Polar Materials Research Articles

Raman spectra of semi-polar (11-22) InGaN thick films

We report the semi-polar (11-22) InGaN thick films (∼1 μm) grown on m-plane sapphire by a low pressure metal-organic vapor phase epitaxy (MOVPE) system. The Raman spectra of semi-polar InGaN thick films have been studied. For Raman spectra excited by the laser with wavelength of 532 nm, the E2(h) modes of GaN around 569 cm−1 and longitudinal optical (LO) phonon-plasma coupled modes (LPP) were mainly discussed. The E2(h) mode of GaN in the InGaN thick film would correspond to the lower frequency with wavenumber of 569.1 cm−1, compared to that in the InGaN thinner film (569.6 cm-1) in our case. Meanwhile, LPP modes also exhibited red shift with the increase of InGaN film thickness, which would be attributed to the stress relaxation and the decrease of free carrier concentration. The E2(h) modes of InGaN around 560 to 565 cm-1 and A1(LO) modes of InGaN around 729 to 731 cm-1 were found in Raman spectra excited by the laser with wavelength of 325 nm, but not probed in Raman spectra excited by a 532 nm laser. With the increase of In component, both modes were shifted towards low frequency. In addition, it was found that the Frölich electron-phonon interaction would significantly affect the peak position (729.2 cm-1) and full width at half maximum (FWHM, 17.2 cm-1) of A1(LO) mode of InGaN in the thicker film. Moreover, we have compared the Raman spectra of polar and semi-polar InGaN thick films so that the difference of Raman spectra between the two counterparts could be indicated due to lattice mismatch, In component incorporation efficiency, crystal quality and phase separation. The stress distribution of semi-polar InGaN materials is not as uniform as that of polar materials.

Sorption isotherm study on vacuum and freeze-dried jamun pulp

Fruits play the most important role in nutrition. In India many underutilized medicinal fruits are available, and the most important fruit is jamun which is otherwise called black plum. Drying of underutilized jamun fruits helps in minimizing their post-harvest loss which occurs during harvesting season. The freeze-dried powder results with polar sites in molecular structure material which is occupied with water in wet conditions. During drying the molecules which were holding the water particles are attracted closely to each other. The study on sorption isotherms was carried out on the dried powder. These results gave a suitable model to fit sorption behaviour. The empirical equations frequently used to model drying kinetics are Newton, Henderson–Pabis, Page, Modified Page, Wang– Singh, Logarithmic, Two-Terms, Modified Henderson–Pabis and many mathematical models to describe the water sorption behaviour of foods. The GAB equation was fitted as the best fit for vacuum-dried jamun pulp powder stored at 27°C and 37°C.

Q-POP-Thermo: A general-purpose thermodynamics solver for ferroelectric materials

Q-POP-Thermo is a program designed to compute thermodynamic monodomain equilibrium states and their properties for ferroelectric single crystals and thin films based on the Landau-Ginzburg-Devonshire (LGD) Theory. Utilizing symbolic manipulation with the SymPy Library, the governing equations along with appropriate boundary conditions are solved for speedy minimization of the free energy of a crystal. Utilizing the popular Differential Evolution algorithm, with appropriate hybridization, multiple phase diagrams, such as the pressure-temperature phase diagram for bulk single crystals and the common strain-temperature phase diagram for monodomain thin-film systems can be readily generated. Furthermore, a variety of material properties of stable ferroelectric phases, including dielectric, piezoelectric, and electrocaloric properties, can simultaneously be calculated. Validation studies are presented for both thin-film and single crystal systems to test the effectiveness and capability of the open-source program. Program summaryProgram title: Q-POP-ThermoCPC Library link to program files:https://doi.org/10.17632/wd6228g9ww.1Code Ocean capsule:https://codeocean.com/capsule/1245708Licensing provisions: MITProgramming language: PythonExternal routines/libraries: numpy (Version 1.20.3), sympy (Version 1.8), numerical optimization (available with Q-POP-Thermo), pandas (Version 1.1.3), scipy (Version 1.6.3)Nature of program: Python-based program to perform energy minimization to determine the stable states and thermodynamic properties of ferroelectric systems.Solution method: Algebraic manipulation of boundary conditions and governing equations followed by a hybridized and improved a priori Differential Evolution solver to calculate equilibrium polar states and material properties.

Nanopolyhedron Co–C/Cores triggered carbon nanotube in-situ growth inside carbon aerogel shells for fast and long-lasting lithium–sulfur batteries

The improved physicochemical immobilization and catalytic redox conversion of lithium polysulfides (LiPSs) intermediates are considered to be a desirable solution to enhance the sulfur electrochemistry in lithium-sulfur (Li–S) batteries. Herein, we for the first time, reported the fabrication of the core-shell structure composed of cobalt-doped carbon nano-tube (CNT) assembled polyhedron core derived from the cobalt metal-organic frameworks (Co-MOFs)@graphitized porous carbon aerogel shell as the sulfur reservoir material for Li–S batteries. The obtained sulfur cathodes exhibited excellent electrochemical performance, including a high reversible capacity (939.9 mAh g−1 at 0.1C), outstanding areal capacity (3.35 mAh cm−2 after 50 cycles, under a low electrolyte/8.3 μL mgs−1), and superior cycling stability (the capacity decay rate of 0.087% per cycle after 500 cycles at 1C). The improvement in electrochemical performance could be attributed to the unique core-shell architecture: the multiple polyhedron Co–C cores not only provide a multiple-point catalytic center for LiPS conversion, but also serves as the polar material to inhibit the migrating of polysulfides by chemical interaction; More importantly, the graphitized porous carbon aerogel shell provides a fast transport channel for Li+/e− diffusion, and also sufficient free space for the sulfur reservoir and Li2S2/Li2S deposition.

Polar lanthanide copper iodates LnCu(IO3)5 (Ln = La, Ce, Pr, and Nd): Synthesis, crystal structure and characterization

Four new polar lanthanide copper iodates LnCu(IO3)5 (Ln ​= ​La, Ce, Pr, and Nd) were synthesized by the hydrothermal method at 220 ​°C. The four compounds are isostructural and they can be viewed as derivation from two parts: the [Ln(IO3)3] layers from the Ln(IO3)3 with 3D framework and the [Cu(IO3)2] chain from the α-Cu(IO3)2 with 2D layer structure. As the compounds crystallize in the noncentrosymmetric orthorhombic space group Pna21, they may find interesting applications as nonlinear optical crystals. The second-harmonic generation (SHG) response of powder LaCu(IO3)5 is measured to be around 0.5 times that of KDP. The measurement of SHG response versus particle sizes of samples indicates that LaCu(IO3)5 can achieve phase matching. In order to interpret the origination of SHG effects, the dipole moment of LaO9, CuO6 and IO3 groups were calculated. It is suggested that the IO3 groups contribute mostly (∼90.7%) and the CuO6 groups contribute little (∼1.6%) to the SHG response of LaCu(IO3)5. The results of this research show that the combination of lanthanide and copper elements with the electron lone-pair I5+ cations can be a feasible way to fabricate new polar materials in the rare-earth and transition metal iodate system.

Insight into the stacking and the species-ordering dependences of interlayer bonding in SiC/GeC polar heterostructures

Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the π–π orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si–C and C–Ge species orderings but weak hybridization in the case of the C–C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si–C and C–Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C–C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si–C ordering (or under the AB stacking with C–C ordering). While a direct band gap of 2.00–2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.

Polaritonic quantization in nonlocal polar materials.

In the Reststrahlen region, between the transverse and longitudinal phonon frequencies, polar dielectric materials respond metallically to light, and the resulting strong light-matter interactions can lead to the formation of hybrid quasiparticles termed surface phonon polaritons. Recent works have demonstrated that when an optical system contains nanoscale polar elements, these excitations can acquire a longitudinal field component as a result of the material dispersion of the lattice, leading to the formation of secondary quasiparticles termed longitudinal-transverse polaritons. In this work, we build on previous macroscopic electromagnetic theories, developing a full second-quantized theory of longitudinal-transverse polaritons. Beginning from the Hamiltonian of the light-matter system, we treat distortion to the lattice, introducing an elastic free energy. We then diagonalize the Hamiltonian, demonstrating that the equations of motion for the polariton are equivalent to those of macroscopic electromagnetism and quantize the nonlocal operators. Finally, we demonstrate how to reconstruct the electromagnetic fields in terms of the polariton states and explore polariton induced enhancements of the Purcell factor. These results demonstrate how nonlocality can narrow, enhance, and spectrally tune near-field emission with applications in mid-infrared sensing.

The Influence of Edible Oils' Composition on the Properties of Beeswax-Based Oleogels.

This study aimed to find relationships between the properties of beeswax-based oleogels and the type of oil used. The influence of linseed, sunflower, olive, and fish oils was studied. For these oils, the fatty acid composition, the content of total polar components, and the iodine value were characterized. Textural and thermodynamic properties were determined for oleogels, the oil-binding capacity was estimated, and the morphology of crystals was studied. The concentration of beeswax in all oleogels was 6.0% w/w. It was shown that the type of oil has a significant influence on all characteristics of the oleogels. The use of different oils at the same technological treatment leads to the formation of crystals of diverse morphology—from platelets to spherulites. At the same time, it was revealed that some characteristics of oils have a varying contribution to the properties of oleogels. The content of total polar materials in oils is associated with a decrease in strength parameters (yield value and elastic modulus) and the oil-binding capacity of oleogels. In its turn, the iodine value of oils has a close positive correlation with the melting and crystallization temperatures of oleogels. The results obtained in this article indicate that the properties of beeswax-based oleogels can be directed by changing the oil composition.

Directional detectability of dark matter with single phonon excitations: Target comparison

Single phonon excitations are sensitive probes of light-dark matter in the keV-GeV mass window. For anisotropic target materials, the signal depends on the direction of the incoming dark matter wind and exhibits a daily modulation. We discuss in detail the various sources of anisotropy and carry out a comparative study of 26 crystal targets, focused on sub-MeV dark matter benchmarks. We compute the modulation reach for the most promising targets, corresponding to the cross section where the daily modulation can be observed for a given exposure, which allows us to combine the strength of dark matter-phonon couplings and the amplitude of daily modulation. We highlight ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ (sapphire), ${\mathrm{CaWO}}_{4}$, and h-BN (hexagonal boron nitride) as the best polar materials for recovering a daily modulation signal, which feature $\mathcal{O}(1--100)%$ variations of detection rates throughout the day, depending on the dark matter mass and interaction. The directional nature of single phonon excitations offers a useful handle to mitigate backgrounds, which is crucial for fully realizing the discovery potential of near future experiments.

Crystal growth and functional properties of rare mineral Mn3B7O13Cl

Centimeter-sized Chambersite(Mn3B7O13Cl) crystals, a multifunctional polar material, were grown via a melt growth method. The crystal structures are determined by single-crystal and powder X-Ray diffraction(XRD). Furthermore, the properties of phase transition, pyroelectricity and low-temperature magnetic ordering are characterized. Mn3B7O13Cl crystallizes a polar space group Pca21 at room temperature which makes it a unity of pyroelectric and ferroelectric crystal. The pyroelectric coefficients of Mn3B7O13Cl keep almost unchanged from 300 K to 370 K with the values about 10 μC/m2/K, and the figures of merit (FOMs) of pyroelectric performance of 0.035 m2/C (voltage responsivity) and 0.036 × 10−10 m V−1 (current responsivity) are identified. These features indicate that Mn3B7O13Cl crystal can generate infrared detection in many application scenarios. Our works point out that Mn3B7O13Cl can be used as a low-cost substitute for LiTaO3 and a non-toxic substitute for PbTiO3 in the field of infrared detection.

Switchable out-of-plane shift current in ferroelectric two-dimensional material CuInP2S6

Polar materials are interesting platforms for fundamental research because they exhibit the spontaneous electric polarization (SEP) and the shift current photovoltaic effect, both originating from the inherent Berry connection. Owing to the electrical controllability, these phenomena are often studied in ferroelectric materials. Recently, the SEP and the shift current are enthusiastically studied in two-dimensional materials, but an electrical control has not been realized. In this study, we observed an out-of-plane shift current and demonstrated its electrical control at room temperature in a ferroelectric two-dimensional material CuInP2S6, by utilizing a multilayer graphene as a transparent electrode. The shift current origin was confirmed by an analysis of the excitation power dependence. Our results are an important step in the study of the Berry connection physics as well as put forward a device concept to utilize out-of-plane shift current photovoltaic effect for optoelectronic devices.

Hydrovoltaic power generation from multiwalled carbon nanotubes

The hydrovoltaic effect, which is a voltage generated at the interface of water with polarizable materials, is an exciting new frontier for environmentally friendly electrical power generation.

Synaptic transistor with tunable synaptic behavior based on a thermo-denatured polar polymer material

Artificial synaptic transistors have shown great potential in artificial intelligence due to their low energy consumption, high scalability, similarity to biological neurons and precise regulation of channel conductance.

Evaluating fast methods for static polarizabilities on extended conjugated oligomers.

Given the importance of accurate polarizability calculations to many chemical applications, coupled with the need for efficiency when calculating the properties of sets of molecules or large oligomers, we present a benchmark study examining possible calculation methods for polarizable materials. We first investigate the accuracy of the additive model used in GFN2, a highly-efficient semi-empirical tight-binding method, and the D4 dispersion model, comparing its predicted additive polarizabilities to ωB97XD results for a subset of PubChemQC and a compiled benchmark set of molecules spanning polarizabilities from approximately 3 Å3 to 600 Å3, with some compounds in the range of approximately 1200-1400 Å3. Although we find additive GFN2 polarizabilities, and thus D4, to have large errors with polarizability calculations on large conjugated oligomers, it would appear an empirical quadratic correction can largely remedy this. We also compare the accuracy of DFT polarizability calculations run using basis sets of varying size and level of augmentation, determining that a non-augmented basis set may be used for large, highly polarizable species in conjunction with a linear correction factor to achieve accuracy extremely close to that of aug-cc-pVTZ.

Vol4 num3-19 Development and characterization of polypropylene nano-composites

Modification of polymer matrices has a great insterest in the field of new materials, based on the possibilities offered by the additivation, being able to modulate the properties of the base material depending on the incorporated aggregates. Among the improvements searched include the increase in the mechanical strength of the material or the improvement in the interaction with other materials (adhesion), in addition to providing multifunctionality, combining properties of materials separately in order to obtain a composite with improved properties. This study focuses on the modification of a polypropylene-ethylene co-polymer by the incorporation of nanoclays and carbon nanotubes (MWCNTs) in low concentrations (0.1% by weight). In order to facilitate the dispersion of the nanomaterials in the matrix by mixing and extrusion, maleic anhydride was used as a compatibilizer. The behavior of these composites was characterized by studying the variation of torque during the compounding, in addition to analize the melt flow index (MFI) and perform an analysis by DSC, TGA and TEM of the composites obtained. Based on the low polarity of polypropylene, the introduction into the matrix of maleic anhydride provides a certain polarity in the composite, so the increase in the surface energy of the different formulations is studied by contact angle measurements (using the OWRK/Fowkes method). The increase in surface energy involves a greater affinity for polar materials, such as polyurethane (PU) or other foams.

Antioxidant effect of natural rosemary on the oxidation of mid-oleic sunflower frying oil on chicken wings

Fried foods are hugely popular and very much a part of our modern cuisine. Guarding against oxidation is crucial, due to the absorption of oil during the frying process. This paper presents how, the degree of resistance of sunflower oil was evaluated during repeated fries of chicken wings by adding the natural antioxidant extracted from rosemary. It was compared to tocopherol and to a control sample. A preliminary test of accelerated aging demonstrated the effectiveness of rosemary extract by using the Rapidoxy technique on sunflower oil. This proved that the adequate dose of this antioxidant should be 600 ppm. Many physicochemical transformations were inflicted on the oil during its oxidation. The kinetics monitoring of this phenomenon was determined by measuring the total polar materials (TPM), free fatty acids (FFA), and the peroxide index (PI). The obtained results showed that all the parameters analysed tended to increase over time. However, the effect of the rosemary antioxidant was positive on the stability of the oil and the slowing down of its oxidation. Moreover, its efficiency was higher than tocopherol. Rosemary antioxidants could be a safer alternative to synthetic antioxidants which represent toxicological risks, such as buthylated hydroxyanisole BHA, buthylated hydroxytoluene BHT, and tert-butylhydroquinone TBHQ.

Collective Phonon-Polaritonic Modes in Silicon Carbide Subarrays.

Localized surface phonon polaritons (LSPhPs) can be implemented to engineer light-matter interactions through nanoscale patterning for a range of midinfrared application spaces. However, the polar material systems studied to date have mainly focused on simple designs featuring a single element in the periodic unit cell. Increasing the complexity of the unit cell can serve to modify the resonant near-fields and intra- and inter-unit-cell coupling as well as to dictate spectral tuning in the far-field. In this work, we exploit more complicated unit-cell structures to realize LSPhP modes with additional degrees of design freedom, which are largely unexplored. Collectively excited LSPhP modes with distinctly symmetric and antisymmetric near-fields are supported in these subarray designs, which are based on nanopillars that are scaled by the number of subarray elements to ensure a constant unit-cell size. Moreover, we observe an anomalous mode-matching of the collective symmetric mode in our fabricated subarrays that is robust to changing numbers of pillars within the subarrays as well as to defects intentionally introduced in the form of missing pillars. This work therefore illustrates the hierarchical design of tailored LSPhP resonances and modal near-field profiles simultaneously for a variety of IR applications such as surface-enhanced spectroscopies and biochemical sensing.

Surface engineered polar CeO2-based cathode host materials for immobilizing lithium polysulfides in High-performance Li-S batteries

The particle morphology of CeO2 nanocrystals with different exposed crystal facets is a crucial factor influencing the surface-related materials performance. In this report, shape-controlled synthesis of CeO2 nanocrystals with various preferentially exposed crystal facets (CeO2 nanorods with (110)/(100)/(111), CeO2 nanocubes with (100) and CeO2 nanoctahedra with (111)) was conducted aiming to investigate the crystal plane effect of polar CeO2 as a cathode host on the immobilization of lithium polysulfides and electrochemical performance of the assembled Li-S batteries. The strong chemical bonding between lithium polysulfides and CeO2 host, including Ce-S and Li-O bonds formed on the exposed (110)/(100) and defected (111) crystal facets of CeO2 nanorods during reversible electrochemical conversion from soluble long-chain polysulfides to insoluble short-chain Li2S/Li2S2, results in superb diffusion restriction of lithium polysulfides towards Li anode and endows CeO2 nanorods@CC electrode with a superior electrochemical property among three tested electrodes of CeO2 nanorods@carbon cloth (CC), CeO2 nanocubes@CC, and CeO2 nanoctahedra@CC. However, such strong chemical interaction against polysulfides was not observed by CeO2 nanocubes with preferentially exposed (100) crystal planes and CeO2 nanoctahedra with preferentially exposed (111) crystal planes. In addition to the factor of the exposed crystal planes, CeO2 nanorods possess defect-rich surfaces (i.e., oxygen vacancies and Ce3+) also serving as possible polysulfides anchoring sites, which can contribute to effective immobilization of lithium polysulfides. Benefiting from the above-mentioned advantages, CeO2 nanorods are considered as an outstanding candidate of cathode host materials for long life and high-performance Li-S batteries.

Oxygen vacancy-rich MnO nanoflakes/N-doped carbon nanotubes modified separator enabling chemisorption and catalytic conversion of polysulfides for Li-S batteries

A modified separator for improving the electrochemical performance in Li-S batteries is fabricated by functional composites coating, comprised of MnO nanoflakes with rich oxygen vacancies and N doped carbon nanotubes (MnO-OVs/NCNTs). On the one hand, MnO as a polar material can anchor lithium polysulfides (LiPSs) on the interface via chemical bonding. In addition, introducing oxygen vacancies into MnO by heat treatment under a reducing atmosphere can regulate the electronic structure and provide extra active sites for further boosting the chemical adsorption capability of LiPSs, facilitating the redox reaction of LiPSs, as well as enhancing the electron transfer efficiency. On the other hand, the MnO-OVs/NCNTs layer is a barrier to block the LiPSs directly diffusing through the separator and acts as an upper collector to reduce the interface resistance reactivate the trapped sulfur species, thereby enhancing the sulfur utilization. Given these advantages, the MnO-OVs/NCNTs modified separator employed in Li-S batteries exhibit considerable capacity (1516 mAh g−1 at 0.1C), enhanced long-term cycling stability (capacity retention of 618 mAh g−1 for over 500 cycles at 1C), and rate performance (550 mAh g−1 at 3C).

Temporal dynamics of strongly coupled epsilon near-zero plasmonic systems

Subwavelength epsilon-near-zero (ENZ) films with decorated nanoantennae are an emerging platform for coupling radiation into the ENZ mode: recent experiments have shown how strong coupling between the two systems underpins significant nonlinear effects. Field enhancement and the temporal dynamic of the radiation in ENZ films strongly coupled with plasmonic antennae play a substantial role in the light–matter interaction, and the latter has not yet been fully disclosed. We numerically investigate the pulse shaping of radiation impinging on two representative strongly coupled systems: a transparent conductive oxide with ENZ in the NIR band (ITO) and a polar material with ENZ in the MIR (SiC). In both cases, we demonstrate that the temporal dynamics and field enhancement are particularly pronounced within the strong coupling region, and we highlight the different polarization responses of the ITO-based case from the SiC one. The latter, owing to lower losses, shows extreme reshaping of resonant radiation close to the ENZ spectral region and is, therefore, a promising candidate for slow-light-enhanced effects.