We perform extensive first-principles calculations to simulate the topographical atomic-force-microscope image of an adatom on the $\mathrm{S}\mathrm{i}(111)\mathrm{\text{−}}(7\times 7)$ surface, demonstrating the feasibility of imaging not only the atoms but also the atomic orbitals. Our comparative study of tip terminations shows that two subatomic features can appear for a single adatom when it is imaged by a Si(001)-type tip having two dangling bonds on its apex, while only one feature would appear if it were imaged by a Si(111)-type tip having one dangling bond on the apex. The key condition for seeing the atomic orbitals is to bring the tip so close to the surface that the angular-dependent force dominates the tip-surface interaction.

• Received 3 December 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.256101