K.-H. Chew

• University of Malaya

Polarization dehazing imaging has been an emerging topic to improve image quality by suppressing the scattering effects in complex scenarios. Most of these works are focused on the restoration of images in homogeneous scattering environments. Dehazing imaging in dynamic inhomogeneous scattering scenes becomes a challenging topic due to the potentia...

The nonlinear interactions between structured beams with spatially varying polarization and matter extend the boundaries of fundamental nonlinear optics, opening new avenues for applications across various fields. In this work, the second-harmonic generation (SHG) of vector beams with two orthogonal polarization components of vortices in a periodic...

Imaging technologies based on vector optical fields hold significant potential in the biomedical field, particularly for non-invasive scattering imaging of anisotropic biological tissues. However, the dynamic and anisotropic nature of biological tissues poses severe challenges to the propagation and reconstruction of vector optical fields due to li...

Exploration of two-dimensional (2D) metallic electrodes with high energy density and fast rate performance is important in rechargeable ion batteries. Aluminum-ion batteries (AIBs) are one of the most promising candidates for next-generation rechargeable batteries. Using first-principles computations, we investigate pristine and defective borophene...

Evolution of polarization components with a high anisotropic scattering medium (HASM) has been an important and challenging topic due to its rich fundamental physics and potential applications. In this work, a vector transfer matrix (VTM) method is extended to describe the linear-circular polarization conversion of two orthogonal polarization compo...

The acousto-optic Raman–Nath (RN) diffraction effects of vector beams diffracted by the chiral ultrasonic grating are demonstrated experimentally and theoretically. The deviation of left- and right-handed circularly polarized components in higher-order diffraction light leads to the rearrangement of their polarization states and intensity due to th...

Optical imaging through scattering media has become important due to its fundamental physics interest and various applications. The reconstruction of a structured optical field with various states of polarization passing through a scattering medium with a speckle pattern behind the scattering medium remains challenging since existing restoring tech...

Sodium (Na) ion batteries (SIB) hold great importance in energy storage due to their potential to offer a sustainable and cost-effective alternative to traditional lithium-ion batteries. Na is abundantly available...

In this study, we demonstrate both theoretically and experimentally second harmonic generation (SHG) of a twisted vector vortex optical field (TVVOF) using a nonlinear type-II phase-matched β-BaB2O4 (BBO) crystal. Our study introduces a novel method to manipulate SHG by independently modulating the two orthogonal polarization components of a TVVOF....

Based on the two-dimensional (2D) nonlinear Schrödinger equation, we investigate the collapse dynamics of a vector vortex optical field (VVOF) in nonlinear Kerr media with parity–time (PT)-symmetric modulation. The critical power for the collapse of a VVOF in a Kerr-ROLP medium (Kerr medium with a real optical lattice potential) is derived. Numeric...

Underwater target detection is an essential topic in the applications of underwater exploration. However, underwater target detection faces serious challenges, such as complex scattering, low visibility, and target clutter. Here a polarization-enhanced underwater multiple material target detection method is proposed to address these challenges. The...

Manipulation of polarization states in a complex structured optical field during propagation has become an important topic due to its fundamental interest and potential applications. This work demonstrates the effect of the caustic and twisting phases on the polarization states of a vector beam experimentally and theoretically. The novel properties...

This study investigates the influence of high-order twisting phases on polarization states and optical angular momentum of a vector light field with locally linear polarization and a hybrid state of polarization (SoP). The twisted vector optical field (TVOF) is experimentally generated based on the orthogonal polarization bases with high-order twis...

We study the influence of high-order twisting phases on polarization states and optical angular momentum of a vector light field with locally linear polarization and a hybrid state of polarization (SoP). The initial SoP of a twisted vector optical field (TVOF) modulated by the high-order twisting phase possesses various symmetric distributions. The...

Polarization dehazing imaging has been used to restore images degraded by scattering media, particularly in turbid water environments. While learning-based approaches have shown promise in improving the performance of underwater polarimetric dehazing, most current networks rely heavily on data-driven techniques without consideration of physics prin...

We theoretically investigated the effect of a new type of twisting phase on the polarization dynamics and spin–orbital angular momentum conversion of tightly focused scalar and vector beams. It was found that the existence of twisting phases gives rise to the conversion between the linear and circular polarizations in both scalar and vector beams d...

The electromechanical properties of monolayer 1-T NiTe2 under charge actuation were investigated using first-principles density functional theory (DFT) calculations. Monolayer 1-T NiTe2 in its pristine form has a work area density per cycle of up to 5.38 MJ m-3 nm upon charge injection and it can generate a strain and a stress of 1.51% and 0.96 N m...

Application of deep-learning to polarization imaging technology for image restoration has led to many technological breakthroughs, especially in underwater image recovery and recognition. In this work, a four-input deep learning model with the Polarimetric Residual Dense Network is proposed for underwater image recovery. The diverse polarization co...

The manipulation of the polarization states of the light transmitted through a scattering medium has become an emerging field due to the novel fundamental physics interest and potential applications. Here, the manipulation of the polarization states in the focusing high-resolution optical field (points and vector beams) after passing a scattering m...

The effect of twisting phases on the polarization dynamics of a vector vortex beam with a spatially variant state of polarization (SoP) is investigated theoretically and experimentally. The twisted vector vortex optical field with the cross-phase modulation is experimentally generated and observed. The presence of the twisting phases on the vector...

We revisit the Kittel's model of antiferroelectricity by extending the model to study the phase transitions, hysteresis loop behaviors and electrocaloric effect (ECE) of antiferroelectrics (AFEs). By considering both the first- and second-order AFEs, explicit expressions for the physical and staggered polarizations of AFEs in the stable states are...

In this study, monolayer up to few-layer of Mn3O4 nanosheets grown on c-Si (111) substrates using a thermal chemical vapor deposition (TCVD) technique were investigated in detail, where the growth reaction pressure was varied from 0.12 to 0.72 mbar. The morphology of the triangular-shaped Mn3O4 nanosheet greatly depends on the atomic ratio of O to...

We propose a thermodynamic model to investigate the polarization and dielectric behaviors of antiferroelectric–ferroelectric (AFE–FE) superlattices by taking into account the electrostatic coupling effect. Coupling at the interface between the AFE and FE layers is mediated by local polarizations, which favors an FE ordering. The Kittel’s model of a...

We study the effect of thickness ratio on the ferroelectric polarization and hysteresis behaviors of BaTiO3/SrTiO3 superlattices using Landau-Ginzburg-Devonshire theory by considering the electrostatic coupling and interface intermixing. Interface intermixing gives rise to inhomogeneous internal electric field and polarization in superlattices. The...

We demonstrate the dynamical properties of a vector vortex optical field (VVOF) in a strongly nonlocal nonlinear medium (SNNM) with sine and cosine parity-time-symmetric potentials (SCPT) by using the coupled vector Snyder-Mitchell model. Our study shows that the shape of the optical field is chaotically distorted in different propagation distances...

We study the dynamics of polarization and internal electric field in the PbTiO3/SrTiO3 (PT/ST) superlattices using the Landau–Khalatnikov equation. Apart from the polarization hysteresis loop, the hysteresis loop of the internal electric field is also observed. The effects of thickness ratio and temperature on the switching dynamics of superlattice...

We perform theoretical and experimental studies on the tight focusing properties of a vector vortex beam with fractional order topology charges. The fractional-order vector vortex optical fields (FO-VVOF) are experimentally generated by using the 4 f system and the hologram technology. In comparison to the integral-order vortex, the 3-dimensional (3...

In this work, we systematically studied the deposition, characterization, and crystal structure modeling of ScAlN thin film. Measurements of the piezoelectric device’s relevant material properties, such as crystal structure, crystallographic orientation, and piezoelectric response, were performed to characterize the Sc0.29Al0.71N thin film grown us...

Based on first-principles calculations, we propose a new two-dimensional (2D) van der Waals (vdW) heterostructure that can be used as a photocatalyst for water splitting. The heterostructure consists of vertically stacked 2D NbSe2H and graphene-like ZnO (g-ZnO). Depending on the stacking orders, we identified two configurations that have high bindi...

It was recently shown by Jeon et al. [Angewandte Chem. 2018, 57, 4607] that air stability more than 1000 hours under light illumination can be achieved in methyl-ammonium (MA) lead...

Ab initio calculations within the density-functional theory (DFT) are carried out to investigate the electronics and magnetic properties of the p-block elements doped two-dimensional GaN (2D GaN). We have selected Al, Si, P and S dopants as the representative for Group III, IV, V and VI elements, respectively. Depending on the type of dopant and su...

A phenomenological model for studying the polarization and phase transition of the ferroelectric superlattice is developed within the framework of Landau-Ginzburg theory. The interface energy which accounts for the interface intermixing effect and the electrostatic coupling are incorporated into the model. We use the BaTiO3/SrTiO3 superlattices as...

Halide perovskites have emerged as the most potential candidate for the next-generation solar cells. In this work, we conduct a comprehensive first-principles study on the photo-energy conversion efficiency (PCE) of CH3NH3PbI3/C60 heterojunction. Since perovskite solar cells (PSCs) are generally exposed to substantial temperature variations that af...

Two-dimensional (2D) materials have recently emerged as ideal candidates for high-capacity lithium-ion batteries anode materials because of their compelling physicochemical and structural properties. In the present study, we use first-principles calculations to investigate the performance of 2D Mg2C as anode materials for Li, Na, K and Ca-ions batt...

Based on first-principles calculations, we predict that the recently synthesized two-dimensional (2D) NbSe2 can be changed from the metallic to the semiconducting phase upon the adsorption of H with an indirect bandgap of 2.99 eV. The bandgap opening of the 2D NbSe2 only occurs when the hydrogen coverage is high, and it is sensitive to mechanical s...

We propose a thermodynamic model to the study the antiferroelectric (AFE) phase transitions in antiferroelectric-ferroelectric (AFE-FE) superlattices in which the coupling at the interface between two layers is mediated by local polarizations. Phase diagram of the AFE layer in term of the degree of interfacial effect λ and temperature T involving f...

Propagation of a vector vortex optical field (VVOF) with both fractional order of polarization topological charge $m$ and fractional order of vortex topological charge $n$ with spatially variant states of polarization (SoP) in a strongly nonlocal nonlinear medium (SNNM) is studied. The optical field always evolves reciprocally with a cycle of stret...

Based on density functional theory, we have investigated the effects of in-plane biaxial strain on the electronic and magnetic properties of the two-dimensional GaN (2D GaN) with Ga- (VGa) or N-vacancy (VN). We considered two different levels of vacancy concentration, i.e., θ=1/62 and θ=1/34. While the pristine GaN 2D structures are intrinsically s...

Although improved magnetic and piezoelectric performances were discovered in BiFeO3 rhombohedral-tetragonal mixed-phase, the associated electronic conduction mechanisms are less investigated. In the present work, we systematically investigated the leakage current and dielectric response as a function of temperature, frequency and bias field for pur...

In this work, the feasibility of a monolayer Be2C as the anode material for lithium-ion battery (LiB) was investigated using the density functional theory. Our study reveals that the adsorption of Li atoms changes the electronic conductivity of a monolayer Be2C from semiconducting to metallic. This resulted in a low Li diffusion barrier of 0.11 eV,...

The 0.5 mol.% Mn-doped 0.3 Pb(In1/2Nb1/2)O3-0.4 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (Mn-PIMNT) single crystal was grown by a modified Bridgman technology. A comprehensive study involving the electrical properties, as well as phase transitions and domain configuration behavior of (001)-oriented Mn-PIMNT single crystal has been carried out. Three anomalies ar...

The dynamical properties of radial-variant vector beams in strongly nonlocal nonlinear (SNN) media are theoretically demonstrated. The analytical expressions for the variation of root-mean-square (RMS) beam width and the critical powers Pcr that keep the RMS beam widths invariant during propagation are derived using the moments method. When the ini...

Superlattices (SLs) consisting of multiferroic BiFeO3 (BFO) and dielectric Ba0.7Sr0.3TiO3 were epitaxially grown on a (001)-oriented Nb:SrTiO3 substrate using pulsed laser deposition. An improved ferroelectricity with a high-temperature polarization of ∼63.7 μC/cm² at 470 K was observed. The SL exhibited both dielectric and magnetic relaxation prop...

The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer, and thus alters the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge tr...

A stable single layer Pmma-CO with direct bandgap and excellent mechanical stability has been predicted recently by Teng et al. (Nanoscale. 2017, 9, 5445). Motivated by this finding, we have carried out first-principles calculations based on DFT to systematically investigate the structural, electronic and magnetic properties of a monolayer Pmma-CO...

We have performed computational molecular modelling to study the polarization switching and hysteresis loop behaviours of DNA and RNA nucleobases using the PM3 semi-empirical quantum mechanical approaches. All the nucleobases: adenine (A), thymine (T), guanine (G), cytosine (C), and uracil (U) were modelled. Our study indicates that all the nucleob...

A thermodynamic model based on the Landau-Ginzburg theory is developed to study the polarization and hysteresis loop behaviors in ferroelectric superlattices with technologically important BaxSr1-xTiO3 (BST) solid solutions. Our study shows that the polarization, coercive field, and hysteresis loop behaviors can be tailored by changing the thicknes...

The effect of magnetic and electric fields on the electrical and magnetic properties of BiMnO3 films within the framework of Landau-Ginzburg theory had been investigated. We also calculated and discussed the hysteresis loops of polarization and magnetization as a function of electric and magnetic fields. The results reveal that, the possibility of...

The corrosion of iron presents an important scientific problem and a serious economic issue. It is also one of the most important subjects in materials science because it is basically an electrochemical process and closely related to other topics such as electrocatalysis of the oxygen reduction reaction. So far, many studies have been conducted to...

The conversion of the spin-to-orbital optical angular momentum (AM) of an optical field with hybrid states of polarization (SOP) in the near-field region is studied based on the angular spectrum method. The spin-to-orbital optical AM conversion occurs in the longitudinal component of an optical field with hybrid SOP under a highly nonparaxial circu...

The vectorial structure of an optical field with hybrid states of polarization (SoP) in the near-field is studied by using the angular spectrum method of an electromagnetic beam. Physical images of the longitudinal components of evanescent waves are illustrated and compared with those of the transverse components from the vectorial structure. Our r...

Bandgaps, band edges, and structural properties of domain walls (DWs) in multiferroic BiFeO3 (BFO) are studied using density functional theory. The ferroelectric DWs (namely, the 71°, 109°, and 180° DWs) in rhombohedral BFO are considered, with a view of critically examining the relationships between local bandgap, polar ordering, and octahedral di...

Symmetric BaTiO3 slabs of different thickness (6, 8 and 10-unit-cell thick) with BaO (100) surface terminations in tetragonal phase were computed by first-principles. The effects of surface termination on the structural parameters were studied. In contrast to previous literature findings, all interlayer spacings were subjected to expansions except...

The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrödinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to...

The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrӧdinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to...

Magnetoelectric (ME) multiferroic bismuth manganite (BiMnO3) has ferroelectric (FE) and ferromagnetic order parameters that coupled biquadratically. Landau free energy expression in these order parameters is proposed to investigate the phase transition and thermodynamic properties of a BiMnO3 film. The surface energy term is included in the free en...

Bilayers of VDF-TrFE ferroelectric copolymer thin films have been characterised in terms of polarisation behaviour and dielectric nonlinearities. The effective properties of the ferroelectric bilayers have been investigated and compared with those of the individual layers in the stack. It has been demonstrated that the effective permittivity of the...

Effects of polarization discontinuity and interface screening charge in superlattices composed of alternating ferroelectric and dielectric layers are studied based on Landau-Ginzburg theory. Interface mixing gives rise to polarization continuity or discontinuity in the superlattices. At interfaces, screening charge with equal and opposite sign accu...

Based on a pair of coupled 2D nonlinear Schrödinger equations, the collapse dynamics of a vector field with hybrid states of polarization (SoP) in a Kerr medium is demonstrated. The critical power for an optical field to collapse is present, and the full vectorial numerical simulations provide detailed information about the evolution and partial co...

Ferroelectric superlattices with polarization perpendicular to the surface or interface are studied within the framework of the Landau-Ginzburg theory. An interface energy is introduced in the free energy to describe the effect of mixing and local polarization coupling at interface. Internal electric field is considered in the model. For superlatti...

A caustic vortex vector optical field is experimentally generated and demonstrated by the caustic-based approach. The desired caustic with arbitrary acceleration trajectories, as well as the structured states of polarization (SoP) and vortex orders located in different positions in the field cross-section, can be generated by imposing the correspon...

The propagation dynamics of a vector field with inhomogeneous states of polarization (SoP) imposed a vortex is studied using the angular spectrum method. The evolution of SoP in the cross section of the field during propagation is analyzed numerically by the Stokes polarization parameters. The results indicate that SoP in the field cross section ro...

Based on the Landau-Ginzburg theory, the screening charge compensation phenomena for polarization discontinuities at interface in ferroelectric superlattices are investigated. Interface mixing leads to polarization continuity or discontinuity in superlattices. Free charge with equal but of opposite sign for alternate interface, driven by internal e...

The nonlinear dynamics of an Airy beam in a saturated medium is presented. An analytical expression for the evolution of the Airy beam width in the root-mean-square sense is derived. The novel features of the collapsing beams of an Airy beam in a saturated medium are demonstrated by numerical calculation. These collapsing beams shift laterally and...

We have developed a thermodynamic model based on the Landau–Ginzburg theory to study the effect of composition and interface intermixing on ferroelectric properties of BaTiO3/BaxSr1−xTiO3 (BT/BST) superlattices. Dependence of the lattice parameter and the substrate-induced misfit strain of BST layer in BT/BST superlattices on Ba/Sr content are obta...

Polarization switching of ferroelectric materials is influenced by extensive variables such as electric field, temperature and stress. Currently a variety of theoretical approaches are used to gain a deeper understanding of the influence of extensive variables on the dynamic properties of ferroelectrics. In this paper a Landau-type model for second...

A thermodynamic model to study the effect of interface intermixing on polarization of ferroelectric superlattices composed of a ferroelectric and paraelectric layers is developed. Interface intermixing forms an intermixed layer with property different from its individual layers, leading to inhomogeneous ferroelectric properties in the superlattices...

The vector structure of evanescent and propagating wave components of a cylindrical vector optical field with different states of polarization in the cross-section of the field is demonstrated using the vector angular spectrum. The physical pictures of transverse electric (TE) and transverse magnetic (TM) terms of the evanescent and propagating wav...

Using a one-dimensional lattice model, we studied the switching characteristics of superlattices formed out of alternate ferroelectric and dielectric layers. The two layers interact with each other through the dipole lattices located at interface. Switching characteristics of pulsed field such as hysteresis loop, differential electric susceptibilit...

We investigate the dynamic characteristics of electric polarization P(t) in a ferroelectric junction under ac applied voltage and stress, and calculate the frequency response and the cut-off frequency f0, which provides a reference for the upper limit of the working frequency. Our study might be significant for sensor and memory applications of nan...

Fatigue and ferroelectric properties of multiferroic (Ba 0.7Sr0.3)TiO3/(Bi1.05La 0.05)FeO3 (BST/BLF) epitaxial heterostructures are studied and compared to those of BLF single-layer films. Our studies show that oxygen vacancies V O • • are the most likely mobile defects in bilayers, whereas defect dipole complexes (F e F e 3 + ′ - V O • •) dominate...

A thermodynamic model for describing interface intermixing in a superlattice combining a ferroelectric and a paraelectric is developed. Formation of intermixed layer at interfaces leads to a periodic modulation of ferroelectric properties in these superlattices. Spatially-varying internal electric field, dielectric susceptibility and polarization o...

The polarization switching properties of ferroelectric materials have been extensively studied, both experimentally and theoretically owing to their wide applications in industry and hence generating a need to gain a deeper understanding of factors affecting their switching behaviour. In this paper, an analytical Landau theory incorporating the Lan...

A thermodynamic model is developed to study the effect of interface intermixing and modulation period on the internal electric field of a superlattice comprising alternate layers of ferroelectric and dielectric. The intermixed layer plays an important role in determining both the polarization and internal electric field modulation profiles of the s...

Landau-Ginzburg free energy expression with the normalized coefficients is used to elucidate the phase transition properties of strained ferroelectric films. In particular, we investigate the need to include higher order free energy terms for epitaxial strained BaTiO3 thin films. Our study reveals that the inclusion of eighth-order expression into...

Here we study systematically the self-focusing dynamics and collapse of vortex Airy optical beams in a Kerr medium. The collapse is suppressed compared to a non-vortex Airy beam in a Kerr medium due to the existence of vortex fields. The locations of collapse depend sensitively on the initial power, vortex order, and modulation parameters. The coll...

Analytical far-field expressions for the transverse electric mode and transverse electric magnetic mode terms, and the energy flux distributions of vortex Airy beams are derived based on the vector angular spectrum of the beam and the stationary phase method. The physical pictures of vortex Airy beams from the vectorial structure are illustrated an...

A thermodynamic model of interface intermixing in ferroelectric superlattices with appropriate electrostatic boundary condition is developed. Interface intermixing forms intermixed layers with properties different from its constituent layers. In this work, the polarization reversal in ferroelectric superlattices with “switchable” polarization in in...

We develop a simple model of superlattices consisting of alternate ferroelectric and multiferroic layers with interface intermixing based on the Landau-Ginzburg theory. Multiferroic system is described using a Landau-Ginzburg potential with a positive biquadratic coupling between magnetization and polarization. Intermixing at interfaces forms inter...

The Landau theory of phase transitions has been widely used to study the static and dynamic properties of ferroelectric materials but mainly through numerical procedures. However the exact solution of the Landau-Khalatnikov equation produces several important consequences. Derivation of explicit expressions for the polarization switching time and t...

The dynamical properties of cos-Gaussian beams in strongly nonlocal nonlinear (SNN) media are theoretically investigated. Based on the moments method, the analytical expression for the root-mean-square (RMS) of the cos-Gaussian beam propagating in a SNN medium is derived. The critical powers that keep the RMS beam widths invariant during propagatio...

We investigate the propagation properties and M-2 factor of a vortex Airy beam. The expression of M-2 factor as a function of the modulation parameters a(x) and a(y) is analytically obtained. The results indicate that the M-2 factor can achieve minimum M-2=2.33 when a(x)=a(y)=1.026 for the m= 1st order vortex Airy beam. For m=2, the M-2 factor can...

A thermodynamic model is developed to study electrostatic coupling and interface intermixing in superlattices comprising alternate layers of ferroelectrics and paraelectrics. Interface intermixing leads to inhomogeneous internal electric field and polarization in superlattices. The spatial distribution of polarization extends into the layer over a...

This article briefly reviews recent developments of Landau-Ginzburg theory to ferroelectric phase transitions in superlattices. An overview of the contributions of Landau-type theory to study ferroelectric superlattices is given. Recent findings from first-principles calculations and experiments on intermixing, local polarization coupling and polar...

We study the switching characteristics of a superlattice consisting of a periodic ferroelectric and paraelectric layer with interlayer coupling using the Landau - Khalatnikov equation. The inhomogeneity of polarization at the ferroelectric or paraelectric surface is described by the extrapolation length delta. The effects of various parameters such...

(Ba0.8Sr0.2)(Zr0.2Ti0.8)O-3 (BSZT) films were grown on La0.5Sr0.5CoO3 buffered (001) SrTiO3 substrates by pulsed laser deposition. Effects of Co doping on electrical properties of the films were investigated to establish material design through defects control. The doping led to a significant improvement in the electrical properties with reduction...