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Characterization of Zeolite Catalysts
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
Photoemission spectroscopy (PES) involves the absorption of a photon by an electron of the solid in a one-electron excitation process, which is followed by the emission into vacuum of a fraction of the excited electrons without energy loss. The kinetic energy distribution of these electrons is measured. X-ray photoemission spectroscopy (XPS) is the branch of PES.
Surfaces
Published in Gerald L. Schneberger, Adhesives in Manufacturing, 2018
The effect of the environment in which polymers are prepared has been carefully studied with electron spectroscopy for chemical analysis (ESCA). Electron spectroscopy for chemical analysis, or x-ray photoemission spectroscopy (XPS) as it is currently called, permits analysis of surfaces by measuring both the energies associated with electron levels in atoms and molecules and shifts in electron energies accompanying various chemical reactions. It is a surface-sensitive tool.
Few-Layer Graphenes
Published in Tran Ngoc Thanh Thuy, Shih-Yang Lin, Chiun-Yan Lin, Ming-Fa Lin, Geometric and Electronic Properties of Graphene-Related Systems, 2017
Tran Ngoc Thanh Thuy, Shih-Yang Lin, Chiun-Yan Lin, Ming-Fa Lin
ARPES is a direct experimental technique used to observe the distribution of valence electrons in the reciprocal space of solids. This technique, a refinement of ordinary photoemission spectroscopy, is available for studying photoemission of electrons from a sample usually achieved by illumination with soft X-rays. Figure 3.6 illustrates the process of an ARPES experiment. Photoelectrons are stimulated by incident photons and escape the material into the vacuum; they are counted by an angle-resolved electron energy analyzer. The momentum of photoelectrons can be calculated by 2mEp, where m is the bare electron mass and Ep is its kinetic energy. The momentum components, which are parallel and perpendicular to the sample surface, are determined by the polar angle and the azimuthal angle ( θ and φ, respectively in Figure 3.6). During the process of photoemission, the total energy and the parallel-component momentum are conserved, while the opposite is true for the perpendicular-component momentum. This is due to the breaking of translational symmetry along the normal direction. ARPES measurements are mainly focused on the valence bands with energy dispersions along the high symmetry points in the (kx, ky)-space, e.g., the low-lying occupied states of graphene-related systems near the k-point. In addition, ARPES can also measure energy widths of valence electrons, which is useful in understanding the decay rates, i.e., the deexcitation behavior. Improvements in energy and angular resolutions have been key in advancing this technique into a precision tool for the investigation of various phenomena. Up to now, the highest resolutions for energy and angular distributions are, respectively, ~1 meV and 0.1° in the UV regime [231].
Charge transfer enabled by the p-doping of WSe2 for 2D material-based printable electronics
Published in Journal of Information Display, 2023
Taoyu Zou, Haksoon Jung, Ao Liu, Soonhyo Kim, Youjin Reo, Taesu Choi, Yong-Young Noh
Ultraviolet photoemission spectroscopy (UPS) is a direct measurement method to demonstrate the doping effect and work function change [29]. The secondary electron cut-off spectrum (Figure 3(c)) shows a downward shift in the Fermi level from −4.11 eV to −4.55 eV after the FeCl3 treatment of the WSe2 thin film. The distance between the valence-band maximum (EVBM) to the Fermi level (EF) also shifts from 1.47 eV to 0.98 eV (Figure 3(d)). The downshift of EF to EVBM indicates the occurrence of considerable electron transfer from the WSe2 to FeCl3 molecules, i.e. the p-type doping effect in the WSe2 film, which may be attributed to the low electron affinity (EA) of the oxidizing agent, FeCl3 (EA = −4.65 eV) [21,30].