Development of a Classical Force Field for the Oxidised Si Surface: Application to Hydrophilic
Daniel J. Cole,1
Mike C. Payne,1
S. Mark Spearing,3
Lucio Colombi Ciacchi4,5
1Theory of Condensed Matter Group, Cavendish Laboratory,
University of Cambridge, Cambridge CB3 0HE, UK
2Centre for Micromechanics, Department of Engineering,
University of Cambridge, Cambridge CB2 1PZ, UK
3Engineering Materials Group, School of Engineering Sciences,
University of Southampton, Southampton SO17 1BJ, UK
4Fraunhofer Institut für Werkstoffmechanik, 79108 Freiburg, Germany
5Institut für Zuverlässigkeit von Bauteilen und Systemen,
University of Karlsruhe, 76131 Karlsruhe, Germany
Journal of Chemical Physics 127, 204704 (2007)
We have developed a classical two- and three-body interaction potential to simulate the
hydroxylated, natively oxidised Si surface in contact with water solutions, based on
the combination and extension of the Stillinger-Weber potential and of a potential
originally developed to simulate SiO2 polymorphs.
The potential parameters are chosen to reproduce the structure, charge distribution,
tensile surface stress and interactions with single water molecules of a natively oxidised
Si surface model previously obtained by means of accurate density functional theory
We have applied the potential to the case of hydrophilic silicon wafer bonding at
room temperature, revealing maximum room temperature work of adhesion values for
natively oxidised and amorphous silica surfaces of 97 mJ/m2 and 90 mJ/m2,
respectively, at a water adsorption coverage of approximately 1 monolayer.
The difference arises from the stronger interaction of the natively oxidised surface
with liquid water, resulting in a higher heat of immersion (203mJ/m2 vs.
166 mJ/m2), and may be explained in terms of the more pronounced water structuring
close to the surface in alternating layers of larger and smaller density with respect to
the liquid bulk.
The computed force-displacement bonding curves may be a useful input for cohesive
zone models where both the topographic details of the surfaces and the dependence of
the attractive force on the initial surface separation and wetting can be taken into account.