Stability and annealing of alucones and alucone alloys

Abstract

Hybrid organic–inorganic alucone films have been deposited using trimethylaluminum and ethylene glycol by molecular layer deposition (MLD). The stability of the coatings was monitored in ambient as well as in dry air. Alloys have also been deposited using alucone and Al2O3. The effect of thermal annealing as a function of the Al2O3 content was assessed. The stability and morphology of such organic–inorganic alloys are finely tuned by their composition. The alucones and alucone/Al2O3 alloys with the ratio of 5 cycles to 1 cycle resulted in a compact layer after thermal treatment, whereas the 1:1 composite showed numerous cracks. Slow thermal annealing at the rate of 10 °C/h of the 5:1 alloy leads to the decrease of refractive index from n = 1.52 to n = 1.34 with a thickness loss of ∼28%. Fast heating rate of 120 °C/h results in a larger thickness loss of ∼37% and the development of a more dense film with an effective refractive index of n = 1.40. The slow thermal annealing facilitates the formation of larger pores resulting in films with considerably lower refractive index. The atomic layer deposition/MLD approach is highly promising to develop novel, nanoporous, low index functional materials for different applications in optical coatings, catalysis, or gas separation.