Journal
ACS NANO
Volume 8, Issue 7, Pages 7538-7547Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn503000w
Keywords
two-dimensional materials; silicene; surface reconstruction; scanning tunneling microscopy; molecular beam epitaxy
Categories
Funding
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility [DE-AC02-06CH11357]
- National Science Foundation [DGE-0824162]
- U.S. Department of Energy SISGR [DE-FG02-09ER16109]
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Having fueled the microelectronics industry for over 50 years, silicon is arguably the most studied and influential semiconductor. With the recent emergence of two-dimensional (2D) materials (e.g., graphene, MoS2, phosphorene, etc.), it is natural to contemplate the behavior of Si in the 2D limit. Guided by atomic-scale studies utilizing ultrahigh vacuum (UHV), scanning tunneling microscopy (STM), and spectroscopy (STS), we have investigated the 2D limits of Si growth on Ag(111). In contrast to previous reports of a distinct sp(2)-bonded silicene allotrope, we observe the evolution of apparent surface alloys (ordered 2D silicon-Ag surface phases), which culminate in the precipitation of crystalline, sp(3)-bonded Si(111) nanosheets. These nanosheets are capped with a root 3 honeycomb phase that is isostnxtural to a root 3 honeycomb-chained-trimer (HCT) reconstruction of Ag on 54111). Further investigations reveal evidence for silicon intermixing with the Ag(111) substrate followed by surface precipitation of crystalline, sp(3)-bonded silicon nanosheets. These conclusions are corroborated by ex situ atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Even at the 2D limit, scanning tunneling spectroscopy shows that the sp(3)-bonded silicon nanosheets exhibit semiconducting electronic properties.
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