Electromechanical properties of an ultrathin layer of directionally aligned helical polypeptides.

The electromechanical properties of a monomolecular film of poly-gamma-benzyl-L-glutamate (PBLG) 15 nanometers thick grafted at the carboxyl-terminal end to a flat aluminum surface were measured. The field-induced change in film thickness, dominated by a large inverse-piezoelectric effect, demonstrates that the "grafting-from" technique forces the chains into a parallel arrangement. The mechanical plate modulus of the film as determined by electrostriction agrees with the theoretical prediction for a single PBLG molecule along the chain axis. The experiments show that ultrathin polypeptide layers with large persistent polarization can be fabricated by the grafting approach.