Transmission spectral and diffraction pattern study on optical trapping and assembling of dielectric nanoparticles at solution/glass interface

Polystyrene and silica nanoparticles are gathered and form a single disk-like assembly at glass/solution interface upon optical trapping with a focused laser and its size evolves much larger than the focal volume. In addition, linearly aligned aggregates of nanoparticles are prepared at specific edge sites of the assembly, which looks like horns. Transmission spectral and diffraction pattern measurements were carried out, confirming a correlation between the central arrangement of the nanoparticles and the horn formation. This dynamics and mechanism characteristic of optical trapping at interface is discussed from the viewpoint of optical propagation of the trapping laser. The assembly formation started at the focus where trapping laser light is scattered, and the trapping laser propagated trough the prepared assembly expanding its size.