Electron dynamics in MoS-graphite heterostructures.

The electron dynamics in heterostructures formed by multilayer graphite and monolayer or bulk MoS were studied by femtosecond transient absorption measurements. Samples of monolayer MoS-multilayer graphite and bulk MoS-multilayer graphite were fabricated by exfoliation and dry transfer techniques. Ultrafast laser pulses were used to inject electron-hole pairs into monolayer or bulk MoS. The transfer of these photocarriers to the adjacent multilayer graphite was time resolved by measuring the differential reflection of a probe pulse. We found that photocarriers injected into monolayer MoS transfer to graphite on an ultrafast time scale shorter than 400 fs. Such an efficient charge transfer is key to the development of high performance optoelectronic devices with MoS as the light absorbing layer and graphite as electrodes. The absorption coefficient of monolayer MoS can be controlled by the carriers in graphite. This process can be used for interlayer coupling and control. In a bulk MoS-graphite heterostructure, the photocarrier transfer time is about 220 ps, due to the inefficient interlayer charge transport in bulk MoS. These results provide useful information for developing optoelectronic devices based on MoS-graphite heterostructures.