Moumita Dutta

BaTiO3 Coated CoFe2O4–Core-Shell Magnetoelectric Nanoparticles (CSMEN) Characterization

Multiferroic behavior of magnetoelectric nanoparticles exhibiting both ferromagnetic and ferroelectric properties find significance in various applications. In this study, core-shell magnetoelectric nanoparticles (CSMEN) have been fabricated by coating CoFe2O4 nanoparticles with BaTiO3 by weight using hydro-thermal method. The core-shell structure was confirmed by electron microscopy and topographic scanning probe microscopic measurements were performed for further structural analysis. While magnetic force microscopy and ferromagnetic hysteresis loop measurements substantiated ferromagnetic behavior of the core, piezo response force microscopy confirmed ferroelectric behavior and single crystalline nature of BaTiO3 shell. As analyzed by TEM diffraction pattern both core and shell are in cubic phase with their respective diffraction spots depicting their single crystalline nature.

Magneto-elasto-electroporation (MEEP): In-vitro visualization and numerical characteristics

A magnetically controlled elastically driven electroporation phenomenon, or magneto-elasto-electroporation (MEEP), is discovered while studying the interactions between core-shell magnetoelectric nanoparticles (CSMEN) and biological cells in the presence of an a.c. magnetic field. In this paper we report the effect of MEEP observed via a series of in-vitro experiments using core (CoFe2O4)-shell (BaTiO3) structured magnetoelectric nanoparticles and human epithelial cells (HEP2). The cell electroporation phenomenon and its correlation with the magnetic field modulated CSMEN are described in detail. The potential application of CSMEN in electroporation is confirmed by analyzing crystallographic phases, multiferroic properties of the fabricated CSMEN, influences of d.c. and a.c. magnetic fields on the CSMEN and cytotoxicity tests. The mathematical formalism to quantitatively describe the phenomena is also reported. The reported findings provide insights into the underlying MEEP mechanism and demonstrate the utility of CSMEN as an electric pulse-generating nano-probe in electroporation experiments with a potential application toward accurate and efficient targeted cell permeation.

Current Status of Oxide Dielectric Materials for Terahertz Applications–An Overview

Terahertz electromagnetic radiation, its generation, detection and material interaction is an emerging field of study. Diverse range of researches is going on to explore and understand this frequency range and its potential applications. Situated between microwave and optical frequency domain, THz radiation is non-responding to the techniques commonly used for these two domains, thus insufficiency of supporting technology, high atmospheric absorption, lack of high power source have kept this spectrum away from technical and commercial interest for a long time. Advancements in Photonics like high power ultrafast lasing devices, high-power THz generation by means of nonlinear effects, band-engineered hetero-structures have greatly extended its potential. In order to explore all its merits and realize it as a full-fledged functional frontier, more high power sources, more sensitive sensors and efficient waveguides need to be developed. In order to achieve that, the main focus of the research world has moved towards the study of various classes of materials so that they can be categorized based on the applications they can be used for. In this overview article, recent studies on THz dielectric material interaction, their observations, outcomes and their prospect have been presented in a condensed manner so that the information can be used for further developments in this frequency regime.

Core-shell magnetoelectric nanorobot – A remotely controlled probe for targeted cell manipulation

We have developed a remotely controlled dynamic process of manipulating targeted biological live cells using fabricated core-shell nanocomposites, which comprises of single crystalline ferromagnetic cores (CoFe2O4) coated with crystalline ferroelectric thin film shells (BaTiO3). We demonstrate them as a unique family of inorganic magnetoelectric nanorobots (MENRs), controlled remotely by applied a.c. or d.c. magnetic fields, to perform cell targeting, permeation, and transport. Under a.c. magnetic field excitation (50 Oe, 60 Hz), the MENR acts as a localized electric periodic pulse generator and can permeate a series of misaligned cells, while aligning them to an equipotential mono-array by inducing inter-cellular signaling. Under a.c. magnetic field (40 Oe, 30 Hz) excitation, MENRs can be dynamically driven to a targeted cell, avoiding untargeted cells in the path, irrespective of cell density. D.C. magnetic field (−50 Oe) excitation causes the MENRs to act as thrust generator and exerts motion in a group of cells.

Terahertz attenuators based on dielectric stacks with alternating refractive indices

Abstract. This article demonstrates the design of dielectric terahertz (THz) attenuators comprising of periodically placed x-cut and z-cut ion-sliced lithium niobate dielectric layers. Changes introduced in the propagating wave due to alternating refractive indices of a ferroelectric material have been exploited for the design of an effective attenuator. The electrical and optical properties gathered from experimental investigations have been used to study the influence of different crystalline orientations on the design. The conduit comprising the periodically placed dielectric slabs has been configured as a tristate switch by modulating the amplitude of the traversing THz wave by altering its angle of incidence. Full-wave finite-element simulations have been conducted over a series of parametric configurations to come up with the optimized design. A modulation depth as high as 94.76% is achieved. The proposed low-cost, easily configurable THz dielectric attenuators operating around 0.625 THz can be potentially used as an external modulator for THz quantum cascade lasers.

Low frequency piezoresonance defined dynamic control of terahertz wave propagation.

Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

Optical and microstructural characterization of multilayer Pb(Zr0.52Ti0.48)O3 thin films correlating ellipsometry and nanoscopy

Optical and microstructural characteristics of sol–gel-deposited multilayer Pb(Zr0.52Ti0.48)O3 thin films were investigated employing several analytical techniques both invasive and non-destructive types. Optical responses probed by variable angle spectroscopic ellipsometry (VASE) were used to derive the optical properties and geometrical parameters of the multilayer thin films. STEM and TEM studies were performed to verify the nano-structural specifics and to correlate the results obtained using VASE. Crystallographic orientation and epitaxial interrelations of the layers were also investigated using selected area diffraction patterns with compositional profiles derived from energy dispersive X-ray analysis. Ferroelectric domain switching of the sol–gel-deposited films were studied by Piezoelectric Force Microscopy (PFM) revealing both the polarization–electric field hysteresis (P-E loop) relation and the butterfly-shaped surface displacement amplitude responses. The advantages and limitations of the non-invasive VASE characterization technique in terms of resolving a multilayer structure of thin films were explored in detail.

Directional dependence figure of merit analysis of piezoelectric materials

ABSTRACT Efficiency of a piezo-electric transducer is defined by the relative electrical output induced in response to the mechanical stress it encounters. Thus an efficient device design demands an insightful figure of merit analysis of the piezoelectric material used for the sensor fabrication. In this article we have performed a directional dependence figure of merit analysis of some popular piezoelectric materials to determine the cut orientations along which optimal proficiency can be achieved. The materials chosen for the study are PZT-5H, PMN-PT, PZN-PT, PMN-PZT, SbSI, SBN, BT and BCZT such that a comparative perspective can be deduced.

Photoacoustic and magnetoelastic property of cobalt ferrite nanoparticles and its attenuation with barium titanate coating

We report an experimental study, where Cobalt Ferrite (CoFe2O4) nanoparticles exhibit Photoacoustic (PA) emission peak intensity of 235.2V/J when analyzed under the Opto-Acoustic measurement setup. PA emission peak intensity decreases to 210V/J when AC Magnetic field is applied and further when Barium Titanate coated cobalt ferrite nanoparticles were analyzed, the PA peak further reduces to 68.76667V/J and with application of AC magnetic field the peak completely disappears. The measurement depicts the Photoacoustic and magnetoelastic behavior of cobalt ferrite nanoparticles.

Terahertz electrical and optical properties of LiNbO3 single crystal thin films

A study of Terahertz response of single crystal LiNbO3 thin films subjected to different structural and experimental configuration has been conducted in this work. In this work z-cut and x-cut ion-sliced Lithium Niobate thin films with and without embedded electrodes have been studied employing both Transmission and Reflection mode of Terahertz Spectroscopy along with z-cut single crystal in bulk form. The measurements have been performed in room temperature to probe distinctive THz-material interactions in the frequency range of 0.1-3 THz (3.34cm-1 - 100cm-1). The information thus obtained from the experimental investigation has been used to deduce a conclusive study on the influence of different polar domains on electrical and optical properties in THz frequency regime. Single Lorentzian oscillator model has also been used to define the THz signature thus acquired.