Extended Data Fig. 5: Surface morphologies of 40-UC FeTe films after each Te-annealing cycle.
a–f, STM images (500 × 500 nm2) of 40-UC FeTe films: as-grown FeTe (a) (Vs = 1.5 V and Is = 50 pA), cycle I (b) (Vs = 3.5 V and Is = 50 pA), cycle II (c) (Vs = 1.5 V and Is = 20 pA), cycle III (d) (Vs = 1.5 V and Is = 20 pA), cycle IV (e) (Vs = 1.5 V and Is = 20 pA) and cycle V (f) (Vs = 1.5 V and Is = 20 pA). The STM images are acquired using a PtIr tip at T = 4.2 K. g–l, Atomic force microscopy images (5 × 5 μm2) of 40-UC FeTe films: as-grown FeTe (g), cycle I (h), cycle II (i), cycle III (j), cycle IV (k) and cycle V (l). The as-grown 40-UC FeTe film exhibits atomically flat terraces with square pyramidal structures. During the Te-annealing treatments, these square terraces gradually expand and their edges become rounded, suggesting the formation of new FeTe layers. Scale bars, 100 nm (a–f); 1 μm (g–l).
