title: Unusual non-bulk properties in nanoscale materials: thermal metal-metal bond contraction of gamma-alumina-supported Pt catalysts.
abstract: Variable-temperature X-ray absorption spectroscopy measurements of sub-nanometer Pt nanoparticles on a high-surface-area gamma-alumina support reveal that the Pt-Pt bonds exhibit contraction upon heating [i.e., negative thermal expansion (NTE)]. Bare clusters under a He environment show an average linear expansion coefficient of -2.5 x 10-5 K-1 over the temperature range studied. Adsorption of hydrogen results in an overall bond relaxation and less dramatic Pt-Pt thermal bond-length contraction. From the temperature effect on bond length, disorder parameters, and the X-ray absorption near edge structure (XANES) spectra, temperature-dependent charge transfer between the support and the Pt clusters was concluded to be responsible for the observed behavior.
authors.affiliation: School of Chemical Sciences and Frederick-Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Joo H
authors.initials: JH
authors.lastname: Kang
authors.forename: Laurent D
authors.initials: LD
authors.lastname: Menard
authors.forename: Ralph G
authors.initials: RG
authors.lastname: Nuzzo
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Frenkel