Numerical investigation of ultrasound reflection and backscatter measurements in cancellous bone on various receiving areas

In this study, new ultrasound reflection and backscatter measurements in cancellous bone using a membrane-type hydrophone are proposed. A membrane hydrophone made of a piezoelectric polymer film mounted on an annular frame allows an incident ultrasound wave to pass through its aperture because it has no backing material. Therefore, in measurements using the membrane hydrophone, the receiving area could be located independently from the transmitting area. In addition, the size and shape of the receiving area, which corresponded to those of the electrode deposited on the piezoelectric film, could be arranged in various ways. To investigate the validity of the proposed measurements, before bench-top experiments, the reflected and backscattered waves from cancellous bone were numerically simulated using a finite-difference time-domain method. The reflection and backscatter parameters were measured on various receiving areas, and their correlation coefficients with the structural parameters in the cancellous bone were derived. The simulated results suggested that appropriate receiving areas for the reflection and backscatter measurements could exist and that the proposed measurements could be more effective for evaluating bone properties than conventional measurements.     

超声背散射法评价松质骨状况的研究

超声背散射法评价松质骨状况及诊断骨质疏松症是近年来医学超声领域内的研究热点之一,现已取得了显著的进展。本文将介绍近年来超声背散射法及其参量评价松质骨状况的研究进展,并分析超声背散射相关参量频谱质心偏移量（SCS）和平均骨小梁间距（TbSp）与骨矿密度（BMD）的相关性。研究结果表明,超声背散射参量与BMD有较高的相关性。最后提出了将来研究中需要努力的方向。     

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.     

A correlative optical microscopy and scanning electron microscopy approach to locating nanoparticles in brain tumors

The growing use of nanoparticles in biomedical applications, including cancer diagnosis and treatment, demands the capability to exactly locate them within complex biological systems. In this work a correlative optical and scanning electron microscopy technique was developed to locate and observe multi-modal gold core nanoparticle accumulation in brain tumor models. Entire brain sections from mice containing orthotopic brain tumors injected intravenously with nanoparticles were imaged using both optical microscopy to identify the brain tumor, and scanning electron microscopy to identify the individual nanoparticles. Gold-based nanoparticles were readily identified in the scanning electron microscope using backscattered electron imaging as bright spots against a darker background. This information was then correlated to determine the exact location of the nanoparticles within the brain tissue. The nanoparticles were located only in areas that contained tumor cells, and not in the surrounding healthy brain tissue. This correlative technique provides a powerful method to relate the macro- and micro-scale features visible in light microscopy with the nanoscale features resolvable in scanning electron microscopy.     

时间分辨电子显微镜的可行性研究

文章从理论上分析了飞秒激光与金属阴极的相互作用过程．将飞秒激光与金属阴极产生的超短电子脉冲作为电子源，提出了一种具有时间分辨能力的电子显微镜(TREM)的概念设计．文章作者详细地研究了这种电子显微镜的可行性，并讨论了超短电子脉冲的传输和控制问题．     

时间分辨电子显微镜的可行性研究

文章从理论上分析了飞秒激光与金属阴极的相互作用过程.将飞秒激光与金属阴极产生的超短电子脉冲作为电子源,提出了一种具有时间分辨能力的电子显微镜(TREM)的概念设计.文章作者详细地研究了这种电子显微镜的可行性,并讨论了超短电子脉冲的传输和控制问题.     

石墨烯的透射电子显微学研究

石墨烯（Graphene）是近几年迅速发展起来的研究热点材料之一.利用透射电子显微镜（TEM）研究Graphene的结构特征和原子动态过程,是 Graphene研究的重要进展.文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

Electron optics for high throughput low energy electron microscopy

Novel electron-optical components and concepts aiming at improving the throughput and extending the applications of a low energy electron microscope (LEEM) have been developed. An immersion magnetic objective lens can substantially reduce e-e interactions and the associated blur, as electrons do not form a sharp crossover in the back-focal plane. The resulting limited field of view of the immersion objective lens in mirror mode can be eliminated by immersing the cathode of the electron gun in a magnetic field. A dual illumination beam approach is used to mitigate the charging effects when the LEEM is used to image insulating surfaces. The negative charging effect, created by a partially absorbed mirror beam, is compensated by the positive charging effect of the secondary beam with an electron yield exceeding 1. On substrates illuminated with a tilted beam near glancing incidence, large shadows are formed on even the smallest topographic features, easing their detection. On magnetic substrates, the magnetic flux leaking above the surface can be detected with tilted illumination and used to image domain walls with high contrast.     

超快时间分辨光电子显微镜技术及应用

光电子显微镜是一种基于光电效应的电子显微镜,利用样品不同空间位置光电子产量的差异作为图像衬度进行投影成像。其成像速度快、空间分辨率高、探测无损伤等特点和优势,在表面科学、表面等离激元学、半导体学等学科有着广泛应用。另外,结合超快光泵浦探测技术为光电子显微镜提供了高时间分辨能力,特别适用于高时空分辨的动力学过程研究。时间分辨光电子显微镜是具备多维度直观测量的技术方法,为研究人员开辟了新的道路。文章首先简要回顾电子显微成像技术的发展,然后介绍在表面等离激元学和半导体物理领域中应用光电子显微镜的最新进展,最后介绍北京大学最近建设的超快光电子显微镜系统和相关研究工作及展望。     

电子显微学进展及其在材料科学中的应用

文章简要介绍了高分辨电子显微学方法和电子能量损失谱的进展.文中特别指出,随着电子显微技术的发展,原子分辨电子显微图像对结构问题的深入研究有重要作用.装备有能量单色器的新一代电子显微镜,可以直接给出高能量分辨率的电子能量损失谱(优于 0.1eV).这些先进技术方法的应用,推动了晶体结构学、材料科学、物理学、纳米科学及生命科学的发展,也为解决很多重要结构问题奠定了基础.文章重点讨论了几个典型功能材料体系的结构问题：利用大角度会聚束电子衍射技术,分析了应变硅器件中的应变分布;利用原位电子显微技术,研究了新型电子铁电体LuFe2O4电荷序和物理性能的关系;深入探讨了强关联体系中电子关联效应对电子能量损失谱和电子结构的影响.     

原位透射电子显微学进展及应用

文章简要介绍了近年来原位透射电子显微学的进展,并指出,原位透射电子显微技术的发展使得在纳米、原子层次观察样品在力、热、电、磁作用下以及化学反应过程中的微结构演化成为可能。通过研究物质在外界环境作用下的微结构演化规律,揭示其原子结构与物理化学性质的相关性,指导其设计合成和微结构调控,促进新物质的探索和深层次物质结构研究,为解决凝聚态物理学中的具体问题提供了直接、准确和详细的方法。     

原位透射电子显微学进展及应用

文章简要介绍了近年来原位透射电子显微学的进展,并指出,原位透射电子显微技术的发展使得在纳米、原子层次观察样品在力、热、电、磁作用下以及化学反应过程中的微结构演化成为可能。通过研究物质在外界环境作用下的微结构演化规律,揭示其原子结构与物理化学性质的相关性,指导其设计合成和微结构调控,促进新物质的探索和深层次物质结构研究,为解决凝聚态物理学中的具体问题提供了直接、准确和详细的方法。     

Micro- and nano-structural analyses of damage in bone

Skeletal fractures represent a significant medical and economic burden for our society. In the US alone, age-related hip, spine, and wrist fractures accounted for more than $17 billion in direct health care costs in 2001. Moreover, skeletal fractures are not limited to the elderly; stress fractures and impact/trauma-related fractures are a significant problem in younger people also. Gaining insight into the mechanisms of fracture and how these mechanisms are modulated by intrinsic as well as extrinsic factors may improve the ability to define fracture risk and develop and assess preventative therapies for skeletal fractures. Insight into failure mechanisms of bone, particularly at the ultrastructural-level, is facilitated by the development of improved means of defining and measuring tissue quality. Included in these means are microscopic and spectroscopic techniques for the direct observation of crack initiation, crack propagation, and fracture behavior. In this review, we discuss microscopic and spectroscopic techniques, including laser scanning confocal microscopy (LSCM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopic imaging for visually observing microdamage in bone, and the current understanding of damage mechanisms derived from these techniques.     

High-resolution electron microscopy of grain boundaries

Our ability to observe atomic-scale features of grain boundaries has tremendously improved during the past decade. In this paper we give, aided by a number of examples, a select overview, on progress in the field of grain boundary research directly related to the advent of modern high-resolution electron microscopy (HREM) instruments (point-to-point resolution better than 0.2 nm). Examples of grain boundary issues addressed by atomic structure observations of grain boundaries in oxides and metals will be given with emphasis on systematic investigations of the role of macroscopic and microscopic grain boundary parameters. Since comparisons between observed interface structures and atomistic computer modeling results are quite important, considerable efforts towards quantification have been undertaken recently by a number of authors. Most valuable insights have been obtained by the systematic examination of a range of grain boundary structures, using a combination of experimental observations and computer modeling results. In this manner HREM observations have been invaluable not only as a test of theoretical models, but also by exposing common atomic-scale features of high-angle grain boundaries. This has brought us closer to the goal of generating a general understanding of the interface structure and its connection to properties. Such studies have given valuable insights regarding the correlations between macroscopic grain boundary geometry, interfacial energy, and atomic relaxation modes.Work supported by the U.S. Department of Energy, Basic Energy Sciences, under contract W-31-109-Eng-38.     

直拉硅单晶中原生氧沉淀的透射电镜研究

利用透射电镜对掺氮(NCZ) 和普通 (CZ) 直拉硅单晶中的原生氧沉淀进行研究. 研究表明，在NCZ样品中，有高密度的粒径为5nm的氧沉淀生成，而在CZ样品中，没有观察到这种氧沉淀. 初步认为，这种细小的氧沉淀是以650℃低温下形成的N-O复合体为核心在随后的冷却过程中形成. 关键词： 直拉硅 透射电镜 氧沉淀     

Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques

The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature. The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method. A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained. The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations, as demonstrated in the electron backscattered diffraction. A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites, as indicated by energy dispersive X-ray spectroscopy.     

Contamination mitigation strategies for scanning transmission electron microscopy

Modern scanning transmission electron microscopy (STEM) enables imaging and microanalysis at very high magnification. In the case of aberration-corrected STEM, atomic resolution is readily achieved. However, the electron fluxes used may be up to three orders of magnitude greater than those typically employed in conventional STEM. Since specimen contamination often increases with electron flux, specimen cleanliness is a critical factor in obtaining meaningful data when carrying out high magnification STEM. A range of different specimen cleaning methods have been applied to a variety of specimen types. The contamination rate has been measured quantitatively to assess the effectiveness of cleaning. The methods studied include: baking, cooling, plasma cleaning, beam showering and UV/ozone exposure. Of the methods tested, beam showering is rapid, experimentally convenient and very effective on a wide range of specimens. Oxidative plasma cleaning is also very effective and can be applied to specimens on carbon support films, albeit with some care. For electron beam-sensitive materials, cooling may be the method of choice. In most cases, preliminary removal of the bulk of the contamination by methods such as baking or plasma cleaning, followed by beam showering, where necessary, can result in a contamination-free specimen suitable for extended atomic scale imaging and analysis.     

A method of correlative light and electron microscopy for yeast cells

Correlative light and electron microscopy (CLEM) is a method of imaging in which the same specimen is observed by both light microscopy and electron microscopy. Specifically, CLEM compares images obtained by light and electron microscopy and makes a correlation between them. After the advent of fluorescent proteins, CLEM was extended by combining electron microscopy with fluorescence microscopy to enable molecular-specific imaging of subcellular structures with a resolution at the nanometer level. This method is a powerful tool that is used to determine the localization of specific molecules of interest in the context of subcellular structures. Knowledge of the localization of target proteins coupled with the functions of the structures to which they are localized yields valuable information about the molecular functions of these proteins. However, this method has been mostly applied to adherent cells due to technical difficulties in immobilizing non-adherent target cells, such as yeasts, during sample preparation. We have developed a method of CLEM applicable to yeast cells. In this report, we detail this method and present its extension to Live CLEM. The Live CLEM method enabled us to link the dynamic properties of molecules of interest to cellular ultrastructures in the yeast cell. Since yeasts are premier organisms in molecular genetics, combining CLEM with yeast genetics promises to provide important new findings for understanding the molecular basis of the function of cellular structures.     

高分辨扫描透射电子显微镜原理及其应用

扫描透射电子显微术是目前应用最广泛的电子显微表征手段之一,具有分辨率高、对化学成分敏感和图像直观易解释等特点。其中高分辨扫描电子显微镜可以直接获得原子分辨率的Z 衬度像,结合X射线能谱(EDS)和电子能量损失谱(EELS),可在亚埃尺度上对材料的原子和电子结构进行分析。文章简述了扫描透射电子显微镜的基本原理及其应用现状,重点论述了高角环形暗场(HAADF)和环形明场(ABF)像的成像原理、特征和应用。此外,文中还对原子尺度分辨率的X射线能谱及电子能量损失谱元素分析方法进行了简述。