Critical Temperature in Zigzag Graphene Nanoribbon: a First-principles Study

The critical (Néel) temperature in the zigzag graphene nanoribbon was calculated using the mean-eld approximation within the generalized Bloch theorem. This calculation was carried out over the Brillouin zone of the magnon spectrum. We found a nearly at magnon dispersion at the high energy in one-third of the Brillouin zone. Our calculation showed the critical temperature below room temperature, in good agreement with the prediction in the previous works. Our last work (Prayitno 2021 Physica E 129 114641) revealed that the critical temperature may be enhanced by increasing the ribbon width. In this brief report, we justified that the critical temperature becomes almost constant up to a certain ribbon width. This result indicates that the critical temperature in the graphene nanoribbon will never reach room temperature for any ribbon widths, thus it is likely difficult to apply pristine graphene nanoribbon in any practical devices working near room temperature.

Feature-Rich Geometric and Electronic Properties of Carbon Nanoscrolls

How to form carbon nanoscrolls with non-uniform curvatures is worthy of a detailed investigation. The first-principles method is suitable for studying the combined effects due to the finite-size confinement, the edge-dependent interactions, the interlayer atomic interactions, the mechanical strains, and the magnetic configurations. The complex mechanisms can induce unusual essential properties, e.g., the optimal structures, magnetism, band gaps and energy dispersions. To reach a stable spiral profile, the requirements on the critical nanoribbon width and overlapping length will be thoroughly explored by evaluating the width-dependent scrolling energies. A comparison of formation energy between armchair and zigzag nanoscrolls is useful in understanding the experimental characterizations. The spin-up and spin-down distributions near the zigzag edges are examined for their magnetic environments. This accounts for the conservation or destruction of spin degeneracy. The various curved surfaces on a relaxed nanoscroll will create complicated multi-orbital hybridizations so that the low-lying energy dispersions and energy gaps are expected to be very sensitive to ribbon width, especially for those of armchair systems. Finally, the planar, curved, folded, and scrolled graphene nanoribbons are compared with one another to illustrate the geometry-induced diversity.

Study of the Influence of Geometric Parameters in an Innovative Scraped Surface Heat Exchanger With Helical Ribbon

This work aims to characterize the hydrodynamic and thermal behaviors in an innovative scraped surface heat exchanger (SSHE) equipped with helical ribbon by means of the numerical simulation approach. In this study, the conservation equations of continuity, momentum, and energy in the laminar, steady-state and isothermal conditions are resolved using a specific computational fluid dynamics (CFD) code based on the 3D finite volume method. The effects of the gap between the exchanger wall and the tip of the ribbon, the ribbon width, and the number of turns in the ribbon on the hydrodynamic and thermal behaviors are studied. Varying the gap values leads to reveal an optimum value giving the highest heat transfer coefficient. Moreover, numerical results have shown that increasing the ribbon width improves the heat transfer. Furthermore, the influence of the number of turns is carried out for Reynolds number ratios (Rer/Rea) inferior and superior to 1. Results revealed that increasing the number of turns avoids the back-mixing phenomenon and thus improves the heat transfer. In this study, the establishment of correlation is determined with the introduction of dimensionless and geometrical groups to predict the heat transfer coefficient in SSHE.

Modulation of the optical properties of zigzag silicene nanoribbons by double carbon chains

Using first-principles calculations, we investigate the electronic and optical properties of zigzag silicene nanoribbons substituted with double carbon chains. The results show that the chains are pulled nearly straight and produce a rather obvious transverse contraction in the width direction of the ribbon. The double carbon chains introduce defect states that appear as two degenerate bands across the Fermi level. These nanoribbons are always metallic regardless of the position of the carbon chains or the ribbon width. Under the same bandwidth, the imaginary parts of the dielectric functions in the Ex and Ey directions reveal red- and blue-shifts, respectively, with increasing distance between the two C chains. The imaginary parts of the dielectric functions in the Ex and Ey directions reveal blue- and redshifts, respectively, with increasing ribbon width. Three major peaks in the imaginary part of the dielectric function correspond to the intrinsic plasma frequencies originating from electron transitions of silicon and carbon. Such excellent electronic and optical properties may lead to some important applications of the nanoribbons in short-wavelength optoelectronic devices.

Electronic and magnetic properties of the Janus MoSSe/WSSe superlattice nanoribbon: a first-principles study

The electronic structure properties of Janus MoSSe/WSSe superlattice nanoribbons (SLNRs) are investigated by first-principles calculations. The ribbon width, combination ratio and period length have a great effect on the properties of the SLNRs.

Electronic structures and transport properties of SnS–SnSe nanoribbon lateral heterostructures

Zigzag lateral heterostructures of 2D group-IV monochalcogenides have an interesting negative differential resistive effect, independent of the ribbon width.

Even–odd oscillation of bandgaps in GeP3 nanoribbons and a tunable 1D lateral homogenous heterojunction

Band gap of armchair GeP3 nanoribbons shows strong even-odd oscillation as a function of ribbon width. Based on this unique feature, a one dimensional lateral homogenous heterojunction is designed to investigate the potential application.