E. Stoll

Atomic Resolution with Atomic Force Microscope

The atomic force microscope (AFM) is a promising new method for studying the surface structure of both conductors and insulators. In mapping a graphite surface with an insulating stylus, we have achieved a resolution better than 2.5 A.

Topography of defects at atomic resolution using scanning tunneling microscopy

Abstract The topography of highly-ordered pyrolytic graphite is studied with scanning tunneling microscopy (STM). Large areas of typically 5 × 5 nm2 were mapped with constant tunneling current and gap voltages from 10 to 700 mV. No clear trigonal symmetry is observed for different samples and tips. Ordered and disordered regions are found and the atomic resolution persists even in the disordered areas. Along one of the principal axes, line dislocations are visible in the topography. Small terraces formed by double-atomic steps are discerned.

Connectivity and the fracton dimension of percolation clusters

The vibrational density of states of percolation clusters at threshold has been calculated for scalar models in two space dimensions. The effective fracton dimension is found to increase significantly with the spread of the short-range interactions. This is attributed to the gain in connectivity associated with an increased spread. Although the simulations do not ascertain the asymptotic scaling behavior, they are of direct relevance to experiments which are always performed on samples that are fractal over a limited range of scales.