Gallium-Catalyzed Silicon Oxide Nanowire Growth

Silicon oxide nanowires tend to assemble into various complex morphologies through a metalcatalyzed vapor-liquid-solid （VLS） growth process. This article summarizes our recent efforts in the controlled growth of silicon oxide nanowire assemblies by using molten gallium as the catalyst and silicon wafer, SiO powder, or silane （Sill4） as the silicon sources. Silicon oxide nanowire assemblies with morphologies of carrotlike, cometlike, gourdlike, spindlelike, badmintonlike, sandwichlike, etc. were obtained. Although the morphologies of the nanowire assemblies are temperatureand silicon source-dependent, they share similar structural and compositional features： all the assemblies contain a microscale spherical liquid Ga ball and a highly aligned, closely packed amorphous silicon oxide nanowire bunch. The Ga-catalyzed silicon oxide nanowire growth reveals several interesting new nanowire growth phenomena that expand our knowledge of the conventional VLS nanowire growth mechanism.     

带隙渐变纳米线的制备及其非线性光学效应研究

由于一般的半导体纳米材料只有单一带隙,限制了其应用范围。通过搭建气–液–固法生长纳米线的实验装置,引入金作为催化剂,并加入移动源,成功制备出单根带隙渐变的硫硒化镉纳米线。其成分从一端的纯硫化镉连续过渡到另一端的纯硒化镉,对应的带隙从2.44 e V渐变到1.74 e V。并使用波长为405 nm的激光照射该纳米线,得到它的荧光光谱图来证实其带隙呈渐变状态。利用波长为1 064 nm的激光,将其耦合进单根纳米线中,产生了532 nm的绿色倍频光和双光子荧光,这说明硫硒化镉纳米线具有二阶和三阶的非线性光学效应。     

Reducing Zn diffusion in single axial junction InP nanowire solar cells for improved performance

In this work axial n-i-p junction InP nanowires were grown by selective-area metal organic vapor phase epitaxy (SA-MOVPE) technique with the growth sequence starting from n-segment. The optical properties and carrier lifetimes of the n-, i- and p-type segments were studied and compared using time-resolved photoluminescence (PL) and cathodoluminescence (CL) measurements. We demonstrate for the first time that CL is capable of resolving the electrical profile of the nanowires, namely the varied lengths of the n-, i- and p-segments, providing a simple and effective approach for nanowire growth calibration and optimization. The CL result was further confirmed by electron beam induced current (EBIC) and photocurrent mapping measurements performed from the fabricated single nanowire solar cell devices. It is revealed that despite a non-optimized device structure (very long n-region and short i-region), the n-i-p nanowire solar cells show improved power conversion efficiency (PCE) than the previously reported p-i-n (growth starts with p-segment) single nanowire solar cells due to reduced p-type dopant (Zn) diffusion during the growth of n-i-p solar cell structure.     

金纳米线阵列的制备及其光学性能研究

采用二次阳极氧化法制备了高度有序的多孔氧化铝模板,并基于该氧化铝模板,采用脉冲直流电化学沉积的方法制备了金纳米线阵列.利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）和X线衍射仪（XRD）对所制备的金纳米线的形貌及晶体结构进行分析.结果表明：不同的沉积电压下制备的金纳米线具有不同的生长取向性,当沉积电压为3V时制备出的金纳米线沿[200]方向具有明显的生长取向性.利用紫外-可见光谱（UV-Vis）对金纳米线阵列光学性能进行研究,发现金纳米线的等离子体共振吸收峰随着沉积电压的增大先蓝移而后发生红移.     

电沉积Ni纳米线阵列及其磁学性能研究

为了解决因受阳极氧化铝(AAO)孔道直径限制导致合成的金属纳米线尺寸单一、磁性受限的问题,采用二次阳极氧化法制备了不同孔径的阳极氧化铝(AAO)模板,依据模板辅助电沉积法,在不同孔径AAO模板内生长了Ni纳米线阵列,利用SEM,TEM,XRD和EDS等技术对制备的Ni纳米线阵列形貌、微观结构和成分进行表征,通过物理性能...     

金催化合成硫化锌纳米线及其发光性质的研究

采用金催化和直接蒸发ZnS粉末的方法,合成出大量具有纤锌矿结构的单晶ZnS纳米线。该纳米线的线径均匀,线形规则,直径在80~120 nm,长度约几十微米。研究发现纳米线的形貌对合成的温度很敏感,合成温度的升高会导致纳米线直径的迅速增加。单根纳米线EDS分析表明,ZnS纳米线线体中均匀分布着Au元素,Au元素的掺入是纳米线生长形成后由端部颗粒通过固态扩散进入纳米线中。室温光致发光谱显示:ZnS纳米线有两个发光峰,分别位于446 nm和520 nm处。446 nm的发光峰是由缺陷所致,而520 nm左右的发光峰是由Au元素掺杂所致。     

Si纳米线的制备方法与器件应用

以气-液-固(VLS)、气-固-固(VSS)、固-液-固(SLS)和氧化物辅助生长(OAG)机制为主线,着重介绍与评论了几种主要的Si纳米线的制备方法,如激光烧蚀沉积(LAD)、化学气相沉积(CVD)、热蒸发和金属(Au,Fe,Ni和Al)催化生长等.简要介绍了Si纳米线及其阵列在场效应晶体管、场发射器件、太阳电池、传感器以及集成电子器件等方面的应用.最后,讨论了各种制备方法的优势与不足,指出了该研究领域今后的发展方向.     

氧分压对Mn-Co-Ni-O纳米结构生长的影响

在脉冲激光沉积（pulsed laser deposition,PLD）法生长氧化物纳米材料的过程中,环境中的氧气对氧化物纳米结构的形成起着至关重要的作用。在溅射了Au纳米层的Si(111)衬底上,采用PLD法在不同氧分压下制备了Mn-Co-Ni-O纳米结构,并用X射线衍射仪（X-ray diffractometer,XRD）和场发射扫描电子显微镜（scanning electron microscope,SEM）表征了Mn-Co-Ni-O的结构特性和表面形貌。研究发现生长温度为750 ℃的Mn-Co-Ni-O微观结构与氧分压密切相关。在较低的氧分压环境下(1 Pa和5 Pa),Si衬底上生长的Mn-Co-Ni-O纳米锥结构是由Au催化的气–液–固(vapor-liquid-solid,VLS)生长机制控制。当氧分压增加到15 Pa,Mn-Co-Ni-O纳米结构的形态从纳米锥向纳米线转变,该过程是由VLS和气–固(vapor-solid,VS)生长机制共同作用。深入研究Mn-Co-Ni-O纳米结构的生长机制为获得更多的纳米线提供了理论基础。     

A III-V nanowire channel on silicon for high-performance vertical transistors

Silicon transistors are expected to have new gate architectures, channel materials and switching mechanisms in ten years' time. The trend in transistor scaling has already led to a change in gate structure from two dimensions to three, used in fin field-effect transistors, to avoid problems inherent in miniaturization such as high off-state leakage current and the short-channel effect. At present, planar and fin architectures using III-V materials, specifically InGaAs, are being explored as alternative fast channels on silicon because of their high electron mobility and high-quality interface with gate dielectrics. The idea of surrounding-gate transistors, in which the gate is wrapped around a nanowire channel to provide the best possible electrostatic gate control, using InGaAs channels on silicon, however, has been less well investigated because of difficulties in integrating free-standing InGaAs nanostructures on silicon. Here we report the position-controlled growth of vertical InGaAs nanowires on silicon without any buffering technique and demonstrate surrounding-gate transistors using InGaAs nanowires and InGaAs/InP/InAlAs/InGaAs core-multishell nanowires as channels. Surrounding-gate transistors using core-multishell nanowire channels with a six-sided, high-electron-mobility transistor structure greatly enhance the on-state current and transconductance while keeping good gate controllability. These devices provide a route to making vertically oriented transistors for the next generation of field-effect transistors and may be useful as building blocks for wireless networks on silicon platforms.     

基于蒙特卡洛法的硅纳米线热导率研究

声子在纳米尺度下的输运需要考虑量子效应与边界效应,通过解析方法获得其传输特性比较困难,采用蒙特卡洛方法(Monte Carlo,MC)构建了声子在体态硅与硅纳米线结构中的输运模型,简化了边界散射的选择机制与处理方法.在15～1 000 K的温度范围内,对体态硅的热导率进行了模拟,验证了MC模型对本征散射处理方法的正确性,进而模拟了等效直径为22,37与56 nm的硅纳米线在15～315 K温度范围内的热导率,37和56 nm硅纳米线热导率与实验值符合较好,22 nm硅纳米线热导率比实验值偏大.分析认为随着等效半径的减小,声子色散曲线发生改变,迟豫时间减小,声子发生边界散射的频率增加,导致热阻增大.基于以上分析,通过对边界散射迟豫时间的修正,获得了与实验值较为一致的模拟结果.     

SnO2纳米线的制备及结构表征

以SnO₂粉末和碳粉的混合物为源,高纯氮气为载气,利用化学气相沉积法在1 000 ℃下,在溅有Au的单晶Si衬底上制备了SnO₂纳米线。用SEM、XRD测试技术对样品进行了结构、形貌的表征,利用PL技术分析了样品的发光特性。由分析可知,样品均为四方金红石结构,退火时间对样品形貌具有一定的影响,但不影响其结构。所制备的SnO₂纳米线结晶质量较高,其生长遵循VLS机制。     

基于SPH方法连续液滴撞击固壁面模拟

 为了研究连续液滴对固壁面的撞击影响, 引入一种纯Lagrange、无网格计算方法, 即光滑粒子流体动力学方法(SPH)。对连续液滴撞击固壁面的扩散、回弹及飞溅进行了数值模拟并与实验测试进行比对。结果表明:连续液滴撞击固壁面时, 液滴的自由表面变化具有许多不确定性, 其中次生液滴的产生和韦伯数的作用是影响液滴撞击扩散的主因。次生液滴的出现使得液滴扩散及飞溅变得更为明显, 韦伯数越大, 连续液滴的无量纲直径变化越快。模拟效果真实反映了液滴撞击过程, 可为类似撞击问题的仿真分析提供借鉴。     

Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures

Substantial effort has been placed on developing semiconducting carbon nanotubes and nanowires as building blocks for electronic devices--such as field-effect transistors--that could replace conventional silicon transistors in hybrid electronics or lead to stand-alone nanosystems. Attaching electric contacts to individual devices is a first step towards integration, and this step has been addressed using lithographically defined metal electrodes. Yet, these metal contacts define a size scale that is much larger than the nanometre-scale building blocks, thus limiting many potential advantages. Here we report an integrated contact and interconnection solution that overcomes this size constraint through selective transformation of silicon nanowires into metallic nickel silicide (NiSi) nanowires. Electrical measurements show that the single crystal nickel silicide nanowires have ideal resistivities of about 10 microOmega cm and remarkably high failure-current densities, >10(8) A cm(-2). In addition, we demonstrate the fabrication of nickel silicide/silicon (NiSi/Si) nanowire heterostructures with atomically sharp metal-semiconductor interfaces. We produce field-effect transistors based on those heterostructures in which the source-drain contacts are defined by the metallic NiSi nanowire regions. Our approach is fully compatible with conventional planar silicon electronics and extendable to the 10-nm scale using a crossed-nanowire architecture.     

钛纳米线力学、热学和电子性质的结构与尺寸依赖性

为了研究金属纳米物理性质与结构和尺寸之间的关系,我们选择不同结构和生长序列的几个典型的超细Ti纳米线,即四边形、五边形和六边形序列,以及六边形序列的两个较大体系,以分别考察结构和尺寸效应.我们计算了Ti纳米线的角关联函数和振动谱,电子态密度用平面波赝势的密度泛函电子结构自洽场计算.采用分子动力学方法研究Ti纳米线的热力学融化行为.结果表明,Ti纳米线的振动性质和电子性质表现出渐进的尺寸演化和明显的结构关联;较小的纳米线的电子态密度是类似分子的离散谱,而当线的直径大于1*!nm时便表现为类似体材料的电子结构.Ti纳米线的融化行为既不同于团簇也不同样块体材料,表现出明显的结构和尺寸依赖性.对较大尺寸的纳米线,我们观察到从螺旋多壳的圆柱体到类似块体的结构相变.     

碳热还原制备碳化硅纳米线

以二氧化硅粉和竹炭粉为原料,在无催化剂的条件下,于1 400℃下用碳热还原制备了SiC纳米线.采用X射线衍射(XRD)、扫描电镜(SEM)和能谱(EDS)分析了该纳米线的形貌和化学组成,同时探讨了SiC纳米线的形成机理.结果表明,所制备的纳米线为β-SiC,纳米线直径为100～150 nm,长度可达数毫米.     

ZnO纳米线膜的可控生长及其量子限域效应研究

针对ZnO半导体低维纳电子/光电子器件中纳米线膜的可控性差及其所导致的特性不稳定问题,利用ZnO纳米籽晶层作为引导层,以实现ZnO纳米线膜的垂直取向生长和尺度分布可控制备,并研究低维量子限域效应对ZnO纳米线膜光电特性的影响机制,利用湿化学法在氧化铟锡导电玻璃上制备ZnO籽晶层,随后利用低温水热法进行ZnO纳米线膜的引导生长,样品的显微结构和物相分析表明,通过调节籽晶热处理温度和生长液浓度能够实现ZnO纳米线直径在10～100nm内可调,籽晶热处理温度对纳米线尺度分布影响尤其显著.室温光致发光(PL)谱测试及分析表明,直径小于20nm的ZnO纳米线薄膜样品的PL谱的近紫外带边发射峰相比于更大直径的纳米线样品发生了明显的蓝移,而且半高宽显著减小.利用量子限域效应理论对PL谱带边发射峰随纳米线的尺度分布发生变化的规律进行了合理分析.     

GaN纳米线的成核及生长机制研究

报道了利用CVD方法研究GaN纳米线的成核和生长机理的最新结果,着重强调了生长温度和催化剂对纳米线生长的影响。通过分析GaN纳 米线的形貌、显微结构与生长温度、催化剂等影响因素之间的依赖关系,详细研究了GaN纳米线的生长过程。这一结果有助于了解一维纳米结构的生长机理,实现纳米材料的可控制生长,并有可能直接应用于GaN纳米器件的制备。     

取向ZnO纳米线阵列的生长机理及发光特性

用化学气相沉积法制备了圾向纳米氧化锌（ZnO）阵列；用扫描电镜（SEM）和透射电镜（TEM）观察了制备的纳米ZnO的形貌结构;用荧光光谱仪（PL）分析了样品的发光特性；以气-液-固（VLS）生长模型和Ehrlich-Schwoebel势垒理论解释讨论了ZnO纳米线的生长结构与机理。     

纳米金修饰硅纳米线电极阳极溶出法测定痕量铅、铜

以浸入沉积的方法在硅纳米线上修饰了金纳米颗粒,并通过电子扫描显微镜（SEM）和X射线荧光分析（XRF）对金纳米粒子修饰的硅纳米线电极表面形貌进行了表征.以修饰后的硅纳米线电极作为工作电极,采用阳极溶出法检测水中痕量铅和铜,考察pH值、富集电位和富集时间对溶出峰的影响,优化出最佳实验条件.在优化的实验条件下,铅Pb2＋和铜Cu2＋的灵敏度分别为0.649μA/（μg.L-1）和0.177μA/（μg.L-1）.检测极限达到0.26μg.L-1和0.67μg.L-1.峰电流与离子浓度在质量浓度25~200μg.L-1的范围内形成良好的线性关系.     

Si纳米线的Au催化固-液-固生长与结构表征

为:Au膜层厚度为5～10 nm,温度为1 100 ℃,N2气流量为1.5 L/min.