Stacking Arrangements Research Articles

Enhancing Near-Infrared Photothermal Performance by Molecular Aggregation Optimization in Semiconductive Coordination Polymers.

Near-infrared (NIR) photothermal conversion materials have recently received widespread attention due to their potential in diverse applications. However, highly efficient organic-based NIR photothermal agents remain limited. Developing strategies to enhance the efficiency of NIR photothermal materials and elucidating the relationship between the NIR photothermal performance and molecular aggregation are highly desired. Herein, we report two coordination polymers {[Cd2(ONDI)(ox)]·2/3(H2O)}n (1) and [Ba(ONDI)(H2O)2]n (2), in which the ONDI2- ligands assemble into different π-π stacking arrangements. Compound 1 exhibits H-aggregation, while compound 2 displays X-aggregation. The X-aggregation in compound 2 extends the optical absorption into the NIR region and enhances the absorption intensity. Consequently, compound 2 demonstrates a 1.8-fold increase in NIR photothermal efficiency (68.6%) compared to compound 1 (38.8%), attributed to more effective π-π interactions in X-aggregation. In addition, both compounds show semiconductive properties, with conductivities of 2.1 × 10-7 S/cm for compound 1 and 3.0 × 10-7 S/cm for compound 2 at 30 °C in a nitrogen atmosphere. These properties arise from the synergistic effects of "band-like" charge transport within crystals and "hopping" charge transport across grain boundaries. By integration of their NIR photothermal effects and semiconductive properties, compounds 1 and 2 show interesting NIR photoelectrical responses.

Water-Driven Stacking Structure Transformation of Ultrathin Ru Nanosheets for Efficient Hydrogen Evolution Reaction.

Ultrathin crystalline materials are a class of popular materials that can potentially exhibit fascinating physical and chemical properties dictated by their unique stacking freedom. However, it is challenging to achieve the controllable synthesis over their stacking structure for ultrathin crystalline materials. Herein, water is employed as a key regulatory factor to realize phase engineering in ultrathin nanosheets (NSs), thereby altering stacking faults to achieve distinct stacking arrangements. Ruthenium (Ru) NSs with consistent specific surface areas but different stacking manners are fabricated through the systematic regulation of water. Based on this, it is demonstrated that the hydrogen evolution reaction (HER) performance can be significantly influenced by their stacking structures. Further in-depth investigations reveal that the distinct stacking structures of Ru NSs, featuring a limited area of side facets, will influence the energy barrier of sluggish Volmer step in HER. Ru NSs with ABC stacking exhibit an accelerated Volmer process with outstanding catalytic activity, demonstrating a remarkably low overpotential (25mV at 10mAcm-2) and Tafel slope (29mVdec-1) than most of the reported HER catalysts. The work will advance the understanding of controllable synthesis methods and illuminate the structure-activity relationships in ultrathin crystalline nanomaterials.

Investigation of Temperature at Al/Glass Fiber-Reinforced Polymer Interfaces When Drilling Composites of Different Stacking Arrangements

This attempt covers an investigation of cutting temperature at interfaces of Fiber Metal Laminates (FMLs) made of glass fiber-reinforced polymer (GFRP) stacked with an Al2020 alloy. GFRP/Al/GFRP and Al/GFRP/Al composite stacks are both investigated to highlight the effect of stacking arrangement on thermal behavior within the interfaces. In a first test series, temperature history is recorded within the metal/composite stack interfaces using preinstalled thermocouples. In a second test series, a wireless telemetry system connected to K-type thermocouples implanted adjacent to the cutting edge of the solid carbide drill is used to record temperature evolution at the tool tip. Focus is put on the effects of cutting speed and stacking arrangement on the thrust force, drilling temperature, and delamination. From findings, the temperature histories show high sensitivity to the cutting speed. When cutting Al/GFRP/Al, the peak temperature is found to be much higher than that recorded in GFRP/Al/GFRP and exceeds the glass transition point of the GFRP matrix under critical cutting speeds. However, thrust force obtained at constitutive phases exhibits close magnitude when the stacking arrangement varies, regardless of cutting speed. Damage analysis is also discussed through the delamination factor at different stages of FML thickness.

Effect of interlayer stacking arrangement on the dielectric properties of hexagonal boron nitride thin films

Electrostatic properties of hexagonal boron nitride (hBN) thin films with different stacking arrangements were investigated using density functional theory combined with the effective screening medium method. Our calculations showed that the dielectric properties across layers of hBN thin films are sensitive to both the interlayer stacking arrangement and the number of layers. The polarization of bilayer hBN gradually decreases with increasing lateral displacement from AB stacking, and polarity inversion occurs for particular stacking arrangements. The polarity of bilayer hBN is sensitive to twisting displacement. The polarity monotonically increases with increasing the number of layers in hBN films with rhombohedral stacking arrangement.

Improvement of Perovskite Solar Cells Efficiency by Management of the Electron Withdrawing Groups in Hole Transport Materials: Theoretical Calculation and Experimental Verification.

Management of functional groups in hole transporting materials (HTMs) is a feasible strategy to improve perovskite solar cells (PSCs) efficiency. Therefore, starting from the carbazole-diphenylamine-based JY7 molecule, JY8 and JY9 molecules are incorporated into the different electron-withdrawing groups of fluorine and cyano groups on the side chains. The theoretical results reveal that the introduction of electron-withdrawing groups of JY8 and JY9 can improve these highest occupied molecular orbital(HOMO)energy levels, intermolecular stacking arrangements, and stronger interface adsorption on the perovskite. Especially, the results of molecular dynamics (MD) indicate that the fluorinated JY8 molecule can yield a preferred surface orientation, which exhibits stronger interface adsorption on the perovskite. To validate the computational model, the JY7-JY9 are synthesized and assembled into PSC devices. Experimental results confirm that the HTMs of JY8 exhibit outstanding performance, such as high hole mobility, low defect density, and efficient hole extraction. Consequently, the PSC devices based on JY8 achieve a higher PCE than those of JY7 and JY9. This work highlights the management of the electron-withdrawing groups in HTMs to realize the goal of designing HTMs for the improvement of PSC efficiency.

Electromagnetic and thermal performance study on a canted stack of REBCO tapes

Abstract Due to the critical current limitation of a single REBCO tape, stacking methods are generally employed to increase the current carrying capacity in practical high-temperature superconducting (HTS) applications. However, the overall critical current is strongly dependent on the self-magnetic field, which is influenced by the geometrical arrangement of conductors in the stack. Due to the brittle ceramic property, REBCO tapes are conventionally bent along the thickness side of the tape. However, the difference in bending radii of the outer and inner tape surfaces in the stack may lead to fracture deformation, thereby limiting the stacking number of REBCO tapes. To balance the stacking number with the bending issue, canted stack is proposed as a variant of normal stack for REBCO tapes. As a potential HTS intermediate component, it is imperative to conduct a comprehensive study on electromagnetic and thermal performance of canted stack. The unique geometrical arrangement of canted stack introduces new factors that affect critical current and transport AC loss. This paper concludes the special influencing factors of canted stack, including canted angle, stacking number, tape width, and spatial structure. The metal interleaving method is introduced for spatial distribution changing and thermal stability. Furthermore, orthogonal analysis is performed to elucidate the comprehensive correlation among these multiple factors. This study provides insights into the overall critical current and transport AC loss for different combinations of canted stack and establishes a predicting function for critical current to support the structural design of canted stack. Based on the specific case study, the improvement effect of canted stack is confirmed by both experiments and simulations.

Hesperetin–4,4′-bipyridine cocrystal: Polymorphism, crystal structures, and thermodynamic relationship

The investigation of cocrystal polymorphism remains relatively limited compared to that of single-component crystals. This study focuses on the cocrystallization of hesperetin (HES), a typical flavonoid substance, with 4,4′-bipyridine (BPY), resulting in the formation of two distinct 1:1 cocrystal phases. Single crystal X-ray diffraction analysis reveals that the O—H···N hydrogen interaction serves as the hetero-synthon of the cocrystals, driving the formation of featured 1D molecular chains in both structures. The presence of rotatable C—C bonds in both HES and BPY introduces the possibility of the molecular conformational variations, contributing to differing molecular stacking arrangements between the two structures. Thermal analysis, solvent-mediated polymorphic transformation, and theoretical calculations confirm a monotropic relationship between the two cocrystals.

Exploring interlayer coupling in the twisted bilayer PtTe2

We have investigated interlayer interactions in the bilayer PtTe2 system, which influence the electronic energy bands near the Fermi level. Our diffusion Monte Carlo (DMC) calculations for the high-symmetry bilayer stackings (AA, AB, AC) manifest distinct interlayer binding characteristics among the stacking modes by revealing significantly different interlayer separations depending on the stacking, which is critical to understanding the interlayer coupling of the twisted bilayers consisting of various local stacking arrangements. Furthermore, a comparison between the interlayer separations obtained from DMC and density functional theory (DFT) shows that meta-generalized gradient approximation (GGA)-based van der Waals–DFT results agree with DMC for different layer stackings, including twisted bilayers, but only the ground-state AA stacking matches well with GGA-based DFT predictions. This underscores the importance of accurate exchange-correlation potentials even for capturing the stacking-dependent interlayer binding properties. We further show that the variability in DFT-predicted interlayer separations is responsible for the large discrepancy of band structures in the 21.79∘ twisted bilayer PtTe2, affecting its classification as metallic or insulating. These results demonstrate the importance of obtaining a correct description of stacking-dependent interlayer coupling in modeling delicate bilayer systems at finite twists. Published by the American Physical Society 2024

Hydrogen production and spin-orbit interaction in blue phosphorene and janus transition metal dichalcogenides vdw heterostructures: A first-principles study

Accumulating lamination of weak attractive interactions is a crucial process for strategically altering the physical features of materials, which is an essential step in crafting cutting-edge functional electronic applications. In this study, we explore the electronic, Rashba spin splitting, optical, and photocatalytic properties of novel vdW heterostructure comprising blue phosphorene (P(blue)) and Janus monolayers (JTMDCs) like JMXY (Mo, W/X = S, Se; Y = Te) using first-principles calculations. We study two different stacking arrangements as Model-I and Model-II, which arise from the alternating order of chalcogen atoms at opposite surfaces in the Janus monolayer. AIMD simulations confirm the geometric stability of P(blue)-JMXY heterostructures at room temperature. All the investigated vdW heterostructures exhibit indirect bandgap and both models have Type-II band alignment calculated by weighted band alignment. Rashba spin splitting is observed in P(blue)-JMXY heterostructures, where Bader charge and work function analyses show that JMXY donates electrons to P(blue). Moreover imaginary part of the dielectric ε2(ω) function indicates that excitons predominantly govern energy conversions in visible and infrared regions. Furthermore, the promising photocatalytic activity of P(blue)-JMXY vdW heterostructures for water splitting under acidic conditions (pH=0) is demonstrated, with Model-I P(blue)-JMoSeTe and P(blue)-JWSeTe, as well as Model-II P(blue)-JMoSTe and P(blue)-JWSeTe vdW heterostructures being particularly noteworthy.

Structural features of neat 5-hydroxymethylfurfural (HMF) in the liquid state

Here we investigate the local structural organization in liquid neat 5-hydroxymethylfurfural (HMF) by the synergic use of high energy X-ray scattering, NMR spectroscopy and molecular dynamics simulations, providing atomistic insight into the correlations that characterise HMF liquid state.HMF has been acknowledged as one of the “sleeping giants” among those renewable compounds, with yet underexploited market potential. It can be obtained from renewable carbohydrate sources via a few consecutive steps and, due to its different functional groups, it can be potentially transformed into a plethora of compounds.An adequate knowledge of the driving interactions into its liquid state can be of fundamental relevance in individuating successful solvents, where HMF can be dissolved, extracted and treated to deliver new compounds. As such, this study has then the potential to provide new, sustainable routes in HMF manipulation, alternatively to current methods.The X-ray scattering validated MD study reveals the existence of a distinct π–π stacking arrangement, characterising the mutual ordering between neighbour HMF molecules. Further correlations involve hydrogen bonding between aldehyde and hydroxyl oxygen and hydroxyl hydrogen. Furthermore, indication of the existence of OH···π hydrogen bonding interaction has been detected.An NMR strategy has been applied to confirm the existence of these mutual interactions, identifying the associated structural motifs.These findings underscore the complex and heterogeneous nature of the structural organization of liquid HMF.

Stacking effects on dynamic mechanical behavior of bilayer hexagonal boron nitride under impact

Hexagonal boron nitride (h-BN) is a promising material for ballistic armor due to its excellent mechanical properties, enriched by different bilayer stacking arrangements. Molecular dynamics methods are used to study the stacking effects on the static and dynamic mechanical properties of bilayer h-BN. The AB (nitrogen) stacked bilayer structure attracts our attention because of its superior interlayer synergistic ability to resist projectile indentation up to a maximum force of 152.89 nN, which is about 22.9 % higher than the average value of other stacked bilayers. The impact response of bilayer h-BN with AB (nitrogen) stacking arrangement is then investigated at velocities of 2–4 km/s, which has the highest critical perforation velocity of 3.075 km/s, increased by 36.7 % compared to monolayer h-BN. At a low impact velocity of 2.5 km/s, the AB (nitrogen) stacked h-BN bilayer spends the shortest time to dissipate the impact energy of projectile and remains intact, while the top layers of other stacked bilayers are penetrated. At high impact velocities, a perforation event occurs, accompanied by multiple deflections of crack tips from zigzag to armchair to zigzag again, which intrinsically enhances the toughness of material. This study provides more understanding of the dynamic mechanical behavior of bilayer h-BN, as well as the design of armor structures based on stacking arrangements of 2D materials.

Electronic and thermal properties of Nb2CCl2 MXenes

The molten salt synthesis has recently opened up new opportunities to functionalize two-dimensional MXenes with uniform halogen terminations. In this work, we synthesize Nb2CCl2 MXenes by etching the Al layer from the Nb2AlC precursor in the melt of CuCl2 Lewis acid. In Cl-terminated MXenes, intercalation of water is negligible, so that MXenes get closer to ideal, ordered van der Waals solids. We identify the preferential atomic stacking arrangement, which is of the AB type, as opposed to the AA stack assumed in previous works. We combine X-ray absorption near edge spectroscopy with density functional theory to clarify the local chemical environment of Cl atoms. Using vibrating sample magnetometry and specific heat measurements, we confirm that Nb2CCl2 MXenes are superconducting with a transition temperature of 6.0 K and find a Debye temperature of 320 K. We further show that the transition temperature slightly decreases with applied isostatic pressure.

Directional and Orderly Arranged Ni0.9Mn0.1(OH)2 Enables the Synthesis of Single-Crystal Ni-Rich Co-Free LiNi0.9Mn0.1O2 with Enhanced Internal Structural Stability.

In this paper, the effect of the structure characteristics of the precursor on the electrochemical properties of a single-crystal cobalt-free high-nickel LiNi0.9Mn0.1O2 cathode is systematically studied. Precursors with different morphologies are synthesized by adjusting the coprecipitation reaction conditions. The results of SEM and XRD show that with the increase in the orderly stacking arrangement of internal primary nanosheets of Ni0.9Mn0.1(OH)2, the exposed active {010} planes at the surface increase. The prepared cathode materials finally inherit the structural features of the precursor, and the single-crystal Co-free Ni-rich LiNi0.9Mn0.1O2 cathode with highly exposed active {010} planes shows a well-ordered crystal structure and low Li+/Ni2+ cation mixing. The characterization results reveal that the high percentage of {010} planes will improve the Li+ transportation kinetics, decrease electrochemical impedance, and significantly alleviate the accumulation of rock-salt phases. Therefore, the material with this structure shows good electrochemical performance.

Theoretical Perspective of Enhancing Order in n-Doped Thermoelectric Polymers through Side Chain Engineering: The Interplay of Counterion-Backbone Interaction and Side Chain Steric Hindrance.

Donor-acceptor (D-A) copolymers doped with n-type dopants are widely sought after for their potential in organic thermoelectric devices. However, the existing structural disorder significantly hampers their charge transport and thermoelectric performance. In this Letter, we propose a mechanism to mitigate this disorder through side chain engineering. Utilizing molecular dynamics simulations, we demonstrate that strong Coulomb interactions between counterions and charged polymer backbones induce a transition in the stacking arrangement of the polymer backbones from a slipped to a vertical configuration. However, the presence of side chain steric hindrance impedes the formation of closely packed and ordered vertical stacking arrangements, resulting in greater distances between adjacent backbones and a higher level of structural disorder in the doped films. Therefore, we propose minimizing side chain steric hindrance to enhance the structural order in doped films. Our findings provide essential insights for advancing high-performance thermoelectric polymers.

Control of Polar/Antipolar Layered Organic Semiconductors by the Odd-Even Effect of Alkyl Chain.

Some rodlike organic molecules exhibit exceptionally high layered crystallinity when composed of a link between π-conjugated backbone (head) and alkyl chain (tail). These molecules are aligned side-by-side unidirectionally to form self-organized polar monomolecular layers, providing promising 2D materials and devices. However, their interlayer stacking arrangements have never been tunable, preventing the unidirectional arrangements of molecules in whole crystals. Here, it is demonstrated that polar/antipolar interlayer stacking can be systematically controlled by the alkyl carbon number n, when the molecules are designed to involve effectively weakened head-to-head affinity. They exhibit remarkable odd-even effect in the interlayer stacking: alternating head-to-head and tail-to-tail (antipolar) arrangement in odd-n crystals, and uniform head-to-tail (polar) arrangement in even-n crystals. The films show excellent field-effect transistor characteristics presenting unique polar/antipolar dependence and considerably improved subthreshold swing in the polar films. Additionally, the polar films present enhanced second-order nonlinear optical response along normal to the film plane. These findings are key for creating polarity-controlled optoelectronic materials and devices.

Luminescent Porous Organic Crystals for Adsorptive Separation of Toluene and Methylcyclohexane.

A butterfly-shaped phenothiazine derivative, PTTCN, was synthesized to obtain pure organic porous crystals for the highly efficient absorptive separation of toluene (Tol) and methylcyclohexane (Mcy). Due to the presence of three polar cyano groups and nonplanar conformation, these molecules self-assembled into a hydrogen-bonded organic framework (X-HOF-5) with distinct cavities capable of accommodating Tol molecules through multiple hydrogen-bonding interactions. Upon solvent removal via heating, the activated X-HOF-5 retained its cavity structure albeit with altered stacking arrangements, accompanied by a remarkable fluorescent color change from cyan to green. X-HOF-5a can undergo a phase transformation into X-HOF-5 upon reabsorption of Tol, while exhibiting no accommodation of Mcy due to the weak intermolecular interaction between PTTCN and Mcy. This suggests that the activated HOF material prefers Tol over Mcy. Moreover, X-HOF-5a may selectively accommodate Tol in a Tol/Mcy equimolar mixture, and the purity of Tol can reach 97% after release from the framework. Additionally, it is noteworthy that the HOF material exhibits recyclability without any discernible loss in performance.

Investigating the performance of a solid oxide electrolyzer multi-stack module with a multiphysics homogenized model

Limited by the lower power of a solid oxide electrolyzer (SOE) stack, the scaling-up of the SOE technology requires multiple stacks to be integrated into a hotbox to form a multi-stack module (MSM). It is critical to guarantee the uniformity of stacks in an MSM, which has a prominent impact on its performance and durability. However, the thermo-fluid-electrical couplings between different stacks in an MSM are highly dependent on its structure and stack arrangement, which flowsheet models with lumped parameters cannot describe. This study proposes a three-dimensional (3D) multiphysics MSM model accelerated by the homogenization approach to investigate the MSM performances. By simplifying the stack structure using the homogenization method, the number of mesh elements is remarkably reduced, making it possible to complete the simulation of a four-stack MSM model within 3min. Simulation shows that a 33% drop in maximum power and a 30°C increase in temperature difference are induced by uneven gas distribution and unequal stack resistances for an MSM with serial electrical arrangement. It is also shown that the parallel arrangement is less susceptible to non-ideal factors than the serial arrangement, which enlightened the possibility of optimizing the stack arrangement to improve the MSM’s performance.

Toroid-rod supramolecular polymorphism derived from conformational isomerism of a π-conjugated system.

Hydrogen-bonded supermacrocycles (rosettes) composed of dinaphthylethene π-conjugated systems show unique supramolecular polymorphism affording nanorings and nanorods via kinetically controlled self-assembly. Molecular modeling and molecular dynamics simulations proposed that conformational isomerism of the π-conjugated systems leads to planar and convex rosette geometries, which results in their distinct stacking arrangements.

Silver nanowires/cellulose flexible transparent conductive films for electromagnetic interference shielding and electrothermal conversion.

Currently, electromagnetic shielding materials need to meet the characteristics of lightweight, high transmittance, and robust conductivity. Silver nanowires (AgNWs) have progressively found applications in recent years owing to their excellent aspect ratio, conductivity, and flexibility. The properties of AgNWs vary with different aspect ratios, and the length and diameter of AgNWs often exert diverse influences on the photoelectric properties of conductive films. In this study, we combined AgNWs with hydroxypropyl methylcellulose (HPMC) and employed a directional stacking arrangement method to apply AgNWs onto the PET substrate, investigating the properties of four distinct aspect ratios of AgNWs (1000, 750, 625, and 531). Ultimately, the prepared four films achieved electromagnetic shielding capabilities ranging from 26.6 dB to 32.8 dB, with a transmittance range of 89.8% to 94.6%, showing excellent electromagnetic shielding properties. Moreover, the prepared films showed an exceedingly low roughness value (RMS = 7.07 nm), remarkable flexibility, and superior oxidation resistance with the facilitation of HPMC. The films also showed exceptional electrothermal conversion prowess, achieving saturation temperature within a mere 8 seconds, thereby displaying a rapid thermal response. Furthermore, when a voltage of 4 V was applied, the temperature of the thin film remained essentially constant for a duration of 2500 seconds, highlighting its admirable thermal stability, which is of great significance for the development of flexible and transparent electromagnetic shielding materials in the future.

Polyvalent anion-induced J-aggregation and its use in ratiometric fluorescence tracking of hypotonic in Arabidopsis

J-aggregate dyes have been widely used in biomedicine, chemical engineering, etc., due to their structure and photophysical properties. J-aggregation theory describes the nearest-neighbor molecules' transition dipole moments in a sliding stacking arrangement. However, we found that the intervention of polyvalent anions can induce the J-aggregation of dyes via the intermolecular van der Waals and electrostatic interactions, which is an essential way once overlooked. Experimental results and theoretical calculations revealed that the more negatively charged or large size of anions within a specific range, the more efficiently the dye will form J-aggregates. As an application, the content of polyvalent anion salts in a salt-stressed Arabidopsis model was evaluated based on the ratiometric fluorescence emission resulting from the polyvalent anion-induced dye J-aggregation.