Electrical detection of spin precession in a metallic mesoscopic spin valve

To study and control the behaviour of the spins of electrons that are moving through a metal or semiconductor is an outstanding challenge in the field of 'spintronics', where possibilities for new electronic applications based on the spin degree of freedom are currently being explored. Recently, electrical control of spin coherence and coherent spin precession during transport was studied by optical techniques in semiconductors. Here we report controlled spin precession of electrically injected and detected electrons in a diffusive metallic conductor, using tunnel barriers in combination with metallic ferromagnetic electrodes as spin injector and detector. The output voltage of our device is sensitive to the spin degree of freedom only, and its sign can be switched from positive to negative, depending on the relative magnetization of the ferromagnetic electrodes. We show that the spin direction can be controlled by inducing a coherent spin precession caused by an applied perpendicular magnetic field. By inducing an average precession angle of 180 degrees, we are able to reverse the sign of the output voltage.     

Spintronics: spin accumulation in mesoscopic systems

In spintronics, in which use is made of the spin degree of freedom of the electron, issues concerning electrical spin injection and detection of electron spin diffusion are fundamentally important. Jedema et al. describe a magneto-resistance study in which they claim to have observed spin accumulation in a mesoscopic copper wire, but their one-dimensional model ignores two-dimensional spin-diffusion effects, which casts doubt on their analysis. A two-dimensional vector formalism of spin transport is called for to model spin-injection experiments, and the identification of spurious background resistance effects is crucial.     

Electronic spin transport and spin precession in single graphene layers at room temperature

Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.     

具有自旋-轨道耦合作用的二维介观电子气中的自旋累积效应研究

建立了在含自旋-轨道耦合相互作用的二维介观多端格子模型中求解散射波函数，进而在Landauer-Buttiker框架中得到计算多端的电导和自旋电导，以及任意非平衡局域物理量（如电流驱动之下的非平衡自旋累积）的一般方法．作为散射波函数法的一个直接应用，我们研究了具有Rashba型自旋-轨道耦合的二维电子气的二端结构，在给定电流密度条件下，我们得到线性输运区的非平衡自旋累积效应的结果，发现与其它的理论结果和最近的实验结果是定性一致的．     

Water-driven structure transformation in nanoparticles at room temperature

The thermodynamic behaviour of small particles differs from that of the bulk material by the free energy term gammaA--the product of the surface (or interfacial) free energy and the surface (or interfacial) area. When the surfaces of polymorphs of the same material possess different interfacial free energies, a change in phase stability can occur with decreasing particle size. Here we describe a nanoparticle system that undergoes structural changes in response to changes in the surface environment rather than particle size. ZnS nanoparticles (average diameter 3 nm) were synthesized in methanol and found to exhibit a reversible structural transformation accompanying methanol desorption, indicating that the particles readily adopt minimum energy structural configurations. The binding of water to the as-formed particles at room temperature leads to a dramatic structural modification, significantly reducing distortions of the surface and interior to generate a structure close to that of sphalerite (tetrahedrally coordinated cubic ZnS). These findings suggest a route for post-synthesis control of nanoparticle structure and the potential use of the nanoparticle structural state as an environmental sensor. Furthermore, the results imply that the structure and reactivity of nanoparticles at planetary surfaces, in interplanetary dust and in the biosphere, will depend on both particle size and the nature of the surrounding molecules.     

秦美猕猴桃的室温贮藏

采用ＰＥ袋和保鲜剂方法对室温下贮藏秦美猕猴桃进行了研究．结果表明，袋内Ｏ２体积分数为１０％以上，ＣＯ２体积分数在２．５％～６％范围情况下，果实呼吸峰的出现推迟，峰值降低，果实贮藏期显著延长．袋内ＣＯ２体积分数高于６％，Ｏ２体积分数低于１０％时，则产生伤害．ＣＯ２体积分数低于２．５％时，贮藏期缩短．适合的ＰＥ－３袋加保鲜剂室温贮藏三个月，其猕猴桃果实硬度可保持在４．１０ｋｇ／ｃｍ２，好果率达９６．４％．     

FeO的制备及其室温下稳定性研究

采用草酸亚铁在高纯Ar气条件下加热分解制备FeO,借助于XRD图谱探讨保护气氛对FeO制备的影响以及FeO在常温下存放的稳定性。结果表明,Ar气保护流量低于400mL/min时,产物相除FeO相外,还分别含有Fe3O4、Fe相,甚至有Fe2O3相杂质;较佳的Ar气保护流量为400mL/min,此时制备的FeO纯度高,其他杂质较少。新制备的FeO样品在干燥、潮湿和室内自然环境中保存,90d内未发生明显相的变化。     

常温干燥法制备纳米炭粉

以煤焦油沥青为原料,浓硫酸和浓硝酸为氧化剂,利用溶胶-凝胶方法制备水性中间相沥青.将水性中间相沥青溶解于氨水中得到水相炭基凝胶,经过乙醇与水交换后进行常温干燥和热处理制备纳米炭粉.利用FT-IR光谱、TG、XRD和TEM等分析手段对水性中间相沥青、纳米炭原粉以及纳米炭粉进行了表征.结果表明:采用常温干燥方法制备纳米炭粉是可行的,制得的纳米炭粉粒度均匀、规则,形状近似于球形,平均粒径为20 nm左右,其炭结构为无序的乱层石墨结构.在沥青与混酸氧化过程中,主要发生硝化、氧化、磺化反应;纳米炭原粉的热解过程分为脱醇脱水、预热解、强烈热分解和结构重排等四个阶段.     

WTe2 在室温下的红外纳米成像

本文用扫描散射近场光学显微镜(s-SNOM)在室温下研究了碲化钨(WTe_2)的近场光学响应,利用有限偶极模型计算了WTe_2样品与金刚石基底的近场散射信号比,发现观测结果并不能完全由块材所描述,从而推测出样品表面具有与块材无耦合作用的WTe_2纳米薄层,并对在样品边缘发现的很强的亮纹做出了可能的解释.这个工作为今后对拓扑材料的光学研究提供了参考.     

介观环中有Dresselhause自旋-轨道耦合效应的持续自旋流

在介观半导体环中,自旋-轨道耦合的存在直接影响持续自旋流的流动.作为自旋分裂的结果,持续自旋流并不与电荷流成一定的比例.我们研究有Dresselhaus自旋-轨道相互作用存在的介观半导体环中持续自旋流的性质.     

常温常压下合成新橙皮苷二氢查尔酮的工艺研究

为了实现以新橙皮苷为原料,在常温常压下催化加氢合成新橙皮苷二氢查尔酮的工业化生产,采用单因素试验对合成反应的关键工艺参数进行了研究。结果表明,当料液比m新橙皮苷∶V(NaOH)=1∶10,ρ(NaOH)=50 g/L,催化剂钯炭与新橙皮苷的质量比为1∶5,转速为500 r/min时,反应8 h后新橙皮苷二氢查尔酮的合成率可达到98%以上。     

Manipulation of atoms across a surface at room temperature

Since the realization that the tips of scanning probe microscopes can interact with atoms at surfaces, there has been much interest in the possibility of building or modifying nanostructures or molecules directly from single atoms. Individual large molecules can be positioned on surfaces, and atoms can be transferred controllably between the sample and probe tip. The most complex structures are produced at cryogenic temperatures by sliding atoms across a surface to chosen sites. But there are problems in manipulating atoms laterally at higher temperatures--atoms that are sufficiently well bound to a surface to be stable at higher temperatures require a stronger tip interaction to be moved. This situation differs significantly from the idealized weakly interacting tips of scanning tunnelling or atomic force microscopes. Here we demonstrate that precise positioning of atoms on a copper surface is possible at room temperature. The triggering mechanism for the atomic motion unexpectedly depends on the tunnelling current density, rather than the electric field or proximity of tip and surface.     

室温高聚物电解质氢催化传感器

分别采用混合压膜法和浸渍还原原位化学沉积法,以Pd为催化剂,高聚物质子导体Nafion膜为电解质,研制复合膜电极构成两种不同的室温固态电解质催化氢传感器。探索出以Pd盐自制Pd黑和浸渍还原制备膜电极的工艺条件,考察了一些因素对传感性能的影响,并进行了讨论。     

室温下氯化锆催化的Baeyer—Villiger氧化反应

研究了以氯化锆为催化剂,H2O2(质量分数为30%)为氧化剂,室温条件下酮的Baeyer-Villiger氧化反应,并探讨了溶剂种类、催化剂用量、氧化剂用量、温度、时间等因素对反应的影响.结果表明,环酮、链酮都可以转化为相应的酯并具有较高的转化率和选择性.     

固相反应制备磷酸锌纳米晶体

用 Zn SO4 · 7H2 O与加有表面活性剂的 Na H2 PO4 · H2 O室温下进行固相反应 ,合成得到前驱体和可溶性无机盐 ,用水洗去可溶性盐 ,烘干 ,将前驱体微波辐射晶化 ,生成磷酸锌晶体 .用均匀设计法对实验条件进行优化 ,按上述方法制备得到的磷酸锌 ,经 XRD和 TEM表征为纳米级晶体     

近室温磁制冷工质的研究现状与发展前景

基于稀土-过渡族金属间化合物Gd-Si-Ge系合金及钙钛矿型猛氧化物的磁热效应及其巨磁热效应机理,对近室温磁制冷材料的研究现状及材料与磁制冷技术的发展前景进行了分析.     

Electrical conductivity measurement of serpentine at high temperature and pressure

The electrical conductivity of serpentine is measured at 1.0-3. 0 GPa and 300-870℃. The effect of frequencies on electrical conductivity measurement is analyzed. The conduction mechanisms of serpentine before and after dehydration are discussed. Our experimental results show that the electrical conductivity of serpentine increases significantly after dehydration of serpentine, through which highly conductive layers (HCL) can be formed in the Earth's interior.     

玉米芯在常温下的水解动力学研究

为解决可渗透反应墙固定化硫酸盐还原菌原位治理酸性矿井水的碳源问题,以玉米芯为材料,通过模拟废水条件下单因素实验,分析温度、质量浓度、pH值、时间等参数对玉米芯水解液中还原糖含量的影响.根据玉米芯水解实验数据建立了玉米芯水解动力学模型,产糖率CG=k1·(e-k1t-e-k2t)/(k2-k1),mg/g;确定了不同温度下还原糖生成速率以及降解速率常数;玉米芯水解活化能Ea为33 342.213kJ/mol;指前因子为3.068×105.说明玉米芯作为缓释碳源在中低温条件下易水解,为以玉米芯固定SRB方法治理酸性矿山废水提供了理论依据.     

铜锰复合氧化物室温催化氧化NO的研究

采用两次沉淀法制备了一系列无载体铜锰复合氧化物催化剂,以NO催化氧化作为目标反应,系统考察了原料液[Cu]/[Mn]比、焙烧温度、焙烧时间等因素对催化剂催化性能的影响。结果表明:在[Cu]/[Mn]=1/6,焙烧温度300℃,焙烧时间8h条件下制备的催化剂具有最优催化氧化NO的活性,在室温下,且不引入任何还原剂的情况下,在6h内将107mg/m3的NO完全消除。此外,原位红外在线检测(FT-IR)结果表明,NO被转化成了亚硝酸盐和硝酸盐,并附着在催化剂表面。