Effects of metal doping on the physical properties of ZnTe thin films

Zinc telluride (ZnTe) thin films were sublimated on a glass substrate using closed space sublimation (CSS) technique. ZnTe thin films of same thickness were tailored with copper (Cu) & silver (Ag) doping, considered for comparative study. X-ray diffraction (XRD) patterns of as-deposited ZnTe thin film and doped ZnTe samples exhibited polycrystalline behavior. The preferred orientation of (111) having cubic phase was observed. XRD patterns indicated that the crystallite size had increased after silver and copper immersion in as-deposited ZnTe thin films. Scanning electron microscopy (SEM) was used to observe the change of as-deposited and doped sample's grains sizes. EDX confirmed the presence of Cu and Ag in the ZnTe thin films after doping respectively. The optical studies showed the decreasing trend in energy band gap after Cu and Ag-doping. Transmission also decreased after doping. Resistivity of as-deposited ZnTe thin film was about 10⁶ Ω cm. The resistivity was reduced to 68.97 Ω cm after Cu immersion, and 10⁴ Ω cm after Ag immersion. Raman spectra were used to check the crystallinity of as-deposited, Cu and Ag-doped ZnTe thin film samples.     

Effects of Cr doping on physical properties of amorphous In-Ga-Zn-O films

Amorphous thin films of InGaZnO₄ (a-IGZO) doped with Cr have been fabricated by using pulsed-laser deposition (PLD). The electrical, optical and magnetic properties of Cr-doped a-IGZO films grown at 25 °C and 150 °C were investigated. The conductivity, optical transmission and band gap of films are remarkably enhanced by increasing the growth temperature. Conductivity, carrier concentration and mobility decrease with increasing the Cr content. However, the optical transmission and band gap are not significantly affected by Cr doping. Moreover, all Cr-doped films exhibit room-temperature ferromagnetism.     

Effects of sediment physical properties on the phosphorus release in aquatic environment

Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.     

Electric and thermal transport properties of topological insulator candidate LiMgBi

We report the transport properties of a topological insulator candidate, LiMgBi. The electric resistivity of the title compound exhibits a metal-to-semiconductor-like transition at around 160 K and tends to saturation below 50 K. At low temperatures, the magnetoresistance is up to ~260% at 9 T and a clear weak antilocalization effect is observed in the low magnetic-field region. The Hall measurement reveals that LiMgBi is a multiband system, where hole-type carriers (n_h~10¹⁸ cm^-3) play a major role in the transport process. Remarkably, LiMgBi possess a large Seebeck coefficient (~440 μV/K) and a moderate thermal conductivity at room temperature, which indicate that LiMgBi is a promising candidate in thermoelectric applications.     

Al-2N掺杂量对ZnO光电性能的影响

与本文相近的Al-2N掺杂量的范围内, 对ZnO掺杂体系吸收光谱分布红移和蓝移两种实验结果均有文献报道, 但是, 迄今为止对吸收光谱分布尚未有合理的理论解释. 为了解决该问题, 本文采用基于密度泛函理论的广义梯度近似 平面波超软赝势方法, 用第一性原理构建了两种不同掺杂量的Zn_0.98148Al_0.01852O_0.96296N_0.03704和Zn_0.96875Al_0.03125O_0.9375N_0.0625超胞模型. 在几何结构优化的基础上, 对模型能带结构分布、态密度分布和吸收光谱分布进行了计算. 计算结果表明, 在本文限定的掺杂量范围内, Al-2N掺杂量越增加, 掺杂体系的体积越减小, 体系总能量越升高, 体系稳定性越下降, 形成能越升高, 掺杂越难; 所有掺杂体系均转化为简并p型化半导体, 掺杂体系最小光学带隙均变窄,吸收光谱均发生红移; 同时发现掺杂量越增加, 掺杂体系最小光学带隙变窄越减弱, 吸收光谱红移越减弱. 研究表明: 要想实现Al-2N共掺在ZnO中最小光学带隙变窄、掺杂体系发生红移现象, 除了限制掺杂量外, 尺度长短也应限制; 其次, Al-2N掺杂量越增加,掺杂体系空穴的有效质量、浓度、 迁移率、电导率越减小,掺杂体系导电性能越减弱. 计算结果与实验结果的变化趋势相符合. 研究表明, Al-2N共掺在ZnO中获得的新型半导体材料可以用作低温端的温差发电功能材料.     

Reactive chemical doping of the Bi2Se3 topological insulator

Using angular resolved photoemission spectroscopy we studied the evolution of the surface electronic structure of the topological insulator Bi(2)Se(3) as a function of water vapor exposure. We find that a surface reaction with water induces a band bending, which shifts the Dirac point deep into the occupied states and creates quantum well states with a strong Rashba-type splitting. The surface is thus not chemically inert, but the topological state remains protected. The band bending is traced back to Se abstraction, leaving positively charged vacancies at the surface. Because of the presence of water vapor, a similar effect takes place when Bi(2)Se(3) crystals are left in vacuum or cleaved in air, which likely explains the aging effect observed in the Bi(2)Se(3) band structure.     

Effects of Sb doping on the structure and properties of SnO2 films

Transparent heat-insulating SnO₂ films were prepared on the glass substrate with sol-gel. The effects of Sb doping on the structure and photoelectric properties of the films were investigated. The films were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Ultraviolet–Visible-Near Infrared Spectrometer (UV-VIS-NIR) and Hall Effect tester. The results show that the doping of Sb did not change the basic crystal structure of the SnO₂ film, but reduced the crystallinity of the film. With the increase of Sb doping, the grain size decreases first and then maintains basically invariable. The sheet resistance of the film decreases first and then increases. The transmittance of the substrate glass coated with this film (hereinafter referred to as the film's transmittance) in the near-infrared region (780–2500 nm) decreases from 92.55% to 60.48%, and increases a little when the doping amount exceeded 11 mol%. And its transmittance of visible light (380–780 nm) fluctuated slightly between about 81% and 86%.     

Effects of Ni and Co doping on the physical properties of tetragonal FeSe0.5Te0.5 superconductor

Isoelectronic Tellurium (Te) substitution for Selenium (Se) in the tetragonal phase of FeSe (β-FeSe) increases the superconducting transition temperature (T_c) by applying a negative pressure on the lattice. However, the normal state resistivity increases and shows semi-metallic behavior for samples with higher Te concentration. With increasing Te concentration, the T_c increases and reaches a maximum for FeSe_0.5Te_0.5 and then decreases with further increase of Te. We have investigated the effect of Cobalt (Co) and Nickel (Ni) doping in FeSe_0.5Te_0.5 in the nominal composition range Fe_1?xTM_xSe_0.5Te_0.5 (TM = Co (x = 0.05, 0.1, 0.15, 0.2) and Ni (x = 0.05, 0.1)). Both Co and Ni doping suppress T_c and drives the system to metal–insulator transition. The in-plane (‘a’) and out-of-plane (‘c’) lattice constants decrease with increasing dopant concentration.     

Effect of 3d doping on the electronic structure of BaFe2As2

The electronic structure of BaFe(2)As(2) doped with Co, Ni and Cu has been studied by a variety of experimental and theoretical methods, but a clear picture of the dopant 3d states has not yet emerged. Herein we provide experimental evidence of the distribution of Co, Ni and Cu 3d states in the valence band. We conclude that the Co and Ni 3d states provide additional free carriers to the Fermi level, while the Cu 3d states are found at the bottom of the valence band in a localized 3d(10) shell. These findings help shed light on why superconductivity can occur in BaFe(2)As(2) doped with Co and Ni but not Cu.     

Effects of nitrogen doping on optical properties of TiO2 thin films

The potential for extending the optical absorption range of TiO₂ by doping with nonmetallic elements was examined in nitrogen-containing TiO₂ thin films. Thin films of TiO_2-xN_x were synthesized on glass and silicon substrates by ion-beam-assisted deposition to obtain a wide range of nitrogen concentrations. The compositions of the films were determined by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. The structures of the films were analyzed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The optical properties of the films were measured by UV-Vis spectroscopy and ellipsometry. A characteristic decreasing trend in band-gap values of the films was observed within a certain range of increasing dopant concentrations. As the nitrogen concentration increased, the structure of the films evolved from a well-defined anatase to deformed anatase. The reduced band gaps are associated with the N 2p orbital in the TiO_2-xN_x films. PACS 78.66.-w; 78.20.Ci     

过渡金属原子掺杂对单层MoS_2磁性的影响

本文利用基于密度泛函理论的第一性原理平面波赝势方法分别计算了本征及过渡金属掺杂单层MoS_2的晶格参数、电子结构和磁性性质.计算结果显示,过渡金属掺杂所引起的晶格畸变与杂质原子的共价半径有联系,但并不完全取决于共价半径的大小.分析电子结构可以看到,VIIB、VIII和IB族杂质中除Ag和Re外的掺杂体系都对外显示磁性,磁矩主要集中在掺杂的过渡金属原子上.掺杂体系的禁带区域都出现了数目不等的杂质能级,这些杂质能级主要由杂质的d、S的3p和Mo的4d轨道组成.     

Effect of in addition on some physical properties of the As2Se3 amorphous system

The effect of In content on do electrical conductivity and DTA of the system (As₂Se₃)_1-x. In_x, x=0, 0.01, 0.05, has been studied. The electrical energy gap was found to increase for an In content 0.01% and decrease for an In content 0.05%. The samples exhibit the three conduction mechanisms proposed by Mott and Davis. The activation energy was calculated for each mechanism. The effect of heating rate on the transition temperatures (T _g,T _c,T _m) was studied and the variation of the crystallization-peak position was used to calculate the activation energy and the order of the crystallization process.     

Study of carrier doping across the parent Mott insulator La2CuO4

Ce substituted La₂CuO₄ single crystals are investigated to try doping electrons into the parent Mott insulator. Transport properties of slightly Ce substituted La₂CuO₄ show that carriers are still holes activated from an impurity level of which activation energy is the same as the parent La₂CuO₄.     

Variation of physical properties in the nominal Sr4V2O6Fe2As2

We show using a combination of powder X-ray and neutron diffraction, first-principles calculations, temperature- and field-dependent magnetization, heat capacity and resistivity data that the superconducting behavior of ‘Sr₄V₂O₆Fe₂As₂’ is dependent on synthesis conditions, particularly, heating profiles result in unintentional chemical doping. This compound can be tuned from a state in which the vanadium electrons are itinerant with a high electronic density of states, to a state where the vanadium-oxide layers are insulating and presumably magnetic.     

Effects of substitution on low-temperature physical properties of LuFe2Ge2

The low-temperature magnetic phase transition in LuFe₂Ge₂ is thought to be associated with itinerant magnetism. The effects of Y and Sc substitutions on the Lu site, as well as Ru and Co substitutions on the Fe site, on the low-temperature magnetic phase transition of the LuFe₂Ge₂ compound have been studied in single crystals via microscopic, thermodynamic and transport measurements. On one hand, Co substitution suppresses the transition below our base temperature of 2?K even at our lowest substitution level. On the other hand, Sc substitution enhances the transition temperature, and Y or Ru substitution suppresses the transition to lower temperature. Phase diagrams for Y, Sc and Ru substitutions have been constructed and the possibility of a unifying, composite diagram is discussed.     

Effect of doping and annealing on the physical properties of ZnO:Mg nanoparticles

Well-dispersed undoped and Mg-doped ZnO nanoparticles with different doping concentrations at various annealing temperatures are synthesized using basic chemical solution method without any capping agent. To understand the effect of Mg doping and heat treatment on the structure and optical response of the prepared nanoparticles, the samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), UV–Vis optical absorption, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The UV–Vis absorbance and PL emission show a blue shift with increasing Mg doping concentration with respect to bulk value. UV–Vis spectroscopy is also used to calculate the band-gap energy of nanoparticles. X-ray diffraction results clearly show that the Mg-doped nanoparticles have hexagonal phase similar to ZnO nanoparticles. TEM image as well as XRD study confirm the estimated average size of the samples to be between 6 and 12 nm. Furthermore, it is seen that there was an increase in the grain size of the particles when the annealing temperature is increased.     

S掺杂对锐钛矿相TiO2电子结构与光催化性能的影响

采用基于第一性原理的平面波超软赝势方法研究了掺杂不同价态S的锐钛矿相TiO2的晶体结构、杂质形成能、电子结构及光学性质.计算结果表明硫在掺杂体系中的存在形态与实验中的制备条件有关;掺杂后晶格发生畸变、原子间的键长及原子的电荷量也发生了变化,导致晶体中的八面体偶极矩增大;S 3p态与O 2p态、Ti 3d态杂化而使导带位置下移、价带位置上移及价带宽化,从而导致TiO2的禁带宽度变窄、光吸收曲线红移到可见光区.这些结果很好地解释了S掺杂锐钛矿相TiO2在可见光下具有优良的光催化性能的内在原因.根据计算结果分析比较了硫以不同离子价态掺杂对锐钛矿相TiO2电子结构和光催化性能影响的差别.     

Laboratory measurements of physical properties on submicronic particles candidate as cosmic dust

Summary We present here a compendium of our laboratory measurements of the physical properties of submicronic particles of materials candidate as cosmic dust: amorphous carbon, silicon carbide and graphite. Comparison with data obtained by other authors is presented and discussed in view of astrophysical applications. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.     

Effects of Ca doping on the electrochemical properties of LiNi0.8Co0.2O2 cathode material

LiNi_0.8Co_0.2O₂ and Ca-doped LiNi_0.8Co_0.2O₂ cathode materials were synthesized via a rheological phase reaction method. It is found that the Ca doping significantly improves reversible capacity, cycling performance, thermal stability and rate capability. The Ca-doped LiNi_0.8Co_0.2O₂ cathode material maintains nearly its initial discharge capacity up to 100 cycles at room temperature. It also delivers an initial discharge capacity of 183 mA h g^− 1 and still keeps 131 mA h g^− 1 even after 120 cycles at 60 °C. These results, together with the X-ray diffraction and electrochemical impedance spectroscopy analysis, reveal that Ca²⁺ ions occupy Li⁺ ion sites to form Ca_Li defects and lithium vacancies (V_Li′), which reduce the resistance and increases conductivity of LiNi_0.8Co_0.2O₂.