Doped Graphene Research Articles

Efficient Charge Transfer in Graphene/CrOCl Heterostructures by van der Waals Interfacial Coupling.

Due to the large volume of exposed atoms and electrons at the surface of two-dimensional materials, interfacial charge coupling has been proven as an efficient strategy to engineer the electronic structures of two-dimensional materials assembled in van der Waals heterostructures. Recently, heterostructures formed by graphene stacked with CrOCl have demonstrated intriguing quantum states, including a distorted quantum Hall phase in the monolayer graphene and the unconventional correlated insulator in the bilayer graphene. Yet, the understanding of the interlayer charge coupling in the heterostructure remains challenging. Here, we demonstrate clear evidences of efficient hole doping in the interfacial-coupled graphene/CrOCl heterostructure by detailed Raman spectroscopy and electrical transport measurements. The observation of significant blue shifts and stiffness of graphene Raman modes quantitatively determines the concentration of hole injection of about 1.2 × 1013 cm-2 from CrOCl to graphene, which is highly consistent with the enhanced conductivity of graphene. First-principles calculations based on density functional theory reveal that due to the large work function difference and the electronegativity of Cl atoms in CrOCl, the electrons are efficiently transferred from graphene to CrOCl, leading to hole doping in graphene. Our findings provide clues for understanding the exotic physical properties of graphene/CrOCl heterostructures, paving the way for further engineering of quantum electronic states by efficient interfacial charge coupling in van der Waals heterostructures.

Disorder-dependent superconducting pairing symmetry in doped graphene

Disorder-dependent superconducting pairing symmetry in doped graphene

The robust design of PMIA braided tube reinforced PFA hollow fiber membranes with graphene doping for water-in-oil separation

In order to solve the problem of oily wastewater, the poly(m-phenyleneisophthalamide)(PMIA) braided tube reinforced (PBR) poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether)(PFA) hollow fiber membrane with thermal and solvent resistant property was prepared via no-solvent green method. The membrane surface and pore structure was optimized by changing the sintering temperature and graphene (GE) content. The morphologies showed that the spherical surface with good lipophilicity was formed, and the excellent mechanical strength with favorable interface bonding state could be obtained due to the PFA melts permeating into the supporting layer. The doping of GE produced synergistic effects with the sintering temperature owing to its good thermal conductivity and pore formation. The PBR-PFA/GE hollow fiber membrane exhibited good hydrophobicity and lipophilicity with more than 97% separation efficiency for different oil products at -0.02 MPa. With the addition of GE, the average pore size first increases and then decreases, and the porosity gradually decreases. In addition, the hollow fiber membrane showed high separation ability to the water-in-oil emulsion, and maintained stable flux recovery rate after recycling, making it possible to apply in the field of oily wastewater treatment.

Characterizations and Energy Analysis of Hydroxyl Group Functionalized Graphene (Nanomaterial) Mixed with Paraffin Wax (Polymer Pcm) as Thermal Energy Storage Materials And Applications

This work comprised of Paraffin wax as phase change material mixed/doped with functionalized graphene (hydroxyl group) for countering the poor thermal conductivity of the pristine phase change material. Firstly, Experiments were conducted on Thermal energy storage system during charging (melting) of the doped PCM. The main outcomes of these experiments were that as the volume concentrations of doped PCM and flow rate of the heat transfer fluid (HTF) were increased the charging time decreases along with increments in PCM temperature and accumulated energies. In case of OH functionalized graphene mixed with paraffin wax the charging time decreases by 38.4% to 84.61% for the HTF flow rate 25 ml/s over pure paraffin wax. Secondly, the advanced functional materials i.e., Paraffin wax mixed with functionalized hydroxyl group graphene was characterized by FTIR, XRD, TGA, DSC and FESEM, . The latent heat of melting obtained was 179.36 J/g for 1% graphene doping by DSC.

Sodium vanadates doped boron phosphorus graphene quantum dots: A novel nanosensor for the fluorescence detection of rutin

Rutin, a naturally occurring flavonoid compound, possesses notable antioxidant properties along with anti-inflammatory and antiviral effects. This research aimed to improve the selectivity and high fluorescence behavior of novel nanomaterial BPGQDs@NaV, which was synthesized by hydrothermal methods. Through comprehensive characterization utilizing TEM, SEM, XRD, EDS, FT-IR, UV–Vis, TCS-PC, and XPS techniques, the prepared BPGQDs, NaV, and BPGQDs@NaV were thoroughly examined. The resulting BPGQDs@NaV nanomaterials demonstrated stable, reproducible fluorescence responses and exhibited selective recognition capabilities towards rutin. The sensor developed in this study displayed remarkable performance in rutin detection, offering a broad linear range from 5 to 110 nM and an outstanding detection limit of 15.16 nM. A computational study was used to examine energy, stability, band gap, and how rutin interacted with the BPGQDs@NaV, and it also favored the detection mechanism. A portable smartphone-based sensor was also developed for the detection of rutin.

Data-driven deep learning prediction of boron-doped graphene work function

The atomic-scale doping plays a crucial role in determining the work function of doped graphene. However, it is a challenge to comprehensively investigate its work function due to the large range of possible molecular configurations. In this study, more than 30,000 pieces of data of the work functions from boron-doped graphene with different doping concentrations and positions is calculated via DFT, and the dataset is further expanded to 115,000 based on the molecular structural symmetry. Then, a simple structural descriptor-based method is developed to characterize the surface of the doped graphene. Finally, a deep learning model is proposed to predict the work function. The results show that the proposed model can accurately predict the work function with the R2 > 0.95 and MSE < 0.0013 for a 3×3 supercell. In addition, this study also provides the possibility to quickly investigate the work function of other heteroatom 2D materials.

Charge transfer plasmons in nanoparticle arrays on graphene: Theoretical development

The properties of charge transfer plasmons (CTPs) in periodic metallic nanoparticle arrays (PMNPAs) on the single-layer graphene surface are studied within a computationally efficient original hybrid quantum-classical model. The model is based on the proven assumption that the carrier charge density in doped graphene remains unchanged under plasmon oscillations. Calculated CTP frequencies for two PMNPA geometries are shown to lie within the THz range and to be factorized, i.e., presented as a product of two independent factors determined by the graphene charge density and the PMNPA geometry. Equations are derived for describing the CTP frequencies and eigenvectors, i.e., oscillating nanoparticle charge values. It is shown that the CTP plasmons having a band structure containing a wave vector and a band number, like to phonons in periodic media, can be divided into an acoustic mode and optical CTP modes. For the acoustic modes, the CTP group velocity tends to zero at k→0, but reaches a value of ∼VFermi in graphene inside the Brillouin zone, while for the optical modes, the group velocity dispersion is extremely weak, although their energy is higher than the acoustic plasmon energies. It is shown that the calculated dependence of CTP frequencies on the carrier concentration in graphene is in good agreement with experimental data. We believe that the proposed model can help in designing various graphene-based terahertz nanoplasmonic devices of complex geometry due to very high computational efficiency.

Electrochemical co-reduction of N2 and CO2 to urea using In2S3 anchored on S-doped reduced graphene oxide

The generation of urea by electrocatalysis using N2 and CO2 as feedstock is considered as a promising and green sustainable alternative to conventional energy-consuming industrial processes. Based on the existing studies, it was found that the effective adsorption and activation of N2 and CO2 on the catalyst surface is the primary condition for electrocatalytic generation, while the main by-product hydrogen evolution reaction (HER). Should be avoided as much as possible in order to improve the yield. In this paper, an In2S3-loaded electrocatalyst on sulfur-doped reduced graphene oxide for urea synthesis was designed and prepared with an average Faraday efficiency (FE) of 37.17 % and a urea yield of 7.24 mmol h−1 g−1, while maintaining long-term stability. In2S3@S-RGO has a unique porous structure of doped graphene, with continuous micron-sized pores that facilitate fast mass transfer, improve kinetic efficiency, and expand electroactive sites, thus enhancing the urea synthesis performance. Interestingly, the In2S3@S-RGO electrocatalyst not only exhibits excellent electrochemical performance, but also facilitates the adsorption and activation of reactants (N2 and CO2) due to the inhibitory effect of the indium-based material on HER. This work may provide new ideas for advanced catalysts to improve the efficiency of electrochemical synthesis of urea Faraday and to facilitate CN coupling applications.

Achieving High Substitutional Incorporation in Mn-Doped Graphene.

Despite its broad potential applications, substitution of carbon by transition metal atoms in graphene has so far been explored only to a limited extent. We report the realization of substitutional Mn doping of graphene to a record high atomic concentration of 0.5%, which was achieved using ultralow-energy ion implantation. By correlating the experimental data with the results of ab initio Born-Oppenheimer molecular dynamics calculations, we infer that direct substitution is the dominant mechanism of impurity incorporation. Thermal annealing in ultrahigh vacuum provides efficient removal of surface contaminants and additional implantation-induced disorder, resulting in Mn-doped graphene that, aside from the substitutional Mn impurities, is essentially as clean and defect-free as the as-grown layer. We further show that the Dirac character of graphene is preserved upon substitutional Mn doping, even in this high concentration regime, making this system ideal for studying the interaction between Dirac conduction electrons and localized magnetic moments. More generally, these results show that ultralow energy ion implantation can be used for controlled functionalization of graphene with substitutional transition-metal atoms, of relevance for a wide range of applications, from magnetism and spintronics to single-atom catalysis.

Interface Characterization of Graphene‐Silicon Heterojunction Using Hg Probe Capacitance–Voltage Measurement

AbstractInvestigating the intrinsic properties of the Schottky interface between graphene and 3D bulk silicon is crucial. However, the semiconductor technology introduces extra doping and defects in graphene, which significantly disturbs the property of the graphene‐silicon interface. Here, the interface parameters of graphene/n‐Si heterojunction are derived by the damage‐free Hg‐probe capacitance–voltage measurement. Due to its low‐density states, the Fermi level of graphene can be pushed upward, which results in a lower Schottky barrier height (ΦB0) of Hg/graphene/n‐Si (HGS) heterostructure than that of Hg/n‐Si (HS) structure. Additionally, the series resistance (Rs) of HGS becomes lower than that of HS, which can be attributed to the narrowed depletion layer width (WD) and the decreased interface state density (Nit). Furthermore, the frequency characteristic is also investigated. Because of the weak interface state charge trapping–detrapping process and the decreased Nit at high frequency, electrons will accumulate in graphene, and the Fermi level will be pushed up. Hence, the ΦB0 and Rs will decrease with increasing frequency. This study contributes to a deep understanding of the graphene/silicon heterojunction interfaces, which is crucial for designing and optimizing the new electronic and optoelectronic devices based on 2D/3D heterostructure.

Dual role of two-dimensional graphene in silica aerogel composite: Thermal resistance and heat node

Incorporating two-dimensional graphene sheets, known for their high in-plane thermal conductivity, into silica aerogel enhances both the thermal insulation and mechanical properties of the composite. This work delves into the impact of graphene doping on the solid thermal conductivity of silica composites and their mechanical characteristics, employing molecular dynamics simulations that encompass both amorphous silica bulk and porous silica aerogel structures. Our findings reveal that graphene–silica interface thermal resistance notably restricts heat conduction in graphene doped silica aerogel, with the most pronounced effect occurring when graphene aligns vertically with the heat flux. Within porous silica aerogel, graphene serves as a “heat node”, bridging and connecting adjacent pores. A notable “trade-off” emerges: high weight percentages of graphene sheets augment heat transfer through the “heat node effect”, whereas the interfacial thermal resistance between graphene and aerogel reduces solid heat transfer, leading to decreased thermal conductivity. Additionally, while the inclusion of graphene sheets offers limited mechanical property enhancements, their two-dimensional structure can cause detachment and slipping from the silica matrix, leading to localized improvements in mechanical strength. This work sets the stage for advancing graphene-based aerogel composites characterized by low thermal conductivity and enhanced mechanical properties.

A novel synthesis route with large-scale sublattice asymmetry in boron doped graphene on Ni(111)

One of the promising ways to functionalize graphene is incorporation of heteroatoms in carbon sp2 lattice, as it is proven to be an efficient and versatile method for controllably tuning chemistry of graphene. We present unique, contamination-free method for selectively doping graphene with B dopants, which are incorporated in layer from a reservoir created in the bulk of Ni(111) single crystal, during standard CVD growth process, leading to clean, versatile and efficient method for creating B-doped graphene. We combine experimental (STM, XPS) and theoretical (DFT, simulated STM) studies to understand structural and chemical properties of substitutional B dopants. Along with previously reported substitutional B in fcc sites, we have observed, for the first time, two more defects, namely substitutional B in top sites and interstitial B in octahedral subsurface sites. Extensive STM investigations confirm presence of low and high concentration regions of B dopants in as-prepared B-doped graphene, indicating non-uniform boron incorporation. Among two substitutional sites, no preference is observed in low-concentration B-doped regions, whereas in high B concentration regions, one of the sublattices is preferred for incorporation, along with alignment of defects. This generates an asymmetric sublattice doping in as-grown B-doped graphene, which is theoretically predicted to result in notable band gap.

Optically Active Defect Engineering via Plasma Treatment in a MIS‐Type 2D Heterostructure

AbstractAt the interface of 2D heterostructures, the presence of defects and their manipulation play a crucial role in the interfacial charge transfer behavior, further influencing the device functionality and performance. In this study, the impact of deliberately introduced photo‐active defects in the h‐BN layer on the interfacial charge transfer and photoresponse performance of a metal‐insulator‐semiconductor type heterostructure device is explored. The formation and concentration of defects are qualitatively controlled using an inductive coupled plasma treatment method, as evidenced by enhanced h‐BN defect emission and more efficient optically induced doping of graphene at the graphene/h‐BN interface. Besides, the use of the h‐BN layer between graphene and WS2 not only suppresses charge carriers in the dark state, but also promotes the separation of photo‐generated electron‐hole pairs and interfacial charge transfer due to the existence of defect levels, leading to orders of magnitude improvement in the light on/off ratio and self‐driving performance of the heterostructure photodetector. This strategy of controlling defect states in the insulating layer provides a new approach to optimize the charge transfer processes at the 2D interfaces, so as to expand its potential applications in the fields of electronic and optoelectronic devices.

Facile design and superior electrochemical performance of fluorine doped graphene slice for supercapacitor electrodes

A facile method has been developed to enhance the electrochemical characteristics of graphene by synthesizing fluorine-doped graphene (FG) slice via a hydrothermal reaction involving graphene oxide and hydrofluoric acid. The resultant FG slice demonstrates enhanced volumetric capacitance and robust cycling durability. The advancements in electrochemical behavior are owing to the integration of covalent C-F and semi-ionic C-F bonds aligned perpendicularly to the graphene planes. This FG slice is suitable for a range of practical applications, including use in sensors, as catalysts, and within the realm of nanomaterial-based electronics.

Enhanced nonlinear optical properties and optical limiting performance of graphene modified polyaniline composite under pulsed laser regime

Polyaniline (PANI) and its graphene-doped composite (PANI-GNP) were subjected to open-aperture (OA) z-scan studies to investigate their nonlinear optical (NLO) properties and optical limiting (OL) behavior. The z-scan experiments were carried out using a nanosecond pulsed Nd:YAG laser at a wavelength of 532 nm. The z-scan studies revealed that PANI and PANI-GNP composites exhibited a reverse saturable absorption (RSA), and graphene doping modified the NLO behaviour and improved the OL property. The nonlinear absorption coefficient (β), OL threshold, and imaginary part of nonlinear susceptibility ( χi(3) ) of PANI and PANI-GNP were calculated for three different laser input pulse energies and found to be in the order of 10−9 cm W−1, 106 W cm−2, and 10−10 esu, respectively. These results qualify the PANI-GNP composite as having potential applications in OL and optoelectronic devices. The successful incorporation of graphene into PANI in PANI-GNP composite was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Linear optical properties were analysed using UV–visible absorption spectroscopy. To the best of our knowledge, the present work is the first attempt to explore the intensity-dependent NLO properties, OL behaviour and the calculation of their related NLO parameters of PANI-GNP composites.

Controlled n-type doping in graphene using a photobase generator and polyethylene oxide blends

Achieving stable n-type doping in graphene is a critical challenge in materials science, which is essential for various device applications. We present a novel approach using a photobase generator (PBG), specifically 2-(9-oxoxanthen-2-yl)propionic acid-1,5,7-triazabicyclo[4.4.0]dec-5-ene, in combination with polyethylene oxide (PEO) under UV irradiation to achieve controlled and stable n-type doping. This method effectively reduces PBG crystallization and allows precise modulation of doping transitions by varying PBG concentrations and UV exposure times. Our innovative hybrid approach provides enhanced control over doping transitions, resulting in optimized graphene-based devices with sustainable functionalities. In particular, the method demonstrated long-term stability of more than 160 days, making it viable for practical applications in thermoelectric devices and other areas. This represents a significant advancement over previous methods in terms of cost, scalability, and stability.

One-step thermal-plasma synthesis of sulphur and nitrogen dual-doped graphene with improved microwave-absorption efficiency

This study presented the one-step synthesis of sulphur (S) and nitrogen (N) dual-doped graphene using atmospheric thermal plasma. The doped graphene was synthesized in the magnetically rotating arc plasma with CS2 as the sulphur source, N2 as the nitrogen source and CH4 as the carbon source. At the same reaction temperature, the concentrations of S and N in S and N dual-doped graphene were higher than those in S/ N -doped graphene, which indicated that the dual-doped mode had a promoting effect on the doping level. In addition, increasing the input power effectively increased the doping levels of S and N atoms, which were up to 15.0 at% and 6.9 at%, respectively, at an input power of 19 kW. The S and N dual-doped graphene displayed excellent microwave absorption capability, with an optimal reflection loss of −56.4 dB at 16.3 GHz, and the effective absorption bandwidth reached 5.7 GHz when the doping levels of S and N atoms were 12.2 at% and 5.1 at%. This simple and rapid method for preparing S and N dual-doped graphene might facilitate the application of heteroatom doped graphene.

Reinforcing cementitious composites with nitrogen-doped graphene: insights into molecular interactions and interfacial behavior

Graphene materials are useful functional fillers in cementitious materials. They are essential in creating intelligent cementitious materials, enabling the construction of internal conductive networks and the addition of thermoelectric properties. The success of this process hinges on the functional filler's compatibility with the cement matrix, which must be excellent to ensure optimal results. In this study, we delved into the interactions between nitrogen-doped graphene and calcium silicate hydrate (C-S-H), which is the principal binding phase in cementitious materials, employing Density Functional Theory (DFT) calculations. In this study, we explored diverse nitrogen doping configurations and levels, while concurrently analyzing the influence of calcium cations at the C-S-H matrix interface. The findings indicate that nitrogen atoms in doped graphene interact considerably with nucleophilic oxygen atoms on silicate chains, forming covalent N-O bonds with high bonding energies (length 1.4 A, −107.81 kcal/mol) during graphitic nitrogen doping. The presence of calcium ions further strengthens the interaction energy between C-S-H and graphene, suggesting a synergistic effect between different types of nitrogen doping. The binding and total bond energies under the synergistic effect were −479.52 kcal/mol and −183.23 kcal/mol, respectively. These values were 1.5 times higher than those of single nitrogen doping. These findings offer significant insights into the molecular-level interaction between CSH and carbon nanoparticles.

N, S, P tri-doped porous graphene electrocatalyst with excellent oxygen reduction activity for zinc-air battery

The heteroatom-doped graphene has attracted a lot of research due to its excellent physical, chemical and electrochemical properties considered to be the most promising electrocatalytic material for oxygen reduction reaction (ORR). Multi-doping can exert the synergistic effect between different doped heteroatoms and effectively improve the catalytic activity of doped graphene catalysts. N, P, S tri-doped graphene catalysts were prepared by simple and convenient hydrothermal and high-temperature treatment. The experimental results show that different phosphorus sources have a significant impact on the structure and performance of the prepared catalyst materials. The NSP-Gr-1 catalyst shows the high onset potential (1.035 V), half-wave potential (0.79 V) and limiting current density (−5.33 mA cm−2) for ORR. The power density of the zinc-air battery assembled with the NSP-Gr-1 catalyst achieves 163.1 mW cm−2 at 186.7 mA cm−2, which is much higher than the maximum power density of 140.0 mW cm−2 at 190 mA cm−2 for commercial Pt/C. The discharge stability under different current densities is outstanding.

Impact of Electron-Phonon Coupling on Graphene Intercalation Compounds from Self Energy: Polynomial Models Selection

In our pursuit of understanding electron-phonon coupling (EPC) and their impact on material properties, we delved deep into the intricate role played by the Eliashberg function in governing electron self-energy. Through meticulous evaluation of tailored polynomial models approximating this function, we unearthed profound insights into how phonon interactions intricately modify electronic energy bands. Employing numerical computations, we meticulously unraveled both the real and imaginary aspects of electron self-energy, crucial in comprehending EPC effects in various materials. Investigating superconductivity within monolayer graphene and its interaction with diverse doping substances, our study led us to identify optimal polynomial models that accurately capture EPC behaviors, offering invaluable implications for predicting critical temperatures in superconducting materials. Expanding the parameters within our models allowed us to anticipate changes in self-energy models for higher-order configurations not explored in this study. Our selection of polynomial spanning degrees from n = 1 to 10 the efficacy of n = 2 (Debye) as the most realistic and accurate model, closely followed by n = 1, albeit occasional deviations observed in specific materials. These discrepancies often stemmed from noise model inaccuracies and parameter approximations. Our comprehensive approach outshone the traditional Kramer-Kronig transform in assessing electron-phonon interactions. Looking ahead, the application of multiple models to the Eliashberg function diagram holds immense promise for enhancing accuracy, despite the challenge of concurrently adjusting multiple input parameters. This integration of numerical modeling with experimental data forms a robust framework, empowering the prediction and fine-tuning of material properties vital for the future fabrication of devices. HIGHLIGHTS Exploring the use of polynomial models to approximate the Eliashberg function, enabling a detailed analysis of electron-phonon coupling (EPC) in materials. Confirm the Debye model's accuracy in predicting the electronic structure of doped graphene. The findings suggest enhanced EPC in materials like CaC6 and its potential to induce superconductivity in monolayer graphene. This work offers a framework for future research and applications in superconducting materials using ARPES data. GRAPHICAL ABSTRACT