254 W. Wulfhekel et al. / Applied Surface Science 234 (2004) 251–255 Fig. 3. SEM images <str<strong>on</strong>g>of</str<strong>on</strong>g> an (a) area <strong>on</strong> the c<strong>on</strong>cave-shaped surface after H2 erosi<strong>on</strong> for 1 h at 1700 8C; (b) equivalent area <strong>on</strong> the same sample after an additi<strong>on</strong>al H 2 erosi<strong>on</strong> at 1800 8C for 20 min. Fig. 4. (a,c,d) SEM images taken <strong>on</strong> different areas <str<strong>on</strong>g>of</str<strong>on</strong>g> the reorganised c<strong>on</strong>cave-shaped surface, the inset in (a) shows a zoom <str<strong>on</strong>g>of</str<strong>on</strong>g> the same area. (b) indicates the locati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the imaged areas within the dimple.
18008 enables the removal <str<strong>on</strong>g>of</str<strong>on</strong>g> all rough step bunches, which are still visible in (a), but which are absent in (b). Very straight and regular steps were obtained, which give rise to a very narrow terrace width distributi<strong>on</strong> with a parallel step orientati<strong>on</strong> al<strong>on</strong>g {1 1 2 0}. SEM studies have been performed <strong>on</strong> selected parts <str<strong>on</strong>g>of</str<strong>on</strong>g> the dimple to study the influence <str<strong>on</strong>g>of</str<strong>on</strong>g> the azimuthal directi<strong>on</strong> <strong>on</strong> the structural re-organisati<strong>on</strong> within the c<strong>on</strong>cave-shaped surface.. The chosen areas reflect the symmetry <str<strong>on</strong>g>of</str<strong>on</strong>g> the crystal. Fig. 4(a), (c) and (d) show SEM images <str<strong>on</strong>g>of</str<strong>on</strong>g> areas as indicated in Fig. 4(b). As already shown in Fig. 3, <strong>on</strong> all areas a very smooth morphology with very regular, straight step edges was observed. The step directi<strong>on</strong> shows systematic changes depending <strong>on</strong> the azimuthal misorientati<strong>on</strong> in the dimple. Three different energetically stable alignments can be distinguished. In (a) this directi<strong>on</strong> corresp<strong>on</strong>ds to the family <str<strong>on</strong>g>of</str<strong>on</strong>g> {1 1 2 0} directi<strong>on</strong>s, in (c) and (d) they follow the {2 1 1 0} and {121 0} directi<strong>on</strong>s, respectively. Line scans al<strong>on</strong>g the SEM images <str<strong>on</strong>g>of</str<strong>on</strong>g> the curved surface area at a fixed azimuthal angle give a first, rough analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> the morphological changes as a functi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the polar misorientati<strong>on</strong>. The SEM images shown in Fig. 4 reflect some dependences for small polar angles. In (c) the terrace width is around 1 mm whereas in (d) steps are separated by terraces around 300 nm wide. This larger terrace size in (c) as compared to (b) reflects the smaller polar misfit <str<strong>on</strong>g>of</str<strong>on</strong>g> area (c) due its closer proximity to the centre <str<strong>on</strong>g>of</str<strong>on</strong>g> the dimple. More detailed experiments with increased lateral resoluti<strong>on</strong> were performed by AFM and will be published elsewhere [14]. 4. Summary and outlook Etching c<strong>on</strong>diti<strong>on</strong>s (substrate temperature: 1800 8C, etching time: 20 min, hydrogen flux: 13 mbar) leading to very smooth structural <str<strong>on</strong>g>reorganisati<strong>on</strong></str<strong>on</strong>g>s <str<strong>on</strong>g>of</str<strong>on</strong>g> initially rough, curved silic<strong>on</strong> carbide <str<strong>on</strong>g>surfaces</str<strong>on</strong>g> were established. First results obtained by SEM show straight step alignments in some distinct, energetically stable directi<strong>on</strong>s. Step heights <str<strong>on</strong>g>of</str<strong>on</strong>g> 1.5 nm corresp<strong>on</strong>ding to the height <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>on</strong>e unit cell <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>6H</strong>-<strong>SiC</strong> were imaged. A more detailed study by scanning tunnelling- and atomic force micro- W. Wulfhekel et al. / Applied Surface Science 234 (2004) 251–255 255 scopy <str<strong>on</strong>g>of</str<strong>on</strong>g> the polar and azimuthal dependencies <str<strong>on</strong>g>of</str<strong>on</strong>g> the observed step arrangements are in preparati<strong>on</strong> and will be published elsewhere [14]. Acknowledgements DS and WW gratefully acknowledge the friendly hospitality and support by the CNRS, the Université d’Aix-Marseille 2 and the CRMC2. MH gratefully acknowledges the friendly hospitality <str<strong>on</strong>g>of</str<strong>on</strong>g> the Max- Planck-Institut für Mikrostrukturphysik. FD gratefully acknowledges the c<strong>on</strong>tinuous hospitality <str<strong>on</strong>g>of</str<strong>on</strong>g> the CRMC2. Very efficient help <str<strong>on</strong>g>of</str<strong>on</strong>g> Francis Quintric, CRMC2, is acknowledged. References [1] W.J. 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