Quantum growth defects in 7-ML Pb film consist of eithera, two-atom layer deep voids or b, two-atom layer tall mesas, in films with a small shortage or excess of Pb, respectively. Similar quantum growth defects are evident in 9-ML films, with c, voids or d, mesas. The 700×700 nm2 images are obtained with STM. The area density of defects is comparable to the density of vortices in a ‘matching field’ of ∼5 kG. The corresponding d.c. magnetic response of these films, nominally 3×3 mm2, is shown in e–h. Quantum voids produce ‘hard’ hysteresis loops as shown in e and g, whereas quantum mesas produce ‘soft’ hysteresis loops shown in f and h. Hard hysteresis indicates strong vortex pinning by the voids.