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Abstract: Incorporating the recent bond order–length–strength correlation mechanism [C.Q. Sun, Phys. Rev. B 69 (2004) 045105] to the size dependence of Auger photoelectron coincidence spectra of Cu nanoparticles with and without being passivated has enabled us to gain quantitative information about the 2p and 3d level energies of an isolated Cu atom and their shift upon bulk formation. The developed approach also enabled us to discriminate the effect of crystal-field screening from the effect of valence recharging (due to surface passivation and substrate–particle interaction) on the binding energies to the electrons at different energy levels of a specimen. [Copyright &y& Elsevier]

Abstract: The electronic processes of Cu(Ag, V, Rh)(001) surface oxidation are comparatively analyzed based on the recent ‘chemical bond–valence band–potential barrier’ (BBB) correlation mechanism [C.Q. Sun, Prog. Mater. Sci. 48, 521–685 (2003)], which allows reaction formulae for all the observed phases with identification of individual atomic valence and the binding kinetics at the surfaces with the same geometry. It is consistently understood that the forming kinetics of the primary oxide tetrahedron and its derivative on the valence density-of-states (DOS) are intrinsically common for all these analyzed systems, though the patterns of observation in terms of morphology and crystallography vary from situation to situation. However, the lattice size and electronegativity of the host surfaces determine extrinsically the site selectivity of the oxygen, the order of bond formation and the orientation of the oxide tetrahedron. [Copyright &y& Elsevier]

Surface oxidation and porosity variation play significant roles in the dielectric performance of porous silicon (PS) yet discriminating the contribution of these events is a challenge. Here we present an analytical solution that covers contributions from the components of silicon oxide surface, silicon backbone and voids using a serial–parallel capacitance structure. Agreement between modeling predictions and measurement has been realized, which turns out an effective method that enables us to estimate the extent of surface oxidation of a specimen by measuring the porosity dependent dielectric response of the chemically passivated PS, and provides guidelines that could be useful for designing dielectric porous structures with surface oxidation. [Copyright &y& Elsevier]

To design a catalyst for the dissociation of H 2 with better CO-tolerance performance is very important for proton exchange membrane fuel cells (PEMFCs) towards high efficiency. With slab model, the catalytic properties of overlayer Pt on Cu substrate (Pt/Cu) are analyzed by first-principle calculations. The CO saturation coverage (40%) on Pt 2 /Cu is found to be lower than that of pure Pt (about 75%). The dissociation barrier from H 2 to H is less than 0.4 eV under the saturation coverage of CO. On the basis of kinetics of proton formation, the CO-tolerance ability on double-layer Pt with Cu is found to be greatly improved compared with that on pure Pt. It is expected that Pt overlayer on Cu(1 1 1) is a potential anode material with lower cost for PEMFCs. [ABSTRACT FROM AUTHOR]

An incorporation of the hydrogen bond (O:H O or HB) cooperativity notion, contact angle detection, and the differential phonon spectrometrics (DPS) has enabled us to gain refined information on the HCl, KCl and KOH solvation resolved solute-solvent molecular interactions and the solution surface stresses. Results show that ionic polarization stiffens the solvent H O bond phonon from 3200 to 3480 cm −1 in the hydration shells. The HO − in alkaline solution, however, shares not only the same H O phonon redshift of compressed water from 3200 to < 3100 cm −1 but also the dangling bonds of H 2 O surface featured at 3610 cm −1 . Salt and alkaline solvation enhances the solution surface stress by K + and Cl − ionic polarization. The excessive H + proton in acid solution forms a H↔H anti-HB that depresses the solution surface stress, instead. The solute capability of transforming the fraction of the O:H O bonds of the solvent matrix is featured by: f H = 0 and f x ∝ 1-exp(-C/C 0 ) (x = HO − , K + and Cl − ) towards saturation. Exercises not only confirm the presence of the H↔H anti-HB point fragilization, the O:⇔:O super-HB point compression, and ionic polarization dominating the performance of the respective HCl, KOH, and KCl solutions, but also demonstrate the power of the DPS that enables high resolution of solute-solute-solvent interactions and correlation between HB relaxation and solution surface stress. [ABSTRACT FROM AUTHOR]

Exploiting efficient visible light active photocatalyst is a great challenge with potential applications such as environmental pollution and solar energy conversion. Herein, a series of CaIn 2 S 4 /WS 2 hybrids was fabricated via a simple hydrothermal method. WS 2 as cocatalyst increases the visible light absorption and separation efficient of charge carrier at the interface, leading to the enhanced photocatalytic activity of CaIn 2 S 4 /WS 2. CaIn 2 S 4 /20 wt% WS 2 hybrid shows the highest Cr(VI) reduction rate of 98% and methyl orange degradation rate of 96%. This work could offer some thought for designing and fabricating hybrid photocatalyst with high efficient and stable activity. CaIn 2 S 4 /WS 2 hybrids display excellent photocatalytic activity for Cr(VI) reduction and MO degradation under visible light irradiation. Unlabelled Image • Visible light active CaIn 2 S 4 /WS 2 hybrid photocatalysts are reported. • CaIn 2 S 4 /WS 2 hybrids exhibit excellent photo-reduction and degradation activity. • High Cr(VI) reduction and MO degradation rates are achieved under visible light irradiation. • Photo-generated electrons and O 2 − govern the photo-reduction and degradation process. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The magnetic moment of two-dimensional geometric structures of hexagon Y metal is expected to be 6.66 µB. • The core band and valence band are equally important for the magnetic spin state. • Larger spin orbit splitting results in larger spin shifts. Abstract We investigated the bond relaxation and electronic and magnetic behaviour of yttrium (Y) atoms adsorbed on lithium (Li)(1 1 0) surface by using a combination of bond-order-length-strength (BOLS) correlation and density-functional theory (DFT). We found that adsorption of Y atoms on Li(1 1 0) surfaces forms two-dimensional (2D) geometric structures of hexagon, nonagon, solid hexagon, quadrangle and triangle. Their magnetic moments are 6.66 µB, 5.54 µB, 2.81 µB, 0.28 µB and 1.04 µB, respectively. In addition, this work could pave the way for design of new 2D metals and understanding of their electronic and magnetic properties. [ABSTRACT FROM AUTHOR]

By studying the tantalum (Ta)(111) surface with X-ray photoemission spectroscopy and density functional theory, we determined binding energy values for the clean Ta(111) (+3.068 eV) and hydrogenated Ta(111) (+3.421 eV) surfaces with an isolated atom level of 18.977 eV. Using the bond–band barrier and zone-selective electron spectroscopy correlation, we investigated the mechanism of hydrogenation adsorption on the Ta(111) surface. We found the local densities of states of the first layer of Ta atoms in the reconstructed structure, which formed on the adsorbent hydrogen of the surface chemical bond contracts and dipole polarization. Moreover, we showed that on the Ta(111) surface, the hydrogen-induced surface core level shifts are dominated by quantum entrapment and are proportional to the calculated hybridized orbitals of the valence band. The latter is therefore correlated to the local surface chemical reactivity and is useful for other adsorbate systems on transition metals. [ABSTRACT FROM AUTHOR]

A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O Ta bonding, lone pairs of oxygen, Ta + electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta + ; the sp 3 -orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4 f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent insight into the electronic dynamics of metal oxidation. [ABSTRACT FROM AUTHOR]

We have examined the atomic coordination effect on the local bond strain and the 3p core-level shift of K(1 1 0) skin and nanoclusters using a combination of the bond order–length–strength correlation notion, tight-binding approach, density functional theory calculations, and photoelectron spectroscopy measurements. It turns out that: (i) the 3p core-level shifts from 15.595 ± 0.003 eV for an isolated K atom by 2.758 eV to the bulk value of 18.353 eV; (ii) the effective atomic coordination number reduces from the bulk value of 12 to 3.93 for the first layer and to 5.81 for the second layer of K(1 1 0) skin associated with the local lattice strain of 12.76%, a binding energy density 72.67%, and atomic cohesive energy −62.46% for the skin; and (iii) K cluster size reduction lowers the effective atomic coordination number and enhances further the skin electronic attribution. Results have revealed that the 3p core-level shifts of K(1 1 0) and nanoclusters originate from perturbation of the Hamiltonian by under-coordination induced charge densification and quantum entrapment. [ABSTRACT FROM AUTHOR]

Bi 2 O 3 –Ag 2 O hybrid photocatalysts were successfully synthesized via a co-precipitation method. The morphology, structure and photocatalytic performance in the degradation of phenol were characterized by using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, electrochemical impedance spectra and UV–vis absorption spectroscopy, respectively. The results show that Bi 2 O 3 –Ag 2 O hybrid photocatalysts exhibit enhanced photocatalytic performance in the degradation of phenol with a maximum degradation rate of 92% for 60 min under visible light irradiation compared with pure Bi 2 O 3 (57%), which is ascribed to the increase in light adsorption and the reduction in electron–hole pair recombination with the introduction of Ag 2 O. [ABSTRACT FROM AUTHOR]

Consistency between density functional theory calculations and photoelectron spectroscopy measurements confirmed our predications on the undercoordination-induced local bond relaxation and core level shift of Na and K clusters. It is clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and local potential well depression and shift the electron binding-energy accordingly. Numerical consistency turns out the energy levels for an isolated Na ( E 2p = 31.167 eV) and K ( E 3p = 18.034 eV) atoms and their respective bulk shifts of 2.401 eV and 2.754 eV, which is beyond the scope of conventional approaches. This strategy has also resulted in quantification of the local bond length, bond energy, binding energy density, and atomic cohesive energy associated with the undercoordinated atoms. [ABSTRACT FROM AUTHOR]

Numerical reproduction of the measured 4 f 7/2 energy shift of Ir(1 0 0), (1 1 1), and (2 1 0) solid skins turns out the following: (i) the 4 f 7/2 level of an isolated Ir atom shifts from 56.367 eV to 60.332 eV by 3.965 eV upon bulk formation; (ii) the local energy density increases by up to 130% and the atomic cohesive energy decreases by 70% in the skin region compared with the bulk values. Numerical match to observation of the temperature dependent energy shift derives the Debye temperature that varies from 285.2 K (Surface) to 315.2 K (Bulk). We clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and quantum entrapment of electron binding energy, which perturbs the Hamiltonian and the core shifts in the skin region. [ABSTRACT FROM AUTHOR]

Defect generation forms an important means modulating the photocatalytic ability of TiO 2 with mechanisms that remain yet unclear. Here we show that a spectral distillation clarifies the impact of defect on modulating the band gap, electroaffinity, and work function of the substance. Firstly, by analyzing XPS measurements, we calibrated the 2p 3/2 level of 451.47 eV for an isolated Ti atom and its shifts by 2.14 and 6.94 eV, respectively, upon Ti and TiO 2 bulk formation. Spectral difference between the defected and the un-defected TiO 2 skin revealed then that the 2p 3/2 level shifts further from 6.94 to 9.67 eV due to the defect-induced quantum entrapment. This entrapment is associated with an elevation of the upper edges of both the 2p 3/2 and the conduction band by polarization. The shortening and strengthening of bonds between undercoordinated atoms densify and entrap the core electrons, which in turn polarize the dangling bond electrons of defect atoms. The entrapment and polarization mediate thus the band gap, the electroaffinity, the work function, and the photocatalytic ability of TiO 2 . [ABSTRACT FROM AUTHOR]

Abstract: We present an approach for quantifying the heterogeneous interface bond energy using X-ray photoelectron spectroscopy (XPS). Firstly, from analyzing the XPS core-level shift of the elemental surfaces we obtained the energy levels of an isolated atom and their bulk shifts of the constituent elements for reference; then we measured the energy shifts of the specific energy levels upon interface alloy formation. Subtracting the referential spectrum from that collected from the alloy, we can distil the interface effect on the binding energy. Calibrated based on the energy levels and their bulk shifts derived from elemental surfaces, we can derive the bond energy, energy density, atomic cohesive energy, and free energy at the interface region. This approach has enabled us to clarify the dominance of quantum entrapment at CuPd interface and the dominance of polarization at AgPd and BeW interfaces, as the origin of interface energy change. Developed approach not only enhances the power of XPS but also enables the quantification of the interface energy at the atomic scale that has been an issue of long challenge. [Copyright &y& Elsevier]

Abstract: BeW is an important medium for radiation protection in the International Thermonuclear Experimental Reactor (ITER) devices. However, the mechanism for the radiation-protection ability of BeW remains unclear. An extension of the BOLS correlation mechanism into the X-ray photoelectron spectroscopy (XPS) has enabled us to examine the energy and charge distribution of the specimen and clarify that the Be 1s and W 4f7/2 energy levels undergo an elevation by 0.136 and 0.184 times those of the respective bulk constituents standing alone up-on BeW compound formation associated with polarization of the valence density of states. It is suggested that the interface potential barrier creation due to bond order distortion and bond nature alteration perturbs essentially the Hamiltonian and hence leads to the binding energy shifts. The established interface potential barrier and the polarized charge may screen the nuclear irradiation in the thermonuclear fusion devices. Findings may provide guideline for searching materials for such purpose. [ABSTRACT FROM AUTHOR]

Abstract: Materials at heterojunction interfaces demonstrate many physical and chemical properties that are indeed fascinating with mechanisms that need yet to be explored. We show herewith that the “interface charge and energy quantum entrapment due to bond order distortion and bond nature alteration” perturbs essentially the Hamiltonian and hence the binding energy of the CuPd alloy interface. Analyzing the X-ray photoelectron emission of the thermally induced evolution of the Cu 2p and Pd 3d core-level energies at the Cu–Pd interface before and after thermally alloying revealed that the Pd 3d and Cu 2p interfacial potential traps are 0.36 and 0.95 times deeper than the potential wells of the corresponding bulk constituents standing alone. [Copyright &y& Elsevier]

Abstract: An in situ X-ray photoelectron emission investigation revealed that the size trend of the 2p3/2 binding-energy shift (BES) of Ni nanoclusters grown on SiO2 substrate follows the prediction of the bond order–length–strength (BOLS) correlation theory . Theoretical reproduction of the measurements turns out that the 2p3/2 binding energy of an isolated Ni atom is 850.51eV and its intrinsic bulk shift is 2.70eV. Findings confirmed that the skin-depth local strain and potential well quantum trapping induced by the shorter and stronger bonds between under-coordinated surface atoms provide perturbation to the Hamiltonian and hence dominate the size dependent BES. [Copyright &y& Elsevier]

Abstract: The influence of sputtering pressure on the electron emission properties of Si tips coated with N-doped SrTiO3 ultrathin films was investigated. X-ray diffraction studies revealed that the N-doped SrTiO3 films deposited at different pressures remain the perovskite structure. However, the threshold electric field of electron emission decreased markedly when the sputtering pressure is increased, and reached a minimum value of 17.37V/μm while deposited at 1.6Pa. The decrease in the threshold field is attributed to the narrowed band gap and the lowered surface energy of SrTiO3 thin films with nitrogen doped, as confirmed using spectroscopic ellipsometry and water contact angle measurement. Furthermore, it is revealed using XPS that such sputtering pressure dependence is accompanied with the change of nitrogen bonding state in the films, which changes from poorly screened γ-N2 state to atomic β-N state when the sputtering pressure is increased. A mechanism of bonding and band-forming was proposed for the enhanced electron emission with nitrogen incorporation in the sputtered SrTiO3 films. [Copyright &y& Elsevier]

• An intrinsic EDL of 2.14 ± 0.01 bond-length thick exists universally to nanocrystals. • EDL bond contraction densifies and entraps core electron and energy. • Densified charge polarizes subjectively edge atoms with localized ending states. • The EDL dictates the atomic-undercoordination derivacy and size dependency. • BOLS-NEP theory reconciles intrinsically defects, surfaces, and nanostructures. We show that nanocrystals share a common and intrinsic skin electric-double-layer (EDL). The EDL is determined to be 2.14 regular-bond-length thick using differential phonon spectroscopy that distills phonon abundance transiting from the core region to the EDL of the sized crystals. Theoretical reproduction of the size-resolved Raman shift for Si, CeO 2 , and SnO 2 nanocrystals, elasticity of ZnO, and the XPS 2p energy shift, band gap expansion and melting point shift of Si crystals confirmed the universality of the EDL of which bonds are shorter and stronger than those inside the bulk or the particle core interior. The EDL bond contraction and the associated electron entrapment and polarization originate, and the EDL volume quantifies the size dependency of nanostructures while the electron entrapment or polarization entitles the undercoordinated single or edge atoms with properties that a bulk does never show. [ABSTRACT FROM AUTHOR]

• The polar nitrobenzene molecule can effectively adjust the electronic structures of g-C 3 N 4. • The most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. • The number of active electrons can accurately estimate the OER/ORR activity of metal-free electrocatalysts. Metal-free catalyst with favorable advantages of nonpolluting, cost-effective and stable catalytic performances may be used in various redox reactions. In this paper, we design a series of C 6 H 4 NO 2 /g-C 3 N 4 composites by combining a polar nitrobenzene molecule with g-C 3 N 4 monolayer using density functional theory calculations. The electrocatalytic performances during oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are substantially improved thanks to the electron redistributions of g-C 3 N 4 substrate. One composite specimen exhibits the lowest bi-directional OER/ORR overpotentials of 0.14/0.14 V, and the most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. The number of active electrons in active atom, as descriptor of catalytic activity, can accurately estimate the OER and ORR activity of metal-free electrocatalysts. The modification strategy would be extended to design high-efficiency metal-free electrocatalysts. [ABSTRACT FROM AUTHOR]