Atomic Layer Deposition of SiO2 and TiO2 in Alumina Tubular Membranes: Pore Reduction and Effect of Surface Species on Gas Transport

Abstract

The pore diameters in alumina tubular membranes were progressively reduced via SiO2 and TiO2 atomic layer deposition (ALD) using sequential surface reactions. The SiO2 ALD was accomplished using alternating exposures of SiCl4 and H2O. The TiO2 ALD was achieved using alternating exposures of TiCl4 and H2O. The reduction of the pore diameter was observed using in situ N2 conductance measurements. The total conductance, Ct = Q/ΔPt, was measured using a mass flow controller to define a constant gas throughput, Q, and two capacitance manometers to monitor the total pressure drop, ΔPt. These N2 conductance measurements revealed that the SiO2 and TiO2 ALD progressively reduced the pore diameter from an initial diameter of 50 A to molecular diameters. Using an aperture model for the conductance, the pore diameter was found to decrease at a rate of 1.3 ± 0.1 A per SiCl4/H2O AB cycle during SiO2 deposition and 3.1 ± 0.9 A per TiCl4/H2O AB cycle during TiO2 deposition. The N2 conductance measurements were also very ...