基于SPM技术的表面纳米计量

用扫描探针显微镜(SPM)技术观察三维表面形态,可以达到纳米级甚至原子量级的分辨率,所以SPM技术在计量方面有着广阔的应用前景。20年来,人们采用各种理论和方法来提高SPM的精度和稳定性,以适应表面计量领域不断提出的新要求。本文在总结表面规范与建模、高分辨率和高时间稳定性测量、图像解释与表面重建、SPM误差和校准以及纳米对准技术等研究结果的基础上,对今后发展的趋势作了展望。     

用于确定表面特性的扫描探针显微法

扫描探针显微法(SPM)常用于半导体和磁盘驱动行业的成象和计量。SPM可在简单如环境空气、复杂如温度控制样品及真空载物台等各种环境下提供定量的3维数据。它和扫描电子显微法(SEM)不同,其样品准备工作极少,在几分钟内就可把圆片放置在SPM载物台上进行扫描。新的扫描尖端使SPM已经不仅仅是获取表面信息的高倍率工具。同样的仪器可用于测量埃等级的表面粗糙度。SPM还能获得和显示诸如摩擦力、磁力、电势能以及表面一致性等表面性质。有极高纵横比的探针还可在斜槽内成像。     

利用图像中的探针信息获取探针形貌的方法

扫描探针显微技术已在纳米甚至原子级的形貌获取中得到了广泛地应用。其分辨本领在很大程度上依赖于探针的形貌尺寸。传统的检测探针的方法大多对针尖的损伤很大或需要复杂的仪器,这就使这些方法带有一定局限性。本文提出利用扫描图像中反映的探针信息数值求解探针形貌的方法,利用探针扫描不同样品所得到的扫描图像还原探针的形貌,结果显示用此算法能够还原出原针尖的形貌。为了更好地与实际结果对比,用原子力显微镜扫描图像来验证此方法的正确性,结果显示反构造的探针形貌结果与MI公司所提供的探针尺寸吻合很好。     

振动与扫描速率综合影响SPM图像的实验研究

探讨了外界激振对扫描探针显微镜(SPM)图像的影响。针对DI扫描探针显微镜MultiMode^TM SPM，以Tektronix任意波形发生器AWG202l驱动PC扬声器作为激振源，以SIOS微型激光干涉测振仪SP—S为测振系统，研究了0～7kHz频带内SPM机体的简谐迫振对扫描图像的影响。实验表明，针尖-样品副所受激振影响不同于SPM机体；0～1kHz频带内的激振影响显著，再高频段则影响甚微；外界激振与SPM扫描的综合作用影响成像的结果；针尖-样品副的粘弹性模型是SPM振动影响研究的指导理论。     

基于双压电陶瓷片的反射模式近场扫描光学显微镜

介绍了一种反射模式近场扫描光学显微镜。该系统以双压电陶瓷片作为控制光纤探针与待测样品之间距离的核心元件,以粘有光纤探针的双压电陶瓷片的第一个谐振频率来驱动光纤探针平行于样品表面振动,采用均方根检测电路测量振动信号的幅度,进而控制光纤探针与样品之间的距离在样品表面的近场范围之内。利用该系统获得了标定光栅和刻录光盘薄膜等样品表面的剪切力形貌图像和反射模式近场光学图像。     

扫描探针显微镜进行细胞扫描时探针对于细胞活性的影响

扫描探针显微镜(scanning probe microsope，SPM)是近几年发展很快的一种形貌表征仪器。它的一个突出优点是，可在溶液中以很高的分辨率对细胞活体进行观察。不同于光学显微镜，SPM是利用探针和样品之间的相互作用来扫描成像，探针对细胞有力的作用。这种作用力会在扫描过程中直接影响细胞的状态。为了研究SPM成像过程中探针作用力对于细胞的影响，我们用SPM的接触模式(contact mode)和敲击模式(tapping mode)对培养液中的生物活细胞进行了较长时间的扫描观察。结果显示，尽管接触模式SPM成像清楚，但长时间的扫描会造成细胞凋零；敲击模式SPM进行长时间扫描时也会造成细胞变形，而细胞会以新的形态来适应外力的影响。     

扫描隧道显微镜图像重建的研究

在扫描隧道显微镜轮廓测量过程中,探针自身的几何形状会混入测量结果中,从而造成相应的测量误差。本文提出了根据对标准样品的测量结果,反算出探针的几何形状的算法,并应用于实没图像示解出探针的几何形状。在求得探针的几何形状后,文中推导了去除探针几何形状造成的误差,对扫描隧道显微镜图像进行重建的算法,并对实测样品进行了处理。结果表明上术坷有效地减少小探针自形状造成的测量误差。     

基于多层膜光栅的AFM探针结构表征研究

原子力显微镜是微纳米测量领域主要测量工具之一。由于原子力显微镜探针不可能无限尖锐,使得测量图像包含了一部分探针信息,这是其图像失真的一大影响因素。通过获取探针形状和尺寸,可以有效去除测量图像的"探针效应"从而提升准确度。文中以研制良好样品内一致性的探针校准器为目标,应用Si/SiO2多层膜光栅技术,初步研制了20 nm标称值的线宽结构用于原子力显微镜探针校准。表征结果显示,RFESP型(Rectangular Front Etched Silicon Probe)探针稳定扫描时探针前角由15°增加至36°左右,探针后角由25°增加至45°左右,呈现钝化趋势。由此表明,基于Si/SiO2多层膜光栅技术研制的线宽型探针表征器可以快速表征出探针侧壁角度信息,是原子力显微镜探针扫描过程中探针形貌快速监测和估计的有效手段,对于促进探针表征与图像准确度提升均具有重要意义。     

用于扩展SPM检测范围的精密定位系统

本文介绍了所研制的二维微定位柔性系统和一维精密转动系统,进行了相关技术的研究并给出了设计参数,使SPM能够满足高精度下的大尺寸平面样品以及球形被测样品的全范围检测,扩大了扫描探针显微镜（SPM）在超精密工程中的应用范围。     

磁力显微镜在钢铁材料磁畴分析中的应用

扫描探针显微镜（SPM）是通过探测针尖与样品间不同的相互作用力而获得表面的不同性质，在扫描探针测量技术上发展起来的磁力显微镜（MFM）主要用于材料表面的磁场力分布。     

A Fast Implementation of a Minimum Variance Estimator for Computerized Tomography Image Reconstruction

Most present day computerized tomography (CT) systems are based on reconstruction algorithms that produce only approximate deterministic solutions of the image reconstruction problem. These algorithms yield reasonable results in cases of low measurement noise and regular measurement geometry, and are considered acceptable because they require far less computation and storage than more powerful algorithms that can yield near optimal results. However, the special geometry of the CT image reconstruction problem can be used to reduce by orders of magnitude the computation required for optimal reconstruction methods, such as the minimum variance estimator. These simplifications can make the minimum variance technique very competitive with well-known approximate techniques such as the algebraic reconstruction technique (ART) and convolution-back projection. The general minimum variance estimator for CT is first presented, and then a fast algorithm is described that uses Fourier transform techniques to implement the estimator for either fan beam or parallel beam geometries. The computational requirements of these estimators are examined and compared to other techniques. To allow further comparison with the commonly used convolution-back projection method, a representation of the fast algorithm is derived which allows its equivalent convolving function to be examined. Several examples are presented.     

Preparation of defined structures on very thin foils for characterization of AFM probes

In atomic force microscopy (AFM), knowledge of the probe (tip) geometry is a critical factor for obtaining reproducible images. This is particularly important for measurements in the contact mode, in which a certain amount of wear of the probe always occurs affecting the image quality of small, flat and/or larger surface structures. In addition to probe geometry, the slope of the probe with respect to the sample is of importance. In this work, probe geometry is determined by the use of structured foils obtained using focused ion beam (FIB). In this manner, we demonstrate the possibility of determining the AFM probe geometry and the slope on the basis of differently-sized structures. An established algorithm was implemented for the reconstruction of the probes. The shape of FIB structured foils was determined separately by scanning electron microscopy (SEM).     

Digital image elasto-tomography: combinatorial and hybrid optimization algorithms for shape-based elastic property reconstruction

Results from the application of three nonlinear stiffness reconstruction algorithms to two simple cylindrical geometries are presented in this paper. Finite-element simulated harmonic motion data with added noise were initially used to represent a measured surface displacement dataset for each geometry. This motion was used as input to gradient-descent, combinatorial optimization, and hybrid reconstruction algorithms that aimed to reconstruct two shape-based parameters describing the internal stiffness of the geometry. Both the combinatorial optimization and hybrid algorithms showed significant advantages in reconstructed parameter accuracy when compared with the traditional gradient-descent approach, with success metrics improving by 13--28%. Results from the hybrid algorithm applied to silicone phantom displacements demonstrated for the first time the ability of this type of algorithm to reconstruct internal stiffness using only experimentally measured surface motion data. Improvements in the sophistication of the hybrid approach should lead to improved accuracy in reconstructed solutions, as well as enabling reconstructions where the geometry is less straightforward.      

Image Blending in a High Frame Rate FPGA-based Multi-Camera System

Panoptic is a custom spherical light field camera used as a polydioptric system where imagers are distributed over a hemispherical surface, each having its own vision of the surroundings and a distinct focal plane. The spherical light field camera records light information from any direction around its center. This paper revises previously developed Nearest Neighbor and Linear blending techniques. Novel Gaussian blending and Restricted Gaussian blending techniques for vision reconstruction of a virtual observer located inside the spherical geometry are presented. These new blending techniques improve the output quality of the reconstructed image with respect to the ordinary stitching techniques and simpler image blending algorithms. A comparison of the developed blending algorithms is also given in this paper. A hardware architecture based on Field Programmable Gate Arrays (FPGA) enabling the real-time implementation of the blending algorithms is presented, along with the imaging results and resource utilization comparison. A recorded omnidirectional video is attached as a supplementary material.     

Deconvolution of atomic force microscopy data for cellular and molecular imaging

The restoration of image features in cellular and molecular images is a crucial problem in nanobiological investigations. Scanning probe microscopy (SPM) offers the potential for direct investigative capability at nanometer resolution necessary for imaging biological units and macromolecular protein control blocks. The distortion of the measured image due to tip-sample interaction is a major challenge for nanoscale metrology, and signal processing solutions are needed for increasing the accuracy and reliability of the data. Two candidate approaches have been described in detail in this article for modeling the tip-sample interaction from a topographical perspective, which is then used for reconstructing the sample surface from known tip geometry. When the aspect ratio of a feature is comparable with that of the tip, the two methods produce similar results, but when the aspect ratio is larger than that of the tip, the MM method produces a sharper estimate than the LT method. When the tip geometry is not known, blind-tip estimations methods are needed for iterative estimations of tip and sample surfaces.     

Two-dimensional ISAR model and image reconstruction with stepped frequency-modulated signal

A two-dimensional (2-D) inverse synthetic aperture radar (ISAR) return signal model that employs stepped frequency (SF) modulation is developed. The geometry of the examined ISAR scenario is described by analytical geometrical equations. The target to be imaged is represented by a rectangular grid of point scatterers, moving along a rectilinear trajectory at constant speed, without any rotational motion. Thus, the inverse synthetic aperture results from the translational motion of the target for a short period of time. The process of ISAR signal modelling through coherent summation of the SF-modulated signals reflected from different point scatterers of the target is thoroughly described. Moreover, an efficient ISAR image reconstruction approach, including cross-correlation-based range compression and fast-Fourier-transform-based azimuth compression, is presented through analytical mathematical expressions. Numerical simulations are carried out for various SF ISAR scenarios and high-resolution ISAR images are obtained by applying the proposed ISAR image reconstruction approach. Simulation results (ISAR images and corresponding entropy values) indicate the validity of the proposed 2-D SF ISAR return signal model and the efficiency of the proposed imaging algorithms. Finally, a numerical simulation result is illustrated, which shows the comparison of the performance of the proposed ISAR image reconstruction algorithms based on SF and linear frequency modulation waveforms. It is shown that the two waveforms attain almost the same ISAR image resolution.     

Plane surface detection and reconstruction using segment-based tensor voting

A Segment-based Tensor Voting (SBTV) algorithm is presented for planar surface detection and reconstruction of man-made objects. Our work is inspired by piecewise planar stereo reconstruction. During the vital procedure to detect and label the planar surface, the two main contributions are: first, tensor voting is used for obtaining the geometry attribute of the 3D points cloud. The candidate planar patches are generated through scene image segment of low variation of color and intensity. Second, we over-segment the scene image into the segment and the candidate 3D planar patch is generated. The SBTV algorithm is used on 3D points cloud sets to identify the co-plane on the candidate patch. After detecting every planar patch, the geometry architecture of object is obtained. The experiments demonstrate the effectiveness of our proposed approach on either outdoor or indoor datasets.     

深孔内表面结构光三维重构

为实现针对深孔内表面几何形状的高精度三维重构,搭建了一套基于结构光的三维检测系统。首先,介绍了该检测系统的构成及相关测量原理,并验证了在某一确定范围内图像距离与实际距离近似呈线性关系,该论断为后续检测奠定了坚实的理论基础;然后,针对深孔模型实物以及对应的内表面展开成平面模型分别进行结构光检测,从而验证了检测方案的可行性以及检测系统的实际效果。结果表明:该检测方案在理论上可行,在实际应用中系统的检测精度能够达到亚像素水平,绝对偏差控制在0.034 7 mm的范围内;最后,在实际应用于深孔类零部件内表面检测的过程中,实现了针对该零部件内表面几何形状的高精度三维重构。     

压缩感知图像重建算法的研究现状及其展望

压缩感知(Compressive Sensing,CS)理论是在已知信号具有稀疏性或可压缩性的条件下,对信号数据进行采集、编解码的新理论.将压缩感知应用于图像压缩具有潜在的应用价值,压缩感知图像重建算法是该领域的热点问题.在对目前压缩感知重建算法的文献进行分析和综合的基础上,首先阐述了压缩感知的基本原理及其各项关键技术,然后简要总结了当前流行的压缩感知图像重建算法,给出了各种图像重建算法的仿真结果及分析,最后对影响压缩感知图像重建算法几个关键问题进行剖析和展望.