  Using recently proposed improvements of Reflection Electron Microsopy (REM)
we study in perfectly controlled thermodynamics conditions spiral shapes and
spirals on Si(111) surface. It is shown that the new method named low
distortion reflection electron microscopy (LODREM) is a powerful instrument,
resolving in much more details (compared with REM) growth or evaporation
spirals at the crystal surface. More precisely, we examine the distance between
two successive steps of a spiral at growth (or evaporation) with respect to the
supersaturation (or undersaturation). It is found that this distance scales
with an exponent close to -1/2. This result, which deviates from the BCF theory
originates from a non local behavior with a slow kinetic of attachment of the
adatoms at the steps.
