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S5.6.1

Optical Properties of Nanostructured Mesoporous Semiconductor Films Iris Nandhakumar1,2, Timothy Gabriel1, Xiahong Li1, George S. Attard1, Matthew Markham2, David C. Smith2 and Jeremy J. Baumberg2 1

School of Chemistry, University of Southampton, Southampton, SO17 1BJ, UK.

2

School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK.

ABSTRACT Direct liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride with mesoporous architectures of extended spatial periodicities. The template mixtures and films were characterised by X-ray diffraction, transmission electron microscopy and polarising optical microscopy to ascertain the presence of a regular nanostructure. UV-VIS reflectance spectroscopy was employed to investigate the films’ optical properties. INTRODUCTION Nanostructuring of materials is now a clear route to optimise and elicit new functional properties. In particular nanostructured semiconducting films with one or more critical dimension in the nanometer range possess novel electronic and optical properties in comparison to their non-mesoporous counterparts.

Such materials are of considerable

fundamental and technological interest for understanding the fundamental physics of lowdimensionality structures and to applications in sensors, optical devices and solar cells because they are entirely composed of surface atoms. In this respect Cadmium telluride (CdTe) is one of the most attractive materials because of its direct bandgap of 1.44 eV [1] which provides an optimal match with the solar energy spectrum. This makes it ideally suited as a component of devices for solar energy conversion. The electrochemical route [26] is particularly promising for low-cost large-scale production of photovoltaic cells, and CdTe prepared in this way is a striking example of the high quality semiconducting materials that can be obtained by electrodeposition.

S5.6.2

It has recently been demonstrated that lyotropic liquid crystalline (LC) mesophases of non-ionic surfactants can act as nano-scale templates for the electrochemical growth of adherent high-quality metal [7] and elemental semiconductor [8-9] films leading to welldefined periodic three-dimensional interconnected nanostructures. LC templating utilises the three-dimensonal supramolecular assemblies formed by surfactant molecules at high concentrations (< ca. 30 wt%) in the presence of water as nano-scale moulds around which a solid material can be formed. These supramolecular assemblies constitute the building blocks of lyotropic liquid crystalline phases. Removal of the surfactant affords a material with a porous nanostructure which is a direct cast of the liquid crystalline phase architecture in which it was formed. Materials prepared in the normal topology hexagonal phase (HI) will have a system of cylindrical pores disposed on a long-range hexagonal lattice whereas those prepared in the normal topology Ia3d cubic (V1) p