We present first-principles density-functional calculations for the adsorption of methylamine $\left({\mathrm{NH}}_2{\mathrm{CH}}_3\right)$ on the Si(001) surface. We find that methylamine which adsorbs on the down atom of the Si dimer undergoes N-H dissociation over an energy barrier of 0.83 eV. Unlike the case of ammonia, methylamine dissociation reverses the buckling configuration of Si dimers, resulting in a rearrangement of the up(down)-buckled side to the $\mathrm{Si}-{\mathrm{NHCH}}_3$ (Si-H) moiety. As a result, the dissociated ${\mathrm{NHCH}}_3$ species can be aligned along the dimer row.

• Received 7 February 2003

DOI:https://doi.org/10.1103/PhysRevB.67.201301