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New technique shines light on nanomaterials

 

On the left is the three dimensional 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 nanometres Credit London Centre for Nanotechnology
 

Advances in X-ray imaging have shone light on the three-dimensional shape of gold nanoparticles, and could be used to reveal the structure of other nanoscale materials.
 

The new technique – developed by researchers at the London Centre for Nanotechnology at UCL – improves the quality of nanomaterial images made using X-ray diffraction by accurately correcting distortions in the X-ray light.
Until recently, electron microscopy has been used for nanomaterial imaging but X-ray imaging has become a more popular alternative as X-ray can penetrate further into the material than electrons, and it can be used in ambient or controlled environments. However, making lenses that focus X-rays is difficult so scientists used coherent diffraction imaging (CDI) to measure the sample without lenses and invert the image by computer.

 

“With nanomaterials playing an increasingly important role in many applications, there is a real need to be able to obtain very high quality images of nanomaterials,” said Dr Jesse Clark, lead author of the study published in Nature Communications.
 

“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.”
 

CDI has previously suffered from poor image quality with broken or non-uniform density, attributable to the imperfect coherence of the X-ray light used. However the technique – which can be performed at Diamond Light Source – is gaining momentum. The dramatic three-dimensional images of gold nanocrystals obtained in this study show that this distortion can be corrected by appropriate modelling 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.
 

This method – which should also work for free-electron-laser, electron- and atom-based diffractive imaging – was originally suggested by Nobel Prize winner Lawrence Bragg in 1939. However, he had no way to determine the missing phases of the diffraction which are today provided by computer algorithms.