AVS 53rd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM12
Reaction Dynamics of NO Gas on Iron Phthalocyanine Thin Films

Monday, November 13, 2006, 11:40 am, Room 2004

Session: Gas-Surface Reaction Dynamics
Presenter: N.L. Tran, University of California at San Diego
Authors: N.L. Tran, University of California at San Diego
S.R. Bishop, University of California at San Diego
G.C. Poon, University of California at San Diego
A.C. Kummel, University of California at San Diego
Correspondent: Click to Email
Metallophthalocyanines (MPcs) have been proposed for use in organic-based chemical field effect transistor (chem-FET) detectors for the measurement of ambient gases such as NO@sub x@, NH@sub 3@ and O@sub 3@. However, the mechanisms of the reaction between these gases and MPc thin films have not been studied. We have investigated the reaction dynamics between NO gas and a monolayer iron phthalocyanine (FePc) on a Au(111) substrate. Sticking probabilities of a molecular beam of NO were measured on both clean Au(111) and ordered monolayer FePc deposited on clean Au(111). The sticking probabilities were measured both as a function of beam energy (0.09eV - 0.4eV) and surface temperature (125K - 325K). The sticking probability of NO onto the FePc film saturates at 3% of a ML for all surface temperatures and all incident kinetic energies consistent with the final chemisorption site being confined to the FePc metal center. In contrast to the saturation coverage, the sticking probability is large (40%) at low surface temperature and low incident kinetic energy and decreases linearly with increasing surface temperature but is independent of beam energy above 0.26eV. Temperature dependent sticking which is independent of kinetic energy is not consistent with simple models of direct chemisorption nor precursor mediated chemisorption. Instead, the data is consistent with NO sticking onto the monolayer FePc via multiple precursor-mediated physisorption pathways in which the NO traps onto the aromatic rings and then diffuses to the metal center on FePc. Density functional theory simulations of NO binding onto the FePc molecule also support this theory. These calculations show a multi-step absorption mechanism in which NO initially binds to the inner ring nitrogens and subsequently migrates to the deep chemisorption well on the metal centers for FePc.