Photostrictive Actuators Based on Freestanding Ferroelectric Membranes

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Complex oxides possess diverse functional properties.
• Freestanding oxide membranes introduce novel mechanical functionalities.
• Photoactuation in thin films is an emerging area of research.

Purpose of the Study:

• To demonstrate and investigate photoactuation in freestanding ferroelectric and paraelectric oxide membranes.
• To compare the photoactuation response of Barium Titanate (BaTiO3) and Strontium Titanate (SrTiO3).
• To elucidate the mechanism behind light-induced strain in ferroelectric BaTiO3.

Main Methods:

• Fabrication of freestanding thin film resonators of BaTiO3 and SrTiO3.
• Illumination with a frequency-modulated laser to induce oscillations.
• Time-resolved X-ray micro-diffraction under illumination.
• Temperature-dependent holographic interferometry.

Main Results:

• Freestanding BaTiO3 and SrTiO3 films acted as nano-drums, oscillating at their resonance frequency when illuminated.
• Light-induced deflections in BaTiO3 membranes were two orders of magnitude larger than in SrTiO3.
• Evidence for photostrictive strain in BaTiO3 due to partial screening of ferroelectric polarization by photo-excited carriers was observed.

Conclusions:

• Photostrictive effect in freestanding ferroelectric BaTiO3 films is demonstrated.
• The mechanism involves photo-excited carriers screening ferroelectric polarization, reducing unit cell tetragonality.
• Freestanding ferroelectric films offer potential as wireless actuators controlled by light.