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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]

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]

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]

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]

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]