AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeA

Invited Paper SS1-WeA1
Structure and Reactivity of Nanoscale Faceted Surfaces

Wednesday, November 2, 2005, 2:00 pm, Room 200

Session: Surface Structure and Morphology Modification
Presenter: T.E. Madey, Rutgers University
Authors: T.E. Madey, Rutgers University
I. Ermanoski, Rutgers University
H. Wang, Rutgers University
W. Chen, Rutgers University
A.S.Y. Chan, Rutgers University
E. Loginova, Rutgers University
N.M. Jisrawi, Rutgers University
W. Swiech, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
Many planar metal surfaces that are rough on the atomic scale, such as fcc Ir(210), hcp Re(12_31), NiAl(111) and bcc W(111), are morphologically unstable when covered by monolayer films of oxygen, or of certain metals: they become "nanotextured" when heated to elevated temperatures. Faceting occurs when an initially planar surface converts to a "hill and valley" structure, exposing new crystal faces of nanometer scale dimensions. Faceting is driven by surface thermodynamics (anisotropy of surface free energy), but controlled by kinetics (diffusion, nucleation). We report here on the relations between structure, reactivity and electronic properties of nanoscale faceted surfaces. Measurements include STM, LEED, TPD, low energy electron microscopy (LEEM) and soft x-ray photoemission (SXPS) using synchrotron radiation. For example, annealing oxygen-covered Re(12_31) gives a sequence of faceted surfaces ranging from from long sawtooth ridges, to complex structures exposing up to 5 different facets. Surface reactivity of O-covered Re is sensitive to facet structure. Oxygen-faceted NiAl(111) is covered by an alumina "skin". Annealing O-covered Ir(210) generates nanoscale pyramids with {311} and (110) facet orientations; average pyramid sizes 5 to 15 nm are controlled by annealing T. Oxygen can be completely removed at low T (by exposing to H@sub2@, to form H@sub2@O) thus creating a clean, faceted surface that is stable to 600K. Faceted Ir is a template for studies of energy-related surface reactions whose rates are sensitive to atomic structure and/or nanoscale (facet) size effects, including decomposition of H@sub2@, C@sub2@H@sub2@ and NH@sub3@. We will discuss structural and electronic properties of the surfaces, nucleation and growth of facets, implications for catalysis, and potential of faceted substrates as nanotemplates for nanoscale cluster growth. Experimental results are compared to theory. @FootnoteText@ @footnote 1@ supported by DOE - BES.