Structural Instability Research Articles

Unraveling the enhanced sodium-storage mechanism in a strongly bonded 2D honeycomb borophene/boron phosphide heterostructure

The growing modern demand for battery capacity is driving the development of high-capacity metal-ion battery anodes for future energy storage. Two-dimensional (2D) material-based heterostructures have shown advantages as alternative anodes due to their enhanced adsorption capacity. The lightweight nature of honeycomb borophene (HB) is beneficial for serving as a high-capacity anode but is constrained by structural instability arising from electron deficiency. In this study, using first-principles calculations, we propose a HB/boron phosphide (BP) heterostructure as an anode for both lithium-ion batteries and sodium-ion batteries (SIBs). The heterostructure engineering not only stabilizes the HB structure but also leads to a bonding heterostructure instead of common van der Walls type. The HB/BP demonstrates robust structural stability and reversibility when multiple ions are stored. In addition, the HB/BP offers stable storage sites and low diffusion barriers for lithium (0.31 eV) and sodium (0.28 eV), indicating rapid charging–discharging performance. Notably, the predicted maximum sodium storage capacity reaches 2402 mAh/g, surpassing that of the constituent monolayers and most 2D heterostructures. The underlying mechanism for high storage capacity is elucidated through detailed charge image model analysis, offering atomistic-scale insights for constructing high-capacity anodes. All results suggest that the presented HB/BP is a promising anode candidate for SIBs and opens an avenue for stabilizing HB in energy storage.

Unique Features of Extremely Halophilic Microbiota Inhabiting Solar Saltworks Fields of Vietnam.

The artificial solar saltworks fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extremely halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with the Italian salterns of Motya and Trapani. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to the Hon Khoi saltworks field ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential.

Is Achilles tendon structure associated with functional ability and chronic ankle instability in military recruits?

ObjectiveTo determine the relationship between Achilles tendon (AT) structure, functional ability and chronic ankle instability (CAI) in military recruits. MethodsThree hundred and sixty newly recruited infantry male soldiers recruited in April 2022 were assessed for AT structure by Ultrasound Tissue Characterization (UTC), for functional abilities (included proprioception ability, heel-raise test, dynamic postural balance, and hopping agility ability) and for CAI (recurrent sprains and a positive perceived instability). ResultsSoldiers that were identified with disorganized tendon had significantly lower heel-raise and agility scores compared to those with organized tendon structures (33.6 ± 18.1(n) vs. 49.9 ± 28.9(n), p < 0.001; and 5.39 ± 2.12(n) vs. 6.16 ± 1.90(n), p = 0.002, respectively). The best discriminator between soldiers with organized vs. disorganized structure, was heel-raise test (AUC = 0.741). Moreover, soldiers with disorganized AT structure had a higher prevalence of CAI compared with those with organized tendon structures (p < 0.05). ConclusionRecruits with disorganized tendon structures displayed reduced heel-raise score, agility ability and dynamic postural-balance and greater ankle instability. Inferior tendon quality at the onset of military service is an important physical indicator to consider when seeking to manage future injuries and potential for physical performance. Pre-recruitment screening of the AT structure, CAI, and functional abilities, especially in high-intensity infantry programs, needs to be considered.

Recent Advances in Structure Design and Application of Metal Halide Perovskite-Based Gas Sensor.

Metal halide perovskites (MHPs) are emerging gas-sensing materials and have attracted considerable attention in gas sensors due to their unique bandgap structure and tunable optoelectronic properties. The past decade has witnessed significant developments in the gas-sensing field; however, their intrinsic structural instability and ambiguous gas-sensing mechanisms hamper their practical applications. Herein, we summarize the recent advances in MHP-based gas sensors. The physicochemical properties of MHPs are discussed at first. The structure design, including dimension design and engineering design, is overviewed as well as their fabrication methods, and we put forward our insights into the gas-sensing mechanism of MHPs. It is believed that enhanced understanding of gas-sensing mechanisms of MHPs are helpful for their application as gas-sensing materials, and structure design can enhance their stability, sensing sensitivity, and selectivity to target gases as gas sensors. Subsequently, the latest developments in MHP-based gas sensors are summarized according to their different application scenarios. Finally, we conclude with the current status and challenges in this field and propose future perspectives.

AGAP duplicons associate with structural diversity at Chromosome 10q11.22.

The 10q11.22 chromosomal region is a duplication-rich interval of the human genome and one of the last to be fully assembled. It carries copy-number variable genes associated with intellectual disability, bipolar disorder, and obesity. In this study, we characterized the structural diversity at this locus by analyzing 64 haploid assemblies produced by the Human Pangenome Reference Consortium. We identified eleven alternative haplotypes that differ in the copy number and/or orientation of large genomic segments, ranging from hundreds of kilobase pairs (kbp) to over one megabase pair (Mbp). We uncovered a 2.4 Mbp size difference between the shortest and longest haplotypes. Breakpoint analysis revealed that genomic instability results from nonallelic homologous recombination between segmental duplication (SD) pairs with varying similarity (94.4-99.6%). Nonetheless, these pairs generally recombine at positions where their identity is higher (>99.6%). Recurrent inversions occur with varying breakpoints within the same inverted SD pair. Inversion polymorphisms shuffle the entire SD arrangement, creating new predispositions to copy-number variations. The SD architecture is associated with a catarrhine-specific subgroup of the AGAP gene family, which likely triggered the accumulation of SDs at this locus over the past 25 million years of human evolution. Our results reveal extensive structural diversity and genomic instability at the 10q11.22 locus and expand the general understanding of the mutational mechanisms behind SD-mediated rearrangements.

Quasi-static and dynamic stab behavior and damage mechanisms of the spiral/laminated structure of CFRP

Stab resistance depends on the material’s strength and stiffness. Puncture energy is absorbed mainly through fracture and friction in the damaged area. To reduce stress concentrations and diffuse impact energy, this paper proposes a spiral CFRP inspired by spiral grass. Comparison of the puncture resistance of spiral CFRP and laminated CFRP by quasi-static and dynamic puncture. After separating the puncture process into longitudinal piercing and transverse cutting, it was found that spiral CFRP had excellent cutting resistance, with a maximum cutting force 44% higher than laminated CFRP. However, the detachment of the central structure leads to weaker perforation resistance of spiral CFRP than laminated CFRP. Laminated CFRP was found to undergo internal delamination damage after perforation by microscopic characterization and finite element analysis. Spiral CFRP has a helical yarn path and the interface distribution parallel to the impact direction, resulting in a greater susceptibility to delamination damage and rapid spiral crack propagation. The damaged area of spiral CFRP is up to 416% larger than that of laminated CFRP. The structural instability also resulted in a higher penetration depth for spiral CFRP than for laminated CFRP. The composite structure provides better puncture resistance than a single structure. Due to the combined advantages of the passivation of spiral CFRP and the structural stability of laminated CFRP, Sprial/laminated CFRP has the highest puncture resistance, with a maximum puncture load of 1,467 N, and is not penetrated at a puncture energy of 24 J. The spiral structure incorporating crack-inducing and transverse damage resistance could offer a promising approach to developing stab-resistant materials.

Influencing Factors, Design Methods, and Buoyancy Reduction Measures for Basement Anti-Flotation Engineering

Basement anti-flotation design is crucial in modern urban construction. An increase in groundwater buoyancy can cause basement structures to uplift, leading to structural instability or even damage. To ensure the stability and safety of underground structures under various hydrogeological conditions, anti-flotation design must comprehensively consider factors such as construction, design, supervision, structure, and hydrology. During construction, improper dewatering measures or unreasonable construction progress may lead to an abnormal rise in groundwater levels, increasing the risk of anti-flotation. Design considerations must include sufficient safety margins, supervision must fully recognize the impact of groundwater, and the structural dead load must be adequate. Anti-flotation stability verification includes both overall and local anti-flotation, involving the calculation of groundwater buoyancy, structural self-weight, and overburden, and selecting appropriate anti-flotation stability safety factors. The assessment and selection of the anti-flotation design water level are also critical. Common anti-flotation measures include adding counterweights, tension-resistant piles, compression and tension-resistant piles, and hydro-pressure reduction methods, while reinforcement and repair methods include epoxy resin grouting and steel plating reinforcement. Through systematic analysis and comprehensive research, scientific basis and technical support are provided for anti-flotation design, enhancing design efficiency and reliability and ensuring the safety and stability of underground spaces. Future research will develop more accurate calculation methods, improve design standards, and explore new anti-flotation technologies and materials.

Enzymatic interlocking aptamer-micelles for enhanced cellular internalization and nucleus-targeted cancer phototherapy

Multifunctional micelles that permit both diagnosis and treatment present enormous advantage and potential for precision medicine. However, the inherent complexities and structural instability of these systems often cause unsatisfactory targeting and therapeutic performances. Herein, by ingenious design of a 2,5-bis(2-thienyl)pyrrole (SNS) modifier to covalently link with AS1411 aptamer and lipid segment, a simple strategy is proposed for one-step enzymatic preparation of interlocked aptamer-micelle (IApM) under bio-friendly conditions. The interlocked poly(SNS) skeleton in IApM can not only stabilize the micelle structure but also enhance near-infrared (NIR) absorption ability, thus further enhancing cellular internalization and photothermal therapy. In addition, the multivalent AS1411 aptamers tethered in the hydrophilic shell can simultaneously increase the specific binding affinity of DNA micelles and induce nucleus-targeted accumulation for DNA damage-triggered apoptosis. This DNA micelle achieves “best of both worlds” with enhanced biostability for cellular internalization and improved NIR photothermal conversion efficiency for nucleus-targeted therapy, which provides a promising formulation strategy for precision cancer treatment.

The mechanism and prevention of rockburst induced by the instability of the composite hard-roof coal structure and roof fractures

Despite the implementation of prevention and control measures, rockburst still occur. The characteristics of composite coal were analyzed by combining monitoring and early warning means. Two types of composite coal in the hard roof were distinguished based on their distinct initiation and destruction processes despite experiencing the same rockburst event. Rockburst caused by structural instability was studied in different mining stages, and the following conclusions were considered. 1) The mechanical model of the instability of composite coal in hard roof was established for different mining stages to reveal rockburst mechanisms. The high-speed advance of working faces changed the fractured structure of upper hard rocks in the pressure-relief protection range. The sudden fracture of long cantilever structures caused dynamic load disturbance to high-stress coal, which resulted in rockburst in the insufficient mining stage. The failure and deformation of coal under high-stress static loads created conditions for the instability and fractures of roof. The disturbance of low hard rock strata aggravated the deformations of damaged coal. Therefore, rockburst appeared in the full mining stage. 2) Structural instability and roof fracture caused by different factors were the main causes of rockburst for composite coal in hard roof in different mining stages. Relevant prevention and control measures were formulated to ensure the safety of working faces, which provided references for the prevention and control of rockburst in working faces under similar conditions.

Enhancing the performance of LiNi0.8Mn0.1Co0.1O2-based pouch cells through advanced electrolyte additive systems for high-temperature lithium-ion batteries

Next-generation lithium-ion batteries, which achieve high energy densities and prolonged cycle performance, require cathode materials with high operating voltages and specific capacities. Because of their high capacity and operating voltage, nickel-rich layered oxides like LiNi0.8Mn0.1Co0.1O2 (NMC811) are attractive cathodes; nevertheless, they have drawbacks such capacity loss, poor cycle performance, structural instability, and thermal instability. Enhancing the stability of the NMC811 cathode-electrolyte interphase demands improvements in both cathode materials and electrolytes. This study explores the enhancement of NMC811-based battery systems through electrolyte modification, focusing on mixed additive combinations to evaluate their synergistic effects at elevated temperatures, relevant for tropical climates. A ternary additive system comprising vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), and p-toluenesulfonyl isocyanate (PTSI) in a LiPF6-based electrolyte showed significant improvements. This system mitigated capacity fading for cells cycled over 3 V–4.2 V at both 25 °C and 45 °C, outperforming the baseline electrolyte. The designed electrolyte stabilized the electrode-electrolyte interface, enhancing cell performance and the cathode's structural integrity. Notably, the graphite/NMC811 pouch cell's cycling performance showed an increase in capacity retention from 82.4% to 90.2% after 150 cycles at C/2 at 45 °C. Moreover, the deactivation of PF5 by PTSI can help to suppress the side reaction from the instability of LiPF6-based electrolytes, especially at elevated temperatures. These findings carried out from this strategic electrolyte additive system can substantially improve nickel-rich LIBs, especially in challenging thermal environments.

Enhanced Water Resistance of TiO2-GO-SMS-Modified Soil Composite for Use as a Repair Material in Earthen Sites.

Most earthen sites are located in open environments eroded by wind and rain, resulting in spalling and cracking caused by shrinkage due to constant water absorption and loss. Together, these issues seriously affect the stability of such sites. Gypsum-lime-modified soil offers relatively strong mechanical properties but poor water resistance. If such soil becomes damp or immersed in water, its strength is significantly reduced, making it unviable for use as a material in the preparation of earthen sites. In this study, we achieved the composite addition of a certain amount of sodium methyl silicate (SMS), titanium dioxide (TiO2), and graphene oxide (GO) into gypsum-lime-modified soil and analyzed the microstructural evolution of the composite-modified soil using characterization methods such as XRD, SEM, and EDS. A comparative study was conducted on changes in the mechanical properties of the composite-modified soil and original soil before and after immersion using water erosion, unconfined compression (UCS), and unconsolidated undrained (UU) triaxial compression tests. These analyses revealed the micro-mechanisms for improving the waterproof performance of the composite-modified soil. The results showed that the addition of SMS, TiO2, and GO did not change the crystal structure or composition of the original soil. In addition, TiO2 and GO were evenly distributed between the modified soil particles, playing a positive role in filling and stabilizing the structure of the modified soil. After being immersed in water for one hour, the original soil experienced structural instability leading to collapse. While the water absorption rate of the composite-modified soil was only 0.84%, its unconfined compressive strength was 4.88 MPa (the strength retention rate before and after immersion was as high as 93.1%), and the shear strength was 614 kPa (the strength retention rate before and after immersion was as high as 96.7%).

Optimizing high-energy lithium-ion batteries: a review of single crystalline and polycrystalline nickel-rich layered cathode materials: performance, synthesis and modification

Layered Ni-rich Li [NixCoyMnz]O2 (NMC) and Li [NixCoyAlz]O2 (NCA) cathode materials have been used in the realm of extended-range electric vehicles, primarily because of their superior energy density, cost-effectiveness, and commendable rate capability. However, they face challenges such as structural instability, cation mixing, and surface degradation, which limit their practical application. This review comprehensively discusses the synthesis, modification, and performance optimization of nickel-rich cathodes, with a focus on single-crystal (SC) NMC cathodes. The unique properties and challenges of single-crystal nickel-rich cathodes are explored in comparison to polycrystalline (PC) cathodes, with a focus on performance-enhancing strategies such as doping and surface modification.

Janus Monolayer of 1T-TaSSe: A Computational Study.

Materials exhibiting charge density waves are attracting increasing attention owing to their complex physics and potential for applications. In this paper, we present a computational, first principles-based study of the Janus monolayer of 1T-TaSSe transition metal dichalcogenide. We extensively compare the results with those obtained for parent compounds, TaS2 and TaSe2 monolayers, with confirmed presence of 13×13 charge density waves. The structural and electronic properties of the normal (undistorted) phase and distorted phase with 13×13 periodic lattice distortion are discussed. In particular, for a normal phase, the emergence of dipolar moment due to symmetry breaking is demonstrated, and its sensitivity to an external electric field perpendicular to the monolayer is investigated. Moreover, the appearance of imaginary energy phonon modes suggesting structural instability is shown. For the distorted phase, we predict the presence of a flat, weakly dispersive band related to the appearance of charge density waves, similar to the one observed in parent compounds. The results suggest a novel platform for studying charge density waves in two-dimensional transition metal dichalcogenides.

Conducting LixPOy Interface Generated From Insulating Residual Lithium Compounds on LiNi0.8Mn0.1Co0.1O2 Surface Improves Cycle Life and Assists in Fast Cycling.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is the most promising cathode material for future Li-ion batteries (LIBs). However, the bulk and surface structural instabilities retard its commercial success. Surface chemical instability toward exposure to moisture (H2O and CO2) leads to the formation of residual lithium compounds (RLCs: Li2CO3, LiOH) on the surface. The alkaline RLCs form a resistive layer on the surface of NMC811 by undergoing parasitic side reactions with electrolytes. Herein, an "Adverse-to-Beneficial" approach is proposed to eliminate RLCs by chemically transforming them into a LixPOy (Li3PO4 and LiPO3) interface. The interface protects the NMC811 surface from moisture attack and unwanted side reactions with electrolytes. It enhances the cycle life by retaining 70% of the initial capacity after 300 cycles at a 0.5C rate and 60% after 500 cycles, even at a 5C rate in a voltage window of 3.0-4.3V versus Li+/Li. The coexistence of two Li-conducting phases lowers the voltage polarization of the kinetically sluggish H1 → M phase transition to unlock fast cycling, reduces cationic disorder, improves coulombic efficiency, enhances ion diffusion kinetics, and minimizes particle crack formation after long-term cycling. Hence, the LixPOy interface yields multifaceted benefits in the storage, processing, and electrochemistry of NMC811.

Synergistic antibacterial effects of selenium-doped gold nanosheets with notable near infrared-II photothermal conversion against multidrug-resistant bacteria

Non-metallic nanoparticles are increasingly acknowledged for their broad-spectrum antibacterial properties, which often face limitations due to structural instability and potential biotoxicity. To address these challenges, integrating non-metallic nanoparticles with plasmonic metal nanostructures offers a promising solution. This fusion not only enhances structural stability but also reduces the required dosage. The synergistic coupling of the inherent antibacterial properties of non-metallic nanoparticles with the plasmonic absorption and photothermal conversion capabilities of metal nanostructures significantly amplifies antibacterial efficacy. In this study, we validate this concept by presenting the successful synthesis of selenium-doped gold nanosheets (AuSe NSs) that demonstrate robust absorption in the second near-infrared (NIR-II) window and exhibit efficient photothermal conversion, followed by testing their antibacterial activity. Notably, Au NSs were synthesized with high shape purity, followed by the introduction of SeO2 and ascorbic acid to facilitate Se doping. The resulting products displayed a uniform distribution of both Au and Se elements, while maintaining the NIR-II absorbance characteristic of Au nanosheets unaffected by the Se doping as evidenced by both experimental and FDTD simulation results. Subsequent assessments of the AuSe NSs demonstrated their potent synergistic antibacterial effects against multidrug-resistant bacteria at minimal inhibitory concentrations (MICs), which suggests that lower dosages can be employed and benefit minimizing potential side effects and optimizing treatment efficiency. Our findings indicate a synergistic boost between the photothermal attributes originating from Au's NIR absorption and Se's inherent antibacterial properties—an aspect minimally explored in prior research and offering a novel solution to tackling antibiotic-resistant bacterial strains.

Achieving Ultra-High-Energy-Density Lithium Batteries: Elimination of Irreversible Anionic Redox through Controlled Cationic Disordering.

Lithium-rich layered oxides (LLOs) capable of supporting both cationic and anionic redox chemistry are promising cathode materials. Yet, their initial charge to high voltages often trigger significant oxygen evolution, resulting in substantial capacity loss and structural instability. In this study, we applied a straightforward low-potential activation (LOWPA) method alongside a relatively stable electrolyte to address this issue. This approach enables precise control over the order-to-disorder transformation of the transition metal layers in LLOs, producing an in-plane cation-disordered Li1.2Mn0.54Co0.13Ni0.13O2 that averts irreversible oxygen evolution at 4.8 V by stabilizing Mn-O2 or Mn-O3 species within the Li/Mn-disordered nanopores. Consequently, an ultrahigh reversible capacity of 322 mAh g-1 (equating to 1141 Wh kg-1), 91.5% initial Coulombic efficiency, and enhanced durability and rate capability are simultaneously achieved. As LOWPA does not alter any chemical composition of LLOs, it also offers a simple model for untangling the complex phenomena associated with oxygen-redox chemistry.

Stress-relieved hollow porous carbon nanoring structures anchored with ZnCo2O4 nanoparticles towards super stable lithium storage

Stress-induced structural mechanical instability is a common occurrence in the electrode material during electrochemical cycling, especially for composite material systems. The structural mechanics engineering of nanocomposites comprising electrochemical active materials and carbon with novel structures holds great promise in addressing this issue. However, conventional carbonaceous materials often encounter challenges in long-term durability and high specific capacity stemming from their intrinsic uneven stress distribution and few active sites. Herein, finite element analysis reveals that the ring-like structure effectively mitigates stress concentration from expansion and possesses high packing density, outperforming traditional nanosphere and nanocube architectures. Accordingly, nanocomposites consisting of hollow porous nanostructured N-doped carbon nanorings (N-CNRs) anchored with bimetallic ZnCo2O4 nanoparticles are designed, which exhibit an extraordinary cycling performance for lithium storage with 96.4 % capacity retention following 1000 cycles and an impressively low storage degradation rate of 0.00357 % per cycle, as well as displaying an excellent specific capacity (1218 mA h/g at 0.1 A g−1) and outstanding rate performance (565 mA h/g at 5.0 A g−1). The well-engineered design nanocomposite features the synergistic effect of electrochemically active ZnCo2O4 nanoparticles integrated with structurally stable carbon nanorings for enhanced electrochemical performance.

Identifying the β-to-α phase transition during the long cycling process in Na2FePO4F cathode

Na2FePO4F has emerged as a promising cathode for large-scale electrochemical energy storage, primarily due to its abundance of raw materials and distinctive two-dimensional ion channels. Counterintuitively, pristine Na2FePO4F lacks the long-term stability typically seen in polyanionic cathodes, which severely impedes its practical application. Traditionally, the origin of this problem has been only phenomenologically attributed to the poor intrinsic electronic conductivity and structural instability of Na2FePO4F. Here, we identify that rapid capacity fading of Na2FePO4F is closely related to the β-to-α phase transition during the long cycling process. Furthermore, we develop a practical high-entropy doping strategy and the corresponding microstructure engineering to mitigate the impact of the phase transition on the crystal structure, thereby increasing the capacity retention from 56 % to 94 % over 400 cycles at 0.5C in coin cell, and attain almost 100 % capacity retention after 300 cycles at 0.1C in pouch cell. Overall, this work unveils the mechanism of rapid capacity decay in Na2FePO4F and lays the groundwork for the rational design of durable polyanionic electrodes.

Intrinsically Multi-Stable Spatial Linkages.

Multi-stable structures can be reconfigured with fewer, lightweight, and less accurate actuators. This is because the attraction domain in the multi-stable energy landscape provides both reconfiguration guidance and shape accuracy. Additionally, such structures can generate impulsive motion due to structural instability. Most multi-stable units are planar structures, while spatial linkages can generate complex 3D motion and hold a more promising potential for applications. This study proposes a generalized approach to design a type of intrinsically multi-stable spatial (IMSS) linkages with multiple prescriptible configurations, which are structurally compatible, and naturally stable at these states. It reveals that all over-constrained mechanisms can be transformed into multi-stable structures with the same design method. Single-loop bi-stable 4R and quadra-stable 6R spatial linkages modules with intrinsic non-symmetric stable states, which are transformed from fundamental kinematic linkage mechanisms unit such as Bennett and Bricard linkages, are designed to illustrate the basic idea and the superiority over the ordinary methods. Multi-loop assembly by these IMSS linkage modules shows potential for practical applications that are required for the deployability and impulsivity of reconfiguration. Two preliminary design cases of a deployable tube and an impulsive gripper are experimentally presented to validate this applicability. Further promisingly, this design method of IMSS linkages paves the way for morphing platforms with lightweight actuation, high shape accuracy, high stiffness, and prescribed impulsive 3Dmotion.

Esterification-Induced Spontaneous Deposition of Nanoparticle Monolayers on Substrates with Percolation Network Morphology.

Nanoparticle monolayers (NPMLs) exhibit unique collective properties that are highly desirable for applications in sensors, catalysts, and optics. However, their practical use is often hindered by structural instability, especially when they are exposed to solvents. In this study, we developed a method for the spontaneous deposition of gold nanoparticle monolayers (AuNPMLs) on silicon substrates via covalent bonding interactions that provides excellent structural stability in solvents with varying polarities. The esterification reaction between carboxyl-functionalized gold nanoparticles and alkyl-chloride-functionalized silicon substrates spontaneously forms AuNPMLs on the substrate in which single-crystalline domains are interconnected, forming a percolation network morphology. The ex situ scanning electron microscopy measurements show that the surface coverage of AuNPMLs rapidly increases up to ca. 60% during the initial 10 min, followed by gradual growth and saturation at ca. 70% at 360 min of deposition time. On the other hand, the single-crystalline domain size reaches its maximum at 45 min and then gradually decreases, which may be attributed to the desorption of AuNPs by the hydrolysis of ester bonds. The reflectance spectra of AuNPMLs showed the red shift as the deposition time increases up to 45 min with a subsequent blue shift thereafter, which is consistent with the change of the single-crystalline domain size with the deposition time. The covalent bonding interaction-mediated nanoparticle deposition method can be used to form stable AuNPMLs with controlled surface coverage and domain size, allowing for fine control of the optical properties and possibly other properties. The excellent structural stability of AuNPMLs and their controlled properties may provide new opportunities for practical applications of NPMLs.