Center for Correlated Electron Systems

Seminar

Optical Spectroscopy on Atomically Thin Two-Dimensional Semiconductor Crystals

February 5, 2016l Hit 1057
Date : February 12, 2016 15:00 ~ 16:00
Speaker : Dr. Jonghwan Kim (UC Berkeley & Material Science Division, LBNL)
Location : Bldg. 19, Rm. 210
Atomically thin two-dimensional semiconductor crystals have recently emerged as a new class of nanomaterials with remarkable properties that hold great promise for electronic and photonic technology. Here, I utilize optical spectroscopy techniques to investigate fascinating optoelectronic properties of few-layer phosphorene and transition metal dichalcogenide MX2 (M= Mo, W; X= S, Se). First, optical absorption spectroscopy reveals the direct band gap structure of phosphorene which sensitively depend on the layer number. Direct band gap of few-layer phosphorene match well with technologically important frequencies at infrared range such as silicon band gap and telecom frequency, which potentially leads to interesting optoelectronic applications. Second, I demonstrate that circularly-polarized femtosecond pulse enables ultrafast and efficient control of valley exciton states in WSe2 monolayers via optical Stark effect. In analogy to spintronics, such control can open up an exciting opportunity for valley states as an information carrier. Lastly, I employ transient absorption spectroscopy to investigate charge transfer process in MoS2/WS2 heterostructure. Observed charge transfer rate is remarkably fast (~ 50 fs), which indicates promising potential as energy harvesting application.