激光等离子体X射线能谱诊断

为了诊断激光装置聚爆靶辐射等离子体内部的分布及运动过程,搭建了基于球面弯曲晶体的能谱成像系统。该系统的核心元件为弯曲半径为200mm的石英球面弯曲晶体(1011),利用晶体的晶格结构进行反射,利用弯曲表面实现聚焦。在中国工程物理研究院神光Ⅲ原型激光装置上利用该能谱成像系统首次进行X射线能谱成像实验。IP成像板得到了清晰的高Z元素Au等离子体X射线能谱。能谱信息分析显示,石英球面弯曲晶体得到的能谱分辨率约为1 380,与能谱分辨模型理论值的误差为3.9%。该结果表明石英球面弯曲晶体具有很好能谱分辨能力。     

椭圆石英弯晶的积分衍射效率标定

椭圆弯晶谱仪具有测谱宽度大,能谱分辨力高等特点,并在"神光II"激光惯性约束聚变实验研究中得到了很好的应用。利用X射线衍射仪铜(Cu)靶X射线管作为X射线线光源,选取合适厚度滤片,抑制Cu-Kβ线及韧致辐射,测量了Cu-Kα能点处二氧化硅石英椭圆弯晶的积分衍射效率和摆动曲线半高全宽,并开展了针对上述两个重要参数随晶体弯曲曲率半径改变的测试验证,预估了能谱分辨力。结果表明,椭圆弯晶的积分衍射效率和摆动曲线半高全宽对晶体弯曲半径改变敏感,通过提高晶体弯曲度可增强晶体"镶嵌"效果。该结果可为下一步优化设计多用途性椭圆弯晶谱仪,以及完善X射线光谱定量化测量提供了数据支撑。     

后处理法制备提高有机无机杂化钙钛矿稳定性的聚甲基丙烯酸甲酯共混材料

有机无机杂化钙钛矿材料由于在光伏领域优异的性能成为了最近的研究热点, 但是这一材料遇水分解稳定性差限制了材料的实际应用. 我们通过后处理的方式将有机无机杂化钙钛矿材料嵌入到聚合物中, 增强了钙钛矿材料的水稳定性. 通过共混的方式, 无需清洗纳米颗粒, 即可获得钙钛矿良好分散性. 尽管这一共混材料中钙钛矿表面存在溴空位, 但是聚甲基丙烯酸甲酯的加入钝化了钙钛矿的表面, 使得钙钛矿减少了缺陷, 增加了荧光寿命. 同时, 这一共混材料良好的颜色纯度和聚甲基丙烯酸甲酯本身具有的良好透过率, 为钙钛矿应用到实际的光子器件中提供了可能.     

MicroCT examination of human bone specimens: effects of polymethylmethacrylate embedding on structural parameters

X‐ray microtomography permits the nondestructive investigation of trabecular and cortical bone specimens without special preparation of the sample. To do a quantitative characterization, the cross‐section images have to be binarized, separating bone from nonbone. For this purpose, a widely used method is uniform thresholding. However, for commonly available microtomography scanners which use a polychromatic X‐ray source, it is unclear what effect the surrounding medium (e.g. air, saline solution, polymethylmethacrylate) has on the threshold value used for the binarization. In the literature an easy procedure to find the optimal uniform threshold value for a given acquisition condition is reported. By applying this procedure, the present work investigated whether a microtomography scan of trabecular bone samples in air or embedded in polymethylmethacrylate gave the same results in terms of structural parameters. The gold standard, that is, histological sections, was used as a reference. Two fixed threshold values were found, one for the microtomography scans performed in air and one for the scans with the same samples embedded in polymethylmethacrylate. These were applied on the correspondent microtomography images for the estimation of structural parameters, such as bone volume fraction, direct trabecular thickness, direct trabecular separation and structure model index. Paired comparisons were made in bone volume fraction between histological sections and microtomography cross‐sections for the same bone samples scanned first in air and then embedded in polymethylmethacrylate, by which no significant differences were found. Paired comparisons were also made in bone volume fraction, direct trabecular thickness, direct trabecular separation and structure model index for the same samples over volumes of interest of 4 × 4 × 4 mm³ between microtomography scans in air and scans with the samples embedded in polymethylmethacrylate. Neither these comparisons showed significant differences. This leads to the conclusion that structural parameters estimated by microtomography for human trabecular bone samples scanned either in air or embedded in polymethylmethacrylate are not affected by the surrounding medium (i.e. presence or absence of polymethylmethacrylate), provided that the corresponding optimal threshold value is applied for each acquisition condition.     

Correlation averaging of a badly distorted lattice: The surface protein of Pyrodictium occultum

The surface protein of the archaebacterium Pyrodictium occultum forms two-dimensional periodic arrays of extremely poor order. Two variants of correlation averaging have been applied in order to retrieve the unit cell structure from electron micrographs of negatively stained samples: straightforward correlation averaging correcting for lateral displacements only and a more elaborate approach, including a partial compensation for rotational disorder. Surprisingly, both routes yield virtually identical structures. Inclusion of molecular motifs from highly disordered domains, which are rejected in the “straightforward” approach, appears not to improve resolution, possibly because the high local strain tends to distort the individual molecules.     

用于去除非共振背景的圆偏振宽带CARS光谱研究

相干反斯托克斯拉曼散射(CARS)是一种受激拉曼现象,在显微成像时,存在非共振背景,会导致光谱产生峰位偏移和谱线变形。本文利用飞秒激光作为光源,通过光栅滤波系统产生窄带泵浦光,飞秒激光激发光子晶体光纤产生超连续谱作为斯托克斯光,两束光被调制为圆偏振光后同时激发样品产生CARS光谱。通过模拟计算说明圆偏振光可以有效去除各向异性材料CARS光谱中的非共振背景,从而使CARS光谱具有和自发拉曼相似的谱线形状。聚苯乙烯微球和液晶样品的CARS光谱实验结果与模拟计算基本相符,说明圆偏振是一种有效去除CARS光谱非共振背景的方法。     

Resonance sensors for measuring dielectric spectra of liquid crystals in a wide frequency range

Designs of resonance sensors covering a wide frequency range of 1–10⁴ MHz and intended for measuring the dispersion of the permittivity of liquid crystals are proposed. Using an example of a 4-methoxybenzyliden-4′-buthylanilin (MMBA) liquid crystal, it is shown that these sensors are characterized by a high sensitivity and allow measurements of temperature and field dependences of dielectric spectra of samples with volumes of ～1 mm³. The behavior of dispersion of the MMBA permittivity observed experimentally is described by the Debye equation with a continuous spectrum of relaxation times within a certain range. A numerical method is proposed that allows reconstruction of the relaxation-time distribution function from the measured spectra of the real component of the permittivity. This distribution function represents the features of both the motion of molecules and the processes of intramolecular vibrations of movable fragments.     

椭圆型晶体谱仪谱测量的解谱研究

对椭圆型晶体谱仪配X射线CCD相机的X射线谱测量系统（EBCS-XCCD）进行了简要描述,研究了CCD相机记录信号的解谱处理方法,推出了对实测原始谱曲线辨认或标识值的计算公式及激光等离子体X射线源在某一波长光谱强度的公式,使之应用在激光打靶产生的等离子体源辐射X射线谱的回推,辨认出了激光等离子体X射线源能谱,并与文献[1]的结果进行了比较,结果基本一致。这一事实有力地佐证了解谱方法的可行性,也表明X射线CCD相机是适宜于椭圆型晶体谱仪的光谱测量记录。在已知晶体的积分反射率、滤片透射率和CCD探测效率的条件下,还可以获得X射线源光谱强度,可为下一步诊断激光等离子体的电子温度和离子密度的空间分布轮廓和进一步细化X激光研究奠定了更深厚的基础。     

Packing of linear molecules: An electron microscope study of disorder in mesophases and binary solids

With the aid of epitaxial orientation techniques originally designed for linear polymer crystallization, it is found that a large assortment of linear chain molecules can be prepared for electron diffraction study in a projection onto the molecular axes. This not only facilitates a study of ordered monodisperse molecular crystal structures but also of the disordered state as well, including thermotropic phase transitions and the structure of binary solids. Representative studies of monodisperse and polydisperse phase behavior based on electron diffraction and differential scanning calorimetry measurements are reviewed for n-paraffins, glycerolipids, and cholesteryl esters. The importance of observing the microcrystalline state is readily apparent from these studies—not only because the symmetry of individual small crystals can be determined, but also because local structural variations not detectable in bulk measurements are readily observed.     

Monte Carlo simulation of charging effects on linewidth metrology

Charging effects of scanning electron microscopes on the linewidth metrology of polymethylmethacrylate (PMMA) insulatorpatterns are investigated using Monte Carlo simulation. It is first revealed in detail how the nonunity yield of electron generation in the PMMA target leads to local charge accumulation and affects the image profile of secondary electrons as charging develops. Then the measurement offset due to charging effects is identified for various target patterns of isolated and array types. Finally, it is concluded that the measurement uncertainty caused by the measurement offset exceeds the error budget limit that will be allowed in the linewidth metrology of the next generation of semiconductors.     

Near-field scanning optical microscopy using polymethylmethacrylate optical fiber probes

We report the first use of polymethylmethacrylate (PMMA) optical fiber-made probes for scanning near-field optical microscopy (SNOM). The sharp tips were prepared by chemical etching of the fibers in ethyl acetate, and the probes were prepared by proper gluing of sharpened fibers onto the tuning fork in the conditions of the double resonance (working frequency of a tuning fork coincides with the resonance frequency of dithering of the free-standing part of the fiber) reported earlier for the case of glass fibers. Quality factors of the probes in the range 2000–6000 were obtained, which enables the realization of an excellent topographical resolution including state-of-art imaging of single DNA molecules. Near-field optical performance of the microscope is illustrated by the Photon Scanning Tunneling Microscope images of fluorescent beads with a diameter of 100 nm. The preparation of these plastic fiber probes proved to be easy, needs no hazardous material and/or procedures, and typical lifetime of a probe essentially exceeds that characteristic for the glass fiber probe.     

激光等离子体X射线极化光谱研究

为了诊断激光等离子体X射线的极化光谱,研制了一种新型的基于空间分辨的极化谱仪。将平面晶体和球面弯晶色散元件在极化谱仪内正交布置,即在水平通道用PET平面晶体作为色散元件,而在垂直通道用Mica球面弯晶作为色散元件,球面半径为380mm。信号采用成像板进行接收,有效接收面积为30×80mm,从等离子体光源经晶体到成像板的光路约为980mm。物理实验首次在中国工程物理研究院激光聚变研究中心“2×10J激光装置”上进行,成像板获得了铝激光等离子体X射线的光谱空间分辨信号。实验结果表明该谱仪具有较高谱分辨率,适合激光等离子体x射线极化光谱的诊断。     

基于等离子体激光的X射线弯晶谱仪研究

X射线光谱议是一种强有力的激光等离子体诊断工具。为了获取激光等离子体发射的X射线中所包含大量信息,基于椭圆几何原理设计制造了X射线弯晶谱议。在上海神光 号装置上利用LiF弯曲晶体分析器,用150J激光能量对Ti靶进行了试验。通过X射线CCD记录获取的谱线,结果表明这种聚焦型晶体分析器的灵敏度有了明显的提高。     

A modification of the commercial ESR900 cryostat to enable three-dimensional electron-paramagnetic-resonance studies of crystals

Complete orientation studies of X-band electron-paramagnetic-resonance spectra of crystals largely benefit from the possibility to measure the spectrum for any orientation of the magnetic field with respect to the crystal without the need to remount the crystal. We report on a modification of a commercial cryostat to allow such experiments down to liquid helium temperatures and demonstrate its performance.     

小波多重分形及其在振动信号分析中应用的研究

不同于许多基于FFT的信号分析方法,多重分形谱分析的是信号的几何结构特征。以前,多重分形谱的计算方法都有其固有的缺点,使多重分形谱的应用受到限制。而小波局部极大模方法因其简单性和有效性,近来在多重分形谱计算方面受到了广泛的关注。较系统地阐述了多重分形的概念和多重分形谱的小波局部极大模计算方法,讨论了多重分形谱在故障诊断领域的应用途径,并用多重分形谱对不平衡、油膜涡动、联轴器不对中和碰摩等旋转机械的4种典型故障的振动信号进行了事例研究。研究结果表明,多重分形谱能够很好的反映振动信号的几何结构特征,为机械设备故障诊断提供了又一种有效的方法。     

Probing nanoscale surface enhanced Raman-scattering fluctuation dynamics using correlated AFM and confocal ultramicroscopy

We have studied the laser-excitation-intensity-dependent and Ag-nanocluster interstitial-site-dependent SERS intensity fluctuations under low molecule surface coverage of rhodamine 6G and cytochrome c. A new two-channel photon time-stamping system coupled with atomic force microscopic (AFM), Raman spectroscopic, and imaging microscopy was developed and applied to record Raman intensity fluctuation trajectories at sub-microsecond resolution correlated with in situ characterization of the nanoparticle clusters. Our experimental results suggest that the nanoconfinement of the local electromagnetic-field enhancement and the interaction of the local field with the molecules, presumably under rotational motions, result in nano-Raman fluctuations. The SERS spectral fluctuation was pertinent to the nanoscale local enhancement and local interaction of the molecules with the surface when the surface coverage of the nanoparticles was less than a monolayer, and the nanoscale interstitial space controlled the finite number of molecules to contribute the microscopic Raman signal collected from a diffraction-limited focus spot. The fluctuation amplitude significantly decreased with the number of molecules confined at the nanolocal field. The nano-SERS fluctuation dynamics were both photo-induced and spontaneous for rhodamine 6G, but only the photo-induced component was observable for cytochrome c. The fluctuation dynamics were also found to be highly inhomogeneous at interstitial sites with heterogeneous geometries. To interpret the observed nano-SERS fluctuation dynamics, we used computer simulation of optical multiple scattering, based on multi-sphere scattering Mie theory, and rotational diffusion of molecules at an interstitial site, based on a random walk in orientation space.     

SA335 P91钢管焊接接头根部裂纹分析

介绍了SA335P91钢管对接全位置固定单面焊双面成形接头焊缝交汇处所产生的背面裂纹。断口电镜扫描和能谱分析的结果表明 :此类裂纹属于结晶裂纹 ,产生的原因是由于该处形成了粗大且方向性极强的胞状树枝晶组织 ,出现了比较严重的结晶偏析并导致晶界上S、P含量偏高 ,此外 ,该处所存在的背面凹坑也会导致收缩时产生较大的应力集中。     

Electron microscopy of tRNA crystals. I. Thin crystals negatively stained with uranyl acetate

The first attempt to study crystal structures of tRNA by electron microscopy is described. Sufficiently thin crystals were prepared from yeast tRNAphe. The thickness of the thinnest was estimated at 130 A corresponding to a bilayer of the molecules. The L-shaped structure seemed to be maintained even after the negative staining with uranyl acetate. Optically filtered images from electron micrographs were compared with those simulated from the drawing of the molecular model by optical transform. The results suggest that the observed images reflect the real molecular arrangements within the crystal lattice although the shape of tRNA molecules seems to be somewhat modified by the uneven staining.     

Small-size terahertz spectrometer using the second harmonic of a femtosecond fiber laser

Possible implementations of a small-size terahertz spectrometer with a subpicosecond resolution on the basis of a femtosecond fiber laser are considered. An experimental sample of a spectrometer is fabricated. This spectrometer employs the method of optical rectification in a ZnTe nonlinear crystal and the Dember (photodiffusion) effect on the InAs semiconductor surface to generate terahertz radiation and the polarization-optical method to detect radiation. System operation is demonstrated by an example of measuring the terahertz absorption spectrum of water and determining the refractive index of the β-BBO crystal. The basic spectrometer parameters are found: spectral range, spectral resolution, and dynamic range of the terahertz spectrum amplitude.     

An investigation of the markings on wear and fatigue fracture surfaces

The worn surfaces of three polymers sliding against a lapped steel disk were studied by scanning electron microscopy (SEM) and transmission electron microscopy. The surfaces of polymethylmethacrylate and high density polyethylene were covered with bands of arced ripples stretched along the transverse direction. The shape of these ripples is consistent with the distribution of tensile principal stress in the contact zone for a hemispherical indenter sliding on a plane surface. The Polyvinylchloride surface suffered severe plastic deformation during sliding as discerned by the dimples on it. The fatigue fracture surfaces of these materials were also examined by SEM. The polymethylmethacrylate surface exhibited a series of striations whose spacing increased in the direction of crack propagation. The striations on high density polyethylene and Polyvinylchloride surfaces were not observed because fracture was accompanied by considerable plastic deformation. This study shows that the mechanism of the separation of a wear particle from the sliding surface is cumulative damage as encountered in fatigue.