High resolution Auger electron spectroscopy and microscopy of a supported metal catalyst

High spatial resolution Auger electron spectra and scanning Auger microscope (SAM) images of supported metal catalysts have been obtained in a UHV scanning transmission electron microscope. Ag/α-Al₂O₃ was used as a model catalyst system, where silver was evaporated, in situ, onto polycrystalline alumina carriers. Silver particles, as small as 2 nm in diameter, were clearly revealed in SAM images with high contrast. On large islands, an edge resolution < 3 nm was achieved. Information about surface and bulk properties of supported catalysts can be extracted from images formed with different signals generated from the same area which are obtained simultaneously.     

A low voltage time of flight electron emission microscope

This paper presents the design of a low voltage time of flight electron emission microscope (TOF-EEM), which should in principle be capable of acquiring spectral chemical information at nano-metre spatial resolution. The system will be able to operate as a photoelectron emission microscope (PEEM), an X-ray photoemission electron microscope (XPEEM), or a secondary electron emission microscope (SEEM). For each pixel in its highly magnified topographic image, the TOF-EEM column should be able to provide the emission spectrum with milli-electron-volt resolution. The system is designed to operate at secondary electron beam voltages of typically less than 100 V, and has the possibility of dynamically correcting for chromatic aberration. Provisional simulation results predict that the TOF-EEM column should be able to provide an image resolution of better than 2 nm.     

结合会聚束电子衍射和高分辨电子显微术来测定十四铌酸锂的结构

我们在一台有0.4nm点分辨率的分析透射电子显微镜上,结合会聚束电子衍射(CBED)和高分辨电子显微术(HREM)研究了十四铌酸锂的结构。CBED结果证明十四铌酸锂的空间群是C2/m,HREM结构象表明十四铌酸锂是由4×4氧八面体方块组成,方块中3×3通道及八面体中心的金属原子可以清楚地看到,其距离是0.38nm。结合CBED和HREM来做结构分析是发展电子晶体学的重要的一步。 关键词：     

Image resolution and sensitivity in an environmental transmission electron microscope

An environmental transmission electron microscope provides unique means for the atomic-scale exploration of nanomaterials during the exposure to a reactive gas environment. Here we examine conditions to obtain such in situ observations in the high-resolution transmission electron microscopy (HRTEM) mode with an image resolution of 0.10nm. This HRTEM image resolution threshold is mapped out under different gas conditions, including gas types and pressures, and under different electron optical settings, including electron beam energies, doses and dose-rates. The 0.10nm resolution is retainable for H(2) at 1-10mbar. Even for N(2), the 0.10nm resolution threshold is reached up to at least 10mbar. The optimal imaging conditions are determined by the electron beam energy and the dose-rate as well as an image signal-to-noise (S/N) ratio that is consistent with Rose's criterion of S/N≥5. A discussion on the electron-gas interactions responsible for gas-induced resolution deterioration is given based on interplay with complementary electron diffraction (ED), scanning transmission electron microscopy (STEM) as well as electron energy loss spectroscopy (EELS) data.     

基底温度对中阶梯光栅厚铝膜质量的影响

大尺寸中阶梯光栅具有大孔径和极高的衍射级次,可以实现普通光栅难以达到的极高光谱分辨率。中阶梯光栅通常是利用刻划机在厚铝膜上刻划而成,所以制备大面积均匀性的高质量铝膜刻划基底是实现高性能大尺寸中阶梯光栅的关键因素。在较厚铝膜的制备工艺中,基底温度是至关重要的工艺参数。本文通过电子束热蒸发镀铝工艺在不同基底温度下制备了厚铝膜样品,并利用原子力显微镜、扫描电镜等手段从宏观和微观尺度详细分析了基底温度对铝膜质量的影响。铝膜平均晶粒尺寸从100℃时的264.34 nm增大到200℃时的384.97 nm和300℃时的596.35 nm,表面粗糙度Rq从100℃时的34.7 nm增长到200℃时的58.9 nm和300℃时的95.1 nm。结果表明,随着基底温度的升高表面粗糙度迅速增大,铝膜的表面质量严重退化。     

基于近场光学的微球超分辨显微效应

在光学成像领域,由于受到衍射极限的限制,常规成像分辨率在200nm左右.科学的不断进步对更高分辨率有着迫切需求,如何突破这个极限来获得更高质量的高分辨率图像是热门研究领域.2011年提出了微球超显微技术:在原有的光学系统中,将直径几微米至几十微米的透明微球直接置于样品表面,就能够成倍提高传统光学显微镜的成像能力.微球超显微技术以其简单直接的特点,受到广泛关注.本文介绍了光学显微镜的研究背景以及国内外团队在微球超分辨显微技术方面的研究进展,包括通过在微球表面进行环刻同心环、中心遮挡和表面涂覆的方法来调节微球所产生的光子纳米喷射方面所开展的一系列研究,并进行了理论模拟和实验验证,进一步提升了微球的超分辨显微效应.最后,展望了今后微球超分辨显微技术的应用与发展方向.     

适用于表面分析的小型低能电子显微镜

介绍并表征了一套单法兰集成的低能电子显微镜. 这套显微镜中采用了10o偏转角的磁分束器,从而有利于将其集成到一个10 in的法兰上. 电子光学系统中的一些修正单元被简化,以使其结构简单,容易操作. 样品被置于地电位,方便各静电透镜浮在高电压上. 通过几个实验展示了这台显微镜在典型的低能电子成像、低能电子衍射和光电子成像模式下的性能. 低能电子成像的空间分辨率为51 nm. 利用飞秒激光做光源,相应的非线性光电子发射过程使得这台设备非常适合进行光学近场现象的观察,并获得110 nm的光电子成像空间分辨率.     

高损伤阈值三倍频分离膜

 设计了Nd：YAG激光用三倍频分离膜,膜层材料为SiO₂和HfO₂。经过优化,膜系在355 nm处的反射率在99%以上,在532 nm和1 064 nm处透射率也在99%以上。采用电子束蒸发技术,在熔融石英基底上制备了样品,经测量,制备的分离膜光学性能与设计值接近。分离膜在355 nm激光辐照下的损伤阈值为5.1 J/cm²,并用微分干涉显微镜表征了薄膜损伤形貌。     

分散良好的二氧化锡纳米团簇制备以及离子液体诱导金属绝缘相变调控研究

本文利用气相纳米团簇设备实现SnO_2纳米团簇的可控制备.高分辨透射电子显微镜用来分析SnO_2纳米团簇形貌及微观结构,结果表明制备的SnO_2纳米团簇分散良好,尺寸均匀(5～7 nm).通过门电压控制的离子液体实现对SnO_2纳米团簇金属绝缘转变的调控.结合第一性原理,从氧空位诱导电子占据角度系统分析了相应的调控机制.     

Synthesis and attachment of silver nanowires on atomic force microscopy cantilevers for tip‐enhanced Raman spectroscopy

Surface‐enhanced Raman spectroscopy is based on the absorption of light by nanometer‐sized metal particles, resulting in large enhancement of the Raman signal. By replacing the metal particles by a metallic nanotip, the enhancement can be localized. The resulting tip‐enhanced Raman spectroscopy is capable of measuring Raman spectra with high spatial resolution, effectively overcoming the diffraction limit. A successful tip‐enhanced Raman spectroscopy experiment depends heavily on the ability to fabricate tips of a definite metal with the appropriate shape and size, which is still a challenging process. We have prepared silver nanowires with a diameter of 200–300 nm by templated electrochemical deposition and attached them onto atomic force microscope cantilevers by focused electron beam induced deposition. We found that they produce a reproducible enhancement of the Raman signal intensity. Other metals and smaller nanostructures might also be produced, suggesting an interesting development potential for these novel nanoprobes. Copyright © 2011 John Wiley & Sons, Ltd.     

Valence state mapping of cobalt and manganese using near-edge fine structures

The properties of transition metal oxides are related to the presence of elements with mixed valences. The spectroscopy analysis of the valence states is feasible experimentally, but a spatial mapping of valence states of transition metal elements is a challenge to existing microscopy techniques. In this paper, with the use of valence state information provided by the white lines and near-edge fine structures observed using the electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM), a novel experimental approach is demonstrated to map the valence state distributions of Mn and Co using the ratio of white lines in the energy-filtered TEM. The valence state map is almost independent of specimen thickness in the thickness range adequate for quantitative EELS microanalysis. An optimum spatial resolution of approximately 2 nm has been achieved for a two-phase Co oxides.     

Imaging the Hydrated Microbe‐Metal Interface Using Nanoscale Spectrum Imaging

PdAu nanocrystals are synthesised by Geobacter sulfurreducens, a dissimilatory metal‐reducing bacterium, and the resulting bimetallic nanocrystal‐decorated microbes are imaged using a range of advanced electron microscopy techniques. Specifically, the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X‐ray (EDX) spectrum imaging within an environmental liquid‐cell is reported. These results are combined with cryo‐TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. It is demonstrated that although Au and Pd are colocalized across the cells, the population of nanoparticles produced is bimodal, containing ultrasmall alloyed nanocrystals with diameters <3 nm and significantly larger core‐shell structures (>200 nm in diameter) which show higher Pd contents and exhibit a Pd enriched shell only a few nanometers thick. The application of high‐resolution imaging techniques described here offers the potential to visualize the microbe‐metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g., metal cycling).     

Microstructure and tribological properties of TiAg intermetallic compound coating

TiAg intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding using Ag powder as the precursor. It has been found that the prepared coating mainly comprised TiAg and Ti phases. The high resolution transmission electron microscopy results further conform the existence of TiAg intermetallic compound in the prepared coating. The magnified high resolution transmission electron microscopy images shown that the laser cladding coating contains TiAg nanocrystalline with the size of about 4 nm. Tribological properties of the prepared TiAg intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiAg intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiAg intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate increased as the normal load increased.     

直接法应用于蛋白质二维晶体的电子晶体学图像处理

试把直接法应用于抗生蛋白链菌素(streptavidin)沿［001］方向投影的模拟像和相应的理论结构因子作图像处理.先用两张高分辨电子显微像作直接法解卷,以互补因衬度传递函数的作用而损失的结构信息,求得的欠焦值比用单张像解卷的结果更接近真实值.把从结构模型计算出的030nm以内的相位,以及025nm以内的振幅作为起始数据,进行直接法相位外 推,并借助团簇分析方法得到030nm至025nm之间的相位.所得分辨率为030nm的解卷像 和分辨率为025nm的晶体结构投影均与理论结构模型的相应投影电 关键词： 高分辨电子显微学 直接法 图像处理     

Characterization of solution-synthesized CdTe and HgTe

We report the characterization of solution-synthesized CdTe and HgTe nanocrystals by X-ray diffraction, transmission electron microscopy, and photoluminescence. Methanol solutions of sodium telluride and cadmium iodide or mercury iodide, respectively, are reacted to precipitate the nanocrystalline metal tellurides, while the sodium iodide byproduct remains in solution. The existence of crystalline CdTe, HgTe, and ternary HgCdTe compounds has been demonstrated by powder X-ray diffraction after a post-synthesis sintering process. Precipitated crystallites from this synthesis were analyzed by transmission electron microscopy, which revealed that crystal diameters can vary from approximately 1 nm to 100 nm and that crystals are stoichiometric within the detection limit of the electron microprobe technique. Narrow size ranges can be selected and investigated due to an in-situ separation process in the electron microscope. Photoluminescence is found at energies above the bulk exciton energy for CdTe and is attributed to near-band-gap recombination which is blue-shifted due to quantum confinement. Both low defect luminescence and dark field imaging suggest a high crystalline quality. A comparative characterization by photoluminescence, transmission electron microscopy, and X-ray diffraction evaluates the effects of heat treatments during and after synthesis.     

Characterization of laser-ablated and chemically reduced silver colloids in aqueous solution by UV/VIS spectroscopy and STM/SEM microscopy

Silver colloids in aqueous solution were studied by different scanning microscopy techniques and UV/VIS spectroscopy. The silver colloids were produced either by chemical reduction or by nanosecond laser ablation from a solid silver foil in water. Variation of laser power and ablation time leads to solutions of metal clusters of different sizes in water. We characterized the electronic absorption of the clusters by UV/VIS spectroscopy. STM (scanning tunneling microscope) imaging of the metal colloids shows atomic resolution of rod- or tenon-like silver clusters up to 10-nm length formed by laser ablation. Our scanning electron microscope measurements, however, show that much larger silver colloids up to 5-μm length are also formed, which are not visible in the STM due to their roughness. We correlate them with the long-wavelength tail of the multimodal UV/VIS spectrum. The silver colloids obtained by chemical reduction are generally larger and their electronic spectra are red-shifted compared to the laser-ablated clusters. Irradiation of the colloid solution with nanosecond laser pulses of appropriate fluence at 532 nm and 355 nm initially reduced the colloid size. Longer irradiation at 355 nm, however, leads to the formation of larger colloids again. There seems to be a critical lower particle size, where silver clusters in aqueous solution become unstable and start to coagulate. Received: 24 June 2002 / Revised version: 25 July 2002 / Published online: 25 October 2002 RID="*" ID="*"This work is part of the thesis of H. M?ltgen RID="**" ID="**"Corresponding author. Fax: +49-211/811-5195, E-mail: kleinermanns@uni-duesseldorf.de     

带纳米金属棒PSTM孔径光纤探针成像的数值模拟

用三维时域有限差分方法对带纳米金属棒孔径光纤探针成像进行了数值模拟。采用等高扫描从分辨率和灵敏度的角度分别讨论了纳米金属棒长度、扫描高度、孔径大小及镀膜厚度对成像的影响。数值模拟结果显示,带纳米金属棒镀膜孔径探针的性能主要受纳米棒的尺寸决定,较普通孔径探针在分辨率和灵敏度方面都有明显改进,并且稳定性更高。     

Modeling tip performance for combined STM-luminescence and aperture-SNOM scanning probe: Spatial resolution and collection efficiency

Finite-element simulations of the performance of the tip intended for use in combined aperture-SNOM and the scanning tunneling microscope (STM)-luminescence microscopy are presented. Tip geometry and the role of the opening in the protective metal coating were addressed. It is shown that the tip shape can affect transmittance for the excitation SNOM mode by nearly two orders of magnitude and the metal coating can enhance collection efficiency for the STM-luminescence mode. Desired tip configuration can be chosen based on the interplay between the improving collection efficiency and the deteriorating spatial resolution with increasing opening size.     

Improving Data Quality in Traditional Low-Dose Scanning Transmission Electron Microscopy Imaging

It has become very important to study and find optimal conditions for imaging electron-beam (e-beam) sensitive materials in scanning transmission electron microscopy under low electron-dose with high signal-to-noise ratio (SNR). Convergence and collection angles and electron-probe current are essential parameters. However, these parameters have rarely been discussed in a systematic way. In this paper, the illumination and collection conditions are optimized according to the resolution requirement of different materials by adjusting the condenser and intermediate lenses in a commercial transmission electron microscope. To demonstrate the significance of optimizing these parameters, two examples, zeolite MFI and metal–organic framework (MOF) MIL-101, are taken among the sensitive materials, with the most important electron incidences along the [010] and <110> directions, respectively. High SNR atomic resolution images of MFI are obtained with e-beam current as low as 0.50 pA, reaching information transfer for reflection up to 18 0 2 corresponding to d-spacing of 0.11 nm, close to the resolution limit of 0.098 nm from resolvable diffraction limit. MOF MIL-101 is characterized under an even lower e-beam 0.2 pA to avoid severe beam damage. High-quality annular dark and bright field images are obtained, which proves the wide applicability of this method on more e-beam sensitive materials.     

采用旋转涂膜法制备基底生长的定向碳纳米管阵列

 采用化学气相沉积技术,利用旋转涂膜法制备催化剂基底材料,通过对涂膜过程中的角速度、旋转时间以及基底还原过程中温度的控制改变催化剂颗粒的分布状态,获得了粒径均匀分布的催化剂基底,该基底上催化剂颗粒集中分布在47～62 nm区间,再利用该基底生长出定向碳纳米管阵列。运用扫描电镜、透射电镜、拉曼光谱仪对样品进行了表征。结果表明旋转涂膜法制备的基底平整性好于普通的滴膜法,且较其它基底制备方法具有简单易控、可使催化剂均匀分散等特点。利用该基底制备的碳纳米管阵列定向性良好。