Structure-Dependent Electronic Relaxation Dynamics of Two-Dimensional Silver Monolayers.

Liu, Matthew W-J; Ulman, Kanchan Ajit; Zheng, Boyang; Jain, Arpit; Heintzelman, Daniel J; Wang, Ke; He, Wen; Dong, Chengye et al. · Nano Lett · 2025

basic_science · Level V

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Abstract

The electronic relaxation dynamics of two-dimensional silver polar metal heterostructures (2D-PMets), isolated with two different Ag lattice structures, were studied with femtosecond transient absorption (fs-TA) spectroscopy. The two 2D Ag phases, called Ag<sub>(1)</sub> and Ag<sub>(2)</sub>, differ in atomic packing density, which leads to phase-specific ultralow frequency (ULF) phonon modes and visible electronic absorption transitions. Time-resolved kinetic traces for both phases were fit to a biexponential decay function, with the first decay component pertaining to ultrafast electronic relaxation and the second corresponding to carrier-phonon scattering. The first decay time constant τ<sub>1</sub> is <400 fs for both phases. In contrast, carrier-phonon scattering exhibited lattice-specific and excitation wavelength-independent relaxation time constants; τ<sub>2</sub> ∼ 2 ps for Ag<sub>(1)</sub> and ∼ 1 ps for Ag<sub>(2)</sub>. The shorter τ<sub>2</sub> in Ag<sub>(2)</sub> is attributed to increased carrier-phonon scattering probability in more close-packed lateral structures. The results indicate that atomic-level structure controls energy flow in spatially confined 2D materials.