Piezoelectrics are materials that can transform mechanical energy into electrical energy and vice versa. This is thanks to their ability to deform under an electric field and, conversely, to produce an electric field when deformed. Because of this unique property, they are the active elements of many everyday applications, from ink-jet printers to ultrasound generators, representing a billion euro industry. They could play an important role in low-power energy harvesting, allowing autonomous powering of small electronics, by converting ubiquitous vibrations (wasted mechanical energy), into electricity.
In order to enable these and other future applications, two main developments are eagerly awaited in the field: 1) miniaturization, for energy efficiency and integration in electronics. For this, further enhancement of the materials responses is required in order to maintain their functionality at the nanometer scale; 2) discovery of non-toxic and abundant piezoelectrics with comparable properties (including temperature stability) as those of the current, lead-based, compounds.
To move towards the realization of these goals, we will synthesize new materials, with sufficiently large piezoelectric responses in thin film form, made of harmless and widely available elements. More specifically, we will venture into Si-based piezoelectric solid solutions grown under epitaxial strain, starting with doped epitaxial α-quartz (the piezoelectric phase of SiO2). Well aware of the challenges associated to this enterprise, we will attack the problem using different innovative experimental approaches that will largely maximize the chances of success and will enable the industrial transfer of the product achieved. We take advantage of very recent developments in the synthesis of crystalline α-quartz using soft-chemistry, as well as in the synthesis of single crystal oxides using nanosheet templating. We will do this, assisted by first-principles calculations, that have demonstrated high predictive power in other areas of piezoelectric oxides synthesis, in order to make the best materials choice/combination possible and to avoid inefficient trial-and-error strategies. In addition, we will prepare the path to the industrial use of these materials by integrating them in Si membranes and cantilevers that can directly be used in devices. This joint effort will bring the two awaited breakthroughs in the field within our reach.