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Thermally-Driven Dynamic Responses of Cu/SnO2 Bilayer Nanoribbons: An In-situ Electron Microscopy Study

. SnO 2 nanoribbons, typically have width and thickness ranging from 10 nm to 1 m m and width/thickness ratios as high as ten [1], were coated with 10 nm-thick Cu layers to form Cu/SnO 2 bilayer nanoribbons. characterizations demonstrated that either epitaxial or untextured Cu layers were formed depending on the crystallographic orientations of the SnO 2 surfaces being coated. The bilayer nanostructures were heated in-situ in a 300kV transmission electron microscope to study the thermally-driven mechanical response and structural evolution. It was found that the bilayer nanoribbons were stable during repeated heating-cooling cycles between 25 and 200 o C. The epi-bilayers bent reversibly governed by the theory for macroscopic bimetallic strips, whereas, the untextured bilayers displayed plastic deformation. Both the epitaxial and untextured Cu films irreversibly converted to thick, flat, pure Cu islands between 225 and 500ºC. The onset of island formation was followed by a rapid increase in island number and then a sustained period of island thickening through surface diffusion of Cu. Above 550ºC the Cu islands underwent a series of solid-state reactions with the SnO 2 substrates. Sn continuously diffused into the thickening Cu islands, leading to formation of various Cu-Sn alloy phases and major changes in morphology. These alloy islands began to etch rapidly into the SnO 2 nanoribbon substrate at above 600ºC.