铜掺杂类金刚石纳米点阵列的制备及场发射性能研究

利用磁过滤等离子体结合氧化铝模板(AA0)技术在室温下制备了具有优异场发射性能的铜掺杂类金刚石(DLC)纳米点阵列.微观分析表明,铜掺杂类金刚石纳米点阵列分布均匀,密度高达109cm-2;利用X射线光电子能谱对制备的铜掺杂类金刚石纳米点阵列进行结构分析,测得铜的掺杂量为3.6;且sp3键含量高达60;;通过对铜掺杂类金刚石纳米点阵列的场发射性能测试,试验结果表明,铜掺杂类金刚石纳米点阵列开启电场和阈值电场分别为0.08V/μm,0.42V/μm,并且在电场值为0.67V/μm时,发射电流密度高达95mA/cm2,场发射性能明显优于无掺杂类金刚石纳米点阵列.     

纳米石墨和纳米碳管薄膜在低电场下的稳定场发射

采用微波等离子体化学气相沉积法(MPECVD)制备出了纳米石墨和纳米碳管混合薄膜材料.通过扫描电镜(SEM)和拉曼光谱(Raman)对薄膜材料的结构和形貌进行了分析.研究了薄膜材料的场发射性能.场发射结果显示:其开启电场为0.7 V/μm1,在较低电场下(3.7 V/μm1)即可获得5.2 mA/cm2的电流密度,此电场下发射点密度可达1.6×107 cm-2,发射点均匀,亮度稳定.迭代法计算结果表明制备的纳米石墨和纳米碳管混合薄膜材料的功函数仅为3.2 eV.这些表明该薄膜材料为优良的场发射冷阴极材料.     

电化学沉淀法制备纳米结构氧化锌的场发射特性

对电化学沉淀法制备的氧化锌纳米棒阵列,通过室温下真空场发射电流密度与外加电压关系的测量,研究其场发射特性.根据测量数据,基于 Fowler-Nordheim 方程,估算了样品场发射效应的增强因子,观察到其取值随外加电压变化具有反常的两阶段性,即当外电场强度在3.3 V/μm 场发射开启值到4.3 V/μm之间时,增强因子值为1339,外加场强大于4.3V/μm 时,增强因子锐减至296;结合样品的光致发光谱和能量散射谱,应用半导体中强电场效应、掺杂半导体中温度对费米能级、载流子浓度和迁移率影响,通过场发射电流密度测量系统的串联电路等效,分析了样品缺陷态对此两阶段性的决定和影响.     

纳米非晶碳薄膜的制备及其场致电子发射特性

采用微波等离子体增强化学气相沉积(MPECVD)法,在涂有FeCl3的硅衬底上制备出了纳米非晶碳薄膜.通 过SEM、XRD和拉曼光谱分析了薄膜材料的形貌和结构.并研究了薄膜材料的场发射特性.结果表明:薄膜的开启电场仅为0.39 V/μm;当电场强度为1.85 V/μm时,电流密度高达3.06 mA/cm2;且场发射点均匀、密集、稳定.迭代法计算表明薄膜材料的功函数为3.1 eV,发射点密度约为1.7×105个/cm2.这些均表明该薄膜是一种性能优良的场发射阴极材料.     

不锈钢衬底的抛光处理对碳纳米管薄膜场发射性能的影响

在抛光的和未抛光的不锈钢衬底上,利用微波等离子体化学气相沉积(MPCVD)方法从甲烷和氢气的混合气体中沉积碳纳米管薄膜,并对其场发射性能进行了研究.实验发现,不锈钢衬底的机械抛光能降低碳纳米管膜的开启场强,增大它的发射电流密度.在同一场强7.5 V/μm下,衬底未抛光样品的电流密度为2.9 mA/cm2,而衬底抛光样品的电流密度达到5.5 mA/cm2.低开启场强和大发射电流密度意味着β增大,说明机械抛光能使碳纳米管膜的β增大.     

旋涂法制备纳米ZnO阴极涂层及场发射性能

采用水热法制备了烟花状的纳米氧化锌,用X射线衍射仪和扫描电子显微镜对样品的结构和形貌进行了表征与分析.然后通过旋涂技术将掺入不同质量的氧化锌沉积到镍衬底上,经过热处理后进行了形貌表征和场发射特性的测试.结果表明:制备的样品是六方纤锌矿结构的花状纳米晶,镍基片上沉积的纳米ZnO涂层具有突出的发射体尖端且分布较均匀;在一定范围内,电流密度随掺杂氧化锌粉末的增多而增大,开启场强逐渐下降.原因是随着ZnO的增加,有效地增强了涂层的电子输运能力,增加了有效发射体数目进而提高了场增强因子.最后,分析了涂层的场发射机制.     

Si基上电沉积Cu薄膜的形貌与择优取向

采用电化学沉积技术在Si衬底上沉积了Cu膜.场发射扫描电镜和X射线衍射分析表明:膜中存在Cu纳米颗粒, 并且表现出择优取向,与衬底的取向和斜切角度以及沉积电流密度有关.在Si(100) 衬底上,铜(220)晶面的织构系数随电流密度的增加而增加.在相同沉积条件下,在斜切角较小的Si(111)和Si(100)衬底上择优取向面都是铜 (220) 面,而在斜切角为4°的Si(111)衬底上铜(111)晶面为择优取向面.     

单晶TiO2纳米线束阵列的水热合成及场发射性能研究

采用水热合成技术,以钛酸丁酯、盐酸和去离子水作为前驱物,在透明导电玻璃(FTO)衬底上合成了垂直于衬底牛长的二氧化钛(TiO2)纳米线束阵列.纳米线束呈四方柱状结构,宽度100～200nm,长度约3μm.HRTEM表明每根纳米线束实际上是由20～40根直径约为4～6 nm的细小纳米线聚集在一起而形成的.系统研究了盐酸浓度对纳米线生长的影响,分析了盐酸在晶体生长中的作用.研究了TiO2纳米线束阵列的场致电子发射特性,其场发射开启电场为5.7 V/ μm(对应电流密度10μA/ cm2),阈值电场为9.5 V/ μm,同时表现出较好的场发射稳定性.低的合成温度和好的场发射性能表明TiO2纳米线束阵列在场发射冷阴极器件上具有良好的应用前景.     

Mn2V2O7纳米棒的制备及电化学储锂性能研究

以NH4VO3和Mn CO3为原料,采用水热法制备了Mn2V2O7纳米棒,采用X射线衍射(XRD)及场发射扫描电子显微镜(FE-SEM)对样品的结构和形貌进行了表征,并对其反应机理进行了探讨。以Mn2V2O7纳米棒作为锂离子电池的负极材料,对其电化学储锂性能进行了初步研究。结果表明:Mn2V2O7纳米棒在50 m A/g条件下的首次放电比容量为962.4 m Ah/g,循环50周后其放电比容量可稳定在389.4 m Ah/g,显示出较好的循环性能。     

铝诱导纳米硅制备大晶粒多晶硅薄膜的研究

本文以超白玻璃为衬底,利用热丝化学气相沉积和磁控溅射法制备了Glass/nc-Si/Al的叠层结构,然后置于管式退火炉中在H2气氛下进行5h诱导晶化,用XRD、光学显微镜、扫描电镜和拉曼光谱对样品进行了表征.结果表明所有样品都是有(111)择优取向的多晶硅薄膜,在425℃诱导时,多晶硅晶粒尺寸最大达400 μm,但薄膜不连续;随着诱导温度升高到450℃,样品表面已形成了连续的多晶硅薄膜,但晶粒尺寸有所减小;475℃下诱导获得的最大晶粒尺寸约为200μm,此时多晶硅薄膜的结晶质量更好.还从动力学的角度分析了铝诱导纳米硅的晶化机理.     

Synthesis and field emission properties of SnO2 nanowalls

SnO₂ nanowalls were synthesized on silicon substrate by the thermal chemical vapor transport method at a low temperature of around 650 °C under atmospheric pressure. The microstructure and morphology of the SnO₂ nanowalls were evaluated by using scanning electron microscopies and X‐ray diffraction. Room temperature photoluminescence spectra of the nanowalls showed a broad emission band centering at about 530 nm. Field emission measurements demonstrated that the nanowalls possessed good performance with a turn‐on field of ∼3.5 V/μm and a threshold field of ∼6.1 V/μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于单体石墨纤维的场发射特性研究

利用化学气相沉积(CVD)法,以甲烷为碳源在管式炉中合成了单体石墨纤维(MGF)。选取长度为3.426 mm,顶端球面半径为11.26 μm的单体石墨纤维直立于圆铜片上作为阴极,以导电ITO玻璃作为阳极,采用二极管结构在真空室中进行直流场发射测试,证实MGF的开启场强为0.477 5 V/μm。基于有限元仿真软件ANSYS进行电磁场分析,计算了MGF在不同电压下的有效发射面积。结果表明,当电压为5.36 kV时,MGF达到最大发射面积为796.226 μm²,在实验测量电压范围内,平均发射电流密度可以达到46.069 A/cm²,单体石墨纤维具有良好的场发射特性。     

高压13.56MHz PECVD法沉积器件质量级本征微晶硅材料

本文国内首次报道了采用高压RF-PECVD技术沉积本征微晶硅材料的结果.实验表明,增大等离子体激发功率和减小硅烷浓度都能够使薄膜材料由非晶硅逐渐向微晶硅转变,而结构上的改变使得电学特性也随之改变.通过工艺参数的优化和纯化器的使用,有效地控制了氧的掺杂,在较高的生长速度下得到了器件质量级的本征微晶硅材料.将实验得到的微晶硅作为太阳电池光吸收层,在没有ZnO背电极和没有优化窗口层材料以及p/i界面时,电池的效率达到5.22;,这进一步表明本征微晶硅材料的良好性能.     

Controllable synthesis of novel In2O3 nanostructures and their field emission properties

Three kinds of novel indium oxide (In₂O₃) nanostructures, namely, nanorods, nanoflowers and nanowhiskers were synthesized on silicon substrate via a simple vapor‐phase transport method under atmospheric pressure. The In₂O₃nanostructures were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive X‐ray spectrometer (EDS) spectrum. The Raman spectra of these nanostructures showed four sharp scattering peaks centered at 308, 365, 522, and 628 cm^‐1, whose position and intensity were characteristic of standard Raman spectra for In₂O₃. The Room‐temperature photoluminescence (PL) spectra showed visible emissions centered around 576, 592, and 624 nm. Field emission measurements demonstrated that the nanoflowers possessed the best performance with a turn‐on field of 3.54 V/µm and a threshold field of 9.83 V/µm. And the field enhancement factors of these nanostructures are high enough for the application of field emission display devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of microcrystalline silicon solar cells on microcrystalline silicon carbide window layers grown with HWCVD at low temperature

N-type microcrystalline silicon carbide layers prepared by hot-wire chemical vapor deposition were used as window layers for microcrystalline silicon n–i–p solar cells. The microcrystalline silicon intrinsic and p-layers of the solar cells were prepared with plasma-enhanced chemical vapor deposition at a very high frequency. Amorphous silicon incubation layers were observed at the initial stages of the growth of the microcrystalline silicon intrinsic layer under conditions close to the transition from microcrystalline to amorphous silicon growth. ‘Seed layers’ were developed to improve the nucleation and growth of microcrystalline silicon on the microcrystalline silicon carbide layers. Raman scattering measurement demonstrates that an incorporation of a ‘seed layer’ can drastically increase the crystalline volume fraction of the total absorber layer. Accordingly, the solar cell performance is improved. The correlation between the cell performance and the structural property of the absorber layer is discussed. By optimizing the deposition process, a high short-circuit current density of 26.7 mA/cm² was achieved with an absorber layer thickness of 1 μm, which led to a cell efficiency of 9.2%.     

Nonlinear optical properties of ZnS nanocrystals incorporated within the polyvinyl alcohole photopolymer matrices

Photoinduced nonlinear optical effects in ZnS nanocrystallites incorporated within the photopolymer polyvinyl alcohol matrices were studied. As a basic method we have used photoinduced optical second harmonic generation (SHG). The Q‐switched HF‐laser (λ = 2.64.μm; pulse duration 30‐40 ps) was used as a source of probing (fundamental) light beam and the pulsed nitrogen (λ = 337.7 nm) was applied as a source of the photoinducing pump light. With increasing photoinducing beam power, the output SHG signal (at λ = 1.32 μm) increases. The maximal second‐order non‐linear optical susceptibility corresponds to tensor component d₁₂₃ = d₁₄ = 3.8 ± 0.2 pm/V at a photoinducing power density equal to about 1.25 GW/cm². With decreasing temperature, the SHG signal increases within the temperature range 25‐30 K. Time‐dependent pump‐probe measurements of the SHG indicate an existence of the SHG maximum for a pump‐probe delaying time 20 ps. The ZnS hexagonal structural components play a crucial role in the observed photoinduced second‐order non‐linear optical effects. Large values of the non‐linear optical constants as well the good technological parameters open a possibility to enhance the non‐linear optical susceptibilities of the investigated ZnS nanocrystallites.     

Infrared semiconductor laser irradiation used for crystallization of silicon thin films

We report the rapid thermal crystallization of silicon films using infrared semiconductor laser. Carbon films were used on silicon films to absorb the laser light. Uniform crystalline regions were achieved by a line shape laser beam with a length of 20 μm. Polycrystalline silicon thin film transistors were fabricated in crystallized regions. The effective electron carrier mobility and threshold voltage were achieved to be 130 cm²/Vs and 0.4 V, respectively, when the crystalline volume ratio of the silicon films was 0.95.     

Directional role of weak magnetic field on the self-fabrication of ordered nickel chains

Novel ordered nickel chains with diameter 250–500 nm and length more than 5 μm were synthesized under weak magnetic field by hydrazine reducing in ethylene glycol. The phase, morphology and magnetic properties were characterized by X-ray diffraction (XRD), scanning electron microanalyzer (SEM) and vibrating sample magnetometer (VSM), respectively. The results reveal that weak magnetic field leads to the fabrication of nickel chains paralleling each other with hierarchical structures. The growth mechanism and fabrication process of nickel magnetic nanocrystallites were discussed.     

Application of Infrared ATR Spectroscopy to Liquid Crystals. III

Infrared absorption measurements of nematic N-(p-ethoxybenzylidene)-p'-cyanoaniline (EBCA) under a DC electric field were performed by means of our previously reported ATR method. DC voltages up to 15V were applied to the nematic liquid crystal 15 μm thick between a silicon ATR prism (probing electrode) and an In₂O₃-coated glass electrode (opposite electrode). By using this method the orientational behavior of molecules in boundary layers about 1 μm thick at the Si electrode was investigated.

The threshold voltage for the dielectric orientation varied from 2 to 6 V depending upon the boundary conditions at the opposite electrode, and the maximum degree of order of homeotropic orientation was found to be 0.6–0.7. A storage effect, in which a homeotropic texture induced by the electric field remains unaltered even if the field is removed or reversed, was observed.