arXiv subjects

Aloka Sinha

Publications and source records attributed to Aloka Sinha.

6 recordsLinked to original sources

arXiv2024

In Situ Growth of Copper Channels within CuCl and PVDF Composite for Durable WORM Device Formation

This study details the creation of a Write Once-Read Many (WORM) memory device utilizing cuprous chloride (CuCl) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymers. Employing an in-plane configuration, a deliberate 1:10 ratio of CuCl to PVDF-HFP has been selected. This ratio aims to establish an in-situ copper channel within the device. The electrical response exhibits consistent memory retention over an extended duration. The WORM characteristics are attributed to the development of multiple conducting filaments or a highly conductive percolative path created by Cu ions within the polymer matrix. The UV-Vis study also reinforces the obtained results. Additionally, the memristor undergoes specific poling and cooling conditions. The fabrication approach employed in this research yields a distinctive type of Resistive Switching Device (RSD). Once the device is activated, it maintains its state even after the applied field is reduced. This specialized device holds potential applications in Compact Disc-Recordable (CD-R), Digital Versatile Disc-Recordable (DVD-R), Blu-ray Disc Recordable (BD-R), and Write Once USB Drives.

cond-mat.mes-hall↗

arXiv2024

A continuous plane of polarization rotator and detector based on the liquid crystal theta-cell

Modulation of the polarization state of optical beams is crucial in advanced optical applications such as polarization microscopy, polarization rotation, and medical imaging. We demonstrate a continuous polarization rotator by utilizing the liquid crystals (LC) in theta-cell configuration comprising of circular and parallel alignment of LC on two aligning glass substrates. A rotation of plane of polarization up to 160 degree is observed using Stokes polarimetry and substantiated by the mathematical analysis using Mueller matrix formalism. Further, the device is demonstrated as a plane of polarization detector with high precision detection angle. The plane of polarization is analyzed through single shot imaging of the intensity distribution of transmitted light through the LC theta-cell.

physics.optics↗

arXiv2024

Dispersion of Multiferroic Nanoparticles in a Bent-Core Nematic Liquid Crystal: Experimental and Theoretical Study

A novel nanocomposite system has been prepared by dispersing multiferroic bismuth ferrite nanoparticles (BiFeO$_3$) in a bent-core nematic liquid crystal (8-F-OH) that exhibits cybotactic clusters. Transition temperature, optical textures, order parameter $S_m$, and dielectric spectroscopy experiments are performed in the doped system, and the results are compared with the pure one. The main experimental outcome is that the doped system has increased orientational order parameters, even though the cybotactic cluster size is reduced due to the incorporation of multiferroic BiFeO$_3$ nanoparticles. The transition temperature, as observed under polarising optical microscopy, clearly indicates a reduction of $1 - 2~ ^\circ{\rm C}$ in the doped system compared to the pure one, and we conjecture this is due to the disordering of the cybotactic cluster in the doped system. Based on the experimental findings, a Landau-de Gennes-type free energy model is developed. The model qualitatively explains the increased mean order parameter and the disordering of cybotactic clusters with increasing polarization value of nanoparticles. This is corroborated by experimental findings.

cond-mat.soft↗

arXiv2021

Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure, macroscopic polarization and fast switching speeds

The twist-bend nematic (Ntb) phase is a recent addition to the nematic (N) phases of liquid crystals (LCs). A net polar order in the Ntb phase under an external electric field was predicted in several recent theoretical studies but yet to be experimentally realized. We investigated the polar nature, dielectric properties, electro-optical switching and optical transmission properties of a bent LC dimer CB7CB. The LC showed a relatively high-temperature nematic (N) phase and a lower-temperature nematic (NX) phase (also called Ntb in literature). A threshold-dependent polarization current response with large polarization values was obtained in the entire mesophase range. The associated switching times were found in sub-millisecond region. This ferroelectric-like polarization resulted from collective reorientation of polar cybotactic clusters. In NX phase, electric field-induced deformation of twisted helical structures also contributed to net polarization. Dielectric measurements confirmed the presence of cybotactic clusters via relaxation processes with large activation energies. Deformation of the NX helical structure under external electric field was corroborated by polarized optical microscopy and optical transmission studies. The field-induced deformations, net polar order and fast switching will contribute towards greater understanding of the NX (or Ntb) phase dynamics. It may also find applications in next-generation electro-optic devices.

cond-mat.soft↗

arXiv2021

Quantum-Dots Dispersed Bent-core Nematic Liquid Crystals and Cybotactic Clusters: Experimental and Theoretical Insights

We study a quantum-dots (QDs) dispersed bent core liquid crystalline system in planar geometry and present experimental measurements of the order parameter, dielectric dispersion and absorption spectra, optical textures, with attention to variations with temperature. A bent core liquid crystal (LC) 14-2M-CH$_3$ is used as the host material and CdSe/ZnS core-shell type QDs are used as the dopant. The nematic (N) phase exhibited by the pristine (undoped) LC 14-2M-CH$_3$ contains cybotactic clusters, which are retained by its QDs incorporated LC nanocomposite. Our notable findings concern the reduction of the orientational order parameter of the QDs dispersed LC system compared to its pristine counterpart, at fixed temperatures, and a reduction of the size of the cybotactic clusters due to the incorporation of QDs. The reduced order parameter for the doped system is accompanied by reduced birefringence, increased activation energy and a qualitative reduction in the dielectric anisotropy. We complement the experiments with a novel Landau-de Gennes type free energy for a doped bent core LC system, that qualitatively captures the doping-induced reduced order parameter and its variation with temperature. The dependency of the mean order parameter on several other factors (e.g. cluster size, coupling parameter) are also analyzed.

cond-mat.soft↗

arXiv2018

Theoretical Remarks on Cybotactic Clusters of Bent-Core Nematic Liquid Crystals in 1D Settings

The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for electro-optic devices. The nematic (N) phase of these LCs possesses highly ordered smectic-like cybotactic clusters which are promising in terms of ferroelectric-like behaviour in the N phase itself. We have studied a one-dimensional (1D) Landau-deGennes model of spatially inhomogeneous order parameters for the N phase of bent-core LCs. We investigate the effects of spatial confinement and coupling (between these clusters and the surrounding LC molecules) on the order parameters to model cluster formation in recently reported experiments. The coupling is found to increase the cluster order parameter significantly, suggesting an enhancement in the cluster formation and could also predict a possible transition to a phase with weak nematic-like ordering in the vicinity of nematic-isotropic transition upon appreciable increase of the coupling parameter γ.

cond-mat.soft↗