Anisotropic optical response of elongated Pb islands in the infrared spectral region

Abstract

AbstractLead forms elongated islands when grown on vicinal Si(111) surfaces. Polarized infrared transmittance studies have shown a strong anisotropic optical response associated with antenna‐like plasmonic resonances, whose spectral position in the region of 0.25 eV is sensitive to the length of the islands. Reflection anisotropy spectroscopy (RAS) using a photoelastic modulator (PEM) should be more sensitive to such optical anisotropies, but becomes difficult below ∼0.5 eV for instrumental reasons. Measurements of the anisotropic response, in reflectance, of Pb islands grown on Si(557)‐5 × 1–Au are extended down to ∼0.12 eV by combining sample rotation with tuneable femtosecond laser irradiation from a difference frequency generator. The extended RAS spectral range allows the full anisotropic nanoparticle plasmon‐polarition optical response in the surface plane to be explored for this type of material system. Reasonable agreement with a simple nanoantenna model of the resonance maximum is obtained, but calculating the full line profile of the RAS response of supported nanoparticles remains challenging.