Lithography-independent and large scale fabrication of a metal electrode nanogap

A lithography-independent and wafer scale method to fabricate a metal nanogap structure is demon-strated. Polysilicon was first dry etched using photoresist (PR) as the etch mask patterned by photolithography.Then, by depositing conformal SiO_2 on the polysilicon pattern, etching back SiO_2 anisotropically in the perpendic-ular direction and removing the polysilicon with KOH, a sacrificial SiO_2 spacer was obtained. Finally, after metal evaporation and lifting-off of the SiO_2 spacer, an 82 nm metal-gap structure was achieved. The size of the nanogap is not determined by the photolithography, but by the thickness of the SiO_2. The method reported in this paper is compatible with modern semiconductor technology and can be used in mass production.

Effects of Thickness on Properties of ZnO Films Grown on Si by MOCVD

High quality ZnO films are successfully grown on Si（100） substrates by metal-organic chemical vapor deposition at 300℃. The effects of the thickness of the ZnO films on crystal structure, surface morphology,and optical properties are investigated using X-ray diffraction, scanning probe microscopy,and photoluminescence spectra, respectively. It is shown that the ZnO films grown on Si substrates have a highly-preferential C-axis orientation,but it is difficult to obtain the better structural and optical properties of the ZnO films with the increasing of thickness. It is maybe due to that the grain size and the growth model are changed in the growth process.

Nano-layer structure of silicon-on-insulator materials

Silicon-on-insulator (SOI) has been recognized as a promising semiconductor starting material for ICs where high speed and low power consumption are desirable, in addition to its unique applications in radiation-hardened circuits. In the present paper, three novel SOI nano-layer structures have been demonstrated. ULTRA-THIN SOI has been fabricated by separation by implantation of oxygen (SIMOX) technique at low oxygen ion energy of 45 keV and implantation dosage of 1.81017/cm2. The formed SOI layer is uniform with thickness of only 60 nm. This layer is of crystalline quality. and the interface between this layer and the buried oxide layer is very sharp, PATTERNED SOI nanostructure is illustrated by source and drain on insulator (DSOI) MOSFETs. The DSOI structure has been formed by selective oxygen ion implantation in SIMOX process. With the patterned SOI technology, the floating-body effect and self-heating effect, which occur in the conventional SOI devices, are significantly suppressed. In order to improve the total-dose irradiation hardness of SOI devices, SILICON ON INSULATING MULTILAYERS (SOIM) nano-structure is proposed. The buried insulating multilayers, which are composed of SiOx and SiNy layers, have been realized by implantation of nitride and oxygen ions into silicon in turn at different ion energies, followed by two steps of high temperature annealing process, respectively, Electric property investigation shows that the hardness to the total-dose irradiation of SOIM is remarkably superior to those of the conventional SIMOX SOI and the Bond-and-Etch-Back SOI.

Effects of annealing time and Si cap layer thickness on the Si/SiGe/Si heterostructures thermal stability

The effects of annealing time and Si cap layer thickness: on the thermal stability of the Si/SiGe/Si heterostructures deposited by disilane and solid-Ge molecule beam epitaxy were investigated. It is found that in the same strain state of the SiGe layers the annealing time decreases with increasing Si cap layer thickness. This effect is analyzed by a force-balance theory and an equation has been obtained to characterize the relation between the annealing time and the Si cap layer thickness. (C) 2001 Elsevier Science B.V. All rights reserved.

The influence of thickness on properties of GaN buffer layer and heavily Si-doped GaN grown by metalorganic vapor-phase epitaxy

The physical properties of low-temperature-deposited GaN buffer layers with different thicknesses grown by metal-organic vapor-phase epitaxy have been studied. A tentative model for the optimum thickness of buffer layer has been proposed. Heavily Si-doped GaN layers have been grown using silane as the dopant. The electron concentration of Si-doped GaN reached 1.7 x 10(20) cm(-3) with mobility 30 cm(2)/V s at room temperature. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

岷江柏种子的形态和发芽特征与贮藏生理动态研究

岷江柏(Cupressus chenggiana S. Y. Hu)是我国川甘地区特有的珍稀濒危乔木，一般生长在干旱的河谷区，在涵养水源和保护水 土等方面起着重要的作用。本文选择4个岷江柏种群，采用了野外调查和室内实验相结合的研究方法，调查岷江柏种群结实状况， 分析种子和球果形态特征，阐明种子发芽的基本特征，研究岷江柏种子贮藏过程中几个生理指标的动态变化特点，目的是为岷江柏 种苗繁育、自然更新能力评估以及珍稀濒危机制分析提供理论依据。研究得出如下结论：1.岷江柏球果呈椭球形，长为1.5～ 2.2cm,宽为1.5～1.9cm，质量为1.7～4.2g，球果鳞片数量为8～11片，球果内种子数量一般在40～70粒。岷江柏种子为椭圆形，长 为3.58～4.02mm，宽为3.10～3.15mm，厚为0.96～1.11mm，千粒重为3.1～3.5g。岷江柏的结实率很低，并且有显著的地理差异和 大小年差异。2. 岷江柏种子发芽温度范围是5℃～30℃,其中种子的适宜发芽温度范围是10℃～25℃。种子最适发芽温度随着贮藏 时间的增加而变化。在适宜温度范围内，种子发芽周期为20d。温度对种子的发芽势和T50有显著影响，对种子发芽率没有显著影响 ；光照有利于种子发芽；岷江柏种子的发芽特征是岷江柏保护种子资源、防止物种濒危的一种环境适应，有助于岷江柏种子提高发 芽率和幼苗的存活率。岷江柏种子是一种耐贮藏的正常性种子，在短期贮藏过程中，贮藏温度和种子含水量对于种子生理指标和种 子发芽没有显著影响。3. 岷江柏种子在短期贮藏过程中，千粒重没有显著变化；含水量都经历了先下降，再稳定的过程；粗脂肪 含量和可溶性糖含量逐渐降低；可溶性蛋白含量和丙二醛含量逐渐增加；脯氨酸含量在贮藏1～7个月时变化差异不明显，但是贮藏 7～10个月后显著增加。岷江柏种子的各个生理指标之间的相关性差异不显著。4. 岷江柏球果和种子的形态特征存在显著的地理差 异。岷江柏种子的发芽能力的地理性差异不大，种群间差异不大。岷江柏种群的地理差异由种群特征、生境特征和气候特征共同决 定。5. 在岷江柏的人工繁育中，对于刚刚采集的种子，发芽温度在15℃～25℃比较适合，其中以25℃最佳；而对于短期贮藏(4～ 10个月)后的种子，发芽温度在10℃～25℃均可，以15℃～20℃为最佳。野外播种的最适时间为4～6月，6～9月的间歇性干旱和降 水波动可能是限制岷江柏自然更新的因素之一。在短期贮藏过程中，种子可以采用常规室温贮藏，可以节约成本。Cupressus chenggiana is a specific and endangered plant in Sichuan and Gansu provinces of China, and it usually grows in dry valley and plays an important role in water supply and soil and water conservation in the dry valley of alpine and canyon region of southwest China. The research selected four Cupressus chenggiana populations and used the methods of the field investigation and the lab experiments. The fruiting characters of Cupressus chenggiana populations, the morphological characters of seeds and cones, the germination characters of seeds and the store physiological dymatics of several factors of seeds have been studied in order to give some theoretical advices on the artificial propagation and the ability of natural regeneration and the endangered principle of Cupressus chenggiana in the paper. The main results may be clarified as follows: 1. The cones of Cupressus chenggiana are ellipsoidal, length ranged from 1.5 to 2.2cm, with ranged from 1.5 to 1.9 cm, weight ranged from 1.7 to 4.2g, the number of cone squama ranged from 8 to 11, and the seed number of per cone ranged from 40 to 70. The seeds of Cupressus chenggiana are elliptical, length ranged from 3.58 to 4.02 mm, width ranged from 3.10 to 3.15 mm, thickness ranged from 0.96 to 1.11 mm, and the weight of 1000 seeds ranged from 3.1 to 3.5g. The fruiting rate of Cupressus chenggiana is very low, and the fruiting period of Cupressus chenggiana has the geographical differences and the big or small year differences. 2. Seed germination temperature is between 5℃ and 30℃, while the suited temperature is between 10℃ and 25℃. The optimum temperature of seed germination will change as the store time of seeds changes logner. The cycle of seed germination can persist 20 days in the range of the suited temperature. The germination temperatures have significant influences on the germination potential and T50, but have no significant infuluences on the germination rate. The photoperiod is in favor of seed germination. The characters of Cupressus chenggiana seed germination represent a kind of environmental adaptability to protect the seed sources and endangered species, and it can give help to increase the germination rate of seeds and the livability of seedings. The seeds of Cupressus chenggiana are a kind of orthodox seeds that can endure the long time storage. In the short time storage, the store temperatures and the moisture contents of seeds have no significant infuluences on the physiological factors and the germination of seeds, but the store time has significant influences on the physiological factors of seeds. 3. In the short store course of Cupressus chenggianna seeds, the 1000 seed weight has no significant variation; The moisture content descends at the beginning of the storage, but has no significant variation later; The crude fat content and the soluble sugar content descend gradually; The soluble protein content and MDA content increase gradually; The praline content has no significant variation after 1～7 months storage, but increase significantly after 7～10 months storage. The correlations of different physiological factors are not significant. 4. The morphological characters of cones and seeds of four populations exist significant differences. The germination of Cupressus chenggiana seeds has no significant geographical variation. The geographical variation of Cupressus chenggiana populations can be ascribed to the population characters, climate and environment. 5. In the course of artificial propagation of Cupressus chenggiana, it is favored that the germination temperature of newly collected seeds is between 15℃ and 25℃, while the optimum temperature is 25℃. After the short storage ranged from 4 months to 10 months, it is favored that the germination temperature is between 10℃ and 25℃, while the optimum temperature is ranged from 15℃ to 20℃. The field sowing optimum time is between April and June, and the interval drought and fallrain fluctuation between July and September may be one of the reasons that restrict natural regeneration of Cupressus chenggiana. In the short storage, seeds can be stored in the condition of room temperature.

Investigation of add-back effects in a segmented Clover detector

The resolution and the summing characteristics of an EXOGAM segmented Clover germanium detector has been studied for use it in gamma spectroscopic experiments. The measurements have been performed with standard radioactive sources of Eu-152, Ba-133 and beta-delayed gamma-rays from Ir-176 decay. The data analytic results, realized by software, are presented in this paper.

Retention modeling and optimization of pH value and solvent composition in HPLC using back-propagation neural networks and uniform design

A novel method for the optimization of pH value and composition of mobile phase in HPLC using artificial neural networks and uniform design is proposed. As the first step. seven initial experiments were arranged and run according to uniform design. Then the retention behavior of the solutes is modeled using back-propagation neural networks. A trial method is used to ensure the predicting capability of neural networks. Finally, the optimal separation conditions can be found according to a global resolution function. The effectiveness of this method is validated by optimization of separation conditions for both basic and acidic samples.

A plasma sputtering decoration route to producing thickness-tunable ZnO/TiO2 core/shell nanorod arrays

We report a radio frequency magnetron sputtering method for producing TiO2 shell coatings directly on the surface of ZnO nanorod arrays. ZnO nanorod arrays were firstly fabricated on transparent conducting oxide substrates by a hydrothermal route, and subsequently decorated with TiO2 by a plasma sputtering deposition process. The core/shell nanorods have single-crystal ZnO cores and anatase TiO2 shells. The shells are homogeneously coated onto the whole ZnO nanorods without thickness change. This approach enables us to tailor the thickness of the TiO2 shell for desired photovoltaic applications on a one-nanometer scale. The function of the TiO2 shell as a blocking layer for increasing charge separation and suppression of the surface recombination was tested in dye-sensitized solar cells. The enhanced photocurrent and open-circuit voltage gave rise to increased photovoltaic efficiency and decreased dark current, indicating successful functioning of the TiO2 shell.

Submicrometre scale single-crystalline gold plates of nanometre thickness: synthesis through a nucleobase process and growth mechanism

Synthesis of submicrometre scale single-crystalline gold plates of nanometre thickness in the presence of nucleobase guanine through chemical reduction of HAuCl4 was investigated. The elemental composition of the as-prepared gold nanoplates was estimated using energy-dispersive x-ray spectroscopy. The as-prepared gold plates were composed of essentially (111) lattice planes, as revealed by both x-ray diffraction (XRD) and transmission electron microscopy (TEM) results. It was found that the molar ratio of HAuCl4 to guanine played a very important role in the formation of gold nanoplates. Gold nanoplates could be produced at a molar ratio of [HAuCl4]/[guanine] = 50: 1 while only smaller gold spherical nanoparticles were obtained at molar ratios of [HAuCl4]/[guanine] <= 20:1. A possible growth mechanism of the as-prepared gold nanoplates is proposed and discussed. The results and conclusion presented in this work may be valuable for our further understanding of the roles of precursor ligands in the control of nanoparticles aggregation states and the preparation of shape-controlled nanoparticles.

Thickness dependence of mobility in CuPc thin film on amorphous SiO2 substrate

Hole mobility in a copper-phthalocyanine (CuPc)-based top-contact transistor has been studied with various organic layer thicknesses. It is found that the transistor performance depends on the thickness of the CuPc layer, and the mobility increases with the increase in the CuPc layer and saturated at the thickness of 6 ML. The upper layers do not actively contribute to the carrier transport in the organic films. The morphology of the organic layer grown on the bare SiO2/Si substrate is also presented. The analysis of spatial correlations shows that the CuPc films grow on the SiO2 according to the mixed-layer mode.