Electronic Core Levels of the II B − VI A Compounds
TL;DR: In this paper, the energy levels of core electrons in ZnO, ZnS and CdTe were determined using X-ray-induced electron-emission measurements.
Abstract: X-ray induced electron-emission measurements were used to determine the energy levels of core electrons in ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgS, HgSe, and HgTe. The investigated energy range extends from the bottom of the valence band to about 1200 eV below the Fermi level. Chemical shifts were determined by comparing our results with experimental values for the pure elements. These shifts are plotted as a function of the fractional ionicity values determined by Phillips and Van Vechten, Pauling, and Coulson. Spinorbit-splitting values were experimentally determined for the first time for several levels including the $\mathrm{Zn}3d$, $\mathrm{Cd}4d$, and $\mathrm{Hg}5d$ levels. Furthermore, our measured energy values for these levels are used to determine the absolute energy values of the initial and final states of transitions normally labeled ${d}_{2}$ in ultraviolet reflectivity and electron-energy-loss measurements. Our results for ZnSe and CdTe are compared with self-consistent relativistic orthogonalized-plane-wave calculations for the excitation energies of these compounds. Agreement with these theoretical calculations is best for the levels closest to the valence band and appears to be angular momentum dependent.
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TL;DR: In this paper, the authors present a review of the status quo of X-ray photoelectron spectroscopy with a historical perspective, provide the technique's operating principles, resolve myths associated with C 1s referencing, and offer a comprehensive account of recent findings.
1,108 citations
TL;DR: In this paper, the pH-dependent photoluminescence (PL) of MPA-and TGA-stabilized CdTe nanoparticles was systematically investigated before and after addition of poly(acrylic acid) (PAA) into the CdTE solutions.
Abstract: The CdTe nanoparticles were prepared in aqueous solution using different mercaptocarboxylic acids such as 3-mercaptopropionic acid (MPA) and thioglycolic acid (TGA) as stabilizing agents following the synthetic route described in ref 9. The pH-dependent photoluminescence (PL) of MPA- and TGA-stabilized CdTe nanoparticles was systematically investigated before and after addition of poly(acrylic acid) (PAA) into the CdTe solutions. Experimental results reveal that lowering the pH can increase the PL efficiency of both MPA- and TGA-stabilized CdTe. Moreover, the PL of the CdTe can further be increased in the presence of PAA in low pH range. X-ray photoelectron spectroscopy (XPS) was employed to investigate the interaction between the carboxyl groups from PAA and CdTe nanoparticles which were assembled in polymer matrix by a layer-by-layer self-assembly method to exclude interference from other species in CdTe solutions. XPS results demonstrate that the S/Te ratio of CdTe particles decreases after the additio...
579 citations
TL;DR: In this paper, a brief historical review has been made of the values assigned to the binding energy of C1s electrons from hydrocarbon contamination on sample surfaces, as well as the particular energy calibration technique used for each electron spectrometer on which the C 1s determination was made has been identified.
Abstract: A brief historical review has been made of the values assigned to the binding energy of C1s electrons from hydrocarbon contamination on sample surfaces. The particular energy calibration technique used for each electron spectrometer on which the C1s determination was made has been identified. There are notable variations in the C1s electron binding energy for a hydrocarbon contamination layer with respect to the substrate on which it was measured. The possible source and nature of adventitious carbon have been discussed, as have factors which can affect its C1s binding energy value. Sodium phosphate salts have been used to illustrate the relative merits of using an internal energy reference line rather than the C1s electrons from the adventitious carbon layers of these salts. Alternative energy referencing techniques, which include deposition of soot from a candle flame and deliberate ‘in situ’ condensation of a volatile organic compound onto the sample surface, have been compared with the method under review. Another possible method is the mixing of powdered samples with reference compounds (e.g. graphite). It is concluded that, although the use of C1s electrons from adventitious carbon layers is often a convenient method of energy referencing, interpretation of binding energy data obtained should be treated with caution.
365 citations
TL;DR: In this article, a WS2/CdS photocatalyst with different amounts of WS2 cocatalyst is prepared by loading WS2 on CdS with an impregnation-sulfidation approach.
Abstract: WS2/CdS photocatalysts with different amounts of WS2 cocatalyst are prepared by loading WS2 on CdS with an impregnation–sulfidation approach. The transformation process of the tungsten species loaded on CdS together with the junctions formed between WS2 and CdS are clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. Photocatalytic H2 production on WS2/CdS catalysts under visible light (λ > 420 nm) shows that WS2 cocatalyst plays a crucial role in H2 production. Under optimum conditions, the rate of H2 evolution can be increased by up to 28 times when CdS was loaded with only 1.0 wt % WS2, and WS2 demonstrates a catalytic performance comparable or even superior to those of noble metals. Photocatalytic reaction results and electrochemical measurements indicate that the significantly enhanced H2 evolution of WS2/CdS catalyst mainly owns to the junctions formed between WS2 and CdS and the excellent performance of WS2 as a cocatalyst in catalyzing H2 evolution.
358 citations
TL;DR: An ab initio pseudopotential method based on density functional theory, generalized gradient corrections to exchange and correlation, and projector-augmented waves is used to investigate structural, energetical, electronic, and optical properties of the ground-state phases rocksalt, cesium chloride, zinc blende, and wurtzite.
Abstract: An ab initio pseudopotential method based on density functional theory, generalized gradient corrections to exchange and correlation, and projector-augmented waves is used to investigate structural, energetical, electronic, and optical properties of $\mathrm{MgO}$, $\mathrm{ZnO}$, and $\mathrm{CdO}$ in rocksalt, cesium chloride, zinc blende, and wurtzite structure. In the case of $\mathrm{MgO}$ we also examine the nickel arsenide structure and a graphitic phase. The stability of the ground-state phases rocksalt $(\mathrm{MgO},\mathrm{CdO})$ and wurtzite $(\mathrm{ZnO})$ against hydrostatic pressure and biaxial strain is studied. We also present the band structures of all polymorphs as well as the accompanying dielectric functions. We discuss the physical reasons for the anomalous chemical trend of the ground-state geometry and the fundamental gap with the size of the group-II cation in the oxide. The role of the shallow $\mathrm{Zn}3d$ and $\mathrm{Cd}4d$ electrons is critically examined.
320 citations