Probing photoresponsivity and thermal transports in few-layer vdW materials using ultrafast laser spectroscopy


Title:Probing photoresponsivity and thermal transports in few-layer vdW materials using ultrafast laser spectroscopy

Speaker: Prof. Xiaohui Qiu

Time:  October 23, Tuesday, 2018, 10:00 am

Location: Communication Building 818 Conference Room, Shahe Campus, UESTC.


Abstract:

I will introduce two recent experiments conducted in my group aiming at understanding the ultrahigh photoresponsivity of In2Se3 ultrathin films and the cross-plane thermal transport through Au/graphene/Au heterostructure. (I) Photodetectors based on a-phase In2Se3 ultrathin films exhibit unusually high photoresponsivity compared to many other two dimensional (2D) materials, such as MoS2. To understand the underlying mechanism, we investigate the exciton dynamics of In2Se3 nanoplates with thickness in the range from 11 nm to 40 nm. Our measurements show that all key parameters determining the photoresponse behavior of these In2Se3 samples are similar to those of MoS2. We thus suggest that the interface effect, i.e. photogating as well as proximity effect of metal electrode contact, might be responsible for the dramatic photoresponsivity reported for two dimensional material-based optoelectronic devices. (II) Heat transport and thermal conductance at the nanometer scale are critical issues for the emerging nanoelectronic devices. Here we employ the transient thermoreflectance approach to measure the cross-plane thermal conductance across the Au/graphene/Au heterostructure. The two orders of magnitude increase of thermal conductance through bilayer graphene as compared to monolayer graphene reveals electron direct transmission dominates the heat conduction through Au/monolayer graphene/Au structure. While for two-layer graphene or thicker films, phonon transmission might be the major contributor for heat conduction.





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