Effect of Atomic Layer Deposited Al2O3 on Sintering Behavior of ZnO Nanopowders

Atomic layer deposition (ALD) is demonstrated as an effective technique for conformally coating nanoparticles with ultrathin diffusion barrier layers to control grain growth during sintering. In this study, ALD aluminum oxide (Al2O3) films are deposited on zinc oxide (ZnO) nanoparticles (similar to 60 nm diameter) and subjected to sintering at 850 degrees C under uniaxial loading of 150 MPa. Uncoated ZnO forms a densified ceramic with grain sizes of 2.76 +/- 0.50 mu m. In contrast, ALD-coated nanoparticles exhibit restricted grain growth. A 1 nm Al2O3 coating limits the sintered ZnO grains to 89 +/- 23 nm, and a 10 nm coating restricts the ZnO grains to 55 +/- 7 nm. These results underscore the effectiveness of ALD to engineer grain boundary diffusion barriers and, when integrated with conventional processing methods, its potential for enabling the scalable manufacturing of nanocrystalline ceramics for use as transparent bulk materials with noncubic crystal structures.