Spectroscopy of Adsorbates and the Role of Interfacial Interactions

We present two test cases showing how electronic and optical spectroscopy techniques and their theoretical understanding by first principles can provide information on the strength of the adsorbate-substrate electronic interaction at interfaces. Results of electronic band structure calculations for two-dimensional silicon sheets (“silicene”) grown on silver are shown, pointing out that the interaction with the metal substrate is strong enough as to disrupt many of the exceptional properties computed for the free-standing material, or to mitigate the differences between various two-dimensional allotropes. The optical properties of silicon surface functionalized by nucleobase molecules are then discussed. Calculations predict that chemical sensitivity of spectra to molecular modifications can be overwhelmed by variations in the substrate response as induced by the adsorbates.