Germanium islands grown on a Si(1 1 1)7×7 surface observed by noncontact atomic force microscopy with simultaneous imaging on damping

We have observed a germanium thin film grown on a Si(1 1 1)7×7 surface by noncontact atomic force microscopy (nc-AFM) while simultaneously imaging the damping of cantilever excitation. The Ge layer grown at 450 °C with a coverage of about 0.7 bi-atomic layer (BL) forms islands on the terraces of the Si(1 1 1) substrate and step flows starting from the step edges of the substrate, which partially coalesce each other. The nc-AFM images clearly exhibit 5×5, 7×7 and 9×9 reconstructions, and their domain boundaries of the Ge thin layer on an atomic scale. Simultaneously obtained damping images also show the atomic corrugation with a local minimum over adatoms. Under bias voltages beyond 1 V between a tip and a sample, strongly enhanced bright spots are observed over corner adatoms on the faulted halves of the 5×5 and 7×7 reconstructions. In damping images, a rapid decrease is found over the corner adatoms possibly due to the strong attractive interaction over the corner adatoms.