AVS 59th Annual International Symposium and Exhibition
    In Situ Microscopy and Spectroscopy Focus Topic Wednesday Sessions
       Session IS+AS+OX+ET-WeM

Paper IS+AS+OX+ET-WeM1
Revealing Gas-Surface Radical Reaction Mechanisms of Self-Assembled Monolayers by Scanning Tunneling Microscopy

Wednesday, October 31, 2012, 8:00 am, Room 007

Session: In Situ Characterization of Solids: Film Growth, Defects, and Interfaces
Presenter: D.Y. Lee, University of Notre Dame
Authors: D.Y. Lee, University of Notre Dame
M.M. Jobbins, University of Notre Dame
S.A. Kandel, University of Notre Dame
Correspondent: Click to Email
Scanning Tunneling Microscopy (STM) in ultra-high-vacuum is used in situ to investigate the surface changes of the octanethiolate self-assembled monolayer (SAM) on Au(111) upon reaction with atomic hydrogen and with atomic chlorine. For both reactions, the surface structure heavily influences the rate of monolayer degradation, but the effect of surface defects on reactivity is completely opposite when comparing the two systems. Monolayer reactivity increases with increasing hydrogen-atom exposure while decreases with further reaction with atomic chlorine. The monolayer-versus-exposure data are examined by kinetic Monte Carlo simulations and reveal that, for H-atom exposure, molecules located near surface defect sites are potentially over 500 times more reactive than close-packed areas. For Cl-atom interactions, however, the opposite occurs: close-packed regions are at least 100 times more reactive than defect sites. These observations result directly from the alkyl hydrogen abstraction and sulfur-gold bond cleavage mechanisms of SAM upon gas-phase radical bombardment.