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Exploration of the biological effects of transition metal ions in acupuncture points is essential to clarify the functional mechanism of acupuncture treatment. Here we show that in the SP6 acupuncture point (Sanyinjiao) the Fe ions are in a high-spin state of approximately t2g4.5eg1.5 in an Fe-N(O) octahedral crystal field. The Fe K-edge synchrotron radiation X-ray absorption fine structure results reveal that the Fe-N and Fe-O bond lengths in the SP6 acupuncture point are 2.05 and 2.13 A, respectively, and are 0.05-0.10 A longer than those in the surrounding tissue. The distorted atomic structure reduces the octahedral symmetry and weakens the crystal field around the Fe ions by approximately 0.3 eV, leading to the high-spin configuration of the Fe ions, which is favorable for strengthening the magnetotransport and oxygen transportation properties in the acupuncture point by the enhanced spin coherence. This finding might provide some insight into the microscopic effect of the atomic and electronic interactions of transition metal ions in the acupuncture point. Graphical Abstract ᅟ.

The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered β-CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3 nm thick β-CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90 % upon irradiation at 350-450 nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H(+) adsorption and H2 desorption. An aqueous suspension of the β-CoOOH nanosheets exhibited a high hydrogen production rate of 160 μmol g(-1) h(-1) even when the system was operated for hundreds of hours.

Producing H2 by means of direct photocatalytic water splitting using suspension system is highly desired in efficiently transforming solar energy to chemical energy. Here, using an ultrathin β-CoOOH nanosheet as photocatalyst suspended in aqueous Na2SO3 solution, we realize highly efficient and stable photocatalytic hydrogen evolution under visible light irradiation. The as-prepared ultrathin β-CoOOH nanosheets suspension can directly photocatalyze hydrogen evolution in a high rate of 1200 μmol/g/h and large quantum efficiencies of 10.7% at 380 nm, 6.9% at 420 nm, and 2.3% at 450 nm. X-ray photoelectron and X-ray absorption measurements reveal that the excellent hydrogen evolution activity of the β-CoOOH nanosheet is attributed to the surface low-coordinated Co catalytic site, which results in a strong hybridization of Co 3d states with the S p states of SO32+, and facilitates the electron transfer to reduce H+. The results may be helpful for designing and understanding two-dimensional oxyhydroxide-based ...

Control over the magnetic interactions in dilute magnetic semiconductor quantum dots (DMSQDs) is a key issue to future development of nanometer-sized integrated "spintronic" devices. However, manipulating the magnetic coupling between impurity ions in DMSQDs remains a great challenge because of the intrinsic quantum confinement effects and self-purification of the quantum dots. Here, we propose a hybrid structure to achieve room-temperature ferromagnetic interactions in DMSQDs, via engineering the density and nature of the energy states at the Fermi level. This idea has been applied to Co-doped ZnO DMSQDs where the growth of a reduced graphene oxide shell around the Zn(0.98)Co(0.02)O core turns the magnetic interactions from paramagnetic to ferromagnetic at room temperature, due to the hybridization of 2p(z) orbitals of graphene and 3d obitals of Co(2+)-oxygen-vacancy complexes. This design may open up a kind of possibility for manipulating the magnetism of doped oxide nanostructures.

Increasing the quantum conversion efficiency in visible-light region is a key issue for the efficient usage of solar energy in the process of photoelectrochemical (PEC) water splitting. Here, based on the N anion and S cation codoped TiO 2 thin film photoanodes, we find experimentally and theoretically that the transport ability of visible-light-induced carriers can be notably enhanced by engineering the dopant electronic energy states. The hole transport resistivity is decreased from 6.8 × 10 4 to 1.3 × 10 4 Ω m via delocalizing the introduced bands, leading to an evident increase of the internal quantum efficiency from 5% to 20% at the visible-light region of 450–550 nm. Further DFT calculations exhibit that the split of the isolated band is induced by a strong N and S hybridization, which favors to decrease the hole effective mass and to improve the hole mobility by three times. The photocurrent of N − S codoped TiO 2 thin film is thus twice that of monodoping cases, the best value for doping modified TiO 2 thin film photoanodes. This work may provide not only a design principle but also a candidate for tailoring and optimizing TiO 2 towards high PEC activity.

Elemental codoping has been an effective way to modify the structural and electronic properties of semiconductors. By use of X-ray diffraction and X-ray absorption fine structure spectroscopy, we s...

We report the microstructure, gas-sensing properties of the ordered mesoporous Co3O4 prepared by modified KIT-6 template method. Highly ordered mesoporous nanostructures of the as-prepared products have been characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), high-resolution transmission electron microscopy (HRTEM) and N2 adsorption/desorption analysis. We find that the ordered mesoporous Co3O4 enables a significant improvement of sensor response and selectivity to ethanol, which demonstrates the potential use of the ordered mesoporous Co3O4 as alcohol gas-sensing material. Through the analysis of microstructure including HRTEM and N2 adsorption/desorption, the sensing properties for the ordered mesoporous Co3O4 can be attributed qualitatively to its large specific surface area and porous morphology. Moreover, the results of EXAFS illustrate that the disorder degree and unsaturated bond of the ordered mesoporous Co3O4 increase, which agree well with the results observed in gas sensors. This makes the nanostructured ordered mesoporous Co3O4 a promising sensor material for detecting the alcohol gas.

X-ray microscopy based on synchrotron radiation has become a fundamental tool in biology and life sciences to visualize the morphology of a specimen. These studies have particular requirements in terms of radiation damage and the image exposure time, which directly determines the total acquisition speed. To monitor and improve these key parameters, we present a novel X-ray microscopy method using a high-resolution zone plate as the objective and the matching condenser. Numerical simulations based on the scalar wave field theory validate the feasibility of the method and also indicate the performance of X-ray microscopy is optimized most with sub-10-nm-resolution zone plates. The proposed method is compatible with conventional X-ray microscopy techniques, such as computed tomography, and will find wide applications in time-resolved and/or dose-sensitive studies such as living cell imaging.

In this contribution we discuss the possibility of designing a modified transmission X-ray microscope by using fractal zone plates (Fzps) as diffractive optical elements. In the modified transmission X-ray microscope optical layout, we first introduced a fractal zone plate as the microscope objective. Indeed, a fractal zone plate cannot only be used as an image-forming component but also as a condenser element to achieve an extended depth of field. Numerical analysis reveals that fractal zone plates and conventional Fresnel zone plates have similar imaging capabilities under different coherent illumination. Using a fractal zone plate as a condenser we also simulated axial irradiance. Results confirm that fractal zone plates can improve focusing capability with an extended depth of field. Although preliminary, these simulations clearly reveal that fractal zone plates, when available, will be of great help in microscope layouts, in particular for foreseen high-resolution applications in the "water window" as strongly required in biological research.

The MFI/MCM-41 composite material with bimetallic Fe and Co incorporation was prepared using templating method via a two-step hydrothermal crystallization procedure. The obtained products were characterized by a series of techniques including powder X-ray diffraction, N2 sorption, transmission electron microscopy, scanning electron microscope, H2 temperature programmed reduction, thermal analyses, and X-ray absorption fine structure spectroscopy of the Fe and Co K-edge. The catalytic properties of the products were investigated by residual oil hydrocracking reactions. Characterization results showed that the FeCo-MFI/MCM-41 composite simultaneously possessed two kinds of stable meso- and micro-porous structures. Iron and cobalt ions were incorporated into the silicon framework, which was confirmed by H2 temperature programmed reduction and X-ray absorption fine structure spectroscopy. This composite presented excellent activities in hydrocracking of residual oil, which was superior to the pure materials of silicate-1/MCM-41.

Si 1− x Mn x diluted magnetic semiconductor films were deposited on the p-Si (100) single crystal wafer using magnetron sputtering method. Post-rapid thermal annealing treatments were performed at temperatures of 700 °C, 800 °C, and 900 °C in an argon atmosphere for approximately 5 min. Alternating gradient magnetometer, scanning electron microscope, atomic force microscope, X-ray diffraction and X-ray absorption near-edge structure spectra were employed to characterize magnetic properties and structure of the as-grown and annealed films. The films were about 2.8 μm thick and the RMS roughness of the surface was about 5–10 nm. All samples exhibit ferromagnetism at room temperature and the saturation magnetization reaches at the maximum value for the sample annealed at 700 °C. The silicide MnSi 1.7 was observed in the annealed samples. X-ray absorption near-edge structure spectra indicated that Mn atoms preferred to occupy substitutional or interstitial sites instead of precipitating to form silicide when annealing at 700 °C. It is inferred that the observed ferromagnetism is attributed to the interstitial and substitutional Mn dimers, which existed mostly in the sample annealed at 700 °C. The weaker ferromagnetism of the 900 °C annealed sample was closely related to the increased content of Mn 4 Si 7 compound.

Here we report that the occupation sites of Co atoms in ZnO matrix could be effectively tuned by the concentration of Cu codopant. The Co–Cu codoping effect has been revealed by a combination of X-ray diffraction and X-ray absorption fine structure spectroscopy techniques for Zn0.95–xCuxCo0.05O (0.005 ≤ x ≤ 0.08) thin films grown by pulse laser deposition at 923 K. Specifically, at the low Cu doping levels (x ≤ 0.02), the Co(+2) ions are substantially incorporated into the ZnO lattice; upon increasing the Cu concentration to 0.03 or higher, partial formation of Co(0) species occurs, and its proportion rises rapidly with the Cu concentration. Further analysis shows that the Cu codopants are precipitated to form Cu(0) metallic phase in all the samples. We propose a competition mechanism between the Co(0)–Cu(0) metallic interactions and the dissolution of Co ions in ZnO to interpret these findings.

The structures of selenium nanoparticles and nanotubes synthesized by the dismutation of precursor Na2SeSO3 under acidic condition in micellar solution are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS). Spherical-like nanoparticles contain both amorphous and crystalline parts while, as shown by XRD patterns, nanotubes have the crystal structure of trigonal selenium (t-Se). They display quite different XANES spectral features indicating different local atomic arrangements. Theoretical XANES calculations show that the local structure around Se atom in the nanotubes is similar to a hexangular cylinder. Quantitative extended XAFS (EXAFS) analysis further shows that the average Se–Se bond length for both nanotubes and nanoparticles is 2.35 A.

The Morlet wavelet transformation (MT) was used to analyze Mn K-edge extended X-ray absorption fine structure (EXAFS) spectra of Mn-doped Si-based diluted magnetic semiconductor (DMS) thin films grown by the magnetron co-sputtering method. MT of EXAFS data shows that the Mn–Mn scattering path can be distinguished by the Mn–Si scattering path in the spectra of Mn x Si1−x DMS thin films. In all DMS thin films Mn atoms fill Si sites without forming Mn–Si compounds while Mn–Si compounds are present in the annealed analogues. From the analysis of experimental data we point out that low-concentration Mn-doped samples are characterized by a more symmetric structure.

The efficient absorption of visible light is crucial for improving the photocatalytic activity of foreign species-doped TiO2. With first-principles calculations, we explore the effects of phosphorus doping on mediating the photocatalytic activity of anatase. It is found that the P impurity tends to occupy the cation site in TiO2; more importantly, there exists a critical phosphorus concentration of about 0.7% for maximizing the absorption of solar light. The optical energy gap is narrowed by ∼0.3 eV at the low doping concentration of 0.7%, whereas it increases with P concentration at the higher P concentration region of 0.7−3.1 atm. %. These results suggest that the dopant concentration dependence might be responsible for numerous seeming controversies of optical absorption observed in experiments. This finding points to a possibility of tailoring the optical absorption of TiO2 by varying the dopant content.

The Co100−xNix (x = 0, 30, 50, and 70) bimetallic nanoparticles (NPs) synthesized by a solvothermal method show interesting shape changes from aggregated clusters to ordered nanorings with increasing Ni concentration. A comprehensive structural study of these Co100−xNix NPs is performed with X-ray diffraction and X-ray absorption fine structure spectroscopy. It is shown that the pure Co NPs consist of a majority of the fcc structure and a minority of the hcp phase. When 30% Ni is added, alloyed Co−Ni NPs with an inhomogenous atomic distribution are formed. The further addition of Ni to ≥50% could considerably improve the crystallinity and homogeneity of the alloyed NPs, as suggested by the fact that the disorder degree (σ2) is gradually lowered and the coordination number ratios NCo−Co/NCo−Ni and NNi−Ni/NNi−Co gradually approach the stoichiometry of the NPs. The ordered and homogeneous fcc structure helps to strengthen the magnetocrystalline anisotropic interactions, which may facilitate the head-to-tail ...

Single phase Co-doped ZnO dilute magnetic semiconductor nanowire was synthesized by a chemical solution method and characterized by X-ray absorption fine structure (XAFS). The Co K-edge XAFS spectroscopy reveals that the doped Co ions are substantially incorporated into the ZnO host lattice. Moreover, the spatial occupation of Co dopants in Zn0.98Co0.02O nanowire is resolved further by the detailed O K-edge XANES analysis. We suggest that the Co ions are randomly doped into the ZnO matrix and located at the Zn sites. The magnetization measurement of the Co-doped ZnO nanowire shows the room temperature ferromagnetic characteristic with a relatively larger saturation magnetization. Furthermore, we suggest that the enhanced ferromagnetism can be ascribed to the coeffect of the size effect and the homogeneity of Co dopants for Zn0.98Co0.02O nanowire, which will make it useful in nanometer spintronic devices.

Hybrid-nanostructure Ag−Zn0.92Co0.08O dilute magnetic semiconductors synthesized by a solvothermal method show that the magnetic property of the nanorods is changed from paramagnetism to room-temperature ferromagnetism when 2% Ag is codoped into Zn0.92Co0.08O nanorods. The detailed analysis of the X-ray absorption fine structure spectra at both Co and Ag K-edge reveals that a substantial part of Ag atoms exists in the tetrahedral interstitial sites of (Zn, Co)O matrix in the Ag(2%)−Zn0.92Co0.08O. We suggest that the interstitial Ag atoms, together with Ag nanoparticles, play a most important role in mediating the high-temperature ferromagnetism of Ag(2%)−Zn0.92Co0.08O, due to the strong hybridization between the Co 3d states and the spin-split impurity band at the Fermi level.

Infrared-to-visible upconversion emission intensities are investigated in Li+ and Er3+ codoped ZnO nanocrystals. Li+ ions doped in ZnO/Er3+ nanocrystals can greatly enhance the upconversion emission intensity of Er3+ ions. The extended X-ray absorption fine structure spectroscopy data show that both the Er−O bond length and coordination number of the Er−Er bond have been altered by introducing Li+ ions in the ZnO/Er3+ nanocrystals. The variation of Er−O bond length leads to the change in the local asymmetry around Er3+ ions. Meanwhile, the greater coordination number of the Er−Er bond causes stronger interaction between neighboring Er3+ ions and, hence, strengthens the reaction Er3+ (4F7/2) + Er3+ (4I11/2) → 2Er3+ (4F9/2). In this process, the 4F9/2 state is a metastable state that could be excited to the 2H9/2 state by absorbing one photon at high excitation power. Li+ ions also can reduce the OH groups in specimen, which is the other reason for enhancing the upconversion emission intensities.

The structural evolutions of the mechanically alloyed ternary Al 70 Cu 20 Fe 10 powders with the milling times and the annealing treatment were studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). It was found that during the milling process, only Cu can incorporate into the lattice of Al to form an Al 2 Cu compound or an AlCu solid solution, depending on the milling times. However, Fe remains the original structure of bcc α-Fe. Annealing treatment at 700 °C for 4 h can drive the α-Fe to react with the Al 2 Cu compounds and AlCu solid solution, and the main products of the annealed Al 70 Cu 20 Fe 10 (10 h) and the annealed Al 70 Cu 20 Fe 10 (40 h) are the icosahedral Al 65 Cu 20 Fe 15 quasicrystal and the Al(Cu, Fe) solid solution, respectively. The local structural disorders around Fe and Cu atoms in the icosahedral QC phase is about 50% larger than those of the Al(Cu, Fe) solid solution.

The interfacial and surface structures of CeO2−TiO2 mixed oxides prepared by the sol−gel method have been investigated in detail by means of X-ray diffraction (XRD), BET surface area measurement, X-ray absorption spectroscopy (XAS), high-resolution transmission electron microscope (HRTEM), and selective chemisorption of methyl orange. TiO2 and CeO2 are in the anatase phase and the cubic fluorite phase in CeO2−TiO2 mixed oxides, respectively. The mixed oxides exhibit much higher surface areas than the individual oxides and are with both mesopores and micropores. XAS results suggest that Ce atoms nucleate as cubic [CeO8] polyhedrons with the formation of a Ce−O−Ti interface in mixed oxides. With the increasing Ce/TiO2 weight ratio, the cubic fluorite CeO2 crystallites gradually develop. TiO2 anatase forms ultrafine particles in mixed oxides, whose local structure is stabilized by the presence of CeO2. HRTEM results reveal that the exposed surfaces of mixed oxides depend on the Ce concentration. Chemisorptio...

Fluorescence x-ray absorption fine structure and x-ray diffraction are used to study the structures of super-hard TiN/Si3N4 multilayer films deposited by reactive magnetron sputtering at temperatures of 20, 200, 500 and 800 °C. The results clearly reveal the presence of interfacial intermixing between adjacent TiN and Si3N4 layers. And the interlayer is composed of TiSixN1−x solid solution with an NaCl-like structure. Increasing the growth temperature from 20 to 500 °C, the crystalline quality of the pure TiN layer improves significantly, and the thickness of the interlayer rises from 2.5 to 5.0 A. For the TiN/Si3N4 multilayer film grown at 500°C, the interfacial layer is composed of TiSi0.24N0.76 solid solution, where the Ti–N bond length (2.07 A) is largely shrunk as compared with the value (2.12 A) in the pure TiN layer. When growth temperature rises to 800°C, the composition of the interfacial layer becomes TiSi0.3N0.7 and reaches a thickness of 7.8 A. We propose that the TiSixN1−x interlayer with obviously contracted Ti–N bond length is an important hardening factor for the crystalline/amorphous TiN/Si3N4 multilayer films grown at high temperatures.

A method of incorporating iron onto the mesoporous silica network using potassium ferricyanide (K 3 Fe (CN) 6 ) as the iron source was established. The Fe (CN) 6 3 + ions interact with the template and attached onto the silica network after the as-synthesized sample calcined at 823 K. FT-IR spectroscopy provided a clear evidence for the interaction between cyanide ligands and template. XANES spectroscopic displayed that the Fe 3 + changed from octahedral to tetrahedral coordinated during thermal treatment. XRD and HRTEM results indicated that the iron ions incorporated onto the silica network without destroying the lattice structure of the parent MCM-41. The synthesized material exhibited a good activity for phenol hydroxylation.

There remains a pressing challenge in the efficient utilization of visible light in the photoelectrochemical applications of water splitting. Here, we design and fabricate pseudobrookite Fe2TiO5 ultrathin layers grown on vertically aligned TiO2 nanotube arrays that can enhance the conduction and utilization of photogenerated charge carriers. Our photoanodes are characterized by low onset potentials of ~0.2 V, high photon-to-current efficiencies of 40–50% under 400–600 nm irradiation and total energy conversion efficiencies of ~2.7%. The high performance of Fe2TiO5 nanotube arrays can be attributed to the anisotropic charge carrier transportation and elongated charge carrier diffusion length (compared with those of conventional TiO2 or Fe2O3 photoanodes) based on electrochemical impedance analysis and first-principles calculations. The Fe2TiO5 nanotube arrays may open up more opportunities in the design of efficient and low-cost photoanodes working in visible light for photoelectrochemical applications. Metal oxides are desirable photoanode materials due to their low cost and chemical stability, but they only work in the ultraviolet range. Here, Liu et al. design anode architecture that can absorb the visible light, while maintaining photon-to-current efficiency of 40% at an onset potential of 0.2 V.

We present a x-ray microscopy technique based on structured illumination in a microscope that characterizes the size of the subresolution-limit features. The technique is effective for characterizing fine structures substantially beyond the Rayleigh resolution of the microscope. We carried out optical experiments to demonstrate the basic principle of this new technique. Experimental results show good agreement with theoretical predictions. This technique should find a wide range of important imaging applications with a feature size down to nanometer scale, such as oil and gas reservoir rocks, advanced composites, and functional nanodevices and materials.

Elemental codoping has been an effective way to regulate the structural and electronic properties of semiconductors. By using x-ray diffraction and x-ray absorption fine structure spectroscopy, we investigate the local structure and spatial occupations of Co dopants in Cu-doped ZnO thin films prepared by pulsed-laser deposition method. It is revealed that the Co dopants are substantially incorporated into ZnO matrix when the deposition temperature is increased up to 650 °C, although the preferential orientation of ZnO film is changed. The results provide experimental guidance in the synthesis of the co-doped ZnO based dilute magnetic semiconductors.

The mesoporous ferrisilicates (MFS) with high iron content were synthesized by pH-modification method, and the iron content could be up to 10.5 wt.% (Si/Fe = 8). The pH was kept less than 2 at pre-hydrothermal synthesis step and was adjusted to 11 during hydrothermal step. The samples were characterized by XRD, HRTEM, N2-sorption, XRF, FTIR, DRUV–vis, Fe K-edge EXAFS, EPR, and DSC. The results suggested that the MFS materials were ordered 2D hexagonal mesophase of MCM-41, and the iron atoms were tetrahedral coordinated in the silica framework. This material could efficiently catalyze the hydroxylation of phenol in water medium using H2O2 as an oxidant, and the phenol conversion could be up to 52% under the optimal experimental conditions.

Single-walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X-ray absorption near edge structure, along with X-ray photoemission by following the total valence bands and C 1s core-level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp 2 hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence-band X-ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/ semiconducting composition.

First-principles study on the energetic stability, electronic structure, and magnetic coupling in Mn-doped silicon with various configurations has been performed systematically. The results show that the poly-Mn atoms prefer to aggregate in the Mn-doped silicon dilute magnetic semiconductor. It is found that the tetrahedral interstitial Mn $({\text{Mn}}_{T})$ atoms assemble together via an intervening substitutional Mn $({\text{Mn}}_{\text{Si}})$ ion, subsequently forming the generally favored ${\text{Mn}}_{T}{\text{-Mn}}_{\text{Si}}{\text{-Mn}}_{T}$-type complexes. The dominant $d\text{\ensuremath{-}}d$ exchange interactions between the ${\text{Mn}}_{\text{Si}}$ and ${\text{Mn}}_{T}$ make all Mn ions in the ${\text{Mn}}_{T}{\text{-Mn}}_{\text{Si}}{\text{-Mn}}_{T}$ structures interact ferromagnetically with each other.

Structural studies become increasingly important for understanding the nature of magnetic properties in dilute magnetic semiconductors (DMSs) [K. Ando, Science 312, 1883 (2006)]. In this work, x-ray absorption fine structure (XAFS) at both Co and $\text{O}\text{ }K$ edges is used to investigate the Co occupation sites and distributions in ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ thin films with low Co concentrations $(x=0.005,0.02)$. $\text{Co}\text{ }K$-edge XAFS analysis indicates unambiguously that the doped Co ions are substantially incorporated into the ZnO host lattice. However, the $\text{O}\text{ }K$-edge XAFS spectral features are strikingly different from those of ZnO and ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ reported in the literature so far, and can be reproduced by the assembling of substitutional Co ions around intervening oxygen atoms. This provides experimental evidence for numerous theoretical predications that the substitutional Co ions in ZnO tend to gather together. It is expected that similar phenomenon can also be observed by XAFS in a number of other ZnO-, GaN-, and ${\text{TiO}}_{2}$-based DMSs for which the clustering of substitutional dopants have been previously predicted.

XAFS technique is used to determine the atomic and electronic structures of NiP amorphous alloys with different P concentrations prepared by chemical reduction method. From the radial structural function (RSF) obtained from EXAFS, it is found that the amorphous alloys with P content less than 10 at.% still present strong peaks corresponding to high coordination shells just like crystalline Ni. This indicates the prominent existence of Ni‐rich phase with the fcc‐structure, which is not remarkably modified by the P atoms. As the P content is as large as 14 at.%, only the first shell peak in the RSF can be observed and the higher shell peaks disappear. Therefore the sample is totally amorphous. The XANES results show that as the P concentration is above 26 at.%, charge transfers from Ni atoms to P atoms. For P concentration lower than 20at.%, on the contrary, charge transfers from P atoms to Ni atoms, and 3d electron density of Ni atoms reaches the maximum when P concentration is about 14∼20 at.%.

The local structures of Si(20 monolayer)/Gen/Si(100) (n=1, 2, 4 and 8 monolayer) heterostructure films grown by molecular beam epitaxy (MBE) at 400 deg. C are investigated by grazing incidence fluorescence x-ray absorption fine structure. The Ge K-edge EXAFS analysis shows that the local structure of Ge atoms in the 1 or 2 monolayer (ML) Ge heterostructure film where the Ge atoms are dominantly surrounded by Si, is similar to that in Si0.95Ge0.05 alloy. With the thickness of the Ge monolayer increasing to 4 ML, the coordination environment around Ge atoms is close to that of Si70Ge30 alloy. Even for the 8-ML-thick Ge heterostructure film, the fraction of Ge-Si coordination pair in the first shell is as high as 55%, almost the same as that in Si0.50Ge0.50 alloy. These results clearly indicate the Ge migration effect in all Si/Gen/Si(100) heterostructure films, which is due to surface segregation of Ge atoms during growth process caused by large surface mobility of adatoms allowing for decreasing the surface strain.

There are many excellent charaters with adcanced ceramic composite materials, such as synthetical mechanic properties, wearability, anticorroseveness, heat resistance and high hardness. Therefore, these materials as an important part of the structural material are eagerly needed in modern industry, especialy for cutting tools, bearing, engine etc. It is common knowledge that composites are compounded by matrix and reinforced fibers or s, their physical, chemical and mechanical properties are of considerable difference. In order to achieve the optimum multiple qualities of composites, there must be an integral interface between fibers and matrix. The interface is the most important part of composite materials as following reason: (1) The interface directly affects the stress transmission and dispersion between the fiber and matrix, and affects the strength of the composite. (2) The interface controls the process of defect accumulation and transmission, and affects the breaking toughness of composite. (3) The interface strongly affects the stability via environmental and medium changes.1 The characterization and optimization of interface have been considered to be one of the main research techniques about composites, called the surface and interface engineering of composite.

ZnO-based nanogenerators with excellent performance and convenient functionalization are particularly desirable for self-powered technology, which is however difficult to achieve simultaneously in traditional piezoelectric ZnO nanogenerators. Here, we report a design of electrostatic ZnO nanogenerator by virtue of a type-II ZnO/ZnS core/shell nanostructure electrets, which can turn acoustic waves into electric power with an energy conversion efficiency of 2.2%. The ZnO/ZnS core/shell electrets are charged by ultraviolet irradiation with a long-term stability of the electrostatic charges under ambient condition. The electronic and atomic structure evolution in the charged ZnO/ZnS core/shell electrets are also discussed by detailed experimental and theoretical investigations. This design opens up an alternative path for fabricating robust ZnO-based nanogenerator for future nanotechnology application.

Bimetallic nanoparticles play an important role in potential industrial applications, such as catalysis, optoelectronics, information storage and biological labeling. Herein, homogeneous Cu-Pt core-shell nanoparticles with the averaged size of 8 nm have been synthesized by chemical methods. Cu atoms diffusion process, which motivated by heating, was observed in-situ by using temperature-dependent x-ray absorption fine-structure (XAFS) spectroscopy. Results show that Cu diffuse gradually from Cu core to Pt shell in these nanoparticles with increasing temperature. We also found the surface ligand (O) bonded Pt at the room temperature and were removed gradually by heating the sample. The analysis of the diffusion process in bimetallic nanoparticles will provide important guideline for their designing and tuning.

Pt-based alloys have recently triggered a lot of attentions due to their important potential industrial applications. They provide great opportunities for the development of low-cost and high-performance fuel-cell catalysts. Many studies have already pointed out the excellent physico-chemical properties of Pt-based alloys, intimately related to their internal structure. Great efforts have been spent to characterize shape, homogeneity, dispersion, alloying extent and kinetic growth of Pt-based nano-particles. Here, we present Cu-Pt bimetallic nano-particles synthesized by the thermal decomposition method under oleylamine and OE coordination. HRTEM images show that Cu-Pt nanostructures having size of about 1.2 nm includes about 35 atoms capped by the surfactant with OA. Accurate structural information of this system has been obtained by XRD and XAFS. A charge transfer mechanism has been observed and Pt occupied Cu sites in these Cu-Pt nanoparticles.

The controllable synthesis route of Co doped GaN nanowires was developed and the structural and magnetic properties of Co doped GaN nanowires were studied. The results indicate that Co atoms substitute Ga sites in GaN lattice, suggesting the intrinsic nature of ferromagentism at room temperature.

Homogeneous distribution of magnetic dopants in semiconductor hosts is highly desired for practical applications in spintronics. Herein, we show that codoping 2 at. % Cu with Zn0.98Co0.02O could change the magnetic behavior from paramagnetism to room temperature ferromagnetism. For Zn0.96Cu0.02Co0.02O nanocrystals prepared by a modified solid-state reaction method, the combination of x-ray absorption fine structure spectra at Co, Cu, and O K-edge reveals that the Cu and Co ions are substitutionally incorporated into the ZnO matrix and distribute randomly in the host. First-principles calculations further indicate strong hybridization between Co 3d states and Cu-induced donor impurity bands at the Fermi level, which effectively enhances the indirect ferromagnetic superexchange of Co ions and is responsible for the occurrence of ferromagnetism in (Co,Cu)-codoped ZnO.

The phase transition from tetragonal to hexagonal of crystalline BaTi1−xCoxO3 (0.01≤x≤0.20) powders prepared by solid state reaction has been studied by x-ray diffraction and x-ray absorption fine structure (XAFS). At the low Co doping level of x≤0.03, the structure of the samples is tetragonal, and it is transformed gradually to a hexagonal structure upon increasing Co content to ≥0.05. The detailed analysis of Co K-edge XAFS indicated unambiguously that the doped Co ions are substantially incorporated into the BaTiO3 host and likely serve as a trigger in leading the structure transition. On the basis of the formation energy calculations, we find that there exists a critical Co concentration in the x range of 0.027–0.055 for inducing the tetragonal-to-hexagonal structure transition of BaTi1−xCoxO3, in good agreement with the experimental observations.The phase transition from tetragonal to hexagonal of crystalline BaTi1−xCoxO3 (0.01≤x≤0.20) powders prepared by solid state reaction has been studied by x-ray diffraction and x-ray absorption fine structure (XAFS). At the low Co doping level of x≤0.03, the structure of the samples is tetragonal, and it is transformed gradually to a hexagonal structure upon increasing Co content to ≥0.05. The detailed analysis of Co K-edge XAFS indicated unambiguously that the doped Co ions are substantially incorporated into the BaTiO3 host and likely serve as a trigger in leading the structure transition. On the basis of the formation energy calculations, we find that there exists a critical Co concentration in the x range of 0.027–0.055 for inducing the tetragonal-to-hexagonal structure transition of BaTi1−xCoxO3, in good agreement with the experimental observations.

X-ray absorption near-edge structure (XANES) and first-principles calculations are employed to determine the Co spin state in the Co-doped TiO2 thin films. Based on the experiments and the theoretical calculations, we find that the transition of Co 1s electron to the unoccupied Co 3d eg states is clarified from the pre-edge single-peak in the Co K-edge XANES spectrum of the Co-doped TiO2 thin film, and that the Co 3d t2g states are occupied while the eg states are partially unoccupied. This suggests a low-spin configuration of the substitutional Co2+ in the Co-doped TiO2 thin film. The studies demonstrate the ability of Co K-edge XANES to provide information on spin state of Co ions in the Co-doped TiO2.

Substitutionally doped Si1−xMnx thin films were fabricated by a magnetron cosputtering method at a low growth temperature. X-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) techniques were used to investigate the structures of the Si1−xMnx thin films. The XRD results exhibit that no secondary phases such as metallic Mn or Mn–Si compound can be detected. The detailed analysis of the extended XAFS together with the x-ray absorption near-edge structure spectra at the Mn K-edge unambiguously reveals that the doped Mn atoms are incorporated into the Si matrix and substitute for the Si sites in the Si lattice. The results clearly indicate that the Mn occupations in silicon thin films are quite sensitive to the growth conditions and the postannealing treatment.

The local structure of the doped Mn in the MnxSi1-x dilute magnetic semiconductors (DMSs) fabricated by magnetron cosputtering method are studied by fluorescence X-ray absorption fine structure (XAFS) at Mn K-edge. It is found that the occupation of Mn atoms in the MnxSi1-x DMS strongly depends on the Mn content. The Mn K-edge XAFS results indicate that for the sample with low Mn content (x = 0.03~0.08), the Mn atoms are incorporated into the lattice of Si, and substitute part of the Si sites. As the Mn content reaches 0.15, Mn atoms mainly form the phase of Mn1Si1 compound.

Fluorescence X-ray absorption fine structure (XAFS) technique was used to investigate the local structures of the doped Mn in the MnxGe1-x dilute magnetic semiconductors (DMSs) with different Mn content (x=0.07, 0.25, 0.36) prepared by magnetron cosputtering method. The results indicate that for the sample with low Mn content (x=0.07), the Mn atoms are mainly incorporated into the lattice of Ge, and locate at the substitutional sites of Ge atoms with the ratio of 75%. With the Mn content increasing to 0.25 or higher, only part of Mn atoms enter the lattice of Ge and the others exist in the form of the Mn5Ge3 phase whose content increases with the doped Mn concentration. It is found that, in the Mn0.07Ge0.93 the bond length of the first (Mn-Ge) shell is RMn-Ge = 2.50 A, which is bigger than the first (Ge-Ge) shell distance in Ge by about 0.05 A. These results imply that local structure expansion is induced by dilute Mn substituting into Ge sites.

X-ray absorption fine structure (XAFS) and first-principles calculations are effectively combined to establish correlations of fabrications, atomic and electronic structures as well as ferromagnetism for the Mn-doped dilute magnetic semiconductors (DMS), and to shed light on the magnetism origin for a variety of ZnO-, GaN-, and Si-based DMSs. The results of Mn:ZnO and (Mn,N):ZnO thin films reveal that either the existence of Zn vacancy or N substitution of O sites can stabilize the ferromagnetic interactions between neighboring Mn-Mn pairs, and enhance the magnetic moment per Mn. In a 2.5at.% Mn-doped GaN film, a part of substantial Mn ions is found to locate at the interstitial sites near the substitutional Mn ions, forming Mn-Mn dimers that possess unique electronic and magnetic properties. Similar phenomena have also been found in the Mn-doped Si system in which the interstitial Mn atoms intend to assemble together via an intervening substitutional Mn ion. We have proposed a pathway to understand the microscopic origin of ferromagnetism in the DMS materials from the viewpoint of experimental determination and theoretical calculations.

The x-ray absorption near-edge structure (XANES) and first-principles calculations were employed to study the local structure and magnetic origin of Co-doped rutile TiO2 thin film. It is found that the experimental Co K-edge XANES can be reproduced by the calculated spectrum of substitutional Co (CoTi) with O vacancy (VO), suggesting the coexistence of CoTi and VO in this system. First-principles total energy calculations further reveal that the O vacancy prefers to reside near the Co ion and substantially facilitates the impurity doping. The electronic structure analysis indicates that the O vacancy can mediate the ferromagnetic interaction between the CoTi ions and thus is responsible for the observed room-temperature ferromagnetism in the Co-doped TiO2-δ thin films.

We performed a first-principles study on the magnetism and electronic character of rutile Fe:TiO2(110) mediated by oxygen vacancies (OVs) and codopant. The results show the magnetic interaction between Fe ions is a ferromagnetic (FM) superexchange nature, while the presence of OV makes it turn to an antiferromagnetic behavior. It is found when the system is codoped with oppositely charged P, the interactions are rehabilitated to FM coupling. The electronic structure analysis reveals that this is principally attributed to the sp-d hybridizations between P and Fe, which finally activate a long-ranged FM interaction between the Fe ions, and substantially facilitate the electron transport.

The complicated three-dimensional interior structures of the polycrystalline hollow zinc oxide microspheres were clearly obtained by the nondestructive nanocomputed tomography (nano-CT) technique. The parameters such as diameter, volume, porosity, and surface area were calculated by the quantitative analysis of reconstructed data. Especially, three single selected particles with different typical structures were separated and compared. With these results, the distinction of the particles can be clearly understood in nanoscale. This study reveals that nano-CT is an effective and competent tool for investigating the three-dimensional interior structures of nanomaterials in the natural environment.

Cu and Co ions co-doped Zn0.95?xCuxCo0.05O (0 ? x ? 0.08) diluted magnetic semiconductors (DMSs) prepared by the sol?gel method were investigated by x-ray absorption fine structure (XAFS). Although the Co K-edge XAFS data indicate that the doped Co ions are located substitutionally at the Zn sites for all the Zn0.95?xCuxCo0.05O DMSs, the CuK-edge XAFS analysis combined with XRD results reveals that the doped Cu ions are separated to form a CuO phase for samples calcined at 1073?K. After being sintered at a higher temperature of 1473?K, the Cu ions with low Cu concentration (x ? 0.02) are substantially incorporated into the ZnO host lattice, while a small proportion of CuO clusters still coexist in the samples with a higher Cu concentration (x ? 0.05). The solubility of the doped Cu ions in Zn0.95Co0.05O DMS is estimated as about 0.04. The results provide experimental guidance in the synthesis of the co-doped ZnO based DMSs.

The x-ray absorption near edge structure spectroscopy and first-principles calculations were combined to study the local and electronic structures of rutile Co:TiO2 thin film with room-temperature ferromagnetism. It was revealed that the CoTi2+ substituting the Ti site forms CoTi2+-VO complex with the O vacancy generated in the annealing process. The O vacancy induces a spin-split donor impurity band with a t2g character within the gap region. We proposed that the strong exchange interaction between the localized carriers captured by O vacancy and the substitutional Co ions leads to the ferromagnetism of the Co:TiO2 thin film.