@article { ISI:000241157000039, title = {Evidence for intergranular tunnelling in polyaniline passivated alpha-Fe nanoparticles}, journal = {Nanotechnology}, volume = {17}, number = {18}, year = {2006}, month = {SEP}, pages = {4765-4772}, publisher = {IOP PUBLISHING LTD}, type = {Article}, address = {DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND}, abstract = {

Nanoparticles are of immense importance both from the fundamental and application points of view. They exhibit quantum size effects which are manifested in their improved magnetic and electric properties. Mechanical attrition by high energy ball milling (HEBM) is a top down process for producing fine particles. However, fineness is associated with high surface area and hence is prone to oxidation which has a detrimental effect on the useful properties of these materials. Passivation of nanoparticles is known to inhibit surface oxidation. At the same time, coating polymer film on inorganic materials modifies the surface properties drastically. In this work a modified set-up consisting of an RF plasma polymerization technique is employed to coat a thin layer of a polymer film on Fe nanoparticles produced by HEBM. Ball-milled particles having different particle size ranges are coated with polyaniline. Their electrical properties are investigated by measuring the dc conductivity in the temperature range 10-300 K. The low temperature dc conductivity (I-V) exhibited nonlinearity. This nonlinearity observed is explained on the basis of the critical path model. There is clear-cut evidence for the occurrence of intergranular tunnelling. The results are presented here in this paper.

}, issn = {0957-4484}, doi = {10.1088/0957-4484/17/18/039}, author = {Sunny, Vijutha and Narayanan, T. N. and Sajeev, U. S. and Joy, Pattayil Alias and Kumar, D. Sakthi and Yoshida, Yasuhiko and Anantharaman, Maliemadom R.} } @article { ISI:000283124800028, title = {Synthesis of bio-compatible SPION-based aqueous ferrofluids and evaluation of radiofrequency power loss for magnetic hyperthermia}, journal = {Nanoscale Research Letters}, volume = {5}, number = {10}, year = {2010}, month = {OCT}, pages = {1706-1711}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Bio-compatible magnetic fluids having high saturation magnetization find immense applications in various biomedical fields. Aqueous ferrofluids of superparamagnetic iron oxide nanoparticles with narrow size distribution, high shelf life and good stability is realized by controlled chemical co-precipitation process. The crystal structure is verified by X-ray diffraction technique. Particle sizes are evaluated by employing Transmission electron microscopy. Room temperature and low-temperature magnetic measurements were carried out with Superconducting Quantum Interference Device. The fluid exhibits good magnetic response even at very high dilution (6.28 mg/cc). This is an advantage for biomedical applications, since only a small amount of iron is to be metabolised by body organs. Magnetic field induced transmission measurements carried out at photon energy of diode laser (670 nm) exhibited excellent linear dichroism. Based on the structural and magnetic measurements, the power loss for the magnetic nanoparticles under study is evaluated over a range of radiofrequencies.

}, keywords = {Magnetic heating, Magnetic hyperthermia, Magnetic relaxation, Power loss, Superparamagnetism}, issn = {1931-7573}, doi = {10.1007/s11671-010-9729-4}, author = {Mary, Antony P. Reena and Narayanan, T. N. and Sunny, Vijutha and Sakthikumar, D. and Yoshida, Yasuhiko and Joy, Pattayil Alias and Anantharaman, Maliemadom R.} } @article { ISI:000277203500017, title = {Template-assisted synthesis and characterization of passivated nickel nanoparticles}, journal = {Nanoscale Research Letters}, volume = {5}, number = {5}, year = {2010}, month = {MAY}, pages = {889-897}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Potential applications of nickel nanoparticles demand the synthesis of self-protected nickel nanoparticles by different synthesis techniques. A novel and simple technique for the synthesis of self-protected nickel nanoparticles is realized by the inter-matrix synthesis of nickel nanoparticles by cation exchange reduction in two types of resins. Two different polymer templates namely strongly acidic cation exchange resins and weakly acidic cation exchange resins provided with cation exchange sites which can anchor metal cations by the ion exchange process are used. The nickel ions which are held at the cation exchange sites by ion fixation can be subsequently reduced to metal nanoparticles by using sodium borohydride as the reducing agent. The composites are cycled repeating the loading reduction cycle involved in the synthesis procedure. X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron microscopy, Energy Dispersive Spectrum, and Inductively Coupled Plasma Analysis are effectively utilized to investigate the different structural characteristics of the nanocomposites. The hysteresis loop parameters namely saturation magnetization and coercivity are measured using Vibrating Sample Magnetometer. The thermomagnetization study is also conducted to evaluate the Curie temperature values of the composites. The effect of cycling on the structural and magnetic characteristics of the two composites are dealt in detail. A comparison between the different characteristics of the two nanocomposites is also provided.

}, keywords = {Nickel nanoparticles, Polymer-metal nanocomposites, Strongly acidic cation exchange resin, Stuctural and magnetic properties, Weakly acidic cation exchange resin}, issn = {1556-276X}, doi = {10.1007/s11671-010-9580-7}, author = {Gopalan, E. Veena and Malini, K. A. and Santhoshkumar, G. and Narayanan, T. N. and Joy, Pattayil Alias and Al-Omari, I. A. and Kumar, D. Sakthi and Yoshida, Yasuhiko and Anantharaman, Maliemadom R.} } @article { ISI:000326148700058, title = {Contact potential induced enhancement of magnetization in polyaniline coated nanomagnetic iron oxides by plasma polymerization}, journal = {Applied Physics Letters}, volume = {103}, number = {16}, year = {2013}, month = {OCT}, pages = {162414}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The present work derives motivation from the so called surface/interfacial magnetism in core shell structures and commercial samples of Fe3O4 and gamma Fe2O3 with sizes ranging from 20 to 30 nm were coated with polyaniline using plasma polymerization and studied. The High Resolution Transmission Electron Microscopy images indicate a core shell structure after polyaniline coating and exhibited an increase in saturation magnetization by 2 emu/g. For confirmation, plasma polymerization was performed on maghemite nanoparticles which also exhibited an increase in saturation magnetization. This enhanced magnetization is rather surprising and the reason is found to be an interfacial phenomenon resulting from a contact potential. (C) 2013 AIP Publishing LLC.

}, issn = {0003-6951}, doi = {10.1063/1.4826459}, author = {Sethulakshmi, N. and Sooraj, V. and Sajeev, U. S. and Nair, Swapna S. and Narayanan, T. N. and Joy, Lija K. and Joy, Pattayil Alias and Ajayan, Pulickel M. and Anantharaman, Maliemadom R.} } @article { ISI:000361697400005, title = {Fractional photo-current dependence of graphene quantum dots prepared from carbon nanotubes}, journal = {Physical Chemistry Chemical Physics}, volume = {17}, number = {38}, year = {2015}, month = {AUG}, pages = {24566-24569}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

We report on the photo-conductivity studies of chemically synthesized graphene quantum dots (GQDs) of average size 12 nm obtained by the oxidative acid treatment of MWCNTs. The dependence of photocurrent I-ph (I-ph = I-ill - I-dark) on the laser intensity P under a wide range of laser intensities (5 mW \<= P \<= 60 mW) shows a fractional power dependence of I-ph on light intensity. The temperature dependence (300 K \< T \< 50 K) of I-ph observed in thin films of these GQDs indicates that in the higher temperature region (T \> similar to 100 K), as the temperature increases, the number of thermally generated carriers increase resulting in increased I-ph. At sufficiently low temperatures (T \<= 100 K), a constant I-ph is observed, indicating a constant photocarrier density. Such a behavior is typically observed in many photoactive disordered semiconductors, which are often used in a variety of applications. We believe that the investigations presented here will enhance our understanding of the photocurrent generation phenomenon in chemically obtained GQDs.

}, issn = {1463-9076}, doi = {10.1039/c5cp03306c}, author = {Kundu, Sumana and Ghosh, Sujoy and Fralaide, Michael and Narayanan, T. N. and Pillai, Vijayamohanan K. and Talapatra, Saikat} } @article {43035, title = {Synthesis of N, F and S co-doped graphene quantum dots}, journal = {Nanoscale}, volume = {7}, year = {2015}, month = {MAY}, pages = {11515-11519}, abstract = {

Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of similar to 2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70\%), perhaps due to the interaction of defect clusters and dopants.

}, author = {Kundu, Sumana and Yadav, Ram Manohar and Narayanan, T. N. and Shelke, Manjusha V. and Vajtai, Robert and Ajayan, Pulickel M. and Pillai, Vijayamohanan K.} }