Crystal structure determination by direct inversion of dynamical microdiffraction patterns

The intensity at points where coherent convergent-beam transmission diffraction discs overlap is shown to be described by interference between elements of the same row but different columns of the dynamical scattering matrix for an axial orientation. These intensities are used as the basis for an exact, nonperturbative inversion of the multiple electron scattering problem, allowing crystal structure factors to be obtained directly from the intensities of multiply scattered Bragg beams. Eigenvectors of the structure matrix are obtained using coherent CBED patterns from many crystal orientations. Unique eigenvalues are obtained from these patterns recorded at two accelerating voltages. The inevitable variation in electron probe position at different crystal tilts is considered. The analysis applies to centrosymmetric crystals with anomalous absorption, to centrosymmetric projections of acentric crystals and to acentric crystals if the mean absorption potential only is included. The method would allow the direct synthesis of charge-density maps of unknown crystal structures at high resolution from multiple scattering data, using a scanning transmission electron microscope (STEM). The resolution of this map may be much higher than the first-order d -spacing; however, the STEM need only be capable of resolving this first-order spacing. Such a charge-density map provides fractional atomic coordinates and the identification of atomic species (as in X-ray crystallography) from microcrystalline samples and other multiphase inorganic materials for which large single crystals cannot be obtained or X-ray powder patterns obtained or analysed. In summary, we solve the inversion problem of quantum mechanics for the case of electron scattering from a periodic potential, described by the nonrelativistic Schrödinger equation, in which the scattering is given as a function of some parameter, and the potential sought.     

A precise method to determine the angular distribution of backscattered light to high angles

We present an approach to measure the angular dependence of the diffusely scattered intensity of a multiple scattering sample in backscattering geometry. Increasing scattering strength give rise to an increased width of the coherent backscattering and sets higher demands on the angular detection range. This is of particular interest in the search for the transition to Anderson localization of light. To cover a range of -60 degrees to +85 degrees from direct back-reflection, we introduced a new parallel intensity recording technique. This allows one-shot measurements, with fast alignment and short measuring time, which prevents the influence of illumination variations. Configurational average is achieved by rotating the sample and singly scattered light is suppressed with the use of circularly polarized light up to 97%. This implies that backscattering enhancements of almost two can be achieved. In combination with a standard setup for measuring small angles up to +/-3 degrees , a full characterization of the coherent backscattering cone can be achieved. With this setup we are able to accurately determine transport mean free paths as low as 235 nm.     

Analysis of NM-Scale Scratches on High-Gloss Tribological Surfaces by Using an Angle-Resolved Light Scattering Method

This paper discusses a promising method to investigate defects on high-gloss finished metal surfaces. The main aim is to detect very shallow scratches on such tribological surfaces. The method must be simple in its applicability, insensitive to external disturbances, and sufficiently fast for application in monitoring industrial processes. To achieve this, the principle of light scattering is used by scanning a surface with a compact scattering light sensor using a red LED as a light source. The reflected light is scattered into a specular part and a diffuse part, and collected by a one-dimensional CCD-array. The detected intensity distribution of the scattered light depends on the topography of the reflecting surface. Significant variations in the intensity profile will permit to identify the surface defects. With this system we were able to detect scratches on high-gloss metal sheets with a typical width of 1 μm and a depth as small as 40 nm. The geometrical dimensions of these shallow scratches have been determined with a confocal white light microscope.     

动态光散射颗粒分布软测量

考虑传统动态光散射颗粒粒度分布测量用的反演算法复杂、精度不够、抗噪能力差,本文基于大数据思想,提出了一种动态光散射颗粒分布软测量方法。该方法通过调节颗粒粒度分布形状参数获得大量自相关函数及其对应颗粒分布的数据;使用这些数据对子学习机进行训练。最后,针对训练数据维数较高的特点对传统Bagging算法进行改进,并利用改进的Bagging集成算法集成子学习机以提高软测量模型的精度及泛化能力。通过模拟单峰数据和对300nm标准粒径进行软测量开展了验证实验。结果表明,该方法能够较好地测量出不同动态光散射颗粒分布的峰值及分布宽度,模拟单峰数据测量峰值精度可达1nm,300nm和503nm,标准粒径测量精度分别可达3nm和4nm,优于一般的反演算法。该软测量方法为动态光散射颗粒分布测量开辟了新的途径。     

Calculation of depth distribution functions in films using an electron scattering model

An electron scattering model which has proved reliable in predicting both characteristic and continuous radiation depth distributions in bulk samples is further developed to cope with the quantification of depth distribution curves in thin films. The validity of the extended model is checked by comprehensive comparisons of calculated emitted x-ray intensities with experimental data. The deviations obtained are generally small, the root-mean-square error being ～5%. The results of calculations quantifying the effect of the substrate material on the shape of the depth distribution function in the film are also presented. The curves obtained are discussed in light of known theories and of fundamental physical considerations. The new model generates curves which correspond at least qualitatively with what is to be expected from basic principles and with the results of recent Monte Carlo simulations.     

Discrimination of heavy and light elements in a specimen by use of scanning transmission electron microscopy

Heavier elements have a larger scattering cross-section for elastically scattered electrons than lighter ones. Furthermore, the maximum number of scattered electrons is at higher scattering angles for heavier atoms. These differences can be used, in principle, to distinguish heavy and light elements from each other in dark field Scanning Transmission Electron Microscopy (STEM). We have achieved such discrimination in practice by collecting the electrons in a STEM experiment at two different angles. The information about the elemental composition that these two images together contain is visualized by forming linear combinations of the images which are specific for light and heavy elementsrrespectively. The results are demonstrated for a specimen consisting of platinum grains on a holey carbon film and for granulocytes stained with osmium tetroxide.     

动态线偏振光散射纳米颗粒粒度测量法的研究与分析

多重散射是传统动态光散射法测量纳米颗粒溶液浓度上限受到限制的主要原因。为此文中提出了动态线偏振光散射纳米颗粒粒度测量法,通过改变颗粒入射光和散射光的偏振状态,降低颗粒间多重散射的影响。现利用Mie散射理论分析了入射光与散射光偏振状态之间的关系,并通过实验方法探知偏振光在散射介质中的传输特性,揭示了在动态光散射中使用垂直偏振光作为入射光的实验依据。最后对动态线偏振光散射颗粒测量法和传统光子相关光谱测量法进行了实验及分析,通过两种方法的比较,验证了上述理论的正确性。     

激光散射粒子动态相位多普勒分析系统

研究和建立了以几何光学近似光散射理论为基础的激光相位多普勒空间干涉条纹模型。计算得到了微粒对激光散射的空间相干条纹图形与粒径及散射参数的依从关系。将其应用于研制的双检测器相位多普勒实验系统,给出了系统功能和典型的实验结果。     

基于动态光散射信号分形的颗粒测量技术研究

颗粒的动态光散射信号具有分形特征，通过对其特征值的分析，可以得到颗粒粒径信息。采用100nm、200nm、500nm和1000nm4种亚微米粒径范围的标准聚苯乙烯乳胶颗粒样品，分别求取了它们的动态光散射信号的分形维数。实验结果表明，颗粒粒径越小，对应的动态散射光分形维数越大；粒径越大，分形维数越小。从而证明了用分形维数表征颗粒粒径的可行性。与相关方法相比，分形方法具有所需的采样数据少、计算简便、适于实时测量等特点。     

First measurement of electron temperature from signal ratios in a double-pass Thomson scattering system

This paper presents an experimental demonstration to determine electron temperature (T(e)) with unknown spectral sensitivity (transmissivity) in a Thomson scattering system. In this method, a double-pass scattering configuration is used and the scattered lights from each pass (with different scattering angles) are measured separately. T(e) can be determined from the ratio of the signal intensities without knowing a real chromatic dependence in the sensitivity. Note that the wavelength range for each spectral channel must be known. This method was applied to the TST-2 Thomson scattering system. As a result, T(e) measured from the ratio (T(e,r)) and T(e) measured from a standard method (T(e,s)) showed a good agreement with <∣T(e,r) - T(e,s)∣∕T(e,s)> = 7.3%.     

光学粉尘浓度测量仪响应特性曲线的计算与分析

根据 Mie散射理论计算了 5种光学粉尘浓度测量仪的光散射响应特性曲线 ,对照呼吸性粉尘在人体呼吸道中的沉降效率曲线 ,对这些光学粉尘浓度测量仪的响应特性进行了分析。得出的结论是 :采用近前向型光散射结构、多波长照明光源和大孔径散射光收集系统的光学粉尘浓度测量仪 ,其响应特性曲线更接近于人体对呼吸性粉尘的采集效率     

微米球粒的宽角度光散射的数值模拟研究

采用米氏散射理论，提出一种在传统前向散射布局基础上，增加大角度探测器的实验装置，并对散射光作偏振探测，从而实现对微米直径范围的球粒进行直径分布测量的方法。数值模拟发现散射光强的垂直偏振分量与假设的目标散射光强的垂直偏振分量之间的根均方差为最小。采用Phillips-Twomey算法，设定罗辛-罗姆勒（RR）分布，通过拟合散射光强的垂直偏振分量的角分布曲线获得罗辛-罗姆勒分布中的直径参数和直径分布宽度参数。该方法在理论上快速准确。所提方案在实验上也切实可行。     

A compact setup to study homogeneous nucleation and condensation

An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.     

A study of the method for measuring the local size distribution of spherical particles diffusing in a fluid by L.D.A.

This work concerns a method for measuring the local size distribution of spherical particles diffusing in a fluid. It is based on the light scattering theory and makes use of an ordinary Laser Doppler Anemometry apparatus. The required information is obtained by analyzing and processing the signal from the PM, which observes the measuring volume at the angle of 90. The pinhole is replaced by a slit oriented in such a way that the intensity of the scattered light depends only on the diameter of the particle and on a single space variable. A direct calibration of the response of the optical system is used to compute the size distribution from the scattered light probability density.     

激光粒度测试中的独立模式反演算法研究

在测量微粒系统的散射光强角分布中计算微粒系统的粒径分布,属于典型的反演问题.反演算法一直是激光粒度仪的关键和难点.介绍了基于米氏散射理论的粒度测试,对其求解方法进行了详细分析.针对独立模式算法不需要预先指定粒径分布函数的形式就可获得真实粒度分布,提出了一种改进的独立模式粒度反演算法,并对算法的性能进行了理论分析和实验论...     

Atomic beam spectrometer using a LiF analyzer crystal

An energy analyzer has been constructed and operated in UHV for the purpose of analyzing the energy of neutral atoms scattered from solid surfaces. The analyzer consists of a LiF single crystal located at an angle close to the normal to the sample crystal so that the diffraction pattern obtained by scanning the LiF crystal yields the energy of the scattered atoms. Two designs which have been used are described. The temperature of both sample and analyzer crystal is near 20 K and once cleaned they can be maintained in the state of initial preparation for many weeks. The sample was a (001) Cu surface in this case. Such an energy analyzer can only be used, in most cases, for He atom scattering although Ne atoms could be used if the scattered intensities were adequate. The detector developed in this study is able to detect about 2x10(5) atoms/s. The resolution of the spectrometer depends on the incident energy of the atom and is about 1 meV at an incident energy of 23 meV. This resolution can be improved by a factor of 3 to 4 by cooling the nozzle to a temperature lower than 77 K and using variable size slits which can be inserted into the beam path.     

表面散射浊度测量研究

本文在理论上计算了球形粒子对光的单次散射及多重散射解 ,证明了通过检测 90°方向散射光强度来获得样品浊度方案的优越性。随着样品浊度的增加 ,当考虑样品的多重光散射后 ,90°方向散射光强与浊度的线性度下降。设计了表面散射浊度在线测量系统 ,当 Formazin标准液在 0～ 1 0 0 0 NTU范围内时 ,获得了散射光强与浊度的线性度优于± 3% ,测量结果表明用表面散射法来测量浊度具有测量范围宽、线性好的优点。     

Enabling the measurement of particle sizes in stirred colloidal suspensions by embedding dynamic light scattering into an automated probe head

A novel probe head design is introduced, which enables in-line monitoring of particle sizes in undiluted stirred fluids using dynamic light scattering. The novel probe head separates a small sample volume of 0.65 ml from the bulk liquid by means of an impeller. In this sample volume, particle sizing is performed using a commercially available fiber-optical backscatter probe. While conventional light scattering measurements in stirred media fail due to the superposition of Brownian’ motion and forced convection, undistorted measurements are possible with the proposed probe head. One measurement takes approximately 30 s used for liquid exchange by rotation of the impeller and for collection of scattered light. The probe head is applied for in-line monitoring of the particle growth during microgel synthesis by precipitation polymerization in a one liter laboratory reactor. The in-line measurements are compared to off-line measurements and show a good agreement.     

一种低温极化电子拉曼散射系统简介

本文介绍了一种低温极化电子拉曼散射系统的组成、结构、用法及成果。拉曼散射是一种常见的非弹性光散射现象。通过检测散射光谱,可以对材料的内在基础性质进行深入研究。拉曼散射光中也包含了更深层次的电子激发信息,表现为连续的拉曼谱,并具有很低的信号强度,需要严格控制杂散光的影响,并需低温（液氦）和高真空的极端条件。为此,我们设计并建造了一套低温极化（低温下光的偏振）电子拉曼散射系统,并获得一些科研成果。     

Thomson-scattering measurements in the collective and noncollective regimes in laser produced plasmas (invited)

We present simultaneous Thomson-scattering measurements of light scattered from ion-acoustic and electron-plasma fluctuations in a N(2) gas jet plasma. By varying the plasma density from 1.5×10(18) to 4.0×10(19)?cm(-3) and the temperature from 100 to 600 eV, we observe the transition from the collective regime to the noncollective regime in the high-frequency Thomson-scattering spectrum. These measurements allow an accurate local measurement of fundamental plasma parameters: electron temperature, density, and ion temperature. Furthermore, experiments performed in the high densities typically found in laser produced plasmas result in scattering from electrons moving near the phase velocity of the relativistic plasma waves. Therefore, it is shown that even at low temperatures relativistic corrections to the scattered power must be included.