低能电子显微术及其应用

低能电子显微术是新发展起来的一种显微探测技术。它的特点是利用低能（１－３０ｅＶ）电子的弹性背散射使表面实空间实时成像，具有高的横向（１５ｎｍ）和纵向（原子级）分辩率，且易与低能电子衍射及其他电子显微术相结合。近年来它已有效地应用于金属和半导体表面的形貌观测、表面相变、吸附、反应及生长过程的研究。     

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.     

A comparative study of conventional type II and inverted core–shell nanostructures based on CdSe and ZnS

The objective of this work is to investigate structural, morphological and optical properties of conventional CdSe/ZnS core–shell and inverted ZnS/CdSe core–shell nanostructures for opto-electronic device applications. For this purpose both nanostructures were synthesized using chemical bath deposition technique in thin film form. The structural properties were studied using X-ray diffraction technique with Rietveld refinement and transmission electron microscopy (TEM). The surface morphology of synthesized thin film was illustrated in the form 2D and 3D images using atomic force microscopy (AFM). The optical properties were explained using UV–Vis absorption spectroscopy and photo luminescence (PL) spectroscopy in in situ monitoring process. A comparison of estimated particle size from XRD, high resolution AFM and TEM images was resulted in good agreement as 2.1, 2.4 and 2.1 nm respectively for conventional CdSe/ZnS core–shell and as 2.5, 2.5 and 2.2 nm respectively for inverted ZnS/CdSe core–shell nanostructures.     

Structural characterisation of Ni clusters in AlN via X-ray absorption, X-ray diffraction and transmission electron microscopy

Ni ions were implanted in bulk AlN with the goal to form embedded metallic clusters. Combining several characterisation techniques such as X-ray absorption spectroscopy, X-ray diffraction and high resolution transmission electron microscopy, we determined the lattice parameter of the Ni clusters that display a fcc crystalline structure. The average size increases when the ion fluence is increased or after a thermal treatment. Thanks to moiré fringes observed by high resolution transmission electron microscopy and to satellite peaks seen on the diffraction patterns, we concluded that the annealed Ni clusters orientate their (002) planes on the (101) of AlN. Moreover, the satellite positions allowed us to calculate Ni cluster average diameters, that are in agreement with average sizes deduced by X-ray absorption spectroscopy. Received 25 August 1999 and Received in final form 8 February 2000     

New source of stacking faults in heteroepitaxial systems

A new stacking fault formation mechanism has been observed for the first time in ZnO/LiTaO(3) heteroepitaxial films. High resolution electron microscopy studies combined with electron diffraction and numerical image computation suggest that the observed type I1 intrinsic stacking faults in an epitaxial film can be dominantly formed as a result of tilting of the lattices between films and substrate required to maintain a particular orientation relationship.     

Serial sectioning methods for 3D investigations in materials science

A variety of methods for the investigation and 3D representation of the inner structure of materials has been developed. In this paper, techniques based on slice and view using scanning microscopy for imaging are presented and compared. Three different methods of serial sectioning combined with either scanning electron or scanning ion microscopy or atomic force microscopy (AFM) were placed under scrutiny: serial block-face scanning electron microscopy, which facilitates an ultramicrotome built into the chamber of a variable pressure scanning electron microscope; three-dimensional (3D) AFM, which combines an (cryo-) ultramicrotome with an atomic force microscope, and 3D FIB, which delivers results by slicing with a focused ion beam. These three methods complement one another in many respects, e.g., in the type of materials that can be investigated, the resolution that can be obtained and the information that can be extracted from 3D reconstructions. A detailed review is given about preparation, the slice and view process itself, and the limitations of the methods and possible artifacts. Applications for each technique are also provided.     

远场超分辨随机光重建显微镜(STORM)研究进展

了解细胞内分子尺度的动态和结构的特征是生命科学迫切需要解决的问题,要求远场光学成像要求纳米或亚纳米量级的空间分辨率.介绍了一种实现打破衍射极限的远场荧光显微成像技术--随机光重建显微术(STORM),其分辨率可以达到横向分辨率20 nm,轴向分辨率50 nm,理论上这种方法的空间分辨率可以达到单分子定位的精度.具体介绍...     

Surface imaging using diffracted electrons

Refection electron microscopy has been applied for studying single crystal surfaces of noble metals in a conventional electron microscope using diffracted electrons for the imaging. This is equivalent to dark field imaging in transmission electron microscopy. The image contains far more contrast due to deviation from the ideal surface structure than any other surface imaging technique. A resolution of the order of 20 Å has been achieved for directions perpendicular to the incident beam. In directions parallel to the incident beam the resolution is much worse and the magnification is reduced with a factor 15 to 100 because the surface is viewed at the angle of the diffracted beam used for imaging (foreshortening). Nevertheless the achieved resolution is one to two orders of magnitude better than for other surface imaging methods. Since a correspondence can be established between image and diffraction pattern by means of selected area diffraction, the present technique should be very useful in structure analysis of surfaces.     

2D strain measurement in sub-10 nm SiGe layer with dark-field electron holography

In this paper, we carried out the two-dimensional (2D) strain measurement in sub-10 nm SiGe layer; images were obtained by dark-field electron holography (DFEH). This technique is based on transmission electron microscopy (TEM), in which dark-field holograms were obtained from a (400) diffraction spot. The measured results were compared to the X-ray diffraction (XRD) results in terms of the strain value and the depth of strain distribution in a very thin SiGe layer. Subsequently, we were able to successfully analyze the 2D strain maps along the [100] growth direction of the nanoscale SiGe region. The strain was measured and found to be in the range of 1.8–2.4%. The strain precision was estimated at 2.5 × 10⁻³. As a result, the DFEH technique is truly useful for measuring 2D strain maps in very thin SiGe layers with nanometer resolution and high precision.     

PMP/Cu泡沫材料中Cu颗粒的三维分布

为观测和分析铜掺杂聚-4-甲基-1-戊烯(PMP/Cu)低密度泡沫材料中铜颗粒的三维空间分布,采用高分辨X射线断层扫描技术,扫描PMP/Cu泡沫材料样品,对铜颗粒在聚合物泡沫中的分布进行了成像分析。经过图像处理和三维重构,获得铜颗粒在PMP聚合物泡沫中的三维立体分布图。结果分析显示:铜纳米粒子在PMP泡沫中存在团聚现象;不同尺寸的团聚物形态呈现出明显的多样化特征,小颗粒团聚物趋于球形,大颗粒团聚物趋于不规则的短木棒状,与在电子显微镜下直接观测到的结果一致。研究表明,该技术可以在不破坏样品的前提下,实现对有机聚合物泡沫材料中掺杂金属颗粒空间分布情况的直接观测。     

Phase transitions in Co nanoclusters grown by pulsed laser deposition

The crystalline structure of Co clusters embedded in an amorphous Al₂O₃ matrix was studied by transmission electron microscopy (TEM) and electron diffraction (TED). In the first stage of the growth a metastable structure (body-centred-cubic) is observed. A face-centred-cubic phase (fcc) is found when the size of the clusters increases ( diameter > 4 nm). The hexagonal-close-packed phase arises in the fcc phase by a succession of stacking faults at the largest sizes. The mechanisms of phase transformation have been determined by using high resolution electron microscopy (HREM). The chemical nature of the clusters, in particular the existence of Co-O bonds, was investigated by using electron energy loss spectroscopy (EELS). Received 03 July 2000 and Received in final form 22 December 2000     

Solving modulated structures by X-ray and electron crystallography

X-ray diffraction can be used for accurately determining not only classical, ordinary structures, but also modulated ones. For structures with weak modulations, the modulation induced satellite reflections are often hard to be observed by X-ray diffraction, but they appear clearly in electron diffraction. In these cases, X-ray diffraction will give only average structures whereas electron diffraction will yield information about the modulations. Sr(1.4)Ta(0.6)O(2.9) is a complex modulated compound with weak modulation and small modulated domains. Here we demonstrate the power of combining X-ray and electron crystallography for studying modulated structures on powders. The modulations of Sr(1.4)Ta(0.6)O(2.9) were determined from electron diffraction (SAED) and high resolution electron microscopy (HREM) images. With specially developed image processing techniques, the weak modulations were enhanced, facilitating the interpretation of HREM images in terms of atomic structure.     

类椭球氧化锌纳米结构的制备与表征

"用普通氧化锌晶须作为原材料, 采用高压釜腐蚀法和高温(600 ℃)裂解结合的方法合成纳米棒构成的氧化锌类椭球结构．XRD、SEM和TEM结果表明这种类椭球结构是单晶的,纳米棒取向一致,自组装生长而成．"     

Nd-Ba-Cu-O高温超导体的高分辨电子显微术研究

用电子衍射和高分辨电子显微术研究了Nd-Ba-Cu-O高温超导体,主相属正交晶系,具有畸变钙钛矿亚结构的三倍超结构,晶胞参数为a=3.84?,b=3.87?,c=11.7?,样品中存在大量的缺陷,用点阵象技术观察到刃位错,反向畴,并借助结构象确定了NdBa₂Cu₃O_7-δ的结构模型。在不同成象条件下,高分辨电子显微象上或者重原子为白点,或者氧原子为白点,当成象条件适当时,可以在象上区分氧原子和氧空位。 关键词：     

Atomic resolution imaging of oxygen atoms close to heavy atoms by HRTEM and ED,using the superconductor SmFeAsO0.85F0.15 as an example

Imaging of light atoms has always been a challenge in high-resolution electron microscopy. Image resolution is mainly limited by lens aberrations, especially the spherical aberration of the objective lens. Image deconvolution could correct for the image distortion by lens aberrations and restore the structure projection, the resolution of which is limited by the information limit of the microscope. Electron diffraction unrestricted by lens aberrations could overcome this resolution limit. Here we show a combination of electron diffraction and image deconvolution to reveal simultaneously the atomic columns of O and considerably heavier Sm at a very close distance (1.17 Å) in iron-based superconductor SmFeAsO_0.85F_0.15 using a conventional 200 kV electron microscope. The approach used here, starting from an image and an electron diffraction pattern, has an advantage for those radiation-sensitive samples. Besides, it can be applied to simultaneously imaging light and heavy atoms, even though they have a big difference in atomic number and a much smaller atomic distance than the microscope resolution.     

Bi2Te3/Sb超晶格纳米线的外延生长和热电测量

通过脉冲电沉积,外延生长出小单元长度的Bi₂Te₃/Sb超晶格纳米线.借助哈曼方法,测量了超晶格纳米线阵列的热电性能,330 K时的ZT值可达0.15.研究了Bi₂Te₃/Sb超晶格纳米线阵列器件的制冷或者加热能力,发现器件的上下表面的最大温差可以达到6.6 K.     

New directions in X-ray microscopy

The development of high brightness X-ray sources and high resolution X-ray optics has led to rapid advances in X-ray microscopy. Scanning microscopes and full-field instruments are in operation at synchrotron light sources worldwide, and provide spatial resolution routinely in the 25–50 nm range using zone plate focusing elements. X-ray microscopes can provide elemental maps and/or chemical sensitivity in samples that are too thick for electron microscopy. Lensless techniques, such as diffraction microscopy, holography and ptychography are also being developed. In high resolution imaging of radiation-sensitive material the effects of radiation damage needs to be carefully considered. This article is designed to provide an introduction to the current state and future prospects of X-ray microscopy for the non-expert.     

La3PO7:Eu3+纳米晶的制备和光谱性质

通过燃烧法合成了Eu³⁺掺杂的含氧磷酸镧(La₃PO₇:Eu³⁺)纳米晶颗粒材料。样品的结构、形貌和粒径分别由X射线衍射、扫描电镜和透射电子显微镜得到。测量了样品的发射光谱、激光选择激发光谱和时间分辨光谱。实验结果表明:样品展示的较强红光发射来自于Eu³⁺ 的⁵D₀→⁷F₂辐射跃迁,Eu³⁺在La₃PO₇基质中至少占据两种不同的格位,且具有较低的格位对称性。     

Synthesis and magnetic properties of aligned carbon nanotubes by microwave-assisted pyrolysis of acetylene

Aligned carbon nanotubes with high quality were synthesized at low temperature by microwave-assisted pyrolysis of acetylene in nitrogen atmosphere. The morphology and structure of the products were characterized by field-emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results indicated that the ACNTs with high crystallinity are densely packed, and some Fe₃C nanoparticles are encapsulated in all parts of carbon tubes. In addition, the effect of the reaction temperature on the morphologies of the CNTs was also studied in detail. Magnetic measurements showed that the Fe₃C-filled ACNTs display ferromagnetic properties at room temperature, and can be easily manipulated by an external magnetic field.     

Reversible structural transition in epitaxial manganite film

A reversible structural transition of an epitaxial La(2/3)Sr(1/3)MnO3 film deposited on a LaAlO3 substrate has been investigated by means of in situ high-resolution transmission electron microscopy and electron diffraction, combined with image and diffraction calculations. We observe that the crystallographic symmetry of the film can be lowered via electron beam irradiation, leading to a rhombohedral-monoclinic transition. This transition can be attributed to the cooperating effect of the mismatch stress and the irradiation-induced thermal stress.