arXiv subjects

Avijit Jana

Publications and source records attributed to Avijit Jana.

4 recordsLinked to original sources

arXiv2025

Drastic modification in thermal conductivity of TiCoSb Half-Heusler alloy: Phonon engineering by lattice softening and ionic polarization

A drastic variation (~47%) in thermal conductivity (\k{appa}) for synthesized samples (TiCoSb1+x, x=0.0, 0.01, 0.02, 0.03, 0.04, and 0.06) is observed. The lowest \k{appa} is reported for the TiCoSb1.02 sample. Thermal variation of \k{appa} is estimated from the temperature and power-dependent Raman spectroscopy data. Embedded phases and Co vacancy are analysed, employing scanning electron microscopy and transmission electron microscopy data. X-ray absorption fine structure (XAFS) spectroscopy reveals the Co vacancy in synthesized samples, and the most ordered phase is TiCoSb1.02 amid the synthesized samples. X-ray photoelectron spectroscopy measurement of the synthesized samples provides direct evidence of Co vacancies and their increase with Sb concentration (x). Lattice dynamics are revealed using Raman Spectroscopy (RS) measurements. RS data accomplishes that variation in \k{appa} as a function of Sb concentration is observed owing to an alteration in phonon group velocity, related to lattice softening. The polar nature of the TiCoSb half-Heusler (HH) sample is revealed. Longitudinal Optical and Transvers Optical phonon (LO-TO) splitting in RS is observed due to the polar nature of TiCoSb1+x synthesized samples. Tailoring in LO-TO splitting due to the screening effect, correlated with Co vacancies, is reported for TiCoSb1+x synthesized samples. Lattice softening and LO-TO splitting lead to a minimum \k{appa} for the TiCoSb1.02 synthesized sample.

cond-mat.mtrl-sci↗

arXiv2020

Effect of growth temperature on the CVD grown Fe filled multi-walled carbon nanotubes using a modified photoresist

Fe filled carbon nanotubes were synthesized by atmospheric pressure chemical vapor deposition using a simple mixture of iron acetylacetonate with a conventional photoresist and the effect of growth temperature from 550 to 950 °C on Fe filled nanotubes has been studied. Scanning electron microscopy results show that, as the growth temperature increases from 550 to 950 °C, the average diameter of the nanotubes increases while their number density decreases. High resolution transmission electron microscopy along with energy dispersive X-ray investigation shows that the nanotubes have a multi-walled structure with partial Fe filling for all growth temperatures. The graphitic nature of the nanotubes was observed via X-ray diffraction pattern. Raman analysis demonstrates that the degree of graphitization of the carbon nanotubes depends upon the growth temperature.

physics.app-ph↗

arXiv2019

Site selective synthesis of in situ Ni filled multiwalled carbon nanotubes using Ni(salen) as a catalyst source

The synthesis of Ni filled multiwalled carbon nanotubes was performed by atmospheric pressure chemical vapor deposition with propane on Si at 850 C using a simple mixture of Ni(salen), and a conventional photoresist. Analysis of the carbon nanotubes using scanning electron microscopy together with high resolution transmission electron microscopy show that the nanotubes have grown by a tip growth mechanism and exhibit a multi walled structure with partial Ni filling. The high quality of the Ni filled nanotubes is evidenced by Raman spectroscopy. The magnetic properties of Ni filled nanotubes were analyzed using a superconducting quantum interference device which revealed their ferromagnetic behavior with large coercivity. A scalable as well as site selective growth of high quality Ni filled carbon nanotubes is achieved by a simple photolithographic method.

physics.app-ph↗

arXiv2019

Lithographically defined site-selective growth of Fe filled multi-walled carbon nanotubes using a modified photoresist

Partially Fe filled multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition with propane at 850 °C using a simple mixture of iron (III) acetylacetonate (Fe(acac)3) powder and conventional photoresist. Scanning electron microscopy revealed that catalytic nanoparticles with an average diameter of 70 nm are formed on the Si substrate which governs the diameter of the MWCNTs. Transmission electron microscopy shows that the nanotubes have a multi-walled structure with partial Fe filling. A site-selective growth of partially Fe filled MWCNTs is achieved by a simple photolithographic route.

physics.app-ph↗