The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes(CNTs)by microwave plasma enhanced chemical vapor deposition process has been investigated.Microwave plas...The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes(CNTs)by microwave plasma enhanced chemical vapor deposition process has been investigated.Microwave plasma was characterized in-situ using optical emission spectrometer.Morphology of the films was examined by scanning electron microscopy.Structural analysis was carried out by high resolution transmission electron microscopy(HRTEM)equipped with energy dispersive X-ray spectroscopy(EDS)and micro-diffraction attachments.It is found that oxide films without H_2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes.The embedded particles were found to be of iron carbide(Fe-C)as confirmed by HRTEM,EDS and micro-diffraction analysis.Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles.展开更多
A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, de...A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferromagnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism? in gallium ferrite is primarily due to this exchange between Ga-Fe sites? such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned? while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1? sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s,? Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds.? However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ~59 μC/cm2 along b-axis.展开更多
Nanocrystalline cerium hydroxide （NCs-Ce（OH）4） is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powde...Nanocrystalline cerium hydroxide （NCs-Ce（OH）4） is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powder and film on mass scale for various purposes. The synthesized NCs-Ce（OH）4 was characterized using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, thermo-gravimetric analysis （TGA）, Fourier transform infrared （FTIR）, UV-visible and photoluminescence （PL） spectroscopy. The average crystallite size of NCs-Ce（OH）4 has been estimated by the Scherrer equation to be 3-4 nm. The SEM examinations show that the surface texture was uniformly agglom- erated and homogeneous. Thermal analysis suggests that cerium （IV） ion is in the tetra hydrated form. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices.展开更多
文摘The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes(CNTs)by microwave plasma enhanced chemical vapor deposition process has been investigated.Microwave plasma was characterized in-situ using optical emission spectrometer.Morphology of the films was examined by scanning electron microscopy.Structural analysis was carried out by high resolution transmission electron microscopy(HRTEM)equipped with energy dispersive X-ray spectroscopy(EDS)and micro-diffraction attachments.It is found that oxide films without H_2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes.The embedded particles were found to be of iron carbide(Fe-C)as confirmed by HRTEM,EDS and micro-diffraction analysis.Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles.
文摘A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferromagnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism? in gallium ferrite is primarily due to this exchange between Ga-Fe sites? such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned? while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1? sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s,? Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds.? However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ~59 μC/cm2 along b-axis.
基金CSIR for financial support and the Director of NPL for providing experimental facilities,which is gratefully acknowledged.
文摘Nanocrystalline cerium hydroxide （NCs-Ce（OH）4） is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powder and film on mass scale for various purposes. The synthesized NCs-Ce（OH）4 was characterized using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, thermo-gravimetric analysis （TGA）, Fourier transform infrared （FTIR）, UV-visible and photoluminescence （PL） spectroscopy. The average crystallite size of NCs-Ce（OH）4 has been estimated by the Scherrer equation to be 3-4 nm. The SEM examinations show that the surface texture was uniformly agglom- erated and homogeneous. Thermal analysis suggests that cerium （IV） ion is in the tetra hydrated form. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices.
