Sheo K. Mishra

Enhanced vacuum-photoconductivity of chemically synthesized ZnO nanostructures

We report on the enhanced ultraviolet (UV) photoconductivity of zinc oxide (ZnO) nanostructures in vacuum. Nanoparticles and nanorods of ZnO were fabricated using a simple cost-effective solid state grinding method. Morphology of the nanostructures was studied using transmission electron microscopy, while the optical properties were investigated using UV–visible absorption and photoluminescence spectroscopy. The emission spectra of the nanostructures revealed the existence of various native defect states of ZnO and also indicated the presence of surface adsorbed water molecules. In the photoconductivity measurements, although the ZnO nanoparticles exhibited lower photoconductivity in comparison to the nanorods, a similar trend of photoresponse was observed for both the cases. An initial decrease in the photoconductivity followed by a large enhancement was observed in vacuum compared to that in ambient condition. Such unusually increased photoconductivity has been correlated to the desorption of physisorbed water molecules from nanostructure surfaces under vacuum. This desorption is responsible for the rise in dark current and an initial decrease in photoconductivity. Continual UV irradiation in vacuum leads to the desorption of chemisorbed water molecules from the defect sites of the nanostructures, resulting in the occurrence of high photoconductivity.

Synthesis and optical studies of chemically synthesized PPy/Al2O3 nanocomposites

In the present work, we have synthesised pure and 2wt% Al2O3 doped PPy by the chemical oxidation method. XRD patterns of 2wt% Al2O3 doped PPy shows several broad peaks while pure PPy shows only one single peak indicating poor crystalline phase of PPy. FTIR spectra confirm the formation of PPy and also suggest that doping of Al2O3 in PPy does not affect its structure. PL shows several emission peaks for both samples located at ∼365 nm with two shoulders at ∼473 nm and ∼533 nm. The further synthesis and properties study is under investigation.

Modified photoluminescence and photodetection characteristics of chemically grown SnO coated ZnO nanoneedles

The authors report on the synthesis of tin oxide (SnO) coated zinc oxide (ZnO) needlelike nanostructures and their modified light emission and detection features. The formation of SnO phase on ZnO surface has been revealed from energy dispersive x-ray analysis and secondary ion mass spectrometry studies. The luminescence response of the SnO-coated ZnO nanoneedles gets lowered compared to that of bare ZnO and is assigned to the lowering of radiative emission due to the occurrence of charge-carrier separation. Again in the heterostructured system, due to SnO led surface passivation, the band-edge emission becomes prominent and defect-related emission gets lowered. The photoconductivity response is found to be significantly enhanced for the SnO-ZnO heterostructured material formed with lower Sn:Zn molar ratio. The enhancement of photocurrent has been understood in the light of carrier separation and carrier multiplication processes occurring at the SnO-ZnO heterojunctions.

Investigation of photoresponse in cadmium sulfide nanoparticles

In this work, we report on the photo-response of CdS nanoparticles prepared by simple solid state reaction method. The X-ray diffraction (XRD) study has confirmed the formation of cubical zinc blende (c) phase. In the photo-response study, voltage dependence of photocurrent and darkcurrent as well as temporal rise and decay of photocurrent of CdS nanoparticles have been investigated. The photo-response of prepared sample has been measured under visible illumination using thick film of powder with out any binder. The photocurrent (Ipc) and darkcurrent (Idc) follow power law with applied voltage i.e. I α Vr. The rise and decay of photocurrent show negative photoconductivity.

Investigation of photoconductivity in Pr-doped ZnS powder prepared by simple heat treatment technique

In the present work, we have investigated photoconductivity properties in Pr-doped ZnS powders. ZnS: Pr powder has been prepared by simple heat treatment technique at temperature of 800 °C. I-V characteristics i.e. voltage dependence of photocurrent under UV illumination (λ=365 nm) exhibits non-Ohmic (r < 1) behavior at low as well as high voltage regimes. The crystallite size of ZnS:Pr corresponding to main XRD peak is estimated as 37.25 μm. The micro strain is calculated as 0.46.