A resolution measure for three-dimensional microscopy

A three-dimensional (3D) resolution measure for the conventional optical microscope is introduced which overcomes the drawbacks of the classical 3D (axial) resolution limit. Formulated within the context of a parameter estimation problem and based on the Cramer-Rao lower bound, this 3D resolution measure indicates the accuracy with which a given distance between two objects in 3D space can be determined from the acquired image. It predicts that, given enough photons from the objects of interest, arbitrarily small distances of separation can be estimated with prespecified accuracy. Using simulated images of point source pairs, we show that the maximum likelihood estimator is capable of attaining the accuracy predicted by the resolution measure. We also demonstrate how different factors, such as extraneous noise sources and the spatial orientation of the imaged object pair, can affect the accuracy with which a given distance of separation can be determined.     

High resolution 3D x-ray diffraction microscopy

We have imaged a 2D buried Ni nanostructure at 8 nm resolution using coherent x-ray diffraction and the oversampling phasing method. By employing a 3D imaging reconstruction algorithm, for the first time we have experimentally determined the 3D structure of a noncrystalline nanostructured material at 50 nm resolution. The 2D and 3D imaging resolution is currently limited by the exposure time and the computing power, while the ultimate resolution is limited by the x-ray wavelengths. We believe these results pave the way for the development of atomic resolution 3D x-ray diffraction microscopy.     

High resolution electron spin resonance microscopy

NMR microscopy is routinely employed in fields of science such as biology, botany, and materials science to observe magnetic parameters and transport phenomena in small scale structures. Despite extensive efforts, the resolution of this method is limited (>10 microm for short acquisition times), and thus cannot answer many key questions in these fields. We show, through theoretical prediction and initial experiments, that ESR microscopy, although much less developed, can improve upon the resolution limits of NMR, and successfully undertake the 1 mum resolution challenge. Our theoretical predictions demonstrate that existing ESR technology, along with advanced imaging probe design (resonator and gradient coils), using solutions of narrow linewidth radicals (the trityl family), should yield 64 x 64 pixels 2D images (with z slice selection) with a resolution of 1 x 1 x 10 microm at approximately 60 GHz in less than 1h of acquisition. Our initial imaging results, conducted by CW ESR at X-band, support these theoretical predictions and already improve upon the previously reported state-of-the-art for 2D ESR image resolution achieving approximately 10 x 10 mum, in just several minutes of acquisition time. We analyze how future progress, which includes improved resonators, increased frequency of measurement, and advanced pulsed techniques, should achieve the goal of micron resolution.     

Quantitative atomic resolution scanning transmission electron microscopy

Complete understanding of atomic resolution high-angle annular dark-field (Z-contrast) images requires quantitative agreement between simulations and experiments. We show that intensity variations can be placed on an absolute scale by normalizing the measured image intensities to the incident beam. We construct fractional intensity images of a SrTiO3 single crystal for regions of different thickness up to 120 nm. Experimental images are compared directly with image simulations. Provided that spatial incoherence is taken into account in the simulations, almost perfect agreement is found between simulation and experiment.     

Order in amorphous polystyrenes as revealed by electron diffraction and diffraction microscopy

Ordered regions ranging in size between 15 and 45 Å have been established in several atactic polystyrenes of various molecular weights (4800; 51,000; and 1,800,000) as well as in an amorphous isotactic polystyrene by means of electron diffraction and high-resolution diffraction microscopy. The order is due to long-chain polymer molecules which tend to align more-or-less parallel to one another with a constant average spacing. The orderly chain packing can be disturbed upon cross-linking by electron irradiation, the disturbance being manifested in the irreversible changes in the d spacing and broadening of one of the diffuse rings which is inter-molecular in origin. From the results obtained, the high-resolution diffraction microscopy technique appears to have the potential for resolving the question regarding the presence of order in unoriented amorphous polymers. The technique can also differentiate between a broadened diffuse ring due to small crystallites and another due to paracrystals containing numerous defects.     

原子尺度材料三维结构、磁性及动态演变的透射电子显微学表征

原子表征与操控是实现原子制造必须突破的物理瓶颈之一.像差校正电子显微学方法因其优异的空间分辨率,为实现原子精细制造提供了有力的表征手段.因此,利用电子显微学手段,在原子尺度对原子制造的材料及器件进行三维结构和性能的协同表征,对于深入理解原子水平材料操控的物理机理具有非常重要的意义.纳米团簇及纳米颗粒是原子制造材料与器件研究的主要对象之一,具有丰富的物理化学性质和较高的可操纵性.本文探讨纳米团簇/颗粒结构三维定量表征、使役条件下纳米团簇/颗粒结构演变定量表征、纳米颗粒/晶粒结构-成分-磁性协同定量表征等诸多方法与实例,阐明了电子显微学表征手段的突破和发展为实现精细控制的原子制造材料提供了坚实基础.     

超快电子衍射系统的时间空间分辨能力研究及其优化

超快电子衍射技术是研究物质瞬态结构变化及超快结构动力学的有效手段.研制了国内第一套同时具有超快时间分辨及超高空间分辨能力的超快电子衍射系统,并研究了在该超快电子衍射系统上实现超快时间分辨及超高空间分辨能力的技术手段及其优化方法.实验结果表明：经过优化后该系统可以具有优于500 fs的时间分辨能力,其空间分辨能力达到0.04%的衍射峰位置变化,对应的晶面变化为0.0005?.该系统可以为实时测量超快光脉冲激发的物质瞬态结构变化,特别是为研究晶体材料的超快动力学行为提供了强有力的实验工具. 关键词： 超快电子衍射 空间分辨 时间分辨     

Increasing spatial resolution in the backscattered electron mode of scanning electron microscopy

A new method for increasing spatial resolution in the detection of backscattered electrons and induced current in scanning electron microscopy (SEM) is proposed in terms of regularized Fourier transform. The real size of an electron probe and its blurring in a solid target sample are considered in forming the algorithm. The experiments reveal an almost 100% improvement in resolution in the processed images.     

Ground-state-depletion fluorscence microscopy: A concept for breaking the diffraction resolution limit

We introduce and study a novel concept in farfield fluorescence microscopy fundamentally overcoming the classical diffraction resolution limit. This is accomlished by reducing the spatial extent of the effective focus of a scanning fluorescence microscope. The reduction is achieved by depleting the ground-state energy of the molecules located in the outer region of the focus. Our theoretical study shows that ground-state-depletion fluorescence microscopy has the potential of increasing the resolution of far-field fluorescence microscopy by an order of magnitude which is equivalent to a lateral resolution of 15 NM.     

Atomic force microscopy and transmission electron microscopy of biocompatible magnetic fluids: A comparative analysis

The present study provides a comparative analysis of the size dispersity of magnetic nanoparticles (MNPs) within magnetic fluids as obtained from atomic force microscopy (AFM) and transmission electron microscopy (TEM). Whereas the mean particle diameter obtained from the AFM data presented a reduction of about 34% as compared to the value obtained from the TEM data, the standard deviation obtained from the AFM data is twice the value found from the TEM data. Similarities and differences in the size dispersity parameters are discussed in terms of sample preparation and tip characteristics. A two-dimensional mode for the deposition of the MNPs on top of the mica substrate is discussed as well.     

An assessment of the resolution limitation due to radiation-damage in X-ray diffraction microscopy

X-ray diffraction microscopy (XDM) is a new form of X-ray imaging that is being practiced at several third-generation synchrotron-radiation X-ray facilities. Nine years have elapsed since the technique was first introduced and it has made rapid progress in demonstrating high-resolution three-dimensional imaging and promises few-nanometer resolution with much larger samples than can be imaged in the transmission electron microscope. Both life- and materials-science applications of XDM are intended, and it is expected that the principal limitation to resolution will be radiation damage for life science and the coherent power of available X-ray sources for material science. In this paper we address the question of the role of radiation damage. We use a statistical analysis based on the so-called “dose fractionation theorem” of Hegerl and Hoppe to calculate the dose needed to make an image of a single life-science sample by XDM with a given resolution. We find that the needed dose scales with the inverse fourth power of the resolution and present experimental evidence to support this finding. To determine the maximum tolerable dose we have assembled a number of data taken from the literature plus some measurements of our own which cover ranges of resolution that are not well covered otherwise. The conclusion of this study is that, based on the natural contrast between protein and water and “Rose-criterion” image quality, one should be able to image a frozen-hydrated biological sample using XDM at a resolution of about 10 nm.     

On the characterisation of interfacial defects using high resolution electron microscopy

The characterisation of line defects in interfaces, observed using high-resolution electron microscopy, is discussed. Characterisation is carried out by mapping a closed circuit initially constructed around a defect into a reference space. This process has been generalised to incorporate operations other than translations, and has also been expressed mathematically, and thereby related to recent developments based on symmetry theory. Examples of the characterisation of dislocations in twin interfaces in hexagonal-close-packed crystals and an interfacial dispiration are presented as illustrations.     

High resolution electron microscopy of precipitates in high Co-Ni alloy steel

In the secondary hardening reaction in ultrahigh strength steel of high Co-Ni alloy, the needle-shaped precipitating carbide is the main strengthening phase. Particular attention has been paid to the nucleation, growth and coarsening of the precipitate and its interface with the ferrite matrix. High resolution transmission electron microscopy observations show that when tempered at a low temperature condition of 454 degrees C for 5h, the precipitating carbides begin to nucleate in the form of clusters; at peak hardening tempered at 482 degrees C, the growing carbides are fully coherent with the matrix, exhibit black-white contrast in bright-field images and have their own hexagonal crystalline structure as M(2)C. Coarsening carbides tempered at high temperature lost their coherence and exhibited Moiré fringes. Lattice images directly indicate the crystallographic relationship of M(2)C carbides and ferrite, [100](alpha)//[1101](beta), [100](alpha)//[1120](beta).     

采用高分辨电镜分析Cu掺杂聚-4-甲基-1-戊烯泡沫材料采用高分辨电镜分析Cu掺杂聚-4-甲基-1-戊烯泡沫材料

利用物理掺杂的方法,制备了铜掺杂聚-4-甲基-1-戊烯(PMP)低密度泡沫材料,采用高分辨扫描电子显微镜和透射电子显微镜,分析了泡沫材料的微观结构、成分及微区成分分布。结果表明：与PMP泡沫相比,铜掺杂PMP泡沫的孔洞直径和网络骨架尺寸变大;铜颗粒镶嵌在PMP泡沫的有机骨架上且有团聚现象;泡沫材料中除碳、铜外,还残留有杂质元素氧;铜颗粒被PMP泡沫包裹,与碳网络骨架之间接触紧密。