SCANNING-TUNNELING-MICROSCOPY AT LOW-TEMPERATURES ON THE C(4X2) (2X1)PHASE-TRANSITION OF SI(100)/

Using scanning tunneling microscopy (STM) at low temperatures, we have studied the transition between the c(4X2) and (2X1) phases of Si(100) . The phase transition is resulting from the stabilization and orderin g of asymmetric dimers on reconstructed Si(100) at low temperatures. T he occurrence of asymmetric dimers already at room temperature in prev ious STM results has so far been. associated with defect structures, w hich were believed to produce a local buckling in an arrangement of sy mmetric dimers. By cooling Si(100) we observe growth of c(4X2) domains which, below 200 K, cover the entire surface. The phase transition ca n be explained by freezing in of the vibration of asymmetric dimers, w hich is present on defect-free parts of the surface at room temperatur e.