H-bond mediated dissociation of ammonia on Si(001)

By combining DFT calculation and fast XPS measurements we demonstrate that the low temperature dissociation of NH3 molecules chemisorbed on Si(001)-2x1 is driven by the continuous flux of ammonia molecules from the gas phase.

M. Satta et al., Phys. Rev. Lett. 109, 036102 (2012).

Ammonia chemisorbs dissociatively on Si(001) surfaces with an energy barrier of ~1 eV. However, even at low temperature, intact NH3 molecules are observed on the Si(001)-2x1 surface exclusively after the exposure to very low ammonia doses, whereas only NH2 and H fragments are revealed on the surface dosed at saturation.
We have explained the disappearance of intact chemisorbed NH3 molecules by investigating the interaction between an ammonia molecule chemisorbed on Si(001)-2x1 and a gas phase NH3 molecule. Energetics and structural calculations indicated a H-bonding mediated route for the transfer of an H atom from the chemisorbed NH3 to the Si dangling bond nearby. This process, having an energy barrier of 0.5 eV, is active even at low temperature.

Our model, complemented by synchrotron radiation photoelectron spectroscopy measurements, demonstrates that the low temperature dissociation of chemisorbed NH3 is driven by the continuous flux of ammonia molecules from the gas phase.

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Fundamental Role of the H-Bond Interaction in the Dissociation of NH3 on Si(001)-2x1;
Mauro Satta, Roberto Flammini, Andrea Goldoni, Alessandro Baraldi, Silvano Lizzit, and Rosanna Larciprete;
Phys Rev. Lett. 109, 036102 (2012).
Last Updated on Wednesday, 25 March 2015 14:23