Ti₂CO₂ Nanotubes with Negative Strain Energies and Tunable Band Gaps Predicted from First-Principles Calculations

MXenes, a series of two-dimensional (2D) layered early transition metal carbide, nitride, and carbonitride, have been prepared by exfoliating MAX phases recently. In addition to 2D planar MXene, one-dimensional tubular formsMXene nanotubesare also expected to form. Herein, we design atomic models for Ti₂C as well as Ti₂CO₂ nanotubes in the 1–4 nm diameter range and investigate their basic properties through density functional theory (DFT). It is shown that though the strain energy of Ti₂C nanotubes are always positive, Ti₂CO₂ nanotubes have negative strain energies when diameter beyond 2.5 nm, indicating that they could possibly folded from 2D Ti₂CO₂ nanosheets. Moreover, the band gap of Ti₂CO₂ nanotubes decrease with the growing diameter and the maximum band gap can reach up to 1.1 eV, over 3 times that of their planar form. Thus, tunable band gaps provide strong evidence for the effectiveness of nanostructuring on the electronic properties of Ti₂CO₂ nanotubes

Role of Strain and Concentration on the Li Adsorption and Diffusion Properties on Ti₂C Layer

The performance of Li-ion batteries relies heavily on the capacity and stability of constituent electrodes. Recently synthesized 2D MXenes have demonstrated excellent Li-ion capacity with extremely high charging rates. In this work, first-principles calculations are employed to investigate the effects of external strain and Li concentration on the adsorption and diffusion of Li on Ti₂C layer, a representative MXene. Our calculations demonstrate that the binding energy of Li atoms decreases monotonically with external strains, and the mechanical properties are not influenced by Li adsorption. For multiple Li atoms adsorption, their stable configurations show that the Li atoms tend to reside in one side first, in contrast with other 2D materials. We further show that the binding energy of Li is weakly dependent on the Li concentration. The diffusion barrier is calculated, and the results show that the strain and concentration have limited effects on the diffusion of Li atoms. Finally, the adsorption of Li atoms on two types of Ti₂C double layer are considered. For all studied structures, their stabilities are examined by molecular dynamics simulations carried out at room temperature. The influence of Li adsorption on the electronic structures of Ti₂C layer is also discussed. Our results suggest that Ti₂C could be a promising electrode material for lithium ion batteries in terms of lithium storage capacity and stability at a high Li recycling rate

Long-Term Evolution of Vacancies in Large-Area Graphene

Devices based on two-dimensional (2D) materials such as graphene and molybdenum disulfide have shown extraordinary potential in physics, nanotechnology, and electronics. The performances of these applications are heavily affected by defects in utilized materials. Although great efforts have been spent in studying the formation and property of various defects in 2D materials, the long-term evolution of vacancies is still unclear. Here, using a designed program based on the kinetic Monte Carlo method, we systematically investigate the vacancy evolution in monolayer graphene on a long-time and large spatial scale, focusing on the variation of the distribution of different vacancy types. In most cases, the vacancy distribution remains nearly unchanged during the whole evolution, and most of the evolution events are vacancy migrations with a few being coalescences, while it is extremely difficult for multiple vacancies to dissolve. The probabilities of different categories of vacancy evolutions are determined by their reaction rates, which, in turn, depend on corresponding energy barriers. We further study the influences of different factors such as the energy barrier for vacancy migration, coalescence, and dissociation on the evolution, and the coalescence energy barrier is found to be dominant. These findings indicate that vacancies (also subnanopores) in graphene are thermodynamically stable for a long period of time, conducive to subsequent characterizations or applications. Besides, this work provides hints to tune the ultimate vacancy distribution by changing related factors and suggests ways to study the evolution of other defects in various 2D materials

Drilling Nanopores in Graphene with Clusters: A Molecular Dynamics Study

Using molecular dynamics simulation with empirical potentials, we show that energetic cluster ion beam is a powerful tool to drill nanopores in graphene, which have been proved to possess the potential applications in nanopore-based single-molecule detection and analysis such as DNA sequencing. Two types of clusters are considered, and different cluster size and incident energies are used to simulate the impact events. Our results demonstrate that by choosing suitable cluster species and controlling its energy, a nanopore with expected size and quality could be created in a graphene sheet. Furthermore, suspended carbon chains could be formed at the edge of the nanopore via adjusting the ion energy, which provided a feasible way to decorate the nanopore with chemical methods such as adsorption of large molecules or foreign atoms for biosensing applications

Drilling Nanopores in Graphene with Clusters: A Molecular Dynamics Study

Using molecular dynamics simulation with empirical potentials, we show that energetic cluster ion beam is a powerful tool to drill nanopores in graphene, which have been proved to possess the potential applications in nanopore-based single-molecule detection and analysis such as DNA sequencing. Two types of clusters are considered, and different cluster size and incident energies are used to simulate the impact events. Our results demonstrate that by choosing suitable cluster species and controlling its energy, a nanopore with expected size and quality could be created in a graphene sheet. Furthermore, suspended carbon chains could be formed at the edge of the nanopore via adjusting the ion energy, which provided a feasible way to decorate the nanopore with chemical methods such as adsorption of large molecules or foreign atoms for biosensing applications

Drilling Nanopores in Graphene with Clusters: A Molecular Dynamics Study

Using molecular dynamics simulation with empirical potentials, we show that energetic cluster ion beam is a powerful tool to drill nanopores in graphene, which have been proved to possess the potential applications in nanopore-based single-molecule detection and analysis such as DNA sequencing. Two types of clusters are considered, and different cluster size and incident energies are used to simulate the impact events. Our results demonstrate that by choosing suitable cluster species and controlling its energy, a nanopore with expected size and quality could be created in a graphene sheet. Furthermore, suspended carbon chains could be formed at the edge of the nanopore via adjusting the ion energy, which provided a feasible way to decorate the nanopore with chemical methods such as adsorption of large molecules or foreign atoms for biosensing applications

Drilling Nanopores in Graphene with Clusters: A Molecular Dynamics Study

Using molecular dynamics simulation with empirical potentials, we show that energetic cluster ion beam is a powerful tool to drill nanopores in graphene, which have been proved to possess the potential applications in nanopore-based single-molecule detection and analysis such as DNA sequencing. Two types of clusters are considered, and different cluster size and incident energies are used to simulate the impact events. Our results demonstrate that by choosing suitable cluster species and controlling its energy, a nanopore with expected size and quality could be created in a graphene sheet. Furthermore, suspended carbon chains could be formed at the edge of the nanopore via adjusting the ion energy, which provided a feasible way to decorate the nanopore with chemical methods such as adsorption of large molecules or foreign atoms for biosensing applications

Fabrication of Breathable Multifunctional On-Skin Electronics Based on Tunable Track-Etched Membranes

The on-skin electronics have been extensively studied in various applications such as human–machine interfaces, intelligent prostheses, and health monitoring. However, the current research on flexible electronics tends to focus largely on improving flexibility, functionality, and stability while overlooking the physiological comfort. Therefore, it is necessary to develop a flexible, permeable material and structure to improve long-term wearing comfort for on-skin electronics. Here, the fabrication of breathable multifunctional on-skin electronics based on highly flexible and tunable track-etched membranes is reported. The track-etched membranes are fabricated by a state-of-the-art ion bombardment strategy and feature a smooth surface and unique pore structure regarding precisely tunable pore size and pore density, which offer simultaneously controllable permeability, high functionality, and durability. The track-etched membrane with a pore size of 12.63 μm exhibits an ultrahigh air permeability (190.6 mm s–1) and moisture permeability (2051 g m–2 day–1). Finally, highly flexible and breathable pressure sensors and bioelectric electrodes based on track-etched membranes with advanced thermoregulation are proposed for continuous monitoring of motion and physiological signals

Atomic Layer Deposition Modified Track-Etched Conical Nanochannels for Protein Sensing

Nanopore-based devices have recently become popular tools to detect biomolecules at the single-molecule level. Unlike the long-chain nucleic acids, protein molecules are still quite challenging to detect, since the protein molecules are much smaller in size and usually travel too fast through the nanopore with poor signal-to-noise ratio of the induced transport signals. In this work, we demonstrate a new type of nanopore device based on atomic layer deposition (ALD) Al₂O₃ modified track-etched conical nanochannels for protein sensing. These devices show very promising properties of high protein (bovine serum albumin) capture rate with well time-resolved transport signals and excellent signal-to-noise ratio for the transport events. Also, a special mechanism involving transient process of ion redistribution inside the nanochannel is proposed to explain the unusual biphasic waveshapes of the current change induced by the protein transport

Nanofluidic Pulser Based on Polymer Conical Nanopores

The study of voltage-dependent ion current fluctuation phenomena in synthetic nanopores is important as it is helpful to investigate the mechanism of mass transport in nanoscale systems, which have similarities with natural ion channels in the biological cell membrane. Moreover, we could fabricate some high-performance nanofluidic devices through clearly understanding ion current fluctuation behavior. In this paper, we report a nanofluidic pulser induced by formation and dissolution of weakly soluble salts in conical nanopores. The current fluctuation signals are easily controllable in 1 M KCl electrolyte. Amplitude, frequency, and waveform of ion fluctuation current of the nanofluidic pulser could be controlled by changing the applied negative voltage, and the time ratio of pore opening/closing could be simply manipulated by the concentration of the bivalent cation. A high-quality square wave of ion current signal is found, especially when the negative voltage is below 300 mV. Additionally, we developed a new model about the formation and dissolution process of precipitation. Our work is helpful for the design of nanoscale ion current waveform generators in the future