Characterization and nanoindentation testing of thin ZrO2 films synthesized using layer-by-layer (LbL) deposited organic templates

Thin organic LbL (layer-by-layer) films with negatively charged surface were used as templates for biomimetic deposition of ZrO2 on Si wafers by hydrolysis of Zr(SO4)2 solution. The as-deposited ceramic layers were fully amorphous and were composed of the mixture of zirconia and zirconium sulfate. During transmission electron microscopy (TEM) examination, the amorphous ZrO2 crystallized almost instantaneously to tetragonal (t) ZrO2 under the electron beam. The ≤110 nm thick as-deposited layers were crack-free and adhered well to the LbL surface. Annealing at 500 °C led to complete crystallization of amorphous ZrO2 to nanocrystalline t-ZrO2. Further heating to 900 °C resulted in transformation to monoclinic ZrO2, complete removal of sulfur and twofold shrinkage of the ceramic layer thickness. Both the nanohardness and elastic modulus of the deposited zirconia layers were significantly improved following the heat treatments.