Estimation of gradient size of interfacial strain and its optimization for effective magnetoelectric coupling in (CoFe2O4) – (0.93Na0.5Bi0.5TiO3 – 0.07BaTiO3), 2-2 nano-composites

Strain-mediated coupling between the magnetic and electrically ordered phases plays a significant role in magnetoelectric (ME) nano-composites. This study explores a method to analyse and quantify interfacial strain using a grazing angle scan (α) in a ME composite optimised for a specific microstructure. The details of strain around the interface CoFe2O4 (CFO) – 0.93Na0.5Bi0.5TiO3 – 0.07BaTiO3 (NBT-BT) was determined by performing ‘α’ scan, in order to gather information at various depths of the NBT-BT layer around maximum intensity (110) reflection. The strain around the interface was observed to dominate over a spatial region of ∼20–30 nm away from the interface. The Piezoresponse force microscopy (PFM) studies performed near the interface reveal that the strain constrain experienced by the ferroelectric layer operates such that polarisation rotation and domain wall motion are constrained compared to the strain relaxed region of the film. For effective strain transfer, heterostructures grown with optimised thicknesses (∼20–30 nm) exhibited a superior inverse piezomagnetic effect. © 2021 Elsevier Ltd and Techna Group S.r.l

Multiferroics perspectives on strain, structure and properties

Advances in Highly Correlated Systems explores the fundamentals, recent advances, and applications of the physics of highly correlated materials. This book serves as a handbook/reference for advanced graduate students. Provides fascinating insights into the major developments and applications of strongly correlated materials.Integrates various numerical/theoretical models, such as dynamic mean-field theory, Hubbard model, Ab-Initio Calculation etc.Encompasses a useful experimental and theoretical basis for students, researchers, and scientists

Study of Stiffness and flexible sensing performance of poly-vinylidene fluoride (PVDF) a piezo polymer with varying polarization components

Free standing PVDF thin films synthesized from varying precursor viscosities was fabricated through solution casting method. Polarization tuning from dominant in-plane to out-of-plane for an optimum viscosity range was observed and further its effect on the stiffness property was also studied. It was found that young's modulus increases with enhancement in in-plane polarization within the optimum range, However beyond the optimum range where polarization was negligible the young's modulus was observed to be very high. Effects of polarization tuning also observed on the device performance. The device with dominant in-plane polarization has the high stiffness as well as piezoelectric response whereas device with out-of-plane polarization has least stiffness and piezoelectric response. Thus correlation between viscosity as well as polarization on stiffness and piezoelectric response of device was observed

Grain to Grain Epitaxy-Like Nano Structures of (Ba,Ca)(ZrTi)O3/ CoFe2O4 for Magneto–Electric Based Devices

Multiferroic nanocomposites with grain to grain epitaxy-like feature comprising of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT)/CoFe2O4 (CFO)/BCZT layers were deposited on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. To enhance strain coupling between the phases, vertically ordered continuous nanostructures with grain to grain epitaxy-like feature was achieved by careful choice of material and optimized growth conditions. The columnar grains between the BCZT/CFO and CFO/BCZT interface were optimized such that every column grew in an epitaxy-like growth with grain-over grain crystallographic relation even at nanoscale. Grain to grain epitaxy was evident from TEM analysis (inverse FFT analysis). Elastic strain coupling present between various vibrational modes of BCZT and CFO was confirmed by cross-sectional Raman studies. Ferroelectric polarization of 10 μC/cm2 and out-of-plane remnant magnetization (40emu/cc) was observed in the columnar structure. The morphologically coherent columnar structure of both the phases and the epitaxial registry at the interface of the composite significantly enhanced the strain coupling between the ferroelectric/ferromagnetic phases, which is evident from the magneto-dielectric studies with a 21% change in dielectric constant and the magneto-electric(ME) coefficients (620-840 mV/cm·Oe). The ME values indicate the existence of high elastic strain coupling in continuous columnar structures compared with granular structures with an incoherent interface. Enhanced magneto-electric coupling in these types of nanostructures can be of great potential in realizing devices like actuators and sensors

Layer number dependent optical and electrical properties of CVD grown two-dimensional anisotropic WS2

Engineering 2D transition metal dichalcogenides with precise control over layer number enable tuning of exciting optical and electrical properties at the nanoscale level. We report controlled one-step chemical vapour deposition growth of WS2 monolayer, bilayer, and trilayer for large scale manufacturing and demonstrate layer dependent changes in their work function, photoluminescence, and electrical conductivity. Raman, photoluminescence, and fluorescence imaging revealed that the base WS2 monolayer contains alternating triangular domains with different emission properties. It is observed that bilayer and trilayer grow selectively on less luminescent facet leading to fan-like morphology for second and third layers. We have systematically demonstrated that desired growth and areal coverage of bilayer and trilayer can be achieved by controlling WO3 precursor content. Kelvin probe force microscopic studies suggest a higher work function of thicker layers as compared to the monolayer. It was found that work function increases by 0.04 eV when thickness increases from monolayer to bilayer. FET device measurement on mono and bilayer shows n-type characteristics and two-fold higher photo-current in monolayer in comparison to the bilayer. The studied thickness dependence of the work function of WS2 is vital to the fabrication of metal contacts for WS2 based electronic and optoelectronic devices. © 202

Enhanced optical emission at MoS2-WS2 heterostructure interface with n-N junction

Atomically thin transition metal dichalcogenide based heterostructures are of significant interest for the elec-tronic and optoelectronic device applications. Growth of atomically thin heterostructures have gained remark-able importance due to the unusual electrical response and optical emission at the interface. Here, facile chemical vapour deposition growth of n -N type MoS2-WS2 heterostructure is demonstrated. Multifold enhancement in photoluminescence emission at the interface of MoS2-WS2 heterostructure with local excitonic amplifications arising at the interface is observed. The atomic level structure of interface has been investigated with the aid of aberration corrected scanning transmission electron microscopy. Electrical properties of MoS2-WS2 hetero-structure with n -N semiconductor junction are systematically probed using micromanipulators interfaced with scanning electron microscope. Our microscopic and spectroscopic investigations along with electrical and optical responses at the interface contribute to the fundamental knowledge to empower the development of optical devices based on two dimensional heterostructures with enhanced emissions

Local structural distortion and interrelated phonon mode studies in yttrium chromite

International audienceYCrO3 (YCO) perovskite has been originally reported to be a biferroic with antiferromagnetic and ferroelectric (FE) properties, in which the origin of FE in YCO remains ambiguous. However, further studies reveal the presence of a global orthorhombic Pnma structure with a local structural heterogeneity. In this study, we discuss the high temperature phonon modes and their inter-relation to local structural distortions in YCO perovskite through Raman spectroscopy experiments and density functional theory (DFT) calculations. We observe that the Raman active B3g(3) out of phase scissor mode (SM) disappears above the dielectric transition temperature (T c) commensurate with the local structural distortions. DFT calculations show that the transformation of a room temperature Y-cation distorted orthorhombic structure to a perfect orthorhombic structure above the dielectric transition temperature in which the Y cation is undisplaced could lead to the conversion of SM with symmetry B3g to Raman inactive B1u mode