Replication of ordered block copolymer templates for the preparation of porous metal oxides in supercritical carbon dioxide
Ordered nanostructured materials are of enormous interest in photonics, sensing and detection arrays, catalysis, separations, microfluidics and low dielectric constant (low k) thin films. The traditional approach to preparation of these nanostructured films involves cooperative self-assembly of organic templates (including surfactants) and precursor molecules in solution. The approach has been successful in controlling the pore order at the local length scale, but has limited promise for controlling long-range pore order and orientation over the length scales of the device.
We have developed a novel technique for the preparation of nanostructured metal oxide films by a rapid replication procedure of structured organic templates in supercritical carbon dioxide. The technique enables us to separate the self-assembly of the ordered template film from the formation of the metal oxide network. The structure of the pre-formed template on both the local and device levels can be achieved in three dimensions using established techniques prior to infusion of the inorganic phase. This approach also offers flexibility with regard to framework chemistry and the nature of the copolymer template, which can now be chosen independently without regard to compatibility in solution or concerns about disrupting the coordinated self-assembly process. The application of the technique to preparation of ordered mesostructured silicate/organosilicate films with dielectric constants below 2.2 and desirable mechanical properties is discussed.
Post-synthesis treatments of mesostructured silicate and organosilicate films were also investigated with the aim of reducing the shrinkage associated with the template removal by calcination. In addition, blends of semicrystalline amphiphilic block copolymers and amorphous homopolymers was also studied to improve the wetting properties and reduce the crystallinity. Mesostructured silicate and organosilicate films that were templated with the blends exhibited a higher degree of mesostructural order as compared to the films templated by the amphiphilic block copolymers only.
0794: Materials science