ECE Colloquium - Hsun-Jen Chuang, Naval Research Laboratory

Wed, 10/17/2018 - 10:00am
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Location: 
CoRE Lecture Hall

 

ECE Colloquium

Dr. Hsun-Jen Chuang
ASEE Postdoctoral Fellow
Naval Research Laboratory

Abstract: Van der Waals heterostructures (vdWHs) is an emergent new class of heterostructures where monolayer semiconductors such as transition metal dichalcogenides (TMDs) are mechanically transferred and stacked in any arbitrary order. One unique property that arise from such heterostructures is an interlayer exciton (ILE), a spatially indirect electron-hole pair with the electron in one TMD layer and the hole in the other. However, the observation of such ILE had been rare, likely due to the contaminants trapped between layers during the transfer process. Here, using a clean dry transfer method as well as a new “nano-squeegee” technique utilizing an atomic force microscopy (AFM) tip, we create MoSe2/WSe2 heterostructures encapsulated in hBN with clean interfaces. We observe ILE emission around 1.35 eV at room temperature which can be clearly resolved into two distinct peaks (ILE1 and ILE2) separated by 24 meV at zero field at 5 K. Interestingly, these two emissions also exhibit opposite circular polarizations: up to +20% for ILE1 and -40% for ILE2 when excited with circularly polarized light. Ab initio calculations indicate that this is a result of the doubly indirect character of both electronic transitions: they are indirect in both real and reciprocal space, contrary to previous belief, split by relativistic effects.

Biography: Dr. Hsun-Jen Chuang is currently an ASEE postdoctoral fellow at the Naval Research Laboratory in Washington D.C., working with Dr. Berry Jonker in the Materials Science and Technology Division. Dr. Chuang received his Ph.D. in Physics from Wayne State University in 2016, after a M.Sc. from Western Illinois University in 2011 and B.Sc. from Chinese Culture University in 2006 in Taiwan. His research focuses on exploring the novel optical and electrical properties of layered two-dimensional semiconducting materials such as transition metal dichalcogenides (TMDs) and their heterostructures for the electronics applications, where he has developed clean dry transfer methods, as well as a “nano-squeegee” technique that utilizes an atomic force microscope tip to create clean interface. Dr. Chuang has published 15 papers, and received the Best Thesis Award at Wayne State in 2016, Best Postdoctoral Poster Award at the Naval Research Laboratory in 2017, and several poster awards at scientific conferences.