July 2006 Archives

Professor P. Pershan (Harvard University, USA) and his colleagues recently found a crystalline monolayer at the surface of the eutectic liquid Au₈₂Si₁₈, at temperatures above the alloy's melting point. This is unusual for a liquid surface, as the atomic arrangements are ordinarily strongly disordered. In addition, they found that the gold-silicon eutectic alloy has 7-8 layers near its surface, whereas many metallic liquids typically show only 2-3 distinct atomic layers. The phenomena are considered as indicative of surface freezing. The research group employed X-ray reflectivity and grazing incidence X-ray diffraction techniques for the analysis. For more information, see the paper, "Surface Crystallization in a Liquid AuSi Alloy", Oleg G. Shpyrko et al., Science 313, 77 (2006).

The appearance of the ultimate X-ray microscope, with atomic-scale resolution and capable of seeing deep inside objects, has long been awaited. Professor I. Robinson (University College London, UK) and his team recently made a significant step towards realizing this dream, using the technique of coherent X-ray diffraction imaging, the possibility of which was first pointed out by Sayre (Acta Crystallogr. 5, 843 (1952)) but not demonstrated until 1999 by Miao et al (Nature 400, 342 (1999)). They observed the growth of nanometer-sized Pb crystals inside the vacuum chamber. The results showed that asymmetries in the diffraction pattern can be mapped to deformities, providing a detailed 3-D map of their location in the crystal. This new method shows that the interior structure of atomic displacements within single nanocrystals can be obtained by direct inversion of the diffraction pattern. The technique is an attractive alternative to electron microscopy because of the superior penetration of materials of interest by the electromagnetic waves, which are often less damaging to the sample than electrons. The experiments were done at beamline 34-ID-C at the Advanced Photon Source (APS) in the United States. For more information, see the paper, "Three-dimensional mapping of a deformation field inside a nanocrystal", Mark A. Pfeifer et al., Nature 442, 63 (2006).

A workshop on 'buried' interface science with X-rays and neutrons was held in Yokohama, Japan, on July 3-4. This was one in a series of workshops that have been organized annually since 2001. The precise and non-destructive analysis of nano-structures (dots, wires etc), which are most likely to be 'buried' under several capping layers, has become extremely important from the standpoint of fundamental understanding as well as its application to electronic, magnetic, optical and other devices. Unfortunately, most sophisticated surface-sensitive techniques are not helpful in such cases, but reflectometry and other related methods using X-rays and neutrons are very promising because they are able to explore atomic-scale structures along their depth. Besides the variety of applications, the workshop also featured intensive discussions of several advanced extensions and/or upgrades of the method. One of the most interesting directions is the combination of the method with grazing-incidence small angle scattering (GISAS). Professor Alain Gibaud (Université du Maine, France) was invited to give a lecture on this topic. Another invited speaker from outside Japan was Dr. Burkhard Beckhoff (Physikalisch-Technische Bundesanstalt, Germany). The workshop proceedings are available from Science Information and Library Service Division, High Energy Accelerator Research Organization (KEK), Phone: +81-29-864-5137, Fax: +81-29-864-4604, irdpub@mail.kek.jp. Another workshop contact, particularly with respect to future plans, is Kenji Sakurai, sakurai@yuhgiri.nims.go.jp.