π-Conjugation in Epitaxial Si(111)-($\sqrt{3}$$\times$$\sqrt{3}$) Surface: an Unconventional "Bamboo Hat" Bonding Geometry for Si

Abstract

The newly observed ($\sqrt{3}$$\times$$\sqrt{3}$) surface reconstruction in heteroepitaxial Si(111) thin films on metal substrates is widely considered as a promising platform to realize 2D Dirac and topological states, yet its formation mechanism and structural stability are poorly understood, leading to the controversial terminology of "multilayer silicene". Based on valence bond and conjugation theory, we propose a π-conjugation plus charge-transfer model to elucidate such a unique "bamboo hat" surface geometry. The formation of planar ring-shaped π-conjugation and charge transfer from the rings to upper buckled Si atoms greatly lower the surface dangling bond energy. We justify this unconventional Si structural model by analyzing from first-principles surface energies and surface stress tensors as a function of strain. Within the same formalism, additional metastable surface reconstructions with the similar "bamboo hat" features are predicted which opens possibilities to other exotic electronic states in silicon.

References in corpus (10)

• Two and one-dimensional honeycomb structures of silicon and germanium
• Silicon Quantum Electronics
• Evidence for Dirac Fermions in a honeycomb lattice based on silicon
• Spontaneous Symmetry Breaking and Dynamic Phase Transition in Monolayer Silicene
• Epitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface
• Local Reconstructions of Silicene Induced by Adatoms
• Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling
• Silicite: the layered allotrope of silicon
• New Phases of Germanene
• Crossover between Silicene and Ultra-Thin Si Atomic Layers on Ag(111) Surfaces

Cited by in corpus (1)

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