Although dilute magnetic semiconductors have promising potentials in spintronics applications,the mechanism of their ferromagnetism remains ambiguous.The extensive theoretical models and exotic experimental evidences ...Although dilute magnetic semiconductors have promising potentials in spintronics applications,the mechanism of their ferromagnetism remains ambiguous.The extensive theoretical models and exotic experimental evidences provide self-consistent but usually contradictory explanations on its either intrinsic or extrinsic origins.We find room temperature ferromagnetism in a series of Zn_(1-x)Co_(x)O(0.03≤x≤0.10)thin films prepared using magnetron co-sputtering method and treated with post-annealing at temperatures 350℃ and 500℃.The origin of the ferromagnetism is investigated in terms of electronic structure combining hard x-ray absorption spectroscopy(XAS)at Zn and Co K-edge,and soft x-ray XAS at O K-edge and Co L_(2,3)-edge.The full multiple scattering theory is employed to reinforce the interpretation of the XAS spectra,which concludes that full substitution of zinc by cobalt is responsible for the room temperature ferromagnetism due to the d states of cobalt within the framework of bound magnetic polaron.Moreover,the evidence of cobalt nanoclusters is detected at highly doped and annealed samples.The first principles calculation confirms the electronic structural evidences via the formation energy.展开更多
X-ray magnetic linear dichroism(XMLD)experiments were carried out at beam line 3W1B of the Beijing Synchrotron Radiation Facility.The results demonstrate the experimental XMLD spectra of Co_(35)Fe_(65) alloy film anne...X-ray magnetic linear dichroism(XMLD)experiments were carried out at beam line 3W1B of the Beijing Synchrotron Radiation Facility.The results demonstrate the experimental XMLD spectra of Co_(35)Fe_(65) alloy film annealed with and without oxygen gas,in agreement with the ligand field multiplet calculation.It can be concluded that cobalt atoms are more difficult to oxidize than iron atoms.The oxygen atoms inserting into the sample surface interval lead to the lattice distortion and the fine tuning of the occupation number of absorption atom d-orbits.展开更多
Fe/Sn-codoped In_(2)O_(3)powders and films are prepared by a vacuum annealing process and a pulsed laser deposition technique,respectively.The structural and magnetic properties of the samples are investigated.The obv...Fe/Sn-codoped In_(2)O_(3)powders and films are prepared by a vacuum annealing process and a pulsed laser deposition technique,respectively.The structural and magnetic properties of the samples are investigated.The obvious room-temperature ferromagnetism is observed in both(In_(0.92)Fe_(0.05)Sn_(0.03))_(2)O_(3)powders and films,but their magnetic behaviors are very different.The ferromagnetism of the vacuum-annealed powders is partially due to precipitated Fe_(3)O_(4)impurity.By contrast,the ferromagnetism of the films is intrinsic and does not originate from any magnetic impurity,as confirmed by the extensive x-ray absorption spectroscopy and magnetization studies.展开更多
单原子催化剂具有原子利用率高、活性中心明确、催化中心原子配位数低等优点,有望提高电催化性能.具有相邻杂原子的双原子催化剂(DAC)有望发挥两个原子的协同作用,从而进一步提高活性.在本文中,我们报道了一种PtNi-NC催化剂,该催化剂由...单原子催化剂具有原子利用率高、活性中心明确、催化中心原子配位数低等优点,有望提高电催化性能.具有相邻杂原子的双原子催化剂(DAC)有望发挥两个原子的协同作用,从而进一步提高活性.在本文中,我们报道了一种PtNi-NC催化剂,该催化剂由固定在氮掺杂碳基底上的PtNi双原子构成,该基底采用原子层沉积技术合成.X射线吸收光谱证实了Pt–Ni双原子的存在.所制备的PtNi-NC催化剂具有优异的催化活性,在10 m A cm^(-2)的电流密度下,酸性介质中析氢反应(HER)的过电位为30 m V,与市售20 wt%Pt/C相当.特别值得注意的是,PtNi-NC具有比20 wt%Pt/C更高的质量活性,约为其21倍.密度泛函理论计算表明,Pt–Ni双原子通过调节局部电子结构和优化电荷分布产生协同效应,有助于优化吸附性能和增强电催化性能.这项工作为DAC的制备提供了新途径,揭示了它们在电催化HER等领域的应用潜力.展开更多
Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing d...Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.展开更多
Ca-based additives have been widely used as a sulfur adsorbent during coal pyrolysis and gasification. The Ca speciation and evolution during the pyrolysis of coal with Ca additives have attracted great attention. In ...Ca-based additives have been widely used as a sulfur adsorbent during coal pyrolysis and gasification. The Ca speciation and evolution during the pyrolysis of coal with Ca additives have attracted great attention. In this paper, Ca species in the coal chars prepared from the pyrolysis of Ca（OH）2 or CaCO3-added coals are studied by using Ca K-edge X-ray absorption near-edge structural spectroscopy. The results demonstrate that Ca（OH）2 , CaSO4 , CaS and CaO coexist in the Ca（OH）2-added chars, while Ca（OH）2 and CaSO4 are the main species in the Ca（OH）2-added chars. Besides, a carboxyl-bound Ca is also formed during both the pyrolysis for the Ca（OH）2-added and the CaCO3-added coals. A detailed discussion about the Ca speciation is given.展开更多
To improve the performance of Beamline 3WIB at the Beijing Synchrotron Radiation Facility for the soft X-ray magnetic linear dichroism research at transition metals L2,3 edges, a new monochromator was designed and bui...To improve the performance of Beamline 3WIB at the Beijing Synchrotron Radiation Facility for the soft X-ray magnetic linear dichroism research at transition metals L2,3 edges, a new monochromator was designed and built to replace the original one. After the assemblage, alignment and adjustment of the monochromator system, the first commissioning results were obtained. The photon energy range is from 50 to 1000 eV with spectral resolutions of 1600 at 250 eV and 1000 at 870 eV. The photon flux is of the order of 10s-109 photons/s/200 mA/0.1%BW. In the electron＇s orbital plane the linear polarization degree of the light is higher than 99% at 704 eV. The beamline has satisfied the basic experimental requirements.展开更多
Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By...Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.展开更多
To develop polarizer functioning in the extreme ultraviolet （EUV） and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equati...To develop polarizer functioning in the extreme ultraviolet （EUV） and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility （BSRF）. The reflectivity of the synthetic mica crystal at an angle of grazing incidence of 48° was obtained from the experimental data, which is about 4.8 × 10-3 at 25 nm and 6.0 × 10-4 at 12 nm, and the linear polarizance of the X-ray reflected by the synthetic mica crystal that we measured using an analyzer-rotating method increases from 80% to 96.6% in this EUV region, while higher than 98.2% in the simulation. The result indicates that this synthetic mica crystal works as a practical polarizer in this EUV region of 12-25 nm, and also in an extensive wavelength region higher than 25 nm.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11075176the Graduate Student Inno-vation Fund of NSRL(20090618S).
文摘Although dilute magnetic semiconductors have promising potentials in spintronics applications,the mechanism of their ferromagnetism remains ambiguous.The extensive theoretical models and exotic experimental evidences provide self-consistent but usually contradictory explanations on its either intrinsic or extrinsic origins.We find room temperature ferromagnetism in a series of Zn_(1-x)Co_(x)O(0.03≤x≤0.10)thin films prepared using magnetron co-sputtering method and treated with post-annealing at temperatures 350℃ and 500℃.The origin of the ferromagnetism is investigated in terms of electronic structure combining hard x-ray absorption spectroscopy(XAS)at Zn and Co K-edge,and soft x-ray XAS at O K-edge and Co L_(2,3)-edge.The full multiple scattering theory is employed to reinforce the interpretation of the XAS spectra,which concludes that full substitution of zinc by cobalt is responsible for the room temperature ferromagnetism due to the d states of cobalt within the framework of bound magnetic polaron.Moreover,the evidence of cobalt nanoclusters is detected at highly doped and annealed samples.The first principles calculation confirms the electronic structural evidences via the formation energy.
基金Supported by the National Natural Science Foundation of China under Grant No 11075176。
文摘X-ray magnetic linear dichroism(XMLD)experiments were carried out at beam line 3W1B of the Beijing Synchrotron Radiation Facility.The results demonstrate the experimental XMLD spectra of Co_(35)Fe_(65) alloy film annealed with and without oxygen gas,in agreement with the ligand field multiplet calculation.It can be concluded that cobalt atoms are more difficult to oxidize than iron atoms.The oxygen atoms inserting into the sample surface interval lead to the lattice distortion and the fine tuning of the occupation number of absorption atom d-orbits.
基金the National Science Foundation for Distinguished Young Scholars of China(No 51025101)the National Natural Science Foundation of China(Nos 11274214 and 61204097)+2 种基金the Ministry of Education of China(IRT1156)the Research Fund for the Doctoral Program of Higher Education(20121404110004)the Youth Science Foundation of Shanxi Province(2011021021-2).
文摘Fe/Sn-codoped In_(2)O_(3)powders and films are prepared by a vacuum annealing process and a pulsed laser deposition technique,respectively.The structural and magnetic properties of the samples are investigated.The obvious room-temperature ferromagnetism is observed in both(In_(0.92)Fe_(0.05)Sn_(0.03))_(2)O_(3)powders and films,but their magnetic behaviors are very different.The ferromagnetism of the vacuum-annealed powders is partially due to precipitated Fe_(3)O_(4)impurity.By contrast,the ferromagnetism of the films is intrinsic and does not originate from any magnetic impurity,as confirmed by the extensive x-ray absorption spectroscopy and magnetization studies.
基金supported by the National Natural Science Foundation of China(52122107 and 51972224)the National Research Foundation,SingaporeA*STAR under its LCER FI program Award(U2102d2002)。
文摘单原子催化剂具有原子利用率高、活性中心明确、催化中心原子配位数低等优点,有望提高电催化性能.具有相邻杂原子的双原子催化剂(DAC)有望发挥两个原子的协同作用,从而进一步提高活性.在本文中,我们报道了一种PtNi-NC催化剂,该催化剂由固定在氮掺杂碳基底上的PtNi双原子构成,该基底采用原子层沉积技术合成.X射线吸收光谱证实了Pt–Ni双原子的存在.所制备的PtNi-NC催化剂具有优异的催化活性,在10 m A cm^(-2)的电流密度下,酸性介质中析氢反应(HER)的过电位为30 m V,与市售20 wt%Pt/C相当.特别值得注意的是,PtNi-NC具有比20 wt%Pt/C更高的质量活性,约为其21倍.密度泛函理论计算表明,Pt–Ni双原子通过调节局部电子结构和优化电荷分布产生协同效应,有助于优化吸附性能和增强电催化性能.这项工作为DAC的制备提供了新途径,揭示了它们在电催化HER等领域的应用潜力.
基金Supported by National Natural Science Foundation of China (11075176)
文摘Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.
基金Supported by National Program on Key Basic Research Project (2010CB227005-03)National Natural Science Foundation of China (21076081, 10775150)the University of Saskatchewan for the financial support given to the CLS
文摘Ca-based additives have been widely used as a sulfur adsorbent during coal pyrolysis and gasification. The Ca speciation and evolution during the pyrolysis of coal with Ca additives have attracted great attention. In this paper, Ca species in the coal chars prepared from the pyrolysis of Ca（OH）2 or CaCO3-added coals are studied by using Ca K-edge X-ray absorption near-edge structural spectroscopy. The results demonstrate that Ca（OH）2 , CaSO4 , CaS and CaO coexist in the Ca（OH）2-added chars, while Ca（OH）2 and CaSO4 are the main species in the Ca（OH）2-added chars. Besides, a carboxyl-bound Ca is also formed during both the pyrolysis for the Ca（OH）2-added and the CaCO3-added coals. A detailed discussion about the Ca speciation is given.
基金Supported by National Natural Science Foundation of China (11075176)
文摘To improve the performance of Beamline 3WIB at the Beijing Synchrotron Radiation Facility for the soft X-ray magnetic linear dichroism research at transition metals L2,3 edges, a new monochromator was designed and built to replace the original one. After the assemblage, alignment and adjustment of the monochromator system, the first commissioning results were obtained. The photon energy range is from 50 to 1000 eV with spectral resolutions of 1600 at 250 eV and 1000 at 870 eV. The photon flux is of the order of 10s-109 photons/s/200 mA/0.1%BW. In the electron＇s orbital plane the linear polarization degree of the light is higher than 99% at 704 eV. The beamline has satisfied the basic experimental requirements.
基金Supported by National Natural Science Foundation of China(11075176, 10435050)
文摘Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.
基金Supported by National Natural Science Foundation of China (10275078, 10435050)
文摘To develop polarizer functioning in the extreme ultraviolet （EUV） and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility （BSRF）. The reflectivity of the synthetic mica crystal at an angle of grazing incidence of 48° was obtained from the experimental data, which is about 4.8 × 10-3 at 25 nm and 6.0 × 10-4 at 12 nm, and the linear polarizance of the X-ray reflected by the synthetic mica crystal that we measured using an analyzer-rotating method increases from 80% to 96.6% in this EUV region, while higher than 98.2% in the simulation. The result indicates that this synthetic mica crystal works as a practical polarizer in this EUV region of 12-25 nm, and also in an extensive wavelength region higher than 25 nm.
