Credit: © 2009 NPG

Hard X-rays are capable, in theory, of probing the structure, composition and chemical bonding states of materials and biological samples with single-nanometre spatial resolution. However, researchers have not been able to achieve such resolutions in experiments because the extremely short wavelengths involved mean that even the tiniest imperfections on the surface of an optical component can introduce aberrations into the X-ray beam. Now Hidekazu Mimura of Osaka University and co-workers1 have shown that a technique known as wavefront correction can be used to focus hard X-rays to a spot size of 7 nm.

In experiments at the SPring-8 synchrotron radiation source in Japan, Mimura and co-workers directed a beam of 20 keV X-rays onto a deformable mirror that reflected the beam onto a multilayer focusing mirror, and they measured the intensity profile of the beam reflected by this second mirror. The Japanese team converted these measurements into phase shifts, and then changed the shape of the deformable mirror to compensate for the distortions caused by the two mirrors (see figure), repeating the process until they had broken the 10 nm barrier. Mimura and co-workers believe that it should be possible to produce focal spot sizes as small as 1 nm.