The initial processes of Ge nanocluster formation on Si(110)-16 x 2 reconstructed structure were investigated via scanning tunneling microscopy. For a small amount of Ge deposited on Si(110)-16 x 2 single-domain structure at room temperature, the surface structure did not change significantly. After direct current heating at 973 K for 20 min, the striped structure almost broken and disordered-like structure was formed on the terrace. With increasing the annealing time, the surface structure changed from disordered-like structure to the 16 x 2 double-domain structure and pyramidal nanoclusters were formed at the domain boundary. These results suggest that the surface stress was induced by Ge nanocluster formation and the double-domain structure was formed in order to relax the stress. (c) 2012 Elsevier B.V. All rights reserved.