真空微电子压力传感器的研制

提出了一种带过载保护功能的真空微电子压力传感器.对传感器的压力敏感膜尺寸、阴阳极间距等结构参数进行了分析计算;针对过载保护的问题,在结构上设计了过载保护环,实现了真空微电子压力传感器的过载自保护功能.采用硅的干、湿法结合的腐蚀、氧化锐化和真空键合等工艺技术,成功地研制出传感器实验样品.对传感器实验样品的参数进行了测试分析,其场致发射阴极锥尖阵列密度达24000个/mm²,起始发射电压为0.5～1V,反向电压≥25V,当正向电压为5V时,单尖发射电流为0.2nA,压力灵敏度为0.1μA/KPa.     

碳纳米管场致发射特性的研究

详细论述了碳纳米管的场致发射特性，包括开启电场、阈值电场、发射电流密度、发射电流的稳定性及场发射电子能量分布等；阐述了场发射的机制；分析了发射特性与其几何结构、吸附态及尖端缺陷等因素的关系；并简要介绍了碳纳米管场发射特性在平板显示领域中的实际应用。     

超构表面红外分光阵列设计

超构表面阵列分光具有高透射、低损耗、高集成度的特点,是当前微纳结构领域的研究热点.本文提出了一种由Si和SiO2组成的超构表面红外分光阵列.以不同波长的红外光入射单元,仅改变圆柱半径,分别计算不同波长的透射率和出射相位随半径的变化.根据广义斯涅尔定律,选择具有不同圆柱半径的若干单元组成超构表面分光周期.该周期对不同波长...     

场致发射公式的研究

在用Ｆｏｒｌｅｒ—Ｎｏｒｄｈｅｉｍ方程描述或检验场致阴极发射阵列（ＦＥＡ—ＦｅｉｌｄＥｍｉｔｅｒＡｒ－ｒａｙｓ）的特性时，由于简约，结果不太理想。本文试图给出一个普适的统一的理论公式，它考虑了空间电荷限制效应和温度的影响，并且对场强也没有特别的限制，可用于金属ＦＥＡ的数值计算。     

圆形出液口悬浮阴极平面电化学加工间隙建模及实验研究

提出利用极间电解液液膜支撑阴极悬浮形成加工间隙,通过调节流量和电流实现极间间隙的调节和控制的新方法。以圆形出液口悬浮阴极平面电化学加工为例,基于流体力学和电极过程动力学理论建立加工间隙的数学模型,得到间隙与流量、压差及电流之间的关系。利用Fluent软件对间隙模型流场特性进行分析,得到间隙中电解液的压力场和速度场的分布情况,进而得到进出口压差和出口流速;实验获得不同流量、电流条件下的加工间隙。理论模型计算结果和实验数据结果相近,变化规律基本一致。     

深度与形貌检测的仿生磁致伸缩触觉传感器设计及实验测试

物体表面形貌深度信息对于智能机器人检测物体表面特征、人机交互具有重要意义。 受动物毛发感知机理启发,设 计了一种新型仿生磁致伸缩触觉传感器单元及阵列;基于逆磁致伸缩效应、欧拉-伯努利梁理论和胡克定律,推导了深度检 测的输出电压模型。 仿真研究确定了最佳偏置磁场和阵列间距,实验测试了传感器单元在静态和动态下的输出特性,在 0. 05~ 4. 8 mm 深度检测范围内,灵敏度为 185. 72 mV/ mm,响应时间和恢复时间分别为 31 ms 和 43 ms,且具有良好的重复 性,传感器阵列中单元之间输出电压的耦合影响不超过 2. 4% 。 将传感器单元及阵列安装在机械手上,选择合适的滑动速度 滑过不同物体表面时,根据输出电压波形精确测量各种深度和形貌,结果表明该传感器单元和阵列可为深度与形貌检测提 供参考。     

知识窗

正动圈式弧焊整流器(moving coil type arc welding rectifier)由一三相动圈式弧焊变压器、整流线路和浪涌装置等所组成。其获得下降外特性和输出电流的调节与单相动圈式弧焊变压器相同。浪涌装置是使在小电流时增加熔滴过渡能力,稳定焊接过程。多适用于手弧焊。场致发射(field emission)仅由电场所引起的电子发射。在外加强电场作用下,金属导体表面便能发射电子到真空中(或绝缘体中)。冷阴极场致发射X射线管就是应用场致发射以获得从阴极发射的电子流。     

激光二极管阵列侧泵浦Nd：YAG板条的热效应

为解决激光二极管阵列侧泵浦激光板条引起的热效应问题,通过对侧泵浦板条温度场与热形变场分布的解析研究以及对激光二极管阵列侧泵浦激光板条工作状态的分析,建立了符合实际情况的热模型,提出了求解Poisson方程的新方法,得到了侧泵浦板条温度场与热形变场的一般解析表达式.以Nd:YAG板条为例,分析了侧泵浦Nd:YAG板条温度场、热形变场的分布情况.并结合全固态激光器的设计需要,定量研究了激光二极管阵列取不同泵浦功率与不同泵浦光斑时Nd:YAG板条的温度场分布情况.计算结果表明:使用输出功率为 30 W的激光二极管阵列侧面泵浦Nd:YAG板条,若耦合到板条侧面的高斯光斑半径为150 μm、板条钕离子掺杂质量分数为 1.0%时.板条泵浦面具有102.3 ℃的最高温升,泵浦面与通光端面产生 1.54 μm和2.66 μm的最大热形变量.激光板条温度场解析方法解决了使用数值分析法造成研究精确度不高的问题,该方法还可以应用到激光系统的其他热问题研究中,为减弱激光系统中的热问题提供理论依据.     

基于场致发射理论的EDM平板电容模型及其参数

基于场致发射理论提出描述电火花加工(Electrical discharging machining,EDM)过程的平板电容模型,将单脉冲放电周期依次划分为极间电场建立、极间通道击穿、正常放电加工与消电离四个阶段,并分别进行各阶段的极间电场强度、极间电子自由程、极间介质介电常数和极间电流变化规律的理论分析.讨论EDM加...     

周期和随机分量叠加而成粗糙表面的激光散射

研究了机械加工时由周期分量和随机分量叠加形成的粗糙表面的激光散射特性.基于Helmholtz-Kirchhoff积分定理并结合统计学相关理论,推导得到了上述粗糙表面的散射场强空间分布理论计算公式.根据推导得到的计算公式,计算了不同周期振幅和不同随机粗糙度情况下的散射场强空间分布,并分析了散射场空间分布的特征和形成原因.理论计算结果表明:在随机性粗糙度远小于激光波长时,周期振幅越大,散射场空间分布的“衍射条纹”现象越明显;而在随机性粗糙度和激光波长可比拟时,周期振幅在波长范围内的变化对散射场空间分布特征影响较小,不再有“衍射条纹”出现.在这种情况下,周期振幅的变化所产生的效果相当于是对散射场空间分布进行了调制.     

Effects of hot electron emission on a low-conductivity tetracyanoethylene polymer layer including studies of the corrugation of the film surface

The effect of strong field electron emission (FEE) on a tetracyanoethylene (TCNE) polymer layer was studied by Field Ion Microscopy (FIM) using TCNE and Ne as the imaging gases. The TCNE polymer was formed on each tungsten tip by radical polymerisation before FEE. The FIM images show field emission spots all over the surface of the tip. The FEM images show a random distribution of several field emission areas at the onset of FEE. After sometime at a current of about microA, there is a transition to higher currents at the same voltage, in which the electron emission pattern changes to have only one emitting area. After this transition, two different types of FIM images were observed, depending on the imaging gas that was used. Neon FIM images at low tip voltages show spots in the areas where the electron emission current was greatest, and at much higher voltages these images show emission from other areas with lower surface corrugation. However, the FIM images with TCNE as the imaging gas do not show any differences between the areas with and without electron emission. The FIM images remain as before FEE, which can be explained by the formation of a new polymer by the reaction of the surface layer with the imaging gas. It is assumed that chemically reactive fragments at the polymer/vacuum interface, which are needed for the polymerisation reaction, are formed by pyrolysis and sputtering processes during FEE.     

Measurement of the electric field distribution and potentials on the object surface in an emission electron microscope without restriction of the electron beams

An emission electron microscope without restriction of the electron beams was used to visualize and measure the distribution of electric fields and potentials on the surface under study. Investigations of this kind can be performed in an emission electron microscope without any aperture diaphragm. The potentialities of this method have been demonstrated using measurements with a silicon p–n junction to which a voltage has been applied in the reverse direction. The quantitative analysis becomes more complicated if the specimen is characterized by a heterogeneous intensity distribution of the electron emission from different areas of its surface. In the latter case two images obtained at different accelerating voltages (i.e. different voltages of the microscope extractor) provide the information necessary for an analysis of electric field and potential distributions.     

Modeling and calculation of field emission enhancement factor for carbon nanotubes array

To estimate the apex field enhancement factor associated with carbon nanotubes (CNTs) array on a planar cathode surface, the image model of floated sphere between parallel anode and cathode plates was proposed. Firstly, the field enhancement factor of individual CNT was given as the following expression, beta0=h/rho+3.5, where h is the height and rho is the radius of CNTs. Then the field enhancement factor of CNTs array was discussed and the above expression was modified to be beta=h/rho+3.5-W, in which W is the function of the intertube distance R and represents the coulomb field interaction between the CNTs. All results show that the intertube distance of CNTs array critically affects the field emission. When the intertube distance is less than the height of tube, the field enhancement factor will decrease rapidly with decreasing the intertube distance. According to the calculated results and considering the field emission current density, the filed emission is optimal theoretically when the intertube distance is comparable with the height of CNTs.     

Fabrication of silver tips for scanning tunneling microscope induced luminescence

We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.     

Arrangement and stability of atoms at the apex of a scanning tip

A field ion microscope was used to examine the stability of the atomic arrangement at tip apexes. Although a single W atom at the top layer of a [111]-orientated tip apex protrudes from the underneath layer by only 0·91 Å, the present study suggests that the (111)-orientated W tip is the most desirable tip for scanning tunnelling microscopes because a large activation energy for surface diffusion on the (111) plane immobilizes the apex atom while the tip scans over a specimen surface and the tip apex can be resharpened by simply heating the tip.     

Advantages of stereo imaging of metallic surfaces with low voltage backscattered electrons in a field emission scanning electron microscope

High emission current backscattered electron (HC-BSE) stereo imaging at low accelerating voltages (≤ 5 keV) using a field emission scanning electron microscope was used to display surface structure detail. Samples of titanium with high degrees of surface roughness, for potential medical implant applications, were imaged using the HC-BSE technique at two stage tilts of + 3° and − 3° out of the initial position. A digital stereo image was produced and qualitative height, depth and orientation information on the surface structures was observed. HC-BSE and secondary electron (SE) images were collected over a range of accelerating voltages. The low voltage SE and HC-BSE stereo images exhibited enhanced surface detail and contrast in comparison to high voltage (> 10 keV) BSE or SE stereo images. The low voltage HC-BSE stereo images displayed similar surface detail to the low voltage SE images, although they showed more contrast and directional sensitivity on surface structures. At or below 5 keV, only structures a very short distance into the metallic surface were observed. At higher accelerating voltages a greater appearance of depth could be seen but there was less information on the fine surface detail and its angular orientation. The combined technique of HC-BSE imaging and stereo imaging should be useful for detailed studies on material surfaces and for biological samples with greater contrast and directional sensitivity than can be obtained with current SE or BSE detection modes.     

The role of tip plasmons in near-field Raman microscopy

The enhancement in electric field strength in the vicinity of a metal tip, through the excitation of plasma modes in the tip, is investigated using the finite difference time domain method; such tip enhancement has significant potential for application in scanning near-field Raman microscopy. To represent an experimentally realistic geometry the near-field probe is described by a conical metal tip with a spherical apex, with radii 20 nm and 200 nm considered, in close proximity to a glass substrate. Illumination through the substrate is considered, both at normal incidence and close to the critical angle, with the polarization in the plane of incidence. By modelling the frequency dependent dielectric response of the metal tip we are able to highlight the dependence on the scattering geometry of the nature of the electromagnetic excitations in the tip. In particular, the strongest electric field enhancement with the greatest confinement occurs for the excitation of modes localized at the tip apex, excited only for off-normal incidence. Bulk modes excited in the tip also produce enhancement, although over a larger area and with significantly less enhancement than that of the localized modes; however, the excitation of bulk modes is independent of the angle of incidence.     

Plasmon-coupled tip-enhanced near-field optical microscopy

Near the cut‐off radius of a guided waveguide mode of a metal‐coated glass fibre tip it is possible to couple radiation to surface plasmons propagating on the outside surface of the metal coating. These surface plasmons converge toward the apex of the tip and interfere constructively for particular polarization states of the initial waveguide mode. Calculations show that a radially polarized waveguide mode can create a strong field enhancement localized at the apex of the tip. The highly localized enhanced field forms a nanoscale optical near‐field source.     

Characterization of the cutting edge of glass knives for ultramicrotomy by scanning force microscopy using cantilevers with a defined tip geometry

The geometry of glass knife edges for ultramicrotomy was studied with nanoscale resolution using scanning force microscopy (SFM) in the contact mode. The local shape of the cutting edge was estimated from single line profiles of the SFM topographic images by taking into account the exact radius of the ultrasharp silicon tip. The tip radius was estimated from secondary electron micrographs recorded at low voltage by field emission scanning electron microscopy (FESEM). The radius of the investigated cutting edges was found to be in range 5–20 nm. The results obtained illustrate that the combination of SFM and high resolution FESEM provides a unique means to determine precisely the radius of glass knives.     

Microscopy and computational modelling to elucidate the enhancement factor for field electron emitters

We report on the computation of the electric field at the surface of single-tip field emitters for a variety of geometries and wide range of geometrical parameters. In conjunction with experimental work, this has allowed the determination of quantities useful for characterizing and comparing the performance of field emitters. The ratio of the field at the tip surface to field at a tip supporting base (enhancement factor) has been calculated for hemispherical tips with parallel or conical shanks, for ratios of tip length to tip radius from 1 to 3000. Enhancement factors greater than 1000 are achievable with suitable tip geometry. The threshold voltage dependence on the tip–anode separation for cylindrical tips facing a flat anode has also been calculated and reported.