A vital step towards the ultimate goal of being able to take ‘photographs' of individual molecules in action has been achieved by an international team led by UCL (University College London) researchers at the London Centre for Nanotechnology.

They report in the journal Nature on a novel method of obtaining a full 3-D image of the interior of nanocrystals. Using a process known as coherent X-ray diffraction imaging, they were able to build a picture of the inside of nanocrystals by measuring and inverting diffraction patterns.

Ultimately, the technique will help in the development of X-ray free-electron lasers, which will allow single-molecule imaging. It will also allow researchers to more accurately assess the defects in any given material which gives them specific properties.

Professor Ian Robinson, of the UCL Department of Physics & Astronomy and the London Centre for Nanotechnology, who led the study, says: “This new imaging method shows that the interior structure of atomic displacements within single nanocrystals can be obtained by direct inversion of the diffraction pattern. We hope one day this will be applied to determine the structure of single protein molecules placed in the femtosecond beam of a free-electron laser.

“Coherent X-ray diffraction imaging emerged from the realisation that over-sampled diffraction patterns can be inverted to obtain real space images. It is an attractive alternative to electron microscopy because of the better penetration of the electromagnetic waves in materials of interest, which are often less damaging to the sample than electrons.”

The inversion of a diffraction pattern back to an image has already been proven to yield a unique ‘photograph' in two or higher dimensions. However, previously researchers have encountered difficulties with 3-D structures with deformations as these interfere with the symmetry of the pattern. To overcome this problem, the UCL team used a lead nanocrystal that was crystallised in an ultrahigh vacuum. It showed that asymmetries in the diffraction pattern can be mapped to deformities, providing a detailed 3-D map of the location of them in the crystal.

About UCL

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender, and the first to provide systematic teaching of law, architecture and medicine. In the government's most recent Research Assessment Exercise, 59 UCL departments achieved top ratings of 5* and 5, indicating research quality of international excellence.

UCL is the fourth-ranked UK university in the 2005 league table of the top 500 world universities produced by the Shanghai Jiao Tong University. UCL alumni include Mahatma Gandhi (Laws 1889, Indian political and spiritual leader); Jonathan Dimbleby (Philosophy 1969, writer and television presenter); Junichiro Koizumi (Economics 1969, Prime Minister of Japan); Lord Woolf (Laws 1954, former Lord Chief Justice of England & Wales); Alexander Graham Bell (Phonetics 1860s, inventor of the telephone); and members of the band Coldplay.

The paper ‘Three-dimensional mapping of a deformation field inside a nanocrystal' will be published in the July 6 edition of the journal Nature. The authors are: Mark A. Pfeifer1†, Garth J. Williams1†, Ivan A. Vartanyants1†, Ross Harder1 & Ian K. Robinson1

1 Physics Department, University of Illinois, Urbana, Illinois 61801, USA. †Present addresses: Department of Physics, University of Oregon, Eugene, Oregon 97403, USA (M.A.P.), School of Physics, University of Melbourne, Australia (G.J.W.), HASYLAB, DESY, Hamburg, Germany (I.A.V.), Department of Physics & Astronomy, University College London, UK.