Using first-principles density functional theory calculations we analyze and compare molecular adsorption of methylamine $\left(\mathrm{C}{\mathrm{H}}_3\mathrm{N}{\mathrm{H}}_2\right)$ at $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3\left(0001\right)$ and $\alpha \text{−}{\mathrm{Cr}}_2{\mathrm{O}}_3\left(0001\right)$. We report results for the adsorption structure and bonding nature as documented by the adsorption-induced changes in the electron density and in the projected density of states. We find that methylamine in both cases binds to exposed surface cations via the N lone-pair orbital. However, differences in the covalent bond affects the detail of the adsorption, surface relaxation, and electron transfer deep in the surfaces. We also find that an electrostatic bond between the amino-H and surface-O atoms supplements the N-cation bond for $\alpha \text{−}{\mathrm{Cr}}_2{\mathrm{O}}_3\left(0001\right)$.

• Received 24 August 2006

DOI:https://doi.org/10.1103/PhysRevB.75.035403