Eumelanin Adsorption on Silicon: Optical Properties of Si(001)-Adsorbed Eumelanin Tetrameric Protomolecules

We predict the optical properties (in particular optical absorbance and reflectance anisotropy spectra (RAS)) of the silicon(001) surface organically functionalized by the adsorption of chosen tetrameric eumelanin protomolecules. These Si(001):tetramer systems can be considered as models of hybrid (porous) silicon-eumelanin interfaces, a system with potential applications in photovoltaics. In spite of a weak effect of tetramer adsorption on Si(001) overall absorption spectra, first-principles results based on plane wave density functional theory allowed us to identify specific regions, in the interesting IR and visible range, where the adsorbed molecules yield large enhancements in surface absorbance, and the appearance of new RAS features.