Optical Printing of Electrodynamically Coupled Metallic Nanoparticle Arrays

Optical forces acting on metallic nanoparticles can be used to organize mesoscale arrays for various applications. Here, we show that silver nanoparticles can be deposited as ordered arrays and chains on chemically modified substrates using a simple and facile optical trapping approach that we term optical printing. The deposited patterns show preferred separations between nanoparticles resulting from their electrodynamic coupling (i.e., optical binding) in the electromagnetic field of the optical trapping beam. Centro-symmetric optical traps readily allow simultaneous deposition of nanoparticle pairs and triples maintaining the interparticle geometries present in solution. Repositioning an optical line trap with small intercolumn separations allows selectively sampling low and high energy parts of the interparticle potentials. We find that the preferred particle arrangements controllably change from rectangular and triangular to near-field aggregates as one forces the separation to be small. The separation affects the interactions. Interpretation of the results is facilitated by electrodynamic simulations of optical forces. This optical printing approach, which enables efficient fabrication of dense nanoparticle arrays with nanoscale positional precision, is being employed for quantum optics and enhanced sensing measurements.