Many of graphene's remarkable properties arise from its linear dispersion of the electronic states, forming a Dirac cone at the K points of the Brillouin zone. Silicene, the 2D allotrope of silicon, is also predicted to show a similar electronic band structure, with the addition of a tunable bandgap, induced by spin-orbit coupling. Because of these outstanding electronic properties, silicene is considered as a promising building block for next-generation electronic devices. Recently, it has been shown that silicene grown on Au(111) still possesses a Dirac cone, despite the interaction with the substrate. Here, to fully characterize the structure of this 2D material, we investigate the vibrational spectrum of a monolayer silicene grown on Au(111) by polarized Raman spectroscopy. To enable a detailed ex situ investigation, we passivated the silicene on Au(111) by encapsulating it under few layers hBN or graphene flakes. The observed spectrum is characterized by vibrational modes that are strongly red-shifted with respect to the ones expected for freestanding silicene. By comparing low-energy electron diffraction (LEED) patterns and Raman results with first-principles calculations, we show that the vibrational modes indicate a highly (>7%) biaxially strained silicene phase.

CEITEC BUT Brno University of Technology Purkyňova 123 612 00 Brno Czech Republic

Infineon Technologies Austria AG Siemensstraße 2 9500 Villach Austria

Institut de Ciència de Materials de Barcelona ICMAB CSIC Campus UAB 08193 Bellaterra Spain

Institute of Chemical Technologies and Analytics Technische Universität Wien Getreidemarkt 9 1060 Vienna Austria

Institute of Physical Engineering Brno University of Technology Technická 2 616 69 Brno Czech Republic

Institute of Solid State Electronics Technische Universität Wien Gußhausstraße 25 25a 1040 Vienna Austria

International Center for Materials Nanoarchitectonics National Institute for Materials Science 1 1 Namiki Tsukuba 305 0044 Japan

Research Center for Functional Materials National Institute for Materials Science 1 1 Namiki Tsukuba 305 0044 Japan

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