A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnO and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. The versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.

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Penta-graphene: A new carbon allotrope

Flat carbon (sp(2) and sp) networks endow the graphdiyne and graphyne families with high degrees of π-conjunction, uniformly distributed pores, and tunable electronic properties; therefore, these materials are attracting much attention from structural, theoretical, and synthetic scientists wishing to take advantage of their promising electronic, optical, and mechanical properties. In this Review, we summarize a state-of-the-art research into graphdiynes and graphynes, with a focus on the latest theoretical and experimental results. In addition to the many theoretical predictions of the potential properties of graphdiynes and graphynes, we also discuss experimental attempts to synthesize and apply graphdiynes in the areas of electronics, photovoltaics, and catalysis.

Graphdiyne and graphyne: from theoretical predictions to practical construction

Using density functional theory coupled with Boltzmann transport equation with relaxation time approximation, we investigate the electronic structure and predict the charge mobility for a new carbon allotrope, the graphdiyne for both the sheet and nanoribbons. It is shown that the graphdiyne sheet is a semiconductor with a band gap of 0.46 eV. The calculated in-plane intrinsic electron mobility can reach the order of 10(5) cm(2)/(V s) at room temperature, while the hole mobility is about an order of magnitude lower.

Electronic structure and carrier mobility in graphdiyne sheet and nanoribbons: theoretical predictions

Graphynes (GYs) are carbon allotropes with single-atom thickness that feature layered 2D structure assembled by carbon atoms with sp- and sp2- hybridization form. Various functional theories have predicted GYs to have natural band gap with Dirac cones structure, presumably originating from inhomogeneous π-bonding between those carbon atoms with different hybridization and overlap of the carbon 2pz orbitals. Among all the GYs, graphdiyne (GDY) was the first reported to be prepared practically and, hence, attracted the attention of many researchers toward this new planar, layered material, as well as other GYs. Several approaches have been reported to be able to modify the band gap of GDY, containing invoking strain, boron/nitrogen doping, nanoribbon architectures, hydrogenation, and so on. GDY has been well-prepared in many different morphologies, like nanowires, nanotube arrays, nanowalls, nanosheets, ordered stripe arrays, and 3D framwork. The fascinating structure and electronic properties of GDY make i...

Progress in Research into 2D Graphdiyne-Based Materials

In light of the considerable impact synthetic 2D polymers are expected to have on many fundamental and applied aspects of the natural and engineering sciences, it is surprising that little research has been carried out on these intriguing macromolecules. Although numerous approaches have been reported over the last several decades, the synthesis of a one monomer unit thick, covalently bonded molecular sheet with a long-range ordered (periodic) internal structure has yet to be achieved. This Review provides an overview of these approaches and an analysis of how to synthesize 2D polymers. This analysis compares polymerizations in (initially) a homogeneous phase with those at interfaces and considers structural aspects of monomers as well as possibly preferred connection modes. It also addresses issues such as shrinkage as well as domain and crack formation, and briefly touches upon how the chances for a successful structural analysis of the final product can possibly be increased.

Two‐Dimensional Polymers: Just a Dream of Synthetic Chemists?

The effect of an external magnetic field on the resistivity of dilute magnetic alloys is investigated with the use of the Green's functions. The equation of motion for the Zubarev Green's functions with an external magnetic field included is solved correctly up to order J 3 and to all orders in V , where J is the exchange integral and V the spin-independent potential. The effect of the external magnetic field is involved in the Zeeman term of logarithmic terms and in F σ (ω) which shows the effect of freezing out of spin-flip scattering. The effect of the spin-independent potential is involved in the modified density of states \( \tilde{\rho}\) and in a phase δ v of the t matrix. The magnetoresistance obtained from numerical calculation shows a variety of patterns which are classified by the sign of \(J \tilde{\rho}\) and the value of the phase shift δ v .

Sumiaki Nagai

Papers

Theory of Magnetoresistance in Dilute Magnetic Alloys