合成参数对气-液-固法低温生长MgO纳米线的影响

将Mg(C11H19O2)2(即双(2,2,6,6,-四甲基-3,5-庚二酮酸)镁)作为反应前驱体,用脉冲液滴注入式金属有机物化学气相沉积法,在较低温度(T=600℃)下合成MgO纳米线.纳米线沿着[001]方向生长且Au催化剂位于纳米线顶端,这表明纳米线是由气-液-固机制诱导生长的.通过改变前驱体注入的脉冲周期或周期注入剂量能够控制纳米线的生长模式,使之垂直或平行于样品表面生长.     

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。     

Y掺杂Si纳米线的光致发光特性

以n型单晶Si(111)为衬底,利用Au作为催化剂,在温度、N₂流量和生长时间分别为1 100 ℃,1.5 L·min-1和60 min的条件下,基于固-液-固生长机制,生长了直径为60～80 nm、长度为数十微米的高密度Si纳米线。随后,以Y₂O₃粉末为掺杂源,采用高温扩散方法对Si纳米线进行了钇(Y)掺杂。利用扫描电子显微镜、X射线衍射仪和荧光分光光度计对不同掺杂温度(900～1 200 ℃)、掺杂时间(15～60 min)和N₂流量(0～400 sccm)等工艺条件下制备的Y掺杂Si纳米线的形貌、成分、结晶取向以及激发光谱和发射光谱特性进行了详细的测量和表征。结果表明,在掺杂温度为1 100 ℃,N₂流量为200 sccm、掺杂时间为30 min和激发波长为214 nm时,Y掺杂Si纳米线样品表现出较好的发光特性。样品分别在470～500和560～600 nm范围内出现了两条发光谱带。560～600 nm的发光带由两个发光峰组成,峰位分别为573.6和583.8 nm,通过结构分析可以推测,这两个发光峰是由Y3+在Si纳米线的带隙中引入的杂质能级引起的。而470～500 nm较宽的发光带同样来源于Y离子在Si纳米线带隙中引入的与非晶SiO_x壳层中氧空位能级十分接近的杂质能级。     

锡催化剂助生长法制备孪晶ZnO纳米线及其结构表征

用SnO和Zn的均匀混合物在高温下共烧通过VLS机制制备出孪晶ZnO纳米线的均匀结构。SEM图像显示孪晶ZnO纳米线的直径在100~200nm之间,长度在几十微米到几百微米之间的范围内,有的甚至达到了毫米级,产率也非常的高。TEM图像中ZnO孪晶纳米线顶端的金属Sn颗粒表明了孪晶结构的Sn催化生长。高分辨电子图谱显示了氧化锌纳米线孪晶结构的特征。电子衍射分析发现孪晶氧化锌的晶带轴的方向是[0110],孪晶面为(1013),并且通过明场像和暗场像分析了孪晶纳米线的晶格关系,确定了孪晶纳米线的汽-液-固(VLS)生长机制。     

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     

Eu掺杂Si纳米线的光致发光特性

利用Si(111)衬底, 以Au-Al为金属催化剂, 基于固-液-固生长机理, 在温度为1100℃, N₂气流量为1.5 L/min、生长时间为30–90 min等工艺条件下, 制备了直径约为100 nm、长度为数微米的高密度、均匀分布、大面积的Si纳米线(～10¹⁰ cm^-2). 对Si纳米线进行了Eu掺杂, 实验研究了不同长度的Si纳米线以及不同掺杂温度、掺杂时间等工艺参数对Eu离子红光发射的影响, 利用扫描电子显微镜和X射线衍射仪对Si纳米线表面形貌和Eu掺杂后Si纳米线的结晶取向进行了测量和表征; 室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析. 结果表明: 在Si纳米线生长时间为30 min、掺杂温度为1000℃、 最佳激发波长为395 nm时, 样品最强荧光波长为619 nm (⁵D₀→⁷F₂); 同时, 还出现了576 nm (⁵D₀→⁷F₀), 596 nm (⁵D₀→⁷F₁), 658 nm (⁵D₀→⁷F₃)和708 nm (⁵D₀→⁷F₄)四条谱带.     

分形基底上受限固-固模型动力学性质的数值模拟研究

为了探讨非完整基底结构对生长表面动力学行为的影响,本文在具有相同分形维数而不同谱维数的谢尔宾斯基箭头和蟹状分形基底上对受限固-固(restricted solid-on-solid,RSOS)模型的生长过程进行了大量的数值模拟研究.通过计算表面宽度和饱和表面极值高度的统计行为对生长表面的动力学行为进行了分析.结果表明,分形基底结构对生长表面的动力学行为具有显著的影响.尽管在两种基底上受限固-固模型的表面宽度均表现出很好的动力学标度行为,仍然满足Family-Vicsek标度规律,但由此计算得到的动力学标度指数并不相同.饱和生长表面的极值高度并不能满足三种常用的极值统计分布,即Weibull,Gumbel和Frechet分布,而是能很好地符合Asym2Sig分布.     

非晶碳氧化硅纳米线的合成与光致发光

利用直流电弧放电合成非晶碳氧化硅(SiCO)纳米线,不使用催化剂和模板,独立的SiCO 纳米线沉积在石墨锅的表面．通过XRD、SEM、TEM、XPS、FTIR等对SiCO纳米线进行了表征．结果表明,纳米线长度为20～100 μm,直径为10～100 nm,Si原子同C原子和氧原子分享成键组成SiCO单元．SiCO纳米线的光致发光谱在454和540 nm呈现了强而稳定的白色发光峰． SiCO纳米线的生长机制为等离子辅助气―固生长机制．     

化学气相沉积法制备Zn2GeO4纳米线及其发光性质的研究

利用化学气相沉积法（CVD）,气-液-固（VLS）生长法则在表面溅有金属Au催化剂层的1 cm×1 cm的Si片上制备三元Zn₂GeO₄纳米线。X射线衍射仪（XRD）测试结果表明,锌源与锗源质量比为8：1时可成功制备出Zn₂GeO₄纳米结构;扫描电子显微镜（SEM）测试结果表明,Zn₂GeO₄纳米线直径为100 nm,长度为10~11 μm;光致发光（PL）测试结果表明,Zn₂GeO₄纳米线在432和480 nm处具有两个发光峰,最后对其生长机理进行了分析。     

表面活性剂辅助固相法合成碘化银纳米线束与光谱表征

卤化银具有光致变色特性,广泛应用于光致变色玻璃,照相感光乳剂等。作为一种光信息载体,具有记录和保存光信息的功能,它还是一类重要的半导体光催化剂,有着广泛的应用。以AgNO3与KI为原料,在非离子表面活性剂聚乙二醇(PEG-400)存在条件下,进行室温固相反应,合成了碘化银纳米线束。采用XRD,TEM和SEM等测试手段对产物结构和形貌进行表征,结果表明,产物为一维碘化银纳米线束,其直径在80～100nm之间,长度约为20μm,长径比>200。表面活性剂PEG-400在碘化银纳米线束的形成过程中起到了软模板剂的作用,诱导产物纳米晶沿着某一特定方向定向有序生长从而生成纳米线束。该方法消除了水对反应过程的影响,操作简单,成本较低,对碘化银纳米线束的制备技术研究具有重要意义。     

AuPd CATALYTIC NANOPARTICLE SIZE EFFECT ON THE FORMATION OF AMORPHOUS SILICON NANOWIRES

Amorphous silicon (a-Si) nanowires have been prepared on SiO₂/Si substrates by AuPd nanoparticles / silane reaction method. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The typical a-Si nanowires we obtained are of a uniform diameter about 20 nm and length up to several micrometers. The growth mechanism of the nanowires seems to be the vapor-liquid-solid mechanism. The catalytic particle size effect on the formation of the nanowires and the cause of forming amorphous state Si nanowires are discussed.     

Synthesis of SERS active Au nanowires in different noncoordinating solvents

Au nanowires with length up to micrometers were synthesized through a simple and one-pot solution growth method. HAuCl₄ was reduced in a micellar structure formed by 1-octadecylamine and oleic acid in hexane, heptane, toluene and chloroform, respectively. As the non-polarity of noncoordinating solvents can affect the nucleation and growth rates of Au nanostructures, Au nanowires with different diameters could be obtained by changing the noncoordinating solvents in the synthetic process. The influences of the solvents on the morphology of Au nanowires were systematically studied. When using hexane as reaction solvent, the product turned to be high portion of Au nanowires with more uniform size than the others. Furthermore, surface-enhanced Raman scattering (SERS) spectrum of 2-thionaphthol was obtained on the Au nanowire-modified substrate, indicating that the as-synthesized Au nanowires have potential for highly sensitive optical detection application.     

Silicon nanowires synthesized by vapor–liquid–solid growth on excimer laser annealed thin gold film

The fabrication of Si nanowires has been demonstrated using excimer laser annealed thin gold film as the catalyst and vapor–liquid–solid (VLS) growth. Au nanoparticles with mean diameters of 12, 13 and 15 nm were formed by excimer laser annealing (ELA) of Au film with thickness of 2.5, 5 and 10 nm, respectively. The results show that the silicon nanowires (SiNWs) with desired diameter can be obtained by controlling the Au film thickness and laser power density.     

Ce掺杂Si纳米线的制备及其蓝光发射特性

以抛光和“金字塔”织构表面的单晶Si(100)为衬底,分别以Au和Au-Al为金属催化剂,在温度为1 100 ℃、N₂气流量为1 500 sccm、生长时间为15～60 min等工艺条件下,制备了直径约为50～200 nm、长度为数微米至数十微米和不同分布的Si纳米线。然后,利用CeO₂粉末为掺杂剂,在温度为1 100～1 200 ℃、N₂流量为1 000 sccm、掺杂时间为30～60 min等工艺条件下对Si纳米线进行Ce掺杂。实验研究了不同Si纳米线长度、密度和分布等对Ce3+蓝光发射的影响。室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析,同时利用FLS920全功能型荧光光谱仪对样品的荧光量子效率进行了测试。结果表明,在Si纳米线生长时间为30 min、织构表面和密度相对较低时以及最佳激发光波长为328 nm时,样品发射光波长为405 nm(5d→2F_5/2)荧光强度较大,实现了强的蓝光发射,其荧光量子效率达到了65.57%。通过光谱功率分布和CIE-1931标准公式进行计算,Ce掺杂Si纳米线样品的色坐标为(0.16, 0.03);发光强度大,量子效率高使其在照明、显示等领域有着潜在的应用价值,同时对Si纳米线在发光领域的研究和应用具有一定的参考价值。     

Formation of silicon oxide nanowires directly from Au/Si and Pd–Au/Si substrates

Amorphous silicon oxide (SiO_x) nanowires were directly grown by thermal processing of Si substrates. Au and Pd–Au thin films with thicknesses of 3 nm deposited on Si (0 0 1) substrates were used as catalysts for the growth of nanowires. High-yield synthesis of SiO_x nanowires was achieved by a simple heating process (1000–1150 °C) in an Ar ambient atmosphere without introducing any additional Si source materials. The as-synthesized products were characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy measurements. The SiO_x nanowires with lengths of a few and tens of micrometers had an amorphous crystal structure. The solid–liquid–solid model of nanowire formation was shown to be valid.     

Convenient approaches for the synthesis of gold nanowires by successive utilization of two kinds of reducing agents in the solution of hexadecyl-trimethylammonium bromide

In spite that several empirical approaches for the synthesis of gold nanowires have been reported, there still remains ambiguity and controversy for their mechanisms. In this study, we report very easy and highly-reproducible synthetic method of gold (Au) nanowires with the size and the length of 40–50 nm and several micrometers, respectively. The method includes an extremely higher concentration of hexadecyl-trimethylammonium bromide (CTAB) at room temperature. We successively used two kinds of reducing agents, firstly sodium borohydride for the reduction of Au(III) ion into mostly Au(I) ion, and secondly triethylamine (TEA) leading Au(I) ion to Au(0) and its growth to Au nanowires. The former should be added very slowly, while the latter at once. Effects of oxygen were crucial for the growth to nanowires, and copper ion was quite effective for reductive scavenging of unwanted oxygen. It is strongly suggested that Cu(I) ion first generates the complex with TEA and then reduces Au(I) ion to Au(O). Thus, the Au nanowires grow in higher concentrations of Cu(I) ion. The concentration of CTAB was also found to be very important for the generation of Au nanowires.     

Self-organized transformation to polyaniline nanowires by pulsed energetic electron irradiation in a plasma focus device

An ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale is demonstrated by using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.     

Porous silicon templates for electrodeposition of nanostructures

We report the fabrication and characterization of porous silicon templates for electrodeposition of high aspect ratio one-dimensional metallic nanostructures (nanowires/nanoparticles) in them. Even though nanostructures/nanowires in the past have been fabricated in alumina, polymer or silica templates, the advantages of this approach are the possibility for seamless integration of nanostructures with other silicon components, and silicon based sensors because of better physical and electrical interconnection between the nanostructure and the silicon substrate. In this work, fabrication and characterization of nanowires/nanostructures such as single-segment Ni–Fe and Au and two-segment Ni–Fe/Au electrodeposited in the porous silicon template are presented. The templates with ordered and controlled nanometer-sized pores, 40 nm and 290 nm in diameter, were created through porous Si etching. The morphology, composition and structural characteristics of the template and of the single-segment Ni–Fe and Au and two-segment Ni–Fe/Au nanostructures of diameter 275±25 nm, length up to 100 μm and pitch of 1 μm were analyzed using scanning electron microscopy and X-ray diffraction techniques. The micrographs confirm that the plating parameters have a strong influence on morphology and composition of the structures. Further, the Ni–Fe images show the formation of both vertical and branched nanowires along with nanoparticles, from breakage/discontinuous growth of nanowires. Ni–Fe nanostructures were further analyzed for temperature-dependent magnetization and magnetization vs. magnetic field measurements using a commercial physical property measurement system. They reveal no magnetic anisotropy of the nanostructures probably due to a balance between ‘reduced’ shape anisotropy from branched and rough pore surfaces and magnetocrystalline anisotropy. PACS 61.46.+w; 75.75.+a; 81.07.-b; 81.16.Be     

Growth of amorphous SiO<Subscript>2</Subscript> nanowires on Si using a Pd/Au thin film as a catalyst

Nanowires of amorphous SiO₂ were synthesized by thermal processing of a Si(100) substrate at 1100 °C in the presence of a nitrogen flow, and using a 15 nm thick high silicon-solubility Pd/Au film as a catalyst. The substrate itself was the only source of silicon for the nanowire growth. The nanostructures produced were characterized by high resolution transmission and scanning electron microscopy and by X-ray diffraction. The nanowire growth is consistent with the vapor-liquid-solid (VLS) mechanism, with particles of Pd₂Si and Au(Pd) being observed to form from the reaction between silicon and the catalytic film, and to remain at the tip of the wires. The synthesized nanowires showed a well defined morphology which could be very interesting for lasing applications. PACS 81.05.Ys; 81.10.Bk; 85.40.Ux     

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