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Mechanism of ultraviolet photoconductivity in zinc oxide nanoneedles
Kumar, Sanjeev,Kim, Gil-Ho,Sreenivas, K,Tandon, R P IOP Pub 2007 Journal of Physics, Condensed Matter Vol.19 No.47
<P>Ultraviolet photoconductivity in zinc oxide (ZnO) nanoneedles grown on the surface of a multilayer structure comprised of ZnO film (50 nm)/Zn layer (20 nm)/ZnO film (2 µm) fabricated on a stainless steel substrate using an unbalanced magnetron sputtering technique is reported. It was observed that the multilayered structure with ZnO nanoneedles exhibited enhanced ultraviolet photoconductivity in comparison to the ZnO films that were without nanoneedles. The enhancement in the photoconductivity is attributed to the increase in the quantum yield of the photogenerated charge carriers due to the presence of nanoneedles. A successive slow photoresponse transient following after a fast rise is due to the establishment of equilibrium between the charge carriers in the conduction band and the trapping centers created due to the shallow defects in the ZnO film. The observed photoresponse is critically analyzed on the basis of trapping levels created by the oxygen species during the high pressure deposition of the ZnO multilayer. Results show the promise of ZnO nanostructures in ultraviolet detection applications.</P>
Thermal transition behaviour of iron oxide-polypyrrole nanocomposites
KomillaSuri,S.Annapoorni,R.P.Tandon,C.Rath,V.K.Aggrawal 한국물리학회 2003 Current Applied Physics Vol.3 No.2, 3
Distinct thermal transitions have been observed in nanocomposites based on iron oxide–polypyrrole prepared by simultaneous gelation and polymerization process. The transition behaviour for various iron oxide–polypyrrole compositions was investigated with the help of differential scanning calorimetery. It has been observed that the samples show a magnetic to nonmagnetic transition at 410 C. The presence of exothermic peak at 410 C is a strong indication of magnetic transition corresponding to c-Fe2O3 phase of iron oxide to a nonmagnetic a-Fe2O3 phase in these nanocomposites. However such a transition was not observed in nanocomposites containing lesser concentration of conducting polymer. 2002 Elsevier Science B.V. All rights reserved.
Anupama Sachdeva,Aarushib,Jagneet Kaur Anand,R. P. Tandon 한양대학교 세라믹연구소 2022 Journal of Ceramic Processing Research Vol.23 No.1
Calcium modified lead zirconate titanate ceramic compositions Pb(1-x)CaxZr0.52Ti0.48O3, where x=0, 0.02, 0.04, 0.06, 0.08, 0.1,have been prepared by solid state reaction method using wet milling. Scanning Electron Microscopy (SEM) studies have beencarried out to see the variation in the grain size with calcium addition. A correlation of the dielectric constant and dielectricloss with grain size effect is presented in this paper. A monotonic decrease in the transition temperature along with morediffuseness in paraelectric-ferroelectric phase transition is observed with increasing calcium content. The values of activationenergy (Ea) for the samples, calculated for ferroelectric region near phase transition temperature, are found to be in the rangeof approximately 0.6-1.0 eV which reflects that the main charge carriers responsible for conduction at higher temperaturesare oxygen ion vacancies.
Anupama Sachdeva,Aarushi,Jagneet Kaur Anand,R.P. Tandon 한양대학교 청정에너지연구소 2022 Journal of Ceramic Processing Research Vol.23 No.6
Pb(1-x)CaxZr0.52Ti0.48O3 bulk ceramic compositions where x=0-0.1 in steps of 0.02 are prepared by solid state reaction methodand sol-gel technique. A comparative study on the samples is conducted using XRD and Raman Spectroscopy in order to seethe effect of processing conditions. XRD peaks are indexed as per monoclinic phase. In both the series of samples, volumeshrinkage of the unit cell is observed in calcium modified samples when compared with unmodified samples. It is interestingto note that the samples derived from solid state reaction exhibit pseudo tetragonal structure while sol-gel derived samplesshow pseudo rhombohedral structure of their monoclinic unit cell. Similar inference has been made via Raman spectroscopystudies on the studied ceramic compositions prepared via two methods. Raman spectroscopy also reveals the possibility thatcalcium substitutes for lead.
Degradation analysis of PCDTBT:PC71BM organic solar cells-an insight
Vishal Sharma,Vinamrita Singh,Manoj Arora,Swati Arora,R.P. Tandon 한국물리학회 2016 Current Applied Physics Vol.16 No.3
The current density-voltage (J-V) characteristics were measured for poly [N-900-heptadeca-nyl-2,7- carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzo-thiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM) solar cells and studied for degradation analysis up to 150 h of fabrication. It was observed that the dark J-V characteristics in the degraded cell could be explained using both driftdiffusion (D-D) model and space charge limited current (SCLC) model. The D-D model could explain the J-V characteristics at initial voltage region, while SCLC model fitted well in the later part. By comparing the experimental data with theoretical curves, it was found that the transition from D-D model to SCLC model depends on the span of degradation. The results indicated an increase of traps and decrease of charge carrier mobility which may lead to degradation of organic solar cells. This work gave an insight into the degradation mechanism influencing the performance of organic solar cells.