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

Paper SS2-MoM10
Direct Probing of the Surface Dangling Bond by Means of Evanescent Wave Cavity Ring Down Spectroscopy

Monday, November 13, 2006, 11:00 am, Room 2004

Session: Gas-Surface Reaction Dynamics
Presenter: M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
Authors: M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
I.M.P. Aarts, Eindhoven University of Technology, The Netherlands
A.C.R. Pipino, NIST
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The surface interaction of gas phase species plays an important role in crystal and thin film growth, chemical passivation and heterogeneous catalysis. Adsorbants, with usually a significant coverage, can be measured using scanning probe, optical or nuclear techniques, preferably in situ and real time. The surface kinetics however, are usually controlled through the creation of a so-called dangling bond. In this contribution we demonstrate a novel technique to probe surface dangling bonds directly and in real time. The method employed is based on evanescent wave cavity ring down absorption spectroscopy using an ultralow-loss fused silica monolithic folded resonator.@footnote 1@ On the curved surface of the folded resonator a thin hydrogenated amorphous silicon (~800 nm) is grown by means of hot wire assisted chemical vapor deposition. The broad band absorption feature of the dangling bond is probed between 1170 and 1245 nm with an unprecedented sensitivity. Absorption losses as low as 10@super -7@ per laser pulse can be measured, corresponding with a surface dangling bond coverage of 10@super -6@! The a-Si:H film was dosed using a calibrated atomic hydrogen. Uptake curves were measured as function of atomic hydrogen flux. The saturated surface coverage measured was around 5 10@super -4@ for an H-flux of 2 10@super 14@ cm@super -2@@super-1@ at a measured abstraction probability from the initial up-take curves of around 0.01±0.003. These results, which confirm previous reports on H saturated surfaces, might point towards a hot-precursor related adsorption-desorption mechanism. However we clearly observe a saturated surface coverage that is H-flux dependent, in contrast with predictions based on Langmuir-Hinshelwood or Eley-Rideal mechanism. In addition we report on the self passivating effect of a-Si:H surfaces after the dosing with atomic hydrogen has ended. @FootnoteText@ @footnote 1@ Aarts et al. PRL 95 166104 (2005).