X-ray Imaging Shines Light on Gold Nanocrystals

A new x-ray diffraction technique has revealed the three-dimensional shape of gold nanocrystals and is likely to shine a light on the structure of other nanoscale materials.

The imaging method developed at University College London improves the quality of nanomaterial images by accurately correcting distortions in the x-ray light.

"With nanomaterials playing an increasingly important role in many applications, there is a real need to be able to obtain very high quality three-dimensional images of these samples,” said Dr. Jesse Clark of the London Centre for Nanotechnology, lead author of the study. "Up until now we have been limited by the quality of our x-rays. Here we have demonstrated that with imperfect x-ray sources, we can still obtain very high quality images of nanomaterials."

Until recently, most nanomaterial imaging was done using electron microscopy. Now, x-ray imaging provides an attractive alternative as x-rays penetrate further into the material than electrons and can be used in ambient or controlled environments.

A new advance in x-ray imaging has revealed the dramatic 3-D shape of gold nanocrystals and is likely to shine a light on the structure of other nanoscale materials. The new technique improves the quality of nanomaterial images, made using x-ray diffraction, by accurately correcting distortions in the x-ray light. Shown on the left is the 3-D image of a gold nanocrystal obtained previously, while on the right is the image using the newly developed method. The features of the nanocrystal are vastly improved in the image on the right. The black scale bar is 100 nm. (Image: London Centre for Nanotechnology)

Making lenses that focus x-rays is challenging, so scientists have used the indirect method of coherent diffraction imaging (CDI) — where the diffraction pattern of the sample is measured (without lenses) and inverted to an image by computer — as an alternative.

This method was suggested in 1939 by Nobel Prize winner Lawrence Bragg, but he did not have a way to determine the missing phases of the diffraction, which are now provided by computer algorithms.

CDI can be performed at the UK’s Diamond Light Source synchrotron x-ray source. Although CDI has gained momentum in the study of nanomaterials, it has suffered from poor image quality, with broken or non-uniform density. This has been attributed to imperfect coherence of the x-ray light used.

The 3-D images of gold nanocrystals demonstrated by the scientists showed that this distortion can be corrected by appropriate modeling of the coherence function.

"The corrected images are far more interpretable than ever obtained previously and will likely lead to new understanding of structure of nanoscale materials,” said professor Ian Robinson of the London Centre for Nanotechnology and an author of the paper.

The method should also work for free-electron-laser, electron- and atom-based diffractive imaging.

The study appeared today in Nature Communications.

For more information, visit: www.ucl.ac.uk