Seminars Archive

Nanostructures for PV Conversion, Atomic Physics for VUV Polarisation Analysis

Abstract
This talk is divided in two parts: the first part is related to the use of nanostructures in photovoltaic (PV) devices, while the second part shows how basic atomic physics can be used to measure the degree of polarisation of VUV light. The increasing demand of “green” energy has triggered research focused on the optimization of photovoltaic (PV) devices, where charge made available by the absorption of visible light is pushed into a current flow by means of an internal electric field. In dye sensitized PV devices (Grätzel cells) electrons excited into high molecular states of a dye in a liquid solution are injected into a wide band gap semiconductor, such as TiO2, where they can be transported. One route to improve the performance of Grätzel cells is to replace the currently employed porous TiO2 with a low roughness but still high surface to volume shape of titania that is titania nanotubes. In this talk the growth and characterization of specifically 2D TiO2 species, particularly hexagonal and lepidocrocite type of titania nanosheets on Cu(100) by means of STM and spectroscopic techniques is discussed. Hexagonal and lepidocrocite are respectively three and four layers thick types of titania nano-sheets. The lepidocrocite-TiO2 structure is the same found in nano-tubes but the flat film-shape allows a wider range of experimental tools for their characterization. This is especially important in view of studies including the effect of dispersion of metal clusters on the electronic properties of the titania nanotubes, as metal clusters can help to improve the efficiency of the injection process in the visible range. Interaction of radiation with matter gives rise to scattering and absorption processes that are at the basis of the wide range of spectroscopic tools required to investigate molecular systems and solid state materials. Polarisation spectroscopies rely also on an accurate determination of the degree of linear and circular polarisation. Direct polarisation measurements in the VUV region require rather expensive, low efficiency and low sensitivity reflection optics systems. This talk describes an alternative method of polarisation measurements results and provides the first experimental evidence of its feasibility. This method consists in transforming short wavelength VUV radiation into the longer visible region using atomic resonance absorption in a gas and observing the polarization characteristics of the fluorescent light.