In order to obtain the equilibrium shape of silicon, small monocrystalline silicon columns (diameter similar to 1-5 mu m, height similar to 10 mu m) have been formed on a silicon (111) substrate by photolithography. In-situ observation, in a UHV transmission electron microscope, of the shape changes of these columns upon heating them shows that the equilibrium shape of clean silicon can be installed over the apices, once the columns have become bulbous by evaporation and surface diffusion. Equilibrium profiles, along the (110) and (112) zones, have been visualised in-situ at 1323 K, recorded and analysed. Well-characterised (111) and (113) facets exist on the equilibrium shape at this temperature. They are separated by rounded regions that display a tangential merging into the facets. Hence, all orientations belong to the equilibrium shape at 1323 K. The gamma-plot has been constructed for the (110) zone. It shows cusps at (111) and (113) and rather broad minima at (110) and (100). However, within the resolution of our micrographs, it is not possible to decide whether flat facets exist at (110) and (100) or whether the crystal surface is merely slightly rounded. The anisotropy of the surface specific free energy is found surprisingly weak (similar to 4% maximum). Within the experimental accuracy (similar to 1%), the hierarchy is gamma(111)greater than or equal to gamma(110)>gamma(113)>gamma(100), the relative anisotropies with respect to (111) being 0.99, 0.98 and 0.97 for (110), (113) and (100) respectively. An order of magnitude for the step-free energy beta has been obtained(beta(111) approximate to 3 X 10(-11) J m(-1), beta(113)approximate to 1 X 10(-11) J m(-1)). Our results are compared to those obtained by other authors by using voids in silicon.
