Potential of NanogeneratorAdv. Func Mater., 2008 (18) 1-15.OutlineProof of princ
Reiss, Spencer, Contributing Editor has reference to this Academic Journal, PHwiki organized this Journal Potential of NanogeneratorAdv. Func Mater., 2008 (18) 1-15.OutlineProof of principle of ZnO nanowires power generation triggered by an AFM tip (Wang et al, Science 2006)Nanoscale generator (Wang et al, Science 2007) in addition to potential applicationsControversy regarding the power generation mechanism n-type ZnO nanowire grown on Al2O3 substrate generating electricity by de as long as ming NW with AFM tipAligned ZnO NWs grown on Al2O3Science, 312 (2006) 242-246.
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Output voltage from aligned ZnO nanowiresScience, 312 (2006) 242-246. Sharp output voltage Peak corresponds to maximum deflection of NW Discharge occurs when tip contacts with compressed sideMechanism of ZnO NanogeneratorTransport is governed by metal-semiconductor Schottky barrier as long as PZ ZnO NWScience, 312 (2006) 242-246.The difference of Ohmic in addition to Schottky No output signal as long as m Al-In-coated Si tip (ohmic contactwith ZnO NW)Adv. Func Mater., 2008 (18) 1-15.
ZnO Nanogenerator structureZig-Zag Pt coated Si electrode plays the role of an array of AFM tipsDevice embedded in a polymer protecting layerSchematic view in addition to SEM images of the nanogeneratorNanogenerator immersed in an ultrasonic bathDirect-Current Nanogenerator Driven by Ultrasonic WavesWang et al Science 2007, 316 p102Power generation mechanismsSchematic view of the discharging mechanismsEquivalent circuitSEM cross-section view of the nanogeneratorPower generationDevice size: 2mm2 Power generated: 1pWCurrent, bias in addition to resistance of the generator as a function of timeCurrent generated as a function of timeEstimated power per NW: 1-4 fWPower density after optimization (109 active NW per cm2): 1-4 µW/ cm2
Applications: transistors in addition to LEDA generator providing 10 to 50nW is required to power such a cross NW FETa. Gate dependent IV characteristics of a cross NW FET b. SEM image of a cross NW junction, scale bar is 1µm Huang Y. et al, Science 2001 284 p1313Current in addition to emission intensity of a carbon nanotubes film as a function of gate voltage (Vd was 1V)Chen J. et al, Science 2005, 310, p1171µW power level needed as long as a CNT LEDApplications: wireless sensorsEnergy Harvesting From Human in addition to Machine Motion as long as Wireless Electronic DevicesMitcheson et al, proceedings of the IEEE, Vol 96, N.9, 2008Sensor nodes (motes) applications:Structural monitoring of buildingsMilitary trackingPersonal tracking in addition to record system (Health)Powering motes:Sensor 12µW quiescent powerADC 1µW as long as 8 bit samplingTransmitter 0.65µW as long as 1kbpsMEMS accelerometers already used as long as various applicationsBasic wireless sensor arrangementPiezoelectric transducer as long as energy harvestingMitcheson et al, proceedings of the IEEE, Vol 96, N.9, 2008Test: 608 Hz resonant operation 1g acceleration0.89V AC peakpeak generated2.16 µW power outputFang HB et al, Microelectronics Journal 37 (2006) 12801284
Electrostatic transducer as long as energy harvestingAssembled JFETGenerates 100 µW/cm3 from a vibration source of 2.25 m/s2 at 120 Hzelectret: permanent charge buried in the dielectric layerSEM images of the generator integrated with a FET schematic view of a constant charge electrostatic transducerMitcheson et al, proceedings of the IEEE, Vol 96, N.9, 2008S. Roundy, P. K. Wright, in addition to J. M. Rabaey,Energy Scavenging as long as Wireless SensorNetworks, 1st ed. Boston, MA: KluwerAcademic, 2003.Argument against WangAdvanced Materials 20, 4021 (2008)Origin of the piezoelectric voltageStrain displacive chargeDisplacive charge voltageFor ideal insulator: Generation of piezoelectric charge can be considered equivalent to the generation of a potentialGosele et al. Adv. Mater. 20, 4021 (2008)
Model of ZnO Piezoelectric GeneratorFor semiconducting ZnO:Gosele et al. Adv. Mater. 20, 4021 (2008)Load time constant RL = 500M CL > 5pF L ~ 1sIntrinsic time constant L ~ 10-2 ps Rectification of a Schottky diodeGosele et al. Adv. Mater. 20, 4021 (2008)V ~ kBT/q ~ 25meV quasi-ohmic To get rectification:V >> Vbi ~ 0.3-0.8VWangs data: output ~ 10mVVoltage argumentWang et als previous opinion: Piezoelectric voltage is 0.3V (calculation) High contact resistance leads to low output of 10 mV (experiment)Gosele et al ruled out the possibility of a high contact resistance Load resistor is 500 M no way as long as a contact resistance higher than 500 MWang et al. Nano Lett. 7, 2499 (2007)Gosele et al. Adv. Mater. 20, 4021 (2008)
Voltage argumentWang et als new model: 10 mV: difference of Fermi levels 0.3V: real Schottky diode driving voltage If Wangs new model is true, 0.3V is still a small voltage to rectify the piezoelectric signal Wang et al. Adv. Mater. 20, 1 (2008) Wang et al. Nano Lett. 8, 328 (2008)Unknowns behind the nanogeneratorThere is a lot of more work to be done I. Time constantII. RectificationThe nanogenerator model
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