A variety of fabrication methods for single-walled carbon nanotubes (SWCNTs) has been developed, but none of them has been proven to generate tubes of only one chirality. Hence, a sample of as-produced SWCNTs always consists of a mixture of metallic and semiconducting tubes. By this, the application of SWCNTs in electronics, optics and sensing is limited today. Recently, the sorting of carbon nanotubes using density gradient ultracentrifugation (DGU) has been demonstrated. We report on an improved sorting according to electronic type by applying a two-step procedure: In the first step, we enriched semiconducting SWCNTs via DGU. In the second step, the sorted fractions have been reinserted and a second DGU was performed, winnowing metallic SWCNTs. Employing this procedure, we were able to reduce the content of metallic SWCNTs from 38 to 11%. Furthermore, we assembled carbon nanotube field-effect transistors with a high ON/OFF ratio from the sorted fraction in a single st ep by dielectrophoresis
Methods for the functionalization of polymer biosensor surfaces are applied for the binding of receptors and the sensing of biological particles. In many cases the same biosensor polymer has to perform transduction mechanisms as in the case of optical waveguides. The effects of the functionalization process on the sensor transduction properties like absorption and surface roughness loss should be minimal. In this work we investigate the formation of functional groups by oxygen plasma treatment as a method of precise surface modification for PMMA and SU-8 waveguide materials. Oxygen groups were analyzed by contact angle measurements, XPS, chemical derivatization XPS and fluorescence labeling
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