Band Bending and Valence Band Quantization at Line Defects in MoS2.

The variation of the electronic structure normal to 1D defects in quasi-freestanding MoS2, grown by molecular beam epitaxy, is investigated through high resolution scanning tunneling spectroscopy at 5K. Strong upwards bending of valence and conduction bands towards the line defects is found for the 4|4E mirror twin boundary and island edges, but not for the 4|4P mirror twin boundary. Quantized energy levels in the valence band are observed wherever upwards band bending takes place. Focusing on the common 4|4E mirror twin boundary, density functional theory calculations give an estimate of its charging, which agrees well with electrostatic modelling. We show that the line charge can also be assessed from the filling of the boundary-localized electronic band and the charge induced by the polarization discontinuity across the defect. These calculations elucidate the origin of band bending and charging at these 1D defects in Mo2. The 4|4E mirror twin boundary not only impairs charge transport of electrons and holes due to band bending, but holes are additionally subject to a large potential barrier, which is inferred from the independence of the quantized energy landscape on each side of the boundary.

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