Longitudinal Piezoelectricity in Orthorhombic Amino Acid Crystal Films

The symmetry of orthorhombic amino acid single crystals precludes the existence of a longitudinal piezoelectric response. Here we report the growth of amino acid crystal films on conductive substrates that demonstrate measurable longitudinal piezoelectricity of the same order of magnitude as large piezoelectric biopolymers. Crystal films of the nonproteinogenic amino acid hydroxyproline show a response of the same magnitude as quartz single crystals. This response is deconstructed using density functional theory single crystal predictions and cross-sectional electron microscopy. These results verify that amino acid films can serve as simple piezoelectric transducers, which could be used for a variety of energy harvesting applications.