Spontaneous formation of an ordered c(4x2)-(2x1) domain pattern on Ge(001)

Scanning-tunneling-microscopy measurements of Ge(001) reveal the presence of an ordered domain pattern consisting of c(4X2) and (2X1) domains arranged in stripes with a width of several dimer row spacings, oriented along the dimer rows. We suggest that the existence of a soft domain wall between the domains combined with a difference in the stress component along the dimer bond for the (2X1) and c(4X2) domains, respectively, can conspire to produce such an ordered domain phase. A simple model based on strain relaxation explains the observed size of the domain pattern.