Brussels, 06 Jul 2006
An international team of researchers has used an x-ray microscope to create a 3D image of a nanocrystal. Their findings, reported in the journal Nature, pave the way towards the ultimate goal of taking pictures of individual molecules in action, something which would be of immense value to nanotechnology researchers the world over.
For many years, materials scientists have been using electron microscopes to obtain detailed images of objects and materials. However, this often entails slicing the object to be viewed into extremely thin layers, which is rarely easy and can alter the properties of the material being studied.
In contrast, the ability of x-rays to penetrate more deeply into objects enables researchers to view nanoparticles in three dimensions without destroying them. Recent technological advances mean sources of 'hard' x-rays (those with extremely short wavelengths) are now readily available, making such studies possible.
The researchers, led by Ian Robinson of University College London, used a technique called coherent x-ray diffraction imaging to create an image of a nanoparticle of lead which was just 750 nm across. When crystals reflect x-rays, interesting patterns are formed. These patterns can be mathematically inverted to create an image of the object in three dimensions.
The image revealed not only the flat facets of the particle, but a defect which correlates to the point where the crystal was grown on its glass substrate.
The researchers note that the resolution they achieved, 40 nm, can be improved by developing better detectors and optics or more powerful x-ray sources. When this happens, the methods described in the paper could be extended to atomic resolution.
In an accompanying article, Eric D. Isaacs of the Center for Nanoscale Materials in Illinois explains why such advances in imaging are so important to nanotechnology researchers. The mechanical, electrical and thermodynamic properties of nanoparticles are determined by their surfaces and interfaces with other materials. He points out that binding a single molecule to the surface of semiconductor nanocrystals can change their electronic and optical behaviour.
'To develop materials with useful properties, we must first understand how these properties relate to atomic structure and surface chemistry,' Dr Isaacs writes. 'Robinson and co-workers have taken a substantial step forward in realising the potential of X-ray microscopes.'