Much of what is known about interstellar dust particles comes from astronomical observations of how they absorb and emit light. The strongest spectral signature from the interstellar medium in the ultraviolet portion of the electromagnetic spectrum is the so-called 2175 angstrom (Å) feature or “2175 Å bump.” The feature has been enigmatic: its central wavelength is almost invariant, but its bandwidth varies from one line of sight to another, suggesting that it might be due to the presence of different materials (or the same material with variable properties).

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Atomic-Scale Studies of Ceramic Grain Boundaries

Unique direct atomic resolution images have been obtained that illustrate how a range of rare-earth atoms in sintering additives bond to the interface between the intergranular phase and the matrix grains in an advanced silicon nitride ceramic. It was found that each rare-earth atom bonds to the interface at a specific location, depending on atom size, electronic configuration and the presence of oxygen and that binding location can be correlated to the mechanical properties of these materials. The work is a key breakthrough in the understanding the basis for the mechanical properties in these ceramics.

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Working with a group from Copenhagen University, researchers at the National Center for Electron Microscopy (NCEM) have demonstrated Brownian motion of liquid nanoparticles inside a solid metal and determined the mechanism of this process for the first time. Using NCEM’s electron microscopes together with specially-developed image-analysis software, the team observed rapid motion of nanometer sized particles of molten lead inside solid aluminum when the system was held at elevated temperatures. A detailed analysis of thousands of video frames from many individual particles led to the conclusion that the motion was controlled by the nucleation of steps in the interface between the particle and the matrix. These results provide important new insight into the effect of size and shape on the behavior of materials, offering additional control parameters for materials design.

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A team of researchers at the University of Pittsburgh, working with the staff and facilities of LBNL’s National Center for Electron Microscopy (NCEM), have made a fundamental discovery concerning the mechanism by which nanocrystalline metals respond to mechanical deformation. Their work shows that as nanosized metal grains become smaller, a new deformation mode involving “grain boundary mediated processes” replaces “nucleation and motion of lattice dislocations” as the dominant mechanism of the deformation.

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Carbon Nanotubes as Nanoscale Mass Conveyors

In a development that brings the promise of mass production to nanoscale devices a bit closer, Lawrence Berkeley National Laboratory scientists have used carbon nanotubes to ferry atoms over microscopic distances. In their demonstration experiment, which was performed inside a transmission electron microscope, they used small electrical currents applied to a carbon nanotube to move indium atoms along the tube from one end to the other. This work marks another step towards the high-throughput construction of atomic-scale optical, electronic, and mechanical devices that will fulfill the promise of nanotechnology.

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A collaborative project between IBM Watson researchers and Eric Stach at the National Center for Electron Microscopy has discovered a new type of thin film texture. Coined “axiotaxy,” this texture is characterized by the sharing of only one set of lattice spacings between the film and its growth substrate. A report of the work appeared recently in Nature.

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Toughness-Inducing Additive Atoms Localized

Unprecedented transmission electron microscopy studies performed with the new One-Ångstrom Microscope (OÅM) at the National Center for Electron Microscopy (NCEM) have shown that the observed doubling of the toughness of a silicon nitride ceramic as a result of the addition of small amounts of yttrium oxide can be traced to the localization of the yttrium atoms in amorphous layers in extended SiN grain boundaries. The result is of great importance for the understanding of interfacial bonding and consequently the fracture properties of ceramics.

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A research team led by Alex Zettl in the Berkeley "sp2 Materials" program has demonstrated that individual concentric carbon nanotubes in a multiwall nanotube can "telescope" with minimal resistance, much like a greased radio antenna. These results suggest that these tubes could possibly be used as nanoscale linear bearings with very little friction. A report of this work appeared recently in Science.

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