Kusum Kumari

Effect of surface passivating ligand on structural and optoelectronic properties of polymer : CdSe quantum dot composites

We demonstrate the effect of surface passivation of cadmium selenide quantum dots (CdSe QDs) (~5–7 nm) by tri-n-octylphosphene-oxide (TOPO) and oleic acid (OA) on the structural and optoelectronic properties of their respective polymer : CdSe composites by dispersing them in poly(2-methoxy-5(2-ethylhexyloxy)-1,4-phenylinevinylene) and poly(3-hexylthiophene) polymers. It has been found that OA passivated-QDs (~7 nm), as compared with TOPO passivated CdSe QDs (~5 nm), are of (i) high quality that provide better steric stability against coagulation, homogeneity and photostability to their respective polymer : CdSe composites, (ii) show low value of Stern–Volmer quenching constant (KSV) calculated from photoluminescence quenching measurements. These effects have been attributed to (i) CdSe(OA) (~7 nm) particles having relatively smaller surface energies compared with CdSe(TOPO) (~5 nm) particles thus showing lesser quenching capabilities (ii) dominance of respective processes of photoinduced Forster energy transfer between host polymer (donors) and guest CdSe nanocrystals (acceptors) in polymer : CdSe(OA) composites and charge transfer in polymer : CdSe(TOPO) composites.

Effect of CdSe quantum dots on hole transport in poly(3-hexylthiophene) thin films

This letter demonstrates the effect of cadmium selenide (CdSe) quantum dots on hole transport in poly(3-hexylthiophene) (P3HT) thin films. Current-voltage characteristics of P3HT and P3HT:CdSe thin films have been studied in the temperature range of 288–85K, in hole only device configurations, i.e., indium tin oxide (ITO)/poly(ethylene-dioxthiophene):polystyrenesulphonate (PEDOT:PSS)/P3HT/Au and ITO/PEDOT:PSS/P3HT:CdSe∕Au. The incorporation of CdSe quantum dots in P3HT results in the enhancement in hole current and switches the transport from dual conduction mechanism, viz., trap and mobility models to only trap model. This is attributed to the reduction in characteristic trap energy from 60to32meV and trap density from 2.5×1018to1.7×1018cm−3.

Field-effect control of electrokinetic ion transport in a nanofluidic channel

We have simulated field-effect control of electrokinetic ion transport in a fluidic nanochannel with negative surface charge on its walls. A third electrode, known as a gate, is used on the channel walls to modulate its zeta-potential and ion concentration inside it. The ion current is controlled by the gate-induced ion enrichment/depletion and changes of electric field in the vicinity of the gate. There are four regions of ion current control by gate at low electrolyte concentration: decreasing electric field, cation enrichment, quasi-neutrality, and cation depletion as the gate potential changes from negative values to positive values. The effectiveness of ion current control by gate decreases with increasing surface charge density due to change in zeta-potential and overall electro-neutrality condition. The ion current through the nanochannel is also affected by electrolyte concentration. The proposed nanofluidic device could have broad applications in integrated nanofluidic circuits for manipulation o...

Ion current rectification in a fluidic bipolar nanochannel with smooth junction

We have simulated bipolar nanochannel based fluidic diode for different values of junction sharpness. We can obtain significant ion current rectification even for a smooth junction between oppositely charged zones. The rectification increases with junction sharpness due to increase in unipolar character of electrolyte but a sharp junction is not a necessary condition for rectification. The ion current rectification increases with surface charge density due to increase in unipolar character of electrolyte and decrease in reverse ion current. The fluid enters (exits) the nanochannel through the centre from (to) the opposite directions for reverse (forward) bias due to fluid pressure.

Enhancement in hole current density on polarization in poly(3-hexylthiophene):cadmium selenide quantum dot nanocomposite thin films

We demonstrate the effect of polarization on space charge limited J-V behavior in poly(3-hexylthiophene) (P3HT):cadmium selenide (CdSe) (∼5 nm) quantum dot nanocomposite thin films in hole-only device configuration, indium tin oxide/poly(ethylene-dioxthiophene):polystyrenesulphonate/P3HT:CdSe/Au. Current density has been found to enhance in these hybrid films on polarization. This has been attributed to decrease in characteristic trap energy from 32 to 27 meV, trap density from 1.7×1018 to 1×1018 cm−3 and increase in hole mobility from 2.6×10−6 to 7.7×10−6 cm2 V−1 s−1 due to field induced enhanced order by dipolar alignment and/or trapping of charge carriers at the nanoscale interfacial boundaries of P3HT and CdSe quantum dots.

Improved Sensitivity with Low Limit of Detection of a Hydrogen Gas Sensor Based on rGO-Loaded Ni-Doped ZnO Nanostructures

We report enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO). Ni-doped ZnO nanoplates were grown by radio frequency sputtering, rGO was synthesized by Hummers method and decorated by the drop cast method of various concentration of rGO (0-1.5 wt %). The current-voltage characteristics of the rGO-loaded sensor are highly influenced by the loading concentration of rGO, where current conduction decreases and sensor resistance increases as the rGO concentration is increased up to 0.75 wt % because of the formation of various Schottky heterojunctions at rGO/ZnO interfaces. With the combined effect of more active site availability and formation of various p-n heterojunctions due to the optimum loading concentration of rGO (0.75 wt %), the sensor shows the maximum sensing response of ∼63.8% for 100 ppm hydrogen at moderate operating temperature (150 °C). The rGO-loaded sensors were able to detect a minimum of 1 ppm hydrogen concentration and showed high selectivity. However, a further increase in the rGO concentration (1.5 wt %) leads to the reduction of the relative response of hydrogen gas, ascribed to the formation of interconnections of rGO between electrodes. Therefore, it reduces the total resistance of the sensor and minimizes the effect of p-n heterojunction on sensor response.

SnO2/PANI nanocomposite electrodes for supercapacitors and lithium ion batteries

Abstract Tin oxide (SnO2) nanostructures and SnO2/Polyaniline (PANI) nanocomposites to be used as electrode materials for a lithium ion battery were synthesized using a solution-route technique with chelating agents followed by calcination at 300∘C for 4 h. Structural and morphological properties were studied with powder X-ray diffraction, scanning electron and transmission electron microscopy. Particles of 25-10 nm size are observed in the microscope images. TGA results showed that the PANI-modified SnO2 nanoparticles exhibit higher thermal stability than the SnO2 nanoparticles. Electrochemical properties of SnO2 and SnO2/PANI electrodes were examined in a lithium ion battery and a supercapacitor. The electrode of SnO2/PANI shows higher specific capacity. The cell with SnO2/PANI exhibits a specific capacity of 1450 mAh/g at C/10. Supercapacitor results indicate that the PANI-modified SnO2 composite had a higher current with apparent cathodic and anodic peaks.