Glass formation in amorphous ZnO films revealed by chip calorimetry

In this work, we utilize the high heating/cooling rates of chip calorimetry to perform in situ annealing of an inkjet-printed zinc oxide solgel ink consisting of zinc acetate, 2-methoxyethanol, and monoethanolamine and directly observe the thermodynamic signatures of its corresponding structural phase transformations. We find that rapid solvent removal achieved by annealing above the boiling point of the solvent, similar to an industrial drying technique known as flash drying, induces the formation of ≈ 98 % amorphous zinc oxide films having an unprecedented, largely pronounced glass transition while retaining its semiconductor properties evidenced by field-effect transistor measurements. Thin-films produced at comparable heating rates to those used for calorimetry experiments are used to corroborate these findings using independent measurements. Prepared films exhibit a clear amorphous halo centered about the three most prominent Bragg positions of the wurtzite phase of ZnO and remain thermally stable against crystallization until 250 ° C have a room temperature thermal conductivity of ≈ 1.03 - 1.4 W m - 1 K - 1 (consistent with recent ab initio estimates) with supporting evidence of a structural relaxation near T G consistently observed in both electronic and thermal conductivity.