Elucidating optical field directed hierarchical self-assembly of homogenous versus heterogeneous nanoclusters with femtosecond optical tweezers

Abstract

Insights into the morphology of nanoclusters would facilitate the design of nano-devices with improved optical, electrical, and magnetic responses. We have utilized optical gradient forces for the directed self-assembly of colloidal clusters using high-repetition-rate femtosecond laser pulses to delineate their structure and dynamics. We have ratified our experiments with theoretical models derived from the Langevin equation and defined the valid ranges of applicability. Our femtosecond optical tweezer-based technique characterizes the in-situ formation of hierarchical self-assembled clusters of homomers as well as heteromers by analyzing the back focal plane displacement signal. This technique is able to efficiently distinguish between nano-particles in heterogeneous clusters and is in accordance with our theory. Herein, we report results from our technique, and also develop a model to describe the mechanism of such processes where corner frequency changes. We show how the corner frequency changes enables us to recognize the structure and dynamics of the coagulation of colloidal homogeneous and heterogeneous clusters in condensed media over a broad range of nanoparticle sizes. The methods described here are advantageous, as the backscatter position-sensitive detection probes the in-situ self-assembly process while other light scattering approaches are leveraged for the characterization of isolated clusters.

Optical Force-Induced Dynamics of Assembling, Rearrangement, and Three-Dimensional Pistol-like Ejection of Microparticles at the Solution Surface

“…Not only optical trapping potential but also assembly of NPs can be controlled by femtosecond laser polarization. , Two-photon fluorescence is used for tracking the movement of individual NPs and for analyzing their geometry . Even the hierarchical self-assembly was demonstrated and discussed, which will be a useful reference for fabricating the assembly as the bottom-up approach. The different optical trapping conditions are applied in the present work and their study: at the solution interface vs in solution, by CW vs by the femtosecond laser, for bare vs for dye-doped particles, and in the ensemble level vs the individual particle level, but it is important how laser polarization determines the respective phenomenon.…”

“…53,54 Twophoton fluorescence is used for tracking the movement of individual NPs and for analyzing their geometry. 55 Even the hierarchical self-assembly was demonstrated and discussed, 56 which will be a useful reference for fabricating the assembly as the bottom-up approach. The different optical trapping conditions are applied in the present work and their study: at the solution interface vs in solution, by CW vs by the femtosecond laser, for bare vs for dye-doped particles, and in the ensemble level vs the individual particle level, but it is important how laser polarization determines the respective phenomenon.…”

Anomalously Large Assembly Formation of Polystyrene Nanoparticles by Optical Trapping at the Solution Surface

“…The other is the structuring of NPs will be more controllable by laser power and polarization. For example, Goswami et al demonstrated for different configurations of a few 250 nm PS NPs by utilizing femtosecond laser in solution. − This interesting trial enables individual arrangement in NP assembly at the solution surface and interface too.…”

Nanoparticle Assembling Dynamics Induced by Pulsed Optical Force

“…They manipulated dye‐doped 250 nm PS NPs and constructed a specific 3D geometry, [78,79] where two‐photon fluorescence is used for tracking the movement of individual NPs and for analyzing their geometry [80] . Even hierarchical self‐assembly was demonstrated and discussed, [81] which will be a useful reference for fabricating the assembly as the bottom‐up approach. They reported that not only optical trapping potential shape but also the assembly of NPs can be controlled by femtosecond laser polarization.…”