University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Tuesday, July 7th 2015
Speaker: Kyunghoon Lee, University of Michigan
Subject: Electron transport in two-dimensional materials: Graphene and beyond

Owing to their unique energy band structure and the ease of material synthesis, two dimensional nanomaterials, such as graphene, have become the ideal platform for observing novel electron transport phenomena. In particular, low energy quasiparticles in monolayer graphene behave like massless Dirac fermions, which have led to observations of many interesting phenomena, including Klein tunneling, anomalous Quantum Hall effect, etc. In contrast to the monolayer graphene, quasiparticles in bilayer graphene (BLG) are massive chiral fermions due to its parabolic band structure. Thus, BLG also gives a number of intriguing properties which are very different from those of monolayer graphene, including tunable band gap opening and anti-Klein tunneling, arising from chiral characteristics of charge carriers. However, unlike SLG, experimental works on chiral electron transport in BLG have received less attention.

In addition, other two-dimensional atomic layer crystals, such as atomically thin layered transition metal dichalcogenides (TMDCs), are also attractive material platform with unique electronic and optical properties, including indirect to direct band gap transition, and valley polarized carrier transport. However, study of the low temperature electron transport in atomic thin layered TMDCs is still in its infancy. One of the major hurdles for electron transport study lies in the large metal/semiconductor junction barrier for carrier injection, which leads to the contact resistance dominated charge transport in short channel nanoscale devices.

In this talk, I will show our first demonstrated successful synthesis of wafer scale BLG with high-homogeneity by low-pressure chemical vapor deposition (CVD). Next, I’ll discuss about the importance of chiral electron transport in BLG. I’ll present the signature of electronic cloaking effect with anti-Klein effect as a manifestation of chirality by probing phase coherent transport behavior in CVD bilayer graphene nanostructure. Finally, I’ll talk on the electron transport in two-dimensional TMDCs. I successfully fabricated monolayer MoS2 single electron transistors using low work function metal for the contact electrodes, and observed Coulomb blockade phenomena attributed to single electron charging on a fairly clean quantum dot.

Faculty Host: Vlad Pribiag

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