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

Oxygen 1s x-ray-absorption near-edge structure of Zn-Ni ferrites : a comparison with the theoretical calculations

[[abstract]]We present the electronic structure of ferrimagnetic ZnxNi1-xFe2O4 compounds obtained by a combination of O K-edge x-ray-absorption measurements and first-principles spin-unrestricted calculations using the pseudofunction method. The two distinct preedge features are found to vary systematically as a function of the Zn content. From both experimental and theoretical analyses, we find that substitution of Ni with Zn enhances localization of the 3d states of Fe on the octahedral sites, so that the O 2p–Fe 3d hybridized states can be resolved into two distinct twofold and threefold features.[[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

Tuning the Electronic and Magnetic Properties of Nitrogen-Functionalized Few-Layered Graphene Nanoflakes

In this work, we report on the modification of electronic and magnetic properties of few layered graphene (FLG) nanoflakes via nitrogen functionalisation carried out using radio frequency (rf-PECVD) and electron cyclotron resonance (ECR) plasma processes. Even though the rf-PECVD N2 treatment leads to higher N-doping levels in the FLGs (4.06 at%) as compared to the ECR process (2.18 at.%), the ferromagnetic behaviour of ECR FLG(118.62 x 10⁻⁴ emu/gm) was significantly higher than the rf-PECVD (0.39 x 10⁻⁴ emu/gm) and pristine graphene (3.47 x 10⁻⁴ emu/gm). While both plasma processes introduce electron donating N-atoms in the graphene structure, distinct dominant nitrogen bonding configurations (pyridinic, pyrrolic) were observed for each FLG type. While, the ECR plasma introduces more sp2 type nitrogen moieties, the rf-PECVD process led to the formation of sp3 coordinated nitrogen functionalities, as confirmed through Raman measurements. The samples further characterised using X-ray absorption near edge spectroscopy (XANES) and X-ray, ultraviolet photoelectron spectroscopies revealed an increased electronic density of states and a significantly higher concentration of pyrrolic groups in the rf-PECVD samples. Due to the formation of reactive edge structures and pyridinic nitrogen moieties, the ECR functionalised FLGs expressed highest saturation magnetisation behaviour with the lowest field hysteretic features. In comparison, the rf-PECVD samples, displayed the lowest saturation magnetisation owing to the disappearance of magnetic edge states and formation of stable non-radical type defects in the pyrrole type structures. Our experimental results thus provide new evidence to control the magnetic and electronic properties of few layered graphene nanoflakes via control of the plasma-processing route

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

Mg-induced increase of band gap in Zn1-xMgxO nanorods revealed by x-ray absorption and emission spectroscopy

[[abstract]]X-rayabsorption near-edge structure (XANES) and x-ray emission spectroscopy (XES) measurements were used to investigate the effect of Mgdoping in ZnOnanorods. The intensities of the features in the O K-edge XANES spectra of Zn1−xMgxOnanorods are lower than those of pure ZnOnanorods, suggesting that Mgdoping increases the negative effective charge of O ions. XES and XANES spectra of O 2p states indicate that Mgdoping raises (lowers) the conduction-band-minimum (valence-band-maximum) and increases the band gap. The band gap is found to increase linearly with the Mg content, as revealed by photoluminescence and combined XANES and XES measurements.[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US

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