INTERPRETATION OF SCANNING TUNNELING MICROSCOPE IMAGES SHOWING ANOMALOUS PERIODIC STRUCTURES

Scanning tunneling microscope images of graphite surfaces containing anomalous long-range structures are shown to originate from two distinct mechanisms. A twisted top layer graphite configuration is shown to produce superstructures with divergent periods from 101 to 760 angstrom and decaying amplitudes. A graphite-flake-contaminated tip is shown to yield long-range ordered arrays with constant periodicity, constant amplitudes, and abrupt domain termination. These arrays are consistently reproduced by use of a theoretical crystalline tip model. Hexagonal closed-packed patterns with periods ranging from 48 to 220 angstrom are experimentally observed and theoretically simulated by using this model. The origin of such images is discussed in detail, and a class of the anomalous long-range periodicities observed is attributed to a defect-mediated tip-substrate convolution phenomenon.