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Photoelectron Spectroscopy of Solids and their Surfaces
Published in M. Prutton, Electronic Properties of Surfaces, 2018
R.H. Williams, G.P. Srivastava, I.T. McGovern
The surface exafs technique also requires continuously tunable x-radiation and while conventional exafs is routinely performed using the bremsstrahlung radiation of a local x-ray source, reduced signal-to-noise in sexafs combined with surface-degrading problems demands the use of the higher flux rates of synchrotron radiation. EXAFS effects are integrated over 4π solid angle and hence direct photoemission, which is essentially into 2π, may not carry the full information. Rather the exafs oscillations are observed indirectly through the Auger decay of the core hole—either the direct Auger emission is recorded or the yield of secondary electrons resulting from the inelastic scattering of hot Auger electrons. This technique has been pioneered by workers at the Stanford Synchrotron Radiation Laboratory and an early example due to Stöhr et al (1978) is reproduced in figure 25(c). The sample is a natural oxide layer on aluminium and the oxygen 1s core photoionisation cross section is monitored via the secondary electron yield method. The exafs modulations in the cross section are indicated by arrows and for a single scattering geometry, the relative absorption coefficient modulation χ(k) has the form (A(k)/k) sin (2kd + ϕ(k)), where A (k) is the back-scattering amplitude, k is the photoelectron momentum, d is the distance between the source atom and the scattering atom and ϕ(k) is a k-dependent phase shift arising from the scattering and the motion of the outgoing and incoming waves through the central atom potential. In a complex scattering geometry, the function χ(k)k exp (− iϕ(k))/A(k) is Fourier-transformed into a distance spectrum as shown as an inset in figure 25(c); the dominant peak is attributed to the nearest-neighbour oxygen-aluminium back-scattering and this separation of 1·93 Å compares favourably with the average O—Al distance in bulk Al2O3 of 1·915 Å.
High-throughput analysis of magnetic phase transition by combining table-top sputtering, photoemission electron microscopy, and Landau theory
Published in Science and Technology of Advanced Materials: Methods, 2022
T. Nishio, M. Yamamoto, T. Ohkochi, D. Nanasawa, A. L. Foggiatto, M. Kotsugi
For Fe–Co–Cr alloys, chemical maps and magnetic contrast images were measured using a spectroscopic PEEM instrument (Elimitec, SPELEEM, Germany) installed at BL17SU of SPring-8 [23–25]. Before the XAS/MCD-PEEM measurement, we applied an AC demagnetisation field parallel to SR incidence in an attempt to align the magnetisation of the specimen along the SR incidence. Before SR measurement, the surface was suputtered with Ar+ ions at 1 kV acceleration voltage, 15 mA of emission current, P = 2.0 × 10−5 Torr for approximately 90 min, with gentle annealing at 400 °C in the preparation chamber. The XAS and MCD signals were acquired in the same field of view, and the photon energy was continuously scanned at the L absorption edges of Fe, Co, and Cr. The energy scan ranges for Fe, Co, and Cr were 700–730, 770–805, and 570–600 eV, respectively, with a step size of approximately 0.14 eV. XAS was obtained by measuring total electron yields using PEEM. PEEM measurement was carried out at room temperature (300 K). The composition ratio was determined from the XAS absorption and photoionisation cross-section of each element [26,27]. The edge height of the L3 absorption peak was normalised by the photoionisation cross-section. The chemical composition ratio of the three elements was obtained by the ratio of the normalised intensities using the following formula:
Effect of magnetic field on donor impurity-related photoionisation cross-section in multilayered quantum dot
Published in Philosophical Magazine, 2021
M. V. Chubrei, V. A. Holovatsky, C. A. Duque
For multilayer nanosystems, the diagonalisation method with the use of wave function expansion on the orthonormal basis of exact solutions of the Schrödinger equation requires complicated numerical calculations. Therefore, it would be optimal to use the direct numerical solution of the Schrödinger equation by the finite element method (FEM), which is intensively used to calculate the wave functions and the energy spectrum of electron nanosystems [25–27], especially in cases of nonspherical QD shape [25,26] while the other methods are problematic. Therefore, there is some interest in comparing the results of research performed by the FEM and the diagonalisation method for the same problem. Thus, to achieve the objective, the magnetic field effect on the transition energies and the photoionisation cross-section (PCS) of a non-central impurity at an MSQD is investigated in this paper.
Inner-shell photoabsorption and photoionisation cross-sections of valence excited states from asymmetric-Lanczos equation-of-motion coupled cluster singles and doubles theory
Published in Molecular Physics, 2021
Torsha Moitra, Sonia Coriani, Bruno Nunes Cabral Tenorio
Above the ionisation threshold of the ground state, the photoionisation cross-section is seen to gradually decrease with basically no structure. We refer to Ref. [16] for additional details of the calculation of the ground state XA photoionisation cross-section. Conversely, the continuum region of the valence excited states shows broad peaks when using Stieltjes Imaging and (unphysical) sharp features using the Padé approximant method. As reported for water, the cross-sections of ammonia computed using Padé approximants are higher and narrower than those obtained using Stieltjes Imaging. Also, the Stieltjes cross-sections computed with CVS-ADC(2)-x and at the Franck-Condon geometry [15] show a peak in the continuum which is slightly red-shifted with respect to the CVS-EOM-CCSD peak.