FEM OBSERVATION OF LINEAR ADATOM CLUSTERS

Abstract
The formation of linear adatom clusters on metal surfaces has been studied by FEM for the first time. The following two cases were found : 1) When the Nb (or Ta) tip covered by Cu is heated at ~ 600°C, parallel linear clusters oriented along the [001] direction are formed on the {110} planes. The clusters thus formed are very stable up to ~ 700°C. 2) When Ti is evaporated onto a Re tip at ~ 90°C, adatoms on a (10[MATH]0) plane tend to form a linear cluster lining up along the [001] direction i.e., across close-packed atomic rows with troughs. This cluster is stable up to ~ 150°C under the viewing electric field, but breaks up into several spots with the field-off even at ~ 90°C. By the iterative field-off at a constant temperature between 150 and 160°C, each spot moves randomly along the troughs, which clearly indicates that observed spots are images of single adatoms - not clusters.