The study of systems with nanometer dimensions is an exciting area of research that offers opportunities for innovation and creativity. One challenge that nanotechnology currently faces is the development of tools to manipulate nanoscale building blocks into useful structures over large areas. This control requires a detailed understanding over several length scales in order to achieve (i) precise nanoscale (1-100 nm) manipulation, (ii) assembly into mesoscale (100-1000 nm) strucures, and (iii) connection to the macroscopic (mm). Our approach to this problem is to create patterned, functional arrays on surfaces that can assist in the growth and manipulation of nanomaterials. We focus on a wide range of inorganic nanostructures, with a particular emphasis on nanoscale metal chalcogenide materials. In addition, we are developing functional substrates that can be used to direct the growth, size, and shape of individual nanocrystals as well as organic crystals.
Plasmonics is an exciting and emerging area that uses metal nanostructures to manipulate light on the nanoscale. Depending on their size, shape, and materials properties, noble metal nanoparticles can scatter and absorb light to produce colors ranging from the ultra-violet to the near-infrared. In addition, significantly more light can be transmitted through metal films perforated with subwavelength hole arrays than is permitted by geometric optics, a phenomena known as enhanced optical transmission. The physical basis behind these interesting properties is the interaction between surface conduction electrons and light; these collective excitations are surface plasmons (SPs). In general, there are two types of SPs: localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs).
We focus primarily on the optical properties of two different but complementary systems that can control light on the nanometer scale: (i) metallic films of nanohole arrays and (ii) pyramidal nanoparticles. The former have properties dominated by SPPs, and the latter have properties dominated by LSPs. Such nanostructures are easily made by our innovative fabrication scheme, PEEL, for preparing large-area, free-standing films of nanoscale holes and particles. PEEL is a simple procedure which combines Phase-shifting photolithography, Etching, Electron-beam deposition, and Lift-off of the metal film. In addition, we are interested in how SPs interact with each other over microscale distances. We have developed a high-throughput nanofabrication technique—soft interference lithography (SIL)—that combines the ability of interference lithography to produce wafer-scale nanopatterns with the versatility of soft lithography and used it to create plasmonic metamaterials. Such hierarchical structures have ca. 100-nm features that can be organized in microscale arrays over macroscale (tens of square centimetres) areas.
