The focus of my research is the synthesis of three dimensionally periodic macroporous solids, specifically a class of materials referred to as synthetic opals. These materials posses a periodic arrangement of pores on a length scale which can be controllably altered from tens to hundreds of nanometres. It is this property which presents exciting potential for use as nanoscale templates - this theme is central to all of the research areas in which I am currently involved.
In my current research I am investigating two specific areas where the incorporation of nanostructured materials should have a significant impact. One area is the developing field of renewable energy, I am investigating the synthesis of organic and hybrid organic/inorganic photovoltaic devices. The structure formed by the templating approach theoretically should permit a marked increase in the efficiency in these devices. The materials challenges of this project lie in tuning the properties of the components of the photovoltaic device – I believe that the synthetic strategy employed offers this control.
The second major area in which my current interest lies is the use of synthetic opals to form photonic crystals, again using the template directed synthesis. By forming devices which can predictably alter their properties as a response to external stimuli the properties of the device can be controllably altered. By investigating response to chemical, electrical or magnetic stimuli it will be possible to form nanostructured devices which can be used as sensors and simple switches.
I maintain a strong research interest in the synthesis of the colloidal building blocks used in the formation of the synthetic opals, the common link between all of my research interests. I have developed a reproducible synthesis for the formation of monodisperse spheres in a range of organic and inorganic materials, to develop this I am interested in forming surface functionalised spheres to facilitate the infiltration of target materials into the template – thus obtaining control not only of the chemicals and materials used to obtain the functional structures but also in controlling the chemistry and surface properties of the template.
Transmission electron microscope (TEM) micrograph showing ~100nm polystyrene spheres on a carbon support film. The strong tendency of the spheres to assemble into close-packed arrays can be exploited, controlled and extended to form three-dimensionally ordered arrays extending over several cm2.
A selection of 3-DOM materials which have been fabricated by colloidal crystal templating (a) ZnO, formed thermally via an organic precursor. (b) Copper Phthalocyanine (CuPc), formed via a low temperature solution route using a water soluble CuPc derivative. (c) PZT, formed thermally from a sol-gel precursor. (d) Iron oxide (hematite), formed by hydrolysis of an organic precursor followed by thermal treatment. (e) TiO2, formed via a sol-gel synthesis followed by thermal crystallisation of the precursor.