< BK21+ BEST Seminar Series Announcement> 

Time and Date : 16:00 ~ 17:00 Tuesday 07/02/2019

Place : B201, Engineering Building #2

Title : Van der Waals contacts and single atom vacancy catalysis on 2D Materials
Abstract:
I will describe the realization of ultra-clean vdW contacts between 3D metals and single layer MoS2. Using scanning transmission electron microscopy (STEM) imaging, we show that the 3D metal and 2D MoS2 interface is atomically sharp with no detectable chemical interaction, suggesting van-der-Waals-type bonding between the metal and MoS2. We show that the contact resistance of indium electrodes is ~ 800 Ω-μm – amongst the lowest observed for metal electrodes on MoS2 and is translated into high performance FETs with mobility in excess of 160 cm2-V-s-1 at room temperature without encapsulation. We also demonstrate low contact resistance of 220 Ω-μm on 2D NbS2 and near ideal band offsets, indicative of defect free interfaces, in WS2 and WSe2. I will introduce 2D TMDs and their properties and then describe our efforts on making good contacts on 2D semiconductors.

I will also report catalytic activity from precise number of atomic sulfur vacancy active sites on 2D MoS2. By rationally introducing known concentration of sulfur vacancies and measuring their catalytic activity using micro-electrochemical cells, we have extracted the activity of a single sulfur vacancy. We find that the catalytic activity per vacancy increases with their concentration – reaching the best performance at 5.4 x 1014 cm-2 where the intrinsic turn over frequency (TOF) and Tafel slope of a single atomic vacancy was found to be ~ 6 s-1 and 38 mV/dec, respectively. Our methodology is general and in principle can be used to determine the activity of atomic sites in catalysts for a variety of reactions.

Presenter: Manish Chhowalla, Professor of Materials Science & Metallurgy, University of Cambridge & ACS Nano Associated Editor

Host: Prof. Ahn, Jonghyun, Yonsei EEE