Scanning Tunneling Microscopy Study of 2D Silicon Nanosheets on Ag(111) Thin Film Heterostructures*

Two dimensional (2D) materials have gained interest as promising building blocks for novel 2D electronic devices. Silicon has ruled the electronics industry to date, therefore it is natural to consider 2D silicon nanosheets for next generation device design. Silicene, a single atomic sheet of Si, was proposed and successfully fabricated on single crystalline Ag surfaces. Here we report silicon nanosheet synthesis on a thin film Ag-Si(111) substrate using molecular being epitaxy (MBE). Using scanning tunneling microscopy and spectroscopy, the electronic and atomic structure of this 2D silicon nanosheet is clearly shown. The electronic structure surprisingly shows an insulating band gap for the silicon nanosheet, contrary to the electronic behavior of silicene and bulk silicon counterparts. Interestingly, the dI/dV spectra within the bandgap of the silicon nanosheet displays Ag(111) surface states. In addition, we report novel moiré and LEED patterns for this Si-Ag(111) heterostructure. Importantly, the bandgap of the silicon nanosheet is clearly modulated by the moiré pattern. Finally, we explore growth of different coverage nanosheets and multilayer silicon nanostructures using a two-step MBE growth method.