Electron tomography at 2.4-ångström resolution

Transmission electron microscopy is a powerful imaging tool that has found broad application in materials science, nanoscience and biology. With the introduction of aberration-corrected electron lenses, both the spatial resolution and the image quality in transmission electron microscopy have been significantly improved and resolution below 0.5??ngstr?ms has been demonstrated. To reveal the three-dimensional (3D) structure of thin samples, electron tomography is the method of choice, with cubic-nanometre resolution currently achievable. Discrete tomography has recently been used to generate a 3D atomic reconstruction of a silver nanoparticle two to three nanometres in diameter, but this statistical method assumes prior knowledge of the particle's lattice structure and requires that the atoms fit rigidly on that lattice. Here we report the experimental demonstration of a general electron tomography method that achieves atomic-scale resolution without initial assumptions about the sample structure. By combining a novel projection alignment and tomographic reconstruction method with scanning transmission electron microscopy, we have determined the 3D structure of an approximately ten-nanometre gold nanoparticle at 2.4-?ngstr?m resolution. Although we cannot definitively locate all of the atoms inside the nanoparticle, individual atoms are observed in some regions of the particle and several grains are identified in three dimensions. The 3D surface morphology and internal lattice structure revealed are consistent with a distorted icosahedral multiply twinned particle. We anticipate that this general method can be applied not only to determine the 3D structure of nanomaterials at atomic-scale resolution, but also to improve the spatial resolution and image quality in other tomography fields.     

A simple apparatus to investigate the orientation of walking insects

Summary A simple apparatus to record the track and angular position of walking insects without any servo-mechanism is described. Recordings of fast runningCicindelae are presented.     

一种新型高价锰取代的多金属氧酸盐合成、结构及性质研究

在含有MnⅡ的夹心型多金属氧酸盐水溶液中加入强氧化剂KMnO4,制得一种新型的含有MnⅢ的多金属氧酸盐K5Na3[{MnⅢ(H2O)}2(WO)(H2O) (AsW9O33)2]·18H2O (KNa-1).该化合物的多阴离子结构是基于2个B-α-[AsW9]三缺位Keggin型构筑单元,中间夹着2个{MnⅢ(H2O)}和1个{WⅥO}片段而构成的夹心式构型.对KNa-1进行了变温磁化率测定并采用双核MnⅢ簇为模型进行了拟合,并对该化合物进行了电化学分析.结果表明:KNa-1 中的2个MnⅢ中心存在弱的反铁磁相互作用;化合物中的MnⅢ离子具有不可逆的氧化还原过程.     

Crackling noise

Crackling noise arises when a system responds to changing external conditions through discrete, impulsive events spanning a broad range of sizes. A wide variety of physical systems exhibiting crackling noise have been studied, from earthquakes on faults to paper crumpling. Because these systems exhibit regular behaviour over a huge range of sizes, their behaviour is likely to be independent of microscopic and macroscopic details, and progress can be made by the use of simple models. The fact that these models and real systems can share the same behaviour on many scales is called universality. We illustrate these ideas by using results for our model of crackling noise in magnets, explaining the use of the renormalization group and scaling collapses, and we highlight some continuing challenges in this still-evolving field.     

Carbon nanotubes as nanoscale mass conveyors

The development of manipulation tools that are not too 'fat' or too 'sticky' for atomic scale assembly is an important challenge facing nanotechnology. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms and molecules on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes and the application of such techniques. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry.