The phase transformation of iron silicides from FeSi to beta-FeSi2 on (1 1 1)Si and effects of As+-implantation on the transformation have been investigated by sheet resistance measurements, grazing incidence X-ray diffractometry (GIXRD), scanning transmission electron microscope (STEM) and energy dispersive analysis of X-ray (EDAX). Phase transformation from FeSi to beta-FeSi2 begins at 600 degreesC and completes at 700 degreesC. The transformation is significantly enhanced by the As+-implantation. The annealed As+-implanted samples show a very different sheet resistance versus annealing temperature behavior. Wider than 20 nm decorated grain boundaries were observed in the As+-implanted sample. EDAX data show that the dopant, As, is present only in the wide decorated grain boundary areas. (C) 2003 Elsevier Science B.V. All rights reserved.