Si纳米线的固-液-固可控生长及其形成机理分析

以Au膜作为金属催化剂,直接从n-(111)Si单晶衬底上制备了直径为30—60nm和长度从几微米到几十微米的高质量Si纳米线.实验研究了Au膜层厚、退火温度、N2气流量和生长时间对Si纳米线形成的影响.结果表明,通过合理选择和优化组合上述各种工艺条件,可以实现直径、长度、形状和取向可控的纳米线生长.基于固-液-固生长机理,定性阐述了Si纳米线的形成过程.     

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。     

大规模制备Ni80Fe20纳米线阵列及其磁学特性研究

利用电化学沉积方法在高度有序纳米孔氧化铝模板中大规模制备了Ni80 Fe20纳米线阵列.该方法得到的Ni80Fe20纳米线产率高(约1012-1013/cm2),而且这些纳米线阵列具有(111)择优生长取向和很高的纵横比.与体材料相比,这些Ni80Fe20纳米线阵列具有更高的矫顽力和较大的剩磁比等性能,在微型磁性元件领域将具有广泛应用前景.     

Tl-2212超导薄膜的制备

以铝酸镧晶体为基片,采用两步法制备Tl-2212超导薄膜,包括在低温(150℃)下利用激光脉冲沉积(PLD)工艺沉淀Ba2CaCu2Ox非晶前驱体薄膜和在高温(740～830℃)下前驱体薄膜的铊化结晶、取向生长过程.实验结果表明所制得的膜的相组成为Tl-2212,表面存在大量均匀分布的成分为Tl2Ba2CaCu2Ox的亚微米颗粒.其零电阻温度为101K.薄膜与基片之间界面清晰,没有过渡层,薄膜具有良好的c取向外延条纹.     

硅(001)图形衬底上锗硅纳米线的定位生长

纳米线的定位生长是实现纳米线量子器件寻址和集成的前提.结合自上而下的纳米加工和自下而上的自组装技术,通过分子束外延生长方法,在具有周期性凹槽结构的硅(001)图形衬底上首先低温生长硅锗薄膜然后升温退火,实现了有序锗硅纳米线在凹槽中的定位生长,锗硅纳米线的表面晶面为(105)晶面.详细研究了退火温度、硅锗的比例及图形周期对纳米线形成与否,以及纳米线尺寸的影响.     

T1—2212超导薄膜的制备

以铝酸镧晶体为基片，采用两步法制备T1-2212超导薄膜，包括在低温(150℃)下利用激光脉冲沉积(PLD)工艺沉淀Ba2CaCu2Ox非晶前驱体薄膜和在高温(740～830℃)下前驱体薄膜的铊化结晶、取向生长过程，实验结果表明所制得的膜的相组成为T1-2212，表面存在大量均匀分布的成分为T12Ba2CaCu2Ox的亚微米颗粒，其零电阻温度为101K，薄膜与基片之间界面清晰，没有过渡层，薄膜具有良好的c取向外延条纹。     

不同气氛下SiOx纳米线的制备及形貌、红外、光致发光研究

以N2/H2、N2或NH3为载气,利用碳辅助化学气相沉积法,常压1140℃下在石英衬底上制备了大量直径为20-300 nm,长数百微米的非晶SiOx纳米线.制备得到的纳米线具有高度定向生长的特性.利用透射电子显微镜、扫描电子显微镜及电子能谱对SiOx纳米线的形貌及组分进行了分析,Si与O原子之比为1∶1.8.傅里叶红外吸收谱显示了非晶氧化硅的三个特征峰(482,806和1095 cm-1)及1132 cm-1无序氧化硅结构的强吸收峰.SiOx纳米线光致发光光谱(PL)在440 nm(2.83 eV)处具有较强的荧光峰;N2为载气生长的SiOx纳米线的PL峰强比NH3为载气生长的SiOx纳米线峰强大四个数量级.     

真空热蒸发生长CdX(X=S,Te)纳米线研究性实验

将一维纳米结构的气—液—固生长机制与大学材料物理实验真空热蒸发镀膜结合,设计了生长半导体纳米线的研究性实验.利用金属铋或锡作为催化剂,真空热蒸发生长了CdS,CdTe等半导体纳米线.纳米线产物形貌均匀,并可实现选择性生长.     

等离子体增强化学气相沉积法实现硅纳米线掺硼

用等离子体增强化学气相沉积(PECVD)方法成功实现硅纳米线的掺B.选用Si片作衬底，硅烷 （SiH4）作硅源，硼烷（B2H6）作掺杂气体， Au作催化剂，生长温度440℃.基于气-液-固(VLS)机制，探讨了掺B硅纳米线可能的生长机制.PECVD法化学成分配比更灵活，更容易实现纳米线掺杂，进一步有望生长硅纳米线pn结，为研制纳米量级器件提供技术基础. 关键词： 硅纳米线 化学气相沉积 纳米器件     

高质量镍基超晶格薄膜的制备及表征

自发现镍基超导薄膜之后, 镍基材料体系已成为当前人们的研究热点. 而在相关报道中, 普遍认为高质量的镍基超导前驱体薄膜的制备对其拓扑还原后超导电性的实现具有重要影响. 前期研究表明高质量的前驱体薄膜只生长在SrTiO3 衬底附近, 这与我们的实验结果一致. 为了可控制备高质量的镍基超导前驱体薄膜, 本文利用脉冲激光沉积(PLD) 技术在SrTiO3 (001) 衬底上生长不同厚度的可层选择性还原的[SrTiO3 ]m/[ Nd0 .8Sr0 .2 NiO3 ]n[(STO)m/(NSNO)n ]超晶格薄膜. 采用反射高能电子衍射仪(RHEED) 及透射电子显微镜(STEM) 和 X 射线衍射(XRD) 技术对超晶格薄膜的结构进行原位检测及结构表征, 然后利用综合物性测量系统(PPMS) 测试薄膜的电磁输运性质. 结果表明, 超晶格薄膜的结构质量良好, 超晶格薄膜和高质量单层前驱体薄膜表现出类似的电阻和磁阻现象. 该研究为后续镍基超导薄膜的可重复制备提供了重要的参考.     

Local super-saturation dependent synthesis of MgO nanosheets

Well-crystallized MgO nanosheets have been prepared with MgB₂ as a precursor without any catalyst via a simple chemical vapor deposition (CVD) method. The nanosheets are grown parallel to (2 0 0) plane according to the high-resolution transmission electron microscopy profiles. At the same time, MgO nanowires are formed in the different area of substrate, which is the result of the difference in local super-saturation. Consequently, we propose that the growth mechanism depends on the surface energy and the local super-saturation in the system.     

Photoluminescence and growth mechanism of amorphous silica nanowires by vapor phase transport

Amorphous silica [SiO_x (1<x<2)] nanowires were fabricated on silicon substrate in an acidic environment by heating the mixture of ZnCl₂, and VO₂ powders at 1100 °C. The length of SiO_x nanowires ranges from micrometers to centimeters, with uniform diameters of 10–500 nm depending on substrate temperature. Room-temperature photoluminescence spectra of the SiO_x nanowires showed two strong luminescence peaks in the red and green region, respectively. The photoluminescence was suggested to originate from nonbridging oxygen hole center (red band), and hydrogen-related species in the structure of SiO_x (green band). The study on chemical reactions and growth of the SiO_x nanowires revealed the formation process of silica nanowires in acidic environment was closely related to the vapor–solid–liquid mechanism.     

Effects of growth rate and buffer-layer on Bi2Sr2CaCu2Oy thin film fabrication

The effect of the growth rate on the Bi₂Sr₂CaCu₂O_y (Bi2212) thin film quality on MgO substrate is investigated at several growth rates from 0.175 to 3 nm/min. The maximal step height on the film surface is improved from about 100 to 6 nm by the reduction of growth rate to 0.5 nm/min and simultaneously the superconducting critical temperature attaining to a zero resistance T_c(R=0), is also improved from 50 to 63 K. The surface morphologies of the upmost Bi-superconducting thin films with the intermediate layers on MgO substrate is also studied in contrast to that deposited directly on the MgO substrate.     

Synthesis and electrical characterization of tungsten oxide nanowires

Tungsten oxide nanowires of diameters ranging from 7 to 200~nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour--solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W₁₈O₄₉. I--V curves are measured by an \textit{in situ} transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I--V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I--V curves by using a metal--semiconductor--metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.     

Microstructure characterization of Al2O3 nanowires with networked rectangular nanostructure

L-shaped and U-shaped Al₂O₃ nanowires were synthesized using a vapor phase deposition method. The as-grown nanowires are single crystalline and structurally uniform at the junction of the branches. Detailed TEM analysis revealed that the growth direction of the nanowires is parallel to the a- or b-axis directions, and switched growth from one direction to another forms the rectangular morphology of the peculiar L-shaped or U-shaped nanowires. Possible growth mechanism of the Al₂O₃ nanowires was explained. Our results can provide evidence to understand the growth mechanism of the complicated nanostructure.     

Growth and use of metal nanocrystal assemblies on high-density silicon nanowires formed by chemical vapor deposition

In this paper, we describe the growth and potential application of metal nanocrystal assemblies on metal-catalyzed, CVD-grown silicon nanowires (SiNWs). The nanowires are decorated by chemical assembly of closely spaced (1–5 nm) Ag (30–100 nm diameter) and Au (5–25 nm diameter) nanocrystals formed from solutions of AgNO₃ and NaAuCl₄·2H₂O, respectively. The formation and growth of metal nanocrystals is believed to involve the galvanic reduction of metal ions from solution and the subsequent oxidation of available Si-hydride sites on the surfaces of the nanowires. A native oxide layer suppresses formation of metal nanocrystals; adding HF to the ionic solutions significantly increases the density of nanocrystals on the surfaces of the nanowires. The nanocrystals coating the nanowires were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction. Ag nanocrystals on the nanowires afford sensitive detection of Rhodamine 6G (R6G) molecules in the 100 picomolar–micromolar range by surface enhanced Raman spectroscopy. In addition, Au nanocrystals formed on selected surfaces of a substrate of arbitrary shape can serve as effective nuclei for localized nanowire growth. PACS 81.07.b; 81.15.Gh     

Fabrication and structural characterization of Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> nanowires

This article demonstrates the first reported successful synthesis of Mg₂SiO₄ nanowires. We have thermally heated Au-coated Si substrates, using a quartz tube with its inner surface pre-coated with MgO nanostructures. We have characterized the sample morphologies by using scanning electron microscopy and transmission electron microscopy (TEM). X-ray diffraction analysis and high-resolution TEM observation coincidentally revealed that the nanowires were crystalline with an orthorhombic Mg₂SiO₄ structure. We have discussed the possible growth mechanism of Mg₂SiO₄ nanowires. PACS 81.07.-b; 81.05.Zx; 61.10.Nz; 68.37.Hk; 68.37.Lp     

A new large – Scale synthesis of magnesium oxide nanowires: Structural and antibacterial properties

Large-scale one-dimensional magnesium oxide (MgO) nanowires with diameters of 6 nm and lengths of 10 μm have been successfully synthesized by a new facile and simple reaction. This production was performed via a microwave hydrothermal approach at low temperature growth of 180 °C for 30 min. The structure of as synthesized MgO nanowires were investigated by means of X-ray diffraction (X-ray), Fourier Transformation Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and Energy Dispersive X-ray (EDS). The antibacterial behavior of MgO nanowires concentration in solid media against Gram negative and Gram positive for different bacteria has been tested in details. The results show that the MgO nanowires have bacteriostatic activity against Escherichia coli and Bacillus sp. The antibacterial activity increases with increasing MgO nanowires concentration. Furthermore, the presence of one-dimensional MgO nanowires has high antibacterial efficacy and damages the membrane wall of bacteria. Finally, this study offered the prospect of developing ultrafine nanoscale devices utilizing MgO nanowires and implementing their useful potential in biological control.     

Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique

A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C₂N₄H₄) and Ga₂O₃ as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor-liquid-solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.