How Intrinsic Phonons Manifest in Infrared Plasmonic Resonances of Crystalline Lead Nanowires

Abstract

Single-crystalline lead nanowires with length of about one micrometer and with effective diameters of a few tens of nanometers have been grown on vicinal silicon by a self-assembly process. They show strong plasmonic resonances in the infrared with a remarkable enhancement of the extinction upon the cooling below room temperature. The increase of the plasmonic extinction at resonance is linear with decreasing temperature but saturates before the Debye temperature is approached. This observation is in full accordance with the quasi-static description of plasmonic extinction with the intrinsic damping dominated by phonons and thus linearly temperature dependent well above the Debye temperature. The different slopes of this linear function for different wire thickness indicate the importance of surface and near surface phonon properties that can be described by a Debye temperature that is lower than the bulk value. The careful spectral analysis also yields temperature independent contributions to the electronic scattering rates for various wire thicknesses and, furthermore, a resonance frequency decreasing with temperature, which corresponds to the predicted trend in renormalization theory for electron−phonon interaction in a metal like lead.

Impact of Metal-Optical Properties on Surface-Enhanced Infrared Absorption

“…For thin layers, electronic scattering at the interface can be stronger than on the free surface. Furthermore, there are already differences between the phonon contributions to the Drude parameters for zero frequency and IR frequencies, as discussed, for example in ref . In this reference, it is also shown that the plasmonic resonances of single crystalline lead antennas correspond to electronic scattering rates much smaller than the bulk values from refs and .…”

“…For the analysis of the plasmonic properties of the nanoantenna arrays in the IR, it is important that in the range below 2000 cm –1, the metals under investigation can be well-described by the Drude model. Deviations to the Drude-type behavior because of interband transitions arise only at higher wavenumbers. , According to several previous studies, ,, we extract these parameters from the plasmonic resonance spectra. The relation applied is based on an oscillator model and quantitatively allows the determination of the electronic scattering rate ω τ and the radiation damping ω rad (see the Supporting Information).…”

“…Interestingly, for all metals under investigation, ω τ decreases with an increasing width. This trend is partially because of surface scattering that decreases with the decreasing surface-to-volume ratio of the antennas (≈1/ w + 1/ h ), resulting in less electronic surface scattering . However, a change of the defect density with increasing width cannot be excluded.…”

“…For all plasmonic structures including the plasmonic application of graphene, low plasmonic damping is highly desired. In metallic nanostructures, an important amount of damping is due to intrinsic damping from electronic scattering . The other loss channel is radiation damping.…”

“…In metallic nanostructures, an important amount of damping is due to intrinsic damping from electronic scattering. 24 The other loss channel is radiation damping. It is present for all kinds of materials and is related to the geometry of the radiating particle and to the oscillator strength of the resonance.…”