INVESTIGADORES
PATRITO Eduardo Martin
congresos y reuniones científicas
Título:
Theoretical Investigation of the Reactivity of Halogenated and Hydrogenated Si(100)-2x1 Surfaces toward NH3
Autor/es:
F. A. SORIA; E. M. PATRITO; P. PAREDES OLIVERA
Lugar:
Niza
Reunión:
Congreso; The 61st Annual Meeting of the Internaternational Society of Electrochemistry; 2010
Institución organizadora:
Internaternational Society of Electrochemistry
Resumen:
The adsorption
and reaction of ammonium with silicon surfaces is of great importance because
surface Si-NH2 groups are precursors for the synthesis of thin films
of silicon nitride. Traditionally, the synthesis of Si-NH2 groups
has been performed under UHV conditions on Si(100)-2x1 [1]. However, the
development of procedures [2] to chlorinate the 100 surface of silicon, allowed
the manipulation of this surface in chemistry laboratories, out of expensive
UHV chambers. When the Cl-Si(100)-2x1 surface is exposed to NH3, a partial
amination occurs [3]. However, ammonium does not react on the hydrogenated
surface, H-Si(100)-2x1, despite the fact that the Si-H bond is weaker than the
Si-Cl bond.
In this work we
performed a comparative investigation of the reaction pathways between ammonium
and the hydrogenated and halogenated (Cl and Br) by means of density functional
theory calculations performed on silicon slabs exposing the 100 face with the
2x1 reconstruction. The reaction mechanism involves different number of
elementary steps on both types of surface. On the hydrogenated surface there
are two elementary steps whereas on the chlorinated surface four elementary
steps have been identified. The activation energy barriers explain the
different reactivities. On the hydrogenated surface the activation barrier is 38.7
kcal/mol whereas on the chlorinated surface, the highest activation barrier is
14 kcal/mol.
The reaction of
ammonium on the brominated Si(100)-2x1 surface follows a similar mechanism to
that on the chlorinated surface. However, the activation energy barriers are
higher than on the chlorinated surface due to steric effects. The highest
barrier on this surface is 22.7 kcal/mol.
This shows that the reactivity of the Si(100)-2x1 surface may be tuned
depending on the type of halogenating procedure.