Si-Ag 2√3×2√3R(30°) Surface Alloy Versus Silicene on Ag(111)

Artificial, honeycomb-like 2D mono-elemental materials beyond graphene, from groups III<br/>(B-, Ga, -ene), to groups IV (Si-, Ge-, Sn-, Pb-ene), V (P-, As-, Sb-, Bi-ene) and VI (Se-, Te-ene), have been in spectacular blossom since 2012 [1-5], after the demonstration of the synthesis of silicene on Ag(111) at ~220° C in its striking flower-shaped archetype structure corresponding to a corrugated 3×3 reconstructed silicene sheet matching a 4×4 silver supercell [6]. This achievement was of the utmost importance because silicene is the prototype of a 2D topological insulator.<br/>The debated 2√3×2√3R(30°) superstructure formed upon Si deposition onto Ag(111) at<br/>higher temperatures (~300° C) displays a highly defected honeycomb structure in STM imaging, which has been sometimes assigned to a pure silicene, or, instead, to a fating Si overlayer [7,8].<br/>Herein, angle-resolved photoelectron spectroscopy results and density functional theory<br/>calculations, favour a new interpretation of the 2√3×2√3R(30°) reconstruction in terms of a Si-Ag surface alloy driven by silicon dissolution into the silver sub-surface, through substitutional Si-Ag<br/>sites.<br/>[1] Zhao J. et al., Progress in Materials Science 83, 24 (2016).<br/>[2] J. Yuhara and G. Le Lay, Japanese Journal of Applied Physics 59, SN0801 (2020).<br/>[3] A. Fleurence et al., Phys. Rev. Lett. 108, 245501 (2012).<br/>[4] C.-L. Lin et al., Phys. Rev. Lett. 110, 076801 (2013).<br/>[5] J. Sone et al., New Journal of Physics 16, 095004 (2014).<br/>[6] P. Vogt et al., Phys. Rev Lett. 108, 155501 (2012).<br/>[7] Jamgotchian H. et al., J. Phys.: Condens. Matter 24, 172001 (2012).<br/>[8] Z.-L. Liu et al., APL Materials 2, 092513 (2014).