Room temperature p-orbital magnetism in carbon chains and the role of group IV, V, VI, and VII dopants

Thermal Disorder in Finite-Length Carbon Nanowire

Enhancement in chemisorption is one of the active research areas in carbon materials. To remedy the thermally degraded chemisorption occurring at high temperatures, we report a comprehensive study of kink structures in free-standing monoatomic carbon nanowires upon heating. Our Monte Carlo simulation considers multi-monoatomic carbon chains laterally interacting by van der Waals forces. Our study reveals that carbon nanowires maintain their linearity regardless of chain length at low temperatures, but this is not the case at high temperatures. Disordered kink structure is observed in short carbon chains, especially above the Peierls transition temperature. A severe kink structure may increase the possibility of attaching negatively charged atoms, thereby contributing to the development of next-generation materials for chemisorption at high temperatures. We have also provided an important indication that any physical property of the finite-length carbon chain predicted by ab initio calculation should reconsider the atomic rearrangement due to thermal instability at high temperatures.

A Simulation of the Effect of External and Internal Parameters on the Synthesis of a Carbyne with More than 6000 Atoms for Emerging Continuously Tunable Energy Barriers in CNT-Based Transistors

Transistors made up of carbon nanotube CNT have demonstrated excellent current-voltage characteristics which outperform some high-grade silicon-based transistors. A continuously tunable energy barrier across semiconductor interfaces is desired to make the CNT-based transistors more robust. Despite that the direct band gap of the carbyne inside a CNT can be widely tuned by strain, the size of the carbyne cannot be controlled easily. The production of a monoatomic chain with more than 6000 carbon atoms is an enormous technological challenge. To predict the optimal chain length of a carbyne in different molecular environments, we have developed a Monte Carlo model in which a finite-length carbyne with a size of 4000-15,000 atoms is encapsulated by a CNT at finite temperatures. Our simulation shows that the stability of the carbyne@nanotube is strongly influenced by the nature and porosity of the CNT, the external pressure, the temperature, and the chain length. We have observed an initiation of the chain-breaking process in a compressed carbyne@nanotube. Our work provides much-needed input for optimizing the carbyne length to produce carbon chains much longer than 6000 atoms at ~300 K. Design rules are proposed for synthesizing ~1% strained carbyne@(6,5)CNT as a component in CNT-based transistors to tune the energy barriers continuously.

X-ray Photoelectron Spectra of Ag-Au Colloidal Nanoparticles after Interaction with Linear Carbon Chains

The results of X-ray photoelectron spectra (XPS) characterization of the surface of Ag-Au colloidal nanoparticles (Ag-Au NPs), prepared by laser ablation in water before and after interaction with linear carbon chains (LCC), are presented. No additional features appear in high-energy resolved XPS core level spectra of Ag-Au NPs which indicates that surface is not oxidized. The measurements of XPS Ag 3d-spectrum of (Ag-Au)@LCC manifests the additional low-energy structure that is associated with the formation of Ag–C bonds. The charge transfer between Au atoms on the NPs surface and LCC was established. Additionally, some oxidation of the Ag atoms on the surface of (Ag-Au)@LCC is observed which arises during laser ablation in water. We assume that oxidative species will preferably interact with the areas outside the LCC instead of oxidizing the carbon chains which was confirmed by XPS C 1s spectra.

Novel green phosphorene as a superior chemical gas sensing material

Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH₃, NO, NO₂, CO, CO₂, and H₂O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green's function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO₂, CO, CO₂ are adsorbed on GreenP, stronger than both NH₃ and H₂O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO₂ gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO₂ molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I-V) characteristics of S-doped GreenP exhibit a variation upon NO₂ exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors.

Enormous enhancement of p-orbital magnetism and band gap in the lightly doped carbyne

This paper presents a path to tailor adapted magnetic and electronic properties in carbyne.