Polarization-dependent ultrafast plasmon relaxation dynamics in nanoporous gold thin films and nanowires

Abstract

Metal materials structured at nanoscale are extensively used in a variety of applications, including molecular sensing, nanoscale heaters for photothermal therapy, etc. These applications depend on the strong absorption and electric field enhancements associated with localized surface plasmon resonance (LSPR). Despite multiple investigations of LSPR relaxation dynamics in plasmonic metallic nanoparticles (i.e. nanospheres, nanocubes, etc), no detailed studies of porous thin films or nanowires have been reported so far. In this paper, LSPR relaxation dynamics of nanoporous gold thin film, gold nanowires, and nanoporous gold nanowires (structures with the potential for a vast range of sensing and optical applications) were studied by means of transient absorption spectroscopy (TAS). Au and Au/Cu thin films produced by magnetron sputtering deposition over a nanograted silicon substrate enabled the creation of highly organized nanowire arrays of centimetres length. Nanoporous structures were created by the dealloying of Au/Cu alloy. We found that formation of such a subwavelength period grating structure in gold increases the efficiency of hot electron relaxation compared to continuous film, while the porosity of gold nanostructures has the opposite effect. The results also expressed a clear dependence of the TAS signal on the polarization (i.e. orientation of the electric field with respect to the nanoporous gold nanowires) of the pump and probe pulses, compared to non-porous gold nanowires.

Porous Inorganic Materials for Bioanalysis and Diagnostic Applications

“…These collective oscillations of the conduction band electrons at hot spots enable strong optical absorption and scattering in subwavelength structures, facilitating sensitive detection by Raman spectrometry, fluorescence spectrometry, mass spectrometry, etc. LSPR mediated sensing is highly dependent on the porosity of materials. , To produce hot spots, porous metal nanostructures have been fabricated on a metal thin film or disk or synthesized by wet-chemistry approaches . Both the interpore spacing and pore diameter determine oscillation efficiency and LSPR wavelength, thereby affecting the detection sensitivity. , Yamauchi et al fabricated mesoporous Cu films by micelle self-assembly and investigated EM field enhancements via LSPR .…”

“…LSPR mediated sensing is highly dependent on the porosity of materials. 53,119 To produce hot spots, porous metal nanostructures have been fabricated on a metal thin film or disk 120 or synthesized by wet-chemistry approaches. 121 Both the interpore spacing and pore diameter determine oscillation efficiency and LSPR wavelength, thereby affecting the detection sensitivity.…”