University of Kansas, USA
In this seminar, recent studied on optical and electronic properties of two-dimensional materials by ultrafast laser spectroscopy will be presented. Two-dimensional materials, such as graphene, MoS2, WS2, and black phosphorus are promising materials for future electronic and optoelectronic applications. As a powerful experimental method with high time resolution, ultrafast laser spectroscopy has been used to study two-dimensional materials by many groups worldwide. Several topics will be discussed in this seminar. First, we will present studies of nonlinear optical properties of two-dimensional materials, such as second harmonic generation and two-photon absorption. The former allows detection of the crystal orientation and symmetry of two-dimensional monolayers while the latter can measure the optical bandgap of exciton binding energy of two-dimensional materials. Second, transient absorption microscopy technique will be discussed, which has been used to study photocarrier and exciton dynamics. Third, all-optical injection of ballistic currents in ReS2 studies of the ballistic charge transport will be introduced. Fourth, by performing transient absorption measurements with polarization resolution, spin and valley dynamics of excitons will be discussed. Finally, by performing transient absorption measurements with layer selectivity, we revealed ultrafast electron transfer in hetero-materials formed by stacking two or more two-dimensional materials together. These ultrafast laser measurements of two-dimensional materials and their heterostructures revealed fundamental electronic and optical properties of these materials that are important for their applications as new forms of functional materials.