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Despite the importance of thiorphan as a small molecule with vital biological roles, its interactions with zinc oxide (ZnO) nanomaterials that are prospective in drug delivery and theranostic applications have not yet been sufficiently explored. Here the impact of surface polarity of different ZnO surfaces on thiorphan adsorption is studied experimentally by combined in-situ scanning electron microscope (SEM) and atomic force microscope (AFM). Polar ZnO surfaces cause formation of thiorphan nanodots ( 4 nm or 25 nm), where the size of the nanodots depends on the direction of the surface dipoles. Nonpolar ZnO surfaces cause self-assembly of thiorphan into nanoislands and nanolayers with characteristic 4 nm layer thickness. AFM-in-SEM data shows clear correlation between secondary electron intensity of molecules in SEM and their height in AFM on polar ZnO surface whereas anti-correlation is observed on nonpolar ZnO surface. The secondary electron emission from the same molecule thus depends on its orientation, structure it assembles into and it can be controlled by direction of the substrate surface dipole.
Keywords: Atomic force microscopy, scanning electron microscopy, thiorphan, ZnO surfaces, molecular assembly© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.