Progress in aberration-corrected scanning transmission electron microscopy

A new corrector of spherical aberration (C(S)) for a dedicated scanning transmission electron microscope (STEM) is described and its results are presented. The corrector uses strong octupoles and increases C(C) by only 0.2 mm relative to the uncorrected microscope. Its overall stability is greatly improved compared to our previous design. It has achieved a point-to-point resolution of 1.23 A in high-angle annular dark field images at 100 kV. It has also increased the current available in a 1.3 A-sized probe by about a factor of ten compared to existing STEMs. Its operation is greatly assisted by newly developed autotuning software which measures all the aberration coefficients up to fifth order in less than one minute. We conclude by discussing the present limits of aberration-corrected STEM, and likely future developments.     

New views of materials through aberration-corrected scanning transmission electron microscopy

The successful correction of third-order and, more recently, fifth-order aberrations has enormously enhanced the capabilities of the scanning transmission electron microscope (STEM), by not only achieving record resolution, but also allowing near 100% efficiency for electron energy loss spectroscopy, and higher currents for two-dimensional spectrum imaging. These advances have meant that the intrinsic advantages of the STEM, incoherent imaging and simultaneous collection of multiple complementary images can now give new insights into many areas of materials physics. Here, we review a number of examples, mostly from the field of complex oxides, and look towards new directions for the future.     

Optimizing the environment for sub-0.2 nm scanning transmission electron microscopy

Sub-0.2 nm probes can now be readily obtained on Schottky field-emission microscopes. However, environmental instabilities are proving to be the limiting factors for atomic resolution spectroscopy and distortion-free annular-dark field imaging. This is a result of the long acquisition times and the serial nature of the scanning system where instabilities result in image distortions rather than reductions in contrast. Troubleshooting the most common environmental problems is discussed here. In addition to the expected sensitivity to mechanical vibration, electromagnetic interference and temperature variations, air-pressure fluctuations are found to have a significant impact on microscopes with side-entry goiniometers.     

Scanning electron mirror microscopy and scanning electron microscopy of integrated circuits

The recently developed scanning electron mirror microscope (SEMM) is compared with other types of electron microscopes, such as the electron mirror microscope (EMM) and the scanning electron microscope (SEM), for examining integrated circuits. Potential advantages of the SEMM include high resolution, elimination of electron bombardment damage, and high sensitivity of voltage gradients, magnetic fields, and topography. Preliminary observations of integrated, circuits obtained with the feasibility SEMM at various specimen potentials are discussed.     

Simulation of atomic-scale high-angle annular dark field scanning transmission electron microscopy images

Image simulations for high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) based on the Bethe's eigen-value method are presented. The effects of aperture size and defocus of a probe-forming lens, both of which determine the shape of the probe, and the effect of the distortion, influencing the Bloch wave field on atomic columns channelled by electrons, on the HAADF-image intensity are discussed in terms of dynamical effect. These effects are illustrated by our experimental atomic-scale HAADF-STEM images, detected in a detector range of 50-110 mrad. It is emphasized that the image simulations are indispensable for quantification of experimental HAADF-STEM images and as such provide a valuable compositional analysis for every atomic column along the incident beam.     

铁电纳米结构的浸渍涂敷法制备和微结构STEM表征(英文)

本文利用浸渍涂敷法在硅基多孔氧化铝模版介质(孔径20nm-100nm)上制备了Pb(Zr0.53Ti0.47))3(PZT)铁电纳米结构,并利用扫描透射电子显微镜(STEM)观察了其表面形貌和剖面微结构.TEM像和X-射线能谱分析结果表明在多孔氧化铝模版孔道内形成了PZT纳米结构,其横向尺寸可通过改变氧化铝模版的孔径来调节.采用浸渍涂敷法可使PZT溶液贯穿整个氧化铝纳米孔道,在其内壁形成PZT涂层,厚度为4nm-15nm.氧化铝纳米孔道内的黑色TEM衬度线证实了PZT涂层的存在,其存在方式为连续介质型或离散的晶粒形状.平面STEM像显示PZT纳米结构具有椭球状形貌,这可能是由氧化铝纳米孔道的局部扭曲或PZT溶液在退火过程中的收缩引起的.在硅基多孔氧化铝模版介质上采用浸渍涂敷法制备的PZT有序纳米结构,在将来三维结构的非挥发性铁电存储器方面具有十分诱人的应用前景.     

68例脑胶质瘤透射电镜和扫描电镜观察及其鉴别诊断意义

收集人脑原发性胶质瘤标本68例，其中星形细胞瘤9例，间变性星形细胞瘤22例，胶质母细胞18例，少突胶质细胞瘤3例，间变性光突胶质细胞瘤4例，少突－星形胶质细胞肿瘤12例。另有上皮型和纤维母细胞型脑膜瘤6例。采用透射电镜和扫描电镜观察瘤细胞和间质的超微结构特点。结果显示，各型星形细胞肿瘤瘤细胞共同特点是胞浆及胞突内含有多少不等的胶质细丝；胞膜皱折不平，有多少不一的胞突，这些胞突相互交织在一起。Rosenthal纤维由密集排列的细丝状物围绕不规则的嗜锇性团块构成。脑膜瘤瘤细胞有很多指状突起，细胞间可见桥粒连接，胞膜表面缺乏星形细胞瘤细胞表面的那种皱折。结果表明，透射电镜和扫描电镜可以做为脑胶质瘤病理诊断、鉴别诊断的辅助手段。在普通光镜观察的基础上，结合免疫组化结果，应用扫描电镜还可以比较直观地观察到瘤组织内各种成分之间的相互关系。     

透射电镜与扫描电镜分析

文章简要介绍了透射电镜和扫描电镜两种当前主要的电子显微分析方法的应用,比较了它们的结构和工作原理,讨论了各自的应用范围以及发展方向,指出将两者有机结合可以得到比较全面的材料分析结果。     

Direct imaging of Guinier-Preston zones by high-angle annular detector dark-field scanning transmission electron microscopy

We report atomic resolution imaging of Cu-planar precipitates in aged Al-Cu alloys, known as Guinier-Preston (GP) zones, by high-angle annular detector dark-field scanning transmission electron microscopy. Single layered GP-I zones as small as 2 nm in length were resolved among densely populated GP-I zones, whereas double layered GP zones were clearly identified. The images of GP-II zones showed not only the commonly accepted structure, in which single Cu layers are separated by three Al layers, but also a variant, in which double Cu layers are separated by a single Al layer.     

Electron-beam-induced-current investigation of GaN/AlGaN/Si heterostructures using scanning transmission electron microscopy

An electron-beam-induced-current technique has been applied to scanning transmission electron microscopy to characterize GaN/AlGaN/n-Si heterostructures. The structure was formed by metalorganic vapor phase epitaxy using AlGaN as an intermediate layer. Two samples with nominal intermediate layer thicknesses of 60 and 120 nm were studied. It was found that there is a junction in the n-type Si region underneath the nitride/Si interface irrespective of the intermediate layer thickness, whereas induced current occurred neither in the nitride region nor at the nitride/Si interface. The junction formed was found to be undulated. The sample with the thin intermediate layer had undulations of a shorter periodicity than that with the thick intermediate layer. The formation of the junction is attributed to the diffusion of Al during the nitride growth.     

Advances in energy-filtering transmission electron microscopy

First experiments using a new energy-filtering microscope (Sub-eV-Sub-A microscope, or SESAM) are shown. They make use of the high transmissivity of the 90 degree filter. This allows the mapping of chemical bonding of large specimen areas, even if narrow energy selecting slits are used. Because large scattering angles are accepted by this filter, energy-filtered diffraction patterns extending to 150 mrad can be recorded by a single exposure. This can be used to determine the reduced density function of amorphous materials and reduces the exposure time of the investigated area by three orders of magnitude as compared with previous approaches.     

Study of Ni-Si thin-film interfacial reactions by coupling differential scanning calorimetry measurements and transmission electron microscopy analyses

In this paper, the solid-state interactions between a 500 nm thick Ni layer and a Si wafer are studied for temperatures up to 500 °C by coupling Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM). The phase transformation temperatures determined by DSC are about 250, 300, 350 and 410 °C. Dedicated samples were prepared to identify phase transformations occurring during heating up to these temperatures. TEM analyses show that the reaction product always consists of a continuous layer so that the nature of phase(s) formed at the interface can be determined. The reaction layer thickness is about 25, 50 and 150 nm for samples heated to 250, 300 and 350 °C, respectively. Moreover, from TEM diffraction patterns, it is shown that, for such a thick layer of Ni deposited on Si substrate, the first phase forming at the Ni/Si interface is the metastable Ni₃Si compound.     

New versatile staining reagents for biological transmission electron microscopy that substitute for uranyl acetate

Aqueous uranyl acetate has been extensively used as a superb staining reagent for transmission electron microscopy of biological materials. However, recent regulation of nuclear fuel material severely restricts its use even for purely scientific purposes. Since uranyl salts are hazardous due to biological toxicity and remaining radioactivity, development of safe and non-radioactive substitutes is greatly anticipated. We examined two lanthanide salts, samarium triacetate and gadolinium triacetate, and found that 1-10% solution of these reagents was safe but still possess excellent capability for staining thin sections of plastic-embedded materials of animal and plant origin. Although post-fixation with osmium tetroxide was essential for high-contrast staining, post-staining with lead citrate could be eliminated if a slow-scan CCD camera is available for observation. These lanthanide salts can also be utilized as good negative-staining reagents to study supramolecular architecture of biological macromolecules. They were not as effective as a fixative of protein assembly, reflecting the non-hazardous nature of the reagents.     

Another 60 years in electron microscopy: development of phase-plate electron microscopy and biological applications

It has been six decades since the concept of phase-plate electron microscopy was first reported by Boersch, but an experimental report on a phase plate with a theoretically rational performance has only recently been released by a group including the present author. Currently, many laboratories around the world are attempting to develop a wide range of phase plates to enhance the capabilities of transmission electron microscopy. They are reporting not only advantages of their own developments but also a fundamental problem inherent to electron beam devices, namely charging, i.e. the accumulation of electrostatic charge. In this report, we review the 60-year history of phase-plate development, with a particular focus on the fundamental issue of phase-plate charging. Next, we review biological applications of qualified phase plates, which have been successful in avoiding charging to some extent. Finally, we compare and discuss electron microscopic images, taken with or without phase plates, of biological targets such as proteins (GroEL and TRPV4), protein complexes (flagellar motor), viruses (T4 phage, ε-15 phage and herpes simplex virus), bacterial (cyanobacteria) and mammalian (PtK2) cells.     

水生植物冷冻扫描电镜和常规扫描电镜成像效果比较

比较了三种水生植物(单星藻、芜萍和水蓑衣)的冷冻扫描电镜和常规扫描电镜成像效果,两种方法观察到的样品表面结构差异明显.冷冻扫描电镜下的样品形态饱满、无塌陷皱缩,藻细胞表面的脊状凸起和水生植物叶片上的气孔结构清晰、无变形;而常规扫描电镜冷冻干燥的样品因脱水皱缩变形,甚至表面部分塌陷.冷冻扫描电镜可以有效地解决水生植物样品因脱水而皱缩变形的问题,最大程度地保持样品原本的细微结构特征,非常适合用于含水量高的水生植物样品的超微结构观察.