Figure 2

a AFM image of the Si capping layer after in-situ annealing at 540°C for 7 min. b Cross-sectional profiles of an as grown QD ( dashed ), a Si mound before annealing ( dotted ), the transitional states from mounds to nanopits after annealing at 540°C for 7 min ( solid lines 1–6 ), and a Si nanopit formed after annealing at 640°C for 10 min ( red dash dot ). Cross-sectional TEM images of c a Si mound before annealing, d a Si mound after annealing at 540°C for 7 min, and e a Si nanopit formed after annealing at 640°C for 10 min, the buried QD is also shown. The scale bar in (d) applies to (c) and (e). The two blue lines in (b) and two white lines in (c)–(e) indicate the deepest position of trenches.