Material characteristics of metalorganic chemical vapor deposition of Bi2Te3 films on GaAs substrates

Metal organic chemical vapor deposition has been investigated for growth of Bi₂Te₃ films on (0 0 1) GaAs substrates using trimethylbismuth and diisopropyltelluride as metal organic sources. The results of surface morphology, electrical and thermoelectric properties as a function of growth parameters are given. The surface morphologies of Bi₂Te₃ films were strongly dependent on the deposition temperatures. Surface morphologies varied from step-flow growth mode to island coalescence structures depending on deposition temperature. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's ratio of VI/V and deposition temperature. By optimizing growth parameters, we could clearly observe an electrically intrinsic region of the carrier concentration at the temperature higher than 240 K. The high Seebeck coefficient (of −160 μVK⁻¹) and good surface morphology of this material is promising for Bi₂Te₃-based thermoelectric thin film and two-dimensional supperlattice device applications.     

Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements

Tellurite containing vanadate (50−x)V₂O₅–xBi₂O₃–50TeO₂ glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi₂O₃ content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi₂O₃ content. The observed results confirm that the addition of Bi₂O₃ modifier changes the rigid formula character of TeO₂ to a matrix of regular TeO₃ and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO₄ trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi₂O₃ content are more stable than with high Bi₂O₃ content.     

Aurivillius结构Bi2MoxW1-xO6铁电功能晶体的生长与性质表征

本文采用固相反应法探索了Aurivillius结构Bi₂Mo_xW_1-xO₆体系的合成条件以及能够形成固溶体的成分范围,探索了Bi₂Mo_xW_1-xO₆晶体的助熔剂法生长体系,并对晶体的结构、变温介电性质和电阻率进行了测定和分析。Bi₂Mo_xW_1-xO₆体系中Mo的占比x可以在0~1的范围内连续变化,采用固相反应法可以在500~870 ℃范围内的不同温度合成纯的Bi₂Mo_xW_1-xO₆铁电相。采用Li₂B₄O₇-Bi₂O₃(摩尔比2∶1)作为助熔剂生长得到了厘米级Bi₂WO₆单畴晶体,厚度不小于2 mm,最大尺寸则达到了约40 mm。在n(Bi₂O₃)∶n(MoO₃)∶n(WO₃)∶n(Li₂B₄O₇)=1∶1∶1∶1(摩尔比)体系中生长得到了厚度约1 mm的Bi₂Mo_0.15W_0.85O₆厘米量级单畴晶体,结构解析表明Bi₂Mo_0.15W_0.85O₆属于正交晶系,Aba2(No.41)空间群。变温介电性质测试表明,Bi₂Mo_0.15W_0.85O₆晶体的介电常数ε₃₃由Bi₂WO₆晶体的70提高到了102,介电弛豫现象发生的温度由Bi₂WO₆晶体的430 ℃降到了330 ℃附近。变温电阻率测试表明,Bi₂WO₆与Bi₂Mo_0.15W_0.85O₆晶体的电阻率均随温度升高而降低,在100 ℃以下,Bi₂WO₆的电阻率高于Bi₂Mo_0.15W_0.85O₆晶体,且随温度升高,二者电阻率的差距在逐渐缩小。     

Growth by self-flux method and post-annealing effect of Bi2Sr2Ca1Cu2Ox single crystals

Post-annealing effects on superconducting characteristics have been studied in Bi₂Sr₂Ca₁Cu₂O_x single crystals grown by a conventional flux method. Also, favorable growth conditions and the effect of the pre-sintering process on the starting materials for flux growth have been examined. The best superconducting behavior is obtained in post-annealed crystals grown from pre-sintered powder materials. The critical current density J_c estimated from magnetization hysteresis in annealed crystals grown with pre-sintered materials is roughly 8×10⁵ A/cm² (Hc) and 5×10⁴ A/cm² (Hc) at 4.2 K at zero field.     

铜(Ⅱ)配合物{[Cu(OMBA)2]2·(DMF)2}的合成、CT-DNA结合及细胞毒性

合成了配合物{[Cu(OMBA)₂]₂·(DMF)₂}(OMBA =邻甲基苯甲酸,DMF = N,N-二甲基甲酰胺),配合物结构经元素分析、IR和X射线单晶衍射表征,该配合物属于三斜晶系,P1空间群,晶胞参数为a=1.037 0(5) nm, b=1.053 6(4) nm, c=1.105 9(5) nm, α=62.737(6)°, β=73.355(7)°, γ=63.231(7)°, Z=1, D_c=1.416 g·cm^-3, F(000)=422,最终结构残差因子R₁=0.051 5, wR₂=0.140 4。采用紫外、荧光和黏度法研究了配合物和小牛胸腺DNA (CT-DNA)的相互作用方式。结果表明,配合物与DNA的结合常数K_b=939.61 L·mol^-1,K_sv=3.00×10³ L·mol^-1,猝灭速率常数K_q=3.00×10¹¹ L·mol^-1·s^-1。配合物静态猝灭CT-DNA的荧光,结合常数K_a=5.38×10³ L·mol^-1,结合位点n=1,配合物对胃癌细胞A549、宫颈癌细胞Hela和肝癌细胞HepG2有抗增殖作用。     

X-ray scattering studies of the short and medium range ordering in AsxTe1−x glasses

The structures of As_xTe_1−x(x = 0.2, 0.4, and 0.5) glasses are studied using the differential X-ray anomalous scattering technique. The partial distribution functions have also been obtained for the stoichiometric As₂Te₃ glass, giving information on the medium range ordering. All the glasses show chemical disorder to differing extents, the As₂Te₃ glass being the most disordered. The Te coordination number undergoes a change at x=0.4 where it is 2.5 compared with 2 for AsTe. This change indicates the existence of about 50% of threefold Te sites in the stoichiometric glass, as well as in the Te-rich glasses. Some of the physical properties of the glasses may be explained based on these results.     

NMR studies of Na2O---B2O3---SiO2 glasses of mid-alkali content

¹¹B Fourier transform spectra have been used to study the structure of Na₂O---B₂O₃---SiO₂ glasses of mid-alkali content. Based on the measurements of the fraction N₄ of four-coordinated borons, it has been found that for K = mol.% SiO₂/mol.% B₂O₃ 8 and R = mol.% Na₂O/mol.% B₂O₃ = 1, N₄ is obviously smaller than 1 rather than equal to 1 as assumed in the relevant literature. Only when R reaches a value appropriately greater than 1, can the case where N₄ = 1 occur. A structural model suggested in this paper can satisfactorily explain the fact.     

Study on the Ce substitution effects of BiFeO3 films on ITO/glass substrates

Ce substituted Bi_1−xCe_xFeO₃ (BCFO) films with x=0–0.15 were deposited on indium tin oxide (ITO)/glass substrates by sol–gel process annealed at 500 °C. Rhombohedral phase was confirmed by XRD study and no impure phases were observed till x=0.15. Substantially enhanced ferroelectricity was observed at room temperature due to the substitution of Ce. In the films with x=0.05 and 0.10, the double remnant polarization are 75.5 and 57.7 μC/cm² at an applied field 860 kV/cm. Moreover, the breakdown field was enhanced in the films with Ce substitution.     

具有n-n型异质结的复合材料Bi2S3/MIL-125(Ti)光电性能研究

以硫代硫酸钠·五水合物(Na₂S₂O₃·5H₂O)、硝酸铋·五水合物(BiN₃O₉·5H₂O)为硫源和铋源，尿素(CON₂H₄)为结构导向剂，制备了纳米棒状结构的硫化铋(Bi₂S₃),使其原位生长在MIL-125(Ti)的笼状结构表面。PEC性能测试显示，在0.5 mol·L^-1的硫酸钠电解液(pH=6.0)中，Bi₂S₃/MIL-125(Ti)_0.07(MIL-125(Ti)加入量为0.07 g)的复合材料表现出最高的光电性能。光电性能的显著增强主要取决于Bi₂S₃/MIL-125复合材料的带隙重整效应，对紫外光以及可见光的吸收能力显著提高。但由于Bi₂S₃/MIL-125...     

Crystal growth and structure of MnGa2Te4

Single crystals of MnGa₂Te₄ were grown from the melt using the directional freezing technique. They crystallize in the monoclinic system, a=11.999(3), b=11.999(3), c=24.922(6) Å, β=104.01(2)°, Z=16 MnGa₂Te₄ units, space group C2/c. The structure was solved by direct methods and refined to R_w=0.035 for 791 observed reflections and to R_w=0.062 for 3067 independently measured reflections. Te atoms form an arrangement which is a superlattice of anion lattice of β-Cu₂HgI₄. On the contrary, the same model does not conform cation lattice, because 1/3 of metal atoms occupy positions displaced from tetrahedral sites.     

Bi20TiO32 nanocones prepared from Bi–Ti–O mixture by metalorganic decomposition method

Bi₂₀TiO₃₂ in the form of nanocones are reported for the first time, which have been found during the formation of Bi₂Ti₂O₇ nanocrystals. Bi₂₀TiO₃₂ nanocones were prepared by metalorganic decomposition technique. From X-ray patterns, it was found that Bi₂₀TiO₃₂ is a metastable phase, and can transform gradually into Bi₂Ti₂O₇ phase with the annealing time increasing at a temperature of 550°C. The image of field emission scanning electron microscopy shows that the lengths of the nanocones are up to several micrometers and the diameters of cusps range from 20 to 200 nm. The studies of transmission electron microscopy show that the nanocones are crystalline Bi₂₀TiO₃₂. The growth mechanism of Bi₂₀TiO₃₂ nanocones has been proposed, which is similar to the vapor–liquid–solid growth mechanism.     

Study on phase diagram of Bi2O3---SiO2 system for Bridgman growth of Bi4Si3O12 single crystal

Phase relation of Bi₂O₃---SiO₂ system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi₂SiO₅ in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi₂SiO₅ crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm³ was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO.     

The incorporation behavior of arsenic and antimony in GaAsSb/GaAs grown by solid source molecular beam epitaxy

GaAsSb ternary epitaxial layers were grown on GaAs (0 0 1) substrate in various Sb₄/As₂ flux ratios by solid source molecular beam epitaxy. The alloy compositions of GaAs_1−ySb_y were inferred using high-resolution X-ray symmetric (0 0 4) and asymmetric (2 2 4) glance exit diffraction. The non-equilibrium thermodynamic model is used to explain the different incorporation behavior between the Sb₄ and As₂ under the assumption that one incident Sb₄ molecule produces one active Sb₂ molecule. It is inferred that the activation energy of Sb₄ dissociation is about 0.46 eV. The calculated results for the incorporation efficiency of group V are in good agreement with the experimental data.     

亚铁离子的引入对Bi2Fe4O9纳米颗粒光催化性能的影响

本文通过在水热法过程中添加不同含量的FeCl₂合成了一系列Bi₂Fe₄O₉纯相纳米晶,成功地在Bi₂Fe₄O₉中引入了更多低价态的铁离子。紫外可见吸收谱数据证明FeCl₂的加入使得Bi₂Fe₄O₉的光学带隙从2.06 eV降低到1.96 eV。扫描电子显微镜照片和X射线衍射图谱均证明本文合成的样品为纯相正方形片状Bi₂Fe₄O₉纳米晶。在500 W汞灯照射下,对合成的三个Bi₂Fe₄O₉纳米晶样品(S1、S2、S3,分别对应不同FeCl₂含量x=0,0.2 mmol,0.4 mmol)进行甲基橙染料降解实验,结果表明在添加20 μL双氧水时,三个样品的光催化降解速率均最快,其中S3样品的光催化降解速率比S1、S2更快。因此在适当加入双氧水的情况下,FeCl₂的加入可有效提升Bi₂Fe₄O₉光催化降解染料分子的性能。     

SIMS study of the concentration of dopants in LPCVD silicon thin films

Measurements of solid phase dopant concentration (S) of LPCVD Si thin films as a function of substrate temperature (T_s = 500−640 ° C) and gas phase doping ratio (R = 1 × 10⁻⁵ −4 × 10⁻²) by SIMS indicate different behaviors of P and B in the films. A linear relation S = b(T)R is observed for B-doped film with b(T) varying from 4 to 50 depending on T_s. Boron-doped microcrystalline film has a higher doping efficiency than that of P-doped ones.     

Selective epitaxial growth by UHV-CVD using Si2H6 and Cl2

The conditions under which selective epitaxial growth (SEG) is achieved in UHV-CVD with Si₂H₆ are determined by the amount of Si₂H₆ molecules being supplied, and there is a critical gas supply amount (F_c) beyond which SEG will break down and lose its selectivity. The value of F_c is itself determined by two factors, growth temperature and the material used for masking, i.e. SiO₂, Si₃N₄. We found that this limiting factor of F_c was increased through the addition of a small amount of Cl₂, and that after such addition, the resulting decrease in growth rate is minimal.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Growth anisotropy in the GaN/Al2O3 system

The crystallographic aspect of gallium nitride epitaxy on sapphire were investigated for the vapor phase epitaxy system GaCl/NH₃/HCl/N₂. For this purpose, thick layers of doped gallium nitride were deposited on hemispheres of Al₂O₃ single crystal with the three fold axis of the corundum structure perpendicular to the basal plane. Complete characterization of these layers has been carried out including Laue back diffraction, scanning electron microscopy and cathodoluminescence. After growth, sections were cut along the main crystallographic planes and the growth rate was measured as a function of the substrate orientation. The observed relationship for epitaxy has been interpreted in terms of three-dimensional matching between the gallium nitride and corundum structures.     

Bi4O5Br2/Ti3C2-Ru复合光催化剂的合成及其对磺胺甲噁唑药物废水降解性能研究

Bi_xO_yBr_z光催化剂在有机药物废水处理领域有着非常广阔的潜在应用价值,但光生电子-空穴对的快速复合限制了其应用。本文选用具有优良电子传递性能的Ti₃C₂作为助催化剂,首先利用Ti₃C₂表面丰富的Ti空位缺陷和高还原能力,制备了Ti₃C₂-Ru助催化剂,接着利用Ti₃C₂表面官能团与Bi³⁺的离子键合力实现了Bi₄O₅Br₂在Ti₃C₂-Ru表面的原位生长,得到Bi₄O₅Br₂/Ti₃C₂-Ru复合光催化剂,从而实现了电子由Bi₄O₅Br₂到Ti₃C₂再到反应活性位点Ru的定向传递,最终使催化剂具有较高的光生载流子分离率和较低的界面电荷转移阻力,有效抑制了光生电子-空穴对的复合。同时以磺胺甲噁唑(SMX)为模拟药物污染物进行了光催化性能测试,结果表明所制备的Bi₄O₅Br₂/Ti₃C₂-Ru复合光催化剂展示出了优异的光催化降解SMX性能,在可见光下照射75 min,SMX的降解率达到95.1%,相较于纯的Bi₄O₅Br₂和Bi₄O₅Br₂/Ti₃C₂催化剂,其降解率分别提升了36.9个百分点和25.3个百分点。最后基于自由基捕获实验和催化剂能带结构分析提出了所制催化剂的降解机理。研究结果可为构建具有药物废水净化功能的光催化剂提供设计思路。     

Crystal growth of NdAl3(BO3)4 from K2O/MoO3/Nd2O3/B2O3/KF flux

NdAl₃(BO₃)₄ single crystals were grown by the flux method and the TSSG technique using a K₂O/3MoO₃/B₂O₃/0.5Nd₂O₃/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K₂O = 0.75, NAB crystals could not be grown.