P. Suresh Kumar

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution – Immersion successive ionic layer adsorption and reaction process

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows.

Perspective of electrospun nanofibers in energy and environment

This review summarizes the recent developments of electrospun semiconducting metal oxide/polymer composite nanostructures in energy and environment related applications. Electrospinning technique has the advantage of synthesizing nanostructures with larger surface to volume ratio, higher crystallinity with phase purity and tunable morphologies like nanofibers, nanowires, nanoflowers and nanorods. The electrospun nanostructures have exhibited unique electrical, optical and catalytic properties than the bulk counter parts as well as nanomaterials synthesized through other approaches. These nanostructures have improved diffusion and interaction of molecules, transfer of electrons along the matrix and catalytic properties with further surface modification and functionalization with combination of metals and metal oxides.

Enhanced luminescence and charge separation in polythiophene-grafted, gold nanoparticle-decorated, 1-D ZnO nanorods

In this work, we demonstrate a facile method for fabricating hybrid organic/inorganic structures of vertically oriented 1-dimensional (1-D) ZnO nanorods (NR) coupled with regio-regular poly(3-(2-methoxyethoxy) ethoxymethyl) thiophene-2,5-diyl (PMEEMT). The NRs were synthesized by two-step solution processes and exhibited a hexagonal wurtzite structure with a lattice spacing of 0.248 nm. Cross-section analysis of field-emission scanning electron microscopy (FESEM) analysis confirmed the NRs were vertically oriented and densely packed with diameter of about 250 nm. The hybrid structures were formed by encapsulating the ZnO NRs with polythiophenes, thereby creating a direct heterojunction interface. These interfaces allowed easy electron transport along the NR avoiding loss of mobility due to grain boundary scattering; further, the large aspect ratio and surface area of NR increased the effective interface between polythiophene and the nanorods contributing to efficient charge separation. In addition, decoration of the ZnO hybrid structures by gold nanoparticles (AuNPs) induced enhanced luminescence properties. These functionalized organic/inorganic hybrid structures can pave the way for applications in photovoltaics and sensing.

Synthesis of Vertical ZnO Nanorods on Glass Substrates by Simple Chemical Method

ZnO nanorods (NRs) have been synthesized by a chemical bath deposition (CBD) method on simple glass substrate that had been precoated by successive ionic layer absorption and reaction (SILAR) with a thin ZnO film. ZnO NR array was obtained by using zinc acetate and hexamethylenetetramine as aqueous solutions at optimized pH concentration and deposition time. X-ray diffraction (XRD) and SEM analysis were used to confirm the growth of ZnO nanorods. The pH and deposition time of the solution was found to influence the growth behavior of ZnO NRs. PL analysis also reflected the growth behavior of ZnO NRs.

Synthesis and Controlled Growth of ZnO Nanorods Based Hybrid Device Structure by Aqueous Chemical Method

In the present work, vertical ZnO nanorods (NRs) were grown onto ITO substrates by a simple two step chemical process at relatively low temperature by using successive ionic layer absorption and reaction method (SILAR) and chemical bath deposition (CBD) method. The investigated on n- ZnO/ p-Polythiophene heterojunction device have been fabricated with ZnO nanorods. Structural analysis reveals that the grown ZnO NRs exhibit (002) reflection with higher intensity, indicating that the ZnO NRs grown in c-axis orientation. FESEM image shows the surface morphology of grown ZnO nanorods was of hexagonal wurtzite structure whose diameter varies from 200 nm to 1μm. Room temperature Photoluminescence exhibited strong UV emission at ∼386 nm and a negligible green band confirms the presence of very low concentration of oxygen vacancies in the well-aligned ZnO nanorods. The current–voltage (I –V) characteristics of the heterojunctions show good rectifying diode characteristics. These results indicate that hybrid device fabricated from solution process is a promising approach for future light-emitting diodes (LEDs) devices.

Sensitivity Studies on Vacuum Deposited V2O5 Thin Films

Vanadium pentoxide thinfilms have been deposited by vacuum evaporation method and the effect of deposition temperatures on the surface morphology of the prepared sample has been analyzed. Structural and morphological were carried out on the prepared samples, using X-Ray Diffractometer (XRD) and Scanning Electron Microscopy (SEM). The samples deposited at elevated temperature showed nanopetal like structures on their surface which were found to be around 100-200 nm. The formation of the V2O5 phase has been confirmed through TG/DTA analysis which shows a sharp peak around 690°C corresponding to the melting point of vanadium pentoxide. The best sample was subjected to gas sensing analysis and the change in the resistance of the sensing element with respect to the test gas concentration was measured by noting down the resistance at each concentration for various time intervals. Sensitivity of the material linearly increased with different concentration of the test gas.

Effect of Temperature on the Morphology and Optical Properties of ZnO Nanoparticles Prepared by Forced Condensation Method

Intensive and innovative research is focused on the preparation of various nanostructured materials especially nanostructured metal oxides as applicable to number of applications.The present work mainly emphasis a single step synthesis of ZnO nanoparticles by employing surfactant free forced condensation method. Surface morphology of the sample was precisely controlled by varying the calcination conditions. Investigation on the structure, surface and composition of ZnO nanoparticles is of both fundamental interest and technological importance. X-ray diffraction (XRD) analysis reviled that the ZnO nanoparticles exhibits crystalline with the preferential orientation along (1 0 0) plane. SEM image shows the nanoparticles are in the range of 75 to 150 nm with spherical shape. The room temperature PL spectra of ZnO particles exhibited strong ultraviolet photoluminescence around 380 nm at room temperature.