Manipulating light and matter at the nanoscale

Nanostructured metals and semiconductors are promising building blocks for next generation solar energy conversion devices at low cost. From the optical perspective, nanostructure (NS) ensembles constitute a new class of metamaterial, where the optical properties of the ensemble are tuned by the individual NS type, geometry and collective arrangement. In the case of solar energy conversion into fuels, nanostructured or layered metal and metal oxide co-catalysts display performances that are morphology and size dependent. Nano semiconductors and conducting materials with tailored optical and electrical properties require new characterization methods to unravel the origin of their nano-enabled features. 
This work will describe a set of tools based on scanning probe and 3D microscopy to analyze nanostructures, from the optical, electrical to electrochemical perspective. We will show how fluorescence confocal microscopy can visualize the 3D extinction cross-section of GaAs NWs and to obtain the absorption coefficient and cross-section without the need of a transparent substrate. We demonstrate that by probing ordered arrays with this method, the effective absorption coefficient and cross-section can be obtained without the need of a transparent substrate. Moreover, we show how fluorescence microscopy is an insightful method to probe in real time the chemical environment of electrocatalysts. On the other hand, we will show that conducting atomic force microscopy is an emerging tool for the characterization of nano-wire based solar cells, where poor uniformity has hampered the large area device performance. As a final remark, we will demonstrate that SPM can become the ultimate nano-fabrication technology to create 3D nanostructures on demand.