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O: Fachverband Oberflächenphysik

O 57: 2D Materials beyond Graphene: TMDCs, Slicene and Relatives

O 57.6: Vortrag

Mittwoch, 18. März 2015, 16:30–16:45, MA 005

Hot electron dynamics at 2H-MoS₂ surfaces: Time- and angle-resolved photoelectron spectroscopy results — •Petra Hein, Ankatrin Stange, Kerstin Hanff, Gerald Rohde, Michael Bauer, and Kai Rossnagel — Institute of Experimental and Applied Physics, University of Kiel, Germany

Recent research on the layered semiconductor 2H-MoS₂ has been concentrated on MoS₂ monolayers: In contrast to the bulk crystal, MoS₂ monolayers are direct bandgap semiconductors without an inversion center, making them an appropriate material for valleytronic devices with hot carrier lifetimes in the picosecond regime. However, 2H-MoS₂ surfaces could be equally exciting: Due to the symmetry breaking at the surface or a decoupling of the topmost sandwich, similarities to monolayers seem possible. For an investigation of this system, time- and angle-resolved photoelectron spectroscopy is the method of choice, as it provides high surface sensitivity and momentum resolution, while enabling us to map electronic processes on their fundamental time scales. Here, we present a k^→-resolved study of the transient photoelectron intensity in the conduction band after excitation of 2H-MoS₂ surfaces with 3.2 eV pump pulses. Momentum-dependent intensity rise times between 30 fs and 150 fs and decay times of several 100 fs allow us to identify direct electronic excitations and to track the electrons’ relaxation pathway into the lowest energy states. The conduction band minima are finally depopulated within ∼1 ps. Possible explanations for this observation – such as diffusion processes, optical electron-hole recombination and trapping in defect states – are discussed.