During the initial period of the action, several oxide perovskites were synthesized as thin films and membranes integrated in silicon and flexible polymers. Five lines of work were devised from here:
1 - Strain engineering of ferroelectric membranes: Demonstration of the manipulation of structure and ferroelectric properties of the membranes by using the interlayer stress. This led to ferroelectric capacitor devices integrated on silicon and flexible polymer platforms with strain-engineered properties (Fig.1) showing ultrafast, low-voltage switching operation on silicon, and large dielectric tunability under low stress application on polymers. This work led to two high-impact publications in Advanced Materials and Nature Communications journals, and was presented in a talk by the Experienced Researcher (ER) at the ISAF-ECAPD conference 2021.
2- Strain gradient engineering of ferroelectric membranes: Studies of temperature dependence of flexoelectric coefficient were performed and partially presented in a PhD dissertation thesis from Stanford University, and synthesis of membranes with corrugated (wrinkled or buckled) structures was developed (Fig. 2). The effect of large local curvatures on the ferroelectric domain configuration is currently under exploration, in collaboration with Oak Ridge National Lab (ORNL), and work related to this research will be disseminated in future conferences during 2022.
3- Exploring the microscopic ordering physics of ferroelectrics with complex microscopic order: Nanometric membranes of archetypical ferroelectrics (BaTiO3), ferroelectric relaxors (PMN-PT) and antiferroelectrics (PbZrO3) were transferred to grids for examination in Transmission Electron Microscopy (TEM). These have allowed performing imaging with atomic resolution in the membranes and study the intricate microstructural arrangements of these materials produced by the spontaneous deformations of the membranes (Fig.3).
4- Direct measurement of electrocaloric effects on ferroelectric membranes. Fabrication of suspended capacitor structures failed due to unavoidable mechanical/electrical failure of the devices. As a contingency plan, membranes were transferred to nanocalorimetry chips fabricated by the Group of Thermal Properties of Nanoscale Materials, at ICN2 (Fig.4) allowing for heat capacity measurements on BaTiO3 membranes, which is a milestone result for the further application of this technique on electrocaloric measurement of ferroelectric capacitors.
5– Optomechanical effects on ferroelectric membranes: As an alternative to electrical actuation on suspended membranes, photoexcitation was used. A large mechanical deformation in response to near-UV laser excitation was found, by using an interferometric microscope at ICN2. The physical origin of this enhanced response is currently under investigation.
Further dissemination actions include the publication of two topical review articles on the recent developments of ferro-/pyro- electrics in synthesis, processing, and computational modeling. A third invited review article on recent advances on complex oxide membranes is expected to be published during 2022. The ER also participated in numerous seminars (at University of California Berkeley, Lawrence Berkeley National Lab and at ICN2) and attended exhibitions (e.g. Cal Day) and virtual workshops (e.g. Quorom, INTERSECT2021, III CANN 2021), discussing the topics related to the project with fellow researchers, technological partners and broader audiences.
