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The recent integration of silicene in field-effect transistors (FET) opened new challenges in the comprehension of the chemical and physical properties of this elusive two-dimensional allotropic form of silicon. Intense efforts have been devoted to the study of the epitaxial Silicene/Ag (111) system in order to elucidate the presence of massless Dirac fermion in analogy with graphene; strong hybridization effects in silicene superstructures on silver have been invoked as responsible for the disruption of π and π* bands. In this framework, the measured ambipolar effect in silicene-based FET characterized by a relatively high mobility, points out to a complex physics at the silicene-silver interface, demanding for a deeper comprehension of its details on the atomic scale. The present work aims to elucidate the role of the Ag (111) metallic support in determining the physical properties of the Si/Ag two-dimensional interface, by means of optical techniques combined with theoretical calculations of the optical response of the supported system. The silicene/Ag (111) spectra, which turn out to be strongly non-additive, are analyzed in the framework of theoretical density functional based calculations allowing us to single out different contributions. Electronic transitions involving silver states are found to provide a huge contribution to the optical absorption of silicene on silver, compatible with a strong Si-Ag hybridization. The results point to a dimensionality-driven peculiar dielectric response of the two-dimensional-silicon/silver interface, which is confirmed by means of Transient-Reflectance spectroscopy. The latter shows a metallic-like carrier dynamics,(both for silicene and amorphous silicon), hence providing an optical demonstration of the strong …
Publication date: 
29 Sep 2015

E Cinquanta, G Fratesi, S dal Conte, C Grazianetti, F Scotognella, S Stagira, C Vozzi, G Onida, A Molle

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