Polymer- and surfactant-templated mesoporous inorganic materials offer a unique combination of controllable nanoscale architecture, materials variation and low-cost solution processing. Inorganic materials can be produced with a range of periodic pore structures, with feature size ranging from 2 to 30 nm, and from a diverse set of materials. Unfortunately in thin-film form, the pores of the ubiquitous hexagonal honeycomb phase tend to lie in the plane of the substrate making these materials unsuitable for applications where diffusion into the pores is required. Here, we show that nanometre-scale epitaxy on a patterned substrate can be used to form vertically oriented pores in honeycomb-structured films. We use the surface of cubic mesoporous films to form the pattern; as such, our method does not sacrifice the simple processing advantages of a self-assembled system. A precise lattice match between the hexagonal and cubic films is needed for vertical orientation, a condition that can be achieved using mixed templates or selective pore swelling. Pore orientation is characterized by a combination of microscopy and diffraction. Here, we present alignment data on oriented nanopores in the 10-15 nm range, but the method should be applicable across the 2-30 nm pore size range of these self-organized materials.

Cobalt nanoparticles are incorporated into hexagonal honeycomb mesoporous silica to study the effect of nanoscale confinement on magnetic coupling. The superparamagnetic Co particles can fill a significant fraction of the total pore volume and can constitute up to 22.1 ± 0.9% by mass of the composite. We find that Co particles form chains in the silica pores, which results in altered magnetic coupling. For example, coupling within chains of Co particles in pores produces a higher coercivity than the value found in either noninteracting or randomly aggregated particles. Remanence measurements also indicate that the Co nanoparticles form ferromagnetically coupled chains, thus converting the structural anisotropy of the silica host into magnetic anisotropy in the guest. This work demonstrates a method to create anisotropy in a nanoscale composite using easily synthesized isotropic building blocks.

In this work, we examine the kinetics of titania crystallization in periodic templated mesoporous thin films with a goal of understanding the relationship between atomic-scale crystallization and nanometer-scale structural change. The anatase crystallization proceeds via a surface-nucleation mechanism that rapidly produces relatively large titania grains. The activation energy for this process is about 210 ± 40 kJ/mol. As the crystallization proceeds, the periodic mesoscale order changes as the particles begin to impinge on the pore volume. The activation energy for this nanoscale restructuring is approximately 140 ± 30 kJ/mol, on the same order of magnitude as that observed for the crystallization. By studying the competition between these two processes, we are able to define the optimal conditions for kinetically controlled crystallization of the mesoporous material without appreciable change in the nanometer-scale structure. The grain growth behavior in the wall structure is also examined and is found to be directly affected by the presence of the inherent pore volume. These data contribute to the current understanding of the crystallization process in mesoporous oxide films and may be generally useful for developing crystalline titania-based materials with tunable nanoscale architectures.

Surfactant templating is a method that has successfully been used to produce nanoporous inorganic structures from a wide range of oxide-based material. Co-assembly of inorganic precursor molecules with amphiphilic organic molecules is followed first by inorganic condensation to produce rigid amorphous frameworks and then, by template removal, to produce mesoporous solids. A range of periodic surfactant/semiconductor and surfactant/metal composites have also been produced by similar methods, but for virtually all the non-oxide semiconducting phases, the surfactant unfortunately cannot be removed to generate porous materials. Here we show that it is possible to use surfactant-driven self-organization of soluble Zintl clusters to produce periodic, nanoporous versions of classic semiconductors such as amorphous Ge or Ge/Si alloys. Specifically, we use derivatives of the anionic Ge9(4-) cluster, a compound whose use in the synthesis of nanoscale materials is established. Moreover, because of the small size, high surface area, and flexible chemistry of these materials, we can tune optical properties in these nanoporous semiconductors through quantum confinement, by adsorption of surface species, or by altering the elemental composition of the inorganic framework. Because the semiconductor surface is exposed and accessible in these materials, they have the potential to interact with a range of species in ways that could eventually lead to new types of sensors or other novel nanostructured devices.

This paper describes the process of making ordered mesoporous silicon (Si) thin films. The process begins with mesoporous silica (SiO 2) thin films that are produced via evaporation induced self-assembly (EISA) using sol-gel silica precursors with a diblock copolymer template. This results in a film with a cubic lattice of 15 nm diameter pores and 10 nm thick walls. The silicon is produced through reduction of the silica thin films in a magnesium (Mg) vapor at 675 degrees C. Magnesium reduction preserves the ordered pore-solid architecture but replaces the dense silica walls with 10-17 nm silicon crystallites. The resulting porous silicon films are characterized by a combination of low and high angle X-ray diffraction, combined with direct SEM imaging. The result is a straightforward route to the production of ordered nanoporous silicon.