Degree of p-d hybridization in Zn1-xMnxY(Y=S, Se)and Zn1-xCoxS alloys as studied by x-ray-absorption spectroscopy

[[abstract]]We have measured x-ray-absorption near-edge-structure (XANES) spectra of the diluted magnetic semiconductors Zn1-xMnxY (Y=S,Se) and Zn1-xCoxS alloys at the Mn and Co L3,2 edge. Analysis of the Mn L3,2-edge XANES spectra for Zn1-xMnxY and Co L3,2-edge spectra for Zn1-xCoxS revealed the presence of a white-line feature in each series, whose intensity increased linearly with concentration x. The white-line feature is assigned to Mn(Co) 2p3/2 and 2p1/2photoelectron excitations to nonbonding 3d(e) states and to the relatively broadened band of Mn (Co) 3d(t2)-S 3p hybridized antibonding states for the sulfides, and to Mn 3d(t2)-Se 4p hybridized states for the selenides. The rate of increase of L3,2 white-line intensity with x is associated with the difference in the degree of p-d hybridization of states between Mn (Co) 3d and S 3p for the sulfides, and between Mn 3d and Se 4p for the selenides. Our results indicate that the magnetic-transition-metal 3d(t2)-anion p hybridization is strongest for Zn1-xCoxS, intermediate for Zn1-xMnxS and least for Zn1-xMnxSe. From separate and Co K-edge extended x-ray-absorption fine-structure measurements on Zn1-xMnxS and Zn1-xCoxS at 77 K, we found that the nearest-neighbor (NN) Mn-S (2.42 Å) and Co-S (2.30 Å) bond lengths remained essentially constant with x in these alloys, respectively. The degree of relaxation of the NN Mn (Co)-anion bond lengths is found to be directly related to the strength of p-d hybridization coupling in these alloys.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Extended X-ray absorption fine-structure studies of Zn1-xMnxSe alloy structure

[[abstract]]Bond lengths, Debye-Waller factors, and site occupancy in the diluted magnetic semiconductor Zn1-xMnxSe have been measured using extended x-ray-absorption fine structure. The nearest-neighbor bond lengths at both room temperature and low temperature (77 K) are found to be constant as a function of alloy composition within the experimental uncertainty of 0.01 Å. Because the average cation-cation distance changes with Mn content, these results necessarily imply distortion of the tetrahedral bond angles. The anion sublattice is shown to suffer the largest distortion, but the cation sublattice also exhibits some relaxation. The repercussions of these results are discussed, in terms of the amount of cation and anion sublattice distortion at low temperature and its connection to the superexchange mechanism occurring between the Mn2+ ions and mediated by the intervening anion in Zn1-xMnxSe.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Electronic structure of GaN nanowire studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy

[[abstract]]X-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been employed to obtain information on the electronic structures of the GaN nanowires and thin film. The comparison of the XANES spectra revealed that the nanowires have a smaller (larger) N (Ga) K edge XANES intensity than that of the thin film, which suggests an increase (decrease) of the occupation of N 2p (Ga 4p) orbitals and an increase of the N (Ga) negative (positive) effective charge in the nanowires. The SPEM spectra showed that the Ga 3d band for the nanowires lies about 20.8 eV below the Fermi level and has a chemical shift of about -0.9 eV relative to that of the thin film.[[notice]]補正完畢[[booktype]]紙

Polyacrylate grafted graphene oxide nanocomposites for biomedical applications

[[abstract]]Utilizing a reverse micelle process, we have grafted polyacrylate (P) on graphene oxide (GO) to realize polyacrylate grafted graphene oxide (P-GO) nanocomposites, upon whose subsequent reduction, polyacrylate grafted reduced graphene oxide (P-rGO) nanocomposites are achieved. Using techniques such as ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy, and x-ray absorption near edge structure (XANES) spectroscopy, in conjunction with high-resolution microscopy, Raman spectroscopy, and superconducting quantum interference device analysis, we have studied in depth the electronic, microstructural, electrical, and magnetic properties of these P-GO and P-rGO nanocomposites. While polyacrylate grafting ensures a high solubility of P-GO and P-rGO, the P-rGO nanocomposites additionally show a near doubling of the paramagnetic response (9.6 × 10−3 emu/g) as compared to the r-GO (5.6 × 10−3 emu/g) and P-GO (5.5 × 10−3 emu/g), respectively, at 2 K. The grafting of diamagnetic polyacrylate enhances the magnetic response for the P-GO and P-rGO owing to the increase in the defect states, sp3-type bonding, and enhanced magnetic coupling between the magnetic moments arising due to the presence of nitrogen functionalities. This behavior is further corroborated via the measurements of the electronic structure by XANES and UPS measurements. Thus, the possibility of manipulation of the magnetic behavior along with the abundance of surface functional groups makes both P-GO and P-rGO nanocomposites highly conducive for deriving water-soluble functionalized graphene by linking affinity molecules with polyacrylate backbone for biological and biomedical applications.[[notice]]補正完

Probing Quantum Confinement of Single-Walled Carbon Nanotubes by Resonant Soft-X-Ray Emission Spectroscopy

[[abstract]]We report the band-structure changes near Fermi level for single-walled carbon nanotubes (SWNTs) with diameters down to 1 nm from the study of soft-x-ray absorption and resonant emission spectroscopy. The observed quantum confinement of SWNTs affects both pi and sigma bands and bandgap through the rehybridization of pi and sigma orbitals. The significant changes of electronic structure are proved to be a measure for the mean diameter of the macroscopic amounts of SWNTs. (C) 2008 American Institute of Physics.[[notice]]補正完畢[[booktype]]紙

Publisher Correction: Copper adparticle enabled selective electrosynthesis of n-propanol.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes

[[abstract]]The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt–C and Pt–N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]GB

Design of Ru-Ni diatomic sites for efficient alkaline hydrogen oxidation

Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H2 dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.補正完畢TW

Possible Ferro-electro-magnetic performance of “reduced graphene oxide ”deposited on “ZnO-nanorod (NR) decorated with nanocrystalline (nc) Au particles”

Possible ferro-electromagnetic performance of “reduced graphene oxide (r-GO)” deposited on the surface of “ZnO-nanorod (NR) decorated with nanocrystalline (nc) Au particles” is studied using different spectroscopies and magnetic measurements. The presence of carbon/zinc-interstitials (Zni), nc-Au, and oxygen vacancies are established through electronic property studies using different spectroscopic measurements. The magnetic moment (M) applied magnetic field (H) curve and electrical measurement current (I)–voltage (V) loops show that nc-Au/ZnO-NRs:r-GO is ferromagnetic and partial ferroelectric, respectively. The work functions are obtained from the lower kinetic energy of ultraviolet photoelectron spectroscopy, which is correlated with the enhancement of ferro-electro-magnetic performance. Both ferroelectric and ferromagnetic performance of nc-Au/ZnO-NRs:r-GO nanocomposite material could be useful for ferro-electro-magnetic technological applications.補正完畢TW