Molecule-surface interaction energies are computed at the B3LYP level of theory. The C(111) and Si(111) surfaces, with H, F, or CN covalently bonded to the surface, are studied. The incoming molecule simulates the tip of a probe that should be able to differentiate between the atoms or molecules on the surface. A Sc-tipped probe molecule yields a larger difference for the probe-surface H versus probe-surface F interaction energies than our previously studied. electron-rich pyridine (C5H5N) and (CH3)(3)PO probes. However, it is not always possible to differentiate between the surface H and F atoms because the Sc probe interacts too strongly with the neighboring surface atoms. The difference in the probe-H and probe-F interaction energies is smaller for Si(111) than C(111), making it more difficult to differentiate between these two atoms on Si(111). The larger lattice constant for Si(111) significantly reduces the surface atom-surface atom interaction energy as well as the probe-neighbor interaction energies. This means that the H/CN system, which is not practical for C(111) due to the CN-CN repulsion, is possible for Si(111). The difference in the probe-H and probe-CN interaction energies is very large for the H/CN data storage system, making this the best system studied to date.