Researchers find new way to create large scale 3d nanostructures

The researchers say the breakthrough has been made possible by using a blend of current 'top down' and 'bottom up' approaches. The top down approach is called phase shift lithography, in which a two dimensional mask shapes the intensity of light shining onto a layer of photoresist material - in the same way a photographic negative controls the amount of light reaching different areas of a print. The photoresist is altered only in the areas reached by the light. However, this approach requires very precisely manufactured phase masks, which are expensive and time consuming to make. The bottom up approach is to use self assembling colloidal nanoparticles that form themselves into certain energetically favourable close packed arrangements. These can then be used as a mask for physical deposition methods, such as vapour deposition, or etching of the surface, to produce 2d structures, just as a stencil can be used to control where paint reaches a surface. However, these methods are slow and limited by defects that can form in the self assembly process, so although they can be used for the fabrication of 3d structures, this is made difficult because any defects propagate through the layers. The new method is a hybrid in which the self assembled array is produced directly on a substrate material, performing the function of a mask for the lithography process. The individual nanoparticles that assemble on the surface each act as tiny lenses, focusing the beam into an intensity pattern determined by their arrangement on the surface. According to the researchers, the method can be implemented as a novel technique to fabricate complex 3d nanostructures in all fields of nanoscale research. Depending on the shapes and arrangements of the tiny glass beads used for the self assembly part of the process, it is possible to create a variety of structures all using the exact same system. And, say the team, it's a simple and cheap way to make 3d nanostructures. The first structures to be made will be photonic crystals. Its structure can manipulate the behaviour of light beams passing through them. But the method can also be used to make phononic materials, which control waves of heat or sound, or even to make filters with precisely controlled porosity, which might have biomedical applications.