arXiv subjects

Sanjeev Gautam

Publications and source records attributed to Sanjeev Gautam.

10 recordsLinked to original sources

arXiv2026

Osmotically Induced Shape Changes in Membrane Vesicles

We develop a self-consistent free-energy framework in which membrane shape and osmotic pressure are determined simultaneously in a finite reservoir by minimizing bending elasticity and solute entropy. Solute conservation makes osmotic pressure a thermodynamic variable rather than an externally prescribed parameter, producing a nonlinear coupling between membrane mechanics and solvent entropy. This coupling modifies the classical stability condition for spherical vesicles: instability emerges from global free-energy competition rather than the linear Helfrich stability criterion. The resulting critical pressures differ by orders of magnitude from Helfrich predictions and agree with simulations for small and large unilamellar vesicles. The framework is relevant to cellular environments involving biomolecular condensate confinement as well as synthetic vesicles and the development of osmotic-pressure-driven encapsulation platforms.

cond-mat.soft↗

arXiv2020

Investigating Phase Transition and Morphology of Bi-Te Thermoelectric System

The optimization of secondary phase in thermoelectric(TE) materials can {helps in improvisation of material's efficiency}. Being a potential {contender} for lower temperature TE application, bismuth telluride(Bi$_2$Te$_3$) nanoparticles were synthesized via different routes and profiles to optimize their pure single phase. Systematic characterizations were performed with the help of X-ray diffraction (XRD), Rietveld refinement and field effect-scanning electron microscopy(FE-SEM) for structural and morphological behavior, while TE properties such as Seebeck coefficient, electrical conductivity and power-factor were measured for the purest sample chosen. Rietveld refinement in the XRD pattern of the samples revealed that only a small amount ($\sim$ 1.6\%) of Bi$_2$Te$_3$ was formed in co-precipitation method, while the hydrothermal technique increases this phase with increment in synthesis duration. This work focused on the phase evolution of Bi$_2$Te$_3$ with increasing synthesis duration time at constant temperature and vice-versa. XRD and Rietveld refinement revealed that the hydrothermal technique (150 $^\circ$C for 48 hours) can synthesize purest samples (84\% Bi$_2$Te$_3$ phase in this case). {FE-SEM and Energy Dispersive X-ray analysis unveiled that the impure phases in the system {were} quantitatively reduced, and it supported by decline in atomic percentage of oxygen from 37\% to 11\%, in addition to this, it was also found that particle size was also decreased with increase in temperature.} The observed electrical conductivity of the chosen sample is $\sim$20 times greater, while Seebeck coefficient is $\sim$3 times lower than that of pure Bi$_2$Te$_3$ phase. The detailed analysis has generalized the growth mechanism in Bi$_2$Te$_3$ phase evolution by the diffusion of Bi into Te nanorods to fabricate hexagonal Bi$_2$Te$_3$.

cond-mat.mtrl-sci↗

arXiv2019

Developing ZnO Nanoparticle embedded Antimicrobial Starch Biofilm for Food Packaging

Starch based bio-films act as biodegradable packaging material for coating and wrapping food products, which is alternate to the synthetic polymer. Nanoparticles (NPs) are also alternative to antibiotics to target pathogens. Through interaction of nanoparticles with food packaging material the overall quality of the packaged food also get enhanced. In this research work, ZnO NP embedded corn starch films were developed. First, ZnO NP were synthesized by two approaches (a) Sol-gel approach and (b) Green synthesis approach; and then ZnO NP embedded corn-starch bio-films were developed. In sol-gel technique ZnO NP were synthesized at different pH ranging from 8 to 11, with an average crystallite size of 28 to 53 nm. In green synthesis technique ZnO NP were synthesized by using Azadirachta indica (Neem) at different concentration of 2\% and 3\% with an average crystallite size of 36 nm and 32 nm, respectively. Characterization of synthesized ZnO NPs were done with XRD, UV-DRS, UV-VIS, FTIR and FE-SEM. The functional properties of the ZnO embedded starch film were enhanced with addition of 5\% citric acid solution(w/w) as cross-linker and 0.90 g glycerol(w/w) as plasticizer. Film-F1 embedded with chemically synthesized ZnO NP, Film-F2 embedded with biochemcially synthesized ZnO NP and Film-F3 without being embedded by any NPs. Characterization of synthesized films were done with SEM and XRD. Film solution of F2 showed higher antimicrobial effectiveness than F1; against E.coli and S.aureus bacterial strains with an inhibition zone of 14 mm and 6 mm. 7days biodegradability analysis of the films were also done. Along with this, their current application and future perspectives in the food sector are also explored

physics.app-ph↗

arXiv2018

Phase-evolution in Co-Sb System: CoSb3 Hydrothermal Synthesis

Nanostructure CoSb3 samples were synthesized via hydrothermal technique along with different routes to study the phaseevolution in Co-Sb system. X-ray diffraction (XRD) explored to study the phase evolution in Co-Sb system via. Special emphasis on rietveld refinement and scanning electron microscope (SEM) were evaluated to study morphology of the samples. The samples prepared using ramp-route showed presence of different phases that eventually helps in formation of pure phase CoSb3 skuterrudite. Using different solvents to eliminate NaCl impurity also shows that DI-water eliminates NaCl impurity better because of its high solubility.

cond-mat.mtrl-sci↗

arXiv2013

Magnetic and Electronic Structure study of Fe/MgO/Fe/Co Multilayer Stack Deposited by E-Beam Evaporation

Present work investigates the magnetic and electronic structure of MgO/Fe/MgO/Fe/Co/Au multilayer stack grown on Si(100) substrates by electron beam evaporation method. X-ray diffraction study depicts polycrystalline nature of the multilayers. Results obtained from vibrating sample magnetometry (VSM) and near-edge X-ray absorption fine structure spectra (NEXAFS) at Fe & Co L- and Mg & O K-edges are applied to understand the magnetic and electronic properties of this stack and its interface properties. While the spectral features of Fe L-edge spectrum recorded by surface sensitive total electron yield (TEY) mode shows the formation of FeOx at the Fe/MgO interface, the bulk sensitive total fluorescence yield (TFY), shows Fe in metallic nature. Co L-edge spectrum reveals the presence of metallic nature of cobalt in both TEY and TFY modes. Above results are well correlated with X-ray reflectometry.

cond-mat.mtrl-sci↗

arXiv2012

On the optical properties of Ag^{+15} ion-beam irradiated TiO_{2} and SnO_{2} thin films

The effects of 200-MeV Ag^{+15} ion irradiation on the optical properties of TiO_{2} and SnO_{2} thin films prepared by using the RF magnetron sputtering technique were investigated. These films were characterized by using UV-vis spectroscopy, and with increasing irradiation fluence, the transmittance for the TiO_{2} films was observed to increase systematically while that for SnO_{2} was observed to decrease. Absorption spectra of the irradiated samples showed minor changes in the indirect bandgap from 3.44 to 3.59 eV with increasing irradiation fluence for TiO_{2} while significant changes in the direct bandgap from 3.92 to 3.6 eV were observed for SnO_{2}. The observed modifications in the optical properties of both the TiO_{2} and the SnO_{2} systems with irradiation can be attributed to controlled structural disorder/defects in the system.

cond-mat.mtrl-sci↗

arXiv2010

Magnetic and humidity sensing properties of nanostructured Cu[x]Co[1-x]Fe2O4 synthesized by auto combustion technique

Magnetic nanomaterials (23-43 nm) of Cu$_x$Co$_{1-x}$Fe$_2$O$_4$\ (x = 0.0, 0.5 and 1.0) were synthesized by auto combustion method. The crystallite sizes of these materials were calculated from X-ray diffraction peaks. The band observed in Fourier transform infrared spectrum near 575 cm$^{-1}$ in these samples confirm the presence of ferrite phase. Conductivity measurement shows the thermal hysteresis and demonstrates the knee points at 475$^o$C, 525$^o$C and 500$^o$C for copper ferrite, cobalt ferrite and copper-cobalt mixed ferrite respectively. The hystersis M-H loops for these materials were traced using the Vibrating Sample Magnetometer (VSM) and indicate a significant increase in the saturation magnetization (M$_s$) and remanence (M$_r$) due to the substitution of Cu$^{2+}$ ions in cobalt ferrite, while the intrinsic coercivity (H$_c$) was decreasing. Among these ferrites, copper ferrite exhibits highest sensitivity for humidity.

cond-mat.mtrl-sci↗

arXiv2009

Electronic structure studies of Fe- ZnO nanorods by x-ray absorption fine structure

We report the electronic structure studies of well characterized polycrystalline Zn_{1-x}Fe_xO (x = 0.0, 0.01, 0.03, and 0.05) nanorods synthesized by a co-precipitation method through x-ray absorption fine structure (XAFS). X-ray diffraction (XRD) reveals that Fe doped ZnO crystallizes in a single phase wurtzite structure without any secondary phase. From the XRD pattern, it is observed that peak positions shift towards lower 2θvalue with Fe doping. The change in the peak positions with increase in Fe contents clearly indicates that Fe ions are replacing Zn ions in the ZnO matrix. Linear combination fittings (LCF) at Fe K-edge demonstrate that Fe is in mixed valent state (Fe3+/Fe2+) with a ratio of ~ 7:3 (Fe3+:Fe2+). XAFS data is successfully fitted to wurtzite structure using IFEFFIT and Artemis. The results indicate that Fe substitutes Zn site in the ZnO matrix in tetrahedral symmetry.

cond-mat.mtrl-sci↗

arXiv2007

Effect of silver doping on the electrical properties of a-Sb$_2$Se$_3$

This paper reports the effect of Ag-doping on electrical properties of a-Sb2Se3 in the temperature range 240-340 K and frequency range 5 Hz to 100 kHz. The variation of transport properties with thermal doping has been studied. Ag-doping produced two homogeneous phases in the sample and which are found to be voltage dependent in the temperature range studied and frequency dependent in lower frequency region (0.1 - 10 kHz). Activation energy Eg and C' [=$σ_0$ exp ($γ$/k), where $γ$, is the temperature coefficient of the band gap] calculated from dc conductivity has been found to vary from 0.42 eV to 0.26 eV and 41.08x10$^-6$ to 2.902x10-6 $\ohm^{-1}$cm$^{-1}$ respectively. Ag-doping can be used to make the sample more useful in device applications.

cond-mat.mtrl-sci↗

arXiv1998

Electrical properties of a-antimony selenide

This paper reports conduction mechanism in a-\sbse over a wide range of temperature (238K to 338K) and frequency (5Hz to 100kHz). The d.c. conductivity measured as a function of temperature shows semiconducting behaviour with activation energy $Δ$E= 0.42 eV. Thermally induced changes in the electrical and dielectric properties of a-\sbse have been examined. The a.c. conductivity in the material has been explained using modified CBH model. The band conduction and single polaron hopping is dominant above room temperature. However, in the lower temperature range the bipolaron hopping dominates.

cond-mat↗