Metal-Semiconductor Hetero-Nanostructures: The Formation Chemistry and Study of Their Photo catalytic and Photo response Activities

Biplab Kumar Patra; Principal Investigator: Narayan Pradhan

Indian Association For the Cultivation of Science, Jadavpur,Kolkata 700032, West Bengal, India

Metal-semiconductor hetero-structured nanomaterial’s are emerged as a new class of functional materials for their efficient photo catalytic activities in water splitting, photo-current and photo-response studies, facilitating organic reactions and improving the stability and performance in different device based applications. Even, the chemistry of designing several hetero-structures are well documented, but still the core issue of selective facet dependent binding of metal in semiconductors and the formation of hetero-epitaxy at the junction are not yet been widely investigated. Moreover, the possible electron transfer from metal to semiconductor or semiconductor to metal, particularly in the hetero-structures where both materials have the absorption in solar spectral window, is not yet well established. Hence, for proper utilizations of these materials, these core fundamental issues are needed to be understood. Keeping these in mind, we discuss here the formation chemistry of metal Au coupled with low band gap semiconductors CZTS (Cu2ZnSnS4) and SnS, and analyze the hetero-epitaxy formation at their hetero-junctions. For CZTS, confining the epitaxy formation along {111} planes of Au, it is observed that the wurtzite and tetragonal phases of CZTS follow the coincidental site epitaxy with different periodic intervals. Further investigation suggests that the hetero-structures show increase in the photo-current and photo-response activities compared to only CZTS nanostructures. Similarly for SnS, different sizes of Au particles are attached and peculiarly, here the hetero-structures show the Au particles size dependent tuning in their materials properties. The small Au(0) clusters (< 3 nm) are typically decorated randomly in cube and tetrahedron shapes of SnS but larger plasmonic Au(0) particles form twin structures with coupling at the corner of the SnS cubes. Contrastingly, the non-plasmonic Au cluster-SnS hinders the visible light photo catalytic activity whereas the plasmonic coupled Au-SnS enhances the photo catalytic activity towards the reduction of the organic dye. However, both types of heterostructures show enhanced photo response activities and stability of the device during illumination and measurement of photocurrent. From the aspects of the fundamental of the formation of the hetero-structures and also on the issues of new properties or applications, we believe these finding would help the community and also provide guidelines for investing new functional materials and their utilities.

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