Molecular orientation of DHTAP on the nanostructured Cu-CuO stripe phase
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DPG Frühjahrstagung SKM 2023
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We have studied the preferential adsorption, structure and molecular orientation of 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) layers on the regularly patterned Cu-CuO stripe phase obtained by sub-monolayer oxygen adsorption on the Cu(110) surface. Using Reflectance Difference Spectroscopy (RDS) and Scanning Tunneling Microscopy (STM) we find that the DHTAP molecules preferentially adsorb on the Cu (110) stripes, where they are always lying flat with their long molecular axis aligned parallel to the [-110]-direction. In contrast, on the subsequently covered Cu(110)-(2x1)O stripes, the DHTAP molecules are aligned with their long molecular axis parallel to the -direction. The evolution of the RDS signal allows to monitor the sequential adsorption and orientation of DHTAP during monolayer formation and the subsequent multilayer growth for different oxygen pre-coverages and, hence, different Cu and CuO stripe widths. Interestingly, beyond the first monolayer, the DHTAP molecules adopt a preferential orientation which critically depends on the initial oxygen coverage, revealing the influence of the Cu-CuO stripe width and the possibility to tune the overall optical anisotropy of these films.