Generalized surface thermodynamics with application to nucleation

Gibbs formulated a complete and general thermodynamics for surfaces in multicomponent fluid systems. When considering solid–fluid surfaces, he restricted attention to single-component solids in contact with fluids that could contain multiple components. Attempts that have been offered to generalize Gibbs’ results for surfaces between multicomponent solids and fluid are problematic owing to the difficulty that the surface chemical potentials for components that also reside on substitutional lattice sites in the solids are not well defined. Therefore any expressions involving these surface chemical potentials, such as the conventional definition of the surface energy, will also not be well defined. In order to formulate a general thermodynamics of equilibrium that takes into account capillary effects in systems containing surfaces between a multicomponent solids and fluids, it is shown that the concept of thermodynamic availability (exergy) can be employed that, when applied to surfaces, depends on the extensive but not the intensive variables (such as the chemical potentials) of the surfaces. Using this approach, Gibbs–Thomson–Freundlich effects for finite-size solids, an adsorption equation for solid–fluid surfaces and the thermodynamics of nucleation during solidification can be treated in a straightforward manner without referring to the ill-defined surface chemical potentials. A derivation is given that appears to be the first one that properly generalizes Gibbs’ analysis for the reversible work to form a critical nucleus to the case of solidification.     

晶格失配对异质外延超薄膜生长中成核特性的影响

利用动力学蒙特卡罗方法模拟了异质外延超薄膜生长中的成核过程.研究了薄膜与衬底的晶格失配对超薄膜生长中成核密度、平均核尺寸、标度关系及生长模式的影响.结果发现产生压（张）应变的晶格负（正）失配使生长过程更早（迟）从成核区进入过渡区，失配越大，这一效应越明显.在相同的沉积条件下，负失配导致超薄膜形成较低的成核密度与较大的平均核尺寸，而正失配则相反.成核密度满足标度关系Ns≈(F/D)χ，随着失配度从-0.04增加到0.02，标度系数χ从0.37逐渐减小到0.33，对应超薄膜生长过程从包含二聚体扩散模式转变到无 关键词： 薄膜生长 成核 晶格失配 蒙特卡罗模拟     

片上制备横向结构ZnO纳米线阵列紫外探测器件

将纳米技术与传统的微电子工艺相结合, 片上制备了横向结构氧化锌(ZnO)纳米线阵列紫外探测器件, 纳米线由水热法直接自组织横向生长于叉指电极之间, 再除去斜向的多余纳米线, 其余工艺步骤与传统工艺相同. 分别尝试了铬(Cr)和金(Au)两种金属电极的器件结构: 由于Cr电极对其上纵向生长的纳米线有抑制作用, 导致横向生长纳米线长度可到达对侧电极, 光电响应方式为受表面氧离子吸附控制的光电导效应, 光电流大但增益低, 响应速度慢, 经二次电极加固, 纳米线根部与电极金属直接形成肖特基接触, 光电响应方式变为光伏效应, 增益和速度得到了极大改善; 由于Au电极对其上纵向生长的纳米线有催化作用, 导致溶质资源的竞争, 相同时间内横向生长的纳米线不能到达对侧, 而是交叉桥接, 但却形成了紫外光诱导的纳米线间势垒结高度调控机理, 得到的器件特性为最优, 在波长为365 nm的20 mW/cm²紫外光照下, 1 V电压时暗电流为10^-9 A, 光增益可达8×10⁵, 响应时间和恢复时间分别为1.1 s和1.3 s.     

磁控溅射ZnO薄膜的成核机制及表面形貌演化动力学研究

利用原子力显微镜分析了ZnO薄膜在具有本征氧化层的Si(100)和Si(111)基片上的表面形貌 随沉积时间的演化. 通过对薄膜生长形貌的动力学标度表征，研究了射频反应磁控溅射条件 下，ZnO薄膜的成核过程及生长动力学行为. 研究发现，ZnO在基片表面的成核过程可分为初 期成核阶段、低速率成核阶段和二次成核阶段. 对于Si(100)基片，三个成核阶段的生长指 数分别为β₁=1.04，β₂=0.25±0.01，β₃=0.74；对 于Si(11 关键词： ZnO薄膜 磁控溅射 生长动力学 成核机制     

双栅调控的硅量子线中的库仑振荡效应

基于单电子隧穿和库仑阻塞效应,研究了硅量子线中的单电子输运特性.利用绝缘体上硅薄膜材料作为衬底构建侧栅结构的硅量子线单电子晶体管,通过背栅和侧栅对量子线的电子输运特性进行调制.实验发现,在硅量子线中分别观察到背栅和侧栅调制的单电子效应和库仑振荡现象.从微分电导的二维灰度轮廓图,清楚地观察到了库仑阻塞区,说明由于栅压导致在硅量子线中形成了库仑岛. 关键词： 库仑振荡 单电子效应 硅量子线     

Heterogeneous nucleation and growth of silver nanoparticles on unmodified polystyrene spheres by in situ reduction

The in situ reduction growth of Ag nanoparticles (NPs) on unmodified polystyrene (PS) spheres is investigated via controlling Ag nucleation and growth rates by continuous dripping addition of reductant solution in the absence of surfactants. The sub-micro PS spheres were coated by a uniform coverage of Ag NPs with several shapes like elongated islands, spherical particles, and particle aggregates. The reaction temperature and reductant concentration are demonstrated to influence the crystal structure, distribution, and stability of the Ag NPs on the PS substrates. The heterogeneous nucleation and growth of Ag NPs on PS spheres are found to depend on the inhibition of in-solution reduction and homogeneous nucleation.     

Inexpensive and highly controlled growth of zinc oxide nanowire: Impacts of substrate temperature and growth time on synthesis and physical properties

Zinc oxide nanowires (ZnO NWs) were synthesized using a simple reactive-evaporation method without the use of catalysts. The NWs growth was precisely controlled by adjusting the experimental conditions mainly growth times and substrate temperatures. These experimental parameters are crucial for the growth of NWs. The typical diameter and length of the highly crystalline NWs obtained are several tens and several hundred nanometers, respectively. The nature of early-stages growth, morphology, structure and photoluminescent properties of the NWs grown at low temperatures have been explained and give the basic reasons behind these growth mechanisms. Self-organized ZnO nuclei are primarily formed on FTO pits due to high density of Zn atoms. It can be ascribed to vapour-solid with an area selected growth of NWs which provide a continuous pathway for carrier transport due to direct contact with the substrate. These features are crucial for the application of electronic devices, solar cells, etc.     

单根砷掺杂氧化锌纳米线场效应晶体管的电学及光学特性

采用化学气相沉积（CVD）的方法在砷化镓基底上合成直径为20 nm左右、长约数十微米的氧化锌纳米线,然后采用热扩散的方法,将生长于砷化镓基底之上的氧化锌纳米线通过600 ℃,30 min的有氧退火处理后,获得了砷掺杂的氧化锌纳米线.将获得的掺杂后的氧化锌纳米线采用电子束曝光以及真空溅射镀膜的方法将钛/金合金作为接触电极引出,从而构建成场效应晶体管.文中研究了单根氧化锌纳米线砷掺杂前后的电学特性,证实了通过砷掺杂来获得p型的氧化锌纳米线的可行性.构建的p型砷掺杂氧化锌场效应晶体管的跨导为35 nA/V,载流 关键词： p型ZnO纳米线 砷掺杂 场效应晶体管 光致发光     

A computer simulation of nucleation and growth of thin films

~~A computer simulation of nucleation and growth of thin films~~     

The effect of substrate on magnetic properties of Co/Cu multilayer nanowire arrays

Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.     

Decline of nucleation in the heating process with a high heating rate

The effect of the heating rate on the nucleation of metallic glass in a rapid heating process starting from the glass transition temperature is investigated. The critical nucleus radius increases with the increase of the temperature of the undercooling liquid. If the increment rate of the critical nucleus radius, owing to the heating process, is higher than the growth rate of the nuclei, the nuclei generated at the low temperature will become the embryos at the high temperature. This means that the high heating rate can make no nucleation happen in the heating process. In consideration of the interfacial energy, the growth rate of the nuclei increases with the increase of their size and the growth rate of the critical nucleus is zero. Thus, the lower heating rate can also make the nuclei decline partially. Finally, this theory is used to analyze the nucleation process during laser remelting metallic glass.     

Effect of Mn-doping on the growth mechanism and electromagnetic properties of chrysanthemum-like ZnO nanowire clusters

Chrysanthemum-like ZnO nanowire clusters with different Mn-doping concentrations are prepared by a hydrothermal process. The microstructure, morphology and electromagnetic properties are characterized by x-ray diffractometer high-resolution transmission electron microscopy (HRTEM), a field emission environment scanning electron microscope (FEESEM) and a microwave vector network analyser respectively. The experimental results indicate that the as-prepared products are Mn-doped ZnO single crystalline with a hexagonal wurtzite structure, that the growth habit changes due to Mn-doping and that a good magnetic loss property is found in the Mn-doped ZnO products, and the average magnetic loss tangent tanδ_m is up to 0.170099 for 3% Mn-doping, while the dielectric loss tangent tanδ_e is weakened, owing to the fact that ions Mn^{2 +} enter the crystal lattice of ZnO.     

Ballistic transport and quantum interference in InSb nanowire devices

An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron's wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.     

金属纳米线弹性性能的尺寸效应及其内在机理的模拟研究

本文应用分子动力学(MD)方法和改进分析型嵌入原子模型(MAEAM)研究了Ni, Al和V纳米线的弹性性能尺寸效应及表面对其影响, 并计算了相应完整晶格材料的弹性性能. 结果表明本文计算完整晶格材料的弹性性能与已有实验和理论的结果相符合. 而计算所得各金属纳米线的体模量明显低于相应块体材料的结果, 且随纳米线的尺寸增加而呈指数增加, 并接近于常数. 在此基础上, 通过研究Ni, Al和V纳米线表面能的尺寸效应及其分布特征进一步探讨了自由表面在尺寸影响纳米线弹性性能过程中的作用及其内在机理.     

Dew nucleation and growth

Dew is the condensation of water vapor into liquid droplets on a substrate. It is characterized by an initial heterogeneous nucleation on a substrate and a further growth of droplets. The presence of a substrate that geometrically constrains the growth is the origin of the peculiarities and richness of the phenomenon. A key point is the drop interaction through drop fusion or coalescence, which leads to scaling in the growth and gives universality to the process. As a matter of fact, growth dynamics are only dependent on substrate and drop dimensionality. Coalescence events lead to temporal and spatio-temporal fluctuations in the substrate coverage, drop configuration, etc., which give rise to a very peculiar dynamics. When the substrate is a liquid or a liquid crystal, the drop pattern can exhibit special spatial order, such as crystalline, hexatic phases and fractal contours. Condensation on a solid substrate near its melting point can make the drop jump.The applications of monitoring dew formation are manifold. Examples can be found in medicine (sterilization process), agriculture (green houses) and hydrology (production of drinkable water). To cite this article: D. Beysens, C. R. Physique 7 (2006).     

An analytic model for gate-all-around silicon nanowire tunneling field effect transistors

An analytical model of gate-all-around(GAA) silicon nanowire tunneling field effect transistors(NW-TFETs) is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling(BTBT) efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane’s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.