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There has been growing interest in hybrid organic/inorganic
structures for molecular electronics and chemical/biosensors, and
relevant progresses in fabrication methodologies for organic
functionalization of semiconductors. Si surfaces offer a promising
scenario to exploit existing Si technology and the strength of the
Si-C bond, however there are problems to obtain stable ordered
interfaces. The main cause of disorder in the Si-organic interface
comes from the need to use bi-functional molecules: the molecule
should create stable bonds at the interface, and offer a second
functional group at the outer surface. This might cause
competition in the bonding to the surface, and disorder in the
interface. The microscopic understanding of interactions at the
hybrid interfaces is still poor, and experimental
characterizations do not yet provide atomistic descriptions.
Theoretical studies can be very helpful to investigate details of
interface formation, reaction energetics and kinetics, and predict
final properties of the hybrid structure.
Using state-of-the-art ab initio DFT techniques, specially
designed for the estimation of reaction barriers [1,2], we have
investigated the functionalized di-hydrogenated Si(100)
surface,[3-5] one of the most commonly available and adopted
substrates in experimental studies. We here compare results with
the mono-hydrogenated Si(100), that offers best ordering
possibilities and lower reaction barriers. We analyse
functionalization by molecules with a carboxylic head and reactive
tails: alkenic or alkynic. Carboxylic acids are an usual choice
for sensors, and alkene terminations are an usual choice for a
bond to Si. The issue of competition between head and tail is here
discussed in detail for all the relevant cases: from our results,
we predict a severe competition between energetics and reaction
kinetics in the interface formation for these systems.
[1] G. Henkelman, H. Jonsson, J. Chem. Phys. 22, 9978 (2000). [2]
S. Baroni, A. Dal Corso, S. de Gironcoli, P. Giannozzi (2001),
http://www.pwscf.org. [3] C.S. Cucinotta, A. Ruini, M,J. Caldas, E.
Molinari, J. Phys. Chem. B 108, 17278 (2004). [4] M.J. Caldas, A.
Calzolari, C.S. Cucinotta, J. Appl. Phys. to be publ. (2007). [5]
C.S. Cucinotta, A. Ruini, E. Molinari, C.A. Pignedoli, A. Catellani,
M.J. Caldas subm. (2007). |