Synchrotron white beam X-ray topography (SWBXT), post-oxidation color mapping, atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to study the defect and polytype distribution in a thin film grown on mesas structures on part of a 4H-SiC crystal subjected to a non-optimal version of the previously reported [Appl. Phys. Lett. 77 (2000) 1449] procedure for achieving atomic flatness. This combination of techniques was used to provide confirmation that atomic flatness could only be achieved on mesas containing no screw dislocations. It was also found that the vast majority of the atomically flat mesas were of small size as expected since the probability of a screw dislocation threading a mesa is proportional to its area. For these small mesas, either no 3C-SiC nucleation or complete coverage by one or other of the 3C variants was observed. In mesas containing screw dislocations, mostly those of larger size, either no 3C nucleation or partial coverage by single or double phase 3C was observed. In contrast to our previous observations of on-axis mesa samples grown under different conditions in which polytypes such as 15R were observed [J. Phys. D 28 (1995) A56; in: L. Terminello, N. Shinn, G. Ice. K. D'Amico. D. Perry (Eds.), Applications of Synchrotron Radiation Techniques to Materials Science, Mater. Res. Soc. Symp. Proc. 375 (1995) 327] no polytypes other than 4H, 3C(I) and 3C(II) were detected anywhere on this wafer. In the absence of the stacking sequence template provided by the risers of steps (whether from screw dislocations or off cut angle), this data indicates that no other polytype forms but 3C under these growth conditions. This study indicates that combined use of SWBXT in back-reflection and forward-reflection geometry. post-oxidation color mapping, AFM and SEM, is ideally suited for detailed microstructural and structural mapping in SiC. (C) 2002 Elsevier Science B.V. All rights reserved.