碲、硒碲合金纳米线的可控合成

"采用一种新的化学溶液法合成了具有不同形貌的碲、硒碲合金纳米线．用十二烷基苯磺酸钠作为表面活性剂实现了对纳米线的可控合成,通过控制反应过程可以弯曲状、"V"字型的硒碲纳米线,利用XRD、TEM以及HRTEM对纳米线的形貌结构特征进行表征;以实验结果为依据讨论了纳米线的生长机理．"     

电化学沉积Fe单晶纳米线生长中的取向控制

利用电化学沉积方法，发现了一种能够动态地控制铁纳米线生长方向的沉积方法，利用该方法沉积了包括［110］取向，［200］取向及非晶态三种结构和取向的一维Fe纳米线阵列.对于三种纳米线阵列，测量了它们的磁特性，分析发现具有[200]择优取向纳米线阵列的方形度，各向异性特性和矫顽力都比[110]取向阵列有很大的改善. 关键词： 磁性纳米线 电化学沉积 取向控制     

磁性纳米线反磁化过程的截椭球链模型

依据实际的纳米线形貌，提出了描述磁性纳米线反磁化过程的截椭球链模型.基于此模型，推导了纳米线反磁化过程中不可逆磁化的临界场和矫顽力在一致转动和对称扇形模式下的表达式.同时，还研究了椭球间接触角、单轴磁晶各向异性、外场与链轴方向夹角、截椭球个数和椭球形状因子对临界场和矫顽力的影响.利用该模型解释了镍纳米线的反磁化过程可能是对称扇形的模式. 关键词： 截椭球链模型 反磁化 一致转动 对称扇形     

体超导铟对一维锌超导纳米线超导电性的抑制效应

文章细致研究了超导体铟／一维锌超导纳米线阵列／超导体铟夹心结构的超导电性．实验发现，当锌纳米线的长度在2—6μm、直径等于40nm时，宏观尺寸的超导体铟电极对中间的锌纳米线的超导电性具有反常的抑制作用,即当铟处在超导态时，中间的锌纳米线则停留在正常态．如果施加一个磁场，使超导体铟电极变为正常态，锌纳米线则恢复其超导电性，这种奇异的现象与超导电极材料的类型及锌纳米线的直径和长度有关。     

经典光场相干控制金属纳米线表面等离子体传输

利用全量子力学的方法从理论上研究了利用经典光场相干控制半导体量子点-金属纳米线复合体系中表面等离子体传输特性. 计算中假设金属纳米线表面等离子体具有线性色散关系,半导体量子点具有梯形三能级结构. 分析表明:通过加或不加经典光场,可以控制表面等离子体被反射还是透射;加上光场后,反射峰、透射峰的位置以及两反射峰之间的距离都可以由经典光场控制. 关键词： 表面等离子体 量子点 散射     

基于DNA模板与聚二甲基硅氧烷转移制备钯纳米线的新方法

在聚二甲基硅氧烷衬底上梳理得到DNA阵列,并以DNA为模板通过低温乙醇还原得到Pd纳米线,再通过PDMS转移技术将Pd纳米线转移至不同的衬底,这是一种制备高导电性Pd纳米线的新方法.以DNA为模板的选择性生长控制方法可以显著抑制衬底上无规Pd纳米颗粒的出现. SEM观测制备的Pd纳米线的宽度约为80 nm,连续长度可达14 μm. FESEM、XPS和TEM表征揭示出Pd纳米线是由面心立方结构的Pd纳米晶粒组成,电学测量获得的Pd纳米线的电阻率为1.59 μΩm,仅比体电阻率高约一个量级. 研究还发现通过改变反应时间和温度可以有效调控Pd纳米线的生长过程.     

化学镀制备镍纳米线/管阵列铂钯催化剂载体

以阳极氧化铝作为模板,用化学镀的方法制备了可以用作铂钯复合催化剂载体的镍纳米线和纳米管阵列,利用置换反应将铂钯复合催化剂沉积在镍纳米阵列材料上．SEM图片表明镍纳米线的平均直径 为100 nm,镍纳米管的平均内径为20 nm． EDS扫描的结果表明铂钯元素均匀地分布在阵列材料上．循环伏安研究发现载有铂钯催化剂的镍纳米管阵列对乙醇氧化的电催化活性明显高于载有铂钯催化剂的镍纳米线阵列．     

段化(A/B)m复合纳米线阵列的矫顽力机理

基于球链模型的对称扇形转动机理，考虑了段间的界面交换耦合作用，对利用电化学沉积方法制备的段化复合磁性纳米线六角阵列的磁滞回线进行了系统的研究，提出了矫顽力随复合段数m的变化规律.指出在这种段化复合纳米线阵列中，段间的交换耦合作用对磁化反转起着重要的影响. 关键词： 球链模型 复合纳米线 矫顽力 交换耦合     

Se，Te纳米线系统的结构稳定性研究

采用第一性原理计算及经验方法研究了Se，Te纳米线的结构稳定性. Se与Te的晶体是由三角Se，Te原子链构成并且链间相互作用相对较弱. 小直径的纳米线(<30?)进行了第一性原理计算； 同时对于大直径的纳米线，采用了一种只考虑了链间相互作用的经验方法. 六边形截面的构型比其他各种结构都要稳定，虽然在原子链数目的限制下无法保证其为正六边形. 该结论与被广泛接受的Se，Te纳米线的六边形稳定结构相一致. 关键词： 第一性原理 纳米线 硒 碲     

SOI纳米线波导导光机理的物理分析

SOI（silicon-on-insulator）纳米线波导及其器件是近年来光电子学领域研究的重点内容之一．文章从基本的导波光学理论出发,引入古斯一汉森位移理论,对SOI纳米线波导导光的物理机制进行了分析并给出了物理解释和模拟结果．     

Enhanced Eshelby twist on thin Wurtzite InP nanowires and measurement of local crystal rotation

We have performed a detailed study of the lattice distortions of InP wurtzite nanowires containing an axial screw dislocation. Eshelby predicted that this kind of system should show a crystal rotation due to the dislocation induced torque. We have measured the twisting rate and the dislocation Burgers vector on individual wires, revealing that nanowires with a 10-nm radius have a twist up to 100% larger than estimated from elasticity theory. The strain induced by the deformation has a Mexican-hat-like geometry, which may create a tube-like potential well for carriers.     

Magnetic layer thickness dependence of magnetization reversal in electrodeposited CoNi/Cu multilayer nanowires

The magnetization reversal of electrodeposited CoNi/Cu multilayer nanowires patterned in an array using a hole template has been investigated. The reversal mode is found to depend on the CoNi layer thickness t(CoNi); with increasing t(CoNi) a transition occurs from coherent rotation to a combination of coherent and incoherent rotation at around t(CoNi)=51 nm. The reversal mode has been identified using the magnetic hysteresis loops measured at room temperature for CoNi/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The nanowire samples have a diameter of ∼250 nm and constant Cu layer thickness of 4.2 nm with various t(CoNi) ranging from 6.8 nm to 7.5 μm. With increasing t(CoNi), the magnetic easy axis moves from the direction perpendicular to nanowires to that parallel to the nanowires at around t(CoNi)=51 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped CoNi layers (t(CoNi)=6.8, 12 and 17 nm) is of a coherent rotation type, while that for long rod-shaped CoNi layers (t(CoNi)=150 nm, 1.0, 2.5 and 7.5 μm) can be consistently explained by a combination of coherent rotation and a curling mode. The effects of dipole–dipole interactions between nanowires and between adjacent magnetic layers in each nanowire on the reversal process have been discussed.     

ZnO纳米线的合成与生长机理

采用化学气相沉积系统制备ZnO纳米线,以覆盖一层约5nm厚的Ag薄膜的单晶Si(001)为衬底,纳米线的生长遵循气-液-固(VLS)机理。对得到的样品采用X射线衍射(XRD)和扫描电镜(SEM)进行晶体结构和形貌的表征。XRD结果表明衬底温度在600~700℃时生长的ZnO纳米线具有六方结构和统一的取向。通过扫描电子显微镜分析,比较了生长温度对纳米线直径和长度的影响。实验表明我们可以通过催化剂和温度来实现ZnO纳米线生长的可控。与传统的VLS生长方式不同的是在我们制备的ZnO纳米线顶端并没有看到催化剂颗粒,表明纳米线的生长方式是底部生长,我们对其生长机理进行了研究。     

An optical study of cobalt nanowires dispersed in liquid phase

The Co nanowires were electrodeposited in polycarbonate membrane (PCT). SEM, TEM and XPS techniques were used to characterize the morphology, structure and size of nanowires as well as chemical composition. The influence of different mediums was studied on the optical absorption of dispersed cobalt nanowires. The absorption spectrum of cobalt nanowires in water showed a broad shoulder at 290 nm, but in ethanol solution it was not observed in the visible region of the spectra up to 200 nm. Cobalt nanowires dispersed in methanol presented a peak at 236 nm. We attribute the data to oxidation of cobalt in water and low dielectric constant of methanol relative to ethanol and water. We found rather good agreement between the experimental results and the calculation based on Gans’ theory.     

Growth mechanism studies of ZnO nanowire arrays via hydrothermal method

Well-controlled ZnO nanowire arrays have been synthesized using the hydrothermal method, a low temperature and low cost synthesis method. The process consists of two steps: the ZnO buffer layer deposition on the substrate by spin-coating and the growth of the ZnO nanowire array on the seed layer. We demonstrated that the microstructure and the morphology of the ZnO nanowire arrays can be significantly influenced by the main parameters of the hydrothermal method, such as pH value of the aqueous solution, growth time, and solution temperature during the ZnO nanowire growth. Scanning electron microscopy observations showed that the well oriented and homogeneous ZnO nanowire arrays can be obtained with the optimized synthesis parameters. Both x-ray diffraction spectra and high-resolution transmission electron microscopy (HRTEM) observations revealed a preferred orientation of ZnO nanowires toward the c-axis of the hexagonal Wurtzite structure, and HRTEM images also showed an excellent monocrystallinity of the as-grown ZnO nanowires. For a deposition temperature of 90 °C, two growth stages have been identified during the growth process with the rates of 10 and 3 nm/min, respectively, at the beginning and the end of the nanowire growth. The ZnO nanowires obtained with the optimized growth parameters owning a high aspect ratio about 20. We noticed that the starting temperature of seed layer can seriously influence the nanowire growth morphology; two possible growth mechanisms have been proposed for the seed layer dipped in the solution at room temperature and at a high temperature, respectively.     

Thermal stability of silicon nanowires: atomistic simulation study

Using the Stillinger--Weber (SW) potential model, we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics (MD) simulations. We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires. The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions, and that silicon nanowires with perpendicular dimmer rows on the two (100) surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two (100) surfaces. Furthermore, the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.     

Magnetization reversal dynamics in Co nanowires with competing magnetic anisotropies

We present the magnetization reversal dynamics of Co nanowires with competing magnetic anisotropies. The aspect ratio (R) of the nanowires is varied between 2.5 and 60, and we observe a cross-over of the directions of the magnetic easy and hard axes at R=6.8. Micromagnetic simulations qualitatively reproduce the observed cross-over and give detailed insight into the reversal mechanisms associated with the cross-over. The reversal mechanism for a field applied along the long axis of the nanowire exhibits a quasi-coherent rotation mode and a corkscrew-like mode, respectively, above and below the cross-over, with the formation of a Bloch domain near the cross-over region. For a field applied along the short axis, the reversal occurs by nucleation and propagation of reversed domains from the two ends of the nanowires for very high values of the aspect ratio down to the cross-over region, but it transforms into quasi-coherent rotation mode for smaller aspect ratios (below the cross-over region).     

Anisotropic optical response of GaN and AlN nanowires

We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.