This is my first post since recent move to wordpress.
This week we have four items:
1. An excellent review in this week’s Science by Simon Billinge and Igor Levin titled “The Problem with Determining Atomic Structure at the Nanoscale”. The fundamental problem of determining atomic structure of non-periodic materials is an old one, but is becoming especially critical in context of nano-structures, where finite correlation lengths on the order of nanometers, even in case of crystalline structures, makes it impossible to apply standard crystallography methods applicable for materials with long-range periodicity. Authors focus on PDF, TEM, EXAFS and other techniques, but also briefly mention newly available coherent x-ray scattering techniques based on phase-retrieval algorithms.
2. A paper in April’s issue of Nature Materials by Eli and Peter Sutter on “Dispensing and surface-induced crystallization of zeptolitre liquid metal-alloy drops”. Authors use a clever design of “nano-pipette” by melting a small gold particle connected to Ge “pipette” to create tiny “nanodroplets” of AuGe eutectic alloy, with sizes on the order of 30-40 nm. They don’t stop there – by using TEM they observe how these particles crystallize – the nanodroplets can be supercooled by over 50K, and crystallize through surface-induced nucleation, as opposed to nucleation centers formed in the interior of material, as it typically happens in macroscopic suspended droplets. Pretty cool approach – both technologically in producing these tiny “zepto-liter” (my new favorite word – it’s just fun to say it) droplets and in looking at fundamental science of crystallization in nanosized materials.
3. Rev. Mod. Phys. features two papers by U of Chicago/Argonne people: the first one is a review by Tom Whitten on Stress focusing in elastic sheets, and another one is by Igor Beloborodov et al., on Granular electronic systems.
4. Adrian Cho of Science magazine reports from APS March meeting in Denver that the field reached a consensus that supersolidity in He does not involve flowing crystals after all, and is likely to be related to more benign explanation, such as premelting at grain boundaries. This is due to extensive work by Balibar group in France, and experiments such as this week’s PRL by Rittner and Reppy in Cornell (in addition to numerous papers in PRL and Science last year – by these and other groups) indicating that annealing can reduce and eventually eliminate supersolidity effect, while rapid quench can lead to higher supersolid fraction.