NANOSCULPTURE · Exploration of strains in synthetic nanocrystals

I plan to grow nanometre-sized crystals in confined geometries to examine the strain distributions that result. The crystal growth will employ lithographic processing techniques, made possible by the local expertise in the central clean room facilities of the London Centre for Nanotechnology. My group is world-leading in developing a method called Coherent X-ray Diffraction (CXD). Our CXD strain images of a Pb nanocrystal were published in Nature in 2006. CXD is sensitive to strain because the X-ray diffraction pattern surrounding a Bragg peak can be decomposed into symmetric and antisymmetric parts. To a good approximation, the symmetric part can be considered to come from the real part of the electron density, while the antisymmetric part is a projection of the strain field. The phasing of the data is a critical step that uses a computer algorithm, developed by us, which acts like the lens of a 3D X-ray microscope. CXD works best for nanocrystal sizes between 40nm and 5µm, for crystals strongly attached to substrates and for isolated, fiducialised arrays of crystals that can be cross-referenced with other techniques. To create nanocrystals in this size range, we will use both a bottom-up self-assembly of materials deposited onto templated substrates, designed to introduce strain, and a top-down nanosculpture approach will use lithography techniques to create strain patterns in crystalline materials associated with shapes that are carved into them. The interpretation of the images is the main intellectual output of the project. This will be compared with finite element analysis, and the deviations interpreted as unique properties attributable to the nanoscale. All project participants will work in a design, creation, analysis, interpretation, update cycle that will reveal the new basic principles of nanocrystal structure. In the long run we will transfer CXD technology to Europe: beamline I-13 at Diamond will be ready for CXD in 2011.