Light and thermally induced charge transfer and ejection of micro-/nanoparticles from ferroelectric crystal surfaces

Abstract

During real-time operation of photovoltaic optoelectronic tweezers, a novel intriguing phenomenon has been recently observed, namely, silver nanoparti-cles previously deposited on ferroelectric LiNbO3:Fe surfaces are ejected from them by illumination. Here, it is shown that this phenomenon results from the electrical charging of the micro-/nanoparticles previously trapped on the LiNbO3:Fe surfaces and the subsequent Coulomb repulsion. Specific experi-ments are performed to determine the sign of the transferred charges, which is negative/positive for the +c/−c sample face, i.e., it coincides with that of the stored charges on each surface. The charging/ejection process is proved to occur regardless of the illuminated crystal surface, the dielectric or metallic nature of the particles, and in different surrounding media. Besides, the role of the excitation light intensity is also explored. Next, to assess the generality of the ejection phenomenon, similar experiments based on the pyroelectric effect are performed, i.e., generating the electric fields by changing the crystal temperature instead of illuminating it. Thereby, thermally driven particle ejection is demonstrated using different ferroelectric crystals. The similarities found for the two approaches throw light on the charge transfer and ejection mechanism and remark the universality of the phenomenon for ferroelectrics, which can find many technological applications