TABLE OF CONTENTS Graphoepitaxy or "artificial epitaxy" refers to the case where epitaxial relationships exist between epilayer and substrate in the absence of primary bonding between these surfaces. The extreme case of such graphoepitaxy occurs when the substrate is covered by a thin amorphous layer, yet the epilayer over the amorphous layer exhibits an epitaxial relationship with the underlying substrate crystal. How can such a relationship be explained?
Most cases of graphoepitaxy occur when there is weak bonding between epilayer and substrate. In this case, growth occurs via the island mode. Although it has not been mentioned as yet, such islands tend to grow with faceted surfaces to minimize their free energy, because the surface energy is usually anisotropic and has minima parallel to low index planes. Most substrate surfaces are not ideally planar. Rather they consist of terraces and surface steps. The steps are usually along low index directions. If the substrate surface plane has 3-fold rotational symmetry then the steps will mimic this rotational symmetry and there will be step intersections where the angles between steps are either 60 or 120 . Similarly, on substrate surfaces having either 2- or 4-fold rotational symmetry, the angle between intersecting steps will be 90 . Heterogeneous nucleation of the islands will occur preferentially at the step intersections on the substrate. The angles between steps determine whether the islands that nucleate there have the corresponding rotational symmetry. Thus, if the steps on a substrate surface are reproduced on the surface of an amorphous overlayer, then...
