Asymmetric Unit Cell Research Articles

Investigating pump harmonics generation in a SNAIL-based traveling wave parametric amplifier

Abstract Traveling wave parametric amplifiers (TWPAs) are extensively employed in experiments involving weak microwave signals for their highly desirable quantum-limited and broadband characteristics. However, TWPAs’ broadband nature comes with the disadvantage of admitting the activation of spurious nonlinear processes, such as harmonics generation, that can potentially degrade amplification performance. Here we experimentally investigate a Josephson TWPA device with superconducting nonlinear asymmetric inductive element-based unit cells focusing on the amplification behaviour along with the generation of second and third harmonics of the pump. By comparing experimental results with transient numerical simulations, we demonstrate the influence of Josephson junctions’ fabrication imperfections on the occurrence of harmonics and on the gain behaviour.

Experimental validation of group delay in a multi-window electromagnetically induced transparency metasurface

Metasurface analogs of electromagnetically induced transparency (EIT) are attracting sustaining attention due to their ability to maintain transparency windows accompanied by extreme dispersion of propagating waves, which are important for slow light devices and highly sensitive optical sensors. In this paper, we study theoretically, numerically, and experimentally the conditions for the existence of multi-band transparency windows in the metasurface supported by the interaction of dipole modes in an asymmetric unit cell. The unit cell is composed of a single bright resonator and several dark resonators made in the form of rectangular metal patches. The manifestation of EIT is studied for different metasurface configurations by varying the number and positions of resonators used within the unit cell. To validate the slow-down effect caused by EIT, a prototype of the metasurface is fabricated and tested, providing a measurement of the group delay and bandwidth-delay product features. The obtained results clearly confirm the presence of four EIT-like transparency windows in the metasurface transmission spectra originating from the coupling between either quasi-TE or quasi-TM modes of the resonators.

Crystal structure, spectroscopy, DFT, and thermal studies of 3-cyano-2(1H)-pyridones as potential anticancer agents.

A series of 3-cyano-2(1H)-pyridones 4a-c were efficiently synthesized using an expeditious microwave-assisted multicomponent approach. Single-crystal XRD analysis revealed the presence of six independent molecules in the asymmetric unit cell for all compounds, with the crystal packing stabilized by a network of cyclic dimers formed by N-H⋯O[double bond, length as m-dash]C and C-H⋯O[double bond, length as m-dash]C intermolecular interactions. Additional supramolecular interactions, including C-H⋯π, C-N⋯π, and π⋯π, and C-H⋯X (for halogenated derivatives, i.e., 4b and 4c), appear crucial for crystal stabilization. Density Functional Theory (DFT) calculations were employed to understand the electronic structures and potential binding affinities. Comprehensive spectroscopic characterization by FT-IR, UV-Vis, NMR, and HMRS techniques confirmed the structures of all synthesized compounds. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to evaluate the thermal stability of these compounds. The in vitro anticancer activity was evaluated against a panel of 60 human cancer cell lines, demonstrating promising activity against non-small-cell lung and breast cancer cell lines. Notably, compounds 4a and 4c exhibited the highest anticancer activity against the HOP-92 and MCF7 cell lines, with growth inhibition percentages (GI%) of 54.35 and 40.25, respectively.

Orthogonal centre ring field optimization triple-band metamaterial absorber with sensing application

This paper provides a metamaterial for microwave absorbers relying on asymmetric square split rings with a partial E shape in the centre-based resonator. The wideband frequency range shows its sensing capabilities in identifying various oil samples. The optimized MTM unit cell has electrical dimensions of 0.122λο × 0.122λο, where is λο the predicted wavelength at 3.64 GHz resonance frequency, for a total size of 10 × 10 mm2. The FR-4 dielectric substrate, 1.6 mm in thickness, produces the unit cell. The MTM has a maximum absorption peak of 91.46 % at 3.64 GHz, 99.72 % at 5.99 GHz, 96.89 % at 7.47 GHz, and 98.45 % at 10.01 GHz. This MMA has four absorption peaks, making it suitable for use in the triple band (S, C, and X). The centre split gaps and partial E shapes increase unit cell absorption, and the defective CSRR back layer structure improves the transmission coefficient. High absorption is influenced by the central split gaps and an appropriate electric field and magnetic field optimized in the centre ring when the structure is in an Orthogonal orientation. The research used a frequency domain solver operating between 2 and 12 GHz. The scattering characteristics (coefficient of transmission) of the relevant unit cell's equivalent circuit were confirmed using ADS software and the CST result. At frequencies between 3 and 5 GHz, the proposed asymmetric unit cell functions as a double negative (DNG) metamaterial absorber due to its negative permeability and permittivity. Since oil samples have different dielectric constants, the resonance frequency and Q factor are likewise different. Here, we receive a spectrum of frequencies that can be adjusted for use in sensing. The data showed that the suggested sensor is sensitive enough to pick up a variety of oils. The proposed sensor is useful for various applications, from liquid detection to microfluidic sensing and beyond, due to its cheap cost, high sensitivity, high-quality factor, and high electromagnetic radiation (EMR).

Subwavelength-Cavity High-Gain Circularly Polarized Antenna with Planar Metamaterials

We present a specific subwavelength-cavity high-gain circularly polarized ultra-thin antenna made of planar metamaterials. The antenna is designed to operate at 2.80 GHz with a fixed thickness of approximately 1/6 of the operating wavelength in free space. The asymmetric unit cells of the metamaterial antenna exhibit two characteristics, namely, negative permeability and polarization selection. A linear-polarization micro-strip patch, which can realize circular polarization without a complicated feeding network, is embedded in the cavity as a feed. The circular polarization mode of the antenna can be changed by simply rotating the planar metamaterial horizontally. Simulations and experiments conducted on this antenna yielded results that are in good agreement with each other. This new subwavelength planar antenna can have potentially important applications in communication, early warning systems, and radio observation.

Discovering the Solid-State Secrets of Lorlatinib by NMR Crystallography: To Hydrogen Bond or not to Hydrogen Bond

Lorlatinib is an active pharmaceutical ingredient (API) used in the treatment of lung cancer. Here, an NMR crystallography analysis is presented whereby the single-crystal X-ray diffraction structure (CSD: 2205098) determination is complemented by multinuclear (1H, 13C, 14/15N, 19F) magic-angle spinning (MAS) solid-state NMR and gauge-including projector augmented wave (GIPAW) calculation of NMR chemical shifts. Lorlatinib crystallises in the P21 space group, with two distinct molecules in the asymmetric unit cell, Z′ = 2. Three of the four NH2 hydrogen atoms form intermolecular hydrogen bonds, N30-H…N15 between the two distinct molecules and N30-H…O2 between two equivalent molecules. This is reflected in one of the NH21H chemical shifts being significantly lower, 4.0 ppm compared to 7.0 ppm. Two-dimensional 1H–13C, 14N-1H and 1H (double-quantum, DQ)-1H (single-quantum, SQ) MAS NMR spectra are presented. The 1H resonances are assigned and specific HH proximities corresponding to the observed DQ peaks are identified. The resolution enhancement at a 1H Larmor frequency of 1 GHz as compared to 500 or 600 MHz is demonstrated.

Theory of Truncation Resonances in Continuum Rod‐Based Phononic Crystals with Generally Asymmetric Unit Cells (Adv. Theory Simul. 2/2023)

Resonant modes emerging within bandgaps, or truncation resonances, represent a unique phenomenon of phononic materials and play a central role in flow control, edge/surface modes and sensing applications. In article 2200700, Mostafa Nouh and co-workers establish the fundamental factors that contribute to the origination or suppression of truncation resonances and provides an interpretation of localized vibrational modes in finite phononic crystals.

Theory of Truncation Resonances in Continuum Rod‐Based Phononic Crystals with Generally Asymmetric Unit Cells

AbstractPhononic crystals exhibit Bragg bandgaps, frequency regions within which wave propagation is forbidden. In solid continua, bandgaps are the outcome of destructive interferences resulting from periodically alternating material layers. Under certain conditions, natural frequencies emerge within these bandgaps in the form of high‐amplitude localized vibrations near a structural boundary, referred to as truncation resonances. In this paper, the vibrational spectrum of finite phononic crystals which take the form of a one‐dimensional rod is investigated and the factors that contribute to the origination of truncation resonances are explained. By identifying a unit cell symmetry parameter, a family of finite phononic rods, which share the same dispersion relation, yet distinct truncated forms, is defined. A transfer matrix method is utilized to derive closed‐form expressions of the characteristic equations governing the natural frequencies of the finite system and decipher the truncation resonances emerging across different boundary conditions. The analysis establishes concrete connections between the localized vibrations associated with a truncation resonance, boundary conditions, and the overall configuration of the truncated chain as dictated by unit cell choice. The study provides tools to predict, tune, and selectively design truncation resonances, to meet the demands of various applications that require and uniquely benefit from such truncation resonances.

Femtosecond Laser 4D Printing of Light‐Driven Intelligent Micromachines

AbstractIntelligent micromachines that respond to external light stimuli have a broad range of potential applications, such as microbots, biomedicine, and adaptive optics. However, artificial light‐driven intelligent micromachines with a low actuation threshold, rapid responsiveness, and designable and precise 3D transformation capability remain unachievable to date. Here, a single‐material and one‐step 4D printing strategy are proposed to enable the nanomanufacturing of agile and low‐threshold light‐driven 3D micromachines with programmable shape‐morphing characteristics. The as‐developed carbon nanotube‐doped composite hydrogel simultaneously enhanced the light absorption, thermal conductivity, and mechanical modulus of the crosslinked network, thus significantly increasing the light sensitivity and response speed of micromachines. Moreover, the structural design and assembly of asymmetric microscale mechanical metamaterial unit cells enable the highly efficient additive nanomanufacturing of 3D shape‐morphable micromachines with large dynamic modulation and spatiotemporal controllability. Using this strategy, the world's smallest artificial beating heart with programmable light‐stimulus responsiveness for the cardiac cycle is successfully printed. This 4D printing method paves the way for the construction of multifunctional intelligent micromachines for bionics, drug delivery, integrated microsystems, and other fields.

Metamaterial-enabled asymmetric negative refraction of GHz mechanical waves

Wave refraction at an interface between different materials is a basic yet fundamental phenomenon, transversal to several scientific realms – electromagnetism, gas and fluid acoustics, solid mechanics, and possibly also matter waves. Under specific circumstances, mostly enabled by structuration below the wavelength scale, i.e., through the metamaterial approach, waves undergo negative refraction, eventually enabling superlensing and transformation optics. However, presently known negative refraction systems are symmetric, in that they cannot distinguish between positive and negative angles of incidence. Exploiting a metamaterial with an asymmetric unit cell, we demonstrate that the aforementioned symmetry can be broken, ultimately relying on the specific shape of the Bloch mode isofrequency curves. Our study specialized upon a mechanical metamaterial operating at GHz frequency, which is by itself a building block for advanced technologies such as chip-scale hybrid optomechanical and electromechanical devices. However, the phenomenon is based on general wave theory concepts, and it applies to any frequency and time scale for any kind of linear waves, provided that a suitable shaping of the isofrequency contours is implemented.

Insight into the structural basis of the dual inhibitory mode of Lima bean (Phaseolus lunatus) serine protease inhibitor.

Bovine pancreatic trypsin was crystallized, in-complex with Lima bean trypsin inhibitor (LBTI) (Phaseolus lunatus L.), in the form of a ternary complex. LBTI is a Bowman-Birk-type bifunctional serine protease inhibitor, which has two independent inhibitory loops. Both of the loops can inhibit trypsin, however, only the hydrophobic loop is specific for inhibiting chymotrypsin. The structure of trypsin incomplex with the LBTI has been solved and refined at 2.25 Å resolution, in the space group P41, with Rwork /Rfree values of 18.1/23.3. The two binding sites of LBTI differ in only two amino acids. Lysine and leucine are the key residues of the two different binding loops positioned at the P1, and involved in binding the S1 binding site of trypsin. The asymmetric unit cell contains two molecules of trypsin and one molecule of LBTI. The key interactions include hydrogen bonds between LBTI and active site residues of trypsin. The 3D structure of the enzyme-inhibitor complex provided details insight into the trypsin inhibition by LBTI. To the best of our knowledge, this is the first report on the structure of trypsin incomplex with LBTI.

Tuning and switching effects of quasi-BIC states combining phase change materials with all-dielectric metasurfaces

Emission enhancement of quantum emitters is particularly relevant in the development of single-photon sources, which are key elements in quantum information and quantum communications. All-dielectric metasurfaces offer a route towards strong enhancement of local density of optical states via engineering of high quality factor optical modes. In particular, the recently proposed concept of quasi-bound states in the continuum (quasi-BIC) allows for precise control of such resonances in lattices with an asymmetric unit cell. Still, the spectral band of emission enhancement is usually fixed by the geometric parameters of the metasurface. Here, we propose to utilize phase change materials to tune the properties of light-emitting metasurfaces designed to support quasi-BIC states in the telecom wavelength range. In our design, a thin layer of a phase change material, which provides strong contrast of refractive index when switched from the amorphous to the crystalline state, is located on top of the resonators made of amorphous silicon (a-Si). Depending on the selected phase change material, we numerically demonstrate different functionalities of the metasurface, In particular, for low-loss Sb2Se3 we evidence spectral tuning effects, whereas for Ge2Sb2Te5, we report an “on”/“off” switching effect of the quasi-BIC resonance. Furthermore, we investigate the influence of the crystallization fraction and the asymmetry parameter of the metasurface on the results. This work provides concrete design blueprints for switchable metasurfaces, offering new opportunities for nanophotonics devices or integrated photonic circuits.

Extraction of dynamic effective material properties for 2D acoustic Willis media

Acoustic Willis media is characterized by coupling between the kinetic and potential energy through the pressure-strain and momentum density-velocityrelationships. The introduction of additional constitutive properties allows more appropriate characterization of complex unit cells, including effects related to physical asymmetry, finite phase and multiple scattering, and nonreciprocal biases. Similar to traditional composites or other metamaterials, homogenization is a valuable modeling tool that simplifies numerical study of Willis media. However, homogenization schemes must be altered to account for even and/or odd Willis coupling parameters. In this work, we extend a 2D homogenization approach to account for the Willis coupling using the modified dynamic equations. With this homogenization scheme, finite layers of N unit cells and N + 1 unit cells are utilized with different propagation angles and incident directions to isolate the response across a single unit cell. Numerical simulations with the finite element method will then be presented to validate the homogenization model and demonstrate the effective material properties obtained for an asymmetric unit cell. [This work was supported by the Office of Naval Research.]

Full manipulation of transparency and absorption through direct tuning of dark modes in high-Q Fano metamaterials.

Controlling the line shape of Fano resonance has continued to attract significant research attention in recent years owing to its practical applications such as lasing, biosensing, and slow-light devices. However, controllable Fano resonances always require stringent alignment of complex symmetry-breaking structures; therefore, the manipulation can only be performed with limited degrees of freedom and a narrow tuning range. This work demonstrates dark-mode excitation tuning independent of the bright mode for the first time, to the authors' knowledge, in asymmetric Fano metamaterials. Metallic subwavelength slits are arranged to form asymmetric unit cells and generate a broad and bright (radiative) Fabry-Perot mode and a sharp and dark (non-radiative) surface mode. The introduction of the independent radial and angular asymmetries realizes independent control of the Fano phase (q) and quality factor (Q). This tunability provides a dynamic phase shift while maintaining a high-quality factor, enabling switching between nearly perfect transmission and absorption, which is confirmed both numerically and experimentally. The proposed scheme for fully controlled Fano systems can aid practical applications such as phase-sensitive switching devices.

Crystal structure and computational studies of N-((2-ethoxynaphthalen-1-yl)methylene)-4-fluoroaniline

The Schiff base compound, N-((2-ethoxynaphthalen-1-yl)methylene)-4-fluoroaniline, has been synthesized and characterized by X-ray diffraction method. The title compound, C19H16FNO, crystallizes in triclinic, space group P-1 (no. 2), a = 10.6343(9) Å, b = 11.4720(10) Å, c = 13.8297(13) Å, α = 102.466(7)°, β = 104.763(7)°, γ = 98.972(7)°, V = 1552.7(2) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.086 mm-1, Dcalc = 1.255 g/cm3, 24355 reflections measured (3.16° ≤ 2Θ ≤ 51°), 5779 unique (Rint = 0.0794, Rsigma = 0.0696) which were used in all calculations. The final R1 was 0.0373 (I > 2σ(I)) and wR2 was 0.0763 (all data). The title compound contains two molecules with a similar structure in the asymmetric unit cell. The packing of the crystal structure is determined by weak C–H···F and C-H···N intermolecular hydrogen bonds. The contributions of these weak interactions in the crystal structure were calculated by the Hirshfeld surfaces and examined by the intermolecular interactions within the structure. The existence, nature and percentage contribution of different intermolecular interactions H···H, C···H, N···H, and F···H were determined using Hirshfeld surface analysis and fingerprint plots.

Influence of pseudo-polymorphism on the structure and thermal behavior of the new barium β-diketonate complexes [Ba(adtfa)2(18-crown-6)] and [Ba(adtfa)2(18-crown-6)](CDCl3)2

The new barium β-diketonate complexes with 18-crown-6 [Ba(adtfa)2(18-crown-6)] (1) and [Ba(adtfa)2(18-crown-6)](CDCl3)2 (2) (adtfa = 1,1,1-trifluoro-4-(1-adamantyl)-2,4-butanedionato, 18-crown-6 = 1,4,7,10,13,16-hexaoxacycloocta-decane) were synthesized and characterized by elemental analysis, IR-, 1H NMR-spectroscopy and X-ray diffraction analysis. The mutual arrangement of the β-diketonate ligands relative to the barium atoms in 1 and 2 was found to be different. The nature of chemical interactions and charges distribution in 1 and 2 was investigated using an experimental-theoretical approach based on crystal (asymmetric unit–cell aspherical scattering factor) and molecular (whole–molecule aspherical scattering factor) invarioms within the framework of Bader theory. It was shown that the less favorable conformation of complex 2 is stabilized in the crystal by the higher energy of intermolecular interactions as compared to 1. The energy of intermolecular interactions (94.3 kJ/mol) in 1 was estimated by electron density topological analysis and agrees well with the experimentally obtained sublimation enthalpy (83.2 ± 1.1 kJ/mol).

Overlap large polaron sensitivity to phase changes in the first alkali earth organic-inorganic hybrid: [(CH2)7(NH3)2]CaCl4

Crystal structure characterization, lattice potential energy, conductivity relaxation and electric conduction mechanisms of the new alkaline earth metal organic-inorganic hybrid, [(CH2)7(NH3)2] CaCl4 are presented. The new hybrid crystallizes in a triclinic system (S.G. P‾1) with two molecules per asymmetric unit cell (Z = 2). Crystallographic parameters are: a = 7.029 Å, b = 8.003 Å, c = 14.039 Å, α = 65.43°, β = 69.99°, γ = 61.39°, the calculated volume and density are 620.3 A3 and 1.68 Mgm−3 respectively. Room temperature lattice potential energy is ΔUpot = 1932.34 (kJ/mol.) and enthalpy change ΔH = 453.8 (kJ/mol.). DSC results indicated weak peaks at T7 = 239 ± 1 K, T6∼ 258.6 ± 0.5 K, a sharp λ-like peak typical of first order T5∼ 266.5 ± 0.5 K, a commensurate to incommensurate at T4 = 279 K, an incommensurate to unmodulated at T3 = 283 ± 1 K, and a chain melting transition is noted with minor peak at T2 = 326.5 K and major one at T1 = 329.3 K. Dielectric constant measurements in the temperature range (170–420) K and frequency range 60 Hz- 40 kHz confirmed the DSC transitions. It is characterized by a nearly temperature and frequency independent background of low dielectric constant (ε’) except at the transitions and at T ≥ 344 ± 2 K where frequency dispersion takes place. At high temperatures, calculated conductivity relaxation energy and relaxation time, are ΔE = 0.78 eV and (το) = 7.81614 × 10−14 s respectively. Fit of frequency dependent ac-conductivity to super-linear power law σtot = σdc + A1ωs1+ A2ωs2 shows different conduction mechanisms in the different temperature ranges (phases). Overlap large polaron tunneling (OLPT) of small radius dominates in the temperature range (240–290) K, it is very sensitive to the phase transitions in this temperature range where the polaron radius varies as the phase changes, which is reflected as small variations of the fitting parameters. In phase VIII (T < 239 K), phase III (295 < T(K) < 326.5) and phase II (327 < T(K) < 339); quantum mechanical tunneling (QMT) is the conduction mechanism. The lower value of the fitting parameters in phase (II) indicates stronger interaction between mobile ions with the lattice than phase (III). At higher temperatures correlated barrier (CBH) hopping prevails. Comparison to other transition metal hybrids of the same organic chain is discussed.

A new Organic–Inorganic hybrid compound (NH3(CH2)2C6H5)2[SnCl6]: Crystal structure, characterization, Hirshfeld surface analysis, DFT calculation, vibrational properties and biological evaluation

In this study, the crystal structure of a new phase of organic–inorganic hybrid (NH3(CH2)2C6H5)2[SnCl6] was resolved at room temperature (monoclinic system), space group (P21/c), with unit cell parameters (a ​= ​7.345(5) Å, b ​= ​25.667(5) Å, c ​= ​11.971(5) Å), β ​= ​90.106(5)°, volume ​= ​2256.8 (19) Å3 and Z ​= ​4). The asymmetric unit cell consisted of a combination of [SnCl6]2– and two organic ​+ ​NH3C2H4C6H5 cations. The crystal structure comprised alternating organic and inorganic layers stacked along the b-axis. The isolated octahedra formed a zero-dimensional anionic network. The crystal structure was stabilized by hydrogen bonding. Powder X-ray diffraction confirmed the phase purity. Hirshfeld surface and fingerprint plots elucidated the contribution of the H⋅⋅⋅Cl and H⋅⋅⋅H intermolecular interactions. DFT calculations confirmed the assignment of the Raman bands. Vibrational absorption bands were identified by micro-Raman spectroscopy. The antibacterial performance was investigated. Notably, this new compound was active against all of the tested bacteria.

α-Aminophosphonates 4-XC6H4–NH–CH(4-BrC6H4)–P(O)(OiPr)2 (X = H, Br, MeO): Crystal structures, Hirshfeld surface analysis, computational studies and in silico molecular docking with the SARS-CoV-2 proteins

We report structural and computational studies of three α-aminophosphonates 4-XC6H4–NH–CH(4-BrC6H4)–P(O)(OiPr)2, namely diisopropyl((4-bromophenyl)(phenylamino)methyl)phosphonate (X = H, 1), diisopropyl((4-bromophenyl)((4-bromophenyl)amino)methyl)phosphonate (X = Br, 2) and diisopropyl((4-bromophenyl)((4-methoxyphenyl)amino)methyl)phosphonate (X = MeO, 3). The structures of 1–3 were fully confirmed by means of the 31P{1H} and 1H NMR spectroscopy. Crystal structures of 2 and 3 are isostructural and each contain two independent molecules in the asymmetric unit cell. Energy frameworks have been calculated to analyze the overall crystal packing of 1–3. The DFT calculations were performed to verify the structures of 1–3 as well as their electronic and optical properties. Molecular docking was applied to examine the influence of both the (S)- and (R)-enantiomers of 1–3 on a series of the SARS-CoV-2 proteins.

4-Phenylnaphtho[2,3-c]furan-1(3H)-one, 9-Phenylnaphtho[2,3-c]furan-1(3H)-one and 3a,4-Dihydro-9-phenylnaphtho[2,3-c]furan-1(3H)-one Crystal Structures

The crystal structures are reported for two unsubstituted arylnaphthalene lactones, 4-phenylnaphtho[2,3-c]furan-1(3H)-one (2), 9-phenylnaphtho[2,3-c]furan-1(3H)-one (3) and a non-aromatic dihydro arylnaphthene lactone, 3a,4-dihydro-9-phenylnaphtho[2,3-c]furan-1(3H)-one (5). There are only minor differences in the geometrical parameters of these structures. However, in certain cases, both isomers of arylnaphthalene lactones (termed Type I and Type II) were found in the same asymmetric unit cell.