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Nanoporous devices constitute emerging platforms for selective molecule separation and sensing, with great potential for high throughput and economy in manufacturing and operation. Acting as mass transfer diodes similar to a solid-state device based on electron conduction, conical pores are shown to have superior performance characteristics compared to traditional cylindrical pores. Such phenomena, however, remain to be exploited for molecular separation. Here we present performance results from silicon membranes created by a new synthesis technique based on interferometric lithography. This method creates millimeter sized planar arrays of uniformly tapered nanopores in silicon with pore diameter 100 nm or smaller, ideally-suited for integration into a multi-scale microfluidic processing system. Molecular transport properties of these devices are compared against state-of-the-art polycarbonate track etched (PCTE) membranes. Mass transfer rates of up to fifteen-fold greater than commercial sieve technology are obtained. Complementary results from molecular dynamics simulations on molecular transport are reported.
Comprehensive characterization at nanoscale is needed to create novel nanostructures for high efficiency solar cells. To produce consistent results, wide-ranging characterization procedures for integrated nanostructures have been developed. Characterization of a novel nanowire, nanotube and nanocable system includes: chemical, electrochemical, structural, optical and electrical characterization of nanostructures in relation with growth conditions. We present here results on Au and CdTe/Au system that help understanding how surface composition and properties are modified in this system. New challenges in structural characterization were also identified and improved sample preparation techniques were developed.
The interdiffusion of Cadmium Arachidate (CdA) in Langmuir-Blodgett films has been studied by neutron reflection at the Intense Pulsed Neutron Source of Argonne National Laboratory. One of the samples consisted of a few layers of perhydro H-CdA deposited on a silicon support, overlayered with a few layers of deuterated D-CdA, for a total thickness of ∼300 Angstroms. In a second sample the layers of perhydro-and deuterated- CdA were separated by two monolayers of Hn-octadecene/co-maleic acid copolymer. When heated for 15 minutes at 70°C, well below the disorder temperature , approximately 25% of the D-CdA molecules were replaced by H-CdA molecules, although the overall Langmuir-Blodgett film structure is known to remain unchanged . The presence of copolymer layers limited the interdiffusion process to about 5%.
Novel polymers are synthesized by attaching amphiphilic dye groups along a hydrophilic polyether backbone. These polymers are fabricated into noncentrosymmetric films by the Langmuir-Blodgett (L/B) technique. Stacks of molecular bi-layers are assembled by γ-type deposition, interleaving two different dye-substituted polymers. One polymer has the dye's molecular dipole pointing toward the backbone, while in the other polymer, the dye points in the opposite direction. Light from a Nd:YAG laser is passed through these films and the second harmonic is detected.
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