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

McAlinden, Niall and Wang, Jing-Jing and McGilp, John (2012) Anisotropic optical response of elongated Pb islands in the infrared spectral region. Physica Status Solidi B. ISSN 0370-1972

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Abstract

Lead 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.