Enhancing the Electrical and Optoelectronic Performance of Nanobelt Devices by Molecular Surface FunctionalizationOutlineSetupSlide 4Electrical ConductivitySlide 6Enhanced PhotoconductivityEnhanced Gas SensitivityIncreased BiostabilityConclusionsEnhancing the Electrical and Optoelectronic Performance of Nanobelt Devices by Molecular Surface FunctionalizationNano Letters 2007Devesh KhanalNSE C203Spring 2007Outline1. Synthesis/setup2. Enhanced electrical conductivity3. Enhanced photoconductivity4. Enhanced gas sensitivity5. Enhanced biostabilityMotivationNanowires need to show: improved contacts, increased mobility, minimized surface defects, increased device stability.SetupSetup•Dipped nanobelts into solution with desired molecules.•Verified successful coating with molecules via the contact angles of water droplets.Electrical Conductivity•5-6 orders of magnitude increase in conductance•Different functional groups show different levels of conductivityElectrical ConductivityGiven explanation:•Functional groups introduce mid-gap states that act as “transition states” and effectively reduce the Schottky barrier. •COOH COO-, which is a donor.Enhanced Photoconductivity•Measured electrical response from shining 365 nm UV light onto surface of treated and not-treated nanobelts.•HOOC(CH2)10COOH sample - 57.1% enhancement•Untreated – 22%•Explanation: Organic surface groups introduce midgap states that help excite electrons from VB to CB and help separate electron hole pairs.Enhanced Gas Sensitivity•Measured electrical response to the introduction of O2 gas. •HOOC(CH2)10COOH current decreased by 43%•Untreated – 28%•Explanation: T = 300C. At this T, functional groups are decomposed creates oxygen vacancies material more sensitive to oxygen gas.Increased Biostability•Treated samples more resistant to pH 7 buffer solution for 15 minutes.Conclusions•Surface-treated nanobelts and nanowires showed:–Enhanced electrical conductivity–Enhanced photoconductivity–Enhanced gas sensitivity–Enhanced biostability•Regardless physical explanation for observed phenomena it is clear that the high surface to volume ratio of quasi-1D materials allows properties and performance of the material to be very dependent on surface composition and
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