Silicon nano-wires fabricated by a novel thermal evaporation of zinc sulfide

Silicon nano-wires (SiNWs) with diameter of 30 nm and length of tens of micrometers on silicon wafers were synthesized by a novel thermal evaporation of zinc sulfide. After thermal evaporation at 1080°C for 1 h, crystalline SiNWs were produced. It was found that the tip of SiNWs contained sulfur, while the other places of SiNWs did not. It is considered that the decomposition of SiS resulted in the formation of SiNWs. On the basis of the facts, a sulfide-assisted growth model of SiNWs was suggested.     

Sulfide-assisted growth of silicon nano-wires by thermal evaporation of sulfur powders

Silicon nanowires (SiNWs) with a diameter of 20 nm were synthesized by the thermal evaporation of sulfur powders on silicon wafers. The source of the SiNWs came from the silicon substrates. It is considered that the generated SiS compound assisted the formation of SiNWs. Finally, the Raman shift of SiNWs was discussed.     

热蒸发YbF3薄膜的机械特性

 实验研究了热蒸发YbF₃薄膜在大气中的应力和附着力。利用Veeco干涉仪,测试了各种工艺条件下单层YbF₃薄膜的应力。结果发现:YbF₃薄膜的残余应力为张应力,热应力在残余应力中的比重较大;沉积方式对薄膜应力的影响不大;薄膜应力在大气中有一个释放的过程。热处理后,YbF₃薄膜应力增大。     

Fabrication and characterization of ZnO micro and nanostructures prepared by thermal evaporation

A simple method of thermal evaporation to fabricate micro and nanostructures of zinc oxide was presented. ZnO micro and nanostructures, prepared under different quantity of O₂, were characterized by techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and analytical transmission electron Microscope. The SEM images indicated that the products prepared under the condition of sufficient O₂ were needle-like microrods and the samples synthesized under the condition of deficient O₂ were nanorods and nanowires with very high aspect ratio. The results of XRD and Raman shifts revealed that the ZnO micro and nanostructures synthesized under different quantity of O₂ were both single crystalline with the hexagonal wurtzite structure. The HRTEM images indicated that the ZnO nanowire prepared under the condition of deficient O₂ was single crystalline and grown along the direction of [0 0 1]. Photoluminescence measurement was carried out and it showed that the spectra of ZnO micro and nanostructures prepared under different quantity of O₂ exhibited similar emission features. In addition, the growth mechanism of ZnO micro and nanostructures was preliminarily discussed.     

Pulsed laser treatment of gold and black gold thin films fabricated by thermal evaporation

The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm⁻² to 250 mJ·cm⁻² was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm⁻² and 3.5 mJ·cm⁻² for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser treatment.      

Oxide-assisted growth of silicon nanowires by carbothermal evaporation

Silicon nanowires (SiNWs) have successfully been synthesized by carbothermal evaporation method. By ramping-up the furnace system at 20 °C min⁻¹ to 1100 °C for 6 h, the vertically aligned coexist with crooked SiNWs were achieved on the silicon substrate located at 12 cm from source material. The processing parameters such as temperature, heating rate, duration, substrate position and location are very important to produce SiNWs. Morphology and chemical composition of deposited products were investigated by field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray analysis (EDX). The existence of small sphere silicon oxide capped nanowires suggested that the formation of SiNWs was governed by oxide-assisted growth (OAG) mechanism.     

Structural and optoelectronic properties of antimony tin sulphide thin films deposited by thermal evaporation techniques

Thin films of SnSb₂S₄ have been prepared on glass substrate by using thermal evaporation techniques. The films were annealed in argon gas at low pressure in sealed glass ampoules at 85 °C, 150 °C, 275 °C and 325 °C. XRD of the films reveal that the low temperature annealed films are poly crystalline while the as deposited films and high annealed films are in amorphous states. There is no adequate variation in the photoconductivity response of the amorphous and crystalline phases. The transmittance of the films is low and having no transmittance below 740 nm. The band gap calculated by ellipsometry technique is in the range of 1.82–3.1 eV. The films have n-type conductivity but the film annealed at 325 °C show p-type conductivity.     

Pulsed electroluminescence in silicon nanocrystals-based devices fabricated by PECVD

Fully compatible CMOS capacitive devices have been developed in order to obtain electrically stimulated luminescence. By high-temperature annealing in N₂ atmosphere PECVD non-stoichiometric silica layers, silicon nanocrystals were formed. Photoluminescence, as well as structural studies, were carried out on these layers to decide the best material composition, which lies next to 17% of silicon excess. Under pulsed electrical stimulation, devices show sharp, narrow, less than 5 μs and pulse-frequency-independent, luminescence peaks at the end of the stimulation pulse. Current analysis on those capacities show hole injection at the beginning and electron injection at the end of the stimulation pulses. It is seen that no positive pulses are needed for attaining bipolar charge injection. Electroluminescence is detected when biasing with negative pulses at about 15 V and increasing up to 50 V. The electroluminescence spectrum matches photoluminescence one, allowing assigning both luminescent radiation to the same emission mechanism, that is, electron–hole recombination within the silicon nanocrystals.     

Sub-microns period grating couplers fabricated by silicon mold

This paper describes a novel simple process suitable for fabrication of micro-periodic structure in optical waveguide. The mold was fabricated using electron beam lithography and fast atom beam etching. Sub-micron-scale patterns were transferred from silicon mold to polymer layer. Grating coupler was fabricated by the mold and normal optical mask. In the proposed method, no press which is needed for imprint lithography is required and the mold structure can be duplicated with high aspect ratio. Experimental coupling efficiency is about 25%. This technique can also be used to fabricate other nanometer-scale structures.     

Study on the thermoelectric properties of porous Bi-Te films deposited using thermal evaporation on AAO template

The application of thermoelectric films is limited to retain the temperature gradient. In this study, the Bi-Te films are deposited on the AAO template with a pore size of 100 nm using thermal evaporation. The results show that the conductive types of the Bi-Te film are tuned by source temperature. The power factor of the p-type porous film decreases 36% by comparing to that of the p-type nonporous film (1020 μW/mK² at 250 °C). Meanwhile, the temperature difference in the porous device is maintained and is approximately 5.0 °C. Thus, the maximum output power is achieved in the porous device (about 25 pW), which is 5 times higher than that of the nonporous device. This provides a method to improve the conversion efficiency of thermoelectric film device by maintaining the temperature difference by using porous structure.     

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (E_d) and the annealing temperature were varied from 123 to 242 mJ/cm² and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d ≥ 188 mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.     

Photoluminescence of ZnO:Sb nanobelts fabricated by thermal evaporation method

Uniform ZnO nanobelts (NBs) were synthesized by a facile thermal evaporation method. Recombination mechanism of acceptor-related emissions in Sb doped ZnO NBs was investigated by temperature-dependent photoluminescence (PL) spectra. UV near-band-edge (NBE) emissions were dominant by acceptor-bound exciton (A⁰X) at 3.358 eV and free electron-to-acceptor (FA) at 3.322 eV transitions at 81 K. Studies on A⁰X intensity showed a quenching channel, the thermal dissociations of A⁰X to a free exciton and electron hole pair with the temperature increase. The active energy of A⁰X was estimated to be 19 meV using thermal quenching formula. The acceptor ionization energy was calculated to be 190 meV using Haynes rule. These results were very similar to those of antimony or phosphorus doped ZnO films.     

Kinetic study of antibody adhesion on a silicon wafer by laser reflectometry

Antibody adhesion kinetic in real time has been studied by laser reflectometry technique. An ellipsometer is used to measure the light intensity reflected by a silicon wafer. Light intensity reflected by the wafer presents a minimum at the pseudo-Brewster angle. Then, the reflectance increases as the antibodies (monoclonal anti-AB) adhere on interface. Mathematical analysis of reflectance curves versus time verifies that the antibody adhesion at the interface follows Langmuir kinetics (Prog. Biomed. Opt. Imaging 1(5) (2000) 19) for low antibody concentrations. Parameters obtained allow to carry out a detailed study of the antibody adsorption and the antigen–antibody interaction. This conduces to development of an optical immunosensor for detection and quantification of soluble antigens, and a novel method for commercial antiserum quality control. This technique does not require labeled antibodies, being also independent of cellular factors. Also, this technique is quicker and sensible than the conventional immunohematology methods.     

电阻热蒸发镀膜与电子束蒸发镀膜对纳米球刻蚀方法制备二维银纳米阵列结构的影响

在使用纳米球刻蚀法制备二维银纳米点阵的过程中,使用不同的镀膜方法在同样的模板上得到了不同形貌的银纳米阵列结构.使用电阻热蒸发镀膜方法获得了六角排列的银纳米三角形阵列结构,使用电子束蒸发镀膜方法则获得了六角排列的银纳米环阵列结构.研究表明,沉积纳米粒子的粒径、表面纳米曲率效应和热能是形成不同结构形貌的纳米阵列结构的关键因素. 关键词： 银纳米阵列 电阻热蒸发 电子束蒸发 纳米球刻蚀     

An analysis on synthesizing large scales of one-dimensional silicon nano-structures by simple evaporation of sulfur-contained powders

The growth mechanism for synthesizing large scales of one-dimensional silicon nano-structures (silicon nano-wires (SiNWs) or silicon oxide nano-wires (SiO₂-NWs)) by a simple evaporation of sulfur-contained powders on silicon wafer is discussed. A novel sulfide-assisted mechanism referring to oxygen-assisted mechanism is proposed. Amongst this simple method, sulfide or pure sulfur can both assist the formation of SiNWs. The growth is fast and some SiNWs are easily oxidized to be amorphous structure of SiO₂-NWs under the low-vacuum system. The simple method suggests a useful route to achieve plenty of one-dimensional silicon nano-structures for further research.     

Synthesis of nanoporous silicon carbide ceramics by thermal evaporation process

New nanoporous β-SiC ceramics were synthesized by a simple thermal evaporation method with commercial silicon powder and activated carbon fragments. The results of scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction indicated that the microstructure of the β-SiC nanoporous ceramics was uniform and consistent with the pore size of 50-100 nm. The β-SiC nanocrystal grains of 50-200 nm were accumulated together to form a nanopore network. The formation mechanism was attributed to a template synthesis process, in which activated carbon fragments were employed as the template and they reacted with vaporized silicon through a vapor-solid way.     

Influence of pre-surface treatment on the morphology of silicon nanowires fabricated by metal-assisted etching

Herein we demonstrate an improved metal-assisted etching method to achieve highly dense and uniform silicon nanowire arrays. A pre-surface treatment was applied on a silicon wafer before the process of metal-assisted etching in silver nitrate and hydrogen fluoride solution. The treatment made silver ion continuously reduce on silver nuclei adherence on the silicon surface, leading to formation of dense silver nanoparticles. Silver nanoparticles acting as local redox centers cause the formation of dense silicon nanowire arrays. In contrast, an H-terminated silicon surface made silver ion reduce uniformly on the silicon surface to form silver flakes. The silicon nanowires fabricated with a pre-surface treatment reveals higher density than those fabricated without a pre-surface treatment. The volume fraction improves from 18 to 38%. This improvement reduces the solar-weighted reflectance to as low as 3.3% for silicon nanowires with a length of only 0.87 μm. In comparison, the silicon nanowires fabricated without a pre-surface treatment have to be as long as 1.812 μm to achieve the same reflectance.     

Synthesis and characterization of ZnO columns grown on MgO-coated silicon substrates by carbon-thermal evaporation

Zinc oxide columns have been grown on an MgO-coated silicon (111) substrate by the carbon-thermal evaporation method at 1050 °C. The MgO layer obtained from the substrate pre-dripped in Mg(NO₃)₂ solution by the use of a dropper can solve the troublesome lattice mismatch problem in the heteroepitaxy and promote the growth of ZnO columns effectively. The as-prepared ZnO structures were characterized by using X-ray diffraction (XRD), field-emission transmission electron microscope (FETEM), selection area electron diffraction (SAED), and photoluminescence (PL) spectrum. The results show that the columns are highly crystalline with the wurtzite hexagonal structure, and grow along the [0001] in the c-axis direction. Photoluminescence (PL) spectra of the as-synthesized microstructures exhibit broad green emission peaks at ∼514 nm. In addition, the growth mechanism of the two ZnO structures is discussed based on the analysis briefly based on the time-dependent experiment.     

热沉积法制备纳米二硫化钼薄膜及其光电特性研究

以M oS2粉末为原料,以氩气为携载气体,在400～600℃温度范围内利用热蒸发方法在硅衬底表面制备了不同厚度的M oS2薄膜．利用X射线衍射和扫描电子显微镜分析了M oS2薄膜的结构和表面形貌,发现M oS2薄膜由多晶M oS2粒子组成,颗粒均匀,平均纳米颗粒尺寸约为60 nm ．利用紫外可见光光谱仪测量了其吸收特性,发现样品在720 nm附近有很强的吸收．应用霍尔效应和伏安法研究了M oS2/Si样品的接触特性和电子的运输特性,发现该异质结具有良好的整流特性,即正向电压下电流随电压呈指数增长,而在反向偏压下漏电流很小,电子迁移率可达到6．730×102 cm2/（V · s）．实验结果表明MoS2薄膜具有良好的电学特性,可用来制备晶体管和集成电路等器件．