Determination of elastic constants using a scanning acoustic microscope

A cubic single crystal of GaAs with two polished (100)-surfaces was examined with a scanning acoustic microscope (SAM) in transmission mode. The images of the transmitted ultrasound amplitude measured at frequencies of 350–400 MHz contain sufficient information about the acoustic anisotropy of the crystal to determine the complete set of the three elastic constants C₁₁, C₁₂, C₄₄ numerically. This was done by an interactive fitting procedure correlating simulated images with the measured one. This technique seems to be universally applicable to virtually all sorts of single crystals. Compared to plane wave investigations it saves preparatory labour since one single crystal orientation suffices for a determination of all elastic constants.     

All-optical adaptive scanning acoustic microscope

We have constructed a fast laser-based surface acoustic wave (SAW) microscope, which may be thought of as a non-perturbing scanning acoustic microscope. The instrument is capable of rapid high resolution vector contrast imaging at several discrete frequencies, without any damage to the sample. Tailoring the generating optical distribution using computer-generated holograms allows us to both focus the acoustic waves (increasing their amplitude) and to spread the optical power over the sample surface (preventing damage). Accurate quantitative amplitude and phase (velocity) measurements and unique acoustic contrast mechanisms are possible with our instrument based on this technology due to the non-perturbing nature and the instrument geometries.However, the complexity of the optical generation profile leads to a strong dependence on material properties such as the SAW velocity and material anisotropy. We address these issues in this paper, and demonstrate how a spatial light modulator may be used to adapt the generating optical distribution to compensate for the material properties. This facilitates simpler alignment and velocity matching, and, combined with an acoustic wavefront sensor, will allow real-time adjustment of the generating source to enable imaging on anisotropic materials.     

300MHZ scanning laser acoustic microscope

The knife—edge and harmonic technique in the Scanning LaserAcoustic Microscope is studied in this paper.The operating frequency of theSLAM can be increased from 100MHz to 300MHz by using the harmonic tech-nique.The acoustic images of some samples are obtained on our SLAM at300MHz.     

300MHz激光扫描声学显微镜

本文对激光扫描声学显微镜（ＳＬＡＭ）的刀口理论以及利用谐波技术提高其工作频率的方法进行了研究．实验上实现了使基波频率为１００ＭＨｚ的ＳＬＡＭ工作于３００ＭＨｚ三次谐波上．最后给出了一些样品在３００ＭＨｚＳＬＡＭ系统上较清晰的声学图像．     

Distance resolution of the scanning acoustic air microscope

In this paper the experimental results concerning the distance resolution measurements performed with the air microscope operating with a focussing transducer at 1.27 MHz are presented. A distance resolution of 3 nm has been achieved, corresponding to the average distance between two molecules in air at normal conditions. The influence of air temperature variations on the distance measurements has been taken into account.     

基于PC机的一种多功能声显微镜及可视化技术的研究

近来研制成功了一种基于ＰＣ机、我们称为“ＴＨＳＡＭＭ”型的多功能声显微镜。在ＰＣ机内插入采样率１ＧＳＰＳ的超高速Ａ／Ｄ卡和信号产生和接收卡,利用软件完成信号检测、处理、显示功能。仪器工作频率为１－１００ＭＨｚ;在检测样品时,同时多层显示Ａ、Ｂ、Ｃ扫描结果。根据声学理论、Ｍａｒｃｈｉｎｇ Ｃｕｂｅ等值面抽取方法和ＯｐｅｎＧＬ技术完成了三维数据的可视化处理,显示样品的内部三维结构。该系统已成功应用于多     

Measuring scanning acoustic microscope with a harmonic sounding signal

A concept of a scanning acoustic microscope with a harmonic sounding signal for measuring the parameters of local homogeneous regions of flat samples is proposed. The distinctive feature of the device is the utilization of the Doppler effect that occurs in the sounding wave reflected from the sample surface when the sample is uniformly moved relative to the focusing ultrasonic transducer of the microscope. It is theoretically demonstrated that the spectrum of the received signal is determined by the product of the reflection coefficient and the transfer function of the transducer. The errors of the measurement technique are considered, and the sources of signal distortions are analyzed. High sensitivity of the measurement results to the errors of the scanning system is demonstrated. The developed measuring microscope is described, in which an acoustic interferometer is used to provide the necessary precision of the scanning coordinate measurement. The microscope transfer function is measured for the frequency of the sounding signal 65 MHz, and the values of density and bulk wave velocities are determined for a homogeneous sample by the measured phase of the reflection coefficient using the technique of nonlinear estimation of parameters. With fused quartz used as an example, it is shown that the measurement error is 7.2% for density and 2.3 and 0.7% for the velocities of longitudinal and transverse waves, respectively. In addition, the velocity of a leaky surface wave (SAW) is determined by two methods. One method is based on measuring the position of the inflexion point for the experimental phase of the reflection coefficient, and the other is based on calculating the SAW velocity corresponding to the measured values of density and bulk wave velocities. The errors of these methods are found to be equal to 0.42 and 0.17%, respectively.     

虚拟式声显微镜及应用技术研究

本文描述一台虚拟式扫描声显微镜及应用技术研究，它的硬件特别简单，仅由一台带有超高速A/D卡和快脉冲收发卡的PC机和机械扫描系统组成，主要的功能均由软件完成，脉冲收发卡仅包括脉冲产生和高频放大器，A/D卡采用PCI总线，采样率1GSPS，数据传输率100MB/s，系统能采集并实时显示频率达百兆的未检波回波信号，采修订本以的信号经软件处理，可在屏幕上实时显示样品的A、B、C型幅度像或相位像，仪器利用信号处理技术提高信号的信噪比；进行特征提取，识别，该仪器在材料识别，电子、光电子器件和焊接质量检测等方面功能较强，具有广阔的开发应用前景。     

激光扫描声学显微镜光学系统的设计

半导体激光器具有半导体和固体器件的许多优点：结构紧凑、效率高、价格便宜、长寿命，在许多方面优于气体激光器，因此在一些测量领域有较好的应用前景。本文基于棱镜对光的一维压缩及新型半导体激光器，对激光扫描声学显微镜的光学系统进行了新的设计，给出了相关数据及具体技术指标，实验证实其光学性能满足要求。整个光学系统具有结构紧凑、可靠性高、使用方便等特点，现已用于激光扫描声学显微镜定型设计。     

High-frequency attenuation measurements using an acoustic microscope

An acoustic microscope was used to measure excess attenuation of aqueous solutions of sugars and proteins at 1.0 GHz. Interference pattern spacing and peak amplitude reduction of V(z) curves, obtained with these solutions as the acoustic microscope coupling liquid, were related to the solution wavespeed and attenuation, respectively. Consistent with published results for lower frequencies, solutions with molecular weight greater than 10,000 had a higher specific absorption than those with a molecular weight less than 1000 and within these two molecular weight ranges specific absorption was independent of concentration.     

各向同性媒质中的扫描电子声显微镜的信号激发

在前期研究(声学学报;1991;16(3):161—169)的基础上,建立了改进的热源分布模型。利用积分变换和特征函数展开法,求解了强度简谐调制的电子束源在各向同性试样中所激发的各种Lamb波模式,以及耦合在试样背面的压电片的电压输出,并分析了扫描电子声显微镜(SEAM)的信号激发机理。结果表明SEAM是一种高分辨率的近场成像技术,它的最佳横向空间分辨率为22~(1/2)倍的电子束焦斑半径。实验结果表明SEAM的空间分辨率可优于0.5μm,小于试样的热扩散长度,从实验上证实了理论预计的SEAM的近场成像特征。     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

激光扫描声显微镜物理系统的设计及实验

本文对激光扫描声显微镜中刀口及干涉仪二种解调器进行了比较,对干涉仪解调器的实用设计及声台有关问题作了详细分析,提供了各参量的选择依据。最后给出了一些实验结果。     

Point contact tunnelling studies on ceramic YBCO with scanning tunnelling microscope tips

A detailed study of point contact tunnelling into ceramic YBCO with electrochemically etched tips of Pt, Nb and W is reported. The superconducting gap parameter (Δ) has been extracted fromI —V and dI/dV —V curves using various procedures. Our results indicate a gap value of about 20 meV. We observe that the zero bias conductance is strongly dependent on the junction resistance. The normal state conductance varies linearly with bias voltage and the conductance curves are asymmetric with respect to polarity of the bias voltage. With contacts of very high junction resistance, we observe G(0)/G(100 mV) has a value as low as 1/6. This may be the lowest value reported so far.     

Photovoltaic characterization of WSe2 with the scanning tunneling microscope

In the present study we use the Scanning Tunneling Microscope (STM) as an instrument to investigate the photovoltaic properties of semiconducting materials. The surfaces of the layered semiconductor WSe₂ were optically illuminated during the tunneling process. The resulting photo-induced tunneling current (PITC) was measured as a function of the wavelength. Microscopic information on the energy dependent generation and recombination of the photo-electrons in the vicinity of the tunneling tip was obtained by this method without the necessity of covering the surface with a conducting electrode. The analysis of the wavelength dependence of the PITC points at the existence of excitonic excitations. Compared to the spectral response of conventional photosensitive heterodiodes our PITC spectra exhibit a more structured response and an increase of the signal in the UV region. Finally, PITC studies on differently treated WSe₂ surfaces show an improved photoactivity for WSe₂ crystals treated with NaI/I₂ solutions.     

Optical fibre profiling using a scanning optical microscope

A scanning optical microscope is used to measure directly the refractive-index profile of an optical fibre. The effects of illuminating the fibre end with a highly convergent beam of light are considered.     

Three-dimensional surface measurement using the confocal scanning microscope

The use of the depth discriminination property of the confocal scanning microscope for surface profiling has been adapted to provide a method of high-resolution three-dimensional surface profilometry. Measurements on a semiconductor specimen demonstrate the technique; depth variations of the order of 0.1 m are clearly resolved.     

扫描探针声显微镜轻敲模式中相位像的反差机理

根据扫描探针声显微镜(SPAM)轻敲工作模式中探针作周期振动的特点,以及在探针与试样相接触过程中激振力和悬臂探针自由振动的阻尼力很小的假设下,解析求解了探针与试样的碰撞运动方程,得到了最大压痕深度和碰撞时间与探针半径、等效杨氏模量以及界面吸附能等之间的关系式,较直观地说明了SPAM中轻敲模式的相位像反差机理:信号的相位与试样微区的性质、探针振幅、设置点以及试样形貌等有关。并定量预计了纳米金刚石像中的相位差值72.59°,与实验测量平均值73.2°±8.2°一致。同时,合理地解释了实验得到的光学薄膜试样相位像的反差。这些表明SPAM轻敲模式的相位成像是一种纳米分辨率测量材料表面物理性质的成像技术。     

Nanomanipulator-assisted fabrication and characterization of carbon nanotubes inside scanning electron microscope

We have installed two nanomanipulators, which can travel about 20mm with a minimum increment of 1 nm, for manipulation of nanostructured materials inside field-emission scanning electron microscope (FE-SEM). Both manipulators render motions in x, y, and z directions, providing various manipulation freedoms such as moving, bending, cutting, and biasing. In addition, we have conducted in situ characterization of the electrical breakdown of multi-walled carbon nanotubes (MWCNTs). Our results demonstrate the possibility that MWCNTs can be used as a gas sensor.