(Fe1-xNix)2P电子结构与磁学特性的X射线近边吸收谱研究

利用X射线近边吸收谱对Fe₂P,Ni₂P及其掺杂物(Fe_1-xNi_x)₂P(x=01,025,05)中Fe,Ni,P的K边进行了研究.结合多重散射理论近边计算,讨论了金属原子不同位置格点3f,3g对近边谱特征的贡献,得出当Ni原子取代Fe原子时将优先占据Fe(3f)格点位置;根据第一性原理对能态的计算发现,不考虑磁性时不同格点P的pDOS未占据态电子结构与P-K近边吸收谱实验相符合;与考虑铁磁性Fe₂P 的DOS相比较后结果显示Fe₂P的磁性主要来源于Fe(3g)格点,铁磁性Ni₂P计算的Ni不同格点原子磁矩均接近于0,与它一般显顺磁性结论相一致. 关键词： X射线近边吸收谱 电子结构 多重散射理论 态密度     

利用X射线近边吸收谱学方法研究蒙脱石在高温下吸附汞金属的行为

测量了分别用汞水溶液、汞和半胱氨酸混合溶液处理的蒙脱石样品在高温下汞L₃边X射线近边吸收谱. 利用这个方法研究了汞金属在蒙脱石中的吸附和解吸附行为以及氨基酸对吸附汞吸附行为的影响. 研究结果显示在没有氨基酸介入的情况下,蒙脱石中吸附的汞被6个水分子配位,或者被蒙脱石表面的氧原子配位;当引入半胱氨酸时,汞优先于氨基酸中的硫原子配位,形成更稳定的Hg-S键. 这个结果说明氨基酸的引入能够使得蒙脱石更稳定的吸附汞金属离子,大大缓解汞离子向生物圈中迁移.     

C2H4/Ni(100)近边X射线吸收谱的多重散射理论研究

本文用多重散射原子集团方法计算并分析了C₂H₄/Ni(100)系统的碳K边近边X射线吸收精细结构(NEXAFS)谱,确定了乙烯吸附在Ni(100)表面上的几何结构。结果表明,乙烯是吸附在垂直桥位上的,其中碳原子与表面最近的镍原子距离是1.70?,而乙烯分子平面倾斜于表面50°,同时发现,氢和镍之间的相互作用对结构的形成有很大的作用,这些结果得到了不同途径的验证。 关键词：     

同步辐射软X射线近边吸收谱方法研究长期施肥对黑土有机碳官能团的影响

以定位20年的黑土肥料试验为平台,利用同步辐射软X射线近边吸收谱(C-1s NEXAFS)方法,研究了长期施用化肥以及化肥配施玉米秸秆对土壤有机碳官能团的影响。结果表明：与不施肥的空白处理(CK)相比,单施化肥(N,NPK)后土壤的芳香C和羧基C含量增加,脂族C和羰基C含量下降,脂族C/芳香C比值降低;与单施化肥处理相比,化肥配施玉米秸秆后芳香C含量下降而脂族C含量增加,脂族C/芳香C比值增加,并随玉米秸秆用量增加表现的更为明显;无论配施玉米秸秆与否,NPK肥混施处理的芳香C、脂族C以及脂族C/芳香C比值均高于单施N肥处理。上述结果说明,单施化肥比不施肥使土壤有机碳官能团中芳香类化合物的相对比例增加,而脂肪烃类化合物的相对比例下降;化肥配施玉米秸秆则比单施化肥增加了脂肪烃类化合物的相对比例,配施高量比低量玉米秸秆的增加趋势更为明显,同时NPK肥混施比单施N肥有利于提高脂肪烃类化合物的相对比例。C-1s NEXAFS方法能够原位表征长期定位施肥条件下土壤有机碳官能团组成的变化。     

二己二硫醚多层膜局域结构的近边x射线吸收精细结构研究

利用多重散射团簇(MSC)方法计算了二己二硫醚［CH₃(CH₂)₅S］₂单分子和多分子硫原子近边x射线吸收精细结构(NEXAFS)谱，给出了二己二硫醚多层膜的局域结构模型. MSC研究显示多层膜中二己二硫醚分子作平行有序排列，彼此相距0.47nm，其横截面呈规则的正方形. 利用离散变分Xα方法计算了二己二硫醚单分子和多分子的电子结构，验证了MSC的计算结果；并阐明了NEXAFS谱中各峰的物理起源. 对多层膜中分子之间的相互作用进行了讨论，发现多层膜的局域结构有分子自组装的特性. 关键词： 3(CH₂)₅S］₂多层膜')" href="#">二己二硫醚［CH₃(CH₂)₅S］₂多层膜 近边x射线吸收精细结构 多重散射团簇方法 离散变分Xα方法     

Mg_n~-,AlMg_(n-1)(n=2～13)团簇结构和电子性质的密度泛函理论研究

本文从第一性原理出发,利用密度泛函理论的B3PW91方法,在6-311G水平上对Mg-n,AlMgn-1(n=2～13)团簇进行了几何结构优化和频率分析,并对团簇的平均结合能,二阶能量差分,劈裂能等进行了计算.结果表明:与Mgn团簇相比,带负电Mg-n团簇的最低能量结构整体(除n=6,8,11)变化不大.Al原子的掺杂对Mgn(n=2～13)团簇的最低能量结构没有太大影响,Mgn,AlMgn-1团簇有类似的结构生长方式.带一个负电和掺杂一个Al原子均能使Mgn团簇的平均结合能增大,稳定性增强.并发现Mg-n(n=2～13)团簇在n=4,9时比较稳定,在n=11时稳定性较差,与实验结果一致;而等电子的AlMgn-1团簇在n=4,7,9时比较稳定.     

Al_2Be_N(N=1-12)团簇最低能量结构的稳定性和电子特性的密度泛函理论研究

采用密度泛函理论(DFT)的B3LYP方法,在6-311G水平上对Al2Ben(N=1～12)团簇的各种可能构型进行几何结构优化和频率分析,得到了团簇的最低能量结构.并对Al-Be最近邻键长,平均结合能,二阶能量差分,能隙和Al原子的电子位形进行了讨论.结果表明:Al原子掺杂对纯Be团簇结构影响不大:Al-Be最近邻键长和团簇的平均结合能随N的增加表现出了不同的变化趋势;Al原子的化合价出现了由一价到三价的变化;N=7是团簇的幻数.     

S掺杂对锐钛矿相TiO2电子结构与光催化性能的影响

采用基于第一性原理的平面波超软赝势方法研究了掺杂不同价态S的锐钛矿相TiO2的晶体结构、杂质形成能、电子结构及光学性质.计算结果表明硫在掺杂体系中的存在形态与实验中的制备条件有关;掺杂后晶格发生畸变、原子间的键长及原子的电荷量也发生了变化,导致晶体中的八面体偶极矩增大;S 3p态与O 2p态、Ti 3d态杂化而使导带位置下移、价带位置上移及价带宽化,从而导致TiO2的禁带宽度变窄、光吸收曲线红移到可见光区.这些结果很好地解释了S掺杂锐钛矿相TiO2在可见光下具有优良的光催化性能的内在原因.根据计算结果分析比较了硫以不同离子价态掺杂对锐钛矿相TiO2电子结构和光催化性能影响的差别.     

Local electronic structure of phosphorus-doped ZnO films investigated by X-ray absorption near-edge spectroscopy

Using X-ray absorption near-edge structure spectroscopy (XANES), we investigate the local electronic structure of phosphorus (P) and its chemical valence in laser-ablated n-type (as-grown), and p-type (annealed) P-doped ZnO thin films. Both the P L ₁- and P L _2,3-edge XANES spectra reveal that the valence state of P is 3− (P³⁻) in the p-type as well as in the n-type P-doped ZnO. However, the peak intensity is stronger in the former than that in the latter, suggesting that P replaces O (O²⁻ sites with the P³⁻) after rapid thermal annealing. The Zn and O K-edges XANES spectra consistently demonstrate that, in the p-type state, P ions substitutionally occupy O sites in the ZnO lattice.     

Unoccupied electronic structure of TiOCl studied using x-ray absorption near-edge spectroscopy

We study the unoccupied electronic structure of the spin-1/2 quantum magnet TiOCl using x-ray absorption near-edge spectroscopy (XANES) at the Ti L and O K edges. We acquire data both in total electron and fluorescence yield modes (TEY and FY, respectively). While only the latter allows us to access the unconventional low-temperature spin-Peierls (SP) phase of TiOCl, the signal is found to suffer from significant self-absorption in this case. Nevertheless, we conclude from FY data that effects of the SP distortion on the electronic structure are absent in the incommensurate intermediate phase within experimental accuracy. The similarity of room-temperature FY and TEY data, the latter not being obscured by self-absorption, allows us to use TEY spectra for comparison with simulations. These are performed by means of cluster calculations in D(4h) and D(2h) symmetries using two different codes. We extract values of the crystal-field splitting and parameterize our results using the commonly seen notation of Slater, Racah and Butler. In all cases, good agreement with published values from other studies is found.     

Potassium doping effect on the lattice softening and electronic structure of Ba(1-x)K(x)Fe(2)As(2) probed by X-ray absorption spectroscopy

Ba(1-x)K(x)Fe(2)As(2) superconducting samples (x = 0, 0.2, 0.4, 0.5) were synthesized by the solid-state reaction method. In this contribution the doping effect of potassium on the lattice dynamics in this newly discovered Ba(1-x)K(x)Fe(2)As(2) superconductor has been investigated by extended X-ray absorption fine-structure spectroscopy. The analysis shows that with potassium doping an increased disorder in the iron layers is mainly related to the softening of the Fe-Fe bond. Information about the electronic structure of these materials has also been obtained by looking at the X-ray absorption near-edge structure spectra that point out the presence of holes in the Fe-3d/As-4p hybridized orbital of the BaFe(2)As(2)-based system.     

Theoretical calculation of electronic structure and X-ray absorption near-edge structure of cathode materials for Li ion batteries

First principles calculations were performed on the electronic structure, chemical bonding and X-ray absorption near edge structure (XANES) of various lithium transition metal oxides. In the electronic structure using the discrete variational Xα method (DV-Xα), chemical bonding is changed by Li deintercalation. Li is found to be nearly ionized in LiMO₂ and strong covalent bonding between M and O is noted. The larger the difference of covalency between cation and nearest neighbor anion when Li intercalated/deintercalated is, the lower the voltage calculated by Vienna Ab Initio Simulation Package (VASP) is. By calculations of transition state, we reproduce the characteristics of the spectra as well as the chemical shifts and the origin of peaks appearing in the experimental XANES spectra is interpreted in terms of orbital interactions using bond overlap population diagrams.     

Influence of nickel on the electronic structure and magnetic properties in Gd7Pd3-xNix

With increasing amount of nickel in the Gd₇Pd_3-xNi_x series, the unit cell volume decreases due to difference between atomic radius of Pd and Ni but the type of crystal structure is preserved. The paper presents X-ray diffraction, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometer, Transmission Electron Microscopy, AC and DC magnetic susceptibility and magnetocaloric examinations of the series. The Ni substitution into Pd position causes the decrease in the Curie temperature. Moreover, the dispersion observed in the AC-susceptibility at different frequencies vanishes at the Curie point. Just below the ordering temperature, a Hopkinson peak is observed. Complex processes depending on frequency and magnetic field occur in the transition region. The magnetization phenomena are very sensitive to the applied DC magnetic field and even very weak fields producing thermomagnetic hysteresis. A reorientation process around 150 K exists in all compounds and it is connected with increasing interactions at low temperatures. After nickel substitution, the relative cooling power (RCP) is greater in comparison to the parent compound.     

Sulfur speciation in two typical soil samples using X-ray absorption near-edge structure spectroscopy and chemical fractionation

Sulfur K-edge X-ray absorption near-edge structure spectroscopy and chemical sequential extraction was respectively used to study the speciation of sulfur in two sulfur-rich soils samples. Sulfur K-edge X-ray absorption near-edge structure spectroscopy analysis obtained a variety of spectra. Spectral fitting of the X-ray absorption near-edge structure spectra utilizing a large set of model compounds showed great differences between these two sulfur-rich soil samples. It was found that both of the soil samples had high sulfur content (8.40 and 11.57?g?kg^?1, respectively). Chemical extraction results suggested that sulfur mainly existed as organic in the ancient paddy soil (7.37?g?kg^?1) and more reduced sulfur was identified in it. X-ray absorption near-edge structure spectroscopy also got similar results. These organic forms of sulfur existed in organic matter across a range of oxidation states. There was high proportion of oxidized sulfur in the sulfuric acid plant that mainly existed as sulfate.     

Quantitative depth profiling of photoacid generators in photoresist materials by near-edge X-ray absorption fine structure spectroscopy

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to quantify the surface composition and depth profiling of photoacid generators in thin film photoresist materials by varying the entrance-grid bias of a partial electron yield detector. By considering model compositional profiles, NEXAFS distinguishes the surface molar excess within the top 6 nm from the bulk. A surface enriched system, triphenylsulfonium perfluorooctanesulfonate, is contrasted with a perfluorobutanesulfonate photoacid generator, which displays an appreciable surface profile within a 6 nm segregation length scale. These results, while applied to 193-nm photoresist materials, highlight a general approach to quantify NEXAFS partial electron yield data.     

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) study of melt-spun Fe85Ga15 ribbons

The local structure in melt-spun Fe₈₅Ga₁₅ ribbons with a width ∼3 mm and thickness ∼60 μm produced in argon atmosphere was studied by analyzing EXAFS and XANES data. The following results were obtained: Ga–Ga bonds were not detected excluding the tendency to form clusters of Ga atoms; Ga substitutes Fe creating a local strain of about +1% on the first shell Fe–Ga bond, whereas on the second Fe–Ga shell strain quickly relaxes down to +0.3%; XANES spectra are compatible with a random substitution of Fe atoms by Ga atoms in the A2 structure. From the AFM investigation, we observed that at the surface (free side) of the ribbon the particles are elongated along the ribbon (∼2 μm×∼5 μm) and each particle is formed by small grains of average size of 200 nm.