title: Probing the electronic and catalytic properties of a bimetallic surface with 3 nm resolution.
abstract: An atomic- and molecular-level understanding of heterogeneous catalysis is required to characterize the nature of active sites and improve the rational design of catalysts. Achieving this level of characterization requires techniques that can correlate catalytic performances to specific surface structures, so as to avoid averaging effects. Tip-enhanced Raman spectroscopy combines scanning probe microscopy with plasmon-enhanced Raman scattering and provides simultaneous topographical and chemical information at the nano/atomic scale from ambient to ultrahigh-vacuum and electrochemical environments. Therefore, it has been used to monitor catalytic reactions and is proposed to correlate the local structure and function of heterogeneous catalysts. Bimetallic catalysts, such as Pd-Au, show superior performance in various catalytic reactions, but it has remained challenging to correlate structure and reactivity because of their structural complexity. Here, we show that TERS can chemically and spatially probe the site-specific chemical (electronic and catalytic) and physical (plasmonic) properties of an atomically well-defined Pd(sub-monolayer)/Au(111) bimetallic model catalyst at 3 nm resolution in real space using phenyl isocyanide as a probe molecule (Fig. 1a). We observe a weakened N≡C bond and enhanced reactivity of phenyl isocyanide adsorbed at the Pd step edge compared with that at the Pd terrace. Density functional theory corroborates these observations by revealing a higher d-band electronic profile for the low-coordinated Pd step edge atoms. The 3 nm spatial resolution we demonstrate here is the result of an enhanced electric field and distinct electronic properties at the step edges.
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), MOE Key Laboratory of Spectrochemical Analysis &Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Jin-Hui
authors.initials: JH
authors.lastname: Zhong
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), MOE Key Laboratory of Spectrochemical Analysis &Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Jin
authors.affiliation: Department of Physics, Xiamen University, Xiamen 361005, China.
authors.forename: Lingyan
authors.initials: L
authors.lastname: Meng
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), MOE Key Laboratory of Spectrochemical Analysis &Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), MOE Key Laboratory of Spectrochemical Analysis &Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Hai-Sheng
authors.initials: HS
authors.lastname: Su
authors.affiliation: Department of Physics, Xiamen University, Xiamen 361005, China.
authors.forename: Zhi-Lin
authors.initials: ZL
authors.lastname: Yang
authors.affiliation: Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29208, USA.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Williams
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), MOE Key Laboratory of Spectrochemical Analysis &Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Bin
authors.identifier: 0000-0002-9821-5864
authors.initials: B
authors.lastname: Ren