Si衬底上InP纳米线的晶体结构和光学性质

采用金属有机化学气相沉积技术,利用自催化法,在Si(100)、(111)衬底上成功生长了InP纳米线。利用扫描电镜观察样品表面,在Si(100)、(111)衬底上生长的纳米线形貌相似,纳米线面密度不同。利用X射线衍射和透射电镜研究纳米线的生长取向和晶体结构,结果显示纳米线具有闪锌矿结构,生长方向〈111〉,并且具有层状孪晶结构。与InP体材料相比,纳米线的光致发光峰位蓝移,半峰全宽增大,拉曼散射TO和LO峰向低波数频移,频移随激发光功率减弱而减小。     

液晶光学相位共轭镜的研制

本文研制了一种由向列型液晶和非晶硅光导层组成的新型光学相位共轭镜。概述了该器件产生相位共扼波的原理,通过实验测试了器件的性能。测试表明,该器件有灵敏度高(20μW/cm²)、响应速度快(5ms)、光谱响应范围宽、结构紧凑等特点。由于响应快,器件能在没有防振装置的实验桌上输出相位共轭波,这对相位共轭的推广应用有重要意义。为了提高共轭光强,实验中还使用了一种脉冲增强技术,它将共轭光的功率提高了一个量级以上。     

Ensembles of indium phosphide nanowires: physical properties and functional devices integrated on non-single crystal platforms

A new route to grow an ensemble of indium phosphide single-crystal semiconductor nanowires is described. Unlike conventional epitaxial growth of single-crystal semiconductor films, the proposed route for growing semiconductor nanowires does not require a single-crystal semiconductor substrate. In the proposed route, instead of using single-crystal semiconductor substrates that are characterized by their long-range atomic ordering, a template layer that possesses short-range atomic ordering prepared on a non-single-crystal substrate is employed. On the template layer, epitaxial information associated with its short-range atomic ordering is available within an area that is comparable to that of a nanowire root. Thus the template layer locally provides epitaxial information required for the growth of semiconductor nanowires. In the particular demonstration described in this paper, hydrogenated silicon was used as a template layer for epitaxial growth of indium phosphide nanowires. The indium phosphide nanowires grown on the hydrogenerated silicon template layer were found to be single crystal and optically active. Simple photoconductors and pin-diodes were fabricated and tested with the view towards various optoelectronic device applications where group III–V compound semiconductors are functionally integrated onto non-single-crystal platforms.     

Photoluminescence from amorphous silica nanowires synthesized using TiN/Ni/SiO2/Si and TiN/Ni/Si substrates

Photoluminescence characteristics of amorphous silica nanowires (a-SiONWs) grown on TiN/Ni/Si and TiN/Ni/SiO₂ substrates have been studied. A-SiONWs grown on TiN/Ni/Si substrates show a Si-rich composition compared to those grown from TiN/Ni/SiO₂/Si. The emission characteristics of the nanowires were found to depend on the type of substrate. By annealing the a-SiONWs grown on TiN/Ni/Si in air, emission bands shift from blue to green bands. It is likely that silicon to oxygen ratio is an important factor in deciding the types of defects and emission bands of amorphous silica nanowires.     

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.     

Investigation of surface cleaning procedure of InP:S (1 0 0) substrates by high resolution XPS

The angle resolved X-ray photoelectron spectroscopy measurements were used to monitor a level of contamination of the InP:S (1 0 0) substrates during the cleaning processes with deionized water and isopropanol. Some contaminations with carbon and oxygen were found for a broken under ultrahigh vacuum InP:S substrate, indicating the contamination of the crystal during the growth process. The substrates after cleaning with deionized water and isopropanol were contaminated with carbon, oxygen, nitrogen and silicon. Concentration of carbon decreases inwards the substrates while concentration of oxygen is enhanced even in the deeper layers for both processes. The nitrogen concentration is higher for the samples rinsed with water. Roughness of the surfaces is higher for the samples rinsed with water what indicated the AFM measurements.     

Field emission and photoluminescence characteristics of ZnS nanowires via vapor phase growth

Large-area ZnS nanowires were synthesized through a vapor phase deposition method. X-ray diffraction and electron microscopy results show that the products are composed of single crystalline ZnS nanowires with a cubic structure. The nanowires have sharp tips and are distributed uniformly on silicon substrates. The diameter of the bases is in the range of 320-530 nm and that of the tips is around 20-30 nm. The strong ultraviolet emission in the photoluminescence spectra also demonstrates that the ZnS nanowires are of high crystalline perfection. Field emission measurements reveal that the ZnS nanowires have a fairly low threshold field, which may be ascribed to their very sharp tips, rough surfaces and high crystal quality. The perfect field emission ability of the ZnS nanowires makes them a promising candidate for the fabrication of flexible cold cathodes.     

Substrate effects on the microstructure of hydrogenated amorphous carbon films

In this work, plasma enhanced chemical vapour deposition was used to prepare hydrogenated amorphous carbon films (a-C:H) on different substrates over a wide range of thickness. In order to observe clear substrate effect the films were produced under identical growth conditions. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopies were employed to probe the chemical bonding of the films. For the films deposited on silicon substrates, the Raman I_D/I_G ratio and G-peak positions were constant for most thickness. For metallic and polymeric substrates, these parameters increased with film thickness, suggesting a change from a sp³-bonded hydrogenated structure to a more sp² network, NEXAFS results also indicate a higher sp² content of a-C:H films grown on metals than silicon. The metals, which are poor carbide precursors, gave carbon films with low adhesion, easily delaminated from the substrate. The delamination can be decreased/eliminated by deposition of a thin (∼10 nm) silicon layer on stainless steel substrates prior to a-C:H coatings. Additionally we noted the electrical resistivity decreased with thickness and higher dielectric breakdown strength for a-C:H on silicon substrate.     

Thermal stability of silicon nanowires: atomistic simulation study

Using the Stillinger--Weber (SW) potential model, we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics (MD) simulations. We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires. The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions, and that silicon nanowires with perpendicular dimmer rows on the two (100) surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two (100) surfaces. Furthermore, the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.     

Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

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     

Photochemical decoration of silver nanoparticles on ZnO nanowires as a three‐dimensional substrate for surface‐enhanced Raman scattering measurement

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurement, a three‐dimensional (3D) SERS substrate was prepared by the decoration of silver nanoparticles (AgNPs) on the side walls of ZnO nanowires. The prepared 3D SERS substrates provide the advantages of highly loaded density of AgNPs, with a large specific surface area to interact with analytes, and the ease for the analytes to access the surfaces of AgNPs. To prepare the substrates, ZnO nanowires were first grown on a glass plate by wet chemical method. By treating SnCl₂ on the surfaces of ZnO nanowires, Ag seeds could be formed on the side wall of the ZnO nanowires, which were further grown to a suitable size for SERS measurements via photochemical reduction. To optimize and understand the influences of the parameters used in preparation of the substrates, the reaction conditions were systematically adjusted and examined. Results indicated that AgNPs could be successfully decorated on the side wall of the ZnO nanowires only by the assistances of SnCl₂. The size and density of AgNPs were affected by both the concentration of silver nitrate and the irradiation time. With optimized condition, the prepared 3D substrates provided an enhancement factor approaching 7 orders of magnitude compared with conventional Raman intensity. Copyright © 2014 John Wiley & Sons, Ltd.     

InP/SiO2纳米复合膜的微观结构和光学性质

应用射频磁控共溅射方法在石英玻璃和抛光硅片上制备了InP/SiO₂复合薄膜,并在几种条件下对这些薄膜进行退火.X射线光电子能谱和卢瑟福背散射实验结果表明,复合薄膜中InP和SiO₂的化学组分都大体上符合化学计量配比.X射线衍射和激光喇曼谱实验结果都证实了复合薄膜中形成了InP纳米晶粒.磷气氛保护下的高温(520℃)退火可以消除复合薄膜中残存的In和In₂O₃并得到了纯InP/SiO₂纳米复合薄膜.实验观察到了室温下纳米复合薄膜的明显的光学吸收边蓝移现象和光学非线性的极大增强 关键词： InP 纳米晶粒 微观结构 光学性质     

Nanowire-based devices combining light guiding and photodetection

We demonstrate bridged nanowires on a non-single-crystal substrate as a versatile fabrication approach to combine active and passive photonic functionalities on silicon platforms. Silicon nanowires are grown on vertical non-single-crystal surfaces by a vapor-liquid-solid process and bridge a microtrench obtained by etching an amorphous optical rib waveguide. A pair of phosphorous-doped polysilicon electrodes is deposited on the walls of the waveguide microtrench for seeding the nanowire synthesis and for electrical interfacing. The bridged nanowires act as photoconductors and their photoresponse to edge-illumination from waveguided light is characterized. Taking advantage of crystalline nanowire growth on non-single-crystal substrates may ultimately lead to substrate-independent integration of best-of-breed semiconductor nanodevices for applications such as photonic integrated circuits.     

MOCVD自催化法在Si(100)衬底上生长InP/InGaAs核壳结构纳米线

采用自催化法,利用金属有机化学气相沉积技术,在Si(100)衬底上成功制备了InP/InGaAs核壳结构纳米线。通过扫描电子显微镜观察纳米线形貌,在核壳结构纳米线的顶端催化剂转化成了颗粒状晶体。利用X射线衍射和透射电子显微镜研究了InP纳米线上生长InGaAs外壳的过程,并应用X射线能量色散能谱仪对纳米线顶端进行了轴向和径向的线扫描,得到了纳米线上元素组分分布。催化剂的转化发生在制备InGaAs壳之前的升温过程中,且形成的晶体中含有合金成分。InGaAs壳的组分调整可以通过改变生长过程中生长源气体的流量来实现。     

Room temperature NO_2 gas sensing of Au-loaded tungsten oxide nanowires/porous silicon hybrid structure

In this work, we report an enhanced nitrogen dioxide(NO_2) gas sensor based on tungsten oxide(WO_3)nanowires/porous silicon(PS) decorated with gold(Au) nanoparticles. Au-loaded WO_3 nanowires with diameters of 10 nm–25 nm and lengths of 300 nm–500 nm are fabricated by the sputtering method on a porous silicon substrate. The high-resolution transmission electron microscopy(HRTEM) micrographs show that Au nanoparticles are uniformly distributed on the surfaces of WO_3 nanowires. The effect of the Au nanoparticles on the NO_2-sensing performance of WO_3 nanowires/porous silicon is investigated over a low concentration range of 0.2 ppm–5 ppm of NO_2 at room temperature(25℃). It is found that the 10-? Au-loaded WO_3 nanowires/porous silicon-based sensor possesses the highest gas response characteristic. The underlying mechanism of the enhanced sensing properties of the Au-loaded WO_3 nanowires/porous silicon is also discussed.     

Selective formation of silicon nanowires on pre-patterned substrates

In this paper, the selective growth of silicon nanowires (SiNWs) was studied. With the aid of photolithography, the vertically aligned silicon nanowires were selectively formed on the patterned substrates via an electroless metal deposition (EMD) method under normal conditions (room temperature, 1 atm). Low-pressure chemical vapor deposition (LPCVD) silicon nitride was used as the masking layer for SiNWs preparation. The scanning electron microscope was used to examine the etching results. Both the patterned and the unpatterned silicon substrates were used for study. The results indicated that the growth rates of the SiNWs upon the patterned and the unpatterned substrates are different. For the patterned substrates, the growth rate of SiNWs is dependent upon the pattern shape. The influence of length-to-width ratio for the rectangular-shaped patterns was studied. It is concluded that by designing the proper length-to-width ratio, the nanowires with different lengths can be fabricated simultaneously on the same substrate.     

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.     

Flame synthesis of tungsten oxide nanostructures on diverse substrates

One-dimensional (1D) tungsten oxide nanostructures show great potential for applications in the areas of batteries, photoelectrochemical water-splitting, electrochromic devices, catalysts and gas sensors. 1D tungsten oxide nanostructures are currently synthesized by physical or chemical vapor deposition, which are limited by low temperatures, the need for vacuum conditions, frequently expensive catalysts, and difficulty in scaling up for mass-production. These limitations, however, can be overcome by flame synthesis. Here, using a co-flow multi-element diffusion burner, we demonstrate the atmospheric, catalyst-free, rapid, mild and scalable flame synthesis of diverse, quasi-aligned, large density, and crystalline tungsten oxide nanostructures on a variety of substrates. Specifically, under fuel-rich conditions, monoclinic 1D W₁₈O₄₉ nanowires and nanotubes were grown on tungsten, iron, steel and fluorinated tin oxide (FTO) substrates, with controlled diameters ranging from 10 to 400 nm and axial growth rates ranging from 2 to 60 μm/h. Monoclinic 1D WO₃ nanowires and nanotubes were grown, instead, on silicon and silicon dioxide substrates. Under fuel-lean conditions, diverse WO₃ nanostructures, including monoclinic 1D nanowires, cubic 2D nanobelts and monoclinic 3D nanocones were grown on tungsten and FTO substrates. The success of this versatile flame synthesis method is attributed to the large tunability of several synthesis parameters, including the flame stoichiometry, the tungsten source and growth substrate temperatures, the tungsten oxide vapor concentration, and the material of the growth substrate. This flame synthesis method can be extended to synthesize other 1D transition metal oxides as well, enabling many large-scale electronic and energy conversion applications.     

Synthesis of thin silicon nanowires using gold-catalyzed chemical vapor deposition

Silicon nanowires were synthesized using chemical vapor deposition catalyzed by gold nanoparticles deposited on silicon substrates. Silicon nanowires grew epitaxially in 111 directions on (100)-oriented silicon substrates. For a particular set of process parameters, we observed a critical thickness of the nucleating gold film, below which nanowires could not be grown. We studied the dependence of the Au-Si alloy droplet size and size distribution on the starting gold film thickness and the annealing conditions. Increasing the Cl:Si ratio in the gas phase allowed nanowires to grow on smaller Au-Si alloy droplets. We used a modified heating sequence that deconvoluted the effect of silicon substrate consumption and gas-phase silicon supply on the Au-Si alloy formation and allowed growth of nanowires with diameters less than 20 nm. The modified heating sequence was also used to demonstrate the growth of bridging silicon nanowires with diameters less than 20 nm, which is a significant step in producing electronic devices. PACS 81.07.b; 81.15.Gh