Doped Graphene Research Articles

Control of Raman Scattering Quantum Interference Pathways in Graphene.

Graphene is an ideal platform to study the coherence of quantum interference pathways by tuning doping or laser excitation energy. The latter produces a Raman excitation profile that provides direct insight into the lifetimes of intermediate electronic excitations and, therefore, on quantum interference, which has so far remained elusive. Here, we control the Raman scattering pathways by tuning the laser excitation energy in graphene doped up to 1.05 eV. The Raman excitation profile of the G mode indicates its position and full width at half-maximum are linearly dependent on doping. Doping-enhanced electron-electron interactions dominate the lifetimes of Raman scattering pathways and reduce Raman interference. This will provide guidance for engineering quantum pathways for doped graphene, nanotubes, and topological insulators.

Gate‐Tunable Potential Barrier on Dual‐Gate Graphene Transistor with Fluorocarbon Thin Film

AbstractThis article reports on the charge transport characteristics across the potential barrier generated by a local dual‐gate modulation at the surface of p‐doped graphene via surface contact on a fluorocarbon (CF) thin film. Owing to simple physical contact, the strong electron affinity of the fluorine atoms in CF stably increases the hole density of graphene, which leads to a massive p‐doping effect in graphene. Then, potential barrier height can be generated and modulated across the channel by forming a local dual‐gate device structure. Different gate biases in dual‐gate operation can split electrical characteristics of a single graphene into highly conductive region and region of sparse charge density, creating large chemical potential difference at the boundary between the two which determines the value of barrier height. Moreover, the device characteristics follow a simple model of the metal–semiconductor junction well in addition to the effect of charge concentration discrepancy in graphene. These results reveal that it is possible to create an ideal and controllable potential barrier composed of a single material using the highly doped graphene with the local dual‐gate structure.

Electrochemical Performance of Potassium Bromate Active Electrolyte for Laser-Induced KBr-Graphene Supercapacitor Electrodes

In this paper, we have reported a low-concentration active electrolyte of KBrO3 for the supercapacitor’s application. The electrochemical processes were carried out in two concentrations of KBrO3 with 0.2 and 0.4 M. Additionally, we have reported a novel strategy for doping graphene during its fabrication process with a potassium bromide (KBr) solution. The chemical doping of graphene with KBr improved the electrochemical properties of graphene used as supercapacitors. HRTEM images confirmed the multi-layer graphene obtained by CO2 laser based on polyimide. The effect of KBr on the graphene lattice has been studied using Raman spectroscopy. The two electrodes of graphene and KBr-doped graphene were subjected to the electrochemical properties study as a supercapacitor by electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. The results exhibited the successful method of graphene doping and the stability of using KBrO3 as a suitable electrolyte for electrochemical processes with this lower molarity. The specific capacitance of the pristine graphene capacitor in 0.2 M of KBrO3 was 33 Fg−1, while this value increased up to 70 Fg−1 for KBr-doped graphene in 0.4 M of KBrO3. The specific capacity in mAhg−1 has also increased twofold. The results exhibited the possibility of using KBrO3 as an electrolyte. The supercapacitor performance almost showed good stability in the life cycle.

Exploring the adsorption performance of doped graphene quantum dots as anticancer drug carriers for cisplatin by DFT, PCM, and COSMO approaches

Exploring the adsorption performance of doped graphene quantum dots as anticancer drug carriers for cisplatin by DFT, PCM, and COSMO approaches

Fabrication of Carbon Coated Nickel/Nitrogen Doped Graphene Composite Film and as Enhancer for Sensitive and Rapid Determination of Sunset Yellow

The innovative glassy carbon electrode used in the determination of sunset yellow is modified using a carbon-coated nickel/nitrogen doped graphene composite film. (C-Ni/NGE/GCE). The morphology and structure of different materials (C-Ni and NG) were characterized by transmission electron microscope. When HAc-NaAc (pH=4) was selected as the electrolyte solution, the maximum current of C-Ni/NGE/GCE oxidation peak was reached when the electrolyte concentration was 0.15 mol·L−1, which was a reversible redox peak. The maximum linear range is 1.0×10−4 mol·L−1 and the minimum is 4.0×10−6 mol·L−1. Taking the peak current as the vertical coordinate and SY concentration as the horizontal coordinate, the working standard curve equation obtained by differential pulse voltammetry is Ip(μA)=0.187+56.91c (μmol·L−1 )(R2=0.9992). The detection limit was 5.0×10−8 mol·L−1. The electrochemical behavior of SY shows proton number (X=1) and electron transfer number (n=1). The recovery rate of SY in beverage was 101.5%-103.3%. The following research of sensor to nitrite was the linear range, recovery rate and uL, produced in small experiments.

Combined effects of direct plasma exposure and pre-plasma functionalized metal-doped graphene oxide nanoparticles on wastewater dye degradation

The current study investigates the combinatorial effect of the photocatalytic performance of plasma pre-treated Ti-Cu-Zn doped graphene oxide (TCZ-GO) nanoparticles (NPs) and advanced oxidation processes of a non-thermal atmospheric pressure plasma on the degradation of reactive orange-122 (RO-122) dye compounds. Firstly, in order to enhance the photocatalytic performance of the synthesized composite NPs, they were subjected to glow discharge plasma treatments operating in different gases (Ar, air, O2 and N2). Their surface morphology, chemical composition and band gap were examined by means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis spectrophotometry respectively. XPS results revealed that plasma-treated NPs exhibited a higher content of oxygen vacancies and a variation in their oxidation states (Ti4+ → Ti3+, Cu+ → Cu2+). These plasma-induced surface chemical changes hindered the recombination of photo-generated electron-hole pairs which led to a drop in the bandgap of the NPs with N2 plasma-treated NPs acquiring the lowest bandgap. Lastly, the article examined the actual decomposition of RO-122 dye in wastewater by an Ar plasma treatment alone or combined with the plasma-treated TCZ-GO NPs via spectrophotometric analyses, electrical conductivity, pH and total organic carbon (TOC) removal measurements. Moreover, the reactive species produced during the combined plasma/photocatalysis induced degradation were detected in situ by optical emission spectroscopy. Results revealed that the processes carried out by combining N2 plasma-treated TCZ-GO NPs and Ar plasma exhibited the highest degradation efficiency (85 %) due to the generation of more OH and H2O2. Overall, it can be concluded that plasma-aided treatment processes used synergistically as indirect surface functionalization of TCZ-GO NPs and direct plasma treatment of wastewater are extremely efficient in the degradation of toxic compounds and can be extrapolated to various environmental applications.

Co supported on N and S dual-doped reduced graphene oxide as highly active oxygen-reduction catalyst for direct ethanol fuel cells

Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Heteroatom-doped carbon materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co3O4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with different doped graphene nanomaterials (GMs). The effect of the heteroatoms and cobalt oxide nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs for the ORR was studied. Co/SN-rGO presents high ORR performance in terms of onset potential (Eonset), 0.86 V (vs RHE) and half-wave potential (E1/2) 0.72 V (vs RHE). Tafel analysis shows 60 mV dec-1 at low overpotential for potential dependent ORR mechanism. Besides, when Co/SN-rGO performance is evaluated in a DEFC using a fuel cell test station, main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalyst.

Hybrid Heterostructures to Generate Long-Lived and Mobile Photocarriers in Graphene

We report the generation of long-lived and highly mobile photocarriers in hybrid van der Waals heterostructures that are formed by monolayer graphene, few-layer transition metal dichalcogenides, and the organic semiconductor F8ZnPc. Samples are fabricated by dry transfer of mechanically exfoliated MoS2 or WS2 few-layer flakes on a graphene film, followed by deposition of F8ZnPc. Transient absorption microscopy measurements are performed to study the photocarrier dynamics. In heterostructures of F8ZnPc/few-layer-MoS2/graphene, electrons excited in F8ZnPc can transfer to graphene and thus be separated from the holes that reside in F8ZnPc. By increasing the thickness of MoS2, these electrons acquire long recombination lifetimes of over 100 ps and a high mobility of 2800 cm2 V-1 s-1. Graphene doping with mobile holes is also demonstrated with WS2 as the middle layers. These artificial heterostructures can improve the performance of graphene-based optoelectronic devices.

Lateral Controlled Doping and Defect Engineering of Graphene by Ultra-Low-Energy Ion Implantation

In this paper, the effectiveness of ultra-low-energy ion implantation as a means of defect engineering in graphene was explored through the measurement of Scanning Kelvin Probe Microscopy (SKPM) and Raman spectroscopy, with boron (B) and helium (He) ions being implanted into monolayer graphene samples. We used electrostatic masks to create a doped and non-doped region in one single implantation step. For verification we measured the surface potential profile along the sample and proved the feasibility of lateral controllable doping. In another experiment, a voltage gradient was applied across the graphene layer in order to implant helium at different energies and thus perform an ion-energy-dependent investigation of the implantation damage of the graphene. For this purpose Raman measurements were performed, which show the different damage due to the various ion energies. Finally, ion implantation simulations were conducted to evaluate damage formation.

Cross-Linked and Doped Graphene Oxide Membranes with Excellent Antifouling Capacity for Rejection of Antibiotics and Salts.

Graphene oxide (GO) membranes have suffered from the instability of water permeability and low rejection of pollutant separation. In this paper, a reasonable modification protocol for GO nanosheets at the molecular level was proposed. A molecular cross-linking strategy was adopted to regulate the interlayer spacing of GO nanosheets, and nanofiltration membranes with high water stability and excellent antifouling capacity were prepared, which could effectively reject antibiotics and salts. The GO1-MPD0.5 (the mass ratio of GO nanosheets to MPD is 1:0.5) and GO/GO1-MPD0.5-0.25 (the doping ratio of GO1-MPD0.5 is 25%) membranes had stable water permeability of 4.22 ± 0.06 and 3.65 ± 0.11 L m-2 h-1 bar-1, and the rejection rates for ciprofloxacin (CIP) and ofloxacin (OFX) were 93.35 ± 3.62 and 95.48 ± 2.97 and 85.89 ± 6.52 and 88.21 ± 3.67%, respectively. Molecular dynamics simulations well explained the high water stability of membranes, and the cross-linked hydrophobic benzene ring played a role in the rejection of pollutant molecules. Moreover, the GO1-MPD0.5 membrane showed excellent antifouling capacity and the flux recovery ratio (FRR) was more than 98%. This paper provides a new idea for the design of nanofiltration membranes with high stability and good rejection permeability at the molecular level and provides a prospect for the application of nanofiltration membranes in practical water treatment and water purification.

Wiedemann-Franz law in graphene

We analyze a well-known experimental work [J. Crossno et al., Science 351, 1058 (2016)] which reported on the failure of the Wiedemann-Franz law in graphene at $T\ensuremath{\sim}10\text{--}100\phantom{\rule{4pt}{0ex}}\mathrm{K}$, attributing this failure to the non-Fermi liquid nature of the Dirac fluid associated with undoped intrinsic graphene. In spite of serious theoretical efforts, the reported observations remain unexplained. Our detailed quantitative analysis based on Fermi liquid considerations, which apply to extrinsic doped graphene, establishes that one possible explanation for the reported observations is the opening of a gap at the Dirac point, induced perhaps by the boron nitride substrate. We suggest that more experiments are necessary to resolve the issue, and we believe that the experiment may not actually have anything to do with Dirac fluid hydrodynamics but relates to finite-temperature low-density bipolar diffusive transport by electrons and holes in the presence of short- and long-range disorder, and phonons.

CO2 adsorption enhancement and charge transfer characteristics for composite graphene doped with atoms at defect sites

The massive emission of carbon dioxide in the world causes global warming and a series of increasingly serious ecological problems. It is urgent to find efficient adsorbent for large-scale CO2 capture. Graphene as a solid adsorbent has exhibited great potential and development prospects in gas adsorption. Doping atoms at defect sites in composite graphene is considered as one of the promising approaches to enhance the gas adsorption ability. Nevertheless, composite graphene doping with different atoms has not been explored to a large extent so far. In this work, vacancy graphenes with single C-vacancy (VI-G) and with double C-vacancies (VII-G) are doped with nitrogen atoms and metal atoms M (M = Co, Mo, Mn, Fe) to form composite configurations. The Perdew-Burke-Ernzerho (PBE) functional is used under the generalized gradient approximation (GGA) basis set. A comprehensive study of the adsorption effect and charge transfer characteristics of CO2 molecule on different composite graphene configurations is carried out through DFT calculation. By analyzing the adsorption energy, adsorption distance, energy band structure, and atomic Mulliken population, it is found that the composite graphene doped with metal atoms such as Co-3N-VI, Mo-3N-VI, Mn-3N-VI, Fe-3N-VI, and Mo-4N-VII significantly enhanced the CO2 adsorption. Further analysis of charge density and density of states (DOS) demonstrates that CO2 adsorption on M-3N-VI and M-4N-VII reached the same conclusion. Thus, it is concluded that appropriate metal atoms can enhance the adsorption characteristics.

A new teamwork of PEDOT:PSS and zinc peroxide decorated nitrogen doped graphene with high anisotropic thermoelectric functions

Poly(3,4-ethylenedioxythiophene):Poly (styrene sulfonate) (PEDOT:PSS) as an intrinsic conductive polymer has captured much curiosity since the discovery of its high thermoelectric (TE) functions. So, the progress on the enhancement of TE functions of PEDOT:PSS and its composite is still having much attention thanks to its unique merits such as flexibility, low toxicity, as well as its promising TE functions. Thus, in this work, we offer a new teamwork of PEDOT:PSS and Zinc peroxide adorned Nitrogen doped Graphene (PEDOT:PSS/ZnO2NG) to record high TE performance. This teamwork plays in harmony to record a high TE functions as; the doping of graphene (GN) with Nitrogen helps in reducing the thermal conductivity (κ) via the creation of interfaces and voids which lead to scattering the phonons. The decoration of ZnO2 on NG surface helps in increasing the electrical conductivity (σ) by the increase in carrier mobility and declining the κby reducing the stacking nature of NG layers. The anisotropic (through plane ⊥ and in plane //) TE functions have been recorded at 300 K. The system shows that the highest TE functions are achieved at ZnO2NG = 30 wt%. At this concentration, σ//∼1600.45 ± 62 S/cm and σ⊥∼1203.98 ± 56 S/cm have been achieved, thanks to the strong interactions among ZnO2NG and PEDOT:PSS; and the increase in carrier mobility. κ//∼0.47 ± 0.01 W/mK and κ⊥∼0.35 ± 0.01 W/mK have been achieved. The S//∼25.94 ± 0.6 μV/K and S⊥∼23.2 ± 0.59 μV/K have been achieved thanks to the decrease in the carrier concentration. The power factors (PF//∼107.69 ± 3 μW/mK2 and PF⊥∼64.80 ± 4 μW/mK2) have been achieved owing to the energy filtering effects at the interfaces. Accordingly, the obtained figure of merits (zT// ∼0.068 ± 0.001 and zT⊥∼0.055 ± 0.002) have been achieved which can compete the largest zT values when compared with similar systems. Finally, the obtained PEDOT:PSS/ZnO2NG system shows a promising TE functions which elects it to be functionalized in various technologies such as electronic, temperature sensing and wearable devices.

Carrier Relaxation and Multiplication in Bi Doped Graphene.

By introducing different contents of Bi adatoms to the surface of monolayer graphene, the carrier concentration and their dynamics have been effectively modulated as probed directly by the time- and angle-resolved photoemission spectroscopy technique. The Bi adatoms are found to assist acoustic phonon scattering events mediated by supercollisions as the disorder effectively relaxes the momentum conservation constraint. A reduced carrier multiplication has been observed, which is related to the shrinking Fermi sea for scattering, as confirmed by time-dependent density functional theory simulation. This work gives insight into hot carrier dynamics in graphene, which is crucial for promoting the application of photoelectric devices.

One-pot interpenetrating epoxy thermosets from renewable dual biomass to high performance

The 5-hydroxymethylfurfural, honokiol, and magnolol are converted into sustainable epoxy monomers, i.e., 5,5′-(((3′,5-diallyl-[1,1′-biphenyl]-2,4′-diyl)bis(oxy))bis- (methyl-ene))bis(2-((oxiran-2-ylmethoxy)methyl)furan) (MGHF) and 5,5′-(((5,5′-diallyl-[1,1′-biphenyl]-2,2′-diyl)bis(oxy))bis(methylene))bis(2-((oxiran-2-ylmethoxy)- methyl)furan) (MGMF), and they are finally cured by 3,3′-diamino diphenylsulfone (33DDS) and 4,4′-diamino diphenylsulfone (44DDS), thus affording novel interpenetrating polymer networks (IPN). Interestingly, 33DDS induces a twist-stacked structure, whereas 44DDS provides a planar weave matrix. As to the twist-stacked layout MGMF/33DDS, it behaves a superhigh storage modulus (∼5.04 GPa), a high phase transition temperature (Tg, 222.7 °C), and an elevated onset temperature (Td5, 362.8 °C). For planar weave arrays, MGHF/44DDS shows the highest values in Tg (224.9 °C), lap shear strength (∼20.4 MPa), hardness (∼508 MPa), and reduced Young’s modulus (∼6.06 GPa). Furthermore, MGMF/44DDS shows an excellent dielectric property (11.15, 0.02) (∼1 kHz, 25 °C) and a moderate thermal conductivity (0.355 W (m·K)−1) alonging with increased flame retardancy. Besides, those biobased epoxy resin wastes are reclaimable through aerobic or anaerobic pyrolysis. Anaerobic pyrolysis of planar weave networks selectively yields more doped graphene, whereas similar event readily happens to the aerobic pyrolysis of the twist-stacked polymers. In view of these reported advantages, this novel strategy opens new avenues for multifunctional epoxy resins.

Machine learning identification of atmospheric gases by mapping the graphene-molecule van der waals complex bonding evolution

Atmospheric doping of graphene, and the variation in atmospheric composition (e.g., humidity) makes graphene machine learning (ML) models limited to controlled environments (e.g., dry air), and unsuitable for atmospheric applications (e.g., non-invasive medical diagnosis). Herein, using nano-porous activated carbon for atmospheric passivation of the graphene channel, Extreme Gradient Boosting (XGBoost), K-nearest neighbors (KNN), and Naïve Bayes supervised ML models for atmospheric gas identification were developed, with model feature contribution studied using the Game theoretic approach, SHapley Additive exPlanations (SHAP). Unlike conventional graphene-based ML models which only monitor the gas adsorption induced doping and scattering without tuning voltage (Vt) modulation, in this work, the tuning voltage evolution of the gas adsorption induced van der Waals (vdW) complex doping and scattering characteristics was mapped out over time. The accuracy, precision, recall, and F1-score of the developed models in the environments: atmospheric ammonia, atmospheric acetone, ammonia in dry air, and acetone in nitrogen were 100% for XGBoost, 96%, 97%, 97%, 97% respectively for KNN, and 95%, 95%, 96%, 96% respectively for Naïve Bayes, even at single-digit ppb gas concentrations. Hence, our results advance the application of graphene based electronic nose models from conventional controlled environments to actual atmospheric sensing.

Effective carrier doping and quantum capacitance manipulation of graphene through two-dimensional solid electrolytes of ScI3 and YBr3

Effective carrier doping would be expected to enhance the electrical conductivity and further improve the quantum capacitance (Cq) of graphene. In this work, two-dimensional solid electrolytes of ScI3 and YBr3 as buffer layers have been proposed to modulate the carrier density and improve the Cq. By using first-principles calculations, the effective carrier doping has been examined by building heterostructures of graphene/ScI3 and graphene/YBr3 combined with Li, Na, K, Ca, F dopants. The n-type doping with electron density and p-type doping with hole density of graphene reach up to 1.14 × 1014 cm−2 and 6.66 × 1013 cm−2, respectively. Remarkably, the linear band dispersions of graphene are maintained near the Dirac point. Moreover, the Cq is significantly increased around the zero bias due to the increased density of states near the Fermi level. For Li-, Na-, K-, and Ca-doped systems, the Cq in the negative bias region is effectively enhanced while the Cq is improved in the positive bias region for F-doped system. These results provide an ideal route to implement the effective carrier doping and the Cq manipulation of graphene, facilitating the applications of graphene as electrodes in high-performance optoelectronics and energy storage devices, such as light-emitting diodes, solar cells and supercapacitors.

Novel energy bandgap formation of organic solution doped graphene membrane for semiconductor applications

In this work, the electrolyte nano fibrous solution is prepared using corn husk through a chemical process. This study explores the new aspect of producing sizeable and tunable bandgap in graphene by doping organic nanoporous solution as a membrane. The energy bandgap of organic doped graphene membrane varies from 2.313 eV to 2.502 eV. It is noted that the organic nanoporous solution as a membrane also has a bandgap under with (2.665 eV) and without PVA (3.761 eV). The membrane is produced by the phase inversion process. The incorporation of graphene in green solution also exhibits conductive properties like organic nanoporous solution which in terns used as electrolytes to produce electricity. It is the first successful attempt to create a direct graphene bandgap with organic doping but it still requires more research for a better understanding of the properties for future applications. This concept can also be used where bandgap is a very concerning issue. The physical properties of with and without a graphene-based organic membrane are examined by Scanning Electron Microscope Test (SEM), Fourier Transform Infrared Spectroscopy Test (FTIR), and Ultra Violate Test (UV). Sample 4 has a superior surface morphology, which means the particle dispersion is more homogeneous than the others. There are porosities in all the samples.

A Comparison Study of the Electrocatalytic Sulfur Reduction Activity on Heteroatom‐Doped Graphene for Li–S Battery

The complicated multielectron and multiphase electrocatalytic sulfur reduction reaction (SRR) occurring in the Li–S battery is demonstrated, which strongly influences the performances of this battery chemistry. Effective candidates for SRR are often based on heteroatom‐doped carbon‐based electrocatalysts. However, the electrocatalytic sulfur reduction activity of these catalysts is so far insufficiently explored. Herein, a series of graphene doped with nonmetal elements (nitrogen, phosphorus, and sulfur) are designed and synthesized. It is shown that nitrogen‐doped graphene has a superior SRR catalytic activity with highest electrochemical reversibility and best electrochemical kinetics for the liquid–solid two‐phase conversion from long‐chain soluble Li2Sx (4 ≤ x ≤ 8) and the solid‐state Li2S2 to Li2S conversion. The considerably improved kinetics of the liquid–solid and solid–solid phases conversion reduces the continued accumulation of lithium polysulfides in electrolyte and the passivation of the electrode, thus resulting in a significant improvement in electrochemical performance of Li–S cells. Density‐functional theory calculations demonstrates that the highest SRR performance of N/G is originated from the strongest adsorption of the sulfur species and lowest energy barriers for Li2S decomposition among three doped graphene samples. This study is believed to guide the design of efficient electrocatalysts to exceed the performance of the benchmark for Li–S battery.

First-Principles Investigation of Charged Germagraphene as a Cathode Material for Dual-Carbon Batteries.

As part of the concerted effort for development of energy storage technologies, dual-ion batteries (DIBs) or dual-carbon batteries (DCBs) are attracting interest, owing primarily to their eco-friendly active materials. The use of carbon as the active materials of DCBs brings about several challenges involving capacity and stability. This contribution aims to provide an in-depth understanding of the structural and electronic properties of Ge-doped graphene (Germagraphene) as a novel cathode material for DCBs. Density functional theory (DFT) calculations are combined with the effective screening medium (ESM) method for analyzing the electronic and band structure of PF6 - anion-adsorbed Germagraphene under a potential bias. These theoretical investigations indicate that the use of Ge as a dopant for graphene has a positive impact on the adsorption of the anion on the cathode under both neutral and electrically biased conditions.