P. Sundara Venkatesh

Bio: P. Sundara Venkatesh is an academic researcher from Bharathidasan University. The author has contributed to research in topics: Wurtzite crystal structure & Nanorod. The author has an hindex of 11, co-authored 15 publications receiving 310 citations.

Point defects assisted NH3 gas sensing properties in ZnO nanostructures

Abstract: In this report, the NH 3 gas sensing properties of ZnO nanostructures fabricated by radio frequency magnetron sputtering under various argon sputtering pressures have been investigated under various temperatures. The morphological transitions occur from vertical standing nanorods to inclined and tapered nanostructures with increasing the argon sputtering pressure. The dominant green emission at around 2.28 eV in the photoluminescence spectra signifies the presence of oxygen vacancies in the ZnO nanostructures which increases as a function of argon sputtering pressure. Despite low surface area, the nanostructures grown under higher argon sputtering pressure of 10 Pa exhibit excellent NH 3 gas response magnitude since it is exhibiting more oxygen vacancies as compared to other counterparts. For 25 ppm NH 3 gas at room temperature, a response time of 49 s and a fast recovery time of 19 s are attributed to the modification in the intermediate defect states induced by the oxygen vacancies through the adsorption and desorption of gas molecules on the surface of ZnO nanostructures.

Role of point defects on the enhancement of room temperature ferromagnetism in ZnO nanorods

Abstract: Vertically aligned undoped ZnO nanorod arrays (NRAs) have been fabricated on silicon (111) substrates by radio frequency magnetron sputtering. The structural studies illustrate a hexagonal wurtzite structure of the ZnO NRAs with compressive stress. Raman analysis of the E2high phonon mode corroborates the partial relaxation of stress in NRAs by the post growth treatment under oxygen and vacuum atmospheres. The anomalous Raman modes have been attributed to the local vibrations and it corresponds to the silent modes of wurtzite ZnO. The appearance of forbidden modes illustrates the breakdown of the Raman selection rules. The role of point defects on the ferromagnetic behaviour of NRAs was analyzed by optical transitions and correlated with the magnetic properties. Post growth treatment of NRAs under oxygen and vacuum atmospheres significantly suppresses the point defects owing to the enhancement of the crystalline quality. The temperature dependent zero-field cooled and field cooled magnetizations reveal the coexistence of antiferromagnetism and ferromagnetism below 7 K. However, the ferromagnetism is dominant and stable between 7 K and room temperature. The decrease of ferromagnetism in NRAs is directly associated with the compensation of point defects such as zinc and oxygen vacancies as substantiated by the radiative transition between shallow donor and acceptor energy levels. These results confirm that point defects play an important role in enhancing the room temperature ferromagnetism in ZnO NRAs.

Synthesis and characterization of BiVO4 nanoparticles for environmental applications

Abstract: In the present study, a chemical precipitation method is adopted to synthesize bismuth vanadate nanoparticles. The calcination temperature dependent photocatalytic and antibacterial activities of BiVO4 nanoparticles are examined. The structural analysis evidences the monoclinic phase of BiVO4 nanoparticles, where the grain size increases with calcination temperature. Interestingly, BiVO4 nanoparticles calcined at 400 °C exhibit superior photocatalytic behaviour against methylene blue dye (K = 0.02169 min−1) under natural solar irradiation, which exhibits good stability for up to three cycles. The evolution of antibacterial activity studies using a well diffusion assay suggest that the BiVO4 nanoparticles calcined at 400 °C can act as an effective growth inhibitor of pathogenic Gram-negative (P. aeruginosa & A. baumannii) and Gram-positive bacteria (S. aureus).

Post-annealing effects on the structural and optical properties of vertically aligned undoped ZnO nanorods grown by radio frequency magnetron sputtering

Abstract: We report the nature of point defects associated with the visible transitions and X-ray photoelectron emissions of post-growth annealed ZnO nanorods under vacuum and air atmospheres. The ZnO nanorods are vertically aligned along the c-axis with a hexagonal cross section. The compressive strain in the as-grown ZnO nanorods has been completely relaxed by the post-growth annealing under vacuum. The relative quantity of oxygen deficiencies in the as-grown and post-annealed ZnO nanorods is calculated from the X-ray photoelectron spectra. Despite high oxygen deficiencies, the intense bi-donor bound exciton emission with narrow full width at half maximum reflects good optical quality of the vacuum annealed ZnO nanorods. The additional green and red emissions are attributed to electron transitions owing to the oxygen mediated defects in the nanorods.

Zinc Oxide-From Synthesis to Application: A Review.

Abstract: Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized. The modification with organic (carboxylic acid, silanes) and inroganic (metal oxides) compounds, and polymer matrices were mainly described. Finally, we present possible applications in various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic and electrotechnology, photocatalysis were introduced. This review provides useful information for specialist dealings with zinc oxide.

Room-temperature gas sensing of ZnO-based gas sensor: A review

Abstract: Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well.