Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN l... more Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-30...
Current Status of Pressure Standards at NPLI and...................the Key Comparison Data Base (... more Current Status of Pressure Standards at NPLI and...................the Key Comparison Data Base (KCDB) ... Current Status of Pressure Standards at NPLI and Our ... Experiences with the Key Comparison Data Base ... AK BANDYOPADHYAY, SANJAY YADAV and NITA DILAWAR ...
Temperature dependent Raman scattering measurements were carried out to investigate the phonon
be... more Temperature dependent Raman scattering measurements were carried out to investigate the phonon behavior of thermoelectric Cu3SbSe3 nanoparticles. The anomalous behavior of phonon mode (Ag) frequency with temperature indicates the possibility of a lattice instability related to the orderedisorder structural transition at 380 K. In the low temperature region (80e250 K) we found an asymmetric line shape of Ag mode, which is analyzed and discussed in the light of phononecontinuum Fano-interference effect. We have obtained the thermal conductivity (k) ~ 2.04 W/mK at room temperature. The change in thermal conductivity with temperature strongly correlates with the change in total anharmonicity of the Cu3SbSe3 lattice.
Pressure and temperature dependent Raman scattering studies on Ho2O3 have been carried out to
inv... more Pressure and temperature dependent Raman scattering studies on Ho2O3 have been carried out to investigate the structural transition and the anharmonic behavior of the phonons. Ho2O3 undergoes a transition from cubic to monoclinic phase above 15.5 GPa, which is partially reversible on decompression. The anharmonic behavior of the phonon modes of Ho2O3 from 80K to 440K has been investigated. We find an anomalous line-width change with temperature. The mode Gr€uneisen parameter of bulk Ho2O3 was estimated from high pressure Raman investigation up to 29 GPa. Furthermore, the anharmonic components were calculated from the temperature dependent Raman scattering.
The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was inv... more The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was investigated in the temperature range of 80–440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.
This paper reports the behavior of a well-characterized pneumatic piston gauge in the pressure ra... more This paper reports the behavior of a well-characterized pneumatic piston gauge in the pressure range up to 8 MPa through simulation using finite element method (FEM). Experimentally, the effective area of this piston gauge has been estimated by cross-floating to obtain A0 and λ. The FEM technique addresses this problem through simulation and optimization with standard commercial software (ANSYS) where the material properties of the piston and cylinder, dimensional measurements, etc are used as the input parameters. The simulation provides the effective area Ap as a function of pressure in the free deformation mode. From these data, one can estimate Ap versus pressure and thereby Ao and λ. Further, we have carried out a similar theoretical calculation of Ap using the conventional method involving the Dadson's as well as Johnson-Newhall equations. A comparison of these results with the experimental results has been carried out.
The current paper reports the stability of a pressure dynamometer with a full scale pressure of 6... more The current paper reports the stability of a pressure dynamometer with a full scale pressure of 60 bar over nine years of operation. Since the stability of this digital pressure gauge depends on factors like repeatability, hysteresis, non-linearity, relative deviation etc, a systematic study has been carried out on each of these components. Finally, a comparison of the calibration factors and the estimated expanded uncertainty is made from the collected nine years calibration database. It has been found that the performance of the equipment showed consistent results for about 5 years after which a slight shift in the parameters described above has set in. But, the overall performance of the equipment remains excellent over the period studied within the limit of experimental uncertainty.
Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN l... more Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-30...
Current Status of Pressure Standards at NPLI and...................the Key Comparison Data Base (... more Current Status of Pressure Standards at NPLI and...................the Key Comparison Data Base (KCDB) ... Current Status of Pressure Standards at NPLI and Our ... Experiences with the Key Comparison Data Base ... AK BANDYOPADHYAY, SANJAY YADAV and NITA DILAWAR ...
Temperature dependent Raman scattering measurements were carried out to investigate the phonon
be... more Temperature dependent Raman scattering measurements were carried out to investigate the phonon behavior of thermoelectric Cu3SbSe3 nanoparticles. The anomalous behavior of phonon mode (Ag) frequency with temperature indicates the possibility of a lattice instability related to the orderedisorder structural transition at 380 K. In the low temperature region (80e250 K) we found an asymmetric line shape of Ag mode, which is analyzed and discussed in the light of phononecontinuum Fano-interference effect. We have obtained the thermal conductivity (k) ~ 2.04 W/mK at room temperature. The change in thermal conductivity with temperature strongly correlates with the change in total anharmonicity of the Cu3SbSe3 lattice.
Pressure and temperature dependent Raman scattering studies on Ho2O3 have been carried out to
inv... more Pressure and temperature dependent Raman scattering studies on Ho2O3 have been carried out to investigate the structural transition and the anharmonic behavior of the phonons. Ho2O3 undergoes a transition from cubic to monoclinic phase above 15.5 GPa, which is partially reversible on decompression. The anharmonic behavior of the phonon modes of Ho2O3 from 80K to 440K has been investigated. We find an anomalous line-width change with temperature. The mode Gr€uneisen parameter of bulk Ho2O3 was estimated from high pressure Raman investigation up to 29 GPa. Furthermore, the anharmonic components were calculated from the temperature dependent Raman scattering.
The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was inv... more The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2 was investigated in the temperature range of 80–440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.
This paper reports the behavior of a well-characterized pneumatic piston gauge in the pressure ra... more This paper reports the behavior of a well-characterized pneumatic piston gauge in the pressure range up to 8 MPa through simulation using finite element method (FEM). Experimentally, the effective area of this piston gauge has been estimated by cross-floating to obtain A0 and λ. The FEM technique addresses this problem through simulation and optimization with standard commercial software (ANSYS) where the material properties of the piston and cylinder, dimensional measurements, etc are used as the input parameters. The simulation provides the effective area Ap as a function of pressure in the free deformation mode. From these data, one can estimate Ap versus pressure and thereby Ao and λ. Further, we have carried out a similar theoretical calculation of Ap using the conventional method involving the Dadson's as well as Johnson-Newhall equations. A comparison of these results with the experimental results has been carried out.
The current paper reports the stability of a pressure dynamometer with a full scale pressure of 6... more The current paper reports the stability of a pressure dynamometer with a full scale pressure of 60 bar over nine years of operation. Since the stability of this digital pressure gauge depends on factors like repeatability, hysteresis, non-linearity, relative deviation etc, a systematic study has been carried out on each of these components. Finally, a comparison of the calibration factors and the estimated expanded uncertainty is made from the collected nine years calibration database. It has been found that the performance of the equipment showed consistent results for about 5 years after which a slight shift in the parameters described above has set in. But, the overall performance of the equipment remains excellent over the period studied within the limit of experimental uncertainty.
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Papers by Nita Dilawar
behavior of thermoelectric Cu3SbSe3 nanoparticles. The anomalous behavior of phonon mode (Ag) frequency
with temperature indicates the possibility of a lattice instability related to the orderedisorder
structural transition at 380 K. In the low temperature region (80e250 K) we found an asymmetric line
shape of Ag mode, which is analyzed and discussed in the light of phononecontinuum Fano-interference
effect. We have obtained the thermal conductivity (k) ~ 2.04 W/mK at room temperature. The change in
thermal conductivity with temperature strongly correlates with the change in total anharmonicity of the
Cu3SbSe3 lattice.
investigate the structural transition and the anharmonic behavior of the phonons. Ho2O3 undergoes
a transition from cubic to monoclinic phase above 15.5 GPa, which is partially reversible on
decompression. The anharmonic behavior of the phonon modes of Ho2O3 from 80K to 440K has
been investigated. We find an anomalous line-width change with temperature. The mode Gr€uneisen
parameter of bulk Ho2O3 was estimated from high pressure Raman investigation up to 29 GPa.
Furthermore, the anharmonic components were calculated from the temperature dependent Raman
scattering.
anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.
behavior of thermoelectric Cu3SbSe3 nanoparticles. The anomalous behavior of phonon mode (Ag) frequency
with temperature indicates the possibility of a lattice instability related to the orderedisorder
structural transition at 380 K. In the low temperature region (80e250 K) we found an asymmetric line
shape of Ag mode, which is analyzed and discussed in the light of phononecontinuum Fano-interference
effect. We have obtained the thermal conductivity (k) ~ 2.04 W/mK at room temperature. The change in
thermal conductivity with temperature strongly correlates with the change in total anharmonicity of the
Cu3SbSe3 lattice.
investigate the structural transition and the anharmonic behavior of the phonons. Ho2O3 undergoes
a transition from cubic to monoclinic phase above 15.5 GPa, which is partially reversible on
decompression. The anharmonic behavior of the phonon modes of Ho2O3 from 80K to 440K has
been investigated. We find an anomalous line-width change with temperature. The mode Gr€uneisen
parameter of bulk Ho2O3 was estimated from high pressure Raman investigation up to 29 GPa.
Furthermore, the anharmonic components were calculated from the temperature dependent Raman
scattering.
anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.