AVS 61st International Symposium & Exhibition
    Thin Film Thursday Sessions
       Session TF-ThA

Paper TF-ThA3
Pulsed Plasma Enhanced Chemical Vapor Deposition for Nanoscale Control of the Size, Shape and Surface Properties of Asymmetric Membranes

Thursday, November 13, 2014, 3:00 pm, Room 307

Session: Thin Film for Permeation Barriers and Membranes
Presenter: Sanket Kelkar, Colorado School of Mines
Authors: S. Kelkar, Colorado School of Mines
D. Chiavetta, Colorado School of Mines
C.A. Wolden, Colorado School of Mines
Correspondent: Click to Email
The objective of our research is to develop a simple and scalable approach for modification of size and geometry of model membrane supports to fabricate nanopores. In this work, we first employ relatively large template structures (~ 100 nm) produced by track-etching or e-beam lithography. The pore size is then reduced to the desired level by deposition of material using pulsed plasma enhanced chemical vapor deposition (PECVD). Pulsed PECVD has been developed as a high throughput alternative to atomic layer deposition (ALD) to deliver self-limiting growth of thin films. Pulsed PECVD has two growth components that act sequentially: ALD-like component during the plasma off step (γ ~ 0); and PVD-like growth component during the plasma on step (γ ~ 1), where γ is the reactive sticking coefficient. The ALD contribution is constant at ~1 Å /pulse whereas the PVD contribution can be typically varied from 0.5 - 10 Å/pulse by appropriate control of operating conditions. The degree of conformality in pulsed PECVD can thus be engineered by controlling the relative contribution of these 2 growth components. Like ALD, pulsed PECVD provides sub-nm resolution over the pore size. However, pulsed PECVD does not result in perfectly conformal deposition profiles, and as such control of the final nanostructure is more complicated. In this work we develop feature scale modeling tools to predict and design the fabrication of nanostructures, such as asymmetric nanopores, using pulsed PECVD. The model is verified by systematic investigation of deposition profiles on patterned cylinders and trenches through cross-section electron microscopy. Polymeric track etched membrane supports (TEMS) are employed as model template structures to demonstrate the capability of pulsed PECVD for precise pore size reduction. Permeance and solute rejection measurements demonstrate that the pulsed PECVD coated TEMS exhibit higher selectivity without compromising on the flux due to their asymmetric structure. These nanoporous membranes will be utilized to study the effect of pore size and geometry on hindered transport of ions and macromolecules at the nanoscale. Furthermore, the hydrophobicity of polymeric supports will be mitigated by deposition of suitable oxide material.