Mono and dual doped monolayer graphene with aluminum, silicon, phosphorus and sulfur

Theoretical Characterization of Germanene Doped with Main Group Elements

Herein, using density functional calculations, we studied the substitutional doping in germanene with B, C, N, O, Al, Si, P, S, Ga, As, and Se. Nitrogen is the element that can be more easily incorporated into the germanene lattice, followed by silicon, carbon, and boron. Almost all dopants were efficient in opening a band-gap. Yet, caution should be taken because this opening strongly depends on the dopant concentration. Carbon and sulfur were the most effective elements for band-gap opening. C-doping generates the lowest effective masses (me*/m0=mh*/m0=0.09). The equal me and mh values indicate an intrinsic semiconductor behavior, a characteristic shared by the chalcogenides-doped systems. Additionally, we performed a detailed analysis of the preferred disposition of dopants in the germanene lattice. In contrast with the results obtained for graphene, when multiple atoms are introduced in the germanene framework, they do not prefer to be agglomerated, adopting a random disposition, except in the case of sulfur and nitrogen, which favored specific dopant arrangement. Two sulfur dopants showed a notorious preference for replacing a Ge-Ge bond but without forming an S-S linkage, thus adopting a thiophene-like structure that may impart germanene exciting properties, as observed for S and N codoped graphene.

Toward the Production of Super Graphene

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Strain and electric field induced electronic property modifications in two-dimensional Janus SZrAZ2 (A = Si, Ge; Z = P, As) monolayers

Recently, significant attention has been directed towards two-dimensional Janus materials owing to their unique structure and novel properties. In this work, we have introduced novel two-dimensional Janus monolayers, SZrAZ2 (A = Si, Ge; Z = P, As), through first principles. Our primary focus was the investigation of the controllable electronic properties exhibited by the Janus SZrAZ2 structures under the influence of strain and an external electric field. Our research findings indicate the dynamic and thermodynamic stability of Janus SZrAZ2 (A = Si, Ge; Z = P, As) monolayers. In the equilibrium state, these monolayers exhibit properties of an indirect band gap semiconductor. When subjected to biaxial strain and an external electric field, we observed that the dependency of SZrSiAs2 and SZrGeAs2 monolayers on an external electric field is very weak. Their electronic properties can only be modulated by applying biaxial strain. For SZrSiP2 and SZrGeP2 monolayers, their electronic properties can be modulated under biaxial strain and an external electric field, resulting in a transition from semiconducting to metallic behavior. Finally, we calculated the carrier mobility of these four structures and observed that the SZrGeAs2 monolayer exhibits a hole mobility of up to 597.52 cm2 s-1 V-1 in the x-direction, whereas the SZrSiP2 monolayer demonstrates an electron mobility of up to 479.30 cm2 s-1 V-1 in the y-direction. In the x-direction, the electron mobility of SZrSiAs2 and SZrGeP2 monolayers was measured to be 189.88 and 528.44 cm2 s-1 V-1, respectively. These values are greater than or equivalent to that of experimentally synthesized MoS2 (∼200 cm2 s-1 V-1). Our research lays the foundation for utilizing two-dimensional Janus materials in electronic devices.

Heteroatom Codoped Graphene: The Importance of Nitrogen

Although graphene has exceptional properties, they are not enough to solve the extensive list of pressing world problems. The substitutional doping of graphene using heteroatoms is one of the preferred methods to adjust the physicochemical properties of graphene. Much effort has been made to dope graphene using a single dopant. However, in recent years, substantial efforts have been made to dope graphene using two or more dopants. This review summarizes all the hard work done to synthesize, characterize, and develop new technologies using codoped, tridoped, and quaternary doped graphene. First, I discuss a simple question that has a complicated answer: When can an atom be considered a dopant? Then, I briefly discuss the single atom doped graphene as a starting point for this review's primary objective: codoped or dual-doped graphene. I extend the discussion to include tridoped and quaternary doped graphene. I review most of the systems that have been synthesized or studied theoretically and the areas in which they have been used to develop new technologies. Finally, I discuss the challenges and prospects that will shape the future of this fascinating field. It will be shown that most of the graphene systems that have been reported involve the use of nitrogen, and much effort is needed to develop codoped graphene systems that do not rely on the stabilizing effects of nitrogen. I expect that this review will contribute to introducing more researchers to this fascinating field and enlarge the list of codoped graphene systems that have been synthesized.

Electronic and Optical Properties of Twin T-Graphene Co-Doped with Boron and Phosphorus

Twin T-graphene (TTG) is a new two-dimensional carbon allotrope of graphene. Heteroatom co-doping is an effective method for the modulation of the physical and chemical properties of two-dimensional materials. This study explored the structural stability, electronic structures, and optical properties of boron and phosphorus co-doped TTG using first-principles calculations. TTG was doped with B and P atoms (BP) at different positions considering 13 different configurations. Pristine TTG has a band gap of 1.89 eV, and all BP co-doped TTG (TTG/BP) systems remain semiconducting with band gaps that gradually decrease with increasing doping concentration. For a given doping concentration, the TTG/BP-ortho systems had a narrower band gap than the corresponding TTG/BP-para systems. The TTG and TTG/BP systems exhibited significant optical anisotropy. In the infrared region, BP co-doping increased the absorption coefficient, and the reflectance and refractive index increased with increasing doping concentration, except for the vertical component of the TTG/BP-ortho system. In the visible region, the absorption coefficient, reflectance, and refractive index decreased with increasing doping concentration for the vertical component, and the peaks were red-shifted from the near-ultraviolet region to the visible region. In the near-ultraviolet region, the reflectance also decreased with increasing doping concentration. The BP co-doping concentration can regulate the electronic structures and optical properties of the TTG, showing that the BP co-doped TTG has potential for application in nanoelectronics and optoelectronics.

Tailoring Electronic and Magnetic Properties of Graphene by Phosphorus Doping

The electronic and magnetic properties of graphene can be modulated by doping it with other elements, especially those with a different number of valence electrons. In this article, we first provide a three-dimensional reconstruction of the atomic structure of a phosphorus substitution in graphene using aberration-corrected scanning transmission electron microscopy. Turning then to theoretical calculations based on the density functional theory (DFT), we show that doping phosphorus in various bonding configurations can induce magnetism in graphene. Our simulations reveal that the electronic and magnetic properties of P-doped (Gr-P) and/or phosphono-functionalized graphene (Gr-PO₃H₂) can be controlled by both the phosphorus concentration and configurations, ultimately leading to ferromagnetic (FM) and/or antiferromagnetic (AFM) features with the transition temperature up to room temperature. We also calculate core-level binding energies of variously bonded P to facilitate X-ray photoelectron spectroscopy-based identification of its chemical form present in P-doped graphene-based structures. These results may enable the design of graphene-based organic magnets with tailored properties for future magnetic or spintronic applications.

First-principles study of dual-doped graphene: towards promising anode materials for Li/Na-ion batteries

The interaction of Li/Na with various DDG is studied with the help of DFT. Among them, the Be–B DDG systems exhibit exceptional properties, such as large storage capacities, excellent OCVs, good electronic conductivities, and minor changes in their planes. These properties show that Be–B DDG can serve as promising anode materials for LIBs/SIBs.

Modulating the electronic and magnetic properties of graphene

Graphene, an sp²hybridized single sheet of carbon atoms organized in a honeycomb lattice, is a zero band gap semiconductor or semimetal.