We report results of a scanning tunneling microscopy investigation of the bismuth-induced structures at Si(100) surfaces. Long linear chains of bismuth dimers are formed on the Si(100) surface after bismuth deposition at 480 degrees C. This may be self-organized by an enhanced migration of atoms along the chains. Moreover, bismuth atoms adsorbed on the surface induce, by expelling silicon atoms from the substrate surface, a (2 x n) restructuring with linear defects perpendicular to the dimer rows on the Si terrace, (C) 1999 Elsevier Science B.V. All rights reserved.