Transition between light-induced attraction and repulsion of nanoparticles on a lithium niobate surface

Recent investigations have revealed a new phenomenon involving the transfer of charges between metallic as well as dielectric particles and the surfaces of photovoltaic crystals under illumination. Given its potential relevance to microfluidic and nanotrapping applications, understanding and controlling this phenomenon is of considerable interest. In this study, we examine the potential for manipulation of this charge transfer by customizing the induced electric field in terms of its strength and shape. In addition, we explore a method to mitigate this charging effect by introducing a thin layer between the crystal and the particle suspension. Specifically, we investigate the controlled trapping and repulsion of metallic micro-objects and nano-objects using a slowly increasing electric field induced by light in an iron-doped lithium niobate crystal. By employing structured light patterns with modulated amplitudes, we analyze the influence of shape and exposure of the light patterns on the dynamic movement of the particles. Our observations reveal two distinct regimes characterized by an initial attraction followed by repulsion. We present a model based on an electrical resistor-capacitor circuit that explains these two regimes and provides a good estimate of the temporal transition between them. These findings contribute to the advancement of controlled optoelectronic manipulation techniques for particles that utilize ferroelectric crystals.