Numerical Simulation on the Photovoltaic Behavior of an Amorphous-Silicon Nanowire-Array Solar Cell

In this letter, we propose an amorphous-silicon (a-Si) solar cell with a nanowire-array structure. The proposed structure has photon absorption and carrier transport that are perpendicular to each other, which could overcome the efficiency limit of an a-Si solar cell. This nanowire structure has an n-type a-Si nanowire array in which the i-layer and the p-layer a-Si are sequentially grown along the surface of the nanowire. Under illumination, light is absorbed along the axial direction of the nanowire, and carrier transport is along the radial direction. Numerical simulations show that the photocurrent of the a-Si solar cell with a 4000-nm-long nanowire is nearly 40% more than that of a planar a-Si solar cell. A conversion efficiency of 11.6% was obtained, which is around 32% enhancement.      

表面结构和生长方向对WO3纳米线电子结构影响的第一性原理研究

The effects of the surface and orientation of a WO₃ nanowire on the electronic structure are investigated by using first principles calculation based on density functional theory（DFT）.The surface of the WO3 nanowire was terminated by a bare or hydrogenated oxygen monolayer or bare WO₂ plane,and the[010]- and[001]-oriented nanowires with different sizes were introduced into the theoretical calculation to further study the dependence of electronic band structure on the wire size and orientation.The calculated results reveal that the surface structure, wire size and orientation have significant effects on the electronic band structure,bandgap,and density of states （DOS） of the WO₃ nanowire.The optimized WO₃ nanowire with different surface structures showed a markedly dissimilar band structure due to the different electronic states near the Fermi level,and the O-terminated[001] WO₃ nanowire with hydrogenation can exhibit a reasonable indirect bandgap of 2.340 eV due to the quantum confinement effect,which is 0.257 eV wider than bulk WO₃.Besides,the bandgap change is also related to the orientation-resulted surface reconstructed structure as well as wire size.     

Deformation of Top‐Down and Bottom‐Up Silver Nanowires

Atomistic simulations are employed to probe the deformation behavior of experimentally observed top‐down and bottom‐up face‐centered cubic silver nanowires. Stable, <110> oriented nanowires with a rhombic and truncated‐rhombic cross section are considered, representative of top‐down geometries, as well as the multiply twinned pentagonal nanowire that is commonly fabricated in a bottom‐up approach. The tensile deformation of a stable, experimentally observed structure is simulated to failure for each nanowire structure. A detailed, mechanistic explanation of the initial defect nucleation is provided for each nanowire. The three geometries are shown to exhibit different levels of strength and to deform by a range of mechanisms depending on the nanowire structure. In particular, the deformation behavior of top‐down and bottom‐up nanowires is shown to be fundamentally different. The yield strength of nanowires ranging from 1 to 25 nm in diameter is provided and reveals that in addition to cross‐sectional diameter, the strength of the nanowires is strongly tied to the structure. This study demonstrates that nanowire structure and size may be tailored for specific mechanical requirements in nanometer‐scale devices.     

InGaAs纳米线雪崩焦平面探测器发展研究

基于InGaAs纳米线的光电探测器,由于其优异的性能而受到广泛的关注和研究。综述了InGaAs纳米线光电探测器的探测机理、材料结构、器件性能和当前的研究现状。讨论了InGaAs纳米线雪崩焦平面探测器结构设计、纳米线材料精密生长、纳米线材料的界面与缺陷控制、纳米线雪崩焦平面器件制备工艺等关键技术。对发展高光子探测效率、低噪声、高增益InGaAs纳米线雪崩焦平面探测器的前景进行了展望。     

直流电沉积法制备铁纳米线阵列及表征

为了制备结构规整的Fe纳米线阵列,以多孔阳极氧化铝(AAO)为模板,采用直流电沉积法制备了Fe纳米线阵列,并利用SEM、TEM、XRD等测试手段对其微观形貌和结构进行了表征。结果表明:所得的Fe纳米线阵列结构规整、直径与模板孔径基本一致,约为250nm,是结构紧密的多晶体。     

垂直纳米线晶体管的制备技术

对目前垂直纳米线晶体管的制备技术进行了综述.首先根据器件结构取向介绍了纳米线晶体管的分类,即水平纳米线晶体管和垂直纳米线晶体管,比较了这两类不同结构晶体管的优缺点,阐述了垂直纳米线晶体管的优势及其潜在应用价值.重点介绍了两种主流的垂直纳米线晶体管的制造方法,即自下而上方法和自上而下方法,自上而下方法则又分为后栅工艺和先栅工艺.随后详细比较了它们之间的不同.最后,对垂直纳米线晶体管制造过程中的工艺挑战进行了分析,提出了几种可行的解决方案,并预测了垂直纳米线晶体管未来的发展趋势,特别是在低功耗器件及3D存储器等方面的发展走向.     

High Aspect Ratio Silicon Nanowire for Stiction Immune Gate-All-Around MOSFETs

A high aspect ratio silicon nanowire is proposed for a stiction immune gate-all-around (GAA) MOSFET on a bulk substrate with a fully CMOS compatible technology. Epitaxially grown SiGe serves as a sacrificial layer to yield a suspended nanowire structure. A high aspect ratio structure derived from an epitaxially grown thick-Si film provides a stiction immune property. The fabricated GAA device on a bulk substrate shows superior short-channel effects and improved drive current. In addition, an extremely long suspended nanowire structure can be implemented to a nand string composed of 64 or longer cells.      

Study of the electrical properties of individual (Ga,Mn)As nanowires

Arrays of (Ga, Mn)As nanowire crystals are synthesized by molecular-beam epitaxy. Electronbeam lithography made possible the fabrication of electric contacts to individual nanowires. The influence of the annealing temperature on the properties of the contacts is studied. The optical annealing temperature is determined to be 160°C. It is found that an increase in the annealing temperature yields structure degradation. From studies of the current-voltage characteristics of the individual nanowire structures, a number of their electrical parameters, such as the resistivity and the mobility of charge carriers are determined.     

Atomic‐Scale Mechanism of Unidirectional Oxide Growth

A fundamental knowledge of the unidirectional growth mechanisms is required for precise control on size, shape, and thereby functionalities of nanostructures. The oxidation of many metals results in oxide nanowire growth with a bicrystal grain boundary along the axial direction. Using transmission electron microscopy that spatially and temporally resolves CuO nanowire growth during the oxidation of copper, herein, direct evidence of the correlation between unidirectional crystal growth and bicrystal grain boundary diffusion is provided. Based on atomic scale observations of the upward growth at the nanowire tip, oscillatory downward growth of atomic layers on the nanowire sidewall and the parabolic kinetics of lengthening, it is shown that bicrystal grain boundary diffusion is the mechanism by which Cu ions are delivered from the nanowire root to the tip. Together with density‐functional theory calculations, it is further shown that the asymmetry in the corner‐crossing barriers promotes the unidirectional oxide growth by hindering the transport of Cu ions from the nanowire tip to the sidewall facets. The broader applicability of these results in manipulating the growth of nanostructured oxides by controlling the bicrystal grain boundary structure that favors anisotropic diffusion for unidirectional, 1D crystal growth for nanowires or isotropic diffusion for 2D platelet growth is expected.     

Three-dimensional CMOL: three-dimensional integration of CMOS/nanomaterial hybrid digital circuits

The CMOS molecular (CMOL) circuit is a promising hybrid structure incorporating the nanowire crossbar into the CMOS integrated circuit (IC) implementation. In this letter, a novel three-dimensional (3D) architecture of the CMOL circuit is introduced. This structure eliminates the special pin requirement of the original CMOL designs, providing a feasible and efficient solution to build the practical CMOL circuits. In this 3D structure, the density of the nanowire crossbar is doubled. Such a high-density implementation enables the 3D CMOL technology to leap ahead of the IC roadmap by more than three generations.     

Shape Evolution of Highly Lattice-Mismatched InN/InGaN Nanowire Heterostructures

We have investigated the structure and shape of GaN-based nanowires grown on (001) Si substrates for optoelectronic device applications. The nanowire heterostructures contained InN disks and In_0.4Ga_0.6N barrier layers in the active region. The resulting nanowire array comprised two differently shaped nanowires: shorter pencil-like nanowires and longer bead-like nanowires. The two different nanowire shapes evolve due to a variation in the In incorporation rate, which was faster for the bead-like nanowires. Both types of nanowires exhibited evidence of significant migration of both Ga and In during growth. Ga tended to diffuse away and down along the sidewalls, resulting in a Ga-rich shell for all nanowires. Despite the complex structure and great variability in the In composition, the optical properties of the nanowire arrays were very good, with strong luminescence peaking at ～ 1.63 μm.     

High-resolution ultrahigh-vacuum electron microscopy of helical gold nanowires: junction and thinning process

Helical multishell (HMS) gold nanowires were observed in situ by ultra-high-vacuum electron microscopy. During thinning of the helical nanowire, a junction was formed between two nanowires of different diameter. The structure of the gold junction is proposed in comparison with the multiwall carbon nanotube. The gold junction has a dislocation-like core to accommodate the number difference of the atomic rows that compose the HMS nanowires, while the carbon junction has a pair of five- and seven-membered rings. Thinning of the helical gold nanowire by electron-beam radiation can be caused by the climbing motion of the dislocation-like core along the nanowire.     

自组装法合成导电聚吡咯纳米线

以多孔氧化铝为模板,合成导电聚吡咯纳米线。利用SEM对聚吡咯进行了表征,结果表明:在吡咯单体浓度为0.2 mol/L,电压1.0 V,时间1 600 s的条件下,制得的聚吡咯会有大量的微触手结构出现,且表面光滑,比表面积较大,并初步探究了聚吡咯微触手结构的形成机理。     

三维纳米线SAW气体传感器及报警器设计

该文提出了一种全新的三维纳米线结构的声表面波(SAW)气体传感器,详细阐述了谐振型SAW器件上纳米线制备与修饰改性设计,传感器信号提取电路设计及报警器设计等过程,最后研制出气体报警器样品。并利用沙林（GB）模拟剂对传感器性能指标进行了测试,该传感器的响应阈值低达2 mg/m3,响应时间仅约为20 s。结果表明,与传统二维结构的SAW气体传感器相比,三维纳米线结构的SAW气体传感器在响应阈值和响应时间上均有很大的提高。     

Assessment of structure variation in silicon nanowire FETs and impact on SRAM

Impact of device structure variability of silicon nanowire FETs is assessed and SRAM design implication is presented based on 3-D numerical simulation. Both the conventional and junctionless nanowire FETs are shown to be sensitive to structural variation whereas the former is more tolerable. Both the circular wire and non-circular wire cases for feasible SRAM design with a focus on read/write noise margin are included in our study.     

纯闪锌矿结构GaAs纳米线的等高生长研究

本文报道了金辅助生长纯闪锌矿结构GaAs纳米线,它采用金属有机化学气相沉淀技术运用气-液-固生长机制在GaAs(111)B衬底上生长而形成。实验结果显示GaAs纳米线具有圆柱状的均匀形貌,并且生长速率与直径无关。透射电子显微镜研究显示,GaAs纳米线是无缺陷的纯闪锌矿结构的晶体。实验结果表明Au-Ga合金在纳米线生长过程中是作为热解催化剂而不是扩散原子的收集器,较大的催化剂直径以及催化剂液滴中高的过饱和度是得到等高生长的纯闪锌矿结构GaAs纳米线的原因。     

银纳米线表面等离子体波导的传输损耗特性研究

通过远场聚焦光斑激发银纳米线表面等离子体激元(SPP: Surface Plasmon Polariton),并搭建银纳米线路由传输结构改变SPP的传输距离,研究了SPP的传输损耗特性。实验上测量了置于玻璃衬底表面的银纳米线在不同激发波长时SPP的传输损耗系数,发现SPP的传输损耗具有波长依赖性：632.8nm激光激发时,传输损耗系数为0.115 ,780nm激光激发时,传输损耗系数为0.0923 ,即传输损耗系数在长波激发时小,而在短波激发时大。测量结果对基于银纳米线波导的集成微纳光学系统设计有很好的指导作用。     

Scaling of Nanowire Transistors

This paper considers the scaling of nanowire transistors to 10-nm gate lengths and below. The 2-D scale length theory for a cylindrical surrounding-gate MOSFET is reviewed first, yielding a general guideline between the gate length and the nanowire size for acceptable short-channel effects. Quantum confinement of electrons in the nanowire is discussed next. It gives rise to a ground-state energy and, therefore, a threshold voltage dependent on the radius of the nanowire. The scaling limit of nanowire transistors hinges on how precise the nanowire size can be controlled. The performance limit of a nanowire transistor is then assessed by applying a ballistic current model. Key issues such as the density of states of the nanowire material are discussed. Comparisons are made between the model results and the published experimental data of nanowire devices.      

Size-independent growth of pure zinc blende GaAs nanowires

Pure zinc blende GaAs nanowires were grown by metal organic chemical vapor deposition on GaAs (111) B substrates via Au catalyzed vapor-liquid-solid mechanism. We found that the grown nanowires are rod-like in shape and have a pure zinc blende structure; moreover, the growth rate is independent on its diameters. It can be concluded that, direct impingement of vapor species onto the Au-Ga droplets contributes to the growth of the nanowire; in contrast, the adatom diffusion makes little contribution. The results indicate that the droplet acts as a catalyst rather than an adatom collector, larger diameter and high supersatuation in the droplet leads to the pure zinc blende structure of the nanowire.     

The Features of GaAs Nanowire SEM Images

The detailed study of GaAs nanowires synthesized by molecular beam epitaxy performed by scanning electron microscopy allowed to reveal the presence of specific contrast in the images obtained. To understand the causes of the phenomenon the transmission electron microscopy of nanowire crystal structure was carried out. The results showed that it could be caused by the segments having polytypic crystal phase. It was also confirmed by the modelling of the electron beam scattering on such nanowire arrays.