Laser-induced jets of nanoparticles: exploiting air drag forces to select the particle size of nanoparticle arrays

Abstract

In this study, we developed a new method—based on laser-induced jets of nanoparticles (NPs) and air drag forces—to select the particle size of NP arrays. First, the incident wavelength of an excimer laser was varied to ensure good photo-to-thermal energy conversion efficiency. We then exploited air drag forces to select NPs with sizes ranging from 5 to 50 nm at different captured distances. Controlling the jet distances allowed us to finely tune the localized surface plasmon resonance (LSPR) wavelength. The shifting range of the LSPR wavelengths of the corresponding NP arrays prepared using the laser-induced jet was wider than that of a single NP or an NP dimer. We further calculated the relationship between the air drag force and the diameter of the NPs to provide good control over the mean NP size (capture size ≧ 300 μm) by varying the capture distance. Laser-induced jets of NPs could also be used to fabricate NP arrays on a variety of substrates, including Si, glass, plastic, and paper. This method has the attractive features of rapid, large-area preparation in an ambient environment, no need for further thermal annealing treatment, ready control over mean particle size, and high selectivity in the positioning of NP arrays. Finally, we used this method to prepare large NP arrays for acting hot spots on surface-enhanced Raman scattering-active substrates, and 10⁻¹² M R6G can be detected. Besides, we also prepare small NP arrays to act as metal catalysts for constructing low-reflection, broadband light trapping nanostructures on Si substrates.