Hydrogen-bonded amino acid network of histidine on Ge(100)

By controlling the exposing conditions, a highly ordered monolayer of amino acid on the semiconductor surface is observed for the first time. The detailed adsorption structure and the driving force have been explained by using the scanning tunneling spectroscopy (STM) and ab initio calculations. Basically, the most stable adsorption structures of histidine molecules are OH-dissociated and N-dative-bonded ones at low and high coverage. When they reach high coverage to get the interaction between the adsorbed histidine molecules, they are ordered and more stabilized with an additional energy of 0.17 eV/molecule. This additional energy is found to come from the NH•••O hydrogen bonding, which acts as the driving force to form the self-assembled mono layer at high coverage.