http://dspace.cus.ac.in/jspui/handle/1/6331 2026-04-13T16:54:57Z http://dspace.cus.ac.in/jspui/handle/1/6465 Title: Defect mediated magnetic transitions in Fe and Mn doped MoS2 Authors: Singh, Manish Kumar; Chettri, Prajwal; Tripathi, Ajay; Tiwari, Archana; Mukherjee, Bratindranath; Mandal, R. K. Abstract: We report single-phase syntheses of undoped 2H-MoS2 as well as Mn and Fe doped MoS2 by a facile hydrothermal route. The formation of the 2H-MoS2 phase was confirmed by XRD and was corroborated with Raman spectra. The morphology of the doped and undoped MoS2 nanostructures comprised sheets, as revealed by TEM and STEM images. The fine granular structure was observed by high resolution TEM micrographs. The STEM-EDS results show dopant concentrations of ∼1 atom% corresponding to Mn and Fe in doped MoS2. The undoped MoS2 revealed diamagnetic behavior at room temperature and paramagnetic behavior in the range (100 to 300 K). The Mn-MoS2 sample displayed ferromagnetism below 20 K with a coercive field of ∼50 Oe. Such a sample may be utilized for magnetic switching purposes at low temperatures. The onset of the antiferromagnetic interaction was observed below 145 K in Fe-MoS2 samples. They have been understood in terms of long-range magnetic interactions amongst the dipole moments mediated via surface defects as well as the interaction between the dipoles and the surface charges. The findings are corroborated with the help of EPR studies. 2018-01-01T00:00:00Z http://dspace.cus.ac.in/jspui/handle/1/6464 Title: Temperature and pressure induced Raman studies of C60 oxide Authors: Mondal, Trisha; Tripathi, Ajay; Tiwari, Archana; Zhang, Jinying; Shripathi, Thoudinja; Shinohara, Hisanori Abstract: We present temperature, laser power, and pressure dependent Raman spectral analysis of C60 oxide (C60O) thin films prepared by the photolysis method. The first order temperature, laser power, and pressure coefficients of the Raman frequencies are evaluated and are utilized for evaluating the thermal conductivity of C60O. Its thermal conductivity is found to be 0.7 W m−1 K−1 which is marginally higher than that of bulk C60. Raman frequencies corresponding to C–O and C–C bonds blueshift with a decrease in temperature which is attributed to the thermal contraction of C60O molecules. The density functional measurements have been performed to optimize C60O structure. The contraction in the C–O bond length has been corroborated with the experimental Raman shifts at different temperatures and is used to evaluate the linear expansion coefficient of C60O. Pressure induced compression and polymerization of C60O clusters are also illustrated. This study highlights the interplay between thermal and mechanical transformations in the C60O cluster which may regulate its thermoelectric properties by tuning the intermolecular interactions. 2018-01-01T00:00:00Z http://dspace.cus.ac.in/jspui/handle/1/6390 Title: Synthesis of rod-shaped Au-Cu intermetallic nanoparticles and SERS detection Authors: Singh, Manish Kumar; Chettri, Prajwal; Basu, Joysurya; Tripathi, Ajay; Mukherjee, Bratindranath; Tiwari, Archana; Mandal, R.K. Abstract: Intermetallic phases in Au-Cu nanoparticles has been synthesized chemically in liquid phase. The heat-treatment of these nanoparticles at 180 °C for 1 h in solution phase led to the formation of Au-Cu alloy nanoparticles with nearly spherical shapes and monodispersed size of ∼10 nm. Subsequent heat-treatment at 300 °C for 30 min of these Au-Cu alloy nanoparticles not only revealed structural transformation to intermetallic phases (tetragonal AuCu (tP4) and cubic Cu3Au (cP4)) but also shape change occurs from spherical to rods having average aspect ratio ∼3.0. The structural determination at the particle has been carried out through nano-beam electron diffraction coupled with simulation of electron diffraction patterns and high resolution phase contrast images. These Au–Cu intermetallic nanoparticles exhibit an excellent surface enhanced Raman spectroscopic activity with methylene blue compared to that of Au-Cu alloy nanoparticles. 2019-04-16T00:00:00Z http://dspace.cus.ac.in/jspui/handle/1/6338 Title: Laser ablation of natural micas: synthesis of MgO and Mg(OH)2 nanoparticles and nanochains Authors: Vendamani, V.S.; Tripathi, Ajay; Pathak, Anand P.; Rao, S. Venugopal; Tiwari, Archana Abstract: MgO and Mg(OH)2 nanoparticles and nanochains are prepared by laser ablation of natural micas in water. The laser ablation of muscovite and biotite, yielded spherical nanoparticles of average diameter of 36 and 63 nm, whereas the diameter of the obtained nanochains ranged between 40 and 80 nm. The nominal lengths of the network structures are in the range of 400 nm to few microns. The synthesized nanoparticles and nanochains networks show a plasmon resonance band near the UV region. 2017-01-01T00:00:00Z