The films’ surface appeared to be densely packed, smooth, and free of voids. The annealed films showed cluster formation due to aggregation of grains at higher temperature. The surface roughness of the films before and after the annealing was measured and found to increase from 0.5 to 2.3 nm for the 5:10-nm film, while it was 0.4 to 1.8 nm for the 5:5-nm film. Figure 6 AFM images of

(a, b) 5:10- and (c, d) 5:5-nm Al 2 O 3 /ZrO 2 films. (a, c) As-deposited. (b, d) After annealing. Garvie [28] observed that t-ZrO2 is present at room temperature, when the particle size of the tetragonal phase is smaller than 30 nm (critical size). Aita et al. [29] reported a critical layer thickness of 6.2 nm at 564 K for nanolaminates made Q VD Oph from polycrystalline zirconia and amorphous alumina. Teixeira et al. [3] deposited Al2O3/ZrO2 nanolayers by DC reactive magnetron find more sputtering and reported that the tetragonal phase content increased as the ZrO2 layer thickness decreased.

Aita [4, 24] combined ZrO2 with other metal oxides in multilayer nanolaminate films and found that as the thickness of individual layers STAT inhibitor decreased, interfaces play an important role in determining the nanolaminates’ overall properties. Barshilia et al. [25] prepared a nanolayer of Al2O3/ZrO2 and demonstrated that a critical ZrO2 layer thickness ≤10.5 nm at a substrate temperature of 973 K was required in order to stabilize the t-ZrO2 phase. It was observed that the crystallite sizes are of the range 4 to 8 nm (5:5-nm multilayer film) in the temperature range of 300 to 1,273 K. Tetragonal ZrO2 have lower free energy compared to monoclinic ZrO2 for the same crystallite sizes, which means that the t-ZrO2 can be stabilized if the crystallite size is less than

a certain critical value. The critical size of 30 nm for bulk [28, 30], 50 nm for evaporated ZrO2 films [31], and 16.5 nm for CVD [32] were reported. In the present work, multilayer films were prepared by PLD, and it was ID-8 found that the critical layer thickness of ZrO2 is ≤10 nm. There are evidences [4, 21] that the tetragonal zirconia nanocrystallites in zirconia-alumina nanolaminates are less likely to undergo transformation than the dopant-stabilized zirconia microcrystallites in zirconia-alumina composites. Conclusions The Al2O3/ZrO2 multilayers of 10:10-, 5:10-, 5:5-, and 4:4-nm films were deposited on Si (100) substrates by PLD. The XRD and HTXRD studies showed the formation of tetragonal phase of ZrO2 at room temperature when the ZrO2 layer thickness is ≤10 nm. The XTEM investigation of the as-deposited 5:10-nm film showed the distinct formation of nanolaminates. The ZrO2 layer shows lattice fringes and consists of mainly tetragonal phase with no secondary phases at the interfaces and amorphous alumina. The XTEM of the 5:10-nm annealed film showed the inter-diffusion of layers at the interface and amorphization.