(a) Snapshots from a RHEED movie recorded during growth at 5*10−3 mbar O2 in a total pressure of 2*10−2 mbar Ar. Below the snapshots, the intensity profile derived from the blue box and the streak positions derived from the green box are presented. The dashed line indicates the minimum intensity, which is taken as a measure of the crystallization time/thickness. (b) Crystallization times/thicknesses derived with the method depicted in subfigure (a), for samples grown at different pO2 in total presures of 2*10−2 and 1*10−1 mbar Ar. The dashed lines are a guide to the eye.