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Title: Atomic-Level Structure Determines Electron-Phonon Scattering Rates in 2-D Polar Metal Heterostructures
Authors: Steves, Megan A
Rajabpour, Siavash
Wang, Ke
Dong, Chengye
He, Wen
Quek, Su Ying 
Robinson, Joshua A
Knappenberger, Kenneth L
Keywords: Science & Technology
Physical Sciences
Chemistry, Multidisciplinary
Chemistry, Physical
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Science & Technology - Other Topics
Materials Science
2-D materials
electron dynamics
electron-phonon coupling
nonlinear optical microscopy
correlative microscopy
Issue Date: 23-Nov-2021
Citation: Steves, Megan A, Rajabpour, Siavash, Wang, Ke, Dong, Chengye, He, Wen, Quek, Su Ying, Robinson, Joshua A, Knappenberger, Kenneth L (2021-11-23). Atomic-Level Structure Determines Electron-Phonon Scattering Rates in 2-D Polar Metal Heterostructures. ACS NANO 15 (11) : 17780-17789. ScholarBank@NUS Repository.
Abstract: The electron dynamics of atomically thin 2-D polar metal heterostructures, which consisted of a few crystalline metal atomic layers intercalated between hexagonal silicon carbide and graphene grown from the silicon carbide, were studied using nearly degenerate transient absorption spectroscopy. Optical pumping created charge carriers in both the 2-D metals and graphene components. Wavelength-dependent probing suggests that graphene-to-metal carrier transfer occurred on a sub-picosecond time scale. Following rapid (<300 fs) carrier-carrier scattering, charge carriers monitored through the metal interband transition relaxed through several consecutive cooling mechanisms that included sub-picosecond carrier-phonon scattering and dissipation to the silicon carbide substrate over tens of picoseconds. By studying 2-D In, 2-D Ga, and a Ga/In alloy, we resolved accelerated electron-phonon scattering rates upon alloy formation as well as structural influences on the excitation of in-plane phonon shear modes. More rapid cooling in alloys is attributed to increased lattice disorder, which was observed through correlative polarization-resolved second harmonic generation and electron microscopy. This connection between the electronic relaxation rates, far-field optical responses, and metal lattice disorder is made possible by the intimate relation between nonlinear optical properties and atomic-level structure in these materials. These studies provided insights into electronic carrier dynamics in 2-D crystalline elemental metals, including resolving contributions from specific components of a 2-D metal-containing heterojunction. The correlative ultrafast spectroscopy and nonlinear microscopy results suggest that the energy dissipation rates can be tuned through atomic-level structures.
Source Title: ACS NANO
ISSN: 19360851
DOI: 10.1021/acsnano.1c05944
Appears in Collections:Staff Publications

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