Detected contrast and dynamic range measurements of CdZnTesemiconductors for flat-panel digital radiography

The detected contrast and dynamic ranges of Cd_1-xZn_xTe semiconductor detectors have been measured, within the X-ray diagnostic energy range, using a contrast sensitivity phantom. The aim of this study is to optimize the image quality parameters of these solid state ionization devices for flat panel digital radiographic applications. The experimental results of this study indicate that Cd_1-xZn_xTe detectors have excellent detected contrast response and large dynamic range     

Electron and positron energy distributions in Cd0.5Mn0.5Te alloy

We calculated the electron and positron band structure for Cd_0.5Mn_0.5Te alloy and presented electron and positron charge densities as a function of position in the unit cell. The densities of states both electronic and positronic at different points of reciprocal space were performed. In these calculations, we used the empirical pseudopotential method and the virtual crystal approximation coupled with the independent particle model.     

Growth and strain investigation of Cd0.96Zn0.04Te/GaAs by hot-wall epitaxy

A higher quality and a nearly stoichometric composition of Cd_1−yZn_yTe (y=0.04) epilayers have been successfully grown on a GaAs substrate by hot-wall epitaxy (HWE). The growth conditions regarding preheating treatment and Cd reservoir temperature were optimized. The relationship between quality and thickness was examined by four-crystal X-ray rocking curves and the best value of 120 arcsec for full width at half maximum (FWHM) was obtained. The dislocations on the interface, generated from the difference in lattice constants, were directly observed by high-resolution electron microscopy (HREM). The variation of strain with epilayer thickness shows that the density of extended defects in the epilayer decreases rapidly increasing the thickness up to 5 μm. When the epilayer thickness reaches 20 μm, the strain almost becomes zero. This result suggests that the high-quality epilayer, same as the bulk crystal, can be obtained by increasing the thickness. Photoluminescence (PL) spectra at 4.2 K show that bound-exciton (BE) emission is dominative. The strain relaxation by misfit dislocations were also explored by HREM.     

The growth of epitaxial Cd1−xMnxTe films by hot-wall evaporation

In this paper we report the first attempt to prepare epitaxial films of Cd_1−xMn_xTe semimagnetic semiconductor alloys with various compositions by hot-wall evaporation onto NaCl(001) surfaces under a vacuum of 10^-6–10^-7 Torr. The films were deposited from vapour phases of different compositions with various fluxes of CdTe and manganese atoms used as source materials. Both the growth rate and the manganese content were investigated under various conditions.

The structure of the films was examined using transmission electron microscopy and X-ray diffractometry as a function of the temperature of the NaCl substrate between 150 and 450 °C. At low temperatures, polycrystalline films were obtained. The films became highly ordered with increasing substrate temperature. It was found that the films had (001) or (011) planes lying parallel to the NaCl(001) surface and exhibited a cubic sphalerite structure.

No segregation of manganese was found from electron microprobe measurements. Discontinuous growth and the morphology of the early stages of growth were studied using extraction replica electron microscopy. The growth was found to be favoured by a three-dimensional mechanism.     

Structural and Magnetic Properties of MnFe$_1 - rm x$Co$_rm x$Ge Compounds

The structural and magnetic properties of MnFe_1-xCo_xGe compounds with x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.85,0.9, and 1.0 were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD shows that the MnFe_1-xCo_xGe compounds crystallize in the hexagonal Ni₂In-type crystal structure for xles0.8 and in the orthorhombic NiTiSi-type structure for x>0.8. The magnetization measurements show that the MnFe_1-xCo_xGe compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni₂In type structure increase with increasing of x and the saturation of the magnetization in the NiTiSi-type structure also increases with increasing x. We investigated the magnetocaloric effects in these compounds by means of magnetization measurements. The maximum magnetic-entropy change observed in these compounds reaches 9 J/kgK for x=0.8 in a field change from 0 to 5 T at around 289 K     

溶剂熔区移动法生长Cd0.9Zn0.1Te晶体的工艺优化研

为了解决Cd_0.9Zn_0.1Te(CZT)晶体生长温度高、单晶率低、成分不均匀等问题, 采用溶剂熔区移动法(THM)在优化工艺参数下生长了掺In的CZT晶体, 在优化晶体的生长温度、固液界面处的温度梯度、原位退火过程等生长条件后, 生长出直径为45 mm的低Te夹杂浓度、高电阻率、高透过率、均匀的高质量CZT晶体。 X射线衍射结果显示, 晶体的结晶性较好、Zn成分轴向偏析小。红外透过光谱测试结果显示, 晶体内部的杂质、缺陷水平相对较少, 晶体整体的红外透过率在60%左右。紫外-可见光吸收光谱测试结果也进一步表明, 晶体的均匀性良好。采用红外显微镜对晶体内部的Te夹杂形貌及其尺寸进行观察, 结果表明Te夹杂的尺寸主要分布在0~10 μm之间。采用直流稳态光电导技术测得电子的迁移率寿命积约为8×10^-4 cm²/V。     

Formation and magnetostructural characterization of the novelternary compound Ce3Fe29-xMox

Formation and magnetostructural properties of the novel ternary ferromagnetic compound Ce₃Fe_29-xMo_x is reported. It was obtained in alloys with nominal compositions Ce₃ Fe_29-xMo_x, x=1.4, 1.5, and 1.6, prepared by arc melting and annealing during three weeks at 950°C. The crystal structure was well resolved as monoclinic with space group A2/m (No 12). Quantitative phase analysis, based on the processing of the X-ray diffraction patterns by the Rietveld method, was performed. Ce₃ Fe_29-xMo_x is the main phase (78-72 wt.%) with lattice parameters a=10.553(1) Å, b=8.511(1) Å, c=9.688(1) Å, and β=96.78(1)°. It coexists with Ce(Fe,Mo) ₁₂ as main spurious phase. Atomic positions and mean Fe-Fe interatomic distances are reported. Temperature-dependent magnetic susceptibility shows well-defined transitions at 7 and 115°C, which correspond to the 3:29 and 1:12 phases, respectively. Saturation magnetization at 4.2 K is 123 emu/g     

The Dielectric Properties of Ba/sub 0.6S/r/sub 0.4/Cr/sub x/Ti/sub 1-x/O/sub 3/Thin Films Prepared by Pulsed Laser Deposition

Ba_0.6Sr_0.4Cr_xTi_1-xO₃ (BSCT) films were prepared by pulsed laser deposition with the value of x varying from 0 mol% to 2.0 mol%. X-ray diffraction analysis detected an increase in the lattice parameters, which could be due to the characteristics of the growth process. Dielectric properties and tunability of the BSCT films were measured. The dissipation factors of the films decreased with increasing Cr-concentration. The highest figure of merit (FOM) value of 33.3 was obtained in 1.0 mol%-doped BSCT film. As a result, the effect of Cr doping is positive.     

Raman Studies of ${rm Ti}_{bm{ 1-x}} {rm Fe}_{bm x} {rm O}_{bm 2}$ Nanoparticles

Ti_1-xFe_xO₂ (x = 0.00-0.13) nanoparticle samples were prepared by hydrolysis method. We investigated the effects of Fe doping on the structural and magnetic properties of the Ti_1-xFe_xO₂ nanoparticle system. Scanning electron microscopy and X-ray diffraction measurements confirm that the particle size of the powder is in nanoscale, and that the magnetic Fe impurities substitute for the Ti sites in the anatase TiO₂ phase. All the samples with x > 0 were found to be super-paramagnetic at room temperature by magnetization measurements. Raman spectra also strongly support that the Fe atoms go into the Ti-site in theTiO₂ structure. For comparison, ceramic Ti_1-xFe_xO₂ samples were also prepared by usual ceramic method. Ferromagnetism was observed only in the ceramic Ti_1-xFe_xO₂ system. Additional Raman peak at around 610 cm^-1 is observed only in the ceramic samples. This may be related to the clusters created by mixture of various valence state of Fe, which probably would be the cause for ferromagnetism observed in the ceramic Ti_1-xFe_xO₂ system.     

Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ层状复合材料的低频磁电耦合

利用弹性力学模型,推导了低频下磁致伸缩-压电双层复合材料中磁电电压系数的表达式,计算了Tb_1-x Dy_x-Fe_2-y-BaTiO₃层状复合材料中的横向磁电耦合。采用溶胶-凝胶法制备1.0%（摩尔分数）Mn掺杂BaTiO₃（BaTi_0.99Mn_0.01O_3+δ）压电陶瓷片。将Mn掺杂BaTiO₃与Tb_1-xDy_xFe_2-y 胶合制成双层和三层复合材料,研究了复合材料在低频下的横向磁电效应。XRD和DSC分析结果表明,室温下Mn掺杂BaTiO₃保持了其四方钙钛矿结构,降低了BaTiO₃的居里点和相变潜热。在约33 kA/m偏置磁场下,Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ 和Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ-Tb_1-xDy_xFe_2-y 的横向磁电耦合峰值分别为529.4 mV/A和1659.5 mV/A,分别是Tb_1-xDy_xFe_2-y-BaTiO₃和Tb_1-xDy_xFe_2-y-BaTiO₃-Tb_1-xDy_xFe_2-y 的1.48和1.45倍。三层复合材料的横向磁电电压系数约是同类双层的3倍多。     

Probe microanalysis investigation and electroreflectance spectroscopy of Hg1−xCdxTe PLD films on silicon patterned substrates

Hg_1−xCd_xTe films were prepared on Si-patterned substrates by the pulse laser deposition technique from a Hg_1−xCd_xTe target (x≈0.2). The effects of different substrate temperatures, ranging from 293 to 543 K, different laser shots number in the range of 10–380, and the morphological type of the patterned substrate on the x-composition of films were studied by electron probe microanalysis (EPMA) and electroreflectance (ER) spectroscopy. The correlation between a film composition measured by EPMA and one determined from ER spectra data was observed.     

复合磁性催化剂β-MnO2/MnxZn1-xFe2O4的制备与表征

采用化学共沉淀法制备了以Mn_xZn_1-x Fe₂O₄为磁性基体的β-MnO₂/Mn_xZn_1-xFe₂O₄复合磁性催化剂,利用XRD、SEM、FTIR和超导量子干涉仪对复合磁性催化剂的结构和性能进行了表征,以罗丹明B （RhB）为模拟污染物,研究了β-MnO₂/Mn_xZn_1-xFe₂O₄的催化活性,并考察了其稳定性。结果表明,球状的β-MnO₂与块状的磁性基体Mn_xZn_1-xFe₂O₄成功复合,且制备的β-MnO₂/Mn_xZn_1-xFe₂O₄复合磁性催化剂具有良好的催化性能和磁学性能。当Mn_xZn_1-xFe₂O₄与β-MnO₂的质量比为20：100时,在2 mL含量为30%的H₂O₂作用下,1 h内β-MnO₂/Mn_xZn_1-xFe₂O₄复合磁性催化剂对100 mL浓度为10 mg/L的RhB降解率（93.9%）远高于纯β-MnO₂（33.7%）;在磁场作用下,β-MnO₂/Mn_xZn_1-xFe₂O₄复合磁性催化剂的回收率为89%,经过5次循环利用之后其对RhB的降解率仍达76%。     

New improvements of CrO2-related magnetic recording materials

The increase in the magnetocrystalline anisotropy of chromium dioxide by substitution of Cr (IV) with Rh (IV) or Ir (IV) has led the authors to study the Cr1-xRhxO2and Cr1-xIrxO2solid solutions. The use of H3BO3as buffer agent or iron oxalate in the crystal growth process reduces the particle size and greatly improves the coercive field of Cr1-xIrxO2even at low Ir concentrations (x simeq 5.10^{-4}).     

A torsion–effusion study on the sublimation of Cu2Te

The sublimation of Cu₂Te was studied and its vapor pressure was measured by the torsion method. In the covered temperature range, the temperature dependence of the total vapor pressure can be expressed by the following equation: log p (kPa)=(6.17±0.20)−(11 680±300)(K/T) (1084–1234 K). The sublimation process of Cu₂Te is incongruent, and Te(g) and Te₂(g) being the only gaseous species present in the vapor, the partial sublimation reactions were studied: Cu₂Te(s)→2Cu(s)+Te(g), 2Cu₂Te(s)→4Cu(s)+Te₂(g). The standard sublimation enthalpies of these reactions, Δ_rH⁰(298)=254±10 and 248±8 kJ, respectively, were derived by the second- and third-law treatment of the pressure data. The heat of formation of Cu₂Te, Δ_fH⁰(298)=−43±6 kJmol⁻¹, was also derived.     

Deposition of tellurium films by decomposition of electrochemically-generated H2Te: application to radiative cooling devices

The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H₂Te. Pre-treatment of the polyethylene substrates with KMnO₄ to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H₂Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.     

水热合成Zn1-xCrxO稀磁半导体晶体

采用水热法, 以3mol/L NaOH作为矿化剂, 在260℃下, 保温28h进行Cr合金化(x=0.10, 0.15, 0.20, 0.25), 合成Zn_1-xCr_xO稀磁半导体晶体. 研究了Cr合金化对水热合成Zn_1-xCr_xO稀磁半导体粉体结构和性能的影响. XRD测试表明, Cr元素进入到ZnO的晶格内, 实现了Cr的合金化, 晶粒尺寸分别为46.5、46.1、50.6和48.9nm. 从FE-SEM可以观察到, x>0.2时, 晶体的形貌从短柱状转变为长柱状. 通过UV/Vis测试可以观察到Cr离子的吸收, ZnO的禁带宽度依次降低为3.17、3.18、3.19和3.23eV. VSM测试表明, 所制备的Zn_1-xCr_xO纳米晶体在室温下均表现出弱顺磁性.     

Ge掺杂MnTe材料的热电输运性能

MnTe作为一种新型的无铅p型热电材料, 在中温区热电领域具有广阔的应用前景, 但其本身的热电性能不足以与高性能n型热电材料相匹配。本研究通过真空熔炼-淬火和放电等离子烧结的方法制备不同Ge掺杂量的致密且均匀的Mn_1.06-xGe_xTe(x=0, 0.01, 0.02, 0.03, 0.04)多晶块体样品。过量的Mn可以有效抑制MnTe₂相, 提高基体相的热电性能。通过掺杂4%Ge粉末, 材料的载流子浓度提高到7.328×10¹⁸ cm^-3, 电导率在873 K增大到7×10³ S∙cm^-1, 功率因子提升至620 μW∙m^-1∙K^-2。同时, 通过点缺陷增强声子散射使材料的热导率降低到0.62 W∙m^-1∙K^-1, 实现了对材料电声输运性能的有效调控。Mn_1.02Ge_0.04Te在873 K获得了0.86的热电优值ZT, 较纯MnTe材料提高了43%。     

Tb1-xDyxFe2-y-BaTi0.99Cr0.01O3-δ多层复合结构中的磁电效应

采用溶胶凝胶法制备了Cr掺杂BaTiO₃陶瓷片.X射线衍射显示Cr掺杂BaTiO₃依然为四方相钙钛矿结构.差热分析显示,Cr掺杂BaTiO₃的居里温度及相变潜热均比纯净BaTiO₃ 的同类参量略低.将所得BaTi_0.99Cr_0.01O_3-δ陶瓷片与Tb_1-xDy_xFe_2-y粘结成磁电双层及三层复合结构材料.研究了双层Tb_1-xDy_xFe_2-y-BaTi_0.99Cr_0.01O_3-δ和三层Tb_1-xDy_xFe_2-y-BaTi_0.99Cr_0.01O_3-δ-Tb_1-xDy_xFe_2-y复合材料的磁电效应.在28 kA/m 的磁场下,两者的横向ME电压系数均达其峰值,为732.5和2753mV/A.该两数值分别是采用BaTiO₃制备的同类双层及三层复合结构的同类数值的1.54及1.56倍.由于掺杂钛酸钡不含铅、锆等有害物质,因此采用掺杂BaTiO₃替代锆钛酸铅做为“绿色”压电材料制备磁电效应器件具有研究和应用价值.     

Magnetic properties of melt spun NdFe10Cr2-Nd0.67B0.33 pseudobinary alloys

The coercivity of the melt-spun pseudobinary (NdFe₁₀Cr ₂)_1-x (Nd₂B)_x alloys, in which Nd₂B represents a composition of Nd_0.67B_0.33, was systematically studied. It was found that significant coercivities are possible with optimal additions of the Nd-B composition at x=0.5-0.7. The as-spun (substrate velocity=10 m/s) coercivity increased from 0.1 kOe at x=0.0 to maxima of 7.0 and 7.5 kOe at x=0.5 and 0.7, due to the Nd₂ Fe₁₄B and a new Fe-Nd phase, respectively, as evidenced from thermomagnetic analysis and X-ray diffraction. Annealing the overquenched amorphous x=0.7 alloy led to the crystallization of the Nd₂Fe₁₄B phase, and a coercivity of 8.5 kOe was obtained     

具有协同电子结构和形貌调控功能的三元Co1-xVxP纳米针阵列在大电流下的析氢性能研究

制备具有大电流析氢性能的非贵金属电催化剂是一个巨大挑战.协同调控催化剂的电子结构和形貌能够增强其本征催化能力和增加活性位点,被认为是提高催化性能的有效方法.本文以具有协同电子结构和形貌调控功能的三元Co_1-xV_xP纳米针阵列作为碱性析氢的高效电催化剂.实验和理论计算结果表明,其优异的催化性能来源于物理化学性质的提高、活性表面积的增加及反应动力学的加速.此外,组装的(NF@Co_1-xV_x–HNNs(+)||NF@Co_1-xV_xP(-))电解池在1.58、1.75和1.92 V的电压下,能够分别得到10、100和300 mA cm^-2的电流密度.