Coherent X-ray Diffraction from Cubic Silver Single Nanocrystals
The use of microfocus techniques has allowed us to extend synchrotron x-ray-based nanocrystal imaging work to significantly smaller length scales, a current and advancing record of 170nm. Diffraction patterns have been obtained from single cube-shaped nanocrystals of silver, synthesized chemically by reduction of silver nitrate in the presence of a PVP capping agent. The size is close to the regime where all the physical properties of the materials start to change because of confinement effects, in other words because the surface starts to dominate the bulk.
An image of the internal density of the nanocrystal has been obtained by inversion of the diffraction pattern, as shown. The inversion methods represent major scientific advances, ones still under development in the FS-MRL. They are based on 'oversampling' of the band-limited Fourier Transform of the crystal density. The band-limit comes about simply because of the finite size of the crystal. Our result shows that this particular crystal has no defects. Previous experiments, on nanocrystals prepared by evaporation, have found that nanocrystals can contain many residual defects. The new experimental capacities developed in this work enable unprecedented new insights into the structural dynamics of nanoscale materials and will allow here-to-fore unprecedented applications of them in technology.
It is planned to manipulate these nanocrystals in various ways: chemically, mechanically or by ion irradiation. Fundamental questions of materials science will be addressed by studying the induced strain fields due to individual crystal defects so created. Because the method is based on Bragg diffraction from the crystals, it is acutely sensitive to these strain fields.
Senior FS-MRL PI: I.K. Robinson