Chemical Vapor Depositions of Single Walled Carbon Nanotube thin films and their applications for sensors in aqueous sol
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A5.19.1
Chemical Vapor Depositions of Single Walled Carbon Nanotube thin films and their applications for sensors in aqueous solutions Qiang Fu, Lei An, Chenguang Lu and Jie Liu Gross Chemistry Laboratory, Duke Univeristy Durham, NC 27708 Abstract: High-density and high-quality single walled carbon nanotubes are directly grown on surface by Chemical Vapor Depositions. We found that those SWNT thin films could be used to fabricate thin film field-effect transistors. Those transistors are very sensitive to surface charges changes in aqueous solutions and could be used to build chemical sensors. Introductions: Single-Walled Carbon Nanotubes (SWNTs) could be looked as seamless cylinders with only a layer of carbon atoms and diameters about 1 nanometer1. For SWNTs, all the atoms are on surface and exposed to the environments. Because of such unity surface-to-volume ratio, molecules absorbed on SWNT side walls could disturb their electronic structures and affect the conductance of SWNTs. Thus, the molecule absorptions on SWNTs could be detected electrically in SWNT Field-Effect Transistors (FETs). SWNT FETs have been used to fabricate high-sensitivity chemical sensors to detect various chemicals in gas phase and physiological solutions2-4. However, the developments of SWNT sensors are hindered by several limitations. First, electronic properties of SWNTs are very sensitive to their structures. Depending on the chiral angles, SWNTs could be either metallic or semiconducting. Semiconducting SWNT are specifically desired to fabricate FET for sensor applications. However, no methods have been developed to synthesize solely uniform semiconducting or metallic SWNTs, which make fabrication process of SWNT FETs time consuming. Second, the sensing mechanism of SWNT sensor is still not well understood. Although chemical sensors of SWNT have been demonstrated, possible factors affecting SWNTs conductance still remain to be clarified. In this report, using PS-PVP diblock copolymer to deliver highdensity nanoparticles on surface as catalysts, we synthesized dense SWNT thin films on flat surface by Chemical Vapor Depositions (CVD)5. We fabricated thin film FETs from those high density SWNTs thin films and found that those thin film FETs had high sensitivity to surface charges states around SWNTs in aqueous solution. Those results provided more insight of SWNT sensing mechanisms in solutions and pointed a practical route to SWNT sensor designs. Experiments: Preparations of catalyst nanoparticles on surface: 25mg polystyrene (53800)block-poly (2-vinyl-pyridine) (8800) (PS-PVP) (Polymer Source, Inc) diblock copolymer were added to 25ml toluene and then stirred for at least 4hrs at room temperature. 3.3mg FeCl3ยท3H2O (FeIII: PVP=0.6) were then added into the solutions and stirred for another 24hrs. The final solutions were spin-coated on a flat silicon substrate with 1000nm oxide layer (RMS~0.5nm) and treated with oxygen plasma for 15mins prior to CVD process.
A5.19.2
Chemical vapor depositions of SWNTs: The silicon wafer coated with ca
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