Asymmetric Nanopores for Fundamental Studies of Hindered Transport

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1033203Wolden The objective of this research is to develop a simple approach for large area fabrication of asymmetric nanopores, which in turn will be employed for fundamental studies of hindered transport. The research will employ a new variant of pulsed plasma-enhanced chemical vapor deposition (PECVD) to digitally manipulate the openings of model supports. Pulsed PECVD has been engineered as an alternative to atomic layer deposition (ALD) for self-limiting growth of thin films (i.e. 1 Å/pulse). Through control of operating conditions the degree of conformality may be engineered, enabling digital control over pore closure without sacrificing the high porosity/permeability of the underlying supports. The well-defined geometry of the resulting nanopores will serve as model systems for fundamental studies of hindered transport. Well-characterized proteins and inorganic quantum dots will be explored as model solutes. Surface effects often dominate at the length scales in question. This issue will be investigated by using established self-assembly techniques to systematically manipulate the surface termination of both pores and nanoparticles. The basic precepts have been demonstrated in preliminary work using anodized alumina supports. However, these studies also revealed that the pore size distribution in these commercial supports was inadequate for control at the nanoscale. This limitation will be remedied by employing uniform silicon supports fabricated using e-beam lithography through a collaboration with the Center for Nanophase Materials Sciences at ORNL. Intellectual Merit The intellectual merit of this proposal is in nanopore fabrication, thin film deposition, and nanoscale transport phenomena. Existing approaches for nanopore synthesis employ energetic beam technologies that are not amenable to large scale fabrication. The PI's approach employs standard integrated circuit (IC) fabrication techniques and is performed at ambient temperature. Feature scale models will be developed to simulate pore closure by pulsed PECVD, and validated using cross section microscopy. The resulting nanopores will have well-defined cylindrical geometries, creating an ideal platform for rigorous evaluation of theoretical models of hindered transport. Experimental measurements of permeance and solute rejection will be used to test and improve understanding of transport at the nanoscale. Broader Impacts Large area synthesis of well-defined nanopores would be an enabling innovation for the separation of both biological constituents and nanoparticles. Moreover, the resulting channels will serve as an ideal platform for experimental investigations of nanofluidics. The coupling of nanofluidics with electrical manipulation of charged species such as ions and DNA offers a potential alternative to conventional IC technology. The use of silicon wafers as the support structure will facilitate the integration of nanopore arrays with conventional electronic and microfluidic components for Lab-on-a-Chip applications. The broader impacts also include the training of a PhD candidate and the engagement of undergraduate researchers in areas of great technological importance. The PI and his students will continue their work with the CSM K-12 outreach team, developing teacher workshop materials related to membranes and water purification for school districts with large populations of underrepresented students.