光谱滤波提高白光干涉条纹的对比度

本文利用模拟计算的方法,在PC-1500袖珍计算机上,对采用光谱滤波技术提高白光干涉条纹对比度进行了分析计算,实现了一级、二级暗纹与各自相邻亮纹间对比度的提高(>0.93和>0.51),同时讨论了对较高级次条纹对比度的影响,并进行了实验验证。实验结果表明,光谱滤波对白光干涉条纹中低级次条纹对比度有一定的提高作用,它为改善白光干涉条纹对比度提供了一种新途径。     

The contribution of phonon scattering to high-resolution images measured by off-axis electron holography

The contribution of electrons that have been phonon scattered to the lattice fringe amplitude and the background intensity of a high-resolution electron microscope (HREM) image is addressed experimentally through the analysis of a defocus series of energy-filtered off-axis electron holograms. It is shown that at a typical specimen thickness used for HREM imaging approximately 15% of the electrons that contribute to an energy-filtered image have been phonon scattered. At this specimen thickness, the phonon-scattered electrons contribute a lattice image of opposite contrast to the elastic lattice image. The overall lattice fringe contrast is then reduced to 70% of the value that it would have in the absence of phonon scattering. At higher specimen thickness, the behaviour is defocus-dependent, with the phonon image having lattice fringe contrast of either the same or the opposite sense to the elastic image as the defocus is varied.     

Evaluation of fringe effect of electrical resistance tomography sensor

A conventional electrical resistance tomography (ERT) sensor uses pin electrodes for current injection, and the electric field spreads far beyond the electrode plane, as a result of “soft field” nature. This phenomenon is referred to as “fringe effect” and would cause measurement errors and image distortion. The impact of fringe effect on measurement and reconstructed images depends on the object distributions, the conductivity contrast and others. It is not trivial to evaluate the fringe effect of an ERT sensor and its impact on the measurement and the reconstructed images. In this paper the fringe effect of an ERT sensor is evaluated for central core and off-central core distributions at different axial positions and with different axial dimensions and conductivity contrasts. Then, how to compensate for the fringe effect of the ERT sensor is discussed and a method proposed for improving the measurement accuracy and image reconstruction. Finally, the findings and methodology is verified by experiment.     

干涉条纹相位锁定系统

干涉曝光系统中干涉条纹的相位漂移会导致曝光对比度降低,为了有效抑制相位漂移,利用声光调制器对干涉光频率进行实时调制。分析了条纹漂移的特点,指出了主要干扰源是0~5 Hz的空气扰动。应用数值分析法得到了条纹漂移量与曝光对比度的关系曲线,并以此为依据提出了条纹锁定精度的目标值。针对所要达到的锁定精度,给出了系统硬件的选型方法,搭建了基于RTX的干涉条纹相位锁定系统。利用闭环辨识的方法得到了系统的参数模型,完成了反馈控制器的设计,最终实现了实时锁定条纹相位的功能。实验结果表明,在400Hz的控制频率下,干涉锁定系统能够有效抑制0~5Hz的低频扰动,干涉条纹相位漂移的3σ值可以控制在±0.04个条纹周期内,满足干涉光刻的曝光对比度要求。     

Computer simulation of diffraction contrast images and lattice fringe patterns of small hexagonal dislocation loops

Diffraction contrast and lattice fringe images of small hexagonal dislocation loops are investigated by computer simulation combining the diffraction contrast calculation with the Fourier formalism for considering the electron-optical imaging process including aberrations. Simulated images are presented applying this method to investigate systematically the nature of a small prismatic dislocation loop of Frank type inclined to the electron beam. In particular, the relations between the black-white diffraction contrast oscillations and the lattice fringe distortions (including shifting, bending and termination) have been studied in connection with the variations in the contrast of loops with the thickness of the foil, the depth of the defect in the foil, the deviation from the Bragg reflection condition and the influence of image aberrations.     

Aspects regarding measurement of thickness of intergranular glassy films

Materials such as Si₃N₄, SiC and SrTiO₃ can have grain boundaries characterized by the presence of a thin intergranular amorphous film of nearly constant thickness, in some cases (e.g. Si₃N₄) almost independent of the orientation of the bounding grains, but dependent on the composition of the ceramic. Microscopy techniques such as high‐resolution lattice fringe imaging, Fresnel fringe imaging and diffuse dark field imaging have been applied to the study of intergranular glassy films. The theme of the current investigation is the use of Fresnel fringes and Fourier filtering for the measurement of the thickness of intergranular glassy films. Fresnel fringes hidden in high‐resolution micrographs can be used to objectively demarcate the glass–crystal interface and to measure the thickness of intergranular glassy films. Image line profiles obtained from Fourier filtering the high‐resolution micrographs can yield better estimates of the thickness. Using image simulation, various kinds of deviation from an ideal square‐well potential profile and their effects on the Fresnel image contrast are considered. A method is also put forth to objectively retrieve Fresnel fringe spacing data by Fourier filtering Fresnel contrast images. Difficulties arising from the use of the standard Fresnel fringe extrapolation technique are outlined and an alternative method for the measurement of the thickness of intergranular glassy films, based on zero‐defocus (in‐focus) Fresnel contrast images is suggested. The experimental work is from two ceramic systems: Lu‐Mg‐doped Si₃N₄ and SrTiO₃ (stoichiometric and nonstoichiometric). Further, a comparison is made between the standard high‐resolution lattice fringe technique, the standard Fresnel fringe extrapolation technique and the methods of analyses introduced in the current work, to illustrate their utility and merits. Taking experimental difficulties into account, this work is intended to be a practical tool kit for the study of intergranular glassy films.     

Carrier fringe analysis algorithms for three degree of freedom optical probing

In this work, we present a fiber-delivered and fiber-detected, 3-DOF optical probe concept for measuring optical components to be used in conjunction with an optical coordinate measuring machine (OCMM). The optical probe uses a Michelson interferometer to produce carrier fringes and a high density fiber bundle to transmit interferograms that are recorded away from the probe head in a remote imaging system. We compare several different signal FFT processing techniques (parabolic interpolation, windowing, and zero padding) and a single-bin DFT technique to compute and enhance the resolution of the displacement, tip, and tilt of a moving mirror. We simulated varying signal-to-noise ratios and interference fringe contrast ranges to determine the algorithms’ sensitivity to those parameters and compare our simulated values to measured SNR and fringe values. Based on this work, it should be possible to use a carrier fringe algorithm for fiber probing applications if the interferogram can be transmitted through the fiber bundle with sufficient contrast (40%) and SNR (30 dB).     

检测计量光栅均匀性误差的探讨

叙述了统一计量光栅均匀性误差的检测方法.采用莫尔条纹对比度系数,将均匀性误差百分比表示转换成位移值表示.最后对影响均匀性误差的因素作了讨论.     

A comparison of the analysis of the Fresnel contrast in high- and low-resolution images for the characterization of the rigid body displacements at a grain boundary

The Fresnel contrast in high-resolution images of the Σ = 3{112} aluminium twin boundary is quantitatively assessed to determine whether the rigid body displacements might be measured. It is demonstrated that the effects of the shears at the boundary preclude this possibility. By comparison, simulations of low-resolution images of the same boundary show that the Fresnel fringe contrast in this type of image is negligibly affected by the shear displacements as well as being of considerably higher contrast. The reasons why it is thus only the low-resolution images that can provide high-resolution data on the displacements are discussed.     

Off-axis electron holography with a dual-lens imaging system and its usefulness in 2-D potential mapping of semiconductor devices

A variable magnification electron holography, applicable for two-dimensional (2-D) potential mapping of semiconductor devices, employing a dual-lens imaging system is described. Imaging operation consists of a virtual image formed by the objective lens (OL) and a real image formed in a fixed imaging plane by the objective minilens. Wide variations in field of view (100-900 nm) and fringe spacing (0.7-6 nm) were obtained using a fixed biprism voltage by varying the total magnification of the dual OL system. The dual-lens system allows fringe width and spacing relative to the object to be varied roughly independently from the fringe contrast, resulting in enhanced resolution and sensitivity. The achievable fringe width and spacing cover the targets needed for devices in the semiconductor technology road map from the 350 to 45 nm node. Two-D potential maps for CMOS devices with 220 and 70 nm gate lengths were obtained.     

Quasi-quadrature interferometer for plasma density radial profile measurements

A cw Mach Zehnder multichannel interferometer has been developed to measure time-dependent fractional fringe shifts with an accuracy of one-fortieth fringe. The design is quasi-quadrature in that known phase shifts, introduced in the reference beam, are time multiplexed with the normal reference beam. This technique requires only one detector per interferometer channel as compared to two detectors for most quadrature designs. The quadrature information makes the sense of density changes unambiguous, it automatically calibrates the instrument during the plasma event, and it makes fringe shift measurements virtually independent of fringe contrast fluctuations caused by plasma refractive and/or absorptive effects. The interferometer optical design is novel in that the electro-optic crystal used to introduce the 90 degrees phase shifts is located in the common 2-mm-diam HeNe entrance beam to the interferometer, by exploiting polarization techniques, rather than in the expanded 1-2-cm reference beam itself. This arrangement greatly reduces the size, cost, and high-voltage requirements for the phase modulating crystal.     

光栅Talbot象对比度的实验测试系统

本文在理论分析的基础上,阐述了光栅Talbot象对比度的实验测试系统,该系统由激光光源,扩束准直系统,光栅,精密导轨,细分机构及光电倍增管接收器组成,文章对各部分作了详细的介绍,对相应的电路作了说明,并给出了Talbot象对比度的测试结果。光栅Talbot象对比度的实验研究,将对利用莫尔偏转法测量相位物体时取得的条纹质量的分析研究,有很大的好处。     

Coherency strain fields: magnitude and symmetry

This paper considers the various methods available for the measurement of small values of in-situ lattice misfit between a coherent particle and the matrix. Examination of such misfits by Asby-Brown contrast imaging, moiré fringe measurements, lattice fringe imaging and convergent beam electron diffraction (C.B.E.D.) is considered, and the results obtained by these techniques are compared. In addition the nature of the strain fields in the matrix adjacent to a coherent misfitting particle is examined using C.B.E.D.     

用移相比相法动态测量莫尔条纹细分误差

采用移相比相法测量高精度测角仪的莫尔条纹细分器的细分误差获得很好效果,文中叙述了测量原理、测量精度和实测比对结果。     

Imaging and thickness measurement of amorphous intergranular films using TEM

Fresnel fringe analysis is shown to be unreliable for grain boundaries in yttrium-doped alumina: the determined thicknesses do not agree well with those measured from high resolution transmission electron microscopy (HRTEM), the asymmetry between under- and overfocus is very large, and Fresnel fringes are sometimes shown at boundaries which contain no amorphous film. An alternative approach to the analysis of HRTEM images of grain boundary films is demonstrated: Fourier filtering is used to remove the lattice fringes from the image thereby significantly enhancing the visibility of the intergranular films. The apparent film thickness shows a discrepancy between measurements from the original HRTEM image and the filtered image. It was shown that fringe delocalisation and diffuseness of the amorphous/crystalline interfaces will lead to a significant underestimate of the thickness in unprocessed HRTEM images. In contrast to this, the average thickness can be much more accurately measured from the Fourier-filtered image, provided the boundary is oriented accurately edge-on.     

Towards 1.0 Å resolution: taking advantage of dynamical scattering, and the benefits for structure retrieval

This paper is an exploration of the behaviour of high-resolution transmission electron microscope (HRTEM) images at up to 1 Å resolution. The ultimate limits to HRTEM (structure) resolution and the manner in which strong scattering may lead to weak diffraction in heavy fcc metals are discussed. A resolution of 1.0 Å is somewhat better than the ultimate resolution presently achievable in a 400-kV electron microscope. In heavy metals, such as platinum, it is found that the lattice fringe contrast is very low in the [011] projection, but that fringe contrast may be improved by imaging in the [111] projection. For atomic resolution imaging of the heavy metals in the [111] projection a resolution of 1.2 Å is required. For the study of oxygen position in high-temperature superconducting (HTS) oxides a resolution of between 1.2 and 1.4 Å is required. At better than 1.2 Å resolution the thick crystal images in HTS oxides remain simple and are easily interpreted. At such resolution all atomic columns are separated for the HTS [010] projection and the dynamical diffraction effects improve the contrast of oxygen atoms relative to the metal atoms.     

Beam convergence effects in the weak-beam imaging of inclined planar defects

When defects are imaged using weak beam techniques it is common to use a higher beam convergence than when they are imaged under strong two beam conditions because of the way specimen drift limits the exposure times that can be used. It is demonstrated that, for a typical illumination system, as the convergence is increased the range of tilt across the probed area is also increased. This can affect the weak beam imaging behaviour of a defect, and the α-fringe contrast of thin twins is examined in this context. The contrast changes in the field of view associated with the local variation in tilt are discussed in relation to the degree to which the relative effects of convergence on α-fringe and thickness fringe contrast can be qualitatively understood kinematically. However, some effects, such as the observed increase in α-fringe contrast at moderate convergence, are more difficult to model but are also potentially of greater concern in the characterization of the differences in contrast to be expected for intrinsic and extrinsic faults as well as for twins.     

使用全场数据确定光弹材料条纹值的方法

光弹性实验中,材料条纹值是联系光学现象和材料应力的唯一参数,因而在每次实验前计量材料条纹值是非常必要的。条纹值的精确性与选取的实验计量点有密切的关联,同时应考虑残余双折射和残余应力的影响。根据实验获取的全场数据,在试件中选取多个点构成超定方程组,结合相移技术,运用最小二乘法确定材料条纹值。这种方法不仅能够确定条纹值,而且可以得到试样中残余应力的参数。最后,通过聚碳酸酯受压圆盘实验,验证了新方法的可行性。     

一种红外图像增强的新方法

结合红外图像的成像特点,采用各种图像,增强算法对红外图像进行处理,分别实现了对比度提高、抑制噪声及增强边缘的效果。在此基础上,根据不同算法可实现的效果,提出了一种可将几种算法的优点融合为一体的混合算法。这种算法进一步提高了图像的视觉效果。     

自动分析具有闭合条纹干涉图的新方法

提出了一种干涉图自动提取和定级的并行伪等高追迹方法.这种方法不仅能自动分析由任意形状的非闭合条纹组成的干涉图,而且能自动分析由任意形状闭合条纹组成的单心干涉图.