Modification of Porous Alumina Membranes Using Al₂O₃ Atomic Layer Controlled Deposition

Al₂O₃ films were deposited with atomic layer control inside the pores of Anodisc alumina membranes. To achieve this controlled deposition on a high aspect ratio structure, a binary reaction for Al₂O₃ chemical vapor deposition (2A1(CH₃)₃ + 3H₂O → Al₂O₃ + 6CH₄) was separated into two half-reactions: (A) AlOH* + A1(CH₃)₃ → A1-O-A1(CH₃)₂* + CH₄ and (B) AlCH₃* + H₂O → AlOH* + CH₄, where the asterisks designate the surface species. The trimethylaluminum [Al(CH₃)₃] (TMA) and H₂O reactants were employed alternately in an ABAB... binary reaction sequence to deposit the Al₂O₃ film. Because each half-reaction is self-limiting, atomic layer controlled Al₂O₃ deposition was achieved on the surface of the high aspect ratio pores. To determine the necessary reaction conditions, surface species during each half-reaction were periodically monitored using in situ transmission FTIR spectroscopy. Ex situ gas flux and permporometry measurements were also performed to determine the effect of the binary reaction sequence on the pore diameter. Gas flux measurements for H₂ and N₂ were consistent with a progressive pore size reduction versus the number of AB reaction cycles. The permporometry measurements showed that the original pore diameter of ∼220 Å was reduced to ∼140 Å after 120 AB reaction cycles.