2019-FromNanowirestoTunnelingJunctionsFabricationsand從納米線隧道結(jié)的制備-文檔資料

1、Detection of Heavy Metal Ions withNanojunctionsN.J. TaoArizona State UniversityWhy Heavy Metal Ion Sensors?> Heavy metals are toxic-dangerous pollutants second only to pesticides in environmental importance> Heavy metals are not biodegradable-accumulate and persist for many years> Current m

2、ethods fall in two categories:Ex situ: Sensitive but expensive and complicateIn situ: Portable device but less sensitive & reliableHigh sensitivity is necessary for early warningNanojunction ApproachNanocontact SensorAtomic Scale!Sensitivity:The electrodes are separated with an atomic-scale gap,

3、 so a few ions can be detected.Specificity:> Spectroscopy:> Deposition potentialHow to Fabricate Electrodes withAtomic-Scale Separations ?Fabrication MethodEAnode： Etching delocalized, butCathode： Deposition localized at sharpest point,due to: Self-focusing - directional growthDecreasing Gap!S

4、elf-T erminationVoltage Divider: Initially, Rgap» Rext, V,ap V。full speed deposition. Finally, R,ap« Rext, Vgap 0 deposition terminates. The gap resistance is determined by Rext.Fabrication of an atomic-scale gapG0=2e2/h(O0、0)U1O0、0)U1An Array of Atomic-Scale GapsbeforeafterSi3N4/Au/SiO2/S

5、iSEM images(券送oUEonpuoo> Conductance Ouantized! Number of metal atoms Conductance in quantum unit (G0=2e2/h).> Deposition time needed to bridge the gap decreases as the concentration determining the concentration from the deposition time> Wide dynamic range -from mM to at least nMElectrodes

6、 potential: -0.55VIn CuSO4 electrolytes> Deposition time decreases as the concentration-similar to Cu ions> 0>l nM (10ppt) concentration is reached-further improvement canbe made to lower the limitElectrodes potential: -0.85V in Pb(NO3)2 electrolytes805040200Specificity0.55 V-0J5VPotential

7、Cyclingo o o o o o5 4 3 2 1 (qhoz)oOUEonpuooPb2+ <1Potential Cycling> Different metals have different deposition& stripping potentials*SummaryA Nanocontact Sensor:A Polymer Nanoj unction Sensor:Acknowledgements| Arizona StateUniversity Vasant Rajagopalan Salah Boussaad John Zhang Win Ly(M) MOTOROLA