Structural Characterization of Mesoporous Thin Film Architectures: A Tutorial Overview

Abstract

Mesoporous thin film architectures are an important class of materials that exhibit unique properties, which include high surface area, versatile surface functionalization, and bicontinuous percolation paths through a broad library of pore arrangements on the 10 nm length scale. Although porosimetry of bulk materials via sorption techniques is common practice, the characterization of thin mesoporous films with small sample volumes remains a challenge. A range of techniques are geared toward providing information over pore morphology, pore size distribution, surface area and overall porosity, but none of them offers a holistic evaluation and results are at times inconsistent. In this work, we present a tutorial overview for the reliable structural characterization of mesoporous films. Three model samples with variable pore size and porosity prepared by block copolymer (BCP) coassembly serve for a rational comparison. Various techniques are assessed side-by-side, including scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incidence small-angle X-ray scattering (GISAXS), and ellipsometric porosimetry (EP). We critically discuss advantages and limitations of each technique and provide guidelines for reliable implementation.

Fractionation of block copolymers for pore size control and reduced dispersity in mesoporous inorganic thin films

“…Moreover AFM lateral resolution can be affected by tip convolution effects, and therefore some discrepancies between the data obtained by the different techniques may be expected. 50 Nevertheless, a narrower M w distribution of the BCP induced in all cases a lower pore size dispersity in the final mesoporous film. This provides further evidence that the herein presented approach of BCP chromatographic fractionation not only offers a straightforward method to obtain an extensive BCP library with little synthetic effort but also reduced dispersity in inorganic mesoporous films.…”

“…Sample analysis by AFM is limited to the surface topography and, thus, alternative characterization techniques are required to evaluate the obtained results. 50 To this end, ellipsometric porosimetry (EP) has emerged as a reliable characterization technique to probe porosity, pore size and pore morphology of thin films. 50 Fig.…”

“…50 To this end, ellipsometric porosimetry (EP) has emerged as a reliable characterization technique to probe porosity, pore size and pore morphology of thin films. 50 Fig. 4 (left column) shows the EP adsorption isotherms obtained for the respective samples.…”

Fractionation of Block Copolymers for Pore Size Control and Reduced Dispersity in Mesoporous Inorganic Thin Films

“…10.9±1.4 nm for A19, 12.3±1.5 nm for A18 and 14.8±1.6 nm for A17, and with significantly reduced pore dispersity when compared to the non-fractionated BCP (13.0±3.6). Sample analysis by AFM is limited to the surface topography and, thus, alternative characterization techniques are required to evaluate the obtained results [46] . To this end, ellipsometric porosimetry (EP) has emerged as a reliable characterization technique to probe porosity, pore size and pore morphology of thin films.…”

Fractionation of Block Copolymers for Pore Size Control and Reduced Dispersity in Mesoporous Inorganic Thin Films

“…To this end, ellipsometric porosimetry (EP) has emerged as a reliable characterization technique to probe porosity, pore size and pore morphology of thin films. [46] Figure 4 (left column) shows the EP adsorption isotherms obtained for the respective samples. Please note that the films exhibited a porosity in the range of 47% to 54%.…”