Dr. Sreekanth K. M. currently serves as Assistant Professor in Physics, Department of Sciences, School of Engineering, Coimbatore. Dr. Sreekanth K. M. did his postgraduate degree in Physics from Mahatma Gandhi University. He completed his Ph. D. in Material Physics from KTH – The Royal Institute of Technology, Stockholm, Sweden. His thesis work was focused on Magnetism in Band Gap Engineered Sputtered Thin Films. His areas of research include Multifunctional Oxide Material.




Publications

Year of Publication Publication Type Title
2013 Conference Paper S. K. Mahadeva, Quan, Z. - Y., Fan, J. C., Albargi, H. B., Gehring, G. A., Riazanova, A., Belova, L., and Rao, K. V., “Room Temperature Ferromagnetism and Band Gap Investigations in Mg Doped ZnO RF/DC Sputtered Films”, in Symposium F – Oxide Semiconductors and Thin Films, 2013, vol. 1494, pp. 115-120.[Abstract]

Mg @ZnO thin films were prepared by DC/RF magnetron co-sputtering in (N2+O2) ambient conditions using metallic Mg and Zn targets. We present a comprehensive study of the effects of film thickness, variation of O2 content in the working gas and annealing temperature on the structural, optical and magnetic properties. The band gap energy of the films is found to increase from 4.1 to 4.24 eV with the increase of O2 partial pressures from 5 to 20 % in the working gas. The films are found to be ferromagnetic at room temperature and the saturation magnetization increases initially with the film’s thickness reaching a maximum value of 14.6 emu/cm3 and then decreases to finally become diamagnetic beyond 95 nm thickness. Intrinsic strain seems to play an important role in the observed structural and magnetic properties of the Mg @ZnO films. On annealing, the as-obtained ‘mostly amorphous’ films in the temperature range 600 to 800°C become more crystalline and consequently the saturation magnetization values reduce.

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2013 Journal Article S. K. Mahadeva, Fan, J., Biswas, A., Rao, G. M., Sreelatha, K. S., Belova, L., and K Rao, V., “A comparative study of room temperature ferromagnetism in MgO films deposited by rf/dc sputtering using high purity Mg and MgO targets”, Materials Express, vol. 3, pp. 328–334, 2013.[Abstract]

Thin films of nanocrystalline MgO were deposited on glass/Si substrates by rf/dc sputtering from metallic Mg, and ceramic MgO targets. The purpose of this study is to identify the differences in the properties, magnetic in particular, of MgO films obtained on sputter deposition from 99.99% pure metallic Mg target in a controlled Nitrogen + Oxygen partial pressure (O(2)pp)] atmosphere as against those deposited using an equally pure ceramic MgO target in argon + identical oxygen ambience conditions while maintaining the same total pressure in the chamber in both cases. Characterization of the films was carried out by X-ray diffraction, focussed ion beam cross sectioning, atomic force microscopy and SQUID-magnetometry. The `as-obtained' films from pure Mg target are found to be predominantly X-ray amorphous, while the ceramic MgO target gives crystalline films, (002) oriented with respect to the film plane. The films consisted of nano-crystalline grains of size in the range of about 0.4 to 4.15 nm with the films from metallic target being more homogeneous and consisting of mostly subnanometer grains. Both the types of films are found to be ferromagnetic to much above room temperature. We observe unusually high maximum saturation magnetization (MS) values of 13.75 emu/g and similar to 4.2 emu/g, respectively for the MgO films prepared from Mg, and MgO targets. The origin of magnetism in MgO films is attributed to Mg vacancy (V-Mg), and 2p holes localized on oxygen sites. The role of nitrogen in enhancing the magnetic moments is also discussed.

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2013 Journal Article J. Cab Fan, Mahadeva, S. K., Xie, Zd, Chang, S. Le, and Rao, K. Va, “P-Type ZnO materials: Theory, growth, properties and devices”, Progress in Materials Science, vol. 58, pp. 874-985, 2013.[Abstract]

In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p-n junction are the key steps to realize these applications. However, the reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (VO and Zni) and/or hydrogen incorporation. Considerable efforts have been made to obtain p-type ZnO by doping different elements with various techniques. Remarkable progresses have been achieved, both theoretically and experimentally. In this paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, VZn and O i act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Theoretically, the principles of selection of p-type dopant, codoping method and XZn-2VZn acceptor model are introduced. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band-gap engineering and room temperature ferromagnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials. © 2013 Elsevier Ltd. All rights reserved.

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2013 Journal Article S. K. Mahadeva, Fan, J., Biswas, A., Sreelatha, K. S., Belova, L., and Rao, K. V., “Magnetism of Amorphous and Nano-Crystallized Dc-Sputter-Deposited MgO Thin Films”, Nanomaterials, vol. 3, pp. 486–497, 2013.[Abstract]

We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas atmosphere of (N2 + O2) are found to be X-ray amorphous. All these films obtained with oxygen partial pressure (PO2) ~10% to 80% while maintaining the same total pressure of the working gas are found to be ferromagnetic at room temperature. The room temperature saturation magnetization (MS) value of 2.68 emu/cm3 obtained for the MgO film deposited in PO2 of 10% increases to 9.62 emu/cm3 for film deposited at PO2 of 40%. However, the MS values decrease steadily for further increase of oxygen partial pressure during deposition. On thermal annealing at temperatures in the range 600 to 800 °C, the films become nanocrystalline and as the crystallite size grows with longer annealing times and higher temperature, MS decreases. Our study clearly points out that it is possible to tailor the magnetic properties of thin films of MgO. The room temperature ferromagnetism in MgO films is attributed to the presence of Mg cation vacancies.

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2013 Conference Paper S. K. Mahadeva, Quan, Z. - Y., Fan, J. C., Sreelatha, K. S., Belova, L., Puzniak, R., and Rao, K. V., “Suppression of Ferromagnetic Ordering in thicker co-sputtered Mn doped MgO Films”, in Symposium S – Nanostructured Metal Oxides for Advanced Applications, 2013.[Abstract]

We report on preliminary studies of low (14 at.%) and high (53at.%) concentration Mn doped MgO films deposited by co-sputtering from metallic Mn and Mg targets. The structural, surface morphologies and magnetic properties of the films of different thickness were studied. All the as grown films are found to be amorphous and film surfaces are found to be flawless and homogeneous. We observe at room temperature robust ferromagnetic loops with a saturation magnetization value that is a function of film thickness reaching a maximum of ∼38.5 emu/cm3 in the Mn0.53Mg0.47O film at a thickness of ∼92 nm. In thicker films room-temperature ferromagnetic ordering is suppressed and eventually at a thickness around 120nm the expected diamagnetism of the bulk appears. The origin of ferromagnetism may be attributed to cation defects at the Mg-site.

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2013 Conference Paper S. K. Mahadeva, “Band Gap Engineering and Room Temperature Ferromagnetism of MgxZn(1-x)O Thin films”, in Symposium XX:Oxide thin films and Heterostructures for Advanced Information and Energy Technologies, 2013.
2011 Journal Article D. Saratchand A, KV, R., Krishnan, N. Cherupally, and Mahadeva, S. K., “D-Aminoacid Oxidase-Fe2O3 Nanoparticle Complex Mediated Antitumor Activity in Swiss Albino Mice”, Journal of Cancer Therapy, vol. 2, pp. 666-674, 2011.[Abstract]

D-Aminoacid oxidase (DAO) was isolated from fresh porcine kidney; its cytotoxic potential was studied under in vitro and in vivo conditions. The isolated DAO was complexed with Fe2O3 nanoparticles and its potential as an oxidation therapeutic agent was analysed. The ability of the complex in eliciting H2O2 mediated cytotoxicity was studied on Dalton’s lymphoma ascites cells (DLA). The induction of apoptosis in DLA cells by Fe2O3-DAO complex was studied by morphological examination and alkaline single cell gel electrophoresis (comet assay). The antitumor activity of the complex was investigated by oral administration of the complex and the substrate D-alanine to tumor bearing Swiss albino mice and by targeting the complex to the tumor site, using an externally applied magnetic field. Fe2O3-DAO along with D-alanine showed remarkable cytotoxicity in a substrate concentration-dependent manner. Both morphological examination and comet assay revealed that Fe2O3-DAO/D-alanine induced apoptosis. Oral administration of Fe2O3-DAO and D-alanine along with magnetic targeting significantly suppressed tumor growth in mice. The present report provides the first evidence for the promising application of enzyme bound nanoparticles for targeted oxidation therapy.

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Faculty Details
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Ph.D, MSc

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km_sreekanth@cb.amrita.edu