Molecular dynamics simulations and photoluminescence annealed ZnO surfaces
TK Min and TL Yoon and CA Ling and S Mahmud and TL Lim and KG Saw, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 90, 28-36 (2017).
The effect of thermal annealing on wurtzite ZnO, terminated by two surfaces, (0001) (which is oxygen terminated) and (0 0 0 1) (which is Zn-terminated), is investigated via molecular dynamics simulation using reactive force field (ReaxFF). As a result of annealing at a threshold temperature range of 700 K < T-t <= 800 K, surface oxygen atoms begin to sublimate from the (0001) surface, while no atom leaves the (0 0 0 1) surface. The ratio of oxygen leaving the surface increases with temperature T (for T >= T-t). The relative luminescence intensity of the secondary peak in the photoluminescence (PL) spectra, interpreted as a measurement of amount of vacancies on the sample surfaces, qualitatively agrees with the threshold behavior as found in the MD simulations. Our simulations have also revealed the formation of oxygen dimers on the surface and evolution of partial charge distribution during the annealing process. Our MD simulation based on the ReaxFF is consistent with experimental observations.
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