Center for Functional Nanomaterials Seminar

"Multimode spectromicroscopic study of two-dimensional quantum materials"

Presented by Abdullah Al-Mahboob, Energy Sciences Institute, Yale University

Tuesday, August 16, 2022, 10:00 am — Videoconference / Virtual Event (see link below)

The research on Two-Dimensional Quantum Materials (2DQM) received central attention in both theoretical and experimental physics. These materials have potential for technological applications including quantum computing and novel optoelectronic devices. Among 2DQM, graphene (Gr) is a material of special interest. This interest originated not only from well-known Gr stability at ambient conditions, massless Dirac carrier characteristics and feasibility of roll-to-roll production, but also successful use of Gr as a template for other 2DQM.

Recently Transition Metal Dichalcogenides (TMDs) have emerged as promising candidates for "2DQM beyond Graphene". TMDs can find application as materials for valleytronics and optoelectronics. TMDs are available for wide ranges of valence to conduction energy-band gaps, covering from infrared to visible range of the solar spectrum and thus exhibit a huge tunability of optoelectronic properties. However, a limiting factor of TMD's application is their poor light conversion efficiency due to the direct to indirect inter-band transition and low quantum yield in electro/photoluminescence (PL).

In this report, interface chemistry for tuning electronic properties of graphene and growth 2DQM and PL enhancement in TMDs via excitonic energy transfer in heterostructure (HS) will be presented.
The first part of the presentation will outline in-situ Low-Energy Electron Microscopy/ Photoelectron Emission Microscopy (LEEM/PEEM) and Angle-Resolved Photoelectron Emission Spectroscopy (ARPES) study of interface chemistry and interface epitaxy which aims at tuning the electronic properties of Gr grown on Ru(0001) and of silicon allotropes & 2D silica grown at the Gr/Ru interface.

In the second part, time-and momentum-resolved ultrafast PEEM-based direct visualization of dark excitons and valley dynamics in TMDs will be discussed. Also, excitonic and valley-mediated energy transfer in TMD HSs studied by photoluminescence spectroscopy and low-temperature photoluminescence excitation spectroscopy will be presented. TMD HSs leads to novel optical transitions associated with the dark excitonic process. The huge enhancement in PL at heterostructure made of direct band gap TMD-insulator-indirect band gap TMD is observed. The observed PL enhancement could be explained by considering the fact that the electronic excitation energy of dark exciton in the materials having optically forbidden conduction valleys (i.e. valleys outside the light cone of valance band maxima forming optically dark exciton), is being transferred across TMD layers separated even by few tens of nanometer creating excitons in another layer of 2D materials.

Hosted by: Dario Stacchiola

Videoconference Instructions

Topic: CFN Virtual Seminar: Abdullah Al-Mahboob Time: Aug 16, 2022 10:00 AM Eastern Time (US and Canada) Join ZoomGov Meeting https://bnl.zoomgov.com/j/1619330111?pwd=cGtySGpLTCtsaTkwSUxsUzl0UUU2UT09 Meeting ID: 161 933 0111 Passcode: 779434 One tap mobile +16692545252,,1619330111#,,,,*779434# US (San Jose) +16468287666,,1619330111#,,,,*779434# US (New York) Dial by your location +1 669 254 5252 US (San Jose) +1 646 828 7666 US (New York) +1 669 216 1590 US (San Jose) +1 551 285 1373 US Meeting ID: 161 933 0111 Passcode: 779434 Find your local number: https://bnl.zoomgov.com/u/abCR9sJDY Join by SIP 1619330111@sip.zoomgov.com Join by H.323 161.199.138.10 (US West) 161.199.136.10 (US East) Meeting ID: 161 933 0111 Passcode: 779434

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