Laser printing of resonant plasmonic nanovoids

Abstract

Hollow reduced-symmetry resonant plasmonic nanostructures possess pronounced tunable optical resonances in the UV-vis-IR range, being a promising platform for advanced nanophotonic devices. However, the present fabrication approaches require several consecutive technological steps to produce such nanostructures, making their large-scale fabrication rather time-consuming and expensive. Here, we report on direct single-step fabrication of large-scale arrays of hollow parabolic- and cone-shaped nanovoids in silver and gold thin films, using single-pulse femtosecond nanoablation at high repetition rates. The lateral and vertical size of such nanovoids was found to be laser energy-tunable. Resonant light scattering from individual nanovoids was observed in the visible spectral range, using dark-field confocal microspectroscopy, with the size-dependent resonant peak positions. These colored geometric resonances in far-field scattering were related to excitation and interference of transverse surface plasmon modes in nanovoid shells. Plasmon-mediated electromagnetic field enhancement near the nanovoids was evaluated via finite-difference time-domain calculations for their model shapes simulated by three-dimensional molecular dynamics, and experimentally verified by means of photoluminescence microscopy and Raman spectroscopy.

Formation of Periodic Nanoridge Patterns by Ultrashort Single Pulse UV Laser Irradiation of Gold

“…Not only this relaxation drives the already melted matter into the hydrodynamical motion upward, but also results in a mechanical rupture of the subsurface layer (spallation) in the area where the lattice temperature and pressure are high enough [ 16 , 18 , 32 , 49 , 51 , 52 ]. This mechanism allows for generation of arrays of subsurface voids of specific size for their technological applications [ 53 ].…”

Light‐Induced Tuning and Reconfiguration of Nanophotonic Structures

“…Under femtosecond‐pulse irradiation, the local molten part of the noble‐metal thin film, characterized by weaker adhesion to the supporting substrate, detaches through ultra‐fast optical heating and local high‐pressure generation, producing a parabola‐shaped hollow bump or nanovoid (I–IV in Figure a) whose geometric parameters can be tuned precisely by applied fluence . Such nanostructures were produced on surfaces of Au and Ag films, and they demonstrate tunable size‐dependent resonant light scattering in the visible spectral range, supporting excitation and interference of axial and transverse surface plasmon modes in nanovoid shells (see Figure b and c). The spectral position of the resonant peak was shown to follow a simple standing‐wave model suggesting a certain integer number of plasmon wavelengths to fit the effective circumference of the outer nanovoid shell (see Figure d,e), where n eff is the effective refractive index of the plasmon mode supported by the air–metal interface .…”

“…(a) Series of energy‐resolved side‐view SEM images (at 45° angle) of the structures produced under irradiation of a 60‐nm‐thick gold film by a single fs‐laser pulse at different pulse energies (adopted from Ref. []). The shapes are supported with the corresponding dark‐field optical images (b) showing pronounced changes of the scattering colors in the visible spectral range.…”

Light absorption by surface nanoholes and nanobumps

“…Light interaction with basic surface nanostructures, such as holes and ridges, lies at the heart of subwavelength optics, signal processing on the nanoscale, nanophotonics and nanoplasmonics. The presence of these tiny imperfections has been proved to modify the optical properties of the pristine material, contributing to strongly enhanced transmission, anomalous optical absorption, wavelength filtering, and surface plasmon wave excitation on metal surfaces [1][2][3][4][5][6][7][8][9]. Efficient light manipulation on the nanoscale is hence possible nowadays by using optical devices, where diffraction gratings or nanoslits, periodic arrangements of holes or nanoparticles serve as general counterparts.…”