Infrared resonances of self-assembled Pb nanorods

Abstract

The formation of self-assembled Pb nanorods on a vicinal Si(335)/Au surface at 305K was monitored in situ with polarization dependent infrared spectroscopy. The rods have formed from Pb evaporated on a single domain Au-stabilized Si(335) surface under ultrahigh vacuum conditions and reached lengths of about 1μm. As the rods are aligned almost parallel, a large optical anisotropy of the transmitted infrared light was detected. A plasmonic antennalike resonance appeared in the spectra. Since such resonance frequencies are mainly determined by the length of the rods, the growth process was directly monitored via the shift of the resonance frequency. The estimated extinction cross section at resonance frequency indicates field enhancement similar to that observed for gold nanorods.

Infrared spectroscopy of antenna resonances

“…The focal spot on the sample was about 5 mm in diameter and thus smaller than the area with aligned Pb nanowires. Previous studies on lead nanowire formation on gold-stabilized Si(335) 10 have shown a good accordance between the L. Novotny's approximate formula 11 and the measured relationship of growing length to resonance frequency. On other vicinal Si templates the wire growth with increasing coverage proceeds differently.…”

“…3), but nearly no frequency shift could be measured, in accordance to our previous calculations. 10 The observed decrease in transmittance in Fig. 2 means an increase in the farfield extinction-cross section by a factor of 1.4.…”

Surface enhanced infrared spectroscopy using gold nanoantennas

“…For IR antenna-like resonances, the antenna diameter D cannot be neglected in comparison to the length L and also the ratio between skin depth and D is relevant. As we could prove experimentally [26,27], the IR resonances of nanowires with a rather good metallic conductivity (not too high electron scattering) are quite well described by effective wavelength scaling [28] with:…”

“…Therefore, going from spherical particles to prolate spheroids, the main dipolar resonance splits into two branches with one low-energy plasmonic mode for electric field parallel to the long wire axis. Metal nanowires with about 1 mm lengths and 0.1 mm diameter show resonances in the mid IR range [21,[24][25][26][27]. The larger the length ratio of the long axis of the particle to the short one, the lower becomes the frequency of this mode.…”

Surfactant Growth and Optical Studies of Plasmonic Silver Nano-Disks

“…To make the plasmonic enhancement effective, there is a demand to tune the plasmon energy to match with the specific frequency range [3]. Unlike the case of metal particles whose resonant frequency is theoretically limited within ω P / √ 2 and ω P / √ 3 (ω P is plasma frequency of bulk metal), the metal nano-rods offer much stronger tunability [6][7][8]. It is worthwhile to examine whether the quasi two-dimensional films (nano-disks) can support such a dipole resonance with a comparable tunability.…”