Effect of deposition rate on the surface morphology of CeO₂ films deposited by pulsed laser deposition

We have investigated the effect of the deposition rate, as a direct function of the laser pulse repetition rate, on the surface morphology of CeO₂ films deposited by the pulsed laser deposition (PLD) technique on r-cut Al₂O₃ (11̄02) substrates. The critical thickness is defined as the thickness before the onset of increased growth of large islands and abrupt increase in surface roughening. Two regimes of growth were found within the investigated range of deposition rate. It is found out that in the high deposition rate-regime (within 2-4 nm/min), the critical thickness is approx. 90 nm, but in the low deposition rate-regime (less than 1 nm/min), the critical thickness is shifted to approx. 40 nm. Films belonging to these two regimes of crystalline growth were found to have characteristically different formations and surface morphologies. As observed through atomic force microscopy (AFM), the surface morphology is composed of longitudinal islands forming a maze-like pattern in the high deposition rate-regime, while the characteristic morphology was composed of rounded islands in the low deposition rate-regime. Significant reduction in the areal density of large islands and characteristically smoother films was achieved using a low deposition rate.