In order to investigate the allotropic effect on ripple pattern formation, highly oriented pyrolytic graphite (HOPG) and single crystalline diamond were irradiated with 10-200 keV Xe+ at an incident angle of 60 degrees with respective to the surface normal. The irradiation fluence was 2 x 10(17) cm (2) for all irradiations. Ripple patterns were observed on both HOPG and diamond surfaces. However, large differences in ripple wavelengths, amplitudes and surface roughnesses between HOPG and diamond were recognized. The reason for these differences is discussed. (C) 2009 Elsevier B.V. All rights reserved.