Nano-area electron diffraction pattern reconstructed from three-dimensional Fourier spectrum.

A method to obtain a nano-area electron diffraction pattern in transmission electron microscopy (TEM) was proposed, based on three-dimensional (3D)) image formation theory. This method allows us to reconstruct an electron diffraction pattern from a 3D Fourier spectrum of high-resolution through-focus images. As a test case, an electron diffraction pattern from a tilted Si single crystal was reconstructed using the proposed method and compared with the conventional selected-area electron diffraction pattern. The intensity distribution of the reconstructed electron diffraction pattern was confirmed to be qualitatively equal to that of the selected-area electron diffraction pattern, though the degree of the equivalency between these patterns reduces at the high frequency region and the reproducibility of the intensity degrades when the number of images used in the image processing was decreased. By selecting areas in a reconstructed exit wave field, some electron diffraction patterns were obtained from the nano-areas without the influence of spherical aberration.     

The wrap-around problem and optimal padding in the exit wave reconstruction using HRTEM images

A free fast Fourier transform software FFTW (www.fftw.org) is used in the exit wave reconstruction and shown to be able to handle images of any size effectively. The wrap-around problem commonly encountered in the exit wave reconstruction is investigated, and a new padding scheme is proposed and its performance is investigated. It is shown that while the usual wrap-around problem may be solved via padding the input high-resolution transmission electron microscopy (HRTEM) images with zero or averaged image intensities, the reconstructed exit wave at its boundary is inevitably distorted by the discontinuity of image intensities at the boundary. The proposed new padding scheme is shown to be able to provide a good estimate of the image intensities immediately outside the boundaries of the HRTEM images, reducing the estimated image intensity discontinuity across the boundaries and therefore providing a larger undistorted view of the exit wave.     

Atomic‐Scale Imaging and Quantification of Electrical Polarisation in Incommensurate Antiferroelectric Lanthanum‐Doped Lead Zirconate Titanate

Lanthanum doping of zirconium rich lead zirconate titanate gives rise to incommensurate, long‐period antiferroelectric structures. The structure of two stacking sequences in this incommensurate phase is determined using quantitative analysis of high‐resolution scanning transmission electron microscopy images, with the lead atom positions located with an exceptional precision of about 6 pm. This allows the estimation of local polarisation variations across the stacking units, and the polarisation varies in an approximately sinusoidal fashion along the stacking direction. The measured peak Pb atom displacements of about 28 pm and peak polarisation values of about 60 μC cm^?2 match extremely well to reported values for the commensurate antiferroelectric PbZrO₃ phase.     

基于星形金纳米颗粒修饰的81°倾斜光纤光栅生物传感器

提出一种星形金纳米颗粒修饰的81°倾斜光纤光栅(TFG)生物传感器。通过金黄色葡萄球菌蛋白A固定法,将自制的高纯度新城疫病毒(NDV)单克隆抗体固定于81°TFG表面,制成对NDV具有特异性检测功能的生物传感器。结果表明,传感器对NDV的最低探测极限达10~25pg/mL,检测饱和点约为1 000pg/mL;在0~200pg/mL具有较好的线性相关度(R2约为0.911),相应的灵敏度约为1 394pm/(ng/mL)。此外,通过对NDV的特异性和临床性测试,表明该生物传感器对NDV具有高度的特异性和临床有效性。     

Novel local density of state mapping technique for low-dimensional systems

A novel local density of state (LDOS) probing method for low-dimensional electron systems is proposed. By applying a two-dimensional fast Fourier transform to a real-space image obtained by scanning tunneling microscopy (STM), visualization of a complementary image in k-space can be realized. Especially, low-dimensional Fermi contours can be extracted by applying the k-space imaging to real-space images containing sufficient LDOS information around the Fermi level. To realize a more enhanced LDOS visualization in both spaces, we have proposed the use of special materials for STM tips, which have relatively large LDOSs at the Fermi level. To demonstrate this idea, several kinds of STM tips (Ag, Au, W and Nb) with different types of LDOSs were developed. An Au(111)-(22 x square root(3)) reconstructed surface, where Shockley surface-state electrons form a nearly free electron gas, was selected as a test sample for the LDOS extraction. Visualization of standing waves in the surface LDOS modulated by herringbone reconstruction was attempted using the various types of STM tips. Significant effects of the LDOSs of the STM tips were clarified.     

Mechanism of copper diffusion over the Si(110) surface

The mechanism of Cu diffusion over a clean Si(110) surface was studied by Auger electron spectroscopy and low-energy electron diffraction in the temperature range from 500 to 650°C. It is shown that the Cu transport over the Si(110) surface proceeds by Cu atom diffusion through the Si bulk and Cu atom segregation at the surface during diffusion. The temperature dependence of the effective Cu diffusivities at the clean Si(110) surface was found. The results were compared to those previously found for a Si(111) surface.     

The Measurement of Muscle Fiber Conduction Velocity Using a Gradient Threshold Zero-Crossing Method

The conduction velocity of myoelectric potential along muscle fiber is known to be an index of the degree of muscular fatigue or muscular disease. When detecting the myoelectric potential by means of surface electrodes, the conduction velocity must be extracted from an apparently random wave of a myoelectric signal. In this paper, a method for determining conduction velocity is proposed based upon a zero-crossing time delay measurement with reference to the derivative of a myoelectric signal. The slope value of the input signal provides an effective criterion for rejecting undesired zero crossing caused by noise. This method needs no spectral analysis nor correlation calculation. Compared to another previously reported zero-cossing approach using digital filter preprocessing, it shows a more accurate and rapid estimation of velocity.     

原子稀疏结合块结构稀疏的联合表示图像识别算法

针对结构稀疏表示识别算法中稀疏准则的选择以及字典内块的划分两个重要问题,提出两种改进的结构稀疏表示识别算法。首先,针对结构稀疏准则会出现较多系数不为零的情况,提出将结构稀疏准则与原子稀疏准则相结合的思路,包括并行和串行两种结合方式。并行结合是将两者以加权求和的方式同时作为稀疏表示的判别准则进行分类,串行结合则是在结构稀疏表示后,通过重组字典,再对测试样本进行原子稀疏表示实现分类。然后,针对字典中类内样本的块划分问题,提出基于MLP的结构稀疏表示识别算法,先将类内样本经过MLP的划分,保证各个分块分别位于低维的线性子空间中,再进行结构稀疏表示的分类。实验结果证明两种改进的结构稀疏表示识别算法的有效性。      

Wave soldering with a low melting point Bi-Sn Alloy: Effects of soldering temperatures and circuit board finishes

Wave soldering with low solid fluxes at temperatures as low as 175°C on test boards with a Cu/Imidazole surface finish has been shown to be feasible using a Pb-free, Bi-45%Sn-0.33%Ag solder that melts at temperatures of ∼140∼145°C. Other surface finishes such as Pd/Ni, Au/Ni, and Bi exhibit unacceptable soldering at temperatures below 210°C. Intermediate in performance are Sn surface finishes, which exhibit acceptable soldering at 190°C, but not at 175°C. Acceptable joints wave soldered on Cu/Im finishes passed class I/II inspection criterion and exhibited pull strengths in excess of the ultimate strength of the component leads.     

基于VMD的调频连续波雷达生命信号提取

针对生命探测雷达心跳信号能量微弱难于准确提取的问题,提出了一种基于变分模态分解(Variational Mode Decomposition, VMD)的调频连续波雷达生命信号提取算法。该算法首先利用距离维快速傅里叶变换(Fast Fourier Transform, FFT)获得距离剖面图,然后通过最大方差法得到目标所在距离门,接着对低通滤波后的相位信号使用VMD进行分离,并采用模态判别准则对生命信号进行重构,最后对重构信号进行FFT得到呼吸和心跳频率。雷达实测结果表明,相比于应用聚类经验模态分解(Ensemble Empirical Mode Decomposition, EEMD),所提生命信号提取算法能够有效抑制雷达回波中的呼吸谐波和噪声,更加准确有效地提取生命体征信号。     

HRTEM imaging of atoms at sub-Angström resolution

John Cowley and his group at Arizona State University pioneered the use of transmission electron microscopy for high-resolution imaging. Images were achieved three decades ago showing the crystal unit cell content at better than 4 A resolution. This achievement enabled researchers to pinpoint the positions of heavy atom columns within the unit cell. Lighter atoms appear as resolution is improved to sub-Angstr?m levels. Currently, advanced microscopes can image the columns of the light atoms (carbon, oxygen, nitrogen) that are present in many complex structures, and even the lithium atoms present in some battery materials. Sub-Angstr?m imaging, initially achieved by focal-series reconstruction of the specimen exit surface wave, will become commonplace for next-generation electron microscopes with C(S)-corrected lenses and monochromated electron beams. Resolution can be quantified in terms of peak separation and inter-peak minimum, but the limits imposed on the attainable resolution by the properties of the microscope specimen need to be considered. At extreme resolution the 'size' of atoms can mean that they will not be resolved even when spaced farther apart than the resolution of the microscope.     

Band partitioning algorithm for surface reconstruction from planarcontours

A heuristic contour triangulation method is proposed for reconstructing a facet model from a set of wire-frame contours. The proposed band partitioning algorithm (BPA) compensates for the disadvantages of optimal and heuristic methods, and produces an improved reconstructed surface. Furthermore, the maximum deviation criterion in span selection prohibits drastic error propagation in the surface definition procedure. Experimental results show that the proposed method is very stable and efficient, making it suitable for a wide range of applications     

A label-free biosensor based on organic transistors by using the interaction of mercapto DNA and gold electrodes

Organic thin-film transistors (OTFTs) with Au electrodes were successfully used as transducers for label-free deoxyribonucleic acid (DNA) sensors. Single-strand DNA (ssDNA), perfectly-matched double-strand DNA (dsDNA) and mis-matched DNA were immobilized on the surface of the source/drain electrodes of three OTFT devices respectively. The ssDNA molecules with mercapto group (–SH) can be well immobilized on the surface of Au electrode by chemical bond between –SH and Au atom. According to the significant difference in channel current, which was attributed to the changed contact resistances by introducing different DNA molecules on Au electrode, ssDNA, matched-dsDNA and mismatched-dsDNA were differentiated successfully in the experiments. The results may provide a promising approach for detecting DNA specificity and hybridization with label-free.     

Atomic structures of Au and Ag films epitaxially grown on the InP(001)-p(2 × 4) surface

Thin films of Au and Ag deposited onto the InP(001)-p(2 × 4) surface at room temperature have been characterized by means of combined surface-layer analysis of low energy electron diffraction, reflection high energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spec-troscopy-channeling techniques. It has been found that the Au film grows epitaxially in the layer-by-layer mode along the <001> direction, while the Ag film grows in the <110> direction in the Stranski-Krastanov mode. The unit cell of a face-centered cubic lattice of the Au film is rotated azimuthally by 45° with respect to the unit cell of a zinc-blende lattice of the InP substrate. The islands of Ag(110) crystallites prefer to orient their (100) faces along the direction of the 4 times superlattice of the InP(001)-p(2 × 4) surface. The analysis of the RBS-channeling minimum yield of 1.5 MeVHe⁺ ions incident along the [001] direction of the InP(OOl) substrate shows that both the epitaxially grown Au film and Ag crystallite of less than 20Å in thickness are excellent in crystalline quality.     

GaSb基半导体激光器功率效率研究

为了提高GaSb基半导体激光器的功率效率和可靠性,研究了GaSb基半导体激光器欧姆接触形成机理并提出了一种新型四层金属欧姆接触结构(Ni/AuGe/Mo/Au)。进行了Au/Mo/AuGe/Ni/n-GaSb在150 ℃~450 ℃退火温度下欧姆接触的实验研究,结果表明,新结构能够在250 ℃~450 ℃退火温度和10 min退火时间下形成良好的欧姆接触并具有较低的接触电阻率,有效地提高了GaSb基半导体激光器的功率效率。俄歇射线能谱分析表明,新型金属化结构中各原子之间的互扩散减少,结构表面形貌光滑、平整,有助于半导体激光器后续封装的进行,有效地提高了GaSb基半导体激光器的可靠性。     

基于字典学习的毫米波大规模MIMO系统混合预编码

针对毫米波大规模多输入多输出(MIMO)系统混合预编码方案设计的难题,采用字典学习的思想,提出了一种高精度混合预编码方案.该方案首先对全数字预编码矩阵的各列采用稀疏表示;进而按列将字典原子从稀疏表示中分离出来,通过对误差矩阵采用奇异值分解(SVD)来更新对应的字典原子,直到所有字典原子更新,以形成新的字典矩阵;最后,利用更新后的字典矩阵稀疏重构全数字预编码矩阵,以得到模拟预编码矩阵和数字预编码矩阵.仿真结果表明,相较于基于正交匹配追踪(OMP)的混合预编码方案,所提方案在提升系统频谱效率和降低误码率方面具有明显的优势.     

REW软件——高分辨电子显微镜的像模拟与出射波函数重构的应用软件

通过像处理技术分析高分辨电子显微像有助于确定样品结构,提高显微镜的分辨率。本文开发的REW软件同时具有HRTEM像模拟与波函数重构的功能。用户可通过像模拟法来确定已知晶体的结构,另一方面,用户可利用系列离焦的HRTEM像重构样品的出射波函数,从而得到重要的相位信息并提高样品的分辨率。本文将简单介绍REW软件所运用的理论知识,并列举典型例子来描述REW软件的重要功能。     

Comb-Push Ultrasound Shear Elastography (CUSE): A Novel Method for Two-Dimensional Shear Elasticity Imaging of Soft Tissues

Fast and accurate tissue elasticity imaging is essential in studying dynamic tissue mechanical properties. Various ultrasound shear elasticity imaging techniques have been developed in the last two decades. However, to reconstruct a full field-of-view 2-D shear elasticity map, multiple data acquisitions are typically required. In this paper, a novel shear elasticity imaging technique, comb-push ultrasound shear elastography (CUSE), is introduced in which only one rapid data acquisition (less than 35 ms) is needed to reconstruct a full field-of-view 2-D shear wave speed map (40 × 38 mm). Multiple unfocused ultrasound beams arranged in a comb pattern (comb-push) are used to generate shear waves. A directional filter is then applied upon the shear wave field to extract the left-to-right (LR) and right-to-left (RL) propagating shear waves. Local shear wave speed is recovered using a time-of-flight method based on both LR and RL waves. Finally, a 2-D shear wave speed map is reconstructed by combining the LR and RL speed maps. Smooth and accurate shear wave speed maps are reconstructed using the proposed CUSE method in two calibrated homogeneous phantoms with different moduli. Inclusion phantom experiments demonstrate that CUSE is capable of providing good contrast (contrast-to-noise ratio ≥ 25 dB) between the inclusion and background without artifacts and is insensitive to inclusion positions. Safety measurements demonstrate that all regulated parameters of the ultrasound output level used in CUSE sequence are well below the FDA limits for diagnostic ultrasound.     

Quantitative annular dark-field STEM images of a silicon crystal using a large-angle convergent electron probe with a 300-kV cold field-emission gun

Annular dark-field scanning transmission electron microscope (ADF-STEM) images of an Si (001) crystal were obtained by using an aberration-corrected electron microscope, at 30-mrad convergent probe and cold field-emission gun at 300?kV. The intensity of ADF-STEM images, that is, the number of scattered electrons relative to the incident electrons, obtained for specimen thickness from 10 to 50?nm was compared quantitatively with absorptive multi-slice simulation. The column and background intensities were analyzed by column-by-column two-dimensional Gaussian fitting. These intensities were found to increase linearly with the sample thicknesses. However, the simulated image gave higher column intensity and lower background intensity for all the sample thickness. We found that experimental images were reproduced by the simulation with Gaussian convolution of 70?pm full-width at half-maximum for all the sample thicknesses from 10 to 50?nm. The possible factors accounted for this Gaussian convolution is discussed.     

Distortion Compensation of Reconstructed Hologram Image in Digital Holographic Display Based on Viewing Window

A holographic display based on a viewing window enables the converging of a reconstruction wave into a viewing window by means of an optical system. Accordingly, a user can observe a reconstructed hologram image, even with a small diffraction angle. It is very difficult to manufacture an optical system with no aberrations; thus, it is inevitable that a certain amount of wave aberrations will exist. A viewing‐window‐based holographic display, therefore, always includes distortions in an image reconstructed from a hologram pattern. Compensating the distortions of a reconstructed image is a very important technical issue because it can dramatically improve the performance when reconstructing a digital three‐dimensional content image from a hologram pattern. We therefore propose a method for suppressing image distortion by measuring and compensating the wave aberration calculated from a Zernike polynomial, which can represent arbitrary wave aberrations. Through our experimental configuration using only numerical calculations, our proposed method decreased the reconstructed image distortion by more than 28%.