Phosphonate containing hybrid layers using atomic and molecular layer deposition

Phosphorus-containing hybrid organic-inorganic materials demonstrate unique physicochemical properties making them suitable candidates for energy storage, electrocatalysis, and as protective and biocompatible coatings. Of special interest in this regard are metal phosphonate films, where the organic group bound to the P atom can tune functional properties of the films. However, the deposition of such materials in thin-film form remains challenging and has achieved only limited success. In this work, we present two deposition processes employing combination of atomic and molecular layer deposition approaches for the growth of aluminium phosphonates, utilizing trimethylaluminum as the Al source, and dimethyl methylphosphonate and dimethyl phenylphosphonate as the P sources, respectively. Both processes demonstrated saturated growth, and the incorporation of the phosphonate groups was confirmed using ex situ x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. As-grown films demonstrated a P/Al ratio of ca. 0.2–0.3, indicating the formation of a phosphonate-doped alumina matrix. Through density functional theory calculations, we delineated differences in precursor chemistry and their impact on growth characteristics for the processes. These films deposited using these approaches demonstrated superior thermal stability (≥500 °C) and hydrolytic stability under all tested conditions. The findings of this study can inspire the development of efficient processes for the incorporation of organophosphorus groups in such hybrid thin films.