Electronic Properties of Oxidized Graphene: Effects of Strain and an Electric Field on Flat Bands and the Energy Gap

Dual-functionalization of graphene: exploring flat bands and optical behavior

Graphenes exceptional electronic and optical properties make it a promising material for advanced technologies. We performed Density Functional Tight Binding (DFTB) simulations to explore the formation of flat electronic bands in graphene functionalized with epoxy and hydrogen groups. By varying the density of functional groups, we identified the emergence of isolated flat bands at critical functional densities (20%), especially beyond 10 hydrogen and 10 oxygen atoms per 72 carbon atoms. Larger supercells (288C-48H-48O) showed the formation of 14 parallel flat bands, emphasizing the impact of high functional group density. Additionally, odd numbers of H and O atoms induced midgap states. Increasing the functionalization ratio (30%) preserved the integrity of the surface modifiers, enhancing binding energy, unit cell constants, and structural stability. Optical properties, including dielectric function, conductivity, and absorption, exhibited distinct shifts with varying functional densities. These results highlight the tunability of graphene's electronic and optical behavior, providing insights for customized graphene-based materials in future electronic and photonic applications.

Functionalized Graphene via a One-Pot Reaction Enabling Exact Pore Sizes, Modifiable Pore Functionalization, and Precision Doping

Functionalizing graphene with exact pore size, specific functional groups, and precision doping poses many significant challenges. Current methods lack precision and produce random pore sizes, sites of attachment, and amounts of dopant, leading to compromised structural integrity and affecting graphene's applications. In this work, we report a strategy for the synthesis of functionalized graphitic materials with modifiable nanometer-sized pores via a Pictet-Spengler polymerization reaction. This one-pot, four-step synthesis uses concepts based on covalent organic frameworks (COFs) synthesis to produce crystalline two-dimensional materials that were confirmed by PXRD, TEM measurements, and DFT studies. These new materials are structurally analogous to doped graphene and graphene oxide (GO) but, unlike GO, maintain their semiconductive properties when fully functionalized.

Distribution of oxygen-containing functional groups on defective graphene: properties engineering and Li adsorption

In this study, the distribution of oxygen-containing functional groups on graphene with vacancies and topological defects was systematically investigated using advanced computational methods and the structure models for multi-defect graphene oxides (GOs) were proposed. All potential adsorption sites were considered through an automated structure generation program to identify energetically favorable structures. Unlike the pristine graphene surface where oxygen-containing functional groups always aggregate with each other, we observed a tendency for them to preferentially adsorb near defects. Furthermore, they may also be distributed on the same side or both sides of the defective graphene. These multi-defect GOs can exhibit either metallic or semiconducting properties. Notably, upon adsorbing the same oxygen-containing functional groups onto the surface of defective graphene, their electronic characteristics become homogeneous. The coexistence of vacancy/topological defects and oxygen-containing functional groups within the graphene lattice introduces intriguing mechanical anisotropic properties to graphene, including the uncommon negative Poisson's ratio. Additionally, these materials exhibit anisotropic optical behavior, displaying heightened absorption within the infrared and visible regions compared to pristine graphene. Finally, it is found that Li atoms are adsorbed stably on the surfaces of multi-defect GOs via the formation of LinO/LimOH clusters. The research findings presented in this paper, encompassing the development of structural models for multi-defect GOs, could provide crucial insights into the properties and potential applications of graphene oxides.

Confined and spontaneously transformed oxidation structures due to the intrinsic heterogeneous surface morphology of C3N monolayer

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and ab initio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen-C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation.

Enhanced sensing performance of armchair stanene nanoribbons for lung cancer early detection using an electric field

In this study, we analyze the effect of a uniform external electric field on the sensing behavior of armchair stanene nanoribbons (ASnNRs) for early detection of lung cancer biomarkers. The Density functional theory (DFT) and non-equilibrium Green function (NEGF) methods are used to study the sensing behavior. We use Ez = 0.4 V Å-1 and Ez = -0.4 V Å-1 as vertical electric fields and Ey = 0.08 V Å-1 and Ey = -0.08 V Å-1 as transverse electric fields. Our findings demonstrate that applying an electric field in a negative/positive direction considerably increases/decreases the magnitude of the adsorption energy and the transferred charge. In the presence of Ez = 0.4 V Å-1 and Ey = -0.08 V Å-1, a substantial decrease in current was observed. Furthermore, the current curves become more distinguishable compared to the absence of electric fields. The computed results indicate that the negative direction of the applied electric field enhanced the sensitivity and selectivity of ASnNRs for the detection of lung cancer-related biomarkers. The computed results also show that using Ez = -0.4 V Å-1 reduces the adsorption energy to Eads = -8.89 eV and enhances the sensitivity up to 41.83% for styrene detection, demonstrating an improvement in the sensing performance compared to the situation without an electric field. These findings have practical implications, as they can be used to develop highly sensitive early-detection gas sensors, potentially saving human lives.