X-ray spectroscopic investigation of some chromium compounds

The intensity distribution of theKα doublet in chromium metal and some of its compounds, CrB, CrSb, Cr₂Te₃, K₂CrO₄, and CaCrO₄, has been investigated by means of a high resolution X-ray spectrometer provided with a bent topaz crystal (radius one meter). From the results obtained it seems that the bonding of Cr is largely metallic in CrB while it is largely covalent in the CaCrO₄ and Cr₂Te₃ compounds. On the other hand, the bonding is essentially ionic in K₂CrO₄ while it is both ionic and covalent in CrSb. The line width of the six valence compounds are found to be larger than that of chromium metal. This shows that the 2p— 3d electrons interaction is not mainly responsible for the large line width found. It may probably be attributed to the crystal field.     

Preliminary spectroscopic investigation of some PVA membranes gamma irradiated

The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated were investigated by XRD, UV-VIS and Raman spectroscopies. The increase of UV absorbance is observed after irradiation. This behavior is correlated with the scission effect and local ordering of the polymeric chain induced by irradiation. These effects were probed by XRD and Raman spectroscopy.     

X-ray photoelectron spectroscopic investigation of electrochemically oxidised and reduced platinum surfaces

The growing of oxide layer with the time of anodic oxidation in 1M, 3.5M and 8.8M perchloric acid solutions has been investigated by XPS on smooth and platinised Pt surfaces. Pure metallic Pt surfaces were prepared by acidic digestion, ignition and cathodic reduction, and their electron spectra have been compared. The presence of a single species, probably PtO, can be evaluated from the XPS measurements. Calculated values of PtO film thickness for different time intervals of electrolytic oxidation are given at various concentrations of HClO₄.     

X-ray absorption and emission spectroscopic investigation of Mn doped ZnO films

The electronic structure of (Zn,Mn)O films with different Mn concentrations has been investigated by element-selective soft X-ray absorption and emission spectroscopy. The band gap narrowing of (Zn,Mn)O with increase of Mn concentration (<20% Mn) is attributed to the Mn doping and sp-d exchange interactions. According to analysis of the O Kα and resonant Mn L_2,3 X-ray emission spectra, the splitting of Mn 3d subbands is related to Mn-derived states. It indicates that ferromagnetic coupling in (Zn,Mn)O can be taken into account to be carrier-induced. The presence of antiferromagnetism in the heavier Mn-doped films can be explained in terms of the existence of MnO secondary phases.     

X-ray diffraction imaging investigation of silicon carbide on insulator structures

A new process was recently developed to manufacture silicon carbide on insulator structures (SiCOI). The process consists of several steps: (i) hydrogen implantation into an oxidised SiC wafer, (ii) bonding the oxidised surface of this wafer to an oxidised silicon substrate and (iii) high temperature splitting of a thin SiC film from the SiC wafer at the depth of the maximum hydrogen concentration and further annealing of the splitted film. The defect generation occurring during this process was investigated by synchrotron radiation X-ray diffraction topography, with special emphasis on to the last two steps. Various X-ray topographic techniques were used to characterise the lattice defects inside the SiC wafer, to quantify the strong lattice distortion near the edges of the splitted SiC film and to reveal SiC film regions lost during the splitting process. Moreover, we show that the strain fields of dislocations, observed in the silicon substrate after high temperature splitting and annealing of the splitted structure, induce a corresponding deformation in the thin SiC overlayer, despite the presence of the sandwiched oxide film. The defect density is much lower in the central region of the SiCOI structure. Received: 29 June 2001 / Accepted: 8 November 2001 / Published online: 20 March 2002     

An X-ray photoelectron spectroscopic study of some nickel (II) amine complexes

The X-ray photoelectron (XPS) spectra of several Ni(II) diamine complexes, a Ni(II) triamine complex and several Ni(II) diimine complexes are reported in terms of the Ni 2p, Cl 2p and N 1s core level binding energies. Theoretical models are presented to account for the quadratic relationship observed between XPS Ni 2p_{$\text{3}\text{2}$}binding energy shifts and the N-H infrared rocking frequency as related to these complexes. On the basis of this correlation, it is possible to discriminate between free counter-ions coordinated to the metal or involved in cluster-ion formation. Individual XPS data for these complexes are interpreted in terms of the intrinsic nature of the metal environment and an attempt is made to calculate the metal and donor nitrogen atomic charges for selected complexes.     

Magnetic disaccommodation in normal spinel structures

Magnetic disaccommodation is investigated for ferrous ferrites with normal spinel structure. This study shows the presence of a new relaxation process in the temperature region IV (285 K) that has not been detected in inverse spinels. A numerical analysis of the isochronal spectra reveals that it is composed of two simple Debye processes with activation energies close to 0.75 eV and 0.80 eV, and preexponential factors 3×10^–13 s. This relaxation is attributed to the formation of an induced anisotropy due to jumps of B-Fe ions into vacancies (as process III), but in presence of a divalent cation occupying an A-site.     

X-ray absorption investigation of some high oxidation states of six-co-ordinated iron in oxides of perovskite or K2NiF4-type structures

Synchrotron radiation has been used to investigate the X-ray absorption properties (Fe K-edge and EXAFS) of oxides containing iron with a high oxidation state (+3, +4, +5) in regular (O_h) or distorted (D_4h) octahedral co-ordination. It is shown that the usual monotonic variation of the edge energy with oxidation state depends closely on the electrical properties of the material and on the symmetry of the iron site. Moreover, the main absorption line is split when the symmetry of the iron site is lowered from O_h, to D_4h. New evidence is thus given that X-ray absorption spectroscopy can provide useful information about the absorbing atom site: it could be used in principle to point out certain types of distortions of the first shell of neighbors around the absorbing atom. A full EXAFS analysis of this shell and XANES (X-ray absorption near edge structure) data are also reported and discussed.     

X-ray photoelectron spectroscopic observation of nitrogen-containing gases adsorbed at high pressures on some transition metals

The chemisorbed species formed by reaction of nitrogen-containing gases (NO, N₂O, N₂ and dry air) on some transition metals (Ni, Cu, Ti, Co and Pd) at high pressures (1–200 torr) are examined by XPS. At least four adsorption species are observed on the surface at ambient temperature. They can be assigned to ?NO₃ (407.3 eV), ?NO₂ (404.5 eV), ?NO (400.0 eV) and the nitrogen bound directly to metal, which shows a characteristic energy value for each metal. This feature differs from the reported results of low pressure adsorption experiments. Relative abundances among the chemisorbed species vary with individual metals and gases.     

Electroconductivity and electron exchange in spinel structures

The mechanism of conductivity in spinel compounds having ions of one type with different valence in equivalent lattice sites is proposed. This one allows us to explain phase transition from ferromagnetic to ferrimagnetic state in chalcogenide spinels.     

Electronic band structures of the NbC—NbN alloy system from the X-ray photoelectron spectroscopic measurement

The energy distribution curves (EDC's) of valence band of NbC—NbN system have been measured by X-ray photoelectron spectroscopy. The characteristic features of the EDC's are well interpreted by the super-position of the densities of states of NbC and NbN in proportion to their concentration. Each band of NbC and NbN remains rigid and self-asserting in the band structures of NbC_xN_1-x alloy system.     

X-ray spectroscopic study of cobalt-zinc ferrites

K-absorption edges and the associated fine structures of cobalt and iron in cobalt-zinc ferrites of composition, Zn_xCo_1-xFe₂O₄ (x = 0, 0.25, 0.50 and 0.75) have been recorded employing a 40cm curved crystal spectrograph of transmission type. It is found that the cobalt and iron ions in these samples exist in valence states two and three respectively. Bond lengths have been determined using the X-ray fine structure methods. It is noted that estimated bond lengths are close to those obtained from crystallographic data. It is pointed out that the X-ray fine structure methods can be used to complement diffraction methods for the determination of bond lengths in samples containing atoms of nearly equal scattering power.     

An X-ray photoelectron spectroscopic study of some bis(diamine)-copper (II) complexes

XPS data for a series of octahedral copper(II) diamine tetrafluoroborate and perchlorate complexes are interpreted in the following terms; (i) the inductive effect of diamine substituents; (ii) the degree of cation-anion interaction; (iii) the effect of progressive increase in diamine chelate ring size; and (iv) the Jahn-Teller effect in these complexes.     

反式油酸的太赫兹光谱研究

应用太赫兹时域光谱技术研究了反式油酸在THz波段的光学特性,在室温氮气环境下获得了0.5～2.5 THz范围内波段的吸收光谱和折射率谱,结果表明反式油酸在此波段内存在多个特征吸收峰,样品的平均折射率为1.43.采用密度泛函理论的B3LPY方法对反式油酸分子的结构和振动频率进行了模拟,并采用Gaussian View软件...     

X-ray spectroscopic study of zirconium and molybdenum diselenides

The K absorption spectra of zirconium, molybdenum and selenium in ZrSe₂ and MoSe₂ have been recorded photographically using a Cauchois type bent crystal (mica) spectrograph. The absorption edge shifts are used along with the data for NbSe₂ (Bhide and Bahl 1971J. Phys. Chem. Solids 32 1001) to propose bond schemes for these compounds.     

X-ray spectroscopic investigation of the electronic structure of α-quartz and stishovite (SiO2)

The silicon K and L_2,3 X-ray emission bands of stishovite (tetragonal SiO₂, 6:4 co-ordination) are reported and discussed along with the corresponding emission bands of α-quartz (hexagonal SiO₂, 4:2 co-ordination). While the shapes of the Si K-emission bands of stishovite and α-quartz differ considerably, those of the Si L_2,3-emission bands are similar. The measured spectra are compared with theoretical band structure calculations, and good overall agreement is found.     

X-ray investigation of dialkyldimethylammonium bromides

Abstract

A Series of dialkyldimethylammonium bromides (DDAB), (C _n H_2n+1)zN⁺(CH₃)₂Br^?with n = 10, 12, 14, 16 and 18 were investigated using X-ray diffraction. Measurements were performed by the photographic Guinier method as well as by diffractometer on samples aligned on a glass substrate. For a sample with n=12, X-ray high-pressure measurements were also performed which allowed us to confirm the destabilization under pressure of the phase existing on heating above the first transition point. For all the studied compounds, except for that with n =16, strong hysteresis and rich polymorphism were observed. A smectic T phase - high-temperature liquid crystal was confirmed for compounds with n= 16 and 18. All the remaining alkylammonⁱum salts have smectic an E high-temperature liquid crystal phase.     

稀土离子掺杂纳米TiO_2的太赫兹光谱研究

对sol-gel法制备的不同稀土元素(Ce,Nd,Sm)掺杂的纳米TiO2粒子进行研究。X射线衍射(XRD)和X射线光电子能谱(XPS)分析结果表明,稀土离子均以间隙的形式均匀分布在纳米TiO2晶格内。傅里叶变换红外光谱(FTIR)和太赫兹时域光谱(THz-TDS)显示,掺杂TiO2较纯TiO2具有更强的红外活性;在0.2~1.70 THz波段,TiO2的折射率随着频率的增加而减小,并呈现反常色散现象;Ce掺杂引起新的特征吸收,分别为1.35和1.58 THz,且造成太赫兹吸收谱的吸收边发生红移,Nd和Sm掺杂则造成吸收边蓝移。在0.2~1.7 THz范围内,Sm掺杂引起的介电损耗角正切值(taneδ)最小,其平均值为0.05。