title: Vibrational mismatch of metal leads controls thermal conductance of self-assembled monolayer junctions.
abstract: We present measurements of the thermal conductance of self-assembled monolayer (SAM) junctions formed between metal leads (Au, Ag, Pt, and Pd) with mismatched phonon spectra. The thermal conductance obtained from frequency domain thermoreflectance experiments is 65 ± 7 MW/m(2) K for matched Au-alkanedithiol-Au junctions, while the mismatched Au-alkanedithiol-Pd junctions yield a thermal conductance of 36 ± 3 MW/m(2) K. The experimental observation that junction thermal conductance (per molecule) decreases as the mismatch between the lead vibrational spectra increases, paired with results from molecular dynamics (MD) simulations, suggest that phonons scatter elastically at the metal-SAM interfaces. Furthermore, we resolve a known discrepancy between measurements and MD predictions of SAM thermal conductance by using a contact mechanics model to predict 54 ± 15% areal contact in the Au-alkanedithiol-Au experimental junction. This incomplete contact obscures the actual junction thermal conductance of 115 ± 22 MW/m(2) K, which is comparable to that of metal-dielectric interfaces.
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Shubhaditya
authors.initials: S
authors.lastname: Majumdar
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Jonatan A
authors.initials: JA
authors.lastname: Sierra-Suarez
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Scott N
authors.initials: SN
authors.lastname: Schiffres
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Wee-Liat
authors.initials: WL
authors.lastname: Ong
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: C Fred
authors.initials: CF
authors.lastname: Higgs
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Alan J H
authors.initials: AJ
authors.lastname: McGaughey
authors.affiliation: †Department of Mechanical Engineering, ‡Department of Electrical and Computer Engineering, and §Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh 15213, United States.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Malen
keywords: Nanoscale; molecular dynamics; molecular junctions; self-assembly; thermal transport; thermoreflectance