AVS 66th International Symposium & Exhibition
    2D Materials Tuesday Sessions
       Session 2D+AS+MI+NS-TuM

Paper 2D+AS+MI+NS-TuM6
Continuous Silicene, Silicene Ribbons and Surface Reconstructions on h-MoSi2

Tuesday, October 22, 2019, 9:40 am, Room A216

Session: 2D Materials Characterization including Microscopy and Spectroscopy
Presenter: Anna Costine, University of Virginia
Authors: A. Costine, University of Virginia
C. Volders, University of Virginia
M. Fu, Oak Ridge National Laboratory
P. Reinke, University of Virginia
Correspondent: Click to Email
Silicene has emerged as a 2D material of interest because of its spin -orbit coupling, tunable electronic structure, and Dirac type behavior. Synthesis of silicene with preserved Dirac-type electronic structure has proven challenging, but is critical to realizing theoretically predicted quantum states and devices. To date, Ag(111) remains the most popular substrate for silicene synthesis, but is discussed controversially due to its similarity with surface alloys. Silicene has also been synthesized on other substrates including Ir, IrSi3, and ZrB2. Silicene synthesis on a semiconducting substrate with a low buckling conformation to conserve the Dirac-type behavior would be ideal. The synthesis of silicene on new substrates that allow for direct device integration is an important next step.

We developed an alternate approach to silicene synthesis that allows for silicene synthesis on semiconducting silicides. The (0001) surface of h-MoSi2 has hexagonal symmetry and a lattice constant close to that of silicene. Our recent measurements support the assumption that silicene is electronically decoupled from the substrate. The h-MoSi2 crystallites, which are terminated by the (0001) plane are grown by depositing Mo onto a Si (001) or Si(111) surface. Upon annealing to ~800℃, the Si atoms decouple from the underlying surface and form a weakly buckled silicene layer with the √3 x√3 surface as seen by STM.

Our recent work expands this study and uses STM/S at 77 K to achieve a comprehensive description of silicene-on-silicide. The amount of Mo deposited (0.3 nm - 18 nm) and annealing temperature (700- 1000℃) were varied. All surface structures discussed here are on h-MoSi2 crystallites in the (0001) plane,. Three distinct surface structures coexist - silicene ribbons , a 4x4 reconstruction, and a complex reconstruction which is very sensitive to variations in the bias voltage. The electronic structure of silicene-ribbons shows a V-shaped density of states close to EF, indicative of Dirac-like behavior, while the other reconstructions are semiconducting. The surface and electronic structures observed on h-MoSi2 crystallites as a function of the synthesis conditions will be discussed. The preference for silicene-ribbons in the low T STM/STS measurements is currently attributed to a faster post-deposition cooling rate, but the exact mechanism is still open to debate. We will present a detailed discussion of the electronic structure of silicene and silicene ribbons, and suggest mechanisms for the transition from the (0001) surface to silicene. Our goal is to develop synthesis approaches suitable for device integration of both silicene conformations.