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The search for novel and low-cost cocatalysts that can achieve high efficiency, while maintaining high selectivity in photocatalytic CO2 reduction is highly desirable, yet challenging. Herein, we demonstrate that transitional metal borides (TMBs) Ni3B, Co3B and Fe2B can serve as effective and low-cost cocatalysts to enhance the performance of photocatalytic CO2 reduction under visible light, while other TMBs (TaB2, NbB2 and MoB) are almost ineffective. The performance of photocatalytic CO2 reduction depends on the metal site in TMBs, among which Ni3B exhibits the highest selectivity and activity compared to those of other TMBs. Specifically, Ni3B exhibits a CO evolution rate of 157.7 μmol h−1 with selectivity of 93.0% in the presence of [Ru(bpy)3]Cl2 as a light absorber under visible light, representing state-of-the-art cocatalyst. The excellent activity of Ni3B can be ascribed to its metallic feature that can efficiently transport photogenerated electrons from the light absorber, as well as the unique Ni–B bond that acts as an electron accumulator to provide abundant long-lived electrons to be injected into Ni0 active sites for the activation of CO2. These findings may provide the principle guidance for the search and design of efficient cocatalytic materials and systems for solar energy conversion.

Single-molecule tip-enhanced Raman spectroscopy (TERS) has emerged as an important technique for structural analysis at sub-molecular scale. Here in this work, we report a TERS study of an isolated free-base porphyrin molecule adsorbed on the Ag(100) surface at cryogenic temperature ( $\sim$ 7 K). Site-dependent TERS spectra reveal distinct local vibrational information for the chemical constituents within a single molecule. Moreover, distinct spatial features among different Raman peaks can be resolved from the TERS mapping images. These images are found to associate with related vibrational modes, enabling to resolve the mode associated with N-H bonds at the sub-nanometer level. This study will provide deep insights into the symmetry of adsorption configurations and local vibrational information within a single molecule.

Corner and edge sites have long been predicted to play a dominant role in the chemistry of nanomaterials due to their low metal–metal coordination numbers. However, due to the difficulty in directl...

Transport characteristics of graphene field-effect transistors were measured in situ in oxygen/nitrogen atmospheres and at various temperatures. Mobilities of holes were extracted from transport ch...

The interactions between substitutional carbon atoms and S3 {111}, S9 {221}, and S27 {552} twin boundaries (TB) in silicon were investigated by first-principles calculations. The preferential segregation sites and segregation energy for carbon at different TBs were determined. It shows that segregation of carbon atoms at S3 {111} TB is energetically unfavorable while S9 {221} and S27 {552} TBs are efficient gettering centers for carbon. A linear relationship between the atomic-site specific segregation energy for carbon at TBs and the average bond length (ABL) of the atomic site is deduced. © 2017. This is the authors’ accepted and refereed manuscript to the article. LOCKED until 15.4.2019 due to copyright restrictions. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Atomic substitution and doping are two of the most adopted strategies to improve the electrochemical performance of layered cathode materials for Li-ion batteries (LIBs). In this work, we report a comprehensive study on the effects of seven dopants (Al, Ga, Mg, Si, Ti, V, and Zr) on the well-known drawbacks of Ni-rich LiNi1−2yCoyMnyO2 (NCM) (y ≤ 0.1), one of the most promising next-generation cathode materials for LIBs, including phase instability, Li–Ni exchange, Ni segregation, lattice distortion, and oxygen evolution. Our results show that there is not a single dopant that can solve all the problems at the same time and, moreover, while they often improve certain properties, they may have no effect or even worsen others. By comparing different doping sites, we found a strong site preference due to the tradeoff between Mn and Co concentrations. This site preference indicates that a multicomponent-doping strategy should be adopted at both Mn and Co sites. Finally, a rationale for the optimization of the overall electrochemical performance of Ni-rich NCM is proposed, which will ultimately provide practical guidance (Ti or Zr at the Co site and Al at the Mn site) for the design of new Ni-rich layered cathode materials for LIBs.

Phonon dispersion in periodically rippled graphene/Ru(0001) has been studied by high-resolution electron energy loss spectroscopy and density functional theory. We show that, in addition to the usual phonon modes of the free-standing graphene lattice, the phonon spectrum of graphene/Ru(0001) exhibits additional modes arising from the peculiar nanostructured morphology of this system. In particular, the out-of-plane optical phonon has two components at 83 and 105 meV, related to the spectral contribution arising from carbon atoms in the valleys and in the hills of the ripples, respectively.

Exotic metal (EM) doping in LiFePO4 materials could mitigate their poor electronic conductivity and electrochemical performance. This effect is believed to be dependent on the EM dwelling site, which has yet been well clarified due to experimental difficulty. Herein, we report on Mg-doped LiFePO4 samples with dopant in two distinct sites, namely the Li1− 2xMgxFePO4 and LiFe1− xMgxPO4, using a specially designed two-step reaction. The conductivity and electrochemical test results are a clear indication that the performance of the doped LiFePO4 samples is highly Mg site dependent, consistent with theoretical analysis. Keywords: Lithium rechargeable battery, Lithium iron phosphate, Dopant, Conductivity, Electrochemical performance

Using Density Functional Theory, we have investigated the emergence of half-metallicity in a quaternary Heusler compound with both 3d and 4d electrons as constituents, by chemical substitutions at different sites in the lattice. Mn2RhSi, Co2RhSi and CoRhMnSi, the parents-daughter combination where one of the ternary parents is a normal metal is chosen as an example. We find that the substituting site, and the electronic structures of the constituent magnetic components are responsible for sustenance of half-metallicity or absence of it while making quaternary daughter from ternary parents. We have studied the effects of site-dependent substitutions on the finite temperature magnetic properties and predicted that in this family, half-metals with high Curie temperatures can be obtained in substitutionally disordered quaternary compounds, apart from the ordered ones. We have also proposed that similar phenomena can be observed in other parent-daughter combinations having both 3d and 4d elements in the same compound and having same combination of electronic properties in the context of half-metallic behaviour.

The nuclear magnetic resonance of (59)Co was measured over a wide frequency range in a powder sample crushed from a well-characterized single crystal of La-Co co-substituted magnetoplumbite-type strontium ferrite (SrFe12O19), a familiar base material for the ferrite permanent magnet. The simultaneous observation of both high- and low-frequency resonances suggests the coexistence of both high- and low-spin states of the substituted Co or the presence of Co orbital moment at a particular site. The possible presence of trivalent Co was also investigated. The results suggest that the Co atoms are distributed across different crystallographic sites with different local environments, and that the electronic state of Co is much more subtle than the conventional understanding.

Using scanning tunneling microscopy (STM), we investigated the evolution of electrical conductance between a Pb tip and Pb(111) surface from tunneling to atomic point contact at a site that was defined with atomic precision. We found that the conductance evolution depended on the contact site, for instance, on-top, bridge, or hollow (hcp and fcc) sites in the Pb lattice. In the transition from tunneling to contact regimes, the conductance measured at the on-top site was enhanced. In the point contact regime, the hollow sites had conductances larger than those of the other sites, and between the hollow sites, the hcp site had a conductance larger than that of the fcc site. We also observed the enhancement and reversal of the apparent height in atomically resolved high-current STM images, consistent with the results of the conductance traces. Our results indicate the importance of atomic configuration in the conductance of atomic junctions and suggest that attractive chemical interactions have a significant role in electron transport between contacting atoms., Comment: main text: 22 pages, 4 figures, supplemental materials: 9 pages, 10 figures

We examine the adsorption of a single Ni atom on a monolayer of MgO on a Ag substrate using DFT and DFT+U computational approaches. We find that the electronic and magnetic properties vary considerably across the three binding sites of the surface. Two of the binding sites are competitive in energy, and the preferred site depends on the strength of the on-site Coulomb interaction U. These results can be understood in terms of the competition between bonding and magnetism for surface adsorbed transition metal atoms. Comparisons are made with a recent experimental and theoretical study of Co on MgO/Ag, and implications for scanning tunneling microscopy experiments on the Ni system are discussed., Comment: 7 pages, 4 figures

The effect of site selective doping of Sm on the superconducting and flux pinning properties of (Bi, Pb)-2212 superconductor has been investigated. Pure, Sm substituted at different cationic sites such as Bi, Sr and Ca, and Sm added (Bi, Pb)-2212 superconducting samples are prepared by solid state synthesis. Remarkable improvements in the TC, JC and flux pinning properties have been observed both in the Sm substituted and Sm added samples and the properties are found to be highly site dependent. The bulk flux pinning force (FP) calculated from the field dependent JC values shows that the irreversibility lines of Sm doped samples are shifted towards higher fields to different extents depending on the site in which the substitution or addition is made. These changes are due to a decrease in hole concentration and the creation of point-like defects because of the replacement of cations by rare earth ions and also may be due to nanoscale secondary phases present in the samples.

A type of specially designed pin model of Mg-Zn alloy was implanted into the full thickness of lesions of New Zealand rabbits’ femoral condyles. The recovery progress, outer surface healing and in vivo degradation were characterized by various methods including radiographs, Micro-CT scan with surface rendering, SEM (scanning electron microscope) with EDX (Energy Dispersive X-ray analysis) and so on. The in vivo results suggested that a few but not sufficient bridges for holding force were formed between the bone and the implant if there was a preexisting gap between them. The rapid degradation of the implantation in the condyle would result in the appearance of cavities. Morphological evaluation of the specially designed pins indicated that the cusp was the most vulnerable part during degradation. Furthermore, different implantation sites with distinct components and biological functions can lead to different degradation rates of Mg-Zn alloy. The rate of Mg-Zn alloy decreases in the following order: implantation into soft tissue, less trabecular bone, more trabecular bone, and cortical bone. Because of the complexities of in vivo degradation, it is necessary for the design of biomedical Mg-Zn devices to take into consideration the implantation sites used in clinics.

We have studied photoluminescence (PL) properties of Eu 3+ -doped GaN (GaN:Eu 3+ ) epitaxial films. The GaN:Eu 3+ epitaxial films with a Eu 3+ concentration of 1 at.% exhibit red luminescence due to intra-4f transitions of Eu 3+ ions and blue luminescence due to bound excitons of GaN host crystals at 20 K. In microscopic PL imaging spectroscopy experiments, the intensities of the PL due to the Eu 3+ ions and due to the bound excitons are sensitive to the monitored position. The PL mechanisms of the GaN:Eu 3+ epitaxial films are discussed.

We report here a systematic study of the resistivity, ac magnetic susceptibility, and specific-heat (${\mathit{C}}_{\mathit{p}}$) anomalies in Er-1-2-3 systems for both the pure phase and when Cu is partly (0.5%) replaced by Ni, Zn, Fe, Co, and Ga. These substitutions are aimed at studying the role of site-dependent in-plane and out-of-plane disorder, in conjunction with fluctuation effects. Analysis of the results shows that, as compared to in-plane, the out-of-plane substitutions exhibit a domination of the fluctuation effect. This has been explained from the fact that the out-of-plane disorder substantially decouples the interlayer links between ${\mathrm{CuO}}_{2}$ planes across the adjoining unit cells. This transforms the system to be more two dimensional, thereby enhancing the contribution of fluctuations.

The site-selective substitution of $^{18}\mathrm{O}$ for $^{16}\mathrm{O}$ in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{0.8}$${\mathrm{Y}}_{0.2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ has been investigated by Raman spectroscopy. Three prominent Raman bands are observed at 297, 464, and 623 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. They all shift to lower wave numbers as the $^{18}\mathrm{O}$ content increases. The bands at 297 and 464 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ shift at similar rates but the band at 623 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ shifts at a slower rate. These results show that all three bands are due to the vibrations involving oxygen atoms, and that the rate of oxygen substitution is site dependent. Based on these experimental results, tentative mode assignments have been made assuming a tetragonal symmetry: 623 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\rightarrow}${\mathrm{O}}_{\mathrm{pl}}$(${\mathit{A}}_{\mathit{g}}$), 464 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\rightarrow}${\mathrm{O}}_{\mathrm{ap}}$, and 297 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\rightarrow}${\mathrm{O}}_{\mathrm{Bi}}$.

Silica gels doped with Eu3+ ions were studied at temperatures between 10 K and 300 K by site selection spectroscopy in samples heated up to 200°C. The 5D0 → 7F0 transition shows internal structures due to the different environments of the europium ions. Lifetimes, energy levels and homogeneous linewidths are site dependent. In the wet gel the Eu3+ ions prefer a liquid-like environment and only when the liquid is removed by heat treatment, the ion is linked more strongly to the silica network.

Three high-symmetry adsorption sites of CO on Ni(100) have been studied by x-ray photoabsorption spectroscopy. The sites are known to be populated in the CO/H,H 2 /Ni(100) system. The position and width of the CO 2π * resonance is dependent on the adsorption site. The adsorption threshold shifts in accordance with the large shifts observed in x-ray photoelectron spectroscopy. Information about the ground-state population of the 2π * -derived CO orbitals is obtained from the resonance intensity, showing substantially larger population for CO adsorbed in the hollow sites

Site Dependent Pumping in EDFA has similar nature to Spectral Hole Burning effect, thus similar approach for characterization and modeling can be used. The wavelength selective effect on gain can reach several dB in EDFA.

The objective of this paper is to demonstrate a procedure for the durability design of reinforced concrete structures exposed to deicing salts and check the focus on site dependent parameters.

Laser-induced fluorescence line-narrowing has revealed that the emission properties of Nd3+ in various glasses are strongly dependent on the nature of the site. In a mixed anion glass, the multiplicity of ligand combinations causes additional complications. The spectral and kinetic manifestations of these are presented and discussed.

Predictions are given for the chemical trends in (i) deep energy levels associated with 28 ${\mathrm{sp}}^{3}$- bonded substitutional defects, and (ii) energies of Hjalmarson-Frenkel core excitons at the (100) surface of Si, reconstructed according to Chadi's (2\ifmmode\times\else\texttimes\fi{}1) asymmetric-dimer model. The predictions suggest that P at this surface should produce a deep level, and that the Hjalmarson-Frenkel surface core exciton should have a binding energy that is strongly site dependent.

Based on the characteristic site period and the presumed peak ground acceleration, a method is proposed for the construction of smooth site dependent spectra. Smooth spectra are plotted and compared with spectra of many actual records. To show the generality of the proposed method the records used for comparison are selected to have small, intermediate and relatively large predominant periods with various intensities from relatively small, intermediate, to large events. The agreement in all cases is very good. The proposed site dependent spectra are also compared with Newmark's and the Regulatory Guide 1.60 spectra. The comparison is favorable for a limited range of characteristic site periods.