K / inetics of the adsorption of atomic oxygen ( N 20 ) on the Si ( 001 ) 2 × 1 surface as revealed by the change in the surface conductance

The adsorption behaviour of N20 on the Si(001)2 × ! surface at 300 K substrate temperature has been investigated by measuring in situ the surface conductance during the reaction process. For comparison we monitored in the same way the adsorption of 0 2 on the same surface which ultimately leads to the fiat band situation. The adsorption of atomic oxygen as released by decomposition of the N20 molecule, in contrast with molecular oxygen, was found to result in an increase of the band bending. The difference in behaviour of the change of the surface conductance between the two solid-gas reactions can be explained by considering that the adsorption of 0 2 will also remove deep-lying backbond states in addition to the dangling bond (DB) and dimer bond (DM) related surface states. It is well known that only the DB and DM surface states are affected by N20. The surface conductance measurements (SCM) presented in this paper complement our previous spectroscopic differential reflectivity measurements and Auger electron spectroscopic results for the system Si(001)2 × 1 + N20; we have found evidence that the second step of the proposed three-stage adsorption process of atomic oxygen can be divided into two substages. From our SCM data we could derive that the distance between the valence band edge and the Fermi energy of the clean Si(001)2 × 1 surface is 0.32 +_ 0.02 eV, which is in agreement with previous photoemission results.