Synthesis and characterization of silicon nanowires on mesophase carbon microbead substrates by chemical vapor deposition

Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using SiCl(4) as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiO(x) sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.     

Manipulation of the morphology of semiconductor-based nanostructures from core-shell nanoparticles to nanocables: the case of CdSe/SiO(2)

The morphology of CdSe/SiO(2) was manipulated from core-shell-structured nanoparticles to nanocables by using a chemical vapor deposition (CVD) process. The growth of nanocables, with cores no more than 20 nm in diameter, is initiated by the formation of core-shell nanoparticles with SiO(2) as matrix and CdSe clusters dispersed inside. After the subsequent vaporization of the SiO(2) matrix, the follow-up CdSe vapor crystallizes with the remaining CdSe clusters as nuclei to form CdSe nanowires as the furnace was cooled to 1200 degrees C. During the controlled cooling of the furnace, the SiO vapor re-deposits to sheathe the nanowires. The thickness of the shell and the diameter of core were successfully controlled. The photoluminescence measurements show that the CdSe/SiO(2) nanocables have strong visible-light emission bands located at 590 and 688 nm, which are attributed to the defects induced by SiO(2) sheaths nanowires and the quantum confinement effect of the CdSe, respectively. The UV/Vis absorption spectra of the naked CdSe nanowires further validate the above-mentioned quantum confinement effect. The deterministic growth of these nanocables is very important for the design of the nanodevices based on them.     

Synthesis and characterization of iron silicon boron (Fe5Si2B) and iron boride (Fe3B) nanowires

Single-crystal iron silicon boron (Fe(5)Si(2)B) and iron boride (Fe(3)B) nanowires were synthesized by a chemical vapor deposition (CVD) method on either silicon dioxide (SiO(2)) on silicon (Si) or Si substrates without introducing any catalysts. FeI(2) and BI(3) were used as precursors. The typical size of the nanowires is about 5-50 nm in width and 1-20 mum in length. Different kinds of Fe-Si-B and Fe-B structures were synthesized by adjusting the ratio of FeI(2) vapor to BI(3) vapor. Single-crystal Fe(5)Si(2)B nanowires formed when the FeI(2) sublimator temperature was kept in the range of 540-570 degrees C. If the FeI(2) sublimator temperature was adjusted in the range of 430-470 degrees C, single-crystal Fe(3)B nanowires were produced. Fe(3)B nanowires grow from polycrystalline Fe(5)SiB(2) particles, while Fe(5)Si(2)B nanowires grow out of the Fe(5)Si(2)B layers, which are attached to triangle shaped FeSi particles. Both the ratio of FeI(2) vapor to BI(3) vapor and the formation of the particles (Fe(5)SiB(2) particles for the growth of Fe(3)B nanowires, FeSi particles for the growth of Fe(5)Si(2)B nanowires) are critical for the growth of Fe(3)B and Fe(5)Si(2)B nanowires. The correct FeI(2) vapor to BI(3) vapor ratio assures the desired phase form, while the particles provide preferential sites for adsorption and nucleation of Fe(3)B or Fe(5)Si(2)B molecules. Fe(3)B or Fe(5)Si(2)B nanowires grow due to the preferred growth direction of <110>.     

SiO-Au法制备硅纳米线

在低真空的CVD系统中直接热蒸发SiO粉末并以金为催化剂在硅衬底上制备出大量长达几十微米的硅纳米线(SiNWs), 通过X 射线衍射谱(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、选区电子衍射仪(SAED)和Raman光谱等技术对硅纳米线进行形貌及结构分析. 实验结果表明, 在不同生长温度下制备得到的硅纳米线质量不同, 其中在700 ℃温区生长的硅线质量最好; 与晶体硅Raman的一级散射特征峰(TO)520.3 cm−1相比, 纳米硅线的Raman特征峰(TO)红移至514.8 cm−1.     

Formation of well-aligned ZnGa(2)O(4) nanowires from Ga(2)O(3)/ZnO core-shell nanowires via a Ga(2)O(3)/ZnGa(2)O(4) epitaxial relationship

Formation of well-aligned and single-crystalline ZnGa(2)O(4) nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga(2)O(3)/ZnO core-shell nanowires. Ga(2)O(3)/ZnO core-shell nanowires were prepared using a two-step method. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing single-crystalline ZnGa(2)O(4) nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitaxial relationship between ZnGa(2)O(4) and Ga(2)O(3) phases during the solid-state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained at room temperature from the single-crystalline ZnGa(2)O(4) nanowires.     

用金纳米粒子修饰硅纳米线及复合结构的光谱性质研究

在溶液中以正己硫醇作稳定剂, 利用HAuCl4与HF处理后的硅纳米线(SiNWs)的氧化还原反应, 在SiNWs表面负载金纳米粒子(AuNPs). 通过调整HAuCl4的浓度, 得到了AuNPs粒径从3.2到7.0 nm的AuNPs/SiNWs复合结构, 并对这种复合结构进行了紫外-可见吸收光谱和荧光光谱研究. 紫外-可见吸收光谱研究表明, 负载不同粒径的AuNPs的SiNWs在530～580 nm间有明显的由AuNPs表面等离子体共振引起的吸收, 且随着AuNPs粒径的增加, 该吸收峰发生红移. 负载前后的荧光光谱表明, 在红光和绿光区负载AuNPs的SiNWs的荧光峰与HF处理后SiNWs的荧光峰峰形相当, 峰位变化不大; 但在蓝光区, 不同于HF处理前后SiNWs的发射峰(464 nm左右), 负载了AuNPs的SiNWs在423 nm的位置处出现了强荧光峰, 这个峰是AuNPs费米能级的电子与sp或d带的空穴辐射复合产生的.     

High-quality ultralong Bi2S3 nanowires: structure, growth, and properties

A simple one-step hydrothermal method for large-scale synthesis of ultralong single-crystalline Bi2S3 nanowires was reported, and the nanowires were comprehensively characterized. The diameters of the nanowires are about 60 nm, and their lengths range from tens of microns to several millimeters. The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations. Optical absorption experiments revealed that the Bi2S3 nanowires are narrow-band semiconductors with a band gap E(g) approximately 1.33 eV. Electrical transport measurements on individual nanowires gave a resistivity of about 1.2 ohms cm and an emission current of 3.5 microA at a bias field of 35 V/microm. This current corresponds to a current density of about 10(5) A/cm2, which makes the Bi2S3 nanowire a potential candidate for applications in field-emission electronic devices.     

Fine-tuning of catalytic tin nanoparticles by the reverse micelle method for direct deposition of silicon nanowires by a plasma-enhanced chemical vapour technique

The reverse micelle method was used for the reduction of a tin (Sn) salt solution to produce metallic Sn nanoparticles ranging from 85 nm to 140 nm in diameter. The reverse micellar system used in this process was hexane-butanol-cetyl trimethylammonium bromide (CTAB). The diameters of the Sn nanoparticles were proportional to the concentration of the aqueous Sn salt solution. Thus, the size of the Sn nanoparticles can easily be controlled, enabling a simple, reproducible mechanism for the growth of silicon nanowires (SiNWs) using plasma-enhanced chemical vapour deposition (PECVD). Both the Sn nanoparticles and silicon nanowires were characterised using field-emission scanning electron microscopy (FE-SEM). Further characterisations of the SiNW's were made using transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. In addition, dynamic light scattering (DLS) was used to investigate particle size distributions. This procedure demonstrates an economical route for manufacturing reproducible silicon nanowires using fine-tuned Sn nanoparticles for possible solar cell applications.     

Fluoride-assisted synthesis of mullite (Al5.65Si0.35O9.175) nanowires

Novel silicon-deficient mullite (Al5.65Si0.35O9.175) single crystal nanowires were synthesized in large quantities on mica substrates assisted by the intermediate fluoride species. The nanowires have diameters in the range 50-100 nm and typical lengths of several microm. Aligned nanowires were observed at the substrate edge. The nanowires have strong photoluminescence (PL) emission bands at 310, 397, 452 and 468 nm.     

利用Pd催化合成单晶GaN纳米线的光学特性(英文)

基于金属元素钯具有的催化特性,采用射频磁控溅射方法,在Si(111)衬底上沉积Pd:Ga2O3薄膜,然后在950℃下对薄膜进行氨化,制备出大量GaN纳米线.采用扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等技术手段对样品的结构、形貌和成分进行分析.结果表明,制备的样品为具有六方纤锌矿结构的单晶GaN纳米线,直径在20-60nm范围内,长度为几十微米,表面光滑无杂质,结晶质量较高.用光致发光光谱对样品的发光特性进行测试,分别在361.1、388.6和426.3nm处出现三个发光峰,且与GaN体材料相比近带边紫外发光峰发生了较弱的蓝移.对GaN纳米线的生长机制也进行了简单的讨论.     

Catalytic growth and characterization of gallium nitride nanowires.

The preparation of high-purity and -quality gallium nitride nanowires is accomplished by a catalytic growth using gallium and ammonium. A series of catalysts and different reaction parameters were applied to systematically optimize and control the vapor-liquid-solid (VLS) growth of the nanowires. The resulting nanowires show predominantly wurtzite phase; they were up to several micrometers in length, typically with diameters of 10-50 nm. A minimum nanowire diameter of 6 nm has been achieved. Temperature dependence of photoluminescence spectra of the nanowires revealed that the emission mainly comes from wurtzite GaN with little contribution from the cubic phase. Moreover, the thermal quenching of photoluminescence was much reduced in the GaN nanowires. The Raman spectra showed five first-order phonon modes. The frequencies of these peaks were close to those of the bulk GaN, but the modes were significantly broadened, which is indicative of the phonon confinement effects associated with the nanoscale dimensions of the system. Additional Raman modes, not observed in the bulk GaN, were found in the nanowires. The field emission study showing notable emission current with low turn-on field suggests potential of the GaN nanowires in field emission applications. This work opens a wide route toward detailed studies of the fundamental properties and potential applications of semiconductor nanowires.     

钼网衬底上大面积硅纳米线的制备及其光催化性能研究

硅纳米材料广泛应用于光功能导向的各个领域,发展针对光功能应用及一维硅纳米结构的规模化可控制备方法,实现硅纳米结构的宏量制备,将为硅纳米结构的应用提供材料保障。本文采用简单的化学气相沉积法成功地在Mo网衬底上制备了大面积的硅纳米线(SiNWs),并通过扫描电子显微镜、透射电子显微镜、X射线粉末衍射仪、拉曼光谱仪,对制备的SiNWs进行了详细的研究。通过在低功率紫外光照射下SiNWs对罗丹明B和甲基蓝的光降解能力的研究,发现在Mo网衬底上生长的SiNWs对于有机染料具有很好的降解能力。     

C(膜)/Si(SiO2)(纳米微粒)/C(膜) 的光致发光性质研究

用直流辉光溅射法结合真空镀膜法制备出了一种"多层三明治结构"的光致发光材料-C(膜)/Si(SiO2)(纳米微粒)/C(膜)夹层膜,然后分别在400、650和750℃退火1 h.在波长为250 nm的紫外光激发下,刚制备出来未经退火处理的样品具有一个在398nm(3.12 eV)处的紫光宽带PL1峰.在650℃退火后,又出现了一个在360nm(3.44eV)附近的PL2峰.PL1和PL2峰形状和峰位与退火温度和激发波长无关,但强度却与退火温度和激发波长密切相关.结合形态结构分析可知,紫光PL1峰可用量子限制-发光中心(QC-LCs)模型进行解释:即光激发发生在8iO2微粒内部,而光发射源于SiO2与Si界面上的缺陷中心.紫外荧光PL2峰则源自SiC内部的电子-空穴复合发光.     

Bluish-white emission from radical carbonyl impurities in amorphous Al(2)O(3) prepared via the Pechini-type sol-gel process

Many efforts have been devoted to exploring novel luminescent materials that do not contain expensive or toxic elements, or do not need mercury vapor plasma as the excitation source. In this paper, amorphous Al2O3 powder samples were prepared via the Pechini-type sol-gel process. The resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), photoluminescence (PL) excitation and emission spectra, kinetic decay, and electron paramagnetic resonance (EPR). The obtained amorphous Al2O3 powder samples annealed at 500 and 600 degrees C exhibit bright bluish-white emission centered at 430 and 407 nm, respectively. The luminescent mechanisms of the amorphous Al2O3 powder samples can be ascribed to the carbon-related impurities such as radical carbonyl species. The calculated band structure of the defective amorphous Al2O3 agrees well with the results of spectral analysis and the proposed luminescent mechanism.     

Photoluminescence resulting from semiconductor-metal solid solution observed in one-dimensional semiconductor nanostructures

A narrow band photoluminescence (PL) emission peak resulting from CdS-Au solid solution was observed when growing one-dimensional nanostructures of CdS via the vapor-liquid-solid mechanism by using Au as the catalyst. This emission peak was located at 680 nm, a wavelength longer than the near band edge emission of CdS at 520 nm, and was shown not to be caused by the usual trap states of CdS which lead to a broad band emission. Here, the one-dimensional nanostructures of CdS were grown in a simple, low-temperature (360 degrees C) metal-organic chemical vapor deposition process with a single source precursor of CdS. Straight nanowires of diameter 50-70 nm and wormlike nanorods of diameter 100-200 nm were obtained. Both the upper and lower portions of the nanorods/nanowires possessed single crystallinity as judged from the corresponding high-resolution transmission electron microscopy images and selected area electron diffraction data. This work demonstrates the feasibility of adjusting PL emission peaks of optoelectronic semiconductors through alloying with metals.     

Temperature-controlled growth of ZnO nanowires and nanoplates in the temperature range 250-300 degrees C

Starting from a mixture of Zn and BiI3, we grew nanowires and nanoplates on an oxidized Si substrate at relatively low temperatures of 250 and 300 degrees C, respectively. The ZnO nanowires had diameters of approximately 40 nm and grew along the [110] direction rather than the conventional [0001] direction. The nanoplates had thicknesses of approximately 40 nm and lateral dimensions of 3-4 microm. The growth of both the nanowires and nanoplates is dominated by the synergy of vapor-liquid-solid (VLS) and direction conducting. Analysis of photoluminescence spectra suggested that the nanoplates contain more oxygen vacancies and have higher surface-to-volume ratios than the nanowires. The present results clearly demonstrate that the shapes of ZnO nanostructures formed by using BiI3 can be controlled by varying the temperature in the range 250-300 degrees C.     

Synthesis, characterization, and optical properties of In2O3 semiconductor nanowires

In2O3 semiconductor nanowires were synthesized by the chemical vapor deposition method through carbon thermal reduction at 900 degrees C with 95% Ar and 5% O2 gas flow. The In2O3 nanowires were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence spectroscopy (PL). For the first time, we observed the formation of corundum-type h-In2O3 nanowires and branched In2O3 nanowires. The PL spectra of In2O3 nanowires show strong visible red emission at 1.85 eV (670 nm) at low temperature, possibly caused by a small amount of oxygen vacancies in the nanowire crystal structure.     

Array-orderly single crystalline silicon nano-wires

Array-orderly single crystal silicon nano-wires (SiNWs) using self-organized nano-holes of anodically oxidized aluminum were fabricated. By field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), the well-orderly single crystal SiNWs arrays were observed. The interval of the SiNWs is excellent symmetrical and consentaneous. The diameter and the length are around 35 nm and 4 μm, respectively. Furthermore, the energy dispersive X-ray spectroscopy analysis (EDX) indicated that the SiNWs consist of silicon core and silicon oxide sheath mainly. The Raman scattering was also carried out to analyze the structure of the oriented SiNWs. Finally, the growth mechanism of the SiNWs was discussed.     

Organosulfur-functionalized Au, Pd, and Au-Pd nanoparticles on 1D silicon nanowire substrates: preparation and XAFS studies

A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes.     

One-step chemical vapor growth of Ge/SiC(x)N(y) nanocables

Single-step synthesis of one-dimensional Ge/SiCxNy core-shell nanocables was achieved by chemical vapor deposition of the molecular precursor [Ge{N(SiMe3)2}2]. Single crystalline Ge nanowires (diameter approximately 60 nm) embedded in uniform SiCxNy shells were obtained in high yields, whereby the growth process was not influenced by the nature of substrates. The shell material exhibited high oxidation and chemical resistance at elevated temperatures (up to 250 degrees C) resulting in the preservation of size-dependent semiconductor properties of germanium nanowires, such as intact transport of charge carriers and reduction of energy consumption, when compared to pure Ge nanowires.