Non-saturating magnetoresistance in heavily disordered semiconductors

The resistance of a homogeneous semiconductor increases quadratically with magnetic field at low fields and, except in very special cases, saturates at fields much larger than the inverse of the carrier mobility, a number typically of the order of 1 T (refs 1, 2). A surprising exception to this behaviour has recently been observed in doped silver chalcogenides, which exhibit an anomalously large, quasi-linear magnetoresistive response that extends down to low fields and survives, even at extreme fields of 55 T and beyond. Here we present a simple model of a macroscopically disordered and strongly inhomogeneous semiconductor that exhibits a similar non-saturating magnetoresistance. In addition to providing a possible explanation for the behaviour of doped silver chalcogenides, our model suggests potential routes for the construction of magnetic field sensors with a large, controllable and linear response.     

Mobile silver ions and glass formation in solid electrolytes

Solid electrolytes are a class of materials in which the cationic or anionic constituents are not confined to specific lattice sites, but are essentially free to move throughout the structure. The solid electrolytes AgI and Ag2Se (refs 1, 2, 3, 4, 5, 6, 7) are of interest for their use as additives in network glasses, such as chalcogenides and oxides, because the resulting composite glasses can show high electrical conductivities with potential applications for batteries, sensors and displays. Here we show that these composite glasses can exhibit two distinct types of molecular structures-an intrinsic phase-separation that results in a bimodal distribution of glass transition temperatures, and a microscopically homogeneous network displaying a single glass transition temperature. For the first case, the two transition temperatures correspond to the solid-electrolyte glass phase and the main glass phase (the 'base glass'), enabling us to show that the glass transition temperatures for the AgI and Ag2Se phases are respectively 75 and 230 degrees C. Furthermore, we show that the magnitude of the bimodal glass transition temperatures can be quantitatively understood in terms of network connectivity, provided that the Ag+ cations undergo fast-ion motion in the glasses. These results allow us to unambiguously distinguish base glasses in which these additives are homogeneously alloyed from those in which an intrinsic phase separation occurs, and to provide clues to understanding ion-transport behaviour in these superionic conductors.     

Giant magneto resistance and temperature coefficient of resistance in Sm0.55Sr0.30Ag0.15MnO3 perovskite

Silver ions substituted samarium strontium manganite (Sm0.55Sr0.30Ag0.15MnO3) pervoskite was synthesized by using respective oxides in stoichiometric ratio through solid state reaction. The as-prepared sample was characterized by various analytical techniques to confirm its formation and understand the effect of monovalent silver ions in pervoskite lattice. X-ray diffraction pattern confirms the single phase formation while grain morphology in SEM image indicates good connectivity among the grains. The enhancement in metal to insulator transition temperature shows quenched disorder and magnetoresistance phenomena. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) emerge from grain growth factor and homogeneity induced by Ag+ ions in the lattice. The reduction in hysteresis loss resulted from antiferromagnetic - ferromagnetic (TN) and ferromagnetic - paramagnetic (Tc) transitions reveals the removal of disorder in perovskite lattice by Ag+ ions substitution. This increases the magnetic moment across distinct ions on the applying magnetic field. The rise in MR% (~99%) with silver doping emerging from smooth spin tunneling of the grains across the boundary and suppression of the disordered magnetic fluctuations with increase in magnetic field has been reported. The present compound exhibits the first order nature of magnetism and observed first time the highest value of TCR ~ 95%.     

氧化锌/银双层膜负反馈阴极电极的制备及性能研究

提出了一种可显著改善碳纳米管(CNTs)场致发射性能的ZnO/Ag双层膜负反馈阴极电极的制备方法.在条形银电极上溅射沉积一定厚度的Zn膜,经热氧化和湿法刻蚀制备成ZnO/Ag双层膜电极.同单层的Ag或氧化铟锡电极相比,该电极不仅具有足够的负反馈电阻(限流电阻)阻止CNTs场发射中过流的发生,而且降低了条形阴极电极的线性电阻,确保了场发射的均匀性.当溅射沉积Zn膜的厚度从40 nm增到120 nm时,热氧化形成的ZnO由孤岛状的颗粒变为连续体的薄膜,ZnO/Ag双层膜电极的表面光洁度比单层的Ag电极有很大的提高,负反馈电阻层的电阻增大,负反馈的能力增强.CNTs薄膜阴极场发射特性曲线证明,ZnO/Ag双层膜电极能明显降低场发射电流的波动,有效提高器件的稳定性和寿命.     

Ag与Ag20粉末微电极的循环伏安和电化学阻抗对比研究

在Ag电极化成为AgO时,发现只有Ag粉末电极可以氧化得到AgO,而Ag20则不行．分别将Ag和Ag20制作成粉末微电极,对它们进行了循环伏安（CV）和电化学阻抗谱（EIS）测试．通过对测试结果的分析可知,Ag被氧化为Ag20后,Ag电极分为内外两层,外层为富舍离子通道的Ag2O,便于OH-的进入;内层为导电性良好的Ag,便于Ag20氧化为AgO时电子的输出．而Ag20电极所含的离子通道较少,不利于OH-的进入;另外Ag2O的电阻较大,也不利于电子向外输出．这两方面原因使得Ag20电极不能被氧化为AgO．     

Novel Approach to the Design of Optoelectronic Heterostructures Based on Indium and Copper Sulfides

1 Results Heterostructures,based on ternary CuInS(Se2) chalcogenides and related binary compounds (Cu2-xCh,CuCh,In2Ch3 and InCh; Ch=S,Se) are considered appear to be a matter of choice for producing promising optoelectronic devices.In the present work we propose and consider a very simple way for the formation of sulfide and selenide heterostructures.The main idea is assumes a novel two-stage method of synthesis and nonstoichiometry control for heterostructures of InxS(Se)1-x/Si,CuInS(Se)2/Si and InxS1-...     

Mass spectrometric study of Ag’s clustering ability with O, S and Se

Samples Ag/O/S, Ag/O/Se and Ag/S/Se were ablated directly by laser to produce clusters. The detection was performed with a time-of-flight mass spectrometer (TOF MS). The cluster ions produced had the following distribution: Ag/S binary cluster ions for sample Ag/O/S, Ag/Se binary cluster ions for sample Ag/O/Se, and Ag/Se binary cluster ions and Ag/S/Se ternary cluster ions as the main products for sample Ag/S/Se. Laser double ablation reactor was used to study the reaction between Ag/S(Se, O) binary clusters and Se(S) homoclusters. The experiments show that Se clusters can replace S and O in Ag/S and Ag/O clusters while S clusters can replace O in Ag/O clusters. This fact indicates the sequence of the clustering ability of Ag presented as follows: Ag/Se > Ag/S > Ag/O, which was also proved by theoretical calculation. The reason of this tendency was considered to be the different abilities of the elements’ polarization, which acts on the stability of clusters.     

pH值对β-MnO2颗粒光催化去除银离子的影响

The presence of silver ions (Ag(I)) in wastewater has a detrimental effect on living organisms. Removal of soluble silver, especially at low concentrations, is challenging. This paper presents the use of β-MnO₂ particles as a photocatalyst to remove Ag(I) ions selectively from aqueous solution at various pH levels. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), field emission electron microscope (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron microscopy (XPS) were employed to determine the removal efficiency and to characterize the deposition of silver onto the surface of β-MnO₂ particles. The optimum pH for the removal of Ag(I) ions was at pH 4 with 99% removal efficiency under 1 h of visible light irradiation. This phenomenon can be attributed to the electrostatic attraction between β-MnO₂ particles and Ag(I) ions as well as the suppression of electron–hole recombination in the presence of H+ ions.     

Re-emerging superconductivity at 48 kelvin in iron chalcogenides

Pressure has an essential role in the production and control of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature T(c) to a record high of 55?K in these materials. In the same way as T(c) exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned T(c) typically drops monotonically after passing the optimal pressure. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5?GPa, after the T(c) drops from the first maximum of 32?K at 1?GPa. The T(c) of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0-48.7?K for Tl(0.6)Rb(0.4)Fe(1.67)Se(2), K(0.8)Fe(1.7)Se(2) and K(0.8)Fe(1.78)Se(2).     

利用室温转化法合成硒化银量子点

本采用室温转化法、分别用乙二胺与氨水做模板合成硒化银量子点，对合成的硒化银样品进行了X-射线衍射分析，并在透射电子显微镜下研究了模板对合成硒化银形态的影响．     

Magnetic-field-induced superconductivity in a two-dimensional organic conductor

The application of a sufficiently strong magnetic field to a superconductor will, in general, destroy the superconducting state. Two mechanisms are responsible for this. The first is the Zeeman effect, which breaks apart the paired electrons if they are in a spin-singlet (but not a spin-triplet) state. The second is the so-called 'orbital' effect, whereby the vortices penetrate into the superconductors and the energy gain due to the formation of the paired electrons is lost. For the case of layered, two-dimensional superconductors, such as the high-Tc copper oxides, the orbital effect is reduced when the applied magnetic field is parallel to the conducting layers. Here we report resistance and magnetic-torque experiments on single crystals of the quasi-two-dimensional organic conductor lambda-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. We find that for magnetic fields applied exactly parallel to the conducting layers of the crystals, superconductivity is induced for fields above 17 T at a temperature of 0.1 K. The resulting phase diagram indicates that the transition temperature increases with magnetic field, that is, the superconducting state is further stabilized with magnetic field.     

Geometrical enhancement of low-field magnetoresistance in silicon

Inhomogeneity-induced magnetoresistance (IMR) reported in some non-magnetic semiconductors, particularly silicon, has generated considerable interest owing to the large magnitude of the effect and its linear field dependence (albeit at high magnetic fields). Various theories implicate spatial variation of the carrier mobility as being responsible for IMR. Here we show that IMR in lightly doped silicon can be significantly enhanced through hole injection, and then tuned by an applied current to arise at low magnetic fields. In our devices, the 'inhomogeneity' is provided by the p-n boundary formed between regions where conduction is dominated by the minority and majority charge carriers (holes and electrons) respectively; application of a magnetic field distorts the current in the boundary region, resulting in large magnetoresistance. Because this is an intrinsically spatial effect, the geometry of the device can be used to enhance IMR further: we designed an IMR device whose room-temperature field sensitivity at low fields was greatly improved, with magnetoresistance reaching 10% at 0.07?T and 100% at 0.2?T, approaching the performance of commercial giant-magnetoresistance devices. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic-field sensing industry. Moreover, because our device is based on a conventional silicon platform, it should be possible to integrate it with existing silicon devices and so aid the development of silicon-based magnetoelectronics.     

Ag2Se纳米晶的水热合成及表征

在低温水热条件下,以AgNO3、Na2SeO3或单质硒为反应物,制备了金属硫族化合物Ag2Se纳米晶.用X射线粉末衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)分别对Ag2Se纳米晶的结构及形貌进行了表征分析.结果表明,所得样品为正交晶系的Ag2Se纳米晶,主要形貌为不规则的纳米颗粒;同时采用不同硒源及表面活性剂聚乙烯吡咯烷酮(PVP)可以获得不同形貌的纳米晶.     

Ag纳米粒子增强CdS白光量子点器件的研制

半导体量子点材料由于其量子尺寸效应和表面效应的影响,显示出独特的发光特性.表面等离子体荧光增强效应由于其广泛的应用前景近年来成为了研究的热点,在材料科学、生物医学、光电器件等领域都展现了良好的应用前景.本文在十八烯体系中合成CdS量子点,用光诱导法制备银纳米粒子,并将两者复合,制备成四种复合样品,通过分析复合样品的荧光谱,研究银纳米颗粒的表面等离子体共振峰分别对应富含缺陷的硫化镉量子点的带边荧光峰和表面态荧光峰时,会发生带边荧光淬灭而表面态荧光增强的现象.实验结果表明,通过控制金属和量子点之间的距离,能够控制带边荧光辐射和缺陷带荧光辐射的比例,从而控制白光量子点的色温.本文随后用九个395nm紫光LED作为激发光源,将涂有荧光样品的玻片与激发光源组装,并用锡纸挡住多余的激发光,研制出银纳米颗粒/量子点复合结构白光照明器件原型,用实物对比图证明了银纳米粒子能够改变CdS量子点样品发光颜色,增强CdS量子点的荧光效应,且增强程度随着量子点样品的厚度减小而加强的特性.该研究不仅为人们认识荧光物质和金属之间的相互作用提供了新途径,还探讨了该器件在变色发光材料方向的应用前景.     

锂离子电池三维多孔硅/银复合材料负极设计及性能

以商品单质硅为原料,利用金属辅助化学刻蚀方法结合化学镀方法制备了三维多孔硅/银复合负极材料,采用X射线粉末衍射仪、场发射扫描电镜及比表面与孔隙度分析仪对其组成、结构、比表面积及孔隙率进行研究,随后对其电化学性能进行研究.结果表明,三维多孔硅呈现狭缝型的介孔,平均孔径宽度为12.5 nm,比表面积达到6.083 m2/g...     

化学法在Ni-W基带上制备Ag缓冲层研究

在双轴织构的Ni-W基带上,采用化学镀银法为YBa2Cu3O7-δ(YBCO)涂层导体制备Ag缓冲层薄膜,并通过XRD和φ扫描研究烧结温度和镀银次数对Ag薄膜取向的影响。结果表明,在Ar-H2混合气氛下,于870℃镀银5次所制备的薄膜具有(200)晶面单一取向;采用化学法制备的Ag薄膜有较好的外延性,且适用于涂层导体中的单一导电型缓冲层。     

基于Ag+金属中心的硅钨杂多酸配位聚合物的合成及其电化学性能研究

本文利用水热合成法得到了一种基于银离子金属中心的硅钨杂多酸(H₃SiW₁₂O₄₀)配位聚合物材料([Ag₄(BPB)₄SiW₁₂O₄₀])(简称，化合物1).单晶X-射线衍射分析表明，结构中存在Ag1、Ag2和Ag3三种银离子，分别采用2、3、4配位的方式通过Ag-N键连接有机配体，又通过Ag-O键连接多酸分子. Ag1连接有机配体形成左手、右手螺旋链，并连接多酸分子形成梯形链. Ag2连接有机配体和多酸分子形成二维4,4-sql拓扑格子层，梯形链与格子层共用多酸分子. Ag3连接有机配体形成一维链贯穿于二维层，最终形成整体的三维结构.此外，利用复合改性玻碳电极(GCE)作为工作电极对材料的电化学性能进行了研究.电化学分析结果表明，材料可作为还原NaNO₃的电催化剂.     

广东长坑—富湾金银矿床微量元素及稀土元素地球化学

金银矿体位于同一矿田并共存在同一个构造破碎蚀变带内,严格地受控于下石炭统梓门桥组(C1z)和上三叠统小坪组(T3x)之间的滑覆构造破碎带,这一构造带也是C1z和T3x间的平行不整合界面.围岩蚀变以硅化、粘土化和硫化物化为主.本文通过对金、银矿矿石及围岩的微量元素组成特征的分析,认为金、银矿物质来源是不同的:金可能来源于矿区周围的下石炭统梓门桥组地层,银则来源于粤西地区广泛分布的中-新元古代地层(云开杂岩和震旦系).在对金、银矿体和围岩稀土元素地球化学研究的基础上,推断金、银成矿作用和围岩蚀变作用皆属热液交代作用的结果,而非热水沉积作用的产物.     

Transition-metal-based magnetic refrigerants for room-temperature applications.

Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.     

基于磁一重效应对矿物中w( Fe3O4)的快速测定

利用矿物在相同磁场、相同质量下因w(Fe3O4)不同会有不同称重读数,采取不同磁场类型和不同磁场强度对配料进行磁一重效应实验.结果表明,在一定磁场条件下,w( Fe2O3)对磁一重实验结果准确性的影响可以忽略,各实验条件下磁一重效应拟合直线方程决定系数均大干0.996,线性相关明显,磁一重效应可以准确便捷测定矿物中Fe3 O4的质量分数.