths above the absorption edge. For energies close to the edge, spurious spectral features may appear if too much weight is put on broadeningviathe imaginary energy component. Special care should be taken for dichroic spectra at edges which comprise several exchange-split core levels, such as theL3-edge of 3dtransition metals.

scholarly journals Equation-of-Motion Coupled-Cluster Cumulant Green’s Function for Excited States and X-Ray Spectra

2021 ◽  
Vol 9 ◽  
Author(s):  
F. D. Vila ◽  
J. J. Kas ◽  
J. J. Rehr ◽  
K. Kowalski ◽  
B. Peng
Keyword(s):  
Green’S Function ◽  
Spectral Function ◽  
Excited States ◽  
Green's Function ◽  
Coupled Cluster ◽  
X Ray ◽  
Molecular Systems ◽  
Self Energy ◽  
The Core ◽  
Non Linear

Green’s function methods provide a robust, general framework within many-body theory for treating electron correlation in both excited states and x-ray spectra. Conventional methods using the Dyson equation or the cumulant expansion are typically based on the GW self-energy approximation. In order to extend this approximation in molecular systems, a non-perturbative real-time coupled-cluster cumulant Green’s function approach has been introduced, where the cumulant is obtained as the solution to a system of coupled first order, non-linear differential equations. This approach naturally includes non-linear corrections to conventional cumulant Green’s function techniques where the cumulant is linear in the GW self-energy. The method yields the spectral function for the core Green’s function, which is directly related to the x-ray photoemission spectra (XPS) of molecular systems. The approach also yields very good results for binding energies and satellite excitations. The x-ray absorption spectrum (XAS) is then calculated using a convolution of the core spectral function and an effective, one-body XAS. Here this approach is extended to include the full coupled-cluster-singles (CCS) core Green’s function by including the complete form of the non-linear contributions to the cumulant as well as all single, double, and triple cluster excitations in the CC amplitude equations. This approach naturally builds in orthogonality and shake-up effects analogous to those in the Mahan-Noizeres-de Dominicis edge singularity corrections that enhance the XAS near the edge. The method is illustrated for the XPS and XAS of NH3.

scholarly journals One Shot Cluster Based Approach for the Detection of COVID-19 from Chest X-Ray Images

2020 ◽  
Author(s):  
V.N. Manjunath Aradhya ◽  
Mufti Mahmud ◽  
Basant Agarwal ◽  
D.S. Guru ◽  
M. Shamim Kaiser
Keyword(s):  
Virus Disease ◽  
X Rays ◽  
Probabilistic Neural Networks ◽  
X Ray ◽  
The Core ◽  
Wide Range ◽  
Test Instance ◽  
Chest X Ray ◽  
Detection And Diagnosis ◽  
The Way

Corona virus disease (COVID-19) has infected over more than 10 million people around the globe and killed at least 500K worldwide by the end of June 2020. As this disease continues to evolve and scientists and researchers around the world now trying to find out the way to combat this disease in most effective way. Chest X-rays are widely available modality for immediate care in diagnosing COVID-19. Precise detection and diagnosis of COVID-19 from these chest X-rays would be practical for the current situation. This paper proposes one shot cluster based approach for the accurate detection of COVID-19 chest x-rays. The main objective of one shot learning (OSL) is to mimic the way humans learn in order to make classification or prediction on a wide range of similar but novel problems. The core constraint of this type of task is that the algorithm should decide on the class of a test instance after seeing just one test example. For this purpose we have experimented with widely known Generalized Regression and Probabilistic Neural Networks. Experiments conducted with publicly available chest x-ray images demonstrate that the method can detect COVID-19 accurately with high precision. The obtained results have outperformed many of the convolutional neural network based existing methods proposed in the literature.

scholarly journals TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers

2020 ◽  
Vol 27 (3) ◽  
pp. 813-826 ◽  
Author(s):  
Mauro Rovezzi ◽  
Alistair Harris ◽  
Blanka Detlefs ◽  
Timothy Bohdan ◽  
Artem Svyazhin ◽  
...  
Keyword(s):  
Vacuum Chamber ◽  
Solid Angle ◽  
High Vacuum ◽  
Core Hole ◽  
Innovative Design ◽  
X Ray ◽  
The Core ◽  
First Results ◽  
Sufficient Space

The design and first results of a large-solid-angle X-ray emission spectrometer that is optimized for energies between 1.5 keV and 5.5 keV are presented. The spectrometer is based on an array of 11 cylindrically bent Johansson crystal analyzers arranged in a non-dispersive Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allocates a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.

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