Structural comparison of hexagonally ordered mesoporous thin films developed by dip- and spin-coating using X-ray reflectometry and other quantitative X-ray techniques

Abstract

Clear and homogeneous precursors for casting mesoporous thin films (MTFs) were prepared by addition of a triblock polyalkylene oxide amphiphilic surfactant (the structural directing agent) to a clear sol of tetraethylorthosilicate. Films were developed by dip-and spin-coating methods and calcined to yield high quality crack-free coatings containing highly ordered hexagonal arrangements of mesopores. Comparison of the dip-coating and spin-coating methods was made using X-ray methods including powder X-ray diffraction, reciprocal space mapping, X-ray reflectometry and in-plane scattering. In all cases, the films had a highly textured nature with preferential alignment of pores parallel to the substrate. It was found that the dip-coating method resulted in better quality films with greater long range order. The varied X-ray methods provided a detailed structural analysis of the mesoporous thin films which showed a distorted hexagonal arrangement. The results defining pore size could be directly and favourably compared to TEM and N 2 isotherm data. It was found that all the techniques are in reasonable agreement.

Ordered Mesoporous Silicate Structures as Potential Templates for Nanowire Growth

“…The flat substrates have been discussed in depth previously. [11] The presence of well-ordered pore structures is confirmed by using small-angle X-ray scattering (SAXS) measurements shown on Figure 2b. This pattern can be readily assigned to a p6mm 2D hexagonal structure with the pores lying parallel to the substrate surface and in a direction parallel to the X-ray plane.…”

“…1a), a cross-sectional SEM image verified the MTF to have a smooth surface with only a small variation in thickness across the film surface (consistent with previous results). [11] The SEM image also suggests that there is strong adhesive contact between the MTF and the substrate as there are no visible defects seen at the film/substrate interface on any images collected. On the metal-channelled substrate the resultant MTF appears to be heavily disrupted and exhibits long continuous stress cracks at the interface between the metal and the film as well as considerable shrinkage of the film between the metal stacks (Fig.…”

“…The presence of such shoulders and peaks can be assigned to several factors including increasing structural complexity and larger unit cells than that predicted by a perfect hexagonal arrangement of pores as well as film misalignment. [11] Miyata et al [17] have also suggested these features can arise from the divergence of the incident X-ray beam, which is of the same order as the diffraction angle. In this case we believe that the shoulders on the (100) reflection are due to strain effects within the channels leading to distortion of the hexagonal pore arrangement and nonequivalence of the lattice spacing in different {100} directions (see below).…”

“…[4,7,9,10] Along with many authors we have shown that very regular MTFs can be produced at surfaces. [11] The synthesis of highly organized ordered domains using patterned substrates with adjustable dimensions has proved very successful. Trau et al, [12] Stucky and co-workers, [13] and Sibener and coworkers [14] have used the concept of confinement effects initiated by structures such as channel or mould environments to dictate a particular morphologic arrangement.…”

Advances in Ultra Low Dielectric Constant Ordered Porous Materials

“…However, these films are unlikely to exhibit this perfect structure through the entire film and commonly exhibit a poly-grain structure with various structural defects. 36 Often, because of solvent evaporation rates that vary as the solvent front moves through the film during preparation and drying, 37 the films can exhibit a central portion that has a disordered worm-hole type porous structure but are well-ordered at the air and substrate interface (Fig. 6).…”