COLL 122 |
| Transistors fabricated using organic thin films as the channel material have been shown to be highly sensitive and tunable chemical sensors (ChemFETs). The transduction mechanism is critically dependent on the surface chemistry, but is poorly understood. In an organic thin-film transistor (OTFT), an organic or polymer film is deposited on top of an SiO2 gate oxide. Exposure to analyte causes a large change in source-drain current. We have used scanning Kevin probe microscopy (SKPM) to determine that the analytes absorb on the surface of channel material. However, in an OTFT, the conduction occurs in the first few monolayers of organic semiconductor on top of the SiO2 gate oxide; therefore reaction on at the air-organic interface liberate carrier which are transported to the organic-oxide interface. Dynamic Transconductance Spectoscopy (DTS) has been employed directly measure the effect of analyte on charge mobility, trap energy, and fixed charge in real time. For copper or cobalt phthalocyanine(CuPc and CoPc) OTFTs, most analytes change the conductivity by displacing oxygen from surface sites thereby changing the film mobility and trap energy. Measuring the change in mobility as a function of frequency, we can discriminate between different analytes. Additional experiments with molecular beams and modeling with density functional theory allow us to identify the surface adsorption sites and determine how they change the electronic structure of the film. |
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Dynamics of Single Atoms, Molecules and Clusters on Surfaces
8:30 AM-11:40 AM, Monday, 11 September 2006 Sir Francis Drake -- Renaissance Room, Oral
Division of Colloid & Surface Chemistry |