Fabrication, Characterization, and Functionalization of Porous Nanocrystalline Silicon Membranes.

摘要

Porous nanocrystalline silicon (pnc-Si) membranes are promising for a wide range of applications from biofiltration to use as a platform for cell culture. It is an order of magnitude thinner than any commercially available or experimentally fabricated membrane. Because the thickness of a pnc-Si membrane is between 15 nm and 30 nm, comparable to the size of molecules to be separated, mass transport through the membrane is greatly enhanced. The first part of this work focuses on the fabrication of pnc-Si. For applications involving separation and concentration of molecular species, it is crucial that a membrane passes certain species while rejecting others. One manner in which this can be achieved is by tuning the size and density of the pores by changing key fabrication conditions. These parameters are identified and a systematic study was performed to determine their effect on pore morphology. In the second part of this work, a phenomenological model for pore formation is presented based on empirical observations and prior studies on polycrystalline materials. Next, the structural, optical, and mechanical properties of pnc-Si are examined using an array of characterization tools. In the final part of this thesis, post-production methods for pore size control and functionalization are discussed. It is demonstrated that the hydraulic permeability of pnc-Si, in both the unmodified and modified forms, follows theoretical predications for transport through an ultrathin porous material. Additonally, nanoparticle and protein separations are presented as a demonstration of the potential use of pnc-Si membranes in biomedical research and industry.