Triangular Crystals Research Articles

Real-Time Observation for MoS2 Growth Kinetics and Mechanism Promoted by the Na Droplet.

While the molten salt-catalyzed chemical vapor deposition (CVD) technique is recognized for its effectiveness in producing large-area transition metal chalcogenides, understanding their growth mechanisms involving alkali metals remains a challenge. Here, we investigate the kinetics and mechanism of sodium-catalyzed molybdenum disulfide (MoS2) growth and etching through image analysis conducted using an integrated CVD microscope. Sodium droplets, agglomerated via the thermal decomposition of the sodium cholate dispersant, catalyze the precipitation of supersaturated MoS2 laminates and induce growth despite fragmentation during this process. Triangular MoS2 crystals display a distinct self-exhausting exponential behavior and slow growth of thermodynamically favorable crystallographic faces, exhibiting a sulfur-dominant pressure. The growth and etching processes are facilitated by the scooting of sodium droplets along grain edges, displaying comparable rates. Leveraging these kinetics makes it possible to engineer atypical MoS2 shapes. This combined microscope not only enhances the understanding of growth mechanisms but also contributes to the facile development of next-generation nanomaterials.

Random close packing of semi-flexible polymers in two dimensions: Emergence of local and global order.

Through extensive Monte Carlo simulations, we systematically study the effect of chain stiffness on the packing ability of linear polymers composed of hard spheres in extremely confined monolayers, corresponding effectively to 2D films. First, we explore the limit of random close packing as a function of the equilibrium bending angle and then quantify the local and global order by the degree of crystallinity and the nematic or tetratic orientational order parameter, respectively. A multi-scale wealth of structural behavior is observed, which is inherently absent in the case of athermal individual monomers and is surprisingly richer than its 3D counterpart under bulk conditions. As a general trend, an isotropic to nematic transition is observed at sufficiently high surface coverages, which is followed by the establishment of the tetratic state, which in turn marks the onset of the random close packing. For chains with right-angle bonds, the incompatibility of the imposed bending angle with the neighbor geometry of the triangular crystal leads to a singular intra- and inter-polymer tiling pattern made of squares and triangles with optimal local filling at high surface concentrations. The present study could serve as a first step toward the design of hard colloidal polymers with a tunable structural behavior for 2D applications.

In-plane radiation pattern generated by large particles in dielectric substrates

In this work we present the study of in-plane radiation patterns generated by particles with dimensions larger than the excitation wavelength. We studied the in-plane radiation of Au structures focusing on two cases: particles and triangular crystals. We found that the radiation patterns were produced by the scattering of the excitation field at the bottom edges of the studied structures. In addition, we found the in-plane radiation decay exponentially due to the refractive index contrast between the substrate and superstate. Furthermore, we proved that in-plane radiation patterns originating from different structures can interact and generate interesting geometries. Finally, in addition to our experimental studies, we show numerically calculated simulations which agreed with our experimental results and thus confirmed our findings.

Field-induced transformation between triangular and square skyrmion crystals in a tetragonal polar magnet

Field-induced transformation between triangular and square skyrmion crystals in a tetragonal polar magnet

In situ study of microstructural evolution of borosilicate glass–sulfate mixture at high temperatures

AbstractMicrostructural evolution of borosilicate glass–sulfate (BaSO4 or Na2SO4) mixture was observed in situ using a high‐temperature confocal scanning laser microscope. The phase compositions and sulfate retention of the mixture at different temperatures were also examined. The results indicate that for the glass–BaSO4 sample (abbreviated as BS), the borosilicate glass begins to melt at about 900°C, and the triangular BaSO4 crystals grow obviously between 900°C and 1100°C. At temperatures above 1100°C, the BaSO4 crystals gradually melt and decompose. For the glass–Na2SO4 sample (abbreviated as NS), strip‐shaped BaSO4 crystals begin to form at about 820°C after the borosilicate glass melting, and then gradually melt with further increasing temperature. When the temperature increases to 1000°C, the upper layer of the NS sample possesses Na2SO4, LiNaSO4, and BaSO4 phases, while the lower layer possesses an amorphous phase. Moreover, the SO3 retention in the BS sample remains almost unchanged with temperature increases from 900°C to 1100°C, and then decreases with further increasing temperature. The SO3 retention retained in the NS sample decreases rapidly at temperatures above 900°C. These findings can provide a guidance for vitrifying sulfur‐rich high‐level liquid waste.

Controlling the Crystal Growth of DNA Molecules via Strategic Chemical Modifications.

Intermolecular interactions are critical to the crystallization of biomolecules, yet the precise control of biomolecular crystal growth based on these interactions remains elusive. To understand the connections between the crystallization kinetics and the strength of intermolecular interactions, herein we have employed DNA triangular crystals and modified ones as a versatile tool to investigate how the strength of intermolecular interaction affects crystal growth. Interestingly, we have found that the 2'-O-methylation at sticky ends of the DNA triangle could strengthen its intermolecular interaction, resulting in the accelerated formation of smaller crystals. Conversely, phosphorothioate modification could weaken the sticky-end cohesion and delay the nucleation, resulting in formation of fewer but larger crystals. In addition, these modification effects were consistently observed in the crystallization of a DNA decamer. In one word, our experimental results demonstrate that the strength of intermolecular interaction directly impacts crystal growth. It suggests that 2'-O-methylation and phosphorothioate modification represents a rational strategy for controlling DNA molecules grow into desired crystals and it also facilitates structural determination.

Magnetodielectric Effect in a Triangular Dysprosium Single-Molecule Toroics.

Single-molecule toroics are molecular magnets with vortex distribution of magnetic moments. The coupling between magnetic and electric properties such as the magnetodielectric effect will provide potential applications for them. Herein, the observation of significant magnetodielectric effect in a triangular Dy3 crystal with toroidal magnetic moment and multiple magnetic relaxations is reported. The analysis of magnetic and electric properties implies that the magnetodielectric effect is closely related to the strong spin-lattice coupling, magnetic interactions of Dy3+ ions, as well as molecular packing models.

Identification of triangular single crystals of transition metal dichalcogenides based on the detection algorithm.

The distinctive properties and facile integration of 2D materials hold the potential to offer promising avenues for the on-chip photonic devices, and the expeditious and nondestructive identification and localization of diverse fundamental building blocks become key prerequisites. Here, we present a methodology grounded in digital image processing and deep learning, which effectively achieves the detection and precise localization of four monolayer-thick triangular single crystals of transition metal dichalcogenides with the mean average precision above 90%, and the approach demonstrates robust recognition capabilities across varied imaging conditions encompassing both white light and monochromatic light. This stands poised to serve as a potent data-driven tool enhancing the characterizing efficiency and holds the potential to expedite research initiatives and applications founded on the utilization of 2D materials.

Mechanical vibration absorber for flexural wave attenuation in multi-materials metastructure

Vibration isolation is a promise to suppress mechanical vibration from a host structure, similarly, a mechanical vibration absorber, a simple but effective device to attenuate flexural wave propagation, which has been implemented in civil and mechanical engineering. This paper presents a type of composite sandwich phononic crystal to attenuate the flexural wave propagation in a beam structure, which can effectively suppress mechanical vibration in a broad band gap by repetitively arranging phononic crystal. First, the elastic wave dispersion characteristic in a composite sandwich beam structure is derived, and a triangular shape phononic crystal for flexural wave attenuation by taking advantage of destructive interference is presented. Then two dimensional phononic crystals are designed by assembling four different unit-cells of metabeam. Finally, numerical experiments are conducted to verify the effectiveness of the proposed mechanical metamaterial absorbers to attenuate flexural wave propagation, the numerical results indicate that the proposed metamaterial is of good performance in mechanical vibration suppression, which can effectively mitigate structure vibration in low-frequency domain than the structure without phononic crystal and single layer metamaterial beam structure. It is the first attempt to design a mechanical metamaterial absorber with the mechanism of destructive interference with composite sandwich phononic crystal.

Magnetic properties and magnetocaloric effect of a metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal

We report the synthesis, magnetic susceptibility, magnetization, electrical resistivity, heat capacity, and magnetocaloric properties of the metallic triangular lattice antiferromagnetic DyAl2Ge2 single crystal. High-quality rare-earth intermetallic compound DyAl2Ge2 single crystals were synthesized by the metallic flux method. DyAl2Ge2 crystallizes in a trigonal CaAl2Si2-type structure with Dy atoms forming a triangular lattice in the ab plane. The paramagnetic-antiferromagnetic transition occurs at 8 K, as determined by temperature dependencies of magnetic susceptibility and heat capacity. No observable hysteresis was found in the field-induced antiferromagnetic to the ferromagnetic metamagnetic transition of DyAl2Ge2. The electrical resistivity shows an overall metallic behavior with an upturn at the ordering temperature. For a magnetic field change of 0–70 kOe, the maximum magnetic-entropy change is −14.2 J kg−1 K−1 at 11 K and the relative cooling power is 327 J kg−1 with the applied magnetic field along the ab plane.

Molybdenum Disulfide Nanoribbons with Enhanced Edge Nonlinear Response and Photoresponsivity.

MoS2 nanoribbons have attracted increased interest due to their properties, which can be tailored by tuning their dimensions. Herein, the growth of MoS2 nanoribbons and triangular crystals formed by the reaction between films of MoOx (2<x<3)grown by pulsed laser deposition and NaF in a sulfur-rich environment is demonstrated. The nanoribbons can reach up to 10µm in length, and feature single-layeredges, forming a monolayer-multilayer junction enabled by the lateral modulation in thickness. The single-layer edges show a pronounced second harmonic generation due to the symmetry breaking, in contrast to the centrosymmetric multilayer structure, which is unsusceptible to the second-order nonlinear process. A splitting of the Raman spectra is observed in MoS2 nanoribbons arising from distinct contributions from the single-layer edges and multilayer core. Nanoscale imaging reveals a blue-shifted exciton emission of the monolayer edge compared to the isolated MoS2 monolayers due to built-in local strain and disorder. Wefurther report on an ultrasensitive photodetector made of a single MoS2 nanoribbon with a responsivity of 8.72×102 AW-1 at 532nm, among the highest reported up-to-date for single-nanoribbon photodetectors. These findings can inspire the design of MoS2 semiconductors with tunable geometries for efficient optoelectronic devices.

Fine-tuning of colloidal polymer crystals by molecular simulation.

Through extensive molecular simulations we determine a phase diagram of attractive, fully flexible polymer chains in two and three dimensions. A rich collection of distinct crystal morphologies appear, which can be finely tuned through the range of attraction. In three dimensions these include the face-centered cubic, hexagonal close packed, simple hexagonal, and body-centered cubic crystals and the Frank-Kasper phase. In two dimensions the dominant structures are the triangular and square crystals. A simple geometric model is proposed, based on the concept of cumulative neighbors of ideal crystals, which can accurately predict most of the observed structures and the corresponding transitions. The attraction range can thus be considered as an adjustable parameter for the design of colloidal polymer crystals with tailored morphologies.

Skyrmion crystal phases in Kondo lattice model on triangular lattices

Very often the magnetic skyrmions (topologically protected spin textures) form a triangular crystal in chiral magnets. Here we study the effect of itinerant electrons on the structure of skyrmion crystal (SkX) on triangular lattice using Kondo lattice model in the large coupling limit and treating the localized spins as classical vectors. To simulate the system, we employ hybrid Markov Chain Monte Carlo method (hMCMC) which includes electron diagonalization in each MCMC update for classical spins. We present the low-temperature results for system at electron density which show a sudden jump in skyrmion number reducing the size of the skyrmions when we increase the hopping strength of the itinerant electrons. We find that this high skyrmion number SkX phase is stabilized by a combined effect: lowering of density of states at electron filling and also pushing the bottom energy states further down. We show that these results hold for larger system using traveling cluster variation of hMCMC. We expect that itinerant triangular magnets might exhibit the possible transition between low-density to high-density SkX phases by applying external pressure.

Structure evolution of amorphous poly(d-lactic acid) on highly oriented poly(l-lactic acid) film during annealing

Stereocomplex (SC) of poly(lactide)s (PLAs) has attracted much attention owing to its superior properties, and thus been extensively studied for the poly(d-lactide)/poly(l-lactide) (PDLA/PLLA) blend through solution, melt and cold crystallizations. In this work, the structure evolution of layered samples containing an amorphous PDLA layer and a crystalline PLLA layer with highly oriented edge-on α lamellar crystals during annealing at 175 °C has been studied by AFM, electron diffraction and FTIR techniques. It has been found that edge-on PDLA lamellar crystals and both PLA SC edge-on lamellar crystals and flat-on single crystals in shapes of triangular (preferentially) and hexagonal (less pronounced) can form during annealing. The edge-on PDLA and PLA SC lamellar crystals are highly oriented with molecular chains of both PDLA and PLLA parallel to the chain direction of the used PLLA substrate, reflecting the growth of them take place on the crystalline regions of the PLLA substrate. On the other hand, the random orientation of the triangular flat-on SC single crystals with respect to the used PLLA substrate suggests that the growth of them have nothing to do with the oriented PLLA substrate. It is thus conjectured that the formation of SC single crystals is most likely started in the amorphous regions at places with rich loosely folded loops, chain ends, and even free standing random coils of the used PLLA substrate film.

Phonons of electronic crystals in two‐dimensional semiconductor moiré patterns

AbstractWe theoretically studied the phonon properties of the triangular‐, stripe‐, and honeycomb‐type electronic crystals recently found in two‐dimensional semiconductor moiré patterns. By analyzing the phonon dispersions, we found the interaction induced lattice deformation in the zigzag‐stripe crystal results in a much higher dynamical stability than in the linear‐stripe crystal. Moreover, chiral phonons with finite magnetizations and large Berry curvatures can emerge in triangular and honeycomb crystals under time‐reversal or inversion symmetry breaking. The small effective mass of the electrons allows the selective and efficient generation of chiral phonons from the optical activity of zone‐center phonons combined with the anharmonicity, facilitating the realization of the phonon Hall effect. These findings point to an exciting new platform for exploring chiral phonons and related topological phononic devices.Key points The phonons of the electronic crystals in semiconductor moiré systems are systematically analyzed, which can lead to the infrared absorption, Raman scattering, and Hall effect of chiral phonons. The small effective mass of the electrons as compared to their ionic counterparts facilitates tuning the chiral phonons through external fields, which may stimulate further studies about elementary excitations of the intriguing correlated insulators in moiré systems. Our study connects the two active research fields of strongly correlated physics and chiral phonons.

Densest packing of flexible polymers in 2D films.

How dense objects, particles, atoms, and molecules can be packed is intimately related to the properties of the corresponding hosts and macrosystems. We present results from extensive Monte Carlo simulations on maximally compressed packings of linear, freely jointed chains of tangent hard spheres of uniform size in films whose thickness is equal to the monomer diameter. We demonstrate that fully flexible chains of hard spheres can be packed as efficiently as monomeric analogs, within a statistical tolerance of less than 1%. The resulting ordered polymer morphology corresponds to an almost perfect hexagonal triangular (TRI) crystal of the p6m wallpaper group, whose sites are occupied by the chain monomers. The Flory scaling exponent, which corresponds to the maximally dense polymer packing in 2D, has a value of ν = 0.62, which lies between the limits of 0.50 (compact and collapsed state) and 0.75 (self-avoiding random walk).

Effect of Cooling Rate on the Crystalline Morphology of Bi2O3‐Fe2O3 Pseudo‐Binary System

Herein, the crystallographic morphology of the 80%Bi2O3‐20%Fe2O3 pseudo‐binary system under different cooling rates (100, 6.3, 0.12 K s−1) is investigated using an optical microscopy system. The interfacial morphology evolution and interfacial kinetics in two dimensions during crystal growth are systematically studied. At the low cooling rate (ΔT &lt; 10 K), blade‐like crystals appear slowly in the melt. In turn, the emergence of numerous irregularly shaped grains in the melt at the high cooling rate (ΔT &gt; 100 K) indicates a rapid solidification process. Tetragonal crystals appear typically during melt solidification accompanied with triangular crystals simultaneously (15 K &lt; ΔT &lt; 35 K). The X‐ray diffraction and EDS data reveal that both kinds of polygonal crystals are attributed to Bi25FeO40. In addition, the crystal growth kinetics are presented as the dependence of the growth rate on the subcooling, and thus the growth mechanism of crystals is discussed. According to the results, Bi25FeO40 crystals grow through a two‐dimensional nucleation mechanism.

Study of morphology and magnetism of MnFe2O4–SiO2 composites

Mixed magnetic composites of manganese ferrite and cristobalite (MnFe2O4–SiO2) were produced by the solid-state reaction method, using as starting materials in natura ores found in the state of Rio Grande do Norte – Brazil. Based on the stoichiometric proportions of the precursor ores, various composites in the form of powders and pellets were synthesized at a temperature of 1200 °C/12h under ambient atmosphere. Samples in the form of pellets were made at compression pressures of 370 and 740 MPa to investigate the effect of pressure on the physicochemical, and dielectric properties of the material. Structural, morphological and magnetic analyses were studied for the series of samples. X-ray diffractogram (XRD) results confirmed the formation of the mixed spinel phase MnFe2O4 with cubic symmetry and space group Fd-3m:1, together with peaks corresponding to SiO2–cristobalite. The Rietveld refinements identified a predominance of about 90% of the MnFe2O4 phase with crystallite variations of 130–190 nm due to the effect of compaction pressure. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electronic microscopy (TEM) mappings show clusters of triangular crystals in the pellets series. Magnetic hysteresis cycles at room temperature show a fast magnetization saturation (MS) response in a field of ∼4 kOe, with parameters dependent on the size and shape of the crystallites. The magnetically soft ferrites exhibited very low coercive field values. The hysteretic curves measured at 5 K showed a significant gain in the MS of ∼30 emu/g. Analyzes of magnetization as a function of temperature identified a blocked regime with a maximum ∼97 K (powder) and ∼170 K (pellets), and an irreversibility of the ZFC–FC curves up to room temperature. An indication of a spin-glass (SG) like state close to 20 K can also be seen in these results. Dielectric characterization of the pellets was performed from 1.0 to 8.5 GHz, and presented well-defined behavior, where real permittivity can be highly related to Rietveld refinement of XRD, and SEM/EDS results. This research suggests the feasibility of producing manganese ferrite composites directly from minerals, without the use of high-purity chemical reagents, allowing their obtainment on a large scale for commercial use.

Nucleation and growth mechanism for atomic layer deposition of Al2O3 on two-dimensional WS2 monolayer

Nanoelectronics holds significant promise for two-dimensional (2D) semiconducting transition metal dichalcogenide (TMD) applications. On a polycrystalline WS2 monolayer created by metal-organic chemical vapor deposition (MOCVD) at 950 °C, we studied the nucleation, growth, and development of Al2O3 atomic layer deposition (ALD) on a SiO2/Si substrate. In this investigation, we used various complementary characterization methods, such as Raman spectroscopy, elastic recoil detection, atomic force microscopy, and time-of-flight secondary ion mass spectrometry, to understand thoroughly the intrinsic reactivity of WS2. Strong peak intensity changes at the interfaces in the Raman line scans of the SiO2/Si patterns suggest extremely crystalline WS2. After multiple ALD cycles, triangular WS2 crystals were decorated to provide a two-dimensional growth mode with a great selectivity for grain boundaries and step edges. The results of this work can be used for further exploration of the TMD monolayer structure and properties, which is essential for tailoring 2D materials for a specific application in devices.

Structural Optimization of Graphene Triangular Lattice Phononic Crystal Based on Dissipation Dilution Theory.

Nanomechanical resonators offer brilliant mass and force sensitivity applied in many fields, owing to a low mass m and high-quality factor Q. However, in vibrating process, resonant energy is inevitably dissipated. Typically, quality factor does not surpass the inverse of the material loss angle φ. Recently, some exceptions emerged in the use of highly stressed silicon nitride material. As yet, it is interpreted that the pre-stress seems to “dilute” the intrinsic energy dissipation according to the Zener model. Is there any other material that could further break the 1/φ limit and achieve higher quality factors? In our previous research, through theoretical calculation and finite element simulation, we have proved that graphene’s quality factor is two orders of magnitude larger than silicon nitride, on account of the extremely thin thickness of graphene. Based on this, we further optimize the structure of phononic crystals to achieve higher quality factors, in terms of duty cycle and cell size. Through simulation analysis, the quality factor could improve with a larger duty cycle and bigger cell size of triangular lattice phononic crystal. Unexpectedly, the Q amplification coefficient of the 3 × 5-cell structure, which is the least number to compose a phononic crystal with a central defect area, is the highest. In contrast, the minimal cell-number structure in hexagonal lattice could not achieve the brilliant dissipation dilution effect as well as the triangular one. Then we consider how overall size and stress influence quality factor and, furthermore, compare theoretical calculation and finite simulation. Lastly, we start from the primitive 3 × 5 cells, constantly adding cells to the periphery. Through simulation, to our surprise, the largest Q amplification coefficient does not belong to the largest structure, instead originating from the moderate one consisting of 7 × 13 cells.