The properties of bismuth-doped vacuum-evaporated CdS films

The effect of doping with bismuth on various properties of vacuum-evaporated CdS films was studied. The properties specifically studied were (1) the dark conductivity and photoconductivity as functions of the temperature and doping concentration, (2) the Hall mobility and carrier concentration at room temperature, (3) the thermally stimulated current and (4) the optical absorption and spectral response. It was found that on doping with bismuth the dark conductivity decreases and the photosensitivity increases significantly. These phenomena probably arise from the formation of cadmium vacancies due to bismuth doping. Studies of the Hall effect show that the carrier concentration is reduced by doping with bismuth. Investigations of thermally stimulated currents for both pure and doped films show that the trap concentrations are reduced by doping.     

Simultaneous quantitative analysis of arsenic, bismuth, selenium, and tellurium in soil samples using multi-channel hydride-generation atomic fluorescence spectrometry

The basic principles and the application of hydride-generation multi-channel atomic fluorescence spectrometry (HG-MC-AFS) in soil analysis are described. It is generally understood that only one or two elements can be simultaneously detected by commonly used one- or two-channel HG-AFS. In this work, a new sample-sensitive and effective method for the analysis of arsenic, bismuth, tellurium, and selenium in soil samples by simultaneous detection using HG-MC-AFS was developed. The method detection limits for arsenic, bismuth, tellurium, and selenium are 0.19 μg/g, 0.10 μg/g, 0.11 μg/g, and 0.08 μg/g, respectively. This method was successfully applied to the simultaneous determination of arsenic, bismuth, tellurium, and selenium in soil samples.     

The Caloric Properties of Liquid Bismuth

We investigated the enthalpy of liquid bismuth within the temperature range of 580–1325 K in a massive isothermal drop calorimeter using the mixture method. We obtained the approximation equations and determined the isobaric heat capacity. The estimated errors of the data on the enthalpy and the heat capacity are equal to 0.2% and 0.5%, respectively. The results are compared with the literature data. We confirmed the existence of a heat-capacity minimum of liquid bismuth of approximately 800 K. We show that above 940 K the heat capacity depends linearly on the temperature. We developed tables of the recommended values of the caloric properties within the range from the melting point to 1325 K.     

Large area bismuth absorbers for X-ray microcalorimeters

Two challenges facing the use of large area (2 mm×2 mm) bismuth absorbers for microcalorimetry are uncertainties in the heat capacity of bismuth and the effects of lateral heat conduction and position dependence due to the absorber's large size. We have measured the heat capacity of three Bi samples to be 0.3−0.6 J K⁻¹ m⁻³ at 100 mK. These absorbers also exhibit response variations as phonons created by an X-ray event at an absorber edge will take longer to propagate to the thermometer attachment point than those at the absorber center. This effect may degrade the detector's energy resolution if the propagation time is not very short compared to the thermometer time constant. We show that the response of the largest absorber varies by 4% across its area.     

Novel solution route synthesis of low thermal conductivity nanocrystalline bismuth telluride

A novel synthesis approach based on a solution route has been developed for the fabrication of nanocrystalline bismuth telluride. The method consists of dissolving both bismuth and tellurium into the same organic solvent with the assistance of complexing agents and one-step coprecipitation of bismuth telluride. The synthesized nanocrystalline bismuth telluride powders possess rhombohedral crystal structure and are nanosheet/nanorod-like with an average size of between 30 and 40 nm. The thermal conductivity of the hot-pressed compact consolidated from the as-synthesized nanopowders is 0.39-0.45 Wm(-1)K(-1) in the temperature range of 323 to 523 K, which is at most one third of that of bulk bismuth telluride-based materials reported in the literature. Such low thermal conductivity of the investigated bismuth telluride is mainly attributed to substantially high concentration of grain boundaries provided by nanostructuring to scatter phonons intensively.     

改进溶液燃烧法制备Fe3+掺杂Bi24O31Cl10及其光催化性能的研究

采用改进溶液燃烧法,以硝酸铋、柠檬酸、氯化铵和硝酸铁为原材料制备Fe-Bi24O31Cl10光催化物质,并通过在可见光下降解RhB评价Fe^3+掺杂对其光催化性能的影响。采用XRD,XPS,UV-vis,SEM,HTEM,FT-IR等表征手段研究了不同Fe^3+掺杂量对Bi24O31Cl10的物相、元素价态、光吸收性能、微观形貌以及颗粒分布、晶面间距、化学结构组成等的影响。结果表明:掺杂Fe^3+未改变Bi24O31Cl10的物相,片状形貌,但其片状大小明显变小且厚度变薄,光吸收性能增强,光生电子-空穴复合率下降,与纯Bi24O31Cl10相比,Fe^3+掺杂能显著提高Bi24O31Cl10的光催化活性,当Fe^3+掺杂量为0.5%(摩尔分数)时,对Bi24O31Cl10的光催化性能促进最高,在可见光下光照50 min,对RhB的脱色率可达75%,较纯Bi24O31Cl10提高了44%。     

Absorber Materials for Transition-Edge Sensor X-ray Microcalorimeters

Arrays of superconducting transition-edge sensors (TES) can provide high spatial and energy resolution necessary for X-ray astronomy. High quantum efficiency and uniformity of response can be achieved with a suitable absorber material, in which absorber X-ray stopping power, heat capacity, and thermal conductivity are relevant parameters. Here we compare these parameters for bismuth and gold. We have fabricated electroplated gold, electroplated gold/electroplated bismuth, and evaporated gold/evaporated bismuth 8×8 absorber arrays and find that a correlation exists between the residual resistance ratio (RRR) and thin film microstructure. This finding indicates that we can tailor absorber material conductivity via microstructure alteration, so as to permit absorber thermalization on timescales suitable for high energy resolution X-ray microcalorimetry. We show that by incorporating absorbers possessing large grain size, including electroplated gold and electroplated gold/electroplated bismuth, into our current Mo/Au TES, devices with tunable heat capacity and energy resolution of 2.4 eV (gold) and 2.1 eV (gold/bismuth) FWHM at 5.9 keV have been fabricated. A.-D. Brown’s and S. Smith’s research was supported in part by appointments to the NASA Postdoctoral Program at NASA Goddard Space Flight Center administered by Oak Ridge Associated Universities through a contract with NASA.     

Solubility limit and thermoelectric properties of bismuth-supersaturated tellurium

Charge carrier density in bismuth-doped tellurium has been studied as a function of the dopant concentration in order to determine the boundary of the second phase formation in the Bi-Te system. All bismuthdoped tellurium samples, in contrast to the initial undoped material, exhibit hole conductivity. The hole density significantly increases with the dopant content and reaches a maximum value (2.1 × 10¹⁸ cm^?3) at a bismuth concentration of 0.1 at. %, which corresponds to the limiting solubility. This conclusion fully agrees with the character of transformation of the temperature dependence of the thermo emf α of bismuth-doped tellurium, which shows a decrease in α for Y ^Bi > 0.1 at. % as a result of increasing contribution of the second phase (Bi₂Te₃) inclusions possessing electron conductivity.     

Selenium‐Doped Cathodes for Lithium–Organosulfur Batteries with Greatly Improved Volumetric Capacity and Coulombic Efficiency

For the first time a new strategy is reported to improve the volumetric capacity and Coulombic efficiency by selenium doping for lithium–organosulfur batteries. Selenium‐doped cathodes with four sulfur atoms and one selenium atom (as the doped heteroatom) in the confined structure are designed and synthesized; this structure exhibits greatly improved volumetric/areal capacities, and a Coulombic efficiency of almost 100% for highly stable lithium–organosulfur batteries. The doping of Se significantly enhances the electronic conductivity of battery electrodes by a factor of 6.2 compared to pure sulfur electrodes, and completely restricts the production of long‐chain lithium polysulfides. This allows achievement of a high gravimetric capacity of 700 mAh g^?1 close to its theoretical mass capacity, an exceptional volumetric capacity of 2457 mAh cm^?3, and excellent capacity retention of 92% after 400 cycles. Shuttle effect is efficiently weakened since no long‐chain polysulfides are detected from in situ UV/vis results throughout the entire cycling process arising from selenium doping, which is theoretically confirmed by density functional theory calculations.     

纳米管协同碳纳米管导电纸对石墨负极性能的影响

以碳纳米管(Multi-walled carbon nanotubes)为导电剂,协同以碳纳米管和纸纤维复合成的CNTs导电纸为集流体,对石墨负极进行电化学改性。石墨化处理碳纳米管作为负极的添加相,采用XRD、SEM和TGA对其分析。结果表明,对比单纯的石墨/铜箔负极,掺杂0.8%(质量分数)石墨化碳纳米管的石墨/铜箔负极,电池比容量由304mAh/g变为308mAh/g,相差不大,但循环效率由86%升至92%;使用CNTs导电纸做集流体时,掺杂0.8%(质量分数)石墨化碳纳米管的石墨/CNTs导电纸负极,比容量由308mAh/g升至401mAh/g,提高30%,循环效率由92%升至95%,提高3%。说明碳纳米管协同CNTs导电纸对石墨负极具有积极的改性意义。     

Nuclear specific heat of copper potassium tutton salt

The specific heat of copper potassium tutton salt has been measured down to 1 mK in order to investigate the hyperfine interaction of this copper compound. The magnetic ordering of the electronic system occurs at 29.5 mK in zero field. Below the transition temperature the electronic heat capacity decreases and the copper nuclear heat capacity of hyperfine splitting becomes dominant in the heat capacity of the compound. The nuclear heat capacity has a broad peak around 3.5 mK. The entropy of copper nuclear spin, which was calculated from the specific heat data, remains at 40% of ln(2I+1) at 1 mK.     

直读光谱分析银产品中的杂质元素

本文讨论了银产品中杂质元素铜、铁、铅、锑、铋、钯、硒、碲直读光谱分析方法的建立,及各项分析条件的选择与优化。应用于生产实践,效果令人满意。     

Structural Stability, Electronic and Magnetic Properties of Cu Adsorption on Defected Graphene: A First Principles Study

Structural stabilities, electronic structures, and magnetic properties of Cu atom adsorption on pure, B(N)-doped and single-vacancy graphene have been studied using the first-principle method. It was found that the electronic property of graphene can be tuned by B or N doping. B-doped and N-doped graphene turned into a p-type and n-type semiconductor with a band gap of 0.2 eV, respectively. Total energy calculation results demonstrated the most stable site for the Cu atom adsorption on pure, B-doped and N-doped graphene is the top, bridge, and hollow site, respectively. B doping and vacancy both enhance the adsorption capacity for the Cu atom, while N doping weakens the capacity. Furthermore, B and N atoms do not induce magnetism in graphene, while the magnetic moment is induced when Cu is adsorbed on the graphene sheet, which is mainly caused by the unsaturated s-electrons of the Cu atom.     

Synthesis of polycrystalline nanotubular Bi2Te3

Polycrystalline nanotubular Bi₂Te₃ could be prepared via a high-temperature solution process using nanoscale tellurium, decomposed from trioctylphosphine oxide (TOPO) extracted tellurium species (Te-TOPO), as sacrificial template. The formation of such tubular structure is believed to be the result of outward diffusion of Te during the alloying process. The electrical properties (Seebeck coefficient and electrical conductivity) of the polycrystalline nanotubular Bi₂Te₃ have been studied and the experimental results show that the electrical conductivity is approximately three orders of magnitude smaller than bulk bismuth telluride materials mainly due to the much larger resistance brought by the insufficient contact between the nanotubular structures.     

Isothermal crystallization on the surface of Te-15 at % Ge alloy glass

Isothermal surface crystallization is investigated for Te-15 at % Ge alloy glass. This surface-crystalline pure tellurium nucleates by ageing at low temperature below 451 K. Since germanium-rich phases and GeTe chemical compound prevent this growth, the maximum thickness of the surface layer is below 0.005 mm.     

A heat exchanger model for mixtures and pure refrigerant cycle simulations

This paper describes a heat exchanger simulation developed for transient and steady state cycle simulations of mixtures and pure components. The simulation focuses on air to refrigerant condensers and evaporators found in residential heat pumps. The refrigerant differential momentum, continuity, species and energy equations are solved for these components and the steady state results are verified experimentally. Ten different heat transfer correlations for condensation and evaporation are evaluated to determine which best reproduces experimental data. Of those tested Jung and Radermacher's (1989, Int. J. Heat Mass Transfer32 2435–2446) heat transfer correlation worked the best for evaporation while Dobson et al.'s (1994, ACRC Project 37) correlation worked the best for condensation. The experimentally determined capacity of four cross flow heat exchangers operating as condensers and evaporators with four different refrigerants is compared to the simulation results. The capacities predicted by the simulation agreed with the experimental results within ±8.0%. Furthermore, the simulation is used to quantify the effects of using a zeotropic mixture, R-407C, with cross, parallel and counter flow heat exchangers. As compared to a typical cross flow heat exchanger at typical heat pump operating conditions, the simulation predits that a pure parallel flow heat exchanger can decrease capacity by as much as 8.3% while a pure counter flow heat exchanger can increase performance by up to 4.4%.     

Bi_2Te_3纳米粉末的直流电弧等离子体合成

以单质Bi,Te粉末为原材料,采用直流电弧等离子体蒸发法制备了Bi2Te3纳米粉末。通过XRD,EDS,TEM和SAED分析方法对Bi2Te3粉末的物相结构、成分和形貌进行了表征。Bi2Te3纳米粉末的平均粒径约为35 nm,粉末呈不规则的多面体结构,还有一些薄片状和棒状的结构,这与Bi2Te3半导体化合物的高度各向异性是一致的。研究了电弧电流和氩气压力对合成Bi2Te3纳米粉末的粒径和产率的影响,随着电弧电流或氩气气压的增加,粉末的粒径和产率都逐渐增大,但产率的增加并不明显。     

Nuclear cooling using copper and indium

In nuclear demagnetization, the nuclear spins can cool other systems, in particular the conduction electrons and lattice, only if there is a high degree of thermal isolation of the specimen from its surroundings. The temperature that the lattice and conduction electrons can reach depends on the rate of heat influx to the lattice and the rate at which the nuclear spins can absorb it. The cooling power of the nuclear spins depends on the spin-lattice relaxation time and the energy of the nuclear spins, which can be increased by demagnetizing to a finite field. For some substances the nuclear quadrupole energy can be used. Experiments with copper and indium resulted in cooling by the nuclear spins of the lattice and conduction electrons. The main problem is the energy transfer between the various constituent of the nuclear cooling specimen.     

声致发光气泡中原子碰撞发光机制

文章导出一种由两个中性的惰性气体原子之间的碰撞引起的电四极辐射几率,对于热平衡的惰性气体系统,推导出由碰撞引起的总辐射能量的公式（单位体积,在给定波长的每单位波长）,考虑到气体的吸收和周围环境水的折射,用此公式拟合纯氙和纯氨的单气泡声致发光的实验光谱,拟合温度大约为5,000K,结果令人满意。     

Large scale synthesis of highly pure single crystalline tellurium nanowires by thermal evaporation method

Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300 degrees C at 1 torr and condensed on the Si substrate at 100-150 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications.