Composition and morphology control in mesoporous non-ionic templated thin films
by Richman, Erik Karl, Ph.D., UNIVERSITY OF CALIFORNIA, LOS ANGELES, 2008, 108 pages; 3302601

Abstract:

Templated composite materials produced through evaporation induced self-assembly provide a versatile approach to nanoscale structural control via solution processing. Using block copolymers to produce micelle templates, a variety of symmetries with periodicity in the 2-30 nm range are available. Hexagonal honeycomb phases are interesting for their potential anisotropy while cubic phases have interconnected porosity. For film deposition using dip-coating, the film is subject to a shear force during formation, although generally, the honeycomb structure forms with cylinders confined to the plane of the substrate but oriented isotropically. This thesis addresses the issues of pore orientation, film thickness, and finally composition in these inorganic templated composites. The materials examined here are related to aerogels but with the added property of periodic order. We focus on silica as the most common case. For use in devices we need to control symmetry, thickness, and pore orientation. Symmetry is controlled via polymer:inorganic ratio in the precursor solution. Using AFM and varying the deposition conditions, we first show that the periodic order has no effect upon the thickness of the film, allowing thickness to be modeled using standard methods. Second, exploring the surface morphology with AFM, we seek to understand domain structure and formation mechanisms. We see that the deposition conditions can be subdivided into three kinetic categories. Near the isoelectric point of silica (pH 2), mesoporous films are observed to have isotropic ribbon domains independent of the deposition conditions. At pH 1, thick films show similar isotropic domain orientations. By contrast, thin films produce uniaxially-oriented pores and anisotropic surface domains, all aligned with the dip-coating direction. In the third topic pore orientation is again addressed. A combination of XRD and cross-section SEM are used to show that a hydrophobic/hydrophilic pattern match from an FCC (111) oriented cubic film of titania can be used to induce vertical orientation in hexagonal honeycomb silica film. Finally, in the last topic, we show that large pore silica can be converted to mesoporous silicon using a magnesiothermic reduction. The combined results opens the gate to complex solution processed oxides and non-oxides with a high degree of control.

 
AdviserSarah H. Tolbert
SchoolUNIVERSITY OF CALIFORNIA, LOS ANGELES
SourceDAI/B 69-02, p. , Jun 2008
Source TypeDissertation
SubjectsPhysical chemistry
Publication Number3302601
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