Chemical Reactivity and Band-Gap Opening of Graphene Doped with Gallium, Germanium, Arsenic, and Selenium Atoms

Theoretical insights into the adsorption and gas sensing performance of Fe/Cu-adsorbed graphene

The binding mechanism of gas molecules on material surfaces is essential for understanding adsorption and sensing performance. In the present study, we examine the interaction of some volatile organic compounds (VOCs), including HCHO, C2H5OH, and CH3COCH3, on pristine graphene and its Fe/Cu-adsorbed surfaces using first-principles calculations. The results indicate that the adsorption of these molecules on graphene is regarded as physisorption, while chemisorption is observed for Fe/Cu attached surfaces. The binding of sites on molecules and surfaces primarily involves hydrogen bonds for the pure form of graphene. In contrast, stable interactions occur at functional groups such as >CO, -OH with Fe/Cu atoms, as well as CC bonds of π-rings on modified structures of graphene. It is noticeable that stronger adsorption is observed in the case of Fe addition (Gr-Fe) compared to Cu (Gr-Cu), enhancing the gas adsorption and sensing performance on graphene. Remarkably, the graphene surfaces supported by Fe and Cu improved selectivity in detecting VOC molecules, particularly C2H5OH and CH3COCH3 for Gr-Fe, and HCHO for Gr-Cu. Quantum chemical analyses reveal that the Fe/Cu⋯O/C contacts are covalent interactions, contributing significantly to the stability of configurations and sensing properties of Fe/Cu-adsorbed graphene. In summary, the observed improvements in selectivity, enhanced adsorption strength, and the identification of crucial interactions at the surface offer valuable insights into designing highly efficient gas sensors and developing advanced sensing materials.

Chemical reactivity of graphene doped with 3d transition metals: nothing compares to a single vacancy

CONTEXT

Finding catalysts that do not rely on the use of expensive metals is one of the requirements to achieve sustainable production. The reactivity of graphene doped with 3d transition metals was studied. All dopants enhanced the reactivity of graphene and performed better than Stone-Wales defects and divacancies, but were inferior to monovacancies. For hydrogenation of doped-monovacancies, Sc, Ti, Cr, Co, and Ni induced more prominent reactivity on the carbon atoms. However, the metals were the most reactive center for V, Mn, and Fe-doped graphene. Cu and Zn turned the four neighboring carbon atoms into the preferred sites for hydrogenation. The addition of oxygen to doped graphene with Ti, V, Cr, Mn, Fe, Co, and Ni on a monovacancy revealed a more uniform pattern since the metal, preferred to react with oxygen. However, Sc induced a larger reactivity on the carbon atoms. The affinity of the 3d metal-doped graphene systems towards oxygen was inferior to that observed for single-vacancies. Therefore, vacancy engineering is the most favorable and least expensive method to enhance the reactivity of graphene.

METHODS

We applied Truhlar's M06-L method accompanied by the 6-31G* basis sets to perform periodic boundary conditions calculations as implemented in Gaussian 09. The ultrafine grid was employed and the unit cells were sampled employing 100 k-points. Results were visualized employing Gaussview 5.0.1.

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.

Emerging properties of carbon based 2D material beyond graphene

Graphene turns out to be the pioneering material for setting up boulevard to a new zoo of recently proposed carbon based novel two dimensional (2D) analogues. It is evident that their electronic, optical and other related properties are utterly different from that of graphene because of the distinct intriguing morphology. For instance, the revolutionary emergence of Dirac cones in graphene is particularly hard to find in most of the other 2D materials. As a consequence the crystal symmetries indeed act as a major role for predicting electronic band structure. Since tight binding calculations have become an indispensable tool in electronic band structure calculation, we indicate the implication of such method in graphene's allotropes beyond hexagonal symmetry. It is to be noted that some of these graphene allotropes successfully overcome the inherent drawback of the zero band gap nature of graphene. As a result, these 2D nanomaterials exhibit great potential in a broad spectrum of applications, viz nanoelectronics, nanooptics, gas sensors, gas storages, catalysis, and other specific applications. The miniaturization of high performance graphene allotrope based gas sensors to microscopic or even nanosized range has also been critically discussed. In addition, various optical properties like the dielectric functions, optical conductivity, electron energy loss spectra reveal that these systems can be used in opto-electronic devices. Nonetheless, the honeycomb lattice of graphene is not superconducting. However, it is proposed that the tetragonal form of graphene can be intruded to form new hybrid 2D materials to achieve novel superconducting device at attainable conditions. These dynamic experimental prospects demand further functionalization of these systems to enhance the efficiency and the field of multifunctionality. This topical review aims to highlight the latest advances in carbon based 2D materials beyond graphene from the basic theoretical as well as future application perspectives.

Tailoring the Structural and Electronic Properties of Graphene through Ion Implantation

Ion implantation is a superior post-synthesis doping technique to tailor the structural properties of materials. Via density functional theory (DFT) calculation and ab-initio molecular dynamics simulations (AIMD) based on stochastic boundary conditions, we systematically investigate the implantation of low energy elements Ga/Ge/As into graphene as well as the electronic, optoelectronic and transport properties. It is found that a single incident Ga, Ge or As atom can substitute a carbon atom of graphene lattice due to the head-on collision as their initial kinetic energies lie in the ranges of 25–26 eV/atom, 22–33 eV/atom and 19–42 eV/atom, respectively. Owing to the different chemical interactions between incident atom and graphene lattice, Ge and As atoms have a wide kinetic energy window for implantation, while Ga is not. Moreover, implantation of Ga/Ge/As into graphene opens up a concentration-dependent bandgap from ~0.1 to ~0.6 eV, enhancing the green and blue light adsorption through optical analysis. Furthermore, the carrier mobility of ion-implanted graphene is lower than pristine graphene; however, it is still almost one order of magnitude higher than silicon semiconductors. These results provide useful guidance for the fabrication of electronic and optoelectronic devices of single-atom-thick two-dimensional materials through the ion implantation technique.

Hydrogen sulfide molecule adsorbed on doped graphene: a first-principles study

First principles were used to investigate electronic properties of Au-doped graphene, Ag-doped graphene, and Cu-doped graphene and the effect of adsorption behavior of hydrogen sulfide (H₂S) molecule on their electronic properties. Doped graphene exhibits interesting electronic properties. The gap value of Ag-doped graphene is 0.29 eV, whereas Au-doped graphene is 0.48 eV which is the largest one in three doped systems, a clear difference of structure and electronic properties among three doped systems absorbing H₂S molecule. The doped atom and the H₂S molecule are on the same side of the graphene for Au-doped graphene and Cu-doped graphene, which belong to a kind of bonding orbital hybridization of electron cloud showed from charge difference density plots. However, Ag-doped graphene adsorbed with H₂S molecule exhibits a kind of antibonding orbital hybridization. With the analysis in this paper, it is beneficial to research H₂S gas sensors.

Structural, electronic and optical properties of metalloid element (B, Si, Ge, As, Sb, and Te) doped g-ZnO monolayer: A DFT study

Stable geometries, electronic structure, and optical properties of ZnO monolayer doped with metalloid element (M = B, Si, Ge, As, Sb, and Te) atom have been studied using density functional theory. It is found that among these elements Ge, As, and Sb can be effectively doped at Zn site in the ZnO monolayer with the formation energies ranging from -1.02 to -0.96 eV. Except B element, all the metalloid atoms prefer to protrude out of the plane of the ZnO monolayer. The nonmagnetic nature of the ZnO monolayer is retained with the doping of B, Si, Ge, As, and Sb atom, while Te atom induces the magnetism in ZnO monolayer (2 μB). While doping of Si, As, Sb, and Te in ZnO monolayer resulted in a red shift in the absorption spectra of doped ZnO monolayer and the blue shift is observed for B and Ge doped ZnO. The static dielectric constant for ZnO monolayer is 1.49. With the doping of these metalloid elements in ZnO monolayer, the dielectric constant can be tuned from 1.36 to 2.84. These results are potentially useful for optoelectronic applications and the development of optical nanostructures.

Electronic structural critique of interesting thermal and optical properties of C17Ge germagraphene

In this communication, we report a theoretical attempt to understand the involvement of the electronic structure in determining the optical and thermal properties of C17Ge germagraphene, a buckled two-dimensional material. The structure is found to be a direct bandgap semiconductor with low carrier effective mass. Our study has revealed the effect of spin-orbit coupling on the band structure, and the appearance of spin Hall current on the material. The selectively high blue to ultraviolet light absorption, and a refractive index comparable to flint glass, open up the possible applicability of this material for optical devices. From an electronic structural point of view, we investigate the reason behind its moderately high Seebeck coefficient and power factor which are comparable to traditional thermoelectric materials. Besides its narrow bandgap and relatively smaller work function of 4.361 eV, compared to graphene (4.390 eV) and germanene (4.682 eV), ensures easier removal of electrons from the surface. This material turns out to be an excellent alternative for future semiconductor applications, from optical to thermal devices.

Microwave Energy Drives "On-Off-On" Spin-Switch Behavior in Nitrogen-Doped Graphene

The established application of graphene in organic/inorganic spin-valve spintronic assemblies is as a spin-transport channel for spin-polarized electrons injected from ferromagnetic substrates. To generate and control spin injection without such substrates, the graphene backbone must be imprinted with spin-polarized states and itinerant-like spins. Computations suggest that such states should emerge in graphene derivatives incorporating pyridinic nitrogen. The synthesis and electronic properties of nitrogen-doped graphene (N content: 9.8%), featuring both localized spin centers and spin-containing sites with itinerant electron properties, are reported. This material exhibits spin-switch behavior (on-off-on) controlled by microwave irradiation at X-band frequency. This phenomenon may enable the creation of novel types of switches, filters, and spintronic devices using sp² -only 2D systems.

Theoretical characterization of hexagonal 2D Be3N2 monolayers

With the help of DFT calculations, a possible synthesis method for monolayer Be₃N₂ is proposed. Furthermore, its excellent thermal, dynamical, and mechanical stability makes it a material of comparable caliber to that of graphene.

Theoretical studies on the structures and properties of doped graphenes with and without an external electrical field

To expand the applications of graphene in optoelectronic devices, B, Al, Si, Ge, As, and Sb doped graphenes (marked as B-G, Al-G, Si-G, Ge-G, As-G, and Sb-G, respectively) were synthesised. The geometric structures, population analyses, and also electronic and optical properties of these doped graphene materials were investigated employing the density functional theory (DFT) method. It was shown that the band gaps of doped graphenes were opened and their absorption spectra were red-shifted by the addition of doping atoms, and their dielectric functions and refractive indexes of low frequency were decreased compared with those of pure graphene. Moreover, the electronic and optical properties of doped graphenes under an external electrical field ranging from −0.4 to 1.2 eV Å⁻¹ have been explored. It was found that the band gaps of As-G and Sb-G were increased to 0.864 and 1.841 eV under a 1.2 eV Å⁻¹ external electrical field, respectively. On the contrary, the band gaps of B-G, Al-G, Si-G, and Ge-G were decreased with the increase of the external electrical field intensity. Additionally, the absorption peaks of B-G, Al-G, Si-G, and Ge-G were red-shifted upon applying the external electrical field. Correspondingly, their dielectric functions and refractive indexes of low frequency were increased. Surprisingly, the absorption spectra, dielectric functions, and refractive indexes of As-G and Sb-G have no significant changes.

To expand the applications of graphene in optoelectronic devices, B, Al, Si, Ge, As, and Sb doped graphenes (marked as B-G, Al-G, Si-G, Ge-G, As-G, and Sb-G, respectively) were synthesised.

Controlling graphene work function by doping in a MOCVD reactor

Here we demonstrate a new method for doping graphene using Metal Organic Chemical Vapor Deposition (MOCVD) reactor. The original undoped graphene was of a very high quality mounted on Si/SiO₂ substrates, they were then doped in the MOCVD's reactor using tertiarybutylphosphine (TBP) and tertiarybutylarsene (TBA). Post process Raman spectroscopy confirmed the presence of a single layer of phosphor doped graphene (G/P) and Arsine doped graphene (G/As) when doped by TBP or by TBA, respectively. Blue shift of the 2D peak assured p-type doping. The work function determined by ultraviolet photoelectron spectroscopy varied from 4.5 eV for Pristine Graphene to 4.7, 4.8 eV for G/As, G/P, respectively. The increase of the work function is attributed to electron transfer from the graphene to the dopant. Our results suggest that doping graphene by MOCVD with TBA or TBP can easily and effectively alternate the work function by few tenths of eV and improve the electronic properties of graphene. The MOCVD technology of doping graphene opens a new route on which other semiconductors can be epitaxially grown on it in a continues process in the same MOCVD reactor.

Stable and Reversible Triphenylphosphine-Based n-Type Doping Technique for Molybdenum Disulfide (MoS2)

A highly stable and reversible n-type doping technique for molybdenum disulfide (MoS₂) transistors and photodetectors is developed in this study. This doping technique is based on triphenylphosphine (PPh₃) and significantly improves the performance of MoS₂ transistor and photodetector devices in terms of the on/off-current ratio (8.72 × 10⁴ → 8.70 × 10⁵), mobility (12.1 → 241 cm²/V·s), and photoresponsivity ( R) (2.77 × 10³ → 3.92 × 10⁵ A/W). The range of doping concentrations is broadly distributed between 1.56 × 10¹¹ and 9.75 × 10¹² cm^-2 and is easily controlled by adjusting the temperature at which the PPh₃ layer is formed. In addition, this doping technique provides two interesting properties that have not been reported for previous molecular doping techniques: (i) high stability leading to small variations in device performance after exposure to air for 14 days (on-current: 1.34% and photoresponsivity: 1.58%) and (ii) reversibility enabling the repetitive formation and removal of PPh₃ molecules (doping and dedoping).

Implanting Germanium into Graphene

Incorporating heteroatoms into the graphene lattice may be used to tailor its electronic, mechanical and chemical properties, although directly observed substitutions have thus far been limited to incidental Si impurities and P, N and B dopants introduced using low-energy ion implantation. We present here the heaviest impurity to date, namely ⁷⁴Ge⁺ ions implanted into monolayer graphene. Although sample contamination remains an issue, atomic resolution scanning transmission electron microscopy imaging and quantitative image simulations show that Ge can either directly substitute single atoms, bonding to three carbon neighbors in a buckled out-of-plane configuration, or occupy an in-plane position in a divacancy. First-principles molecular dynamics provides further atomistic insight into the implantation process, revealing a strong chemical effect that enables implantation below the graphene displacement threshold energy. Our results demonstrate that heavy atoms can be implanted into the graphene lattice, pointing a way toward advanced applications such as single-atom catalysis with graphene as the template.

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.

Epoxidation of ethylene over Pt-, Pd- and Ni-doped graphene in the presence of N2O as an oxidant: a comparative DFT study

The catalytic activities of Pt-, Pd-, and Ni-doped graphene nanosheets for the oxidation of ethylene to ethylene oxide by N₂O molecule are compared using the density functional theory calculations.

Creation of Ge-Nx-Cy Configures in Carbon Nanotubes: Origin of Enhanced Electrocatalytic Performance for Oxygen Reduction Reaction

High-performance nitrogen and germanium codoped carbon nanotubes (N-Ge-CNTs) were synthesized as oxygen reduction reaction (ORR) catalysts by one-step sintering of carboxyethyl germanium sesquioxide and multiwalled CNTs in NH3 atmosphere. The ORR electrocatalytic activity evaluation was performed by using limited current density, selective reaction pathway, onset potential, H2O2 yields, and kinetic current density. In comparison with Ge or N solely doped CNTs, the codoped samples display more excellent ORR catalytic performance. It was observed that the codoped GeN3C, GeN4, and GeN4 + NC3 microstructures in N-Ge-CNTs are crucial to improving ORR catalytic performance, such as ideal 4 electron pathway (3.95) and positive onset potential (-0.08 V). The high ORR performance is attributed to the synergistic effect of N and Ge doping, which is capable of activating the π electrons of sp(2) hybridized orbital around carbon nantotubes. The ORR catalytic synergistic effect has also been verified by calculating the work function on the basis of density functional theory (DFT).

The effect of the dopant nature on the reactivity, interlayer bonding and electronic properties of dual doped bilayer graphene

Heteroatom doping of bilayer graphene can be used to modify the reactivity, magnetic moment and chemical reactivity of the undoped layer!

Computational study of the structure, UV-vis absorption spectra and conductivity of biphenylene-based polymers and their boron nitride analogues

We calculated electronic and spectral properties of the 1D and 2D carbon and boron nitride materials composed of four-, six- and eight-membered rings by the DFT approach, including the band structure analysis.