Synergy of Nanoparticles Photovoltaic Trapping and Manipulation from Suspension Layer on Ferroelectric Crystal Surface

We experimentally demonstrated that dielectrophoretic (DEP) forces of alternating photovoltaic fields generated near the surface of a photorefractive Fe-doped lithium niobate crystal by an optical Bessel beam with concentric ring structure and 532 nm wavelength exert the structuring of pure glycerin layer on the crystal surface and formation of stationary fluid concentric ring pattern. Taking into account this effect, the manipulation and trapping of the Ag nanoparticles suspended in the thin glycerin layer on the crystal surface with Bessel beam-induced photovoltaic field pattern have been studied. The formation of the clusters of Ag nanoparticles is observed. The localization of the Ag particles on the extremes of fluid lattice rings is detected. The trapping process can be described by a two-stage scenario. In the early stage, the stratification of glycerin thin layer under positive DEP force and localization of the fluid in the maxima of the photovoltaic field take place, thus forming the concentric ring fluid channels on the crystal surface. The flow of viscose glycerin in the radial directions also carries along the Ag nanoparticles. In the advanced stage, the repulsive DEP forces lead to the trapping of Ag particles on the crystal surface at the borderlines of fluid lattice rings. The generated photovoltaic space charge fields are long-living and, as a consequence, the formed patterns remain stable for a long time due to the high resistance of the crystal. The photovoltaic tweezers operating in an autonomous regime and allowing the trapping, manipulation and separation of micro-/nanoparticles are promising for photonics, integrated optics, nanoelectronics and biotechnology.