Novel dark-field imaging of GaN {0001} surfaces with low-energy electron microscopy

We have observed significant dark-field diffraction contrast from adjacent terraces of the GaN (0001) surface in low-energy electron microscopy, an unexpected result, as the surface is not reconstructed and thus has no superlattice reflections. Calculations show that the contrast originates from a 60° rotation of the hexagonal unit cell across odd-multiple bilayer-high steps. The result is general: the terrace morphology from any {0001} surface of würtzite structures can be simply imaged even if the surface is not reconstructed.