表面镀钛对金刚石薄膜场发射特性的影响

利用等离子体化学气相（MWPCVD）沉积法在Si（100）面上沉积了金刚石薄膜,采用SEM、AFM、XRD、Raman、XPS等方法对薄膜的结构及表面形貌进行了分析。为提高薄膜的场发射性能,在金刚石表面溅射了金属Ti,对比金刚石薄膜、金刚石／金属Ti复合薄膜的场发射性能,结果表明,金刚石／金属Ti薄膜的发射电流密度更大,且随着电场的增加电流密度急剧增加,开启电场低,约为3V／μm,当电场为25V／μm时发射电流密度可达到1400mA／cm2,并在机理上进行了一些探索,对金刚石／金属复合结构薄膜的场发射性能研究有重要意义。     

利用前后处理技术改进钛／硅基板上的类金刚石场发射特性

采用微波等离子体化学气相沉积系统存钛/硅基板上沉积类金刚石薄膜,并利用拉曼光谱仪、扫瞄式电子显微镜及原子力显微镜研究了氢等离子体前处理及快速退火后处理对类金刚石薄膜场发射特性之影响.在沉积类金刚石薄膜之前,钛/硅基板使用了两种前处理技术:第一种为研磨金刚石粉末,第二种为研磨金刚石粉末后外加氢等离子体刻蚀处理.成长类金刚石薄膜后进行快速退火处理.发现不论是氢等离子体前处理还是快速退火后处理皆能改善场发射特性,其中经退火后处理的场发射特性比氢等离子体前处理的场发射特性改善更明显.其因之一在于快速退火后处理可在类金刚石薄膜表而形成sp2丛聚,提供了很多的场发射子,也同时增加了表面粗糙度;另一个原因可能是在快速退火后处理期间会使类金刚石薄膜进一步石墨化,因而提供了许多电子在通过类金刚石薄膜时的传输路径.研究结果表明:利用适当的前后处理技术可改进类金刚石薄膜的场发射特性,进而做为冷阴极材料之应用.     

Efficient field emission properties of ZnO (core)/graphite (shell) nanowires

In this work the field emission studies of a new type of field emitter, zinc oxide (ZnO) core/graphitic (g-C) shell nanowires are presented. The nanowires are synthesized by chemical vapor deposition of zinc acetate at 1300 °C Scanning and transmission electron microscopy characterization confirm high aspect ratio and novel core–shell morphology of the nanowires. Raman spectrum of the nanowires mat represents the characteristic Raman modes from g-C shell as well as from the ZnO core. A low turn on field of 2.75 V/μm and a high current density of 1.0 mA/cm² at 4.5 V/μm for ZnO/g-C nanowires ensure the superior field emission behavior compared to the bare ZnO nanowires.     

Nanocrystalline graphite films nucleation by the radio frequency bias pretreatment

New method for nucleation of different nanocrystalline carbon films upon monocrystalline Si substrate was proposed. The process is based on a combination of microwave and radio frequency plasma assisted chemical vapor deposition methods. Potential of the method for nucleation was demonstrated by deposition of nanocrystalline diamond film in pure microwave plasma in one process, immediately after "seeding" procedure. The method was also used for growth of nanocrystalline graphite (NCG) films, which are currently under intensive investigation due to their exceptional electronic properties, particularly fine electron emission characteristics. Deposited NCG films have demonstrated remarkable electron field emission properties having current density of up to 10 A/cm2. The films have also possessed good adhesion to silicon substrate. Carbon films and nucleation layer were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

ZnO薄膜气相法制备

ZnO薄膜具有压电、光电、压敏、气敏、发光等多种特性,应用十分广泛。介绍了ZnO薄膜气相法制备原理中的各类主要方法,包括脉冲激光沉积、磁控溅射、分子束外延、金属有机化合物化学气相沉积、单源化学气相沉积和等离子体增强化学气相沉积等技术;分析了这些方法的优缺点;展望了ZnO薄膜今后的研究方向。     

Enhanced field emission from ZnO nanoneedles on chemical vapour deposited diamond films

ZnO nanoneedles were coated on hot filament chemical vapour deposited diamond thin films to enhance the field emission properties of ZnO nanoneedles. The virgin diamond films and ZnO nanoneedles on diamond films were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The field emission studies reveal that the ZnO nanoneedles coated on diamond film exhibit better emission characteristics, with minimum threshold field (required to draw a current density ~ 1 μA/cm²) as compared to ZnO needles on silicon and virgin diamond films. The better emission characteristic of ZnO nanoneedles on diamond film is attributed to the high field-enhancement factor resulting due to the combined effect of the ZnO nanoneedles and diamond film.     

Field emission from diamond and diamond-like carbon films

Field emission from diamond and diamond-like carbon thin films deposited on silicon substrates has been studied. The diamond films were synthesized using hot filament chemical vapor deposition technique. The diamond-like carbon films were deposited using the radio frequency chemical vapor deposition method. Field emission studies were carried out using a sphere-to-plane electrode configuration. The results of field emission were analyzed using the Fowler-Nordheim model. It was found that the diamond nucleation density affected the field emission properties. The films were characterized using standard scanning electron microscopy, Raman spectroscopy, and electron spin resonance techniques. Raman spectra of both diamond and diamond-like films exhibit spectral features characteristic of these structures. Raman spectrum for diamond films exhibit a well-defined peak at 1333cm^?1. Asymmetric broad peak formed in diamond-like carbon films consists of D-band and G-band around 1550 cm^?1 showing the existence of both diamond (sp³ phase) and graphite (sp² phase) in diamond-like carbon films.     

Growth and characterization of indium phosphide nanowires on transparent conductive ZnO:Al films

The epitaxial growth of indium phosphide nanowires (InP NWs) on transparent conductive aluminum-doped zinc oxide (ZnO:Al) thin films is proposed and demonstrated. ZnO:Al thin films were prepared on quartz substrates by radio frequency magnetron sputtering, then InP NWs were grown on them by plasma enhanced metal organic chemical vapor deposition with gold catalyst. Microstructure and optical properties of InP nanowires on ZnO:Al thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), photoluminescence and Raman spectroscopy at room temperature. SEM shows that randomly oriented and intersecting InP nanowires were grown to form a network on ZnO:Al thin films. Both wurtzite (WZ) and zincblende (ZB) structures coexist in the random orientation InP NWs on ZnO:Al thin film had been proved by XRD analysis. XPS result indicates Zn diffusion exists in the InP NWs on ZnO:Al. The photoluminescence spectra of InP nanowires with Zn diffusion present an emission at 915 nm. Zn diffusion also bring effect on Raman spectra of InP NWs, leading to more Raman-shift and larger relative intensity ratio of TO/LO.     

用于高频声表面波器件的CVD金刚石衬底的研究

使用纳米金刚石粉研磨工艺预处理硅片衬底抛光面,在低气压成核的条件下,以丙酮和氢气为反应物,采用传统的热丝辅助化学气相沉积法,制备了自支撑金刚石膜;通过射频磁控溅射法沉积氧化锌薄膜在自支撑金刚石膜的成核面,形成氧化锌/自支撑金刚石膜结构.通过光学显微镜、扫描电镜及原子力显微镜测试自支撑金刚石膜成核面的表面形貌.研究结果表明:成核期的低气压有助于提高成核密度,成核面表面粗糙度约为1.5 nm;拉曼光谱显示1334 cm-1附近尖锐的散射峰与金刚石SP3键相对应,成核面含有少量的石墨相,且受到压应力的作用;ZnO/自支撑金刚石膜结构的XRD谱显示,氧化锌薄膜有尖锐的(002)面衍射峰,是c轴择优取向生长的.     

Microstructures of microcrystalline silicon thin films prepared by hot wire chemical vapor deposition

Undoped hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the μc-Si:H films with different H₂/SiH₄ ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of μc-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of μc-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si---H bonds in μc-Si:H and in polycrystalline Si thin films are located at the grain boundaries.     

The influence of orientation on the photoluminescence behavior of ZnO thin films obtained by chemical solution deposition

A new type of ZnO thin films synthesized from chemical solution deposition at low temperature has been presented. X-ray powder diffraction and field emission scanning electron microscopy investigation reveal that the novel structured ZnO film is uniform and its [0001] direction is parallel to the substrate. The photoluminescence spectrum of this film shows strong ultraviolet band-gap emission and weak defect-related visible emission comparing to that of [0001]-oriented film, indicating high crystal quality of the non-[0001]-oriented ZnO film.     

Effects of sapphire substrates surface treatment on epitaxial ZnO thin films grown by MOCVD

The surface treatment effects of sapphire substrate on the quality of epitaxial ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) were studied. The sapphire substrates have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best-quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements. Results show that the intensity of (002) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching is strongest. FWHM of (002) diffraction peak is narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

Electron field emission characteristics of different surface morphologies of ZnO nanostructures coated on carbon nanotubes

The optimal carbon nanotube (CNT) bundles with a hexagonal arrangement were synthesized using thermal chemical vapor deposition (TCVD). To enhance the electron field emission characteristics of the pristine CNTs, the zinc oxide (ZnO) nanostructures coated on CNT bundles using another TCVD technique. Transmission electron microscopy (TEM) images showed that the ZnO nanostructures were grown onto the CNT surface uniformly, and the surface morphology of ZnO nanostructures varied with the distance between the CNT bundle and the zinc acetate. The results of field emissions showed that the ZnO nanostructures grown onto the CNTs could improve the electron field emission characteristics. The enhancement of field emission characteristics was attributed to the increase of emission sites formed by the nanostructures of ZnO grown onto the CNT surface, and each ZnO nanostructure could be regarded as an individual field emission site. In addition, ZnO-coated CNT bundles exhibited a good emission uniformity and stable current density. These results demonstrated that ZnO-coated CNTs is a promising field emitter material.     

纳米晶碳化钨薄膜的析氢催化性能

采用等离子体增强化学气相沉积法制备了具有纳米结构的碳化钨薄膜, 采用XRD、EDS、SEM方法表征了薄膜的表面形貌、化学组成和物相结构. 这种碳化钨纳米晶薄膜具有巨大的电化学比表面积、很好的电催化活性和电化学稳定性. 通过测试和计算表明, 几何面积为1cm²碳化钨薄膜/泡沫镍电极、碳化钨薄膜/镍电极的电化学比表面积分别为83.21和64.13cm2; 该薄膜电极材料的a值为0.422～0.452V, 接近低超电势材料; 析氢交换电流密度为4.02～4.22×10^-4A/cm²; 当超电势为263mV时, 其析氢反应的活化能为45.62～45.77kJ/mol.     

双纳米硅p层优化非晶硅太阳能电池

采用等离子体增强化学气相沉积(Plasma Enhanced Chemical Vapor Deposition,PECVD)技术在高功率密度、高反应气压和低衬底温度下制备出不同氢稀释比RH的硅薄膜.高分辨透射电镜(High-Resolution Transmission Electron Microscopy,HRT...     

Field emission characteristics from tapered ZnO nanostructures grown onto vertically aligned carbon nanotubes

Zinc oxide (ZnO) nanostructures were grown on vertically aligned carbon nanotubes (CNTs) using thermal chemical vapor deposition (CVD) to enhance the field emission characteristics. The shape of ZnO nanostructure was tapered. Scanning electron microscopy (SEM) image showed the ZnO nanostructures were grown onto CNT surface uniformly. The field electron emission of pristine CNTs and ZnO-coated CNTs were measured. The results showed that ZnO nanostructures grown onto CNTs could improve the field emission characteristics. The ZnO-coated CNTs had a threshold electric field at about 3.1 V/μm at 1.0 mA/cm². The results demonstrated that the ZnO-coated CNT is an ideal field emitter candidate material. The stability of the field emission current was also tested.     

The effect of microtopography and deposition regime on the field emission properties of graphitelike carbon films

Technological factors controlling the formation of the microtopography of the surface of graphitelike carbon films deposited from the plasma of a microwave gas discharge in ethanol vapor are established. Parameters of the deposition regime and the surface roughness influence the electric conductivity and the field emission properties of the films obtained by this method. Using graphitelike carbon films, an emission current density of up to 0.3 A/cm² was obtained at an electric field strength in the gap of about 7 V/μm.     

Optical emission spectroscopy study of positive direct current bias enhanced diamond nucleation

High nucleation density and crystalline diamond films were deposited on a mirror-polished Si(100) substrate by horizontal microwave plasma chemical vapor deposition using a two step process consisting of positive direct current (dc) bias enhanced nucleation and growth. Optical emission spectroscopy was employed to investigate in situ the plasma emission characterization during positive biasing process. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, C₂, and Ar were observed in the visible and ultraviolet ranges when CH₄, H₂, and Ar were used as the reactant gases. The dependence of plasma emission spectra on the deposition parameters, such as biasing voltage, methane concentration and working pressure was investigated. The relative concentrations of neutral atomic hydrogen were estimated by using the Ar emission at 750.4 nm as an actinometer. A significant variation in the emission intensity of the radicals was measured with a change in the biasing voltage. The correlation between the spectra of some species and the quality of diamond films was studied. The results show that CH and C₂ both were important precursor in the diamond deposition, while C₂ was associated with the presence of amorphous phase in the films during positive dc biasing process.     

掺硼浓度对金刚石薄膜二次电子发射特性的影响

掺硼金刚石薄膜具有负电子亲和势和良好的电子运输性能且容易制备,作为冷阴极材料在图像显示技术和真空技术等领域都存在巨大的应用价值,引起人们的广泛关注。采用MPCVD法利用氢气、甲烷和硼烷的混合气体,制备出不同浓度的掺硼金刚石薄膜。结果表明,掺硼浓度影响金刚石薄膜的物相结构、组织形貌,进而影响其二次电子发射性能,当硼烷的流量为4mL/min时,制备的金刚石薄膜质量最好,二次电子发射系数约为90。     

Realization of nonpolar a-plane ZnO films on r-plane sapphire substrates using a simple single-source chemical vapor deposition

Nonpolar (112?0) ZnO thin films (a-plane ZnO) have been grown on (11?02) sapphire substrates (r-plane sapphire) by a simple atmospheric pressure single-source chemical vapor deposition (SSCVD) approach. The crystallinity, surface morphology and optical property of the films were investigated using high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM) and transmission spectrum, respectively. XRD results revealed that the ZnO films were grown on the substrates epitaxially along (112?0) orientation, and the epitaxial relationship between the ZnO films and the substrates was determined to be (112?0)ZnO∥(11?02) Al2O3, and [1?101]ZnO∥[022?1]Al₂O₃. The SEM image exhibited that the a-plane ZnO films showed a high density of well-aligned ZnO sheets with rectangular structure. The transmission spectrum showed that the ZnO films were highly transparent in the visible region.