Correlation between RHEED patterns and surface morphologies. (a) The broad, streaky RHEED pattern during thermal desorption and (b) the corresponding AFM image showing surface corrugation after the initial deoxidation stage of sample 1 at 591°C. (c) The spotty/chevron RHEED pattern and (d) the corresponding AFM image showing nanoscale droplets formed during subsequent sublimation of sample 2 at 611°C. (e) Expanded RHEED images around the specular beam showing the evolution of the pattern from streaky at 591°C (left image) to spotty at 611°C (middle) which slowly transforms to the chevron pattern (right) when the substrate temperature is held constant. The chevron pattern develops at around T
0 of 611°C, which serves as the reference temperature shown in the temperature profiles in Figure 1.