ABSTRACT This work presents the thermal property study of single wall and multi wall carbon nanot... more ABSTRACT This work presents the thermal property study of single wall and multi wall carbon nanotubes (SWCNT and MWCNT) both in their purified and unpurified forms introduced to silicone elastomer to enhance the thermal diffusivity of this industrial polymer. An increase in thermal diffusivity was observed for incremental loading of both purified and unpurified single wall and multiwall CNT in epoxy at different percentages. An increase of thermal diffusivity as high as 130% was achieved for ∼2 wt% loading of both single wall and multi wall nanotubes. Electrical conductivity measurements showed a percolation threshold for 2% loading of multiwall CNT, below which the nanotube-epoxy composite behaved as an insulator — this is a key property for applications where electrical isolation is required. For single wall CNT-epoxy composite all the samples showed high resistance to the conduction of current. Thermal impedance measurements showed a strong dependency of contact resistance with percentage loading. Finally, the feasibility of deploying carbon nanotube-polymer composites as practical thermal interface materials for electronics thermal management is discussed.
ABSTRACT We report the results of direct measurement of remanent hysteresis loops on nanochains o... more ABSTRACT We report the results of direct measurement of remanent hysteresis loops on nanochains of BiFeO$_3$ at room temperature under zero and $\sim$20 kOe magnetic field. We noticed a suppression of remanent polarization by nearly $\sim$40\% under the magnetic field. The powder neutron diffraction data reveal significant ion displacements under a magnetic field which seems to be the origin of the suppression of polarization. The isolated nanoparticles, comprising the chains, exhibit evolution of ferroelectric domains under dc electric field and complete 180$^o$ switching in switching-spectroscopy piezoresponse force microscopy. They also exhibit stronger ferromagnetism with nearly an order of magnitude higher saturation magnetization than that of the bulk sample. These results show that the nanoscale BiFeO$_3$ exhibits coexistence of ferroelectric and ferromagnetic order and a strong magnetoelectric multiferroic coupling at room temperature comparable to what some of the type-II multiferroics show at a very low temperature.
A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferroce... more A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferrocene was used as the Fe source, and sc-CO(2) acted as both a solvent and oxygen source in the process. Powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and magnetic measurements were used to characterize the products. It was found that the morphology and structure of the product strongly depended on the reaction conditions.
ABSTRACT This work presents the thermal property study of single wall and multi wall carbon nanot... more ABSTRACT This work presents the thermal property study of single wall and multi wall carbon nanotubes (SWCNT and MWCNT) both in their purified and unpurified forms introduced to silicone elastomer to enhance the thermal diffusivity of this industrial polymer. An increase in thermal diffusivity was observed for incremental loading of both purified and unpurified single wall and multiwall CNT in epoxy at different percentages. An increase of thermal diffusivity as high as 130% was achieved for ∼2 wt% loading of both single wall and multi wall nanotubes. Electrical conductivity measurements showed a percolation threshold for 2% loading of multiwall CNT, below which the nanotube-epoxy composite behaved as an insulator — this is a key property for applications where electrical isolation is required. For single wall CNT-epoxy composite all the samples showed high resistance to the conduction of current. Thermal impedance measurements showed a strong dependency of contact resistance with percentage loading. Finally, the feasibility of deploying carbon nanotube-polymer composites as practical thermal interface materials for electronics thermal management is discussed.
ABSTRACT We report the results of direct measurement of remanent hysteresis loops on nanochains o... more ABSTRACT We report the results of direct measurement of remanent hysteresis loops on nanochains of BiFeO$_3$ at room temperature under zero and $\sim$20 kOe magnetic field. We noticed a suppression of remanent polarization by nearly $\sim$40\% under the magnetic field. The powder neutron diffraction data reveal significant ion displacements under a magnetic field which seems to be the origin of the suppression of polarization. The isolated nanoparticles, comprising the chains, exhibit evolution of ferroelectric domains under dc electric field and complete 180$^o$ switching in switching-spectroscopy piezoresponse force microscopy. They also exhibit stronger ferromagnetism with nearly an order of magnitude higher saturation magnetization than that of the bulk sample. These results show that the nanoscale BiFeO$_3$ exhibits coexistence of ferroelectric and ferromagnetic order and a strong magnetoelectric multiferroic coupling at room temperature comparable to what some of the type-II multiferroics show at a very low temperature.
A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferroce... more A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferrocene was used as the Fe source, and sc-CO(2) acted as both a solvent and oxygen source in the process. Powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and magnetic measurements were used to characterize the products. It was found that the morphology and structure of the product strongly depended on the reaction conditions.
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Papers by Saibal Roy