飞秒时间分辨的能谱分析光电子显微镜：异质结超快载流子动力学测量

本文成功搭建了一套集成了能谱分析功能的时间分辨光电子显微镜系统(TR-PEEM),能够对电子密度分布进行时间分辨和能量分辨的成像.这套4D显微镜在空间、时间、能量多维度获取电子动力学信息提供了前所未有的手段.本文使用184 fs的时间分辨、150 meV的能量分辨和优于150 nm的空间分辨对半导体进行了测量,在Si(111)表面的Pb岛上获得了微区光电子能谱和能量分辨的TR-PEEM图像.实验结果表明,这套系统是进行异质结载流子动力学观察的有力工具,有助于在亚微米/纳米空间尺度和超快时间尺度上加深对半导体性质的理解.     

单色化X射线显微成像实验研究

围绕激光惯性约束聚变(ICF)内爆压缩阶段高空间分辨、高能谱分辨的诊断需求,提出了一种将KB显微镜和衍射晶体组合的大视场、单色化成像系统。在实验室条件下,利用Fe靶X射线光管,采用KB显微镜结合高定向热解石墨(HOPG)对网格进行背光成像,晶体选能后的成像结果表明,系统的视场能达到800μm,其中高分辨区域成像的分辨率为37μm。采用能谱探测器测试成像能谱,结果表明,系统的能量分辨率为28,验证了系统的单色性能。该系统兼顾了大视场、空间分辨和能量分辨,对内爆压缩阶段实验中热斑结构及混合效应的研究具有重要应用。     

飞秒时间分辨的能谱分析光电子显微镜:异质结超快载流子动力学测量（英文）

本文成功搭建了一套集成了能谱分析功能的时间分辨光电子显微镜系统(TR-PEEM),能够对电子密度分布进行时间分辨和能量分辨的成像.这套4D显微镜在空间、时间、能量多维度获取电子动力学信息提供了前所未有的手段.本文使用184 fs的时间分辨、150 meV的能量分辨和优于150 nm的空间分辨对半导体进行了测量,在Si(111)表面的Pb岛上获得了微区光电子能谱和能量分辨的TR-PEEM图像.实验结果表明,这套系统是进行异质结载流子动力学观察的有力工具,有助于在亚微米/纳米空间尺度和超快时间尺度上加深对半导体性质的理解.     

基于最大似然法的共焦拉曼光谱成像方法

随着现代科技对纳米微观区域兴趣的增加,如DNA测序、分子纳米器件微结构检测等,其对拉曼光谱技术的空间分辨力提出了更高的要求,而现有共焦拉曼光谱技术受自身原理限制,空间分辨力已无法满足科学需求。针对这一问题,在现有共焦拉曼光谱技术的基础上,提出一种基于最大似然算法的共焦拉曼光谱成像方法。该方法将超分辨图像复原技术与共焦拉曼光谱技术相结合,利用基于Poisson-Markov约束的最大似然超分辨复原算法对共焦拉曼光谱图像进行超分辨图像复原处理,恢复图像高频成分,进而改善共焦拉曼光谱系统的空间分辨能力,实现超分辨成像。仿真分析和实验结果表明,提出的基于最大似然算法的共焦拉曼光谱成像方法在不改变现有共焦拉曼光谱系统光学结构的前提下,仅对单幅拉曼光谱图像进行超分辨图像复原处理,即可将系统空间分辨力提高到200 nm,实现超分辨成像,同时该方法具有较强的噪声抑制能力。该方法有效地提高了共焦拉曼光谱系统的空间分辨力,为物理化学、材料科学等前沿领域中的高空间分辨微区光谱探测提供了一种新的途径,是一种行之有效的高空间分辨的共焦拉曼光谱成像方法。     

KB镜成像模拟以及与菲涅耳波带板成像的比较

采用坐标变换方法自编光线追迹程序模拟了Kirkpatrick-Baez镜在X射线波段的掠入射成像,获得了视场、分辨率等结果.比较了给定参量条件下Kirkpatrick-Baez镜与菲涅耳波带板两种高分辨X射线成像的特性,给出两者各自适用范围.Kirkpatrick-Baez镜成像有比较高的系统效率,在视场中心的空间分辨能力可达0.71μm,但偏离视场中心±200μm,空间分辨能力显著下降至6μm,适用于较小视场的成像.菲涅耳波带板成像不仅在视场中心可以实现0.39μm的空间分辨能力,偏离视场中心达±13 mm,空间分辨能力也几乎不变,可实现大视场高分辨成像.     

时域压缩合成孔径超分辨水声成像算法

提出一种针对水下稀疏目标的时域压缩合成孔径声呐成像方法(TC-SAS),实现了水声目标高分辨实时成像。通过多子阵的孔径合成,在时域上构造出成像网格格点到有效孔径内逐帧阵列的格林函数,并给出成像区域散射强度到数据域的映射矩阵;然后利用该区域空域稀疏的先验知识,通过正交匹配追踪的稀疏重构方式,解算出成像区域散射系数矩阵,实现了稀疏目标高分辨成像.同时,针对线性调频信号提出数据缩减的方法,通过对观测数据和字典矩阵同时脉压后截取,减小了数据规模;进一步结合二维矩阵数表查表的方法,以空间换时间,实现了区块实时成像。数值仿真以及湖试试验表明,所提算法能分辨出传统的时延求和算法难以分辨的目标,并且在图像清晰度指标上平均提升4.9 dB.改善了合成孔径声呐的成像质量.      

基于深紫外激光-光发射电子显微技术的高分辨率磁畴成像

基于磁二色效应的光发射电子显微镜磁成像技术是研究薄膜磁畴结构的一种重要研究手段,具有空间分辨率高、可实时成像以及对表面信息敏感等优点.以全固态深紫外激光(波长为177.3 nm;能量为7.0 eV)为激发光源的光发射电子显微技术相比于传统的光发射电子显微镜磁成像技术(以同步辐射光源或汞灯为激发源),摆脱了大型同步辐射光源的限制;同时又解决了当前阈激发研究中由于激发光源能量低难以实现光电子直接激发的技术难题,在实验室条件下实现了高分辨磁成像.本文首先对最新搭建的深紫外激光-光发射电子显微镜系统做了简单介绍.然后结合超高真空分子束外延薄膜沉积技术,成功实现了L10-FePt垂直磁各向异性薄膜的磁畴观测,其空间分辨率高达43.2 nm,与利用X射线作为激发源的光发射电子显微镜磁成像技术处于同一量级,为后续开展高分辨磁成像提供了便利.最后,重点介绍了在该磁成像技术方面取得的一些最新研究成果:通过引入Cr的纳米"台阶",成功设计出FePt的(001)与(111)双取向外延薄膜;并在"台阶"区域使用线偏振态深紫外激光观测到了磁线二色衬度,其强度为圆二色衬度的4.6倍.上述研究结果表明:深紫外激光-光发射电子显微镜磁成像技术在磁性薄膜/多层膜体系磁畴观测方面具备了出色的分辨能力,通过超高真空系统与分子束外延薄膜制备系统相连接,可以实现高质量单晶外延薄膜制备、超高真空原位传输和高分辨磁畴成像三位一体的功能,为未来磁性薄膜材料的研究提供了重要手段.     

KB镜成像模拟以及与菲涅耳波带板成像的比较

采用坐标变换方法自编光线追迹程序模拟了Kirkpatrick-Baez镜在X射线波段的掠入射成像,获得了视场、分辨率等结果.比较了给定参量条件下Kirkpatrick-Baez镜与菲涅耳波带板两种高分辨X射线成像的特性,给出两者各自适用范围.Kirkpatrick-Baez镜成像有比较高的系统效率,在视场中心的空间分辨能力可达0.71 μm,但偏离视场中心±200 μm,空间分辨能力显著下降至6 μm,适用于较小视场的成像.菲涅耳波带板成像不仅在视场中心可以实现0.39 μm的空间分辨能力,偏离视场中心达±13 mm,空间分辨能力也几乎不变,可实现大视场高分辨成像.     

菲涅耳波带板应用于聚变靶的高分辨X射线成像分析

在惯性约束核聚变研究中,为了实现1μm高空间分辨keV-X射线成像,文中发展了菲涅耳波带板(FZP)直接成像的分析方法,并通过数值计算研究了FZP的成像特性.针对钛K_α线(光子能量4.51 keV,波长0.275 nm),提出了FZP参数,对制作技术的要求较低.研究了靶尺度的影响.FZP的有效视场使它能够对数毫米大尺度靶实现高分辨成像.还研究了入射光的光谱带宽对成像的影响.FZP的色差有助于单色成像,但是带宽超过限度会导致像的反衬度降低.这些结果表明FZP应用于聚变点火靶的高空间分辨X射线成像的能力,也为应用提出了要求. 关键词： X射线成像 惯性约束核聚变 菲涅耳波带板     

高温拉曼光谱技术的实现及应用

基于高温热辐射背景与拉曼光谱的频域和时间域特点,分析并总结了获取高温拉曼光谱谱图的若干技术,并介绍了该实验室已经建立的二套高温拉曼光谱系统,即累积时间分辨高温宏观拉曼和累积时间分辨-共焦相结合的高温显微拉曼系统。实验表明此二套系统可以应用于高温相变和熔体结构,晶体生长边界层及荧光样品的拉曼测定。     

Atomic resolution STEM analysis of defects and interfaces in ceramic materials

Atomic resolution scanning transmission electron microscopy (STEM) analysis, in particular the combination of Z-contrast imaging and electron energy-loss spectroscopy (EELS) has been successfully used to measure the atomic and electronic structure of materials with sub-nanometer spatial resolution. Furthermore, the combination of this incoherent imaging technique with EELS allows us to correlate certain structural features, such as defects or interfaces directly with the measured changes in the local electronic fine-structure. In this review, we will discuss the experimental procedures for achieving high-resolution Z-contrast imaging and EELS. We will describe the alignment and experimental setup for high-resolution STEM analysis and also describe some of our recent results where the combined use of atomic-resolution Z-contrast imaging and column-by-column EELS has helped solve important materials science problems.     

Studies on paint cross sections of a glass painting by using FT‐IR and Raman microspectroscopy supported by univariate and hierarchical cluster analyses

Fourier transform infrared (FT‐IR) and Raman spectroscopy is used for the non‐destructive analysis of painting materials and ageing compounds in micrometric cross sections of a glass painting. The combination of both techniques in conjunction with imaging/mapping function provides the spatial distribution of chemical components identified in vibrational spectra. The aim of our work is to show the applicability of the FT‐Raman mapping technique in the detection of painting materials. We also compare Raman information gained by using two laser excitations at 532 and 1064 nm implemented in microspectrometers with different confocality and spatial resolution. In turn among FT‐IR imaging techniques, we compare chemical images recorded in external reflection and attenuated total reflection modes that give chemical images of different size and spatial resolution. Our FT‐IR and Raman imaging characterize a number of painting materials such as pigments, binders, fillers as well as degradation products. Raman maps are constructed by using the univariate analysis. In turn, a profile of IR images requires the use of a more complex methodology. Here, we compare FT‐IR images of the painting cross sections obtained by using the univariate and hierarchical cluster analysis. We clearly show that the multivariate approach is a powerful tool for the credible construction of IR images, providing the relevant chemical information on the multicomponent stratigraphy of the samples. Moreover, the combination of all the methods allows us to demonstrate their degree of utility for the study on the paint cross sections of the works of art. Copyright © 2013 John Wiley & Sons, Ltd.     

Hybrid Rayleigh,Raman and two‐photon excited fluorescence spectral confocal microscopy of living cells

A hybrid fluorescence–Raman confocal microscopy platform is presented, which integrates low‐wavenumber‐resolution Raman imaging, Rayleigh scatter imaging and two‐photon fluorescence (TPE) spectral imaging, fast ‘amplitude‐only’ TPE‐fluorescence imaging and high‐spectral‐resolution Raman imaging. This multi‐dimensional fluorescence–Raman microscopy platform enables rapid imaging along the fluorescence emission and/or Rayleigh scatter dimensions. It is shown that optical contrast in these images can be used to select an area of interest prior to subsequent investigation with high spatially and spectrally resolved Raman imaging. This new microscopy platform combines the strengths of Raman ‘chemical’ imaging with light scattering microscopy and fluorescence microscopy and provides new modes of correlative light microscopy. Simultaneous acquisition of TPE hyperspectral fluorescence imaging and Raman imaging illustrates spatial relationships of fluorophores, water, lipid and protein in cells. The fluorescence–Raman microscope is demonstrated in an application to living human bone marrow stromal stem cells. Copyright © 2009 John Wiley & Sons, Ltd.     

Multimodal nonlinear optical microscopy

Because each nonlinear optical (NLO) imaging modality is sensitive to specific molecules or structures, multimodal NLO imaging capitalizes the potential of NLO microscopy for studies of complex biological tissues. The coupling of multiphoton fluorescence, second‐harmonic generation, and coherent anti‐Stokes Raman scattering (CARS) has allowed investigation of a broad range of biological questions concerning lipid metabolism, cancer development, cardiovascular disease, and skin biology. Moreover, recent research shows the great potential of using a CARS microscope as a platform to develop more advanced NLO modalities such as electronic‐resonance‐enhanced four‐wave mixing, stimulated Raman scattering, and pump‐probe microscopy. This article reviews the various approaches developed for realization of multimodal NLO imaging as well as developments of new NLO modalities on a CARS microscope. Applications to various aspects of biological and biomedical research are discussed.     

Re_3N的变温拉曼散射与高压同步辐射研究

本工作通过高压固相复分解反应(HPSSM)合成块体Re_3N。利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)和能量色散X射线分析(EDS)对高压样品进行结构表征与元素成分确定,结果表明利用HPSSM法合成的Re_3N具有较高的晶体质量。在77K到873K温度范围内利用拉曼散射研究Re_3N的晶格振动特性。基于三(四)声子耦合模型,研究Re_3N拉曼声子模频率的红移和拉曼峰的宽化现象,结果表明高温条件下Re_3N拉曼散射效应中三声子耦合过程占主导。高压同步辐射研究表明Re_3N具有很高的体弹模量(B0=417GPa),是一种潜在的超硬材料。     

Nonlinear interferometric vibrational imaging

Coherent anti-Stokes Raman scattering (CARS) processes are "coherent," but the phase of the anti-Stokes radiation is lost by most incoherent spectroscopic CARS measurements. We propose a Raman microscopy imaging method called nonlinear interferometric vibrational imaging, which measures Raman spectra by obtaining the temporal anti-Stokes signal through nonlinear interferometry. With a more complete knowledge of the anti-Stokes signal, we show through simulations that a high-resolution Raman spectrum can be obtained of a molecule in a single pulse using broad band radiation. This could be useful for identifying the three-dimensional spatial distribution of molecular species in tissue.     

Mapping the intracellular distribution of carbon nanotubes after targeted delivery to carcinoma cells using confocal Raman imaging as a label-free technique

The uptake of carbon nanotubes (CNTs) by mammalian cells and their distribution within cells is being widely studied in recent years due to their increasing use for biomedical purposes. The two main imaging techniques used are confocal fluorescence microscopy and transmission electron microscopy (TEM). The former, however, requires labeling of the CNTs with fluorescent dyes, while the latter is a work-intensive technique that is unsuitable for in situ bio-imaging. Raman spectroscopy, on the other hand, presents a direct, straightforward and label-free alternative. Confocal Raman microscopy can be used to image the CNTs inside cells, exploiting the strong Raman signal connected to different vibrational modes of the nanotubes. In addition, cellular components, such as the endoplasmic reticulum and the nucleus, can be mapped. We first validate our method by showing that only when using the CNTs' G band for intracellular mapping accurate results can be obtained, as mapping of the radial breathing mode (RBM) only shows a small fraction of CNTs. We then take a closer look at the exact localization of the nanotubes inside cells after folate receptor-mediated endocytosis and show that, after 8-10 h incubation, the majority of CNTs are localized around the nucleus. In summary, Raman imaging has enormous potential for imaging CNTs inside cells, which is yet to be fully realized.     

A review of hyperspectral imaging for nanoscale materials research

As an emerging technology, hyperspectral imaging (HSI), which combines both advanced spectroscopy and imaging techniques, provides sufficient information for spectral and spatial analysis and is thus suitable for distribution and property investigation of nanoscale materials. Considering the applications of HSI have spread from remote sensing to quality control of macro products such as food and milk, this article reviews recent research of HSI in a new field of nanoscale materials. On the basis of fundamental parts of a HSI system, new techniques fitting specifically for nanoscale materials imaging such as dark field and Raman spectroscopy are introduced. Nanoscale materials, including metal nanoparticles, carbon nanotubes and graphene, biological components in cells and tissues, as well as multi-layer nanoscale materials, are the research hotspots utilizing HSI technology. Related research reports of the above materials are reviewed based on the physical distinction of these nanoscale materials. It is believed that HSI technology is a strongly potential technique for property investigation and manipulation of nanomaterial for various applications.     

Some forensic applications of a combined micro‐Raman and scanning electron microscopy system

The structural chemical analyser (SCA) is a novel accessory that allows the analytical advantages of Raman spectroscopy and scanning electron microscopy with energy dispersive x‐ray detection (SEM/EDX) to be realised in a single hybridised instrument. The combined Raman–SEM/EDX system permits in situ characterisation of a sample based on both its molecular and elemental makeup. This article demonstrates the potential of using the SCA for interrogating trace evidence for criminalistic purposes. Illustrative evidentiary examples (taken from our laboratory's archives) include the examination of a white paint fragment consisting of several layers of the same colour and a sample of explosive mixture recovered from a place of interest. The sensitive SEM imaging contrast mechanisms enabled the optically identical multiple layers of the white paint to be distinguished easily. The individual layers were then unambiguously analysed to establish their elemental profile (from energy dispersive x‐ray (EDX)) and this was cross‐referenced with the chemical information derived from in situ Raman measurements. X‐ray mapping was used as a fast and convenient way of characterising simultaneously multiple solids constituting the explosive mixture. Typical particles were targeted and analysed both by EDX and Raman spectroscopy revealing an unusual chlorate‐based energetic mixture that also contained 2, 4, 6‐trinitrotoluene (TNT) and 2, 4, 6‐trinitrophenylmethylnitramine (Tetryl). Copyright © 2009 John Wiley & Sons, Ltd.     

Leucine pools in Escherichia coli biofilm discovered by Raman imaging

In structured communities of bacteria known as biofilms, a variety of biomolecules have been shown to play a unique role as signals and/or regulators in biofilm formation. Here, we report that high levels of the amino acid leucine (leucine pool) were detected, for the first time, within microcolonies in a 30‐h‐old Escherichia coli biofilm by Raman imaging. Localization of leucine revealed by multifrequency Raman images indicates leucine accumulation during the early stage of the E. coli biofilm formation, which may have resulted from physiological environment‐specific metabolic adaptation. We demonstrate that our label‐free Raman imaging method provides a useful platform for directly identifying still unknown natural products produced in biofilms as well as for visualizing heterogeneous distributions of biofilm constituents in situ. Copyright © 2011 John Wiley & Sons, Ltd.