The evolution of surface morphology and reconstructions induced by reducing epitaxial WI3(100) thin films on LaAlO3(100) were studied using scanning tunneling microscopy (STM). As the films were reduced the surface transformed from p (2 X 2) to p (5 X 2) to p (4 X 2) to p (3 X 2) and finally to (1 X 1); at intermediate stages mixtures of the phases were observed. As the surface structure changed the films became progressively darker indicating a connection between surface structure and bulk reduction. The formation of the p (5 X 2) and p (4 X 2) structures from the p (2 X 2) structure could be explained by the ordering of vacancies created by W5+ migration into the bulk into troughs. The ordered troughs gave the surface a stranded appearance in STM images. As the surface was reduced the troughs narrowed to create the p (3 X 2) surface; reduction of this surface gave way to a ( 1 X 1) surface with all the W ions reduced to 5+. Half-height steps due to crystallographic shear planes intersecting the surface characterized the ( 1 X 1) surface. Several defect structures were characteristic of the p (n X 2) surfaces including domain boundaries oriented parallel to the strands and along [011], in-plane line defects across strands, wide strands, and crosslinks above strands. Structural models for these defects are proposed based on STM results. The [011] domain boundaries are attributed to the formation of stress domains on a reconstructed surface with uniaxial stress induced by the strands and troughs. (C) 2004 American Vacuum Society.