An optimized nanoparticle separator enabled by elecron beam induced deposition

J. D. Fowlkes,1 M. J. Doktycz2 and P. D. Rack1,3

1Nanofabricatin Research Laboratory, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
Biological and Nanoscale Systems Group, Biosciences Division, Oak Ridge National Laboratory
Materials Science and Engineering Department, The University of Tennessee, Knoxville, TN


Size–based separations technologies will inevitably benefit from advances in nanotechnology.  Direct–write nanofabrication provides a useful mechanism to deposit/etch nanoscale elements in environments otherwise inaccessible to conventional nanofabrication techniques. Spatially complex surfaces evolve during multilevel micro– and nanoscale fabrication.   Microfluidic  devices, for example, contain channels, reservoirs and cavities.  Once these elements have been transferred into the substrate, conventional top–down fabrication using masking and lithography can become quite challenging to define, accurately and precisely, additional features on or within the structure.  Direct–write, bottom–up methods are well suited to fabricate functional features on topographically complex surfaces and provide methods to circumvent this fabrication challenge. Here, electron beam induced deposition (EBID) was used to deposit an array of nanoscale features in a 3D environment with minimal material proximity effects outside the beam–interaction–region (BIR). 


The membrane component of a nanoparticle separator was fabricated by depositing a linear array of sharply tipped nanopillars, with a singular pitch, designed for sub–50nm nanoparticle permeability.  The nanopillar membrane was used in a dual capacity to control the flow of nanoparticles in the transaxial direction of the array while facilitating the sealing of the cellular–sized compartment in the paraxial direction.  An optimized growth recipe resulted which (1) maximized the growth efficiency of the membrane (which minimizes proximity effects), (2) preserved the fidelity of spacing between nanopillars (which maximizes the size–based gating quality of the membrane) while (3) maintaining sharp nanopillar apexes for impaling an optically transparent polymeric lid critical for device sealing.

Credit: This work was published in Nanotechnology 21 165303, (2010) doi:10.1088/0957-4484/21/16/165303. This Research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.