Strong Covalent Bonds Research Articles

Spontaneous Phase Transition and Multistage Interfacial Mechanical Friction of Liquid Metals Induced CO2 Reduction at Room Temperature

AbstractExcessive emissions of carbon dioxide (CO2) have caused the greenhouse effect and environmental crisis. Therefore, the carbon reduction and negative carbon technologies are particularly important. Among these, the negative carbon technologies that convert CO2 into carbon materials or carbon‐based chemicals for reuse have attracted significant attention. However, the strong double covalent bonds make the CO2 conversion usually require harsh conditions, complex processes, and high energy consumption. Gallium‐based liquid metals (LMs) are the functional materials with both metallic and liquid properties, exhibiting a unique liquid‐phase structure and diverse surface characteristics. Herein, a strategy for reducing CO2 is proposed to carbon materials by utilizing the spontaneous phase transition and mechanical friction of liquid metals. The gallium (Ga) and indium (In) particles are mixed and exposed to CO2, the contact interface of metal particles spontaneously transforms into liquid metals. The system has multistage interfaces, including Ga/In, Ga/eGaIn, and In/eGaIn, capable of generating triboelectrification upon mechanical stimulation, leading to charge transfer. The high electric field generated by friction at the contact interface directly reduces CO2 to carbon materials at room temperature. The carbon materials cover the surface of eGaIn and can be directly stripped for used as fuel, or industrial applications.

Zr-Doping Strategy of High-Quality Cu2O/β-Ga2O3 Heterojunction for Ultrahigh-Performance Solar-Blind Ultraviolet Photodetection.

β-Ga2O3, as an ultrawide band gap semiconductor, has emerged as the most promising candidate in solar-blind photodetectors. The practical application of β-Ga2O3, however, suffers from intrinsic defects and suboptimal crystal quality within the devices. In this work, high-quality β-Ga2O3 was successfully synthesized by employing the Zr-doping strategy, which has facilitated the development of ultrahigh-performance solar-blind photodetectors based on Cu2O/β-Ga2O3 heterostructures. Structural analyses indicate that the strong Zr-O covalent bond effectively stabilizes the material, thereby eliminating oxygen vacancy defects. The Cu2O/β-Ga2O3 heterostructure photodetector demonstrates an ultrahigh responsivity and detectivity coupled with an external quantum efficiency. Furthermore, the device exhibits a photocurrent-to-dark current ratio of 3 × 105, showcasing its superior capability in detecting low-intensity deep ultraviolet signals, markedly surpassing previous heterostructure ultraviolet photodetectors. These exceptional performances are attributed to the effective elimination of oxygen vacancy defects in β-Ga2O3 and the variation of band alignment at the interface, which facilitate rapid separation of photogenerated electron-hole pairs under reverse bias. This study not only provides an enhanced and easy route to mitigate oxygen vacancy defects in oxide materials but also propels further exploration into the next generation of flexible, high-performance, solar-blind ultraviolet photodetectors.

Covalently grafting silane coupling agents onto MXene‐reinforced carbon fibers for epoxy composites with improved mechanical properties

AbstractTwo‐dimensional (2D) MXene (MX) and silane coupling agents are increasingly used to modify carbon materials for the fabrication of composite functional materials, which exhibit enhanced electrical, optical, and mechanical properties due to the synergistic effects of both MX and silane. We demonstrate the modification of carbon fibers (CFs) with MX and three different kinds of silane coupling agents, including 3‐aminopropyltriethoxysilane, 3‐glycidyloxypropyldimethoxymethylsilane, and 3‐mercaptopropyltriethoxysilane, which are named as CF‐MX@N, CF‐MX@O, and CF‐MX@S, respectively, and further prepare the CF‐MX@silane/epoxy (EP) composites. The utilized silane coupling agents serve as bridges between MX and CFs, forming CF‐MX@silane composites. Through comparative analysis, it is found that the CF‐MX@S composites form a strong interface phase through covalent bonds, significantly enhancing the interface compatibility and revealing strong interface adhesion. The interfacial shear strength of the molded CF‐MX@S/EP composites increases to 119.7 MPa, with an 173.9% enhancement comparing to unmodified composites. This work can offer useful guidance and reference for selecting appropriate silane coupling agent to modify CFs with 2D materials to form high‐performance composite materials.Highlights Silane coupling agents are used as bridges to graft MXene‐modified CFs The surface modification of CFs is achieved by a simple one‐step approach Excellent interfacial phase is constructed through forming strong covalent bonds Microstructure and failure interface are responsible to interface strengthen.

Ultra–fast plastic forming of zirconia ceramics under a low temperature and high electric field

The low–temperature plastic forming ability of ceramics with complex structures is unsatisfied due to the strong covalent and ionic bonds, restricting their widespread applications. Herein, a technique is proposed for the ultra–fast plastic forming of zirconia ceramics using a low temperature and high electric field. The high electric field–assisted plastic forming temperature and rate are 1000 °C and 10mm/min, respectively, which are much lower and faster than those of conventional plastic forming methods for ceramics. The deformed “Ω”–shape zirconia part exhibits a uniform microstructure without microcracks/cavities and a high hardness, demonstrating that the high electric field–assisted plastic forming technique enables the rapid fabrication of complex ceramic components with beneficial properties at low temperatures.

Predicting potential hard materials in Nb[sbnd]B ternary boride: First-principles calculations

To identify potential superhard materials, we conducted a comprehensive theoretical investigation of the thermodynamic and kinetic stability, mechanical properties, electronic structure, Debye temperatures and melting point of sixteen ternary transition metal borides NbTMBx (x = 1, 2, 4 and TM = Ti, V, Fe, Co, Ni, Zr, Ru, Hf, W, Os) using first-principles methods. Our findings indicate that, with the exception of NbFeB, NbRuB, and NbWB, all other borides exhibit both thermodynamic and kinetic stability. Notably, NbTiB4, NbVB4, NbZrB4 and NbHfB4 demonstrate superior hardness and enhanced resistance to deformation, with NbTiB4 showing an impressive hardness value of 40.84 GPa, positioning it as a promising candidate for superhard materials. Both NbVB4 and NbTiB4 have very high Debye temperatures and melting points and can be used in high temperature environments. We further explored the mechanical properties of NbTiB4 at elevated temperatures by employing a combination of first-principles and quasi-static methods. Our analysis reveals that the elastic constants and moduli of NbTiB4 decrease with increasing temperature. Additionally, bonding analysis indicates that all NbB ternary borides exhibit hybridization involving metallic, ionic, and covalent interactions, resulting in the formation of exceptionally strong covalent bonds between boron atoms.

Controllable structure, super adhesion, multifunctional, conductive pressure-sensitive adhesive for electronic skin: Enhancing cohesion by cellulose-derived covalent crosslinking

Ensuring firm adhesion to the skin is essential for improving the detection of temperature and movement signals in electronic skin (E-skin). Self-adhesive eutectogel, an ideal material for E-skin, could act as an innovative pressure-sensitive adhesives (PSAs) that can be easily applied through simple pressing without requiring heating or irradiation. Herein, we synthesized a cellulose-derived polymer crosslinking agent (MCCAC) to create a eutectogel-based conductive PSA (CPSA). The MCCAC formed strong covalent bonds with polymer chains, significantly enhancing the cohesion of the CPSAs. As a result, the CPSAs exhibited high tensile lap-shear strength (99.5 kPa) among self-adhesive eutectogels. Unlike the construction of double-network structures, this method included a straightforward chemical reaction and a cohesion-enhancing strategy, and could adjust crosslinking density by changing the MCCAC content. The preparation process was simple, and the products were controllable. More importantly, this cohesion-enhancing strategy did not compromise the fluidity of polymer chains, which ensured that CPSAs maintain effective interfacial adhesion to adhere on skin, offering exceptional capabilities for capturing body temperature signals (−3.66 %/℃) as well as applications in motion detection and information transmission. This work resolved the cohesion and interfacial adhesion imbalances observed in previous self-adhesive eutectogels and provided a promising approach for designing the novel cellulose-reinforced CPSA for E-skins.

Design, preparation and properties of biomedical Ti-Nb quaternary alloys with high strength and low modulus: insights from first-principles calculations

In this paper, we designed and developed biomedical β-type Ti-Nb quaternary alloy materials with high strength and low modulus. Building upon the d-electron alloy design method and the valence electron concentration e/a method, we use a Python program and thermodynamic theoretical parameters to determine a Ti-Nb quaternary alloy with the characteristics of a single-phase solid solution. Subsequently, we engage in theoretical and experimental investigations on the low modulus alloys identified through first-principles calculations. The results show that both Ti7Nb6Zr1Al2 and Ti11Nb2Ta2Al1 maintain a single β phase before and after cold rolling, which is related to the strong electronic density of states of s and p orbitals at low energy levels in the crystal structure of the two alloys. Ti11Nb2Ta2Al1 has a strong charge distribution on the (001) crystal plane, which causes a large amount of internal stress under large deformation conditions to promote grain crushing and weaken the intensity of the (001)[1-10] texture in the ODF diagram of 2 = 45°. The cold-rolled Ti11Nb2Ta2Al1 exhibits better corrosion resistance and biocompatibility than the cold-rolled Ti7Nb6Zr1Al2, and the good biocompatibility is related to the strong covalent bond between Al and Ta that inhibits the diffusion of Al ions. 90% cold-rolled Ti11Nb2Ta2Al1 stands out as an exceptionally promising orthopedic implant material due to its high elastic allowable strain (ReH/E), good corrosion resistance and biocompatibility.

Concept of electrons pairing during the formation of covalent chemical bonds

This research studies the forces acting in an electron pair with antiparallel spins participating in forming a covalent chemical bond between atoms. The first is the force of electrostatic repulsion of electrons. The second is the gravitational attraction of these electrons. The third is the force of electromagnetic attraction between the electron pair. From calculations it follows, that the force of gravitational attraction is negligible, and therefore it is not able to withstand the force of electrostatic repulsion between electrons. However, the force of electromagnetic attraction between a pair of electrons with antiparallel spins turned out to be hundreds of times greater than the force of their electrostatic repulsion. As a result, the formation of stable electron pairs in molecular orbitals becomes possible. Thus, valence electrons of neighboring atoms interact with each other like femto-electromagnets, as a result of which a stable bond is formed between these electrons. Calculations have shown that in hydrogen molecule the force of electrostatic attraction between nuclei and paired electrons of a molecular orbital significantly exceeds the force of electrostatic repulsion of nuclei, which ensures the formation of a strong covalent chemical bond. To form covalent bonds in other molecules, the force of electrostatic attraction between the nuclei and paired electrons of the molecular orbitals must be much greater than the forces of electrostatic repulsion between both the positively charged nuclei and the negatively charged electrons of the atomic orbitals of different atoms.

Advancing the Coupling of III–V Quantum Dots to Photonic Structures to Shape Their Emission Diagram

AbstractThe development of optoelectronic devices based on III–V semiconductor colloidal quantum dots (CQDs) is highly sought after due to their reduced toxicity. While devices based on conventional CQDs (II–VI semiconductors, halide perovskites) have achieved impressive technological leaps since their discovery, the most mature of these compounds contain toxic heavy metal elements (Cd, Hg, or Pb), which are highly undesirable for safe industrial scale applications. The strong covalent bonds of III–V compounds like InP, InAs, or InSb prevent the release of their toxic atoms, making them safer. However, these same bonds create severe material constraints. Namely, their harsher reaction conditions and increased sensitivity to oxidation have kept most of the research focused on material development. Meanwhile, their integration into devices and their coupling to photonic structures lag behind. Here, the integration of InAs/ZnSe core‐shell CQDs is advanced. First, the material parameters necessary to design plasmonic gratings coupled to the CQDs are elucidated and those gratings are fabricated. Angle‐resolved spectroscopy shows that the plasmon modes successfully couple to the CQD layer's emission leading to a tunable directivity with a 15° linewidth. A 3‐fold increase of the PL signal is achieved at normal incidence, thus advancing toward the goal of efficient outcoupling in LEDs.

First-principles study of O3 molecule adsorption on pristine, N, Ga-doped and -Ga-N- co-doped graphene

The adsorption of O3 molecules (ozone) on graphene, N-doped graphene, Ga-doped graphene, and -Ga-N- co-doped graphene with an emphasis on O3 detection was examined in this work. The physical characteristics of -Ga-N-co-doped graphene are significantly altered upon O3 adsorption, which makes it a suitable choice for O3 detection molecular sensors. The interaction between the O3 molecule and the adsorbent is explained on the basis of their adsorption energy, adsorption distance and charge transfer. It was found that the adsorption of ozone molecules on the -Ga-N- co-doped graphene was more favorable in energy than that on the pristine one, representing the superior sensing performance of -Ga-N- co-doped system. In our work, we estimated the charge transfer between the O3 molecule and doped graphene nanostructures based on Mulliken population analysis. The calculated adsorption energy value shows the ozone molecule more firmly adsorbs on the surface of -Ga-N- co-doped graphene nanostructures (Eads = –1.74 eV) than that of pristine graphene (Eads = –0.41 eV), deriving from a stronger covalent bond between the ozone molecule and the -Ga- N- co-doped graphene nanostructures. Our findings thus suggest that -Ga-N- co-doped graphene could be a highly efficient gas sensor device for O3 detection in the environment.

Customization of 2D Atomic-Molecular Heterojunction with Manipulatable Charge-Transfer and Band Structure.

Manipulating the properties of 2Dmaterials through meticulously engineered artificial heterojunctions holds great promise for novel device applications. However, existing research on the crucial charge-transfer interactions and energy profile regulation is predominantly focused on 2D van der Waals structures formed via weak van der Waals forces, limiting regulatory efficiency at high costs. Herein, a refined atomic-molecular heterojunction strategy featuring strong covalent bonds between organic molecule and 2D violet phosphorus (VP) atomic crystal is developed, which enables enhanced charge-transfer dynamics and customizable band structure regulation at the molecular level. Both experimentally and theoretically, it is demonstrated that grafting efficiency, charge redistribution, and energy gap regulation critically depend on organic electronegativity, providing a low-cost yet high-efficiency regulatory effect on a large scale. As a proof of concept, the novel VP-molecular heterojunctions exhibit optimized performance in diverse application domains, presenting a general platform for future high-performance device applications.

First principles study on the dielectric and infrared properties of single crystal Al3BC3

The dielectric and infrared vibrational properties of single crystal Al3BC3 were computed using density functional perturbation theory. Utilizing a group theory approach, the frequencies and vibrational modes of all the infrared active modes at the Brillouin zone center were determined. The study explored the dielectric function, infrared reflectivity, and Born effective charge of Al3BC3 in directions both parallel and perpendicular to the c-axis. The analysis of the Born effective charge confirmed the existence of strong covalent bonds between B and C, as well as ionic bonds between Al and C in Al3BC3 ceramics.

Atomic-scale bonding strength and failure mechanisms of HfC/Ni/Ni3Al interfaces on low-index crystal planes: A combined HRTEM and first-principles study

The carbide/matrix interface in superalloys is susceptible to cracking under mechanical stress, yet the failure mechanisms require further investigation. The cohesive strength and stability of 32 interface models, including HfC(001)/Ni(001), HfC(011)/Ni(001), HfC(111)/Ni(001), HfC(001)/Ni3Al(011), and HfC(111)/Ni3Al(111) within the DZ125 superalloys, were investigated using first-principles calculations and experimental methods. The results indicate that the majority of interfaces demonstrate negative adhesion work (Wad), indicating instability. However, Bridge4 model in HfC(001)/Ni3Al(011) show higher Wad and lower interface energy, suggesting improved stability. The interfacial cohesion is attributable to strong Ni-C covalent bonds. But interfacial fracture toughness results reveal that the majority of models are more susceptible to fracture at the interface. Fracture morphology analysis from tensile tests at room temperature and endurance tests at 760 °C/725 MPa confirms that cracks primarily initiate at the carbide/matrix interface. This study suggests that introducing Ta atoms could improve interface strength, as Ta-rich carbides reduce interfacial energy while increasing elastic energy, resulting in the formation of skeletal structures. The relationship between Hf-rich and Ta-rich carbides and their respective morphology was investigated. The findings provide insights into the failure mechanisms of carbide/matrix interface and offer theoretical guidance for enhancing interface strength in superalloy applications.

ZnO/Gra/Si structure to improve photoelectric properties

To enhance the interface bonding and optoelectronic properties of ZnO/Si, we employed graphene (Gra) as a buffer layer to mitigate lattice mismatch. Density functional theory (DFT) was utilized to analyze the impact of graphene insertion on the interface structure and optoelectronic properties of ZnO/Si. Our findings indicate strong covalent bonds within the ZnO/Si interface, whereas the ZnO/Gra/Si interface exhibits van der Waals interactions. Additionally, the incorporation of graphene shifts the valence band of ZnO/Gra/Si closer to the conduction band, significantly improving its conductivity. Moreover, ZnO/Gra/Si demonstrates a 74 % increase in visible light utilization compared to ZnO/Si, highlighting the substantial potential of this sandwich structure in solar cell applications.

Imine‐linked covalent organic frameworks: Recent advances in design, synthesis, and application

AbstractCovalent organic frameworks (COFs) are new porous organic materials made of organic building blocks precisely constructed by strong covalent bonds. These new materials feature tunable structure, permanent porosity, high crystallinity, high specific surface area, and excellent stability, which enable COFs to be used in many applications. Linkage chemistry is a key factor in the synthesis of COFs and the control of their physicochemical properties. The boroxine, boronate‐ester, imine, hydrazone, imide, and C=C linkages have been widely used in the construction of COFs. Among the various linkages, imine has become the most important linkage for the COFs due to the easy formation of imine linkage with structural and functional diversity. Over the past decade, imine‐linked COFs have made significant progress and become an indispensable part of various applications of COFs. Here, we aim to provide a comprehensive review of the research progress in the field of imine‐linked COFs, especially the advances in topology design and COF powder and film preparation, and their important advances in gas adsorption, catalysis, and optoelectronic devices. Finally, we discuss the challenges in the design, synthesis, and application of imine‐linked COFs, and present our views on the further development of imine‐linked COFs.

Development of Optical Sensors Based on Neutral Red Absorbance for Real-Time pH Measurements.

Measuring pH with an optical sensor requires the immobilization of a chemical recognition phase on a solid surface. Neutral red (NR), an acid base indicator was used to develop two different optical probe configurations. The chemistry of aryl diazonium salts was chosen for the elaboration of this chemical phase, as it enables strong covalent bonds to be established on the surface of metallized glass or metallic surfaces. It also allows the formation of a thick film required to obtain an exploitable spectral response. The surfaces of interest (metallized optical fiber and 316 L stainless-steel mirror) are modelized by flat surfaces (metallized glass plates and 316 L stainless-steel plates). The analytical characterizations carried out (IR, XPS, UV-Visible, and profilometry) show that NR was covalently grafted onto the model surfaces as well as on the surfaces of interest. The supports grafted with NR to develop optical pH probes exhibit spectral changes, particularly the values of pKa, the pH range, and the isosbestic point wavelength. The experimental results show that the optical probe can be used for pH measurements between 4 and 8.

Study of bond strength and electronic properties at the 6H-SiC/Al interface: Based on first-principles calculations

As the medium between the reinforcement and the matrix, the interface plays a critical role in the mechanical properties of silicon carbide particle reinforced aluminum matrix composites. This study used first-principles calculation methods to systematically analyze 14 different 6H-SiC/Al low-index interfaces, including atomic configuration, interface bonding strength, and electronic structure and bonding principles between interfaces. The adhesion work calculations reveal that the C-top-SiC(0001)/Al (111) and SiC(0001)/Al (100) interfaces have larger adhesion work values, specifically 5.09 J/m2 and 5.021 J/m2, respectively. Additionally, the rigid tensile testing confirms that the tensile stress values at the interfaces of C-top-SiC(0001)/Al (111) and SiC(0001)/Al (100) are higher, measuring 36.4 GPa and 32.5 GPa, respectively. The above results show that the interface bonding strength of these two configurations is the highest, the most stable, and most likely to appear in the 6H-SiC/Al interface configuration. The results of the analysis on charge density difference and partial density of states indicate that the interfaces of C-top-SiC (0001)/Al (111) and SiC (0001)/Al (100) are primarily composed of strong ionic and covalent bonds.

Iridium oxide-modified reference screen-printed electrodes for point-of-care portable electrochemical cortisol detection

Cortisol is a well-known stress biomarker; this study focuses on using electrochemical immuno-sensing to measure the concentration of cortisol selectively and sensitively in artificial samples. Anti-cortisol antibodies have been immobilised on polycrystalline Au electrodes via strong covalent thiol bonds, fabricating an electrochemical bio-immunosensor for cortisol detection. IrOx was then anodically electrodeposited as a reference electrode on a commercial screen-printed electrode and electrochemical impedance spectrometry (EIS) studies were used to correlate the electrochemical response to cortisol concentration and the induced changes in charge transfer resistance (Rct). A linear relationship between the Rct and the logarithm of cortisol concentration was found in concentrations ranging from 1 ng/mL to 1 mg/mL with limit of detection at 11.85 pg/mL (32.69 pM). The modification of the reference electrode with iridium oxide has greatly improved the reproducibility of the screen-printed electrode. The sensing system can provide a reliable and sensitive detection approach for cortisol measurements.

First-principle and experimental investigation into the interfacial characters of Ti-doped ZTA and high chromium cast iron

Ti doping can improve the interfacial wettability and bonding condition between ZTA ceramic and high chromium cast iron (HCCI), but the underlying mechanism is still unclear. Therefore, the effects of Ti doping on the interfacial characters between ZTA and HCCI were investigated by experiment and first-principles calculations. Results of XRD, SEM, and high-temperature drop test indicate the presence of Ti at the interface and its effect on the formation of interfacial diffusion layer to improve the interface wettability and bonding obviously. The heat of segregation and work of adhesion obtained by first-principle calculations shows that the improvement in interface wettability and bonding is due to the promotion of dopped Ti atoms on the diffusion of Fe, Al, and Zr elements, but not the diffusion of Ti itself. Further investigation from the electronic level reveals that the doped Ti changes the charge distribution and orbital hybridization, and thus makes the formation or enhancement of strong ionic bonds and covalent bonds at the interface, improving the bonding strength and wettability of interfaces in ZTA/HCCI. The findings of this research can offer new insights into the modification of ceramics and enlarge the application of advanced ceramic materials.

Stability of the B2 phase among refractory metals

Energy efficiency demands finding new materials for applications at elevated temperatures. Refractory multicomponent alloys with a BCC/B2 microstructure promise to serve as alternatives to the current state-of-the-art, Ni-based superalloys for applications at higher temperatures. With the vast compositional space of these alloys, the first fundamental question is whether the B2 phase can form among refractory metals. In this study, we span through the periodic table to investigate the potential for creating ordered B2 intermetallics among the refractory metals, using first principles calculations, and establish the correlation between the nature of the atomic bonds and stability of the B2 structure. We use our newly developed Multi-Cell Monte Carlo method to explore the extensive compositional space of these alloys, refine the trends in ordering, and pinpoint the most promising combinations for detailed analysis. We discover that B2 phases form exclusively with the inclusion of elements from groups VII and VIII, such as Re, Ru, and Os, and we identify these phases among a total of eleven elements. Further analysis of the electronic structure and bonding characteristics of these B2 systems reveals a pseudogap in the electronic density of states at the Fermi level. This pseudogap is attributed to the hybridization of d orbitals, leading to the formation of strong covalent bonds in the most stable compounds. This finding explains why B2 formation is restricted to elements from groups IV-VIII and V-VII refractory metals.