Lattice Dimensions Research Articles

Competition between Hydrogen and Anagostic Bonds in Ruthenocene Phases under High Pressure

High pressure favors anagostic bonds CH···Ru, which leads to a new polymorph of ruthenocene RuCp2, where Cp denotes the cyclopentadienyl ring [C5H5]−. Ruthenocene can be isothermally compressed in its ambient-pressure phase α up to 3.9 GPa, when it transforms to the new phase, β. The transition between phases α and β proceeds with an exceptionally wide hysteresis extending between 0.7 and 3.9 GPa. The transition destroys single crystals of RuCp2, but a single crystal of polymorph β can be obtained by high-pressure nucleation (above 3.9 GPa) and its isochoric growth continued above 1.0 GPa. On decompression, phase β transforms back to phase α at 0.7 GPa. The structures of phases α (space group Pnma) and β (space group Pcmb) have been determined by X-ray diffraction in the pressure range from 0.1 MPa up to 3.9 GPa. The eclipsed conformation of α-RuCp2 is retained in phase β, which contrasts with the conformational phase transitions in ferrocene and nickelocene. The lattice dimensions and molecular orientations in ruthenocene polymorphs are clearly related, which leads to the characteristic twinning-like oriented growth of the crystals of concomitant phases.

Anti- PT flatbands

We consider tight-binding single-particle lattice Hamiltonians which are invariant under an antiunitary antisymmetry: the anti-$\mathcal{PT}$ symmetry. The Hermitian Hamiltonians are defined on $d$-dimensional non-Bravais lattices. For an odd number of sublattices, the anti-$\mathcal{PT}$ symmetry protects a flatband at energy $E=0$. We derive the anti-$\mathcal{PT}$ constraints on the Hamiltonian and use them to generate examples of generalized kagome networks in two and three lattice dimensions. Furthermore, we show that the anti-$\mathcal{PT}$ symmetry persists in the presence of uniform DC fields and ensures the presence of flatbands in the corresponding irreducible Wannier-Stark band structure. We provide examples of the Wannier-Stark band structure of generalized kagome networks in the presence of DC fields, and their implementation using Floquet engineering.

Pairing Phenomena and Superfluidity of Atomic Fermi Gases in a Two‐Dimensional Optical Lattice: Unusual Effects of Lattice‐Continuum Mixing

AbstractThe superfluid behavior of ultracold atomic Fermi gases with a short range attractive interaction in a two‐dimensional optical lattice (2DOL) is studied using a pairing fluctuation theory, within the context of BCS‐BEC crossover. It is found that the mixing of lattice and continuum dimensions leads to exotic phenomena. For relatively large lattice constant d and small hopping integral t, the superfluid transition temperature exhibits a remarkable reentrant behavior as a function of the interaction strength, and leads to a pair density wave ground state, where vanishes, for a range of intermediate coupling strength. In the unitary and BCS regimes, the nature of the in‐plane and overall pairing changes from particle‐like to hole‐like, with an unexpected nonmonotonic dependence of the chemical potential on the pairing strength. The Bose–Einstein condensation asymptotic behaviors exhibit distinct power law dependencies on the interaction strength compared to cases of pure 3D lattice, 3D continuum, and 1DOL. These predictions can be tested in future experiments.

A study on the electronic properties of A site and B site doped SrTiO3 for thermoelectric applications using first-principles calculations

In SrTiO3, the nature of dopants and their substitution at the A or B site becomes a critical factor in determining the electrical conductivity, Seebeck coefficient, and thermal conductivity. The electronic band structure and the density of states (DOS) for the ab-initio study using different dopants were estimated using PBE-GGA approximation. The size, site of substitution, and nature of dopants cause significant changes in the lattice dimensions, band structure, band curvatures, and the density of states, which reflect as changes in the effective mass The effective mass is calculated from the curvature of the bottom-most conduction band using the one-band effective mass approximation. Pentavalent substitutions on the B site of SrTiO3 affect the conduction band’s curvature differently than with trivalent substitutions on the A site. They also exhibit an opposite trend in the change in band curvature according to the dopant’s ionic radius. In contrast, isovalent dopants showed no change in the band curvature except for the bandgap modification. In this paper, we have provided a semi-quantitative understanding regarding the thermoelectric properties like conductivity and Seebeck coefficient that get affected due to the substituent’s nature and site at which it substitutes.

Many-body localization transition from flat-band fine tuning

Translationally invariant flatband Hamiltonians with interactions lead to a many-body localization transition. Our models are obtained from single-particle lattices hosting a mix of flat and dispersive bands, and equipped with fine-tuned two--body interactions. Fine-tuning of the interaction results in an extensive set of local conserved charges and a fragmentation of the Hilbert space into irreducible sectors. In each sector, the conserved charges originate from the flatband and act as an effective disorder inducing a transition between ergodic and localized phases upon variation of the interaction strength. Such fine-tuning is possible in arbitrary lattice dimensions and for any many-body statistics. We present computational evidence for this transition with spinless fermions.

Near-Infrared-Triggered Reversible Transformations of Gold Nanorod-Laden Lipid Assemblies: Implications for Cellular Delivery

Robust drug and gene delivery systems require innovative methods to control payload release and tune delivery efficiency. The most promising delivery materials are lipid-based and their efficiency often hinges on structural transformations activated by endogenous pH changes. Exogenously driving phase transitions in lipid assemblies is a tantalizing idea that could lead to better control of cargo release dynamics. Multiple reports have demonstrated phase transitions induced in lipid systems, achieved via plasmonic heating of entrained gold nanorods. However, undesirable nonlocalized heating is common due to the size mismatch between the nanorods and the lipid architecture in these systems. Lipid assemblies often exhibit lattice dimensions of just a few nanometers, rendering gold particles challenging to integrate due to their incommensurate sizes, especially in lipid nanoparticle or colloidal forms. We investigate these processes using a judiciously chosen ternary lipid system with entrained small gold nanorods that undergoes transitions between bicontinuous cubic and inverse hexagonal phases on exposure to near-infrared light. Utilizing small-angle X-ray scattering alongside electron reconstruction, we show that gold nanorods integrate into the lipid assembly core lattice by colocalizing in the water nanochannels. We also found that plasmonically activated transformations occur in a couple of minutes and are reversible.

Growth, crystal structure, and properties of the Li3Ba2Ln3(MoO4)8 (Ln = Er, Tm) molybdates

The compounds Li3Ba2Ln3(MoO4)8 (Ln = Er, Tm) have been obtained by the high-temperature flux technique using the slow cooling method. Crystals grown spontaneously were used to characterize the materials and investigate their properties using X-ray diffraction (XRD), Raman spectroscopy, and magnetic measurements. Single crystal structures were solved and refined in the monoclinic space group C2/c. Lattice dimensions are a = 5.1935, b = 12.6364, c = 19.1022 Å, β = 91.399° for Er-based triple molybdate (pink crystals) and a = 5.1846, b = 12.5766, c = 19.1557 Å, β = 91.525° for Tm-molybdate (green crystals). The Ln cations, mainly at general position 8f, are coordinated by eight oxygen atoms and adopt a distorted antiprismatic geometry. The distribution of atoms over the three cationic sites is discussed comparatively to literature reports. Unpolarized Raman characterization supports both the disordered cation distribution, and the distortion of the MoO4 units. From the magnetic susceptibility measurements, it is found that the two triple molybdates follow a Curie-Weiss law in the 10–300 K domain, with a negative paramagnetic temperature θCW. The antiferromagnetic character is highlighted by the field-dependent magnetization curves.

An Expanded 2D Fused Aromatic Network with 90‐Ring Hexagons

AbstractTwo‐dimensional fused aromatic networks (2D FANs) have emerged as a highly versatile alternative to holey graphene. The synthesis of 2D FANs with increasingly larger lattice dimensions will enable new application perspectives. However, the synthesis of larger analogues is mostly limited by lack of appropriate monomers and methods. Herein, we describe the synthesis, characterisation and properties of an expanded 2D FAN with 90‐ring hexagons, which exceed the largest 2D FAN lattices reported to date.

Static and dynamic magnetic properties of honeycomb lattice antiferromagnets Na2M2TeO6 , M=Co and Ni

The magnetic structures and spin dynamics of Na$_{2}$Co$_{2}$TeO$_{6}$ and Na$_{2}$Ni$_{2}$TeO$_{6}$ are investigated by means of elastic and inelastic neutron scattering measurements and the results are discussed in the context of a generalized Kitaev-Heisenberg model on honeycomb lattice with strong spin-orbit coupling. The large number of parameters involved in the Hamiltonian model are evaluated by using an iterative optimization algorithm capable of extracting model solutions and simultaneously estimating their uncertainty. The analyses establish that both Co$^{2+}$ ($d^7$) and Ni$^{2+}$ ($d^8$) antiferromagnets realize bond-dependent anisotropic nearest-neighbor interactions, and support the theoretical predictions for the realization of Kitaev physics in 3$d$ electron systems with effective spins $S$=1/2 and $S$=1. Furthermore, by studying the Na-doped system Na$_{2.4}$Ni$_{2}$TeO$_{6}$, we show that the control of Na content can provide an effective route for fine tuning the magnetic lattice dimensionality, as well as to controlling the bond-dependent anisotropic interactions.

Antiphase domain growth: Correlation functions and structure factors in the scaling regime

We study the coarsening of three-dimensional antiphase domain structures via Monte Carlo simulations. Linear lattice dimensions of $N=1024$ enable us to reach a scaling regime covering about 2.5 orders of magnitude of linear scale. With short-range interactions on cubic lattices at temperatures of $0.75\phantom{\rule{0.16em}{0ex}}{T}_{\text{c}}$, the resulting antiphase domain structures are isotropic, which allows us to describe the real-space correlation functions by a common function scaled by a time-dependent parameter. We compare abstract Potts models and realistic models of atomic order in compounds and show that those with same ground-state degeneracy $q$ lead to equivalent antiphase domain structures, while the scaling functions for different $q$ show slight but significant deviations. Finally, we quantitatively discuss notions of real-space scale (specific interface area) and reciprocal-space scale (superstructure peak width) and thus give numerically exact values for the corresponding parameter $K$ of the Scherrer equation.

Nonlinear caging in all-bands-flat lattices

We study the impact of classical short-range nonlinear interactions on transport in lattices with no dispersion. The single particle band structure of these lattices contains flat bands only, and cages non-interacting particles into compact localized eigenstates. We demonstrate that there always exist local unitary transformations that detangle such lattices into decoupled sites in dimension one. Starting from a detangled representation, inverting the detangling into entangling unitary transformations and extending to higher lattice dimensions, we arrive at an All-Bands-Flat generator for single particle states in any lattice dimension. The entangling unitary transformations are parametrized by sets of angles. For a given member of the set of all-bands-flat, additional short-range nonlinear interactions destroy caging in general, and induce transport. However, fine-tuned subsets of the unitary transformations allow to completely restore caging. We derive the necessary and sufficient fine-tuning conditions for nonlinear caging, and provide computational evidence of our conclusions for one-dimensional systems.

Bulk crystal growth, crystalline perfection and optical homogeneities of 2AP4N single crystals for second and third order frequency conversion and terahertz (THz) device applications

Bulk size organic 2AP4N single crystals were grown by a point seed rotation technique using methanol solvent. The lattice dimensions of the grown crystal and their various crystalline planes have been analyzed by XRD measurement and also the lattice strain was calculated. The lattice perfection was examined by HRXRD and found to be extremely good. The optical transparency and cut-off value of the grown crystal were analyzed by the UV–Vis NIR measurement. The crystalline homogeneity has been confirmed by the birefringence and Mach-Zehnder interferometry techniques. The SHG measurement has been carried out with different particles. The refractive indices of grown crystal have been measured in different wavelengths by prism coupling technique and the Sellmeier's co-efficient has been calculated. The Type-I and Type-II phase-matching angles were determined and the crystal was cut along the phase-matching angles. The third order nonlinear optical parameters were analyzed by Z-scan technique. In addition, the crystal shows potential to generate pulsed Terahertz (THz) radiation by optical rectification using 800 nm wavelength at 140 fs, obtained from Ti: Sapphire Laser. The generated THz spectrum is extended up to 3.0 THz. The maximum conversion efficiency of the generated signal is of the order of 0.64 × 10 −5 %. •Optically high quality with bulk size single crystal was grown by seed rotation technique •The grown crystal has high optical homogeneities and crystalline perfection •SHG efficiency is 4.5 times that of KDP material •Type-I and Type-II phase matching elements have been made •Third-order nonlinear susceptibility ‘ χ (3) ’ is 8.68 × 10 −8 esu. •The maximum conversion efficiency of the generated THz signal is 0.64 × 10 −5 %.

Supportless printing of lattice structures by metal fused filament fabrication (MF3) of Ti-6Al-4V: design and analysis

PurposeThis paper aims to investigate the feasibility of supportless printing of lattice structures by metal fused filament fabrication (MF3) of Ti-6Al-4V. Additionally, an empirical method was presented for the estimation of extrudate deflection in unsupported regions of lattice cells for different geometric configurations.Design/methodology/approachMetal-polymer feedstock with a solids-loading of 59 Vol.% compounded and extruded into a filament was used for three-dimensional printing of lattice structures. A unit cell was used as a starting point, which was then extended to multi-stacked lattice structures. Feasible MF3 processing conditions were identified to fabricate defect-free lattice structures. The effects of lattice geometry parameters on part deflection and relative density were investigated at the unit cell level. Computational simulations were used to predict the part quality and results were verified by experimental printing. Finally, using the identified processing and geometry parameters, multi-stacked lattice structures were successfully printed and sintered.FindingsLattice geometry required considerable changes in MF3 printing parameters as compared to printing bulk parts. Lattice cell dimensions showed a considerable effect on dimensional variations and relative density due to varying aspect ratios. The experimental printing of lattice showed large deflection/sagging in unsupported regions due to gravity, whereas simulation was unable to estimate such deflection. Hence, an analytical model was presented to estimate extrudate deflections and verified with experimental results. Lack of diffusion between beads was observed in the bottom facing surface of unsupported geometry of sintered unit cells as an effect of extrudate sagging in the green part stage. This study proves that MF3 can fabricate fully dense Ti-6Al-4V lattice structures that appear to be a promising candidate for applications where mechanical performance, light-weighting and design customization are required.Originality/valueSupportless printing of lattice structures having tiny cross-sectional areas and unsupported geometries is highly challenging for an extrusion-based additive manufacturing (AM) process. This study investigated the AM of Ti-6Al-4V supportless lattice structures using the MF3 process for the first time.

Visible light photocatalysis promoted by homogenously doped (non-metals) anatase from a chelated titanium precursor

The anion-modified titania finds extensive application in many solar energy-mediated processes. The current study addresses the generation of anatase homogeneously co-doped with carbon and nitrogen with the help of the polyaminocarboxylate backbone of EDTA complexed with titanium. Various physicochemical techniques were used to characterize the sample from the hydrothermally hydrolyzed product of Ti-EDTA. The anatase polymorph formed from this reaction was yellow in color and suggested a defective one. The crystallites had an average size of 12 nm. The tetragonal lattice dimensions showed deviation from the pure anatase, confirming the presence of oxygen vacancies. The electron microscopy experiments demonstrated the homogeneity and its tetragonal symmetry. The XPS analysis confirmed 9.5 and 1.5 % of carbon and nitrogen-doped in the anatase as Ti–O–C/N species. Raman spectrum indicated lattice disorder caused by the co-doping carbon and nitrogen. The oxygen vacancies showed paramagnetic signal in the EPR spectrum both at room temperature and at 77 K. Emission in the blue region in the photoluminescence spectrum confirmed the existence of oxygen vacancies. The sample showed absorption in the entire UV region extending up to the visible region and had an optical bandgap of 2.8 eV. The sample exhibited excellent catalytic activity in the visible light, promoted decolorization of crystal violet, rhodamine 6G dye solutions following pseudo-first-order kinetics. The sample also catalyzed 85 % of bisphenol (BPA) degradation under visible radiation, from which salicylaldehyde was identified as the major product by the GC-MS analysis. The catalyst retained its ability up to three times its reuse without undergoing any structural change. OH● radicals have been identified as the reactive oxidation species (ROS) involved in these experiments with scavenger experiments.

The optical and luminescence properties of Hf-doped ZnSe QDs with multiple emission colors for light emitting devices applications

Here, we report the synthesis of Hf-doped ZnSe QDs at various concentrations of hafnium atoms. The HfxZn1−xSe QDs were prepared using poly-yol approach in the presence of ethyleneglycol as strong capping agent to control the size and morphology to attain high luminescent QDs with tunable colors for light emitting devices. The prepared HfxZn1−xSe QDs were emphasized by XRD and TEM measurements. The incorporating of Hf-atoms in the ZnSe crystal lattice instigated an enlargement of the crystal lattice dimensions as well as the crystallites sizes. The Hf-stoms showed an outstanding ability to modify the width of the ZnSe band gaps, where the bandgap values decreased from 3.3 eV to 2.8 eV. The doping of ZnSe with Hf-atoms showed an enhancement of the luminescent intensity by 4 times and reduction of the emission bandwidth by 5 times. The photoluminescence spectrum showed multiple colors in the visible region with quantum yield reached to 82%. Thus, the narrow bandwidth and intense multicolors may open a new door to use the HfxZn1−xSe QDs for LEDs application.

The aqueous structural speciation of binary thallium-hydroxycarboxylic acid systems. Structure-chemical (bio)reactivity correlations

Among transition and non-transition metals, thallium is a unique case of an element which, despite its known toxicity, provides interesting challenges through its biology and chemistry linked to diagnosis of human pathophysiologies. Poised to investigate in-depth the structural and electronic aspects of thallium involvement in physiological processes, the synthetic exploration of aqueous binary systems of Tl(I) with physiological binders from the family of hydroxycarboxylic acids (glycolic, lactic, mandelic and citric acid) was pursued in a pH-specific fashion. The isolated crystalline coordination polymers, emerging from that effort, were physicochemically characterized through elemental analysis, FT-IR, ESI-MS, 1H-/13C-NMR, and X-ray crystallography. The coordination environment of thallium in each molecular Tl(I) assembly, along with lattice dimensionality (2D3D), reflects the contributions of the ligands, collectively exemplifying interactions probed into though BVS and Hirshfeld surface analysis. The results portray a well-defined solid-state and solution profile for all species investigated, thereby providing the basis for their subsequent selection into in vitro biological studies involving the (patho)physiological cell lines 3T3-L1, Saos-2, C2C12, and MCF-7. Biotoxicity profiles, encompassing cell viability, morphology, and cell growth support clearly a concentration-, time-, and cell tissue-specific behavior for the chosen Tl(I) compounds in a structure-specific fashion. Collectively, the chemical experimental data support the biological results in formulating a structure-specific behavior for Tl(I)-hydroxycarboxylato species with respect to biotoxicity mechanisms in a (patho)physiological environment. The accrued knowledge stands as the foreground for further investigation into the relevant biological chemistry of Tl(I) and molecular technologies targeting its sequestration and removal from cellular media.

Synthesis and photoluminescence properties of Mn2+ doped Ca1-xSrxCN2 phosphors prepared by a carbon nitride based route

Mn2+ doped Ca1-xSrxCN2 phosphors were synthesized by a solid-state reaction in only 1 ​h under NH3 atmosphere at 700 ​°C from doped calcium carbonate and carbon nitride as precursors. The samples were characterized by powder X-ray diffraction, scanning electron microscopy and their diffuse reflectance and luminescence properties were investigated in order to evaluate the potential of such systems as red phosphors. All pure and well-crystallized Mn2+ doped samples exhibit broad red emission around 680 ​nm when excited at 270 ​nm at room temperature corresponding to the 4T1g(4G) →6A1g(6S) transition. Maximum emission in CaCN2: Mn is obtained for Mn2+ content of 4 %mol and is stable up to 343 ​K and then shows a 20% decrease at 393 ​K. Finally, the progressive substitution of Sr2+ for Ca2+ evidences a solid solution domain between CaCN2 and β-SrCN2 with continuous increase of the crystal lattice dimensions. However, such substitution has no impact on the wavelength emission but leads to a decrease of the luminescence efficiency of the phosphor.

Flat-band generator in two dimensions

Dispersionless bands -- \emph{flatbands} -- provide an excellent testbed for novel physical phases due to the fine-tuned character of flatband tight-binding Hamiltonians. The accompanying macroscopic degeneracy makes any perturbation relevant, no matter how small. For short-range hoppings flatbands support compact localized states, which allowed to develop systematic flatband generators in $d=1$ dimension in Phys. Rev. B {\bf 95} 115135 (2017) and Phys. Rev. B {\bf 99} 125129 (2019). Here we extend this generator approach to $d=2$ dimensions. The \emph{shape} of a compact localized state turns into an important additional flatband classifier. This allows us to obtain analytical solutions for classes of $d=2$ flatband networks and to re-classify and re-obtain known ones, such as the checkerboard, kagome, Lieb and Tasaki lattices. Our generator can be straightforwardly generalized to three lattice dimensions as well.

Microstructural and phase evolutions of Pt contact to N-type In0.53Ga0.47As driven by rapid thermal annealing and its correlation with specific contact resistivity

In this study, the microstructural and electrical characteristics of Pt contacts to n-type InGaAs were investigated as a function of rapid thermal annealing (RTA) temperatures in the range of 400–600 °C. RTA at 400 °C was inadequate for ensuring a good reaction between the deposited Pt films with InGaAs, forming only a thin amorphous PtAs2 layer, as evidenced from the high-resolution transmission electron microscope and energy dispersive X-ray spectrometer results. A significant reaction occurred upon RTA at 500 °C, leading to the formation of a PtAs2 phase with most of the Pt being unreactive, but with a reduction in the Pt lattice dimensions. With a smaller atomic radius than Pt, the accommodation of Ga and In atoms in a substitutional solid solution could be responsible for the reduction in the Pt lattice. The reaction between the Pt films and InGaAs after annealing at 600 °C resulted in complete consumption of the Pt films, forming PtIn2, Pt13In9, Pt2Ga3, and Pt5Ga3 phases along with the additional PtAs2 phase as clearly distinguishable layers. The minimum value of specific contact resistivity obtained with RTA at 600 °C could be associated with the metallic PtIn2 in combination with the Pt13In9 alloy embedded in the PtAs2 layer, which serves as a good carrier path.

The Luminescence and optical behavior of Cd1-xWxSe QDs synthesized using microwave assisted hydrothermal approach for bioimaging applications

Semiconducting quantum dots are light-emitting nanocrystals that have been flourished as novel kind of fluorescent label for biomedical diagnostics and biomolecular imaging. In comparison to conventional fluorescence probe, quantum dots have exceptional optoelectronic characteristics, narrow and symmetric emission spectra, size-tunable light emission, and wide absorption spectrum that permit the concurrent excitations of numerous fluorescent colors. Furthermore, quantum dots are substantially bright and have high resistance to photo bleaching compared with fluorescent proteins and organic dye. Here, a new family of quantum dots based on Cd1-xWxSe nanocrystals using microwave assisted hydrothermal route has been developed. The X-ray demonstrated the cubic phase of these nanocrystals and the expansion of their lattice dimensions due to the incorporation of W dopant. The TEM inspected the increase of the sizes of the Cd1-xWxSe QDs from 3.5 nm to 10.8 nm due to the increase of W dopant. The W dopant caused redshift of the absorption spectra and reduction of the bandgap from 2.54 eV to 2.32 eV. The inclusion of W dopant in the CdSe improved the intensity of luminescence emission by 8 times with narrow bandwidth and quantum yield of 89 %. These auspicious properties pave the way to use the Cd1-xWxSe QDs as fluorescent label for biomedical diagnostics and biomolecular imaging.