DIFFERENTIATING BETWEEN H AND F OR H AND CN ON C(111) OR SI(111) SURFACES

Molecule-surface interaction energies are computed at the B3LYP level of theory. The C(111) and Si(111) surfaces, with H, F, or CN covalentl y bonded to the surface, are studied. The incoming molecule simulates the tip of a probe that should be able to differentiate between the at oms or molecules on the surface. A Sc-tipped probe molecule yields a l arger difference for the probe-surface H versus probe-surface F intera ction energies than our previously studied. electron-rich pyridine (C5 H5N) and (CH3)(3)PO probes. However, it is not always possible to diff erentiate between the surface H and F atoms because the Sc probe inter acts too strongly with the neighboring surface atoms. The difference i n the probe-H and probe-F interaction energies is smaller for Si(111) than C(111), making it more difficult to differentiate between these t wo atoms on Si(111). The larger lattice constant for Si(111) significa ntly reduces the surface atom-surface atom interaction energy as well as the probe-neighbor interaction energies. This means that the H/CN s ystem, which is not practical for C(111) due to the CN-CN repulsion, i s possible for Si(111). The difference in the probe-H and probe-CN int eraction energies is very large for the H/CN data storage system, maki ng this the best system studied to date.