Abstract
Carbon and silicon pentagonal low-dimensional structures attract a great interest as they may lead to new exotic phenomena such as topologically protected phases or increased spin–orbit effects. However, no pure pentagonal phase has yet been realized for any of them. Here we unveil through extensive density functional theory calculations and scanning tunnelling microscope simulations, confronted to key experimental facts, the hidden pentagonal nature of single- and double-strand chiral Si nano-ribbons perfectly aligned on Ag(110) surfaces whose structure has remained elusive for over a decade. Our study reveals an unprecedented one-dimensional Si atomic arrangement solely comprising almost perfect alternating pentagons residing in the missing row troughs of the reconstructed surface. We additionally characterize the precursor structure of the nano-ribbons, which consists of a Si cluster (nano-dot) occupying a silver di-vacancy in a quasi-hexagonal configuration. The system thus materializes a paradigmatic shift from a silicene-like packing to a pentagonal one.
Highlights
Carbon and silicon pentagonal low-dimensional structures attract a great interest as they may lead to new exotic phenomena such as topologically protected phases or increased spin–orbit effects
Further key information on the system is provided by the high-resolution Si atoms in the MR troughs (Sis)-2p core level photoemission spectrum for the doublestrand NRs (DNRs) displayed in Fig. 1g—that for the strand NR (SNR) is almost identical[24]
Inspired by the nano-dot Ag di-vacancy structure and by recent scanning tunnelling microscopy (STM) and grazing incidence X-ray diffraction measurements[26] pointing towards the existence of a missing row (MR) reconstruction along the [110] direction of the Ag surface, we considered several trial structures for the SNRs by placing Si atoms in the MR troughs (Sis) and adding further adatoms (Siad) on top, while maintaining a 2:1 concentration ratio between the two
Summary
Carbon and silicon pentagonal low-dimensional structures attract a great interest as they may lead to new exotic phenomena such as topologically protected phases or increased spin–orbit effects. Several theoretical studies have hypothesized stable Si pentagonal structures either in the form of one-dimensional (1D) nanotubes[5,6] or at the reconstructed edges of silicene nano-ribbons (NRs)[7,8] or even as hydrogenated penta-silicene[9] or highly corrugated fivefold coordinated siliconeet10 2D sheets, the latter recognized as a topological insulator[11]. Our analysis reveals that this system constitutes the first experimental evidence of a silicon phase solely comprising pentagonal rings. The possibilities that this unprecedented 1D topography opens are manyfold, ranging from Si-based nano-wires in circuits, enlarged spin–orbit effects or even the realization of a new Si allotrope
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