X-ray spectroscopy can observe movement of atoms at 100 times improved resolution

A joint research group from the Universities of Sheffield and Warwick (both in the United Kingdom) and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France have recently reported an interesting application of a dispersive XAFS (X-ray absorption fine structure) spectrometer, which has no moving parts and is thus inherently more stable than a conventional step-scanning instrument, thereby permitting comparative measurements to be taken rapidly. The measurements were performed on a FeCo alloy thin film located between the poles of a magnet, which induces a saturating field in the sample. The magnets were rotated via a stepping motor such that the induced magnetization, causing the strain, lies either along or perpendicular to the X-ray polarization vector. Transmitted X-ray intensity measurements were made repeatedly at every 90 degree angle between the magnetization vector and the polarization vector. An entire four-quadrant measurement took about 1s, with repeated measurements accumulated over a 2h period. The differential absorption spectra obtained in this way can give atomic displacements due to magnetostriction. The research group demonstrated that it is possible to observe the movement of atoms with a resolution of 0.01 Å i.e., an improvement of 100 times on the previous level. For further details, see the paper, "Measurement of femtometre-scale atomic displacements by X-ray absorption spectroscopy", R. F. Pettifer et al., Nature, 435, 78-81 (2005).