|
|
DFT Study of Isocyanide Adsorption on Gold (111) Surface
Y. Gilman, P.B. Allen, and M. Hybertsen
Isocyanides are molecules terminated with the -NC group, which can serve as
the "alligator clip" to connect a molecule to metallic electrodes.
Isocyanides may find application in molecular electronics. Several groups
successfully fabricated self-assembled monolayers of diisocyanide molecules
sandwiched between two gold electrodes and studied electrical transport
through them [1]. At Stony Brook University, work is under way to fabricate
a molecular transistor based on a single diisocyanide molecule.
We study the details of adsorption of two simple isocyanides, HNC and CH3NC
on the gold (111) surface by density functional theory (DFT) methods. The
standard slab calculation scheme is employed, in which the real surface is
modeled by the surface of a slab of several atomic layers of gold (see
Figure 1). Monolayers at various coverages
are considered: one molecule per one Au surface unit cell, one per three,
and one per four. We use the WIEN2K [2] DFT code based on the full-potential
linearized augmented plane wave (FPLAPW) method. The generalized-gradient
approximation (GGA) of Perdew et al. (PBE) is chosen for the
exchange-correlation potential.
We find that molecules can adsorb only at the site on top of a Au atom,
which agrees with experimental evidence [3,4]. The adsorption is weak with
the adsorption energy of only 0.2 eV for both HNC and CH3NC molecules. When
the local density approximation (LDA) is chosen for the exchange-correlation
potential, the results are qualitatively different: adsorption is possible
at all sites, with hollow site preferred, and the adsorption energy is about
1 eV. In the absence of adsorption energy measurements, it is difficult to
tell whether GGA description of these systems is accurate. We repeated the
calculations for the CO molecule (isoelectronic to CNH) for which
experimental values of adsorption energies on Au are known. We find that
while the LDA overestimates adsorption energies, GGA underestimates them by
about 0.2 eV.
References
-
[1] Chen, J., Calvet, L.C., Reed, M.A., Carr, D.W., Grubisha, D.S., and
Bennett, D.W. Chem. Phys. Lett. 313: 741 (1999); Lee J.-O., Lientschnig,
G., Wiertz, F., Struijk, M., Janssen, R.A.J., Egberink, R., Reinhoudt,
D.N., Hadley, P., and Dekker, C. Nano Letters 3: 113 (2003).
-
[2] Blaha, P., Schwarz, K., Madsen, G.K.H., Kvasnicka, D., and Luitz, J.
WIEN2k, An Augmented Plane Wave + Local Orbitals Program for Calculating
Crystal Properties (Karlheinz Schwarz, Techn. Universitat Wien,
Austria), 2001. ISBN 3-9501031-1-2.
-
[3] Robertson, M.J. and Angelici, R.J. Langmuir 10: 1488 (1994).
-
[4] Gilman, Y., Allen, P.B., and Hybertsen, M.S. density-functional
study of adsorption of isocyanides on the gold (111) surface. Phys. Rev.
B. Submitted, 2006.
Last Modified: January 31, 2008
Please forward all questions about this site to:
Claire Lamberti
|
