title: Electron and Phonon Dynamics in Hexagonal Pd Nanosheets and Ag/Pd/Ag Sandwich Nanoplates.
abstract: Pd and its hybrid nanostructures have attracted considerable attention over the past decade, with both catalytic and plasmonic properties. The electron and phonon properties directly govern conversion efficiencies in applications such as energy collectors and photocatalysts. We report the dynamic processes of electron-phonon coupling and coherent acoustic phonon vibration in hexagonal Pd nanosheets and Ag/Pd/Ag sandwich nanoplates using transient absorption spectroscopy. The electron-phonon coupling constant of Pd nanosheets, GPd-nanosheet(8.7 × 1017W/(m3·K)) is larger than that of the bulk GPd(5.0 × 1017W/(m3·K)). The effective coupling constant Geffof Ag/Pd/Ag nanoplates decreases with increasing Ag shell thickness, finally approaching the bulk GAg. The variation of Geffis explained in terms of reduced density of states near Fermi level of Pd nanosheets with 1.8 nm ultrathin thickness. Coherent acoustic phonon vibration in Pd nanosheets is assigned to a fundamental breathing mode, similar to the vibration of benzene. The period increases with increasing Ag shell thickness. For Ag/Pd/Ag nanoplates with 20 nm thick Ag shells, the vibrational mode is ascribed to a quasi-extensional mode. The results show that the modes of the coherent acoustic phonon vibration transform with the geometric variation of Pd nanosheets and Ag/Pd/Ag nanoplates. Our results represent an understanding of quantum-confinement related electron dynamics and bulk-like phonon kinetics in the ultrathin Pd nanosheets and their hybrid nanostructures.
authors.affiliation: Department of Chemistry, School of Science and Technology, Kwansei Gakuin University , Sanda 669-1337, Japan.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Chemistry, School of Science and Technology, Kwansei Gakuin University , Sanda 669-1337, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Sagaguchi
authors.affiliation: Department of Chemistry, School of Science and Technology, Kwansei Gakuin University , Sanda 669-1337, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Okuhata
authors.affiliation: Department of Chemistry, School of Science and Technology, Kwansei Gakuin University , Sanda 669-1337, Japan.
authors.forename: Motohiro
authors.initials: M
authors.lastname: Tsuboi
authors.affiliation: Department of Chemistry, School of Science and Technology, Kwansei Gakuin University , Sanda 669-1337, Japan.
authors.forename: Naoto
authors.identifier: 0000-0002-7343-6564
authors.initials: N
authors.lastname: Tamai
keywords: Pd nanosheet; coherent acoustic phonon vibration; electron−phonon coupling; electron−surface scattering; localized surface plasmon resonance; nanoplate; transient absorption spectroscopy