Dielectric Lattice Research Articles

Dielectric Relaxation, Local Structure and Lattice Dynamics in Mn-Doped Potassium Tantalate Ceramics.

Alkaline niobate and tantalate perovskites have attracted attention as polar dielectrics for electronics and telecommunications. Here, we studied the polar behaviour, lattice dynamics, and local structure in conventionally processed K0.985Mn0.015TaO3±δ ceramics using a combination of variable-temperature dielectric and Raman spectroscopies, and X-ray absorption fine structure (XAFS) measurements, respectively. Mn doping induces a low-frequency dielectric relaxation in KTaO3 (KT), which follows the Arrhenius law with an activation energy U ≈ 105 meV and the characteristic relaxation time τ0 ≈ 4.6 × 10−14 s. Our XAFS results support preferential Mn occupancy of the cuboctahedral sites as Mn2+, with these cations strongly off-centred in the oversized oxygen cages. Such disordered Mn displacements generate electric dipoles, which are proposed as the source of the observed dielectric relaxation. We show that in Mn-doped ceramics, the low-frequency polar TO1 mode softens on cooling and, at low temperatures, exhibits a higher frequency than in undoped KT. This mode displays no detectable splitting, which contrasts with Li-doped KT that also contains off-centred Li+ species on the cuboctahedral sites. Therefore, we conclude that the coupling between the Mn displacements and the lattice is weaker than in the Li case, and Mn-doped KT therefore exhibits a dielectric relaxation but no ferroelectric transition.

Stress-induced phase transitions in nanoscale CuInP2S6

Using Landau-Ginsburg-Devonshire approach and available experimental results we reconstruct the thermodynamic potential of the layered ferroelectric CuInP$_2$S$_6$ (CIPS), which is expected to be applicable a wide range of temperatures and applied pressures. The analysis of temperature dependences of the dielectric permittivity and lattice constants for different applied pressures unexpectedly reveals the critically important role of the nonlinear electrostriction in this material. With the nonlinear electrostriction included we calculated temperature and pressure phase diagrams and spontaneous polarization of bulk CIPS. Using the coefficients of the reconstructed four-well thermodynamic potential, we study the strain-induced phase transitions in thin epitaxial CIPS films, as well as the stress-induced phase transitions in CIPS nanoparticles, which shape varies from prolate needles to oblate disks. We reveal the strong influence of the mismatch strain, elastic stress and shape anisotropy on the polar properties and phase diagrams of nanoscale CIPS. Also, we derived analytical expressions, which allow the elastic control of the nanoscale CIPS polar properties. Hence obtained results can be of particular interest for the strain-engineering of nanoscale layered nanoferroelectrics.

Narrowband mid-infrared absorber based on a mirror-backed low-index dielectric lattice

This paper reports the design of a narrowband mid-infrared absorber using a structure consisting of low-index dielectric pillar arrays on a highly reflective metal plane. Such a hybrid system can support a high-quality lattice resonance with strongly confined electromagnetic fields at the tops of dielectric structures. For mid-infrared wavelengths around 4 µm, the low-index dielectric can be silica by plasma-enhanced chemical vapor deposition, and the metal can be copper. The lattice resonance can lead to perfect absorption with a quality factor around 1000 when considering realistic dissipative losses for the low-index dielectric pillars. According to Kirchhoff’s radiation law, the narrowband absorber can work as a high- Q surface-emitting thermal emitter in the mid-infrared by heating its substrate.

Optical bistability in aperiodic multilayer composed of graphene and Thue-Morse lattices

A theoretical study in the optical bistability of the transmitted light in complex multilayers is provided. The proposal structure is composed of graphene and one-dimensional Thue-Morse dielectric lattices. Low thresholds optical bistability is achieved owning to the enhancement of graphene nonlinearity with a strong electric field localization. Simulations show that the thresholds of optical bistability and the intervals between the upper and lower thresholds can be flexibly modulated by the chemical potential of graphene, incident wavelengths and incident angles. The complex structure provides a candidate for the all-optical switches.

Effects of non-stoichiometry on the structural evolution, microstructure and dielectric properties of rock salt-type Li2Mg3SnO6 ceramics

Abstract The porous morphology and secondary phase originated from lithium evaporation have deteriorated dielectric properties of Li2Mg3SnO6 ceramic. To solve this issue, a set of non-stoichiometric Li2Mg3-2xSn1-xO6 (x = −0.04, −0.02, 0.00, 0.02, 0.04, 0.06) samples were prepared by the solid-state method. Subsequently, the effects of non-stoichiometry on the structural evolution, microstructure and dielectric properties of rock salt-type Li2Mg3-2xSn1-xO6 ceramics were investigated. The Rietveld refinement and SEM results confirmed that moderate non-stoichiometry could eliminate secondary phase and promote densification. For −0.04 ≤ x ≤ 0.04, the upward tendency of dielectric constant (er) and quality factor (Q×f) was dominated by the improved phase purity and densification. As 0.04 ≤ x, the deterioration of dielectric characteristics was explained by the dielectric polarizability, lattice energy and packing fraction. The temperature coefficient of resonance frequency (τf) shifted from −36.41 to −27.23 ppm/°C, which could be attributed to the poor thermostability of Mg2SnO4 (τf = −64 ppm/°C) and enhanced octahedra bond energy.

Efficient all-optical modulator based on a periodic dielectric atomic lattice.

All-optical devices used to process optical signals without electro-optical conversion plays a vital role in the next generation of optical information processing systems. We demonstrate an efficient all-optical modulator that utilizes a periodic dielectric atomic lattice produced in a gas of 85Rb vapor. Four orders of diffraction patterns are observed when a probe laser is passed through the lattice. The frequency shift of the peak of each diffraction order can be tuned by adjusting the control laser power and two-photon detuning, enabling this device to be used as a multi-channel all-optical modulator. Both theoretical simulations and experimental results demonstrate that this modulator can operate over a frequency band extending from about 0 to 60 MHz. This work may pave the way for studying quantum information processing and quantum networking proposed in atomic ensembles.

Optical Effects in Magnetoplasmonic Crystals Based on 1D Metal-Dielectric Lattice

Properties of one-dimensional spatially periodic metal structures formed by a dielectric lattice covered by gold and permalloy films are studied by optical and magnetooptical spectroscopy techniques. It is shown that these structures reveal the excitation of surface plasmon-polaritons, with the resonance frequency that can be controlled by the geometry of the experiment. The magnetooptical Kerr effect modulation, which is absent in the case of a nonprofiled gold/permalloy bifilm, is observed in the spectral vicinity of the plasmon resonance.

Circularly polarized vacuum ultraviolet coherent light generation using a square lattice photonic crystal nanomembrane

Circularly polarized light in the vacuum ultraviolet (VUV) region is important for probing the structural and electronic properties of matter. Moreover, a circularly polarized VUV coherent light enables one to observe the dynamics of biomolecules and electron spins in solids. The development of a table-top technology to directly generate circularly polarized VUV coherent light is of great value, owing to the limitation of polarization control elements for the VUV region. However, solid-state nonlinear media for this purpose, which simplifies the setup, have not been presented. Here, we demonstrate a solid-based method for the direct generation of circularly polarized VUV coherent light using third-harmonic generation in a dielectric square lattice photonic crystal nanomembrane (PCN). We found that the waveguide resonance of PCN with fourfold rotational symmetry, irradiated by a circularly polarized fundamental beam, generates circularly polarized third harmonic at 157 nm with sufficient intensity for VUV spectroscopic applications. The presented results suggest the possibility that the PCN can be used as a practical nonlinear medium for circularly polarized coherent VUV generation.

Properties of omnidirectional gap and defect mode of one-dimensional graphene-dielectric periodic structures

We theoretically investigate the optical response of one-dimensional graphene based photonic crystal (1D-GPC) structures with and without defect layer in the low terahertz (THz) frequency region. The 1D-GPC is composed of alternated layers of isotropic dielectric material (SiO2) and graphene monolayer sheets. Using the transfer matrix method (TMM), the effects of several parameters such as the incidence angle, width, thickness, and refractive index of the defect layer and the chemical potential of graphene sheets on the device response will be explored in detail for both TE and TM polarizations. Our simulation results indicate that when a defect layer is introduced, the structure may support two kinds of defect modes. One kind is created in the Bragg gap and the other one is created in the graphene-induced photonic band gap (GIPBG). Our results reveal that a defect mode can appear within the GIPBG only for an optical thickness of the defect layer greater than that of the alternated dielectric layers of the 1D-GPC. While, the defect modes in the Bragg gap may be created by simply breaking of the periodicity of the dielectric lattice. In addition, the resonance frequency of defect mode in the GIPBG is found to be almost insensitive to the incident angle for both polarizations. Moreover, we show that an effective Brewster angle for our structure can be deduced from the variation of the amplitude of defect mode with the incident angle. Our analysis has shown an innovative idea for the realization of tunable broadband reflectors and narrowband filtering devices.

Corrections to “3D Printed Elastomeric Lattices With Embedded Deformation Sensing”

In the above article <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , Figure 3 should read “Isometric view of two wires forming a capacitor in the measured configuration. The yellow wire is the top plate and the red is the bottom plate of a capacitor. The gray is a dielectric elastomer lattice, the deformation of which can be indirectly determined by measuring the capacitance.” Figure 4 should read “Isometric (A) and bottom view (B) of a lattice with an alternative configuration in four quadrants for selective sensing. The selectivity can be extended to any combination of cells in both vertical and horizontal configurations.” In <xref ref-type="fig" rid="fig9" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Figure 9</xref> , the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> -axis should read “Min Deformation Slow; Min Deformation Fast; Max Deformation Slow; Max Deformation Fast.” A sentence in the introduction should read “Within the context of additive manufacturing, lattices are the focus of significant research since they...” The authors requested this correction for clarity purposes.

Two-dimensional electron gas modeling in strained InN/GaN hetero-interface under pressure and impurity effects

The two-dimensional electron gas (2DEG) density modeling in WZ strained InN/GaN hetero-interface with Ga-face arrangement is considered in this paper. We theoretically investigate the role of an externally applied hydrostatic pressure and impurity's position by analyzing their impact in the presence of built electric field due to the dielectric mismatch between the system and its surrounding matrix. To solve the coupling Schrödinger-Poisson equations, as well as the polarization induced charges, finite element method code is used. Pressure-dependence of dielectric constant, band-gap energy, lattices and internal electric field is considered. The 2DEG appears to be strongly-dependent internal and external perturbations exhibiting a non-monotonic behavior. Our results prove that: (1) the InN channel is more populated for on-center impurity compared to off-center one, (2) the electron density in the triangular shape quantum well increases with the pressure; (3) the 2DEG density is enhanced versus the positive impurity's position and dropped versus pressure.

Extraordinary optical transmission through titanium nitride-coated microsphere lattice

Titanium nitride (TiN), one candidate as an alternative plasmonic material, is deposited by the sputtering method on top of a self-assembled polystyrene microsphere lattice. The optical transmission spectra of the TiN-coated microsphere lattice reveal a transmission pass-band attributed to the extraordinary optical transmission phenomenon, known from subwavelength hole arrays in metal films. Simulations by finite element method show the presence of a hybrid mode resulting from coupling of surface plasmons on the TiN film to photonic guided resonance modes in the dielectric microsphere lattice. The crucial role of the microspheres in the transmission process is also evidenced by dedicated simulations. Such hybrid colloidal photonic-plasmonic crystals based on TiN are promising for future plasmonic applications requiring the thermo-mechanical stability of refractory ceramics complemented by a plasmonic efficiency similar to that of gold, but also for extending the range of current applications beyond the use of the classical noble metals gold and silver.

Exact diagonal representation of normal mode energy, occupation number, and heat current for phonon-dominated thermal transport

Collective excitations of crystal vibrations or normal modes are customarily described using complex normal mode coordinates. While appropriate for calculating phonon dispersion, the mixed representation involving the complex conjugates does not allow the construction of equivalent phonon occupation number or modal dynamical quantities such as the energy or heat current specific to a wave-vector direction (q). Starting from a canonical solution that includes waves going to the left and right directions, we cast the Hamiltonian, normal mode population, and heat current in an exactly diagonalizable representation using real normal mode amplitudes. We show that the use of real amplitudes obviates the need for a complex modal heat current while making the passage to second quantization more apparent. Using nonequilibrium molecular dynamics simulations, we then compute the net modal energy, heat current, and equivalent phonon population in a linear lattice subjected to a thermal gradient. Our analysis paves a tractable path for probing and computing the direction-dependent thermal-phononic modal properties of dielectric lattices using atomistic simulations.

Effect of Mg doping on the infrared emissivity of ZnO powders at high temperature

Infrared emissivity of semiconductor material determines infrared radiation capability of semiconductor material. In recent years, researchers have focused on the infrared emissivity performance of ZnO at room temperature. The infrared emissivity performance of ZnO at high temperatures is rarely studied. In this paper, Zn1-xMgxO powders were prepared by sol-gel method. The infrared emissivity of powders with different x (x = 0, 0.01, 0.03, 0.05, 0.07) were investigated from room temperature to 800 °C. The composition and calcination temperature of precursors were determined by DSC, and the changes in morphology, particle size, microstructure and phase compositions were studied by SEM, EDS and XRD separately. The changes of infrared emissivity of powders with different Mg doping concentrates from room temperature to 800 °C are explained by dielectric mechanism, conduction mechanism and lattice vibration mechanism, and the varies of infrared emissivity with temperature, which showing a U-shaped curve are also explained by the three mechanisms mentioned above. An effective and convenient method for regulating the infrared emissivity of ZnO is provided in this paper.

Highly efficient subwavelength imaging in mid-IR range using high dielectric hexagonal lattice photonic crystals

Two-dimensional hole-type hexagonal lattice photonic crystals with low and high dielectric materials have been investigated for the aim of achieving all-angle negative refraction for subwavelength imaging. Structures composed of Si (eSi = 12 at IR) and PbTe (ePbTe = 36 at mid-IR) have been regarded, as sample materials. All-angle negative refraction has been achieved for the TM polarization in the second band under the light line in a broad bandwidth of 26% and 31% for low and high dielectric materials, respectively. The optimized radii for low and high dielectric PCs equal to 0.31a and 0.35a and provide the spatial full width at half maximum of 0.37λ and 0.38λ, respectively. The structures present TE gap in the operating wavelength range, and this feature of the structures can be applied to design polarization beam splitters in integrated space division multiplexing.

Lattice resonances in dielectric metasurfaces

We present a numerical investigation of collective resonances in lattices of dielectric nanoparticles. These resonances emerge from the enhanced radiative coupling of localized Mie resonances in the individual nanoparticles. We distinguish two similar systems: a lattice of silicon nanoparticles homogeneously embedded in a dielectric and a lattice of silicon nanoparticles in an optical waveguide. The radiative coupling is provided by diffraction orders in the plane of the array for the former system or by guided modes in the optical waveguide for the latter one. The different coupling leads to distinct lattice resonances in the metasurface defined by the array of silicon nanoparticles. These resonances have been extensively investigated in metallic nanoparticle arrays, but remain highly unexplored in fully dielectric systems. We describe the pronounced differences in the intensity enhancement and field distributions for the two systems, providing valuable information for the design and optimization of optical components based on dielectric lattice resonances.

The influence of mechanical activation on the dielectric and dynamic properties and structural parameters of the solid solution of Pb(Zr0.56Ti0.44)O3

The impact of mechanical activation on the dielectric properties, structural parameters, and lattice dynamics of the Pb(Zr0.56Ti0.44)O3 solid solution was investigated. The solution features coexisting metastable tetragonal (T) and rhombohedric (R) phases, whose ratio can be altered by applying the uniaxial compression load up to 320 MPa under torsion in Bridgman anvils. The strain-induced changes of the unit cell parameters, dielectric permittivity, Debye characteristic temperatures, temperature-dependent Debye-Waller factors, and mean square displacements were critically analyzed.

Broadband self-collimating phenomenon in a low-loss hybrid plasmonic photonic crystal.

A 2D planar self-collimating photonic crystal, based on a dielectric square lattice and a hexagonal lattice, is proposed. We demonstrate that the proposed structure can support the propagation of a hybrid surface plasmon polarition (SPP) mode with a loss of -0.017 dB/μm, and the mode size is only 0.33μm. The defined figure of merit is one order of magnitude higher than that of the dielectric-metal structure. In addition, the self-collimating angle of more than 10° can be tuned with a silica index change of 0.08. The proposed structure possesses broad operation bandwidth of 88nm and 58nm for a dielectric square lattice and a hexagonal lattice, respectively. These two kinds of photonic crystals promise potential applications in photonic modulators and SPP photonic devices.

Stereolithographic Additive Manufacturing of Bulky Ceramic Components with Functionally Geometric Micropattern

Abstract In a stereolithographic additive manufacturing (AM), two dimensional (2D) cross sectional patterns were created through photo polymerization by ultraviolet laser drawing on spread resin paste including ceramic nanoparticles, and three dimensional (3D) composite models were sterically printed by layer lamination through chemical bonding. An automatic collimeter was equipped with the laser scanner to adjust beam diameter. Fine or coarse beams could realize high resolution or wide area drawings, respectively. Metal and ceramic bulky components including dendritic networks were geometrically built by using stereolithographic AM. Geometric patterns with periodic, self-similar, graded and fluctuated arrangements were created by computer aided design, manufacture and evaluation (CAD/CAM/CAE) for effective modulations of energy and material flows through dielectric lattices in photonic crystals, porous electrodes in fuel cells and biological scaffolds in artificial bones.

Water-Soluble Multimodal Core/ Shell NaGdF4:Yb,Er@NaGdF4 Upconverting Nanoparticles for Cancer Diagnostics

Water-Soluble Multimodal Core/ Shell NaGdF4:Yb,Er@NaGdF4 Upconverting Nanoparticles for Cancer Diagnostics Upconverting nanoparticles (UCNPs) are promising new generation of imaging probes capable of working as theranostic agents. Upconversion is a nonlinear optical process that converts two or more photons to a higher-energy out-put photon. UCNPs are guesthost systems where trivalent lanthanide ions are dispersed as a guest in an appropriate dielectric host lattice with a dimension less than 30nm. Generally, upconversion emission arises from 4f-4f orbital electronic transitions.