SHAPE UNIVERSALITY OF EQUILIBRATED SILICON-CRYSTALS

In order to check the Prokowski-Talapov (P-T) universality class behav iour, the profiles of equilibrated silicon crystals have been studied in the vicinity of a (111) facet at 900 degrees C. The equilibrium sha pes of three-dimensional (3D) or two-dimensional (2D) crystals have be en produced by thermally equilibrating either an array of small silico n columns on a silicon substrate or a grating of silicon ridges. The s amples have been observed either ex situ, by high-resolution SEM, or i n situ by TEM and REM. The profiles have been measured along a (high s ymmetry) <110> zone, toward (110), within the angular domain 3-17 degr ees. For smaller angles (0-1.5 degrees away from [111]) the profile ha s been reconstructed via the visualisation of steps by REM. The theore tical prediction of a 3/2 power law for the profile equation has been checked. The results are at variance with those obtained for metals. W ithin the angular domain 3-17 degrees, the profile is compatible with a 3/2 power law. From the profile equation, the step interaction const ant can be determined (0.36+/-0.09 J m(-2) at 900 degrees C), in good agreement with previous experiments on the terrace width distributions . No difference can be detected between 3D and 2D crystals. All this i s the signature of a P-K behaviour, only involving repulsive 1/x(2) st ep interactions, again in agreement with previous studies. However, at small angles (0-1.5 degrees), no physically reasonable law can be ass igned to the profile. This behaviour is not understood at present. (C) 1998 Elsevier Science B.V. All rights reserved.