Sublimation of orientated amino acid films for reliable, amplified piezoelectric performance

Abstract: Biomolecular crystals, such as amino acids, peptides, and proteins, have emerged as potential next generation piezoelectric materials due to their low-cost, biocompatibility, eco-friendliness, and reduced permittivity versus ceramics. However, many challenges have limited their acceleration into mainstream sensing applications. Their natural self-assembly from saturated solutions into polycrystalline films reduces their effective piezoelectric output, and results in high variability within individual samples, and across sample batches when scaled-up. Here we validate the sublimation of a variety of amino acids onto conductive substrates as an effective technique for overcoming these challenges. This solvent-free crystallisation technique results in polycrystalline films with uniformly orientated crystals, and a resulting piezoelectric response that exceeds that of single crystals. We report a maximum piezoelectric response of 9.6 pC/N in films of L-Valine, which matches the predicted single crystal response, and a maximum voltage output of 4.6 V. For L-Methionine and L-Valine sublimated films the material properties are consistent at all points on the piezoelectric films and repeatable across any number of films grown under the same conditions.