Nanometals: Identifying the onset of metallic relaxation dynamics in monolayer-protected gold clusters using femtosecond spectroscopy

Chongyue Yi, Hongjun Zheng, Laura M. Tvedte, Christopher J. Ackerson, Kenneth L. Knappenberger

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

Electronic relaxation dynamics were studied for a series of gold monolayer-protected clusters (MPCs) whose sizes ranged from 1.5 to 2.4 nm. Au96(mMBA)42, Au102(pMBA)44, Au115(pMBA)49, Au117(mMBA)50, Au144(pMBA)60, Au250(pMBA)98, and Au459(pMBA)170 (pMBA = para-mercaptobenzoic acid; mMBA = meta-mercaptobenzoic acid) were selected for study because they bridged the expected transition from nonmetallic to metallic electron behavior. Excitation-pulse-energy-dependent measurements confirmed Au144(pMBA)60 (1.8 nm) as the smallest MPC to exhibit metallic behavior, with a quantifiable electron-phonon coupling constant of (1.63 ± 0.25) × 1016 W m-3 K-1. Smaller, nonmetallic MPCs exhibited nanocluster-specific transient extinction spectra characteristic of transitions between discrete quantum-confined electronic states. Volume-dependent electronic relaxation dynamics for ≤1.8 nm MPCs were observed and attributed to a combination of large energy differences between electronic states and phonon frequencies and spatial separation of photoexcited electrons and holes. Evidence for the latter was obtained by substituting mMBA for pMBA as a passivating ligand, which resulted in a 4-fold increase in the relaxation rate constant.

Original languageEnglish (US)
Pages (from-to)6307-6313
Number of pages7
JournalJournal of Physical Chemistry C
Volume119
Issue number11
DOIs
StatePublished - Mar 19 2015

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Fingerprint Dive into the research topics of 'Nanometals: Identifying the onset of metallic relaxation dynamics in monolayer-protected gold clusters using femtosecond spectroscopy'. Together they form a unique fingerprint.

  • Cite this