STRUCTURE AND MORPHOLOGY OF IN ON GE(001) STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The superstructures formed by low coverages of In adsorbed on Ge(001) have been studied using scanning tunneling microscopy. The Ge(001)-(2 x 2)-In reconstruction is similar to the structure of several group-II I metals on Si(001), and consists of symmetric In dimers which are ori ented parallel to the Ge substrate dimers. For the mixed (3 x 3) + (3 x 4) phase we propose a structural model with either two or three line ar In trimers per unit cell. The saturation coverage of a homogeneous (3 x 4) phase corresponds to 0.75 ML. After annealing at 200 degrees C the (5 x 4) reconstruction is formed, in which three-fold coordinated In atoms bond to Ge atoms from three different atomic layers. STM ima ges of the Ge(001)-(n x 4)-In phase are similar to those of the Si(001 )-(4 x 3)-In and Si(001)-c(4 x 2n)-Al reconstructions. Each (n x 4) un it contains six or seven In atoms and involves the removal of four Ge substrate atoms, resulting in a partially dimerized Ge layer.