Plasmonic tuning of silver nanowires by laser shock induced lateral compression

摘要

Laser shock induced lateral compression has been demonstrated to controllably flatten cylindrical silver nanowires. Nanowires with circular cross-sections of diameter 70 nm are significantly shaped laterally, which transformed them to metallic ribbons of huge width of 290 nm and of thickness down to 13 nm, amounting the aspect ratio to as high as 22, at a laser intensity of 0.30 GW cm-2. Above the laser intensity of 0.30 GW cm-2 though, nanowires are observed to be ruptured. Lateral deformations of nanowires are achieved without altering longitudinal dimensions. Selected area electron diffraction patterns on the laterally deformed nanowires reveal that the flattening gives rise to twinning under high strain rate deformation without actually degrading crys-tallinity. As the 1D nanowire turns into a 2D metallic nanoribbon, new plasmonic modes and their combinations emerge. The transverse plasmon mode does not shift substantially, whereas longitudinal modes and their combinations are greatly influenced by lateral deformation. Apart from the transverse mode, which is dominant in a 1D nanowire and diminishes heavily when lateral deformation occurs, there is a presence of several longitudinal plasmonic modes and their combinations for metallic nanoribbons, which are revealed by experimental extinction spectra and also supported by finite-difference time-domain (FDTD) simulation. Such plasmonic tuning of silver nanowires across the visible range demonstrates the capability of a laser shock induced lateral compression technique for various emerging plasmonic applications. The laser shock compression technique has the advantages of flexibility, selectivity and tunability while retaining crystallinity of metallic nanowires, ail of which enable it to be a potential candidate for plasmonic tuning of nanogeometries.