Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle x-ray scattering

TL;DR

This study demonstrates how in situ GISAXS can monitor pore size tuning in mesoporous films during ALD, revealing the relationship between precursor size and achievable pore dimensions.

Contribution

It introduces a novel in situ method combining GISAXS and XRF to analyze pore size changes during ALD in mesoporous films, providing insights into conformality and limitations.

Findings

GISAXS effectively tracks density and surface area changes during ALD

The minimum pore size achievable is limited by Ti-precursor molecule size

Good agreement between GISAXS and XRF data on Ti deposition

Abstract

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (< 10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle x-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO2 in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ x-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both data sets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule.