Unit Cell Research Articles

Enhanced optoelectronic properties of spray deposited antimony-doped tin oxide thin films

Antimony-doped tin oxide (Sb:SnO2) thin films with varying Sb concentrations were deposited using the spray pyrolysis technique. A comprehensive analysis of the films' elemental, structural, and optoelectronic properties is presented. All films possess a polycrystalline single-phase nature and have a tetragonal rutile structure. As Sb concentration increases, the unit cell shrinks continuously, suggesting proper substitution of Sn4+ by Sb5+. This substitution causes a continuous increase in the concentration of charge carriers and a reduction in electron mobility. X-ray photoelectron spectroscopy investigations revealed the presence of asymmetric Sn 3d core-level peaks distinguished by peak splitting, which increases with increasing carrier concentration. Utilizing the plasmon absorption model, an effective mass value of (0.51 ± 0.07)me for the conduction electron at the fermi level is obtained. With increasing Sb concentration, the optical energy gap increases gradually from 3.84 eV for undoped SnO2 to 4.35 eV for 5.0 at. % Sb. After considering the Urbach tailing phenomenon as well as the Moss–Burstein effect, this increase was attributed to the increase in Moss–Burstein energy due to increased charge carrier concentration. Our study revealed that the film doped with 2.0 at. % Sb has the best optoelectronic properties, with a figure of merit of 4.18 (Ω/cm2)−1.

High‐Pressure Growth and Characterization of Seven‐Layered CuBa2Ca6Cu7O17±δ Single Crystals

AbstractIn cuprates, the superconducting transition temperature (Tc) is closely related to the number n of CuO2 planes per unit cell. The studies on multi‐layered cuprates offer insights into the physical properties and pairing mechanisms of superconductivity. However, the synthesis and stability of ultra‐multilayered cuprates pose significant challenges. Here, a newly discovered seven‐layered cuprate CuBa2Ca6Cu7O17±δ grown under high pressure is reported. Magnetization and transport measurements confirm bulk superconductivity with Tc of ≈85 K. The magnetization hysteresis loops, critical current density (Jc), and irreversibility fields of CuBa2Ca6Cu7O17±δ are also investigated. The novel compound CuBa2Ca6Cu7O17±δ provides an ideal platform for studying the physics of multi‐layered cuprates.

Design of Band Stop Filter Using Epsilon-Negative Frequency Selective Surface

This paper focuses on designing a band stop filter based on epsilon-negative frequency-selective surface (FSS). The unit cell has an electrical length of 0.104λ0 × 0.104λ0 which offers a bandwidth of 2.53 GHz from 1.24 GHz to 3.77 GHz. It has a center frequency of 2.44 GHz and the obtained fractional bandwidth is above 100%. Additionally, the behavior of the presented FSS is explained by the equivalent circuit model and surface current distribution. Within the entire bandwidth, it offers a negative permittivity. The refractive index of BSF is almost zero for 2.45−3.98 GHz range of frequency. The proposed FSS structure exhibits polarization-independent properties and offers a stable frequency response for normal and oblique angles under both TE and TM polarization. Good agreement between the simulated and measured results is obtained for the designed prototype.

Selective direct deoxygenation of m-cresol on Heusler alloy catalysts via precise control of electronic structure: An integrated density function theory and microkinetic modeling study

Directional designing a catalyst with high direct deoxygenation selectivity of Phenols during hydrodeoxygenation (HDO), remains a formidable challenge in cost-effectively converting biomass to bio-fuel and chemicals. Herein, we evaluated for the first time the catalytic performance of Heusler alloy surfaces for HDO process of m-cresol at the atomic scale. The direct deoxygenation (DDO) route of m-cresol on the Co2FeGa (110) surface at 573.15 K exhibited relatively low kinetic (1.20 eV) and thermodynamic (−0.04 eV) barriers, leading to high selectivity (near 100 %) for toluene production. The degree of rate control (DRC) analysis revealed that direct dehydroxylation constituted the rate-limiting elementary reaction. Additionally, by tailoring the Ga and Ge ratio on the Co2FeGa1-xGex (110) surface, an almost linear relationship (R2 = 0.95) was discovered between activation energy of C-OH and the d-band center energy of the Fe element in the unit cell. Both the activation energy of C-OH and d-band center energy of the Fe decreased with increasing Ge/Ga substitution ratio. This research unveils for the first time the catalytic performance of Heusler alloy for the selective direct deoxygenation of m-cresol, but also suggest the possibility tuning d-band center of Heusler alloys to precisely tailor the selectivity of DDO during HDO process.

A single dielectric nanoparticle for refractive index sensing

Abstract Refractive index sensing has great application potential in a wide range of chemical and biomedical fields, however, these sensors usually require large-area and fabrication-intense arrays of unit cells. Here, we propose an ultracompact sensor based on a single dielectric nanoparticle for refractive index sensing with a footprint smaller than 2 µm^2 and numerically investigate its sensing performance. A single-mode resonance rather than multimodes interaction is adopted for the spectroscopic feature of refractometric sensing. The elaborate resonator geometry facilitates the excitation of the gapped-vortex mode and enables the exposure of electric hotspots outside the dielectric. Such design enhances the coupling to the sensing medium, thus exhibiting high sensitivity at the level of 345 nm/RIU with a figure of merit of 12.78 per RIU. The single-particle nanostructure together with the single-mode resonance exhibits robust sensing performance to dimension deviations. Importantly, a thin annular beam is employed as the illumination to increase the excitation efficiency of the single-mode resonance, which significantly improves the modulation depth without relying on the near-field coupling of array nanostructures. This work provides a miniaturization platform for the dielectric sensors and other application fields based on enhanced light-matter interaction.

Enhancing optical properties of Ba-Ni ferrite through nonmagnetic ion doping for sustainable green technologies and renewable energy applications

Barium ferrite powder was produced using a standard ceramic procedure, and its structure and optical properties were investigated. X-ray diffraction analysis (XRD) showed that the powder had a w-type hexagonal structure. The crystallite size was at approximately 35–36 nm, with bulk density and lattice constants increasing as zinc concentration rose. Conversely, X-ray density and porosity decreased with the increasing zinc concentration. This material has useful optical properties, as well as the standard ferrimagnetic properties of barium ferrite, which make it suitable for use in recording media. Ferrimagnetic behavior, which is useful for recording media, occurs because the powder's crystallites have their unit cell axes aligned. Up to the near-infrared part of the spectrum, the powder was found to have a very low absorption coefficient. Both of these properties—an arrangement that gives rise to ferrimagnetism and a corresponding low optical density—make barium ferrite very attractive for high-density recording and microwave applications. Fourier transform infrared spectra of the samples were recorded in the wavenumber range of 400–4000 cm−1 and supported the X-ray diffraction findings by confirming the idea of the formation of W-type hexagonal ferrite by the presence of two prominent peaks at 454 and 591 cm−1 in the FTIR spectra. Zinc addition was also found to enhance the optical properties of the material. The UV–VIS analysis confirms that the band gap energy of Ba-Ni ferrite was indeed reduced by zinc doping. Values decrease from 3.34 eV to 3.20 eV for direct transitions and from 2.96 eV to 2.79 eV for indirect transitions, using Tauc equation. That means that zinc doping enhances the optical properties of Ba ferrite without affecting the hexagonal structure of Ba-Ni ferrite. Moreover, key parameters of optical performance such as the dielectric constant, the extinction coefficient, the penetration depth, and the refractive index show a dramatic increase with a rise in zinc concentration. These attributes make zinc-doped Ba-Ni ferrite a promising optoelectronic material. The material also showed high absorbance in the wavelengths ranging from 334 to 338 nm, which makes it good for the solar cell applications. Overall, zinc-doped Ba-Ni ferrite is a good candidate for sustainable and renewable energy applications. Our study of the optical properties of barium ferrite up to the near-infrared part of the spectrum demonstrated that the powdered material has a very low absorption coefficient. Indeed, the combination of ferrimagnetism and low optical density makes barium ferrite particularly appealing for use in high-density recording and microwave technology applications.

Influence of Subvalent Twin-Rattler for High n-Type Thermoelectric Performance in Bi13S18Br2 Chalcohalide.

Metal chalcohalides, owing to their higher stability over halides and greater tunability of electronic features over chalcogenides, open new avenues for investigating properties of materials. Complex metal chalcohalides can be a good choice for thermoelectric studies for their halide-like low thermal conductivity and chalcogenide-like high electrical conductivity. Here, we have investigated the thermoelectric properties of n-type Bi13S18Br2 and utilized the concept of Fajans' polarization to describe the formation of a dimer and explained how it can help achieve high thermoelectric figure of merit (zT) of ∼1.0 at 748 K. This zT value is so far the highest-reported value for pristine metal chalcohalides. The existence of subunit in Bi13S18Br2 is experimentally verified by synchrotron X-ray pair distribution function (X-PDF) analysis. The complex structure of Bi13S18Br2 having a large unit cell exhibits simultaneous dimer-cation rattler (i.e., "twin-rattler"), which decreases the lattice thermal conductivity drastically. We observed evidence of such low-energy rattling vibrations from DFT-calculated eigen mode visualizations of the phonon dispersion. The subvalent nature of accommodates an extra electron in Bi(6pz) orbital, which helps form a weakly dispersed donor band just below the Fermi energy (EF), leading to a significant reduction in band gap (0.77 eV), which is favorable for high thermoelectric performance. Consequently, we obtained a semiconducting nature of n-type Bi13S18Br2 with moderate electrical conductivity, as well as a high Seebeck coefficient. Our investigation presents the importance of fundamental chemistry in thermoelectrics and demonstrates the influence of subvalent twin-rattler in triggering high thermoelectric performance in metal chalcohalides.

Structural multiplicity in a solvated hydrate of the antiretroviral protease inhibitor Lopinavir

Lopinavir is a potent protease inhibitor that is used as a first-line pharmaceutical drug for the treatment of HIV. The multi-component solvated Lopinavir crystal, systematic name (2S)-N-[(2S,4S,5S)-5-[2-(2,6-dimethylphenoxy)acetamido]-4-hydroxy-1,6-diphenylhexan-2-yl]-3-methyl-2-(2-oxo-1,3-diazinan-1-yl)butanamide–ethane-1,2-diol–water (8/3/7) 8C37H48N4O5·3C2H6O2·7H2O, was prepared using evaporative methods. The crystalline material obtained from this experimental synthesis was characterized and elucidated by single-crystal X-ray diffraction (SC-XRD). The crystal structure is unusual in that the unit cell contains 18 molecules. The stoichiometric ratio of this crystal is eight Lopinavir molecules [8(C37H48N4O5)], three ethane-1,2-diol molecules [3(C2H6O2)] and seven water molecules [7(H2O)]. The crystal packing features both bi- and trifurcated hydrogen bonds between atoms.

Flexural behaviors of asymmetric Re-entrant auxetic honeycombs

A family of negative Poisson's ratio honeycombs with asymmetric base units and potential applications in civil and marine industries are introduced by introducing asymmetricities to the geometry of regular re-entrant unit cell. These structures, namely the single symmetry-broken re-entrant (SSR), double symmetry-broken re-entrant (DSR), and hybrid symmetry-broken re-entrant (HSR) honeycomb lattices, are fabricated through fused filament fabrication and subjected to experimental three-point bending (TPB) experiments and simulations. The novel designs showcase exceptional specific energy absorption (SEA) attributes compared to the regular metamaterial, with the SSR structure exhibiting a remarkable 147.2% higher SEA. The asymmetric metamaterials also demonstrate higher flexural modulus (Ef) compared to the benchmark design, with the SSR and DSR models boasting approximately 29% and 19% higher Ef, respectively. Studies on design parameters show that internal angle of unit cells that creates the asymmetricity affects the flexural performance of the unique auxetic honeycombs, significantly. Finally, parametric investigation on out-of-plane bending of the honeycombs showed the dominance of all asymmetric-unit honeycombs over the benchmark due to having organized self-contact regions. The SSR and DSR structures own about 51% and 39% higher SEA than the benchmark honeycomb under out-of-plane TPB, respectively.

A Study on the Compressive Behavior of Additively Manufactured AlSi10Mg Lattice Structures

The mechanical behavior of the metallic components fabricated by additive manufacturing (AM) technologies can be influenced by adjustments in their microstructure or by using specially engineered geometries. Manipulating the topological features of the component, such as incorporating unit cells, enables the production of lighter metamaterials, such as lattice structures. This study investigates the mechanical behavior of lattice structures created from AlSi10Mg, which were produced using the laser beam powder bed fusion (LB-PBF) process. Specifically, their behavior under pure compressive loading has been numerically and experimentally investigated using ten different configurations. Experimental methods and finite element analysis (FEA) were used to investigate the behavior of body-centered cubic (BCC) lattice structures, specifically examining the effects of tapering the struts by varying their diameters at the endpoints (dend) and midpoints (dmid), as well as altering the height of the joint nodes (h). The unit cells were designed with varying parameters in such a way that dend is changed at three levels, while dmid and h are changed at two levels. Significant differences in Young’s modulus, yield strength, and ultimate compressive strength between the various specimen configurations were observed both experimentally and numerically. The FEA underestimated the Young’s modulus corresponding to the configurations with thinner struts in comparison to the higher values found experimentally. Conversely, the FEA overestimated the Young’s modulus of those configurations with larger strut diameters with respect to the experimentally determined values. Additionally, the proposed FE method consistently underestimated the yield strength relative to the experimental values, with notable discrepancies in specific configurations.

Surface Reaction Induced Compressive Strain for Stable Inorganic Perovskite Solar Cells

AbstractCesium‐based inorganic perovskites have emerged as promising light‐harvesting materials for perovskite solar cells (PSCs) due to their promising thermal‐ and photo‐stability. However, obstacles to commercialization remain regarding their phase instability. In this work, we report a facile and effective strategy to regulate the surface compressive strain via in situ surface reaction to stabilize CsPbI3 perovskite. The use of a chelating ligand with a molecular configuration closely matching the integer multiples of the unit cell lattice parameters of CsPbI3 induces compressive strain at the surface of CsPbI3. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite phase degradation, thus significantly improving the intrinsic stability of inorganic perovskite. Consequently, enhanced power conversion efficiency (PCE) of 21.0 % and 18.6 % were respectively achieved in 0.16‐cm2 lab‐scale devices and 25.3‐cm2 solar modules. Further, surface reaction enables PSCs with enhanced thermal and operational stability; these devices retain over 95 % of their initial PCE after damp‐heat tests (i.e., in 85 °C and 85 % R. H. air) for 2000 h, and remain 99 % of their initial PCE after operating for 2000 h, representing one of the most stable inorganic PSCs reported so far.

Low-velocity impact on a CFRP sandwich plate with a reentrant auxetic core

Theoretical analysis is utilized to model the low-velocity impact (LVI) on a Carbon-Fiber Reinforced Polymer (CFRP) sandwich plate with reentrant auxetic core. The Zig-Zag theory is employed to formulate the displacement field of the sandwich plate. The mechanical characteristics of the reentrant auxetic core unit cell are determined through the application of Gibson’s equations. The influences of the unit cell thickness, the unit cell angle, the number of layers of the unit cell along the plate thickness, the impactor radius, and the impactor initial velocity on the LVI study of CFRP sandwich plate with reentrant auxetic core are investigated in detail.

Anomalous wavefront control of Lamb wave with metasurfaces via superposed prism resonance

As a special branch of metamaterials characterized by phase discontinuity, elastic metasurfaces have presented extraordinary capacity for elastic wave manipulation. This class of metamaterials has received extensive attention in recent years. In this paper, a subwavelength elastic metasurface with locally resonant prisms is employed to steer the propagation of the A0 Lamb wave. Based on the dispersion curve and transmission ratio, we establish that the resonant feature of prisms is influenced by the diagonal ratio of cross section. By gradually tuning the diagonal ratio of prism cross section, the pattern of resonance modes and the mechanism of resonance superposition are clarified. In this regard, two different resonant modes can be superimposed at a certain frequency. A complete 2 π phase shift that is crucial for redirecting wave propagation can therefore be realized. To have a broader working frequency range, the influence of prism height on the resonance superposed frequency and the effect of plate thickness on the incident flexural wave are explored. Based on the generalized Snell’s law, negative refraction is verified numerically through a metasurface assembled from unit cells with constant phase change. In addition, other wavefront modulations such as eccentric focusing, nonparaxial propagation are also demonstrated. This novel design introduces new degrees of freedom in many engineering applications such as seismic wave protection, structural health monitoring and energy harvesting.

The temperature evolution of the atomic structure and the influence of the local environment of atoms on the optical properties of the NA2SIF6 crystal

Crystals of sodium hexafluorosilicate Na2SiF6 millimeter size were grown by the hydrothermal method. According to X-ray diffraction analysis, it was revealed that Na2SiF6 samples are twinned according to the merohedral law and crystallize in sp. gr. P321 with unit cell parameters equal at 295 K a = 8.8582(12), c = 5.0396(11) Å, V = 342.47(17) Å3 on average the results of repeated measurements. A multi-temperature diffraction study of Na2SiF6 was carried out, based on the results of which the temperature dynamics of the optical properties of crystals was calculated. The structural similarity of Na2SiF6 crystals with crystals of the langasite family La3Ga5SiO14 was found. This made it possible to explain the optical activity of Na2SiF6 by considering electron density spirals similar to langasite, twisted around a triple axis of symmetry passing through the origin of the Na2SiF6 cell. The fractures in the temperature dependences of the refractive indices and rotation of the plane of polarization of light are explained by taking into account the anomalous features of interatomic interactions along the triple axis of the crystal cell passing through the Si2(2d) position with coordinates (1/3, 2/3, z). It was found that the main factor influencing the temperature dynamics of optical parameters is the Si2(2d)–F2(6g) distance, which increases abnormally with cooling.

Thirty two port super wideband diversity antenna for indoor communications

This paper introduces a novel design featuring a thirty-two port diversity antenna with an elliptical shape, fed by an asymmetric coplanar waveguide (CPW). The antenna incorporates uneven meander lines, tailored for super-wideband (SWB) applications. The structure of the unit cell is of an elliptical patch with an elliptical slot, and it is connected to a rectangular stub and asymmetric meander line. The size of the single element is 22 mm × 20 mm, and it operates from 3 to 40 GHz. The bandwidth dimension ratio of the unit cell is 3911, bandwidth ratio is 13.33:1, and fractional bandwidth is 172.09%. The single element is developed into a 3-D thirty-two port diverse antenna, composed of a horizontal plane and four planes perpendicular to it. The diverse antenna has a peak gain of 12.5 dBi and an efficiency of 94%. The computed envelope correlation coefficient (ECC), as determined using S-parameters and far-field measurements, is less than 0.1. The attained diversity gains (DGs) of the developed MIMO antenna are above 9.9 dB in terms of both S-parameter and far-field computations. The obtained thirty-two port diverse antenna channel capacity loss (CCL) is below 0.25 bits/s/Hz. The mean effective gain (MEG) of the constructed thirty-two port antenna is below 2. To validate the appropriateness of the developed thirty-two port antenna for wireless indoor environment, an enclosure made of acrylonitrile butadiene styrene (ABS) is crafted and fabricated, and the characteristics of the proposed diverse antenna are investigated.

Structural investigation of the liquid crystalline phases of three homologues from the nOS5 series (n = 9, 10, 11) by X-ray diffraction

ABSTRACT Polarizing optical microscopy and differential scanning calorimetry are used to determine the phase sequence of three liquid crystalline 4-pentylphenyl-4’-n-alkyloxythiobenzoates with n = 9, 10, 11. The X-ray diffraction method is applied for structural characterisation of the liquid crystalline phases. The smectic layer spacing, tilt angle, average distance between the long axes of molecules and correlation length of the short-range order are determined as a function of temperature. For the crystal-like smectic phases with the hexagonal or herring-bone packing, the unit cell parameters are obtained. The presence of the tilted hexagonal phase for n = 10, 11 and tilted herring-bone phase for n = 9, 10 is indicated, although the direction of the tilt cannot be determined.

Lattice Distortion Creates Enhancements in Photocatalytic and Electrocapacitive Performance of Sol–Gel‐Derived Cu‐Doped NiTiO3

A remarkable 35% enhancement in the photocatalytic and electrocatalytic abilities of an ilmenite nickel titanate (NiTiO3) material is reported. This boost in catalytic performance is achieved by simply creating a static distortion in the rhombohedral unit cell by replacing a small proportion of a small‐size nondegenerate Ni (69 pm) with a large‐size degenerate Cu (73 pm). The materials are synthesized by using a simple sol–gel method. The appropriate doping amount of Cu facilitates the better separation of intrinsic charge carrier pairs by inhibiting their recombination. The photocatalytic and electrochemical activities of durable materials in aqueous MB dye (10 ppm) and KOH (1 molar) electrolyte solutions are found to be directly associated with this improvement in inherent charge carrier transfer characteristics. The enhanced photodissociation of MB dye (42–56%) and specific capacitance (381–450 F g−1) in a KOH (1 molar) electrolyte are in full accord with the investigations carried out using crystallographic and optoelectronic analysis, charging–discharging measurements, and electrochemical impedance (EIS) spectroscopy investigations. Same material with high textural surface areas or controllable particle morphologies might show a far better photo/electrocatalytic performance in a variety of practical applications.

Design and optimization of dielectric resonator based MIMO antenna with beam tilting at mm-wave for enhanced 5G communication using machine learning

In this paper, a dual-port ceramic-based multiple-input multiple-output (MIMO) antenna is designed for operation at mm-wave frequencies. The design incorporates a partially reflecting surface (PRS) positioned above the dual-port antenna to facilitate beam tilting. Additionally, various machine learning (ML) algorithms are utilized to optimize the unit cell length and the distance between the Dielectric Resonator Antenna (DRA) and the PRS, thereby achieving the desired beam tilting characteristics. The ceramic element is excited through an aperture, which generates the HEM11δ mode in the cylindrical dielectric resonator antenna (CDRA). The proposed antenna demonstrates excellent port isolation, exceeding 35 dB, and operates effectively within the 25.9–27.4 GHz frequency range. The PRS enables a broadside beam tilt of ±30 degrees, incorporating pattern diversity into the design. These characteristics make the proposed antenna an ideal candidate for mm-wave vehicle-to-vehicle and 5G communication systems.

Dissymmetrization in eudialyte-group minerals. I. A model of ordered cation arrangement in the crystal structure of amableite-(Ce) using the P3 symmetry

The crystal structure of the recently discovered eudialyte group mineral, amabellite-(Ce) Na15[(Ce1.5Na1.5)Mn3]Mn2Zr3£Si[Si24O69(OH)3](OH)2 · H2O, found in the hyperagpaitic pegmatite of the Saint-Amable massif (Canada), has been solved by X-ray structural analysis within the space group R3. Amabellite-(Ce) is a member of the eudialyte group with the lowest calcium content and differs from other members of this group by the dominance of lanthanides in the part of the edge-sharing octahedra of the six-membered ring. The unit cell parameters of the mineral are: a = 14.1340(2), c = 30.378(1) Å, V = 5255.6(3) ų. A model of the cation distribution in the crystal structure of amabellite-(Ce) within the low-symmetry space group P3 has been proposed. The obtained 162 independent positions were refined in the isotropic-anisotropic approximation of atomic displacements using 3968 F 3σ(F), R = 4.6%. Despite the fairly close results, the transition from space group R3 to P3 allows for more detailed information on the local distribution of a number of elements over the framework positions. A comparison was made between the crystal structure models of amabellite within the symmetries R3 and P3, as well as other low-calcium eudialyte group minerals previously studied within several space groups.

Tunable enhanced chiroptical response of a twisted L-shaped plasmon nanoparticle system

Chiroptical responses in plasmon systems have aroused widespread interest, manifesting potential application in fields including physics, biology, and pharmacy, as well as other disciplines. However, the enhancement and tunability of chiroptical responses by strong plasmon coupling, which have been seldom discussed, remain wanting. In this paper, we propose a stacked and twisted L-shaped nanoparticle system, which exhibits an enhanced chiroptical response and the dynamic modulation of chiroptical response. By adjusting the twist angle and the gap between L-shaped nanoparticles, the anisotropy factor g, which quantifies the relative strength of the chiroptical response, can reach up to −1.5, and the peak position and linewidth of the g spectrum can be modified. Furthermore, in instances where the chiroptical response is weak, we construct a finite-size 1D chain by using the proposed system as the unit cell. By harnessing the global interaction among the unit cell of the 1D chain, the maximum value of g can be effectively improved and adjusted. Such an L-shaped nanoparticle system as a fundamental structure has potential applications in tunable chiroptical devices and also extends methods for device design.