Substrate‐Controlled Response Coefficients in Thin Films

TL;DR

This paper shows how substrate-induced strain in thin films can control material responses by altering atomic vibrations, demonstrated using strontium titanate.

Contribution

A novel method to control material response coefficients through strain-induced changes in atomic vibrations in thin films.

Findings

Substrate-induced strain significantly alters atomic vibration frequencies and magnitudes in thin films.

The strain-dependent Curie constant was theoretically predicted and experimentally validated in SrTiO3 films.

Strain-induced control of atomic vibrations can lead to unprecedented material responses in thin films.

Abstract

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.

Many material‐specific coefficients, which relate external stimuli and functional responses, are constants governed by atomic vibrations. This work demonstrates the concept of controlling such response coefficients by deformations, or strain, through strain‐induced changes in atomic vibrations. As a proof of concept, the dependence of the Curie constant on substrate‐imposed strain in SrTiO3 films is theoretically predicted and experimentally validated.

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