Azapentacene Derivative Thin Film Growth on TiO2(110): Morphology and Electronics

This study delves into the properties of thin films composed of dihydrotetraazapentacene (DHTAP) molecules, primarily exploring their growth and morphology of resulting structures on titanium dioxide (TiO₂). These molecules are particularly appealing due to their inherent permanent dipole. Employing scanning probe microscopy (SPM) and scanning electron microscopy (SEM) allows for in-depth study of the growth mechanisms. Thermal desorption spectroscopy (TDS) experiments provided deeper insights into the energetics of DHTAP desorption. We have investigated diverse deposition parameters, substrate morphologies, and coverages, revealing intriguing insights into the molecular configurations and their interactions with the substrate. To confirm our experimental findings, we compared the obtained results with density functional theory (DFT) calculations and correlated them also with the growth behavior of pentacene molecules. DHTAP forms distinct structures on TiO₂(110) surfaces, ranging from small clusters to elongated crystalline needles. A pivotal observation is temperature-dependent growth, where a critical temperature threshold dictates the formation of stable structures. STM images unveiled interesting molecular orientations, originating from the complex interaction between DHTAP molecules and the TiO₂(110) substrate. As coverage increases, DHTAP molecules self-assemble into a wetting layer, displaying unique configurations influenced by the substrate’s anisotropy. TDS results confirm the weak molecule–substrate interaction. Comparisons with pentacene, a benchmark material in the field, highlight the unique characteristics and potential applications of DHTAP for advanced devices and as a platform to advanced solid-state physics.