IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS1-TuP

Paper SS1-TuP6
Femtosecond Time-Resolved Photoemission Study of Two-Dimensional Layered Semiconductor MoS@sub 2@ Surface

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Semiconductor Surfaces Poster Session
Presenter: A. Tanaka, Tohoku University, Japan and University of Rochester
Authors: A. Tanaka, Tohoku University, Japan and University of Rochester
N.J. Watkins, University of Rochester
Y. Gao, University of Rochester
Correspondent: Click to Email
A femtosecond time-resolved two-photon photoemission study of 2H-MoS@sub 2@ surface has been carried out in order to investigate in detail the relaxation dynamics of hot electrons in the two-dimensional layered semiconductor. Among the lamellar transition metal dichalcogenides, MoS@sub 2@ is a semiconductor with an indirect gap of about 1.2 eV. The observed two-photon photoemission spectrum with a photon energy of 3.3 eV exhibits a single feature in the intermediate state energy between 2.1 and 3.3 eV above the valence-band maximum (i.e., between 0.9 and 2.1 eV above the conduction-band minimum). From the detailed time-resolved two-photon photoemission measurements as a function of electron excitation energy, it is found that the inverse relaxation lifetime of hot electrons depends linearly on the excess energy above the conduction-band minimum. This result is in strong contrast to the results based on the Fermi liquid theory, which takes into account the electron-electron scattering as the dominant relaxation process and gives the quadratic energy dependent lifetime in the both three- and two-dimensional electron systems within logarithmic corrections. From these results, we discuss the relaxation process of hot electrons in the two-dimensional layered semiconductor.