Substrate-Controlled Response Coefficients in Thin Films

To obtain materials with desired properties, material compositions are primarily altered, whereas thin films offer additional unique avenues. By combining state-of-the-art first-principles calculations and experimental investigations of thin films of strontium titanate as an exemplary representative of a broad class of perovskite oxides and the extensive family of ferroelectrics, a novel approach is presented to achieving superior material responses to external stimuli. The findings reveal that substrate-imposed deformations, or strains, significantly alter the frequencies and magnitudes of atomic vibrations in thin films. Consequently, material-specific response-stimulus coefficients can become strain-dependent. The strain-dependent Curie constant, which characterizes the dielectric response to thermal stimuli, is theoretically justified and experimentally validated. Given that atomic vibrations fundamentally govern various response coefficients in a wide range of materials, and that thin films are typically deformed by substrates, it is anticipated that unprecedented responses can be generally attained through substrate-induced control of atomic vibrations in thin films.