INVESTIGADORES
PATRITO Eduardo Martin
congresos y reuniones científicas
Título:
On the Mechanism of Thermal Oxidation of grafted Si(111) surfaces by H2O and O2. A Density Functional Theory Investigation.
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 chemical and physical properties of hydrogen
terminated silicon surfaces have received much attention because these surfaces
are reasonably stable and can be prepared and manipulated in air as well as in
a number of organic solvents [1]. Thus, high quality materials are available
without the need for expensive vacuum systems.
The hydrogenated
111 surface of silicon can be easily prepared by etching in NH4F
solutions. In this way, surfaces with large terraces can be obtained. Each
silicon atop atom has only one Si-H bond, which is normal to the surface. After several hours of exposure to air, the
surface becomes oxidized. Incorporation of oxygen into silicon is
activated and involves a multistep process. During the initial stages of
oxidation, O2 molecules are incorporated into the SiSi backbonds
without removing surface hydrogen [2, 3]. The oxidation of Si(111)-H requires
the presence of an oxidant, O2, and a nucleophile, H2O
[2]. The mechanisms of oxidation of chlorinated and methylated Si(111) surfaces
in air is not known yet. The chlorinated surfaces readily oxidize in air
whereas the methylated surfaces are more stable than the hydrogenated surface.
In this work we
investigated the mechanism of oxidation of Si(111)-H, Si(111)-Cl and Si(111)-CH3
by H2O and O2. Density functional theory calculations
were performed to calculate reaction pathways which allowed the identification
of the different elementary reaction steps, transition states and
intermediates.
The successive
oxidation of the silicon backbonds make the oxidation reactions more exothermic
[4] and this decreases the activation energy barriers because the increasingly
positive silicon atom favors the attack by nucleophiles such as water. Steric
effects in the fully methylated surface greatly increase the activation energy
barriers for oxidation.