Mechanically Induced Metal–Insulator Transition in Carbyne

First-principles calculations for carbyne under strain predict that the Peierls transition from symmetric cumulene to broken-symmetry polyyne structure is enhanced as the material is stretched. Interpretation within a simple and instructive analytical model suggests that this behavior is valid for arbitrary 1D metals. Further, numerical calculations of the anharmonic quantum vibrational structure of carbyne show that zero-point atomic vibrations eliminate the Peierls distortion in the mechanically free chain, preserving the cumulene symmetry. The emergence and increase of Peierls dimerization under tension then implies a qualitative transition between the two forms, which our computations place around 3% strain. Thus, the competition between the zero-point vibrations and mechanical strain determines a switch in symmetry resulting in the transition from metallic state to a dielectric, with a small effective mass and a high carrier mobility. In any practical realization, it is important that the effect is also chemically modulated by the choice of terminating groups. These findings are promising for applications such as electromechanical switching and band gap tuning via strain, and besides carbyne itself, they directly extend to numerous other systems that show Peierls distortion

Mechanochemistry of One-Dimensional Boron: Structural and Electronic Transitions

Recent production of long carbyne chains, concurrent with advances in the synthesis of pure boron fullerenes and atom-thin layers, motivates an exploration of possible one-dimensional boron. By means of first-principles calculations, we find two isomers, two-atom wide ribbon and single-atom chain, linked by a tension-driven (negative-pressure) transformation. We explore the stability and unusual properties of both phases, demonstrating mechanical stiffness on par with the highest-performing known nanomaterials, and a phase transition between stable 1D metal and an antiferromagnetic semiconductor, with the phase boundary effectively forming a stretchable 1D Schottky junction. In addition, the two-phase system can serve as a constant-tension nanospring with a well-calibrated tension defined by enthalpic balance of the phases. Progress in the synthesis of boron nanostructures suggests that the predicted unusual behaviors of 1D boron may find powerful applications in nanoscale electronics and/or mechanical devices

First-Principles Studies of Li Nucleation on Graphene

We study the Li clustering process on graphene and obtain the geometry, nucleation barrier, and electronic structure of the clusters using first-principles calculations. We estimate the concentration-dependent nucleation barrier for Li on graphene. While the nucleation occurs more readily with increasing Li concentration, possibly leading to the dendrite formation and failure of the Li-ion battery, the existence of the barrier delays nucleation and may allow Li storage on graphene. Our electronic structure and charge transfer analyses reveal how the fully ionized Li adatoms transform to metallic Li during the cluster growth on graphene

Environment-Controlled Dislocation Migration and Superplasticity in Monolayer MoS₂

The two-dimensional (2D) transition metal dichalcogenides (TMDC, of generic formula MX₂) monolayer displays the “triple-decker” structure with the chemical bond organization much more complex than in well-studied monatomic layers of graphene or boron nitride. Accordingly, the makeup of the dislocations in TMDC permits chemical variability, depending sensitively on the equilibrium with the environment. In particular, first-principles calculations show that dislocations state can be switched to highly mobile, profoundly changing the lattice relaxation and leading to superplastic behavior. With 2D MoS₂ as an example, we construct full map for dislocation dynamics, at different chemical potentials, for both the M- and X-oriented dislocations. Depending on the structure of the migrating dislocation, two different dynamic mechanisms are revealed: either the direct rebonding (RB) mechanism where only a single metal atom shifts slightly, or generalized Stone–Wales (SW^g) rotation in which several atoms undergo significant displacements. The migration barriers for RB mechanism can be 2–4 times lower than for the SW^g. Our analyses show that within a range of chemical potentials, highly mobile dislocations could at the same time be thermodynamically favored, that is statistically dominating the overall material property. This demonstrates remarkable possibility of changing material basic property such as plasticity by changing elemental chemical potentials of the environment

Carbyne from First Principles: Chain of C Atoms, a Nanorod or a Nanorope

We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne’s mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5 × 10⁷ N·m/kg, requiring a force of ∼10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be “switched on” by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic semiconductor state by mechanical twisting. We reconstruct the equivalent continuum elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (<i>e.g.</i>, a nominal Young’s modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 2.6 to 4.7 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne–carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm)

Feasibility of Lithium Storage on Graphene and Its Derivatives

Nanomaterials are anticipated to be promising storage media, owing to their high surface-to-mass ratio. The high hydrogen capacity achieved by using graphene has reinforced this opinion and motivated investigations of the possibility to use it to store another important energy carrier – lithium (Li). While the first-principles computations show that the Li capacity of pristine graphene, limited by Li clustering and phase separation, is lower than that offered by Li intercalation in graphite, we explore the feasibility of modifying graphene for better Li storage. It is found that certain structural defects in graphene can bind Li stably, yet a more efficacious approach is through substitution doping with boron (B). In particular, the layered C₃B compound stands out as a promising Li storage medium. The monolayer C₃B has a capacity of 714 mAh/g (as Li_1.25C₃B), and the capacity of stacked C₃B is 857 mAh/g (as Li_1.5C₃B), which is about twice as large as graphite’s 372 mAh/g (as LiC₆). Our results help clarify the mechanism of Li storage in low-dimensional materials, and shed light on the rational design of nanoarchitectures for energy storage

Computational Discovery of Codoped Single-Atom Catalysts for Methane-to-Methanol Conversion

The absence of a synthetic catalyst that can selectively oxidize methane to methanol motivates extensive study of single-site catalysts that possess a high degree of tunability in their coordination environments and share similarities with natural enzymes that can catalyze this reaction. Single-atom catalysts (SACs), in particular doped graphitic SACs, have emerged as a promising family of materials due to their high atom economy and scalability, but SACs are yet to be exhaustively screened for methane-to-methanol conversion. Modulating the coordination environment near single metal sites by means of codopants, we carry out a large-scale high-throughput virtual screen of 2048 transition metal (i.e., Mn, Fe, Co, and Ru) SACs codoped with various elements (i.e., N, O, P, and S) in numerous spin and oxidation (i.e., M(II)/M(III)) states for the challenging conversion of methane to methanol. We identify that the ground-state preference is metal- and oxidation-state-dependent. We observe a weak negative correlation between the oxo formation energy (ΔE(oxo)) and the energy of hydrogen atom transfer (ΔE(HAT)), thanks to the high variability in the coordination environment. Therefore, codoped SACs demonstrate flexible tunability that disrupts linear free energy relationships in a manner similar to that of homogeneous catalysts without losing the scalability of heterogeneous catalysts. We identify energetically favorable catalyst candidates along the Pareto frontier of ΔE(oxo) and ΔE(HAT). Further kinetic analysis reveals an intermediate-spin Fe(II) SAC and a low-spin Ru(II) SAC as promising candidates that merit further experimental exploration

Water-Repellent Properties of Superhydrophobic and Lubricant-Infused “Slippery” Surfaces: A Brief Study on the Functions and Applications

Bioinspired water-repellent materials offer a wealth of opportunities to solve scientific and technological issues. Lotus-leaf and pitcher plants represent two types of antiwetting surfaces, i.e., superhydrophobic and lubricant-infused “slippery” surfaces. Here we investigate the functions and applications of those two types of interfacial materials. The superhydrophobic surface was fabricated on the basis of a hydrophobic fumed silica nanoparticle/poly­(dimethylsiloxane) composite layer, and the lubricant-infused “slippery” surface was prepared on the basis of silicone oil infusion. The fabrication, characteristics, and functions of both substrates were studied, including the wettability, transparency, adhesive force, dynamic droplet impact, antifogging, self-cleaning ability, etc. The advantages and disadvantages of the surfaces were briefly discussed, indicating the most suitable applications of the antiwetting materials. This contribution is aimed at providing meaningful information on how to select water-repellent substrates to solve the scientific and practical issues, which can also stimulate new thinking for the development of antiwetting interfacial materials

Computational Discovery of Codoped Single-Atom Catalysts for Methane-to-Methanol Conversion

The absence of a synthetic catalyst that can selectively oxidize methane to methanol motivates extensive study of single-site catalysts that possess a high degree of tunability in their coordination environments and share similarities with natural enzymes that can catalyze this reaction. Single-atom catalysts (SACs), in particular doped graphitic SACs, have emerged as a promising family of materials due to their high atom economy and scalability, but SACs are yet to be exhaustively screened for methane-to-methanol conversion. Modulating the coordination environment near single metal sites by means of codopants, we carry out a large-scale high-throughput virtual screen of 2048 transition metal (i.e., Mn, Fe, Co, and Ru) SACs codoped with various elements (i.e., N, O, P, and S) in numerous spin and oxidation (i.e., M(II)/M(III)) states for the challenging conversion of methane to methanol. We identify that the ground-state preference is metal- and oxidation-state-dependent. We observe a weak negative correlation between the oxo formation energy (ΔE(oxo)) and the energy of hydrogen atom transfer (ΔE(HAT)), thanks to the high variability in the coordination environment. Therefore, codoped SACs demonstrate flexible tunability that disrupts linear free energy relationships in a manner similar to that of homogeneous catalysts without losing the scalability of heterogeneous catalysts. We identify energetically favorable catalyst candidates along the Pareto frontier of ΔE(oxo) and ΔE(HAT). Further kinetic analysis reveals an intermediate-spin Fe(II) SAC and a low-spin Ru(II) SAC as promising candidates that merit further experimental exploration

Tough, Antifreezing, and Piezoelectric Organohydrogel as a Flexible Wearable Sensor for Human–Machine Interaction

Piezoelectric hydrogel sensors are becoming increasingly popular for wearable sensing applications due to their high sensitivity, self-powered performance, and simple preparation process. However, conventional piezoelectric hydrogels lack antifreezing properties and are thus confronted with the liability of rupture in low temperatures owing to the use of water as the dispersion medium. Herein, a kind of piezoelectric organohydrogel that integrates piezoelectricity, low-temperature tolerance, mechanical robustness, and stable electrical performance is reported by using poly(vinylidene fluoride) (PVDF), acrylonitrile (AN), acrylamide (AAm), p-styrenesulfonate (NaSS), glycerol, and zinc chloride. In detail, the dipolar interaction of the PVDF chain with the PAN chain facilitates the crystal phase transition of PVDF from the α to β phase, which endows the organohydrogels with a high piezoelectric constant d33 of 35 pC/N. In addition, the organohydrogels are highly ductile and can withstand significant tensile and compressive forces through the synergy of the dipolar interaction and amide hydrogen bonding. Besides, by incorporating glycerol and zinc chloride, the growth of ice crystals is inhibited, allowing the organohydrogels to maintain stable flexibility and sensitivity even at −20 °C. The real-time monitoring of the pulse signal for up to 2 min indicates that the gel sensor has stable sensitivity. It is believed that our organohydrogels will have good prospects in future wearable electronics