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(Color online) Schematic illustration of the layer-by-layer electrostatic self-assembling process. (a) Schematic illustration of ionization of molecules on the surface of ZnO NB, which results in negatively charged ZnO NBs in aqueous solutions. (b) Schematic illustration of multilayer deposition of different polymers onto the ZnO NB surface upon electrostatic attraction of the charges on polymers. The green dots represent positively charged PDADMAC. The orange dots represent the negatively charged PNIPAM. (c) Schematic illustration of the polymer functionalized device. The inset SEM image is an actual polymer functionalized device.
(Color online) (a) responses of the PNIPAM polymer functionalized devices upon exposure to 85% (black curve) and 12% (red curve) relative humidities. (b) Current response of an uncoated ZnO NB upon exposure to 85% relative humidity (black) and multilayer polymers (red) showing that neither of them individually is responsible for the reduce of current in (a).
(Color online) Schematic illustration of mechanisms of polymer functionalized piezoelectric field effect transistor (PE-FET). (a) The volume of the polymers increases significantly upon hydration. (b) Schematic illustration of ZnO NB deformation upon polymer swelling and the consequent generated piezoelectric fields across the ZnO NB. The inner and outer surfaces of ZnO NB are negatively and positively charged, respectively. (c) Free electrons are trapped by the positive charged surface. (d) A depletion region is formed by the repelling force of the negative charged surface.
(Color online) (a) Schematic illustration of the phase transition and the corresponding volume changes. (b) Current response of PNIPAM functionalized ZnO NB upon exposure to DI water. (c) Current response of the same devices with temperature increase in aquatic solution. (d) Current response of uncoated ZnO NB (black curve), PNIPAM polymer (red curve), and CMC polymer coated ZnO NB (green curve) upon temperature increase in the temperature range of .
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