Structural,thermal, electrical and magnetic properties of pure and 50% La doped BiFeO3 ceramics

Polycrystalline ceramic samples of pure and 50% La substituted BiFeO₃ have been prepared by standard solid state reaction method using high purity oxides and carbonates. The formation of the single phase compound as well as its chemical analysis has been checked by X-ray diffraction and energy dispersive X-ray microanalysis (EDAX) techniques. A better agreement between observed and calculated X-ray powder diffraction patterns was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group R3c. The lattice parameters in both the cases have been refined but the over-all structure remains the same. The microstructural studies have been carried out using scanning electron microscopy (SEM). Modulated differential scanning calorimetry (MDSC) has been used to detect the Neel/transition temperature in the compounds. The activation energies calculated from log σ vs 1/T curve are 0.81 eV and 1.13 eV respectively. Vibrating sample magnetometer (VSM) has been used to study the magnetic behaviour of the compounds. It has been observed that by 50% La substitution the insulating behaviour of the material has been improved and showing the antiferromagnetic to weak ferromagnetic behaviour.     

Electronic structure,optical dielectric constant and born effective charge of EuAlO3

EuAlO₃ (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8 eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000 eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated.     

Effect of deposition time on structural, electrical, and optical properties of SnS thin films deposited by chemical bath deposition

The effect of deposition time on the structural, electrical and optical properties of SnS thin films deposited by chemical bath deposition onto glass substrates with different deposition times (2, 4, 6, 8 and 10 h) at 60 °C were investigated. The obtained films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and optical absorption spectra. All deposited films were polycrystalline and had orthorhombic structure with small crystal grains. Their microstructures had changed with deposition time, and their compositions were nearly stoichiometric. Electrical parameters such as resistivity and type of electrical conduction were determined from the Hall Effect measurements. Hall Effect measurements show that obtained films have p-type conductivity and resistivity values of SnS films have changed with deposition time. For allowed direct, allowed indirect, forbidden direct and forbidden indirect transitions, band gap values varied in the range 1.30-1.97 eV, 0.83-1.36 eV, 0.93-1.49 eV and 0.62-1.23 eV, respectively.     

Measurement of X-ray production cross-sections of Ti,V, Cr,Mn, Fe,Co, Ni and Cu molecules

K shell X-ray production cross-sections in the Ti, V, Cr, Mn, Fe, Co, Ni, and Cu in the molecules were studied at 59.5 keV excitation energy by using a Si(Li) detector ( FWHM = 155 eV at 5.96 keV). The present results are compared with other theoretical values.     

As(0001) surfaces: Auger,loss, and photoelectron spectroscopic studies

The (0001) surfaces of arsenic single crystals have been characterized by Auger, loss, and X-ray photoelectron spectroscopy. A comparison of the results leads to an unusual suggestion for excitation, conduction, and emission modes in the low-energy region. It is proposed that the dominant 20 eV near-elastic loss is the excitation of N₁(4s) electrons to a conduction level 2 eV above the instrumental vacuum level. It is also proposed that two low-energy “Auger-like” peaks at 12 eV and 1.5 eV are electrons emitted at the surface from permitted bands in the bulk. A strong correlation among Auger and loss signals, integrated secondary-electron emission, elastic peak heights and the Kikuchi display is also reported. A study of the Kikuchi correlation of the 12 eV peak suggests that the surface Debye-Waller effect on As(0001) is a long-range, collective oscillation rather than short-range, individual atomic disorder.     

闪烁晶体碘化铯在紫外光和X射线激发下的发光特性

室温下掺铊碘化铯(CsI∶Tl)晶体的吸收谱在230~320 nm范围内有3个特征峰:310 nm(4 eV)、270nm(4.6 eV)和245 nm(5.1 eV)。采用这3种不同激发能量(对应不同激发机制)的近紫外(UV)光激发得到的荧光(PL)光谱相同。这些PL谱与钨(W)靶X射线激发的辐照致荧光(RL)谱也类似。经分峰计算,PL和RL均含有4种熟知的3.1 eV(400 nm)、2.55 eV(486 nm)、2.25 eV(550 nm)和2.1 eV(590 nm)发光组分,但RL中2.1 eV组分高于PL,同时2.55 eV组分又低于PL。分析认为,这一差异来自于X射线对晶体的辐照损伤Tl+Va+、Tl0Va+,相关的2.1 eV吸收峰与2.55 eV发光带重叠。结果表明:X射线比紫外光更易产生损伤从而影响晶体CsI∶Tl的发光特性。     

Surface sensitivity of x-ray photoelectron spectroscopy for mercury adsorbed on a platinum black

Measurement of the relative intensities of the 4f$\text{7}\text{2}$,$\text{5}\text{7}$ lines of platinum and mercury in a sample of platinum black containing sorbed mercury, gives an escape depth (normal to the surface) of ca. 8 Å for ～ 1400 eV electrons. The result illustrates the applicability of X-ray photoelectron spectroscopy for surface studies of samples which cannot be extensively cleaned.     

Study of amorphous thin films of (Ti, Nb)O2 solid solutions by X-ray absorption at the Ti K edge

As the (Ti, Nb)O₂ amorphous thin films cannot be prepared under a self-supported form, we have recorded the X-ray reflectivity. A new program which allows extraction of the X-ray absorption from the reflectivity is briefly described. The correction of the anomalous dispersion effect is effective, particularly near the edge within 200 eV. Hence, it has allowed a comparison between the amorphous layers and the crystalline analogues for which the X-ray absorption has been recorded by transmission. In the amorphous state, the TiO₆ group is smaller than in the crystalline state because of the relaxation of the crystallographic constraints. The oxygen coordination octahedron is almost regular in the films. On the other hand, in both cases, an electron transfer takes place from Nb to Ti.     

X-ray magnetic circular dichroism imaging with hard X-rays

X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4 microns. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10 eV above the cobalt K-absorption edge (7709 eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32 eV above the cobalt K-absorption edge.     

Electron spectroscopy of graphite,graphite oxide and amorphous carbon

Core-level and valence-band photoelectron spectra and Auger spectra for the basal plane of highly ordered graphite, the edge plane of highly ordered graphite, the basal plane of graphite oxide, and for the basal plane of disordered graphite are compared in an effort to determine spectral features that may be used to identify these chemical species in carbon-rich specimens. The photoelectron spectra were recorded using 1253.6 eV X-ray excitation. The Auger spectra were obtained using both X-ray (1253.6 eV) and electron (3 keV) excitation. The differential X-ray excited C-KVV spectra were the most useful in distinguishing the different types of carbon. In particular, the plasmon structure and the energy separation between the two major excursions were very sensitive to changes in the surface chemistry and structure. Changes in peak position and peak width observed in the valence band and C(1s) photoelectron spectra were also very helpful in distinguishing the pristine, structurally damaged, and the oxidized graphite surfaces. Much of the structural and chemical information apparent in the X-ray excited C-KVV spectra was lost upon electron beam exposure. Differences in the C-KVV Auger lineshapes for X-ray and electron excitation were attributed to both structural and chemical changes induced by electron beam exposure.     

Tunable emission and efficient energy-transfer properties of Ce<Superscript>3+</Superscript> and Mn<Superscript>2+</Superscript> co-doped Ba<Subscript>3</Subscript>Gd(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphors

MgO powders subjected to Q-switched laser pulses in water were characterized by X-ray/electron diffraction and optical spectroscopy to have a significant optical property change with accompanied transformation into the phase assemblages of periclase, brucite and liquid-crystalline lamella. The periclase nanoparticles tended to have {111} habit planes parallel to the basal layers of lamella and brucite flakes more or less rolled as fibers, ribbons or tubes. A significant internal compressive stress was built up for periclase and brucite but not the more flexible lamellar phase. The colloidal suspension containing the densified periclase nanoparticles within the rolled brucite/lamellae flakes showed UV–visible absorption corresponding to a minimum band gap of ca. 5 eV.     

FeS2多晶薄膜电子结构的实验研究

用磁控溅射方法制各纯Fe薄膜，并硫化合成FeS₂. 采用同步辐射X射线近边吸收谱与X射线光电子能谱研究了薄膜的电子结构. 结果表明，合成的FeS₂薄膜，在费米能级附近，有较强的Fe 3d态密度存在，同时，在价带谱中2—10eV处有强度较大的S 3p态密度存在；Fe的3d轨道在八面体配位场作用下分别为t_2g和e_g轨道，实验中由Fe的吸收谱计算得到两分裂能级之差为2.1eV;实验测得FeS₂价带结构中导带宽度约为2.4eV，导带上方仍存在第二能隙，其宽度约为2.8eV. 关键词： 磁控溅射 二硫化铁 X射线吸收近边结构 电子结构     

X-ray photoelectron spectroscopy and Raman microscopy of a ferroan platinum crystal from the Kondyor Massif,Russian Far East

X-ray Photoelectron Spectroscopy was used to study a ferroan platinum crystal from the Kondyor Massif, Russian Far East. Prior to the X-ray Photoelectron Spectroscopic analyses, the nature of the crystal was confirmed by X-ray diffraction. The survey scan showed mainly the presence of Pt and Fe, with smaller amounts of O and Si. The high resolutions spectra of the Pt 4f and Fe 2p showed 18.3 atom% Fe in the crystal, which puts the composition on the lower boundary for ferroan platinum and confirms earlier analyses using other methods such as Scanning Electron Microscopy-Energy Dispersive X-ray analysis/microprobe. The binding energy of the Pt 4f5/2 was 74.0?eV and Pt 4f7/2 70.5?eV, while the Fe 2p3/2 for metallic Fe was observed at 707.2?eV. The Fe 2p3/2 for metallic Fe was significantly sharper than that of Fe 2p3/2 at 710.7?eV associated with surface material. The Raman spectrum was dominated by the Pt–Pt stretching mode at 253?cm^?1. Changed orientation resulted in the observation of two bands at 127 and 139?cm^?1, interpreted as being due to stretching modes of two Pt–Pt bonds with the third bond to Fe and Pt fixed. The presence of Ca-Fe-Al-Mg-Si-O on the surface was probably associated with the presence of a clinopyroxene. These minerals can be expected since the crystal came originally from a clinopyroxenite-dunite matrix. The spectra showed a variety of interferences, e.g. Al 2p with Pt 4f, Mg 2p with Fe 3p, and Ca 2p1/2 with Mg Auger, making exact determinations of the ratios of these elements difficult.     

一种时间分辨三通道软X射线光谱仪

报道了时间分辨的三通道软X射线光谱仪研制工作，重点介绍了研制的三通道能谱仪的工作原理以及210 eV，420 eV和900 eV三个能区的设计参数，谱仪在上海神光Ⅱ高功率激光器三倍频实验中进行了多次实时考核，取得较好实验结果，将多道平面镜、滤光片成功配接于高时间分辨X射线条纹相机上，使该谱仪在亚千电子伏能区内，可同时进行三个波段软X射线的时间和空间分辨测量，提供的实验结果也表明：X射线平面镜结合滤光片的分光技术可应用于高时间分辨的X射线条纹相机上，从而获得高达10 ps的时间分辨. 关键词： 软X射线条纹相机 平面镜 滤光片 掠入射     

Synthesis, characterization, growth mechanism, photoluminescence and field emission properties of novel dandelion-like gallium nitride

Dandelion-like gallium nitride (GaN) microstructures were successfully synthesized via Ni catalyst assisted chemical vapor deposition method at 1200 °C under NH₃ atmosphere by pre-treating precursors with aqueous ammonia. The as-synthesized product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). X-ray diffraction analysis revealed that as-synthesized dandelion-like GaN was pure and has hexagonal wurtzite structure. SEM results showed that the size of the dandelion-like GaN structure was in the range of 30-60 μm. Dandelion-like GaN microstructures exhibited reasonable field emission properties with the turn-on field of 9.65 V μm⁻¹ (0.01 mA cm⁻²) and threshold field of 11.35 V μm⁻¹ (1 mA cm⁻²) which is sufficient for applications of electron emission devices, field emission displays and vacuum micro electronic devices. Optical properties were studied at room temperature by using fluorescence spectrophotometer. Photoluminescence (PL) measurements of dandelion-like GaN showed a strong near-band-edge emission at 370.2 nm (3.35 eV) with blue band emission at 450.4 nm (2.75 eV) and 465.2 nm (2.66 eV) but with out yellow band emission. The room-temperature photoluminescence properties showed that it has also potential application in light-emitting devices. The tentative growth mechanism for the growth of dandelion-like GaN was also described.     

自旋转换配合物[Fe（C4H4N2）｛Pt（CN4）｝]晶体结构及低温相的研究

本文对自旋转换配合物[Fe(C4H4N2){Pt(CN4)}]进行了晶体结构的理论研究,分析表明XRD测量给出的结构只是一个理想化的结构,不适用于理论计算.我们通过第一性原理计算给出的晶格结构空间群为P2/m,相比较XRD的理想结构的空间群P4/m,其对称性降低,该体系实际属于单斜晶系,而不是测量中所给出的四方晶系的结构.通过对比实验数据特别是对低温相的分析,看出对该配合物的理论计算得出的结构常数及键长与实验数据相吻合.用局域密度近似和广义梯度近似算得的低温相的能量分裂分别为2.7824eV和2.5617eV,故低自旋态为低温相的稳态,这也与实验结论很好的吻合.     

FeP(Im)-AB Bonding Energies Evaluated with A Large Number of Density Functionals (P = porphine, Im = imidazole, AB = CO, NO, and O(2))

Sixty-four (64) density functionals, ranging from GGA, meta-GGA, hybrid GGA to hybrid meta-GGA, were tested to evaluate the FeP(Im)-AB bonding energies (E(bond)) in the heme model complexes FeP(Im)(AB) (P = porphine, Im = imidazole, AB = CO, NO, and O(2)). The results indicate that an accurate prediction of E(bond) for the various ligands to heme is difficult with the DFT methods; usually a functional successful for one system does not perform equally well for the other system(s). Relatively satisfactory results for the various FeP(Im)-AB bonding energies are obtained with the meta-GGA funtionals BLAP3 and Bmτ1; they yield E(bond) values of ca.1.1, 1.2, and 0.4 eV for AB = CO, NO, and O(2), respectively, which are in reasonable agreement with experimental data (0.78 - 0.85 eV for CO, 0.99 eV for NO, and 0.44 - 0.53 eV for O(2)). The other functionals show more or less deficiency for one or two of the systems. The performances of the various functionals in describing the spin-state energetics of the five-coordinate FeP(Im) complex were also examined.     

Auger and direct electron spectra in X-ray photoelectron studies of zinc,zinc oxide,gallium and gallium oxide

Auger and direct electron spectra from Zn, ZnO, Ga and Ga₂O₃ have been studied with X-ray photoelectron spectroscopy (ESCA). The chemical shift between zinc electron binding energies in Zn and ZnO is very small, whereas the zinc Auger electron signals are separated by 4.3 eV. In gallium, the oxide and metal signals are separated by 1.9 eV, but the Auger electron energy shift is three times as large. Thus the Auger signals are more sensitive to the chemical environment than the direct electron signals, which is the same relation as earlier observed for copper and copper oxides.     

高能量分辨率的平面晶体位置灵敏谱仪

平面晶体波长色散位置灵敏谱仪是一新型高能量分辨率的X射线分析装置,可用于高能量分辨的元素分析、化学态及原子物理等研究中.这里简要介绍所研制的位置灵敏谱仪装置及其性能,以及位置灵敏谱仪与其核心部件──位置灵敏正比计数器的基本原理.所研制位置灵敏谱仪对55Fe,Ti和Si所达到的能量分辨率(FWHM)分别为25eV,15eV及7eV.因此,它将可以用作高分辨的元素分析.     

两种新型芴衍生物的合成、晶体结构及光谱性能

合成了两种新型芴衍生物:2,7-二（3,5-二（三氟甲基）苯基）-9,9-二乙基芴（1）和2,7-二（4-氟苯基）-9,9-二乙基芴（2）。通过元素分析、红外光谱（IR）、核磁共振氢谱（¹H NMR）以及单晶X射线衍射对其结构进行了表征。化合物1属于单斜晶系,P2₁/c空间群;化合物2属于三斜晶系,P-1空间群。通过紫外-可见吸收和荧光光谱研究了化合物的发光性能。结果表明:在CH₂Cl₂溶液和固态薄膜中,化合物1、2在350～400 nm波段有吸收峰,归属于π-π^*电荷跃迁;化合物1、2的光学带隙E_g分别为3.31 eV和3.30 eV,并且均有强烈的蓝色荧光发射现象（激发波长为330 nm）,在二氯甲烷中的荧光量子效率分别为0.62和0.61,固态荧光寿命分别为6.39 ns和9.00 ns。