Doped Graphene Research Articles

Enhanced proton conductivity of sulfonated poly(ether ether ketone) membranes by constructing cation‐π through doping ammonium ionic liquid and graphene oxide

AbstractIn this paper, sulfonic acid functionalized benzothiazole ionic liquid ([(CH2)3SO3HBth] [H2PO4]) and graphene oxide were combined together through the cation‐π. The sulfonated poly (ether ether ketone) was doped with ionic liquid‐modified GO (IL‐GO) to prepare the SPEEK/IL‐GO composite membrane through the solution casting method. The SO3H and benzothiazole rings act as both proton acceptors and proton donors during proton transport and can replace the role of water in medium‐ and high‐temperature environments, increasing the proton transport sites to a certain extent and increasing the proton conductivity of the SPEEK/IL‐GO composite membrane. The proton conductivity of the SPEEK/IL‐GO‐2 composite membrane achieved an 18.02 mS/cm at 120°C, which is 2.43 times higher than that of the pristine SPEEK membrane. This paper provided a method for increasing proton conductivity and limiting IL loss of the SPEEK membrane.Highlights [(CH2)3SO3HBth][H2PO4] and graphene oxide were combined through cation‐π. The benzothiazole ring and SO3H form acid–base pairs. The proton conductivity of SPEEK/IL‐GO‐2 membrane achieved 18.02 mS/cm.

A DFT study of the optoelectronic properties of B and Be-doped Graphene

The electronic and optical properties of Boron (B) and Beryllium (Be)-doped graphene were determined using the ab initio approach based on the generalized gradient approximations within the Full potential linearized Augmented Plane wave formalism (FP-LAPW) formalism. Our findings demonstrated that doping at the edges of graphene is notably stable. In both systems, Be-doped graphene proves more efficient in manipulating the band gap of graphene. Both B and Be induce P-type doping in graphene. B-doped graphene exhibits a negligible magnetic moment of 0.000742, suggesting its suitability for catalytic semiconductor devices. Conversely, Be-doped graphene displays a large magnetic moment of 1.045 µB indicating its potential in spintronics. Additionally, this study elucidates the influence of the dielectric matrices on the optical properties of graphene. These findings underscore a stable and controllable method for modelling graphene at its edges with B and Be atoms, opening new avenues for designing of these devices.

Investigation of the effect of graphene oxide nanoparticles on the structural and dielectric parameters in zinc oxide semiconductors

In this study, pure and 1%, 3% and 5% doped graphene oxide (GO) reinforced zinc oxide (ZnO) nanoparticles were synthesized by sol-gel method. The aim was to improve the electrical and dielectric properties of ZnO semiconductor metal oxide used in many electronic, optoelectronic and electrochemical technologies. FE-SEM, X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy (FT-IR), were used to show the structural and morphological properties of the synthesized ZnO and GO doped ZnO nanoparticles. Impedance analysis was used to study the dielectric properties of the produced nanoparticles. XRD analysis revealed typical peaks of nGO and ZnO nanoparticles. Through the FE-SEM and XRD analysis, it was shown that the ZnO and GO nanopowders were successfully synthesized. The results revealed that ZnO-GO nanoparticles, having good dielectric constant with loss and AC conductivity values, such materials can be a good candidate for solar cells and photovoltaic devices.Graphical

Density functional theory study on the mechanism of oxygen reduction reaction on nitrogen-doped graphene with adjacent Mn and Ni sites

The catalysts for oxygen reduction reaction (ORR) are of great significance to the development of electrochemical energy systems. In this paper, the ORR catalytic performance of Mn–Ni dual-metal doped N-coordinated graphene is studied by density functional theory (DFT). The results show that the catalysts with dual-metal active sites are more stable than that with single metal site, and all catalysts show certain catalytic activity. The reaction pathway analyses of catalysts with two different adsorption configurations of O2 show that when O2 is adsorbed on two metal sites, OOH will automatically split into OH and O. When O2 is adsorbed on Mn site alone, the other site does not participate in the adsorption of oxygen-containing intermediates. The thermodynamic calculation results show that the catalytic performance is mainly influenced by the adsorption strength of O, which is controlled by the number of active sites involved in the adsorption, bond length and the number of transferred electrons at the active sites. The G-MnNiN6-3 shows the best catalytic performance with an overpotential of 0.453 V and a reaction energy barrier of 0.19 eV. The results of this study highlight the potential application of Mn–Ni dual-metal doped N-coordinated graphene as a highly efficient non-precious catalyst.

Reversible Thermoelectric Regulation of Electromagnetic and Chemical Enhancement for Rapid SERS Detection.

Actively controlling surface-enhanced Raman scattering (SERS) performance plays a vital role in highly sensitive detection or in situ monitoring. Nevertheless, it is still challenging to achieve further modulation of electromagnetic enhancement and chemical enhancement simultaneously in SERS detection. In this study, a silver nanocavity structure with graphene as a spacer layer is coupled with thermoelectric semiconductor P-type gallium nitride (GaN) to form an electric-field-induced SERS (E-SERS) for dual enhancement. After applying the electric field, the intensity of SERS signals is further enhanced by over 10 times. The thermoelectric field enables fast and reproducible doping of graphene, thereby modulating its Fermi level over a wide range. The thermoelectric field also regulates the position of the plasmon resonance peak of the silver nanocavity structure, rendering synchronous dual electromagnetic and chemical regulation. Additionally, the method enables the trace detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A detailed theoretical analysis is performed based on the experimental results and finite-element calculations, paving the way for the fabrication of high-efficient E-SERS substrates.

Graphene-Based Tunable Dual-Frequency Terahertz Sensor.

A tunable dual-band terahertz sensor based on graphene is proposed. The sensor consists of a metal bottom layer, a middle dielectric layer, and single-layer graphene patterned with four strips on the top. The numerical simulations results show that the proposed sensor exhibits two significant absorption peaks at 2.58 THz and 6.07 THz. The corresponding absorption rates are as high as nearly 100% and 98%, respectively. The corresponding quality factor (Q) value is 11.8 at 2.58 THz and 29.6 at 6.07 THz. By adjusting the external electric field or chemical doping of graphene, the positions of the dual-frequency resonance peak can be dynamically tuned. The excitation of plasma resonance in graphene can illustrate the mechanism of the sensor. To verify the practical application of the device, the terahertz response of different kinds and different thicknesses of the analyte is investigated and analyzed. A phenomenon of obvious frequency shifts of the two resonance peaks can be observed. Therefore, the proposed sensor has great potential applications in terahertz fields, such as material characterization, medical diagnosis, and environmental monitoring.

Transfer doping of epitaxial graphene on SiC(0001) using Cs

Control of the charge carrier concentration is essential for applications of graphene. Here, we demonstrate the doping of epitaxial graphene on SiC(0001) via charge transfer from an adsorbed layer of Cs atoms with sub-monolayer coverage. The electronic structure of the graphene is analyzed using x-ray and angle-resolved photoelectron spectroscopy. In H-intercalated, quasi-freestanding monolayer graphene (QFMLG), the Dirac point can be tuned continuously from p-type to strong n-type doping. For strong n-type doping, analysis of the core level binding energies implies a deviation from a rigid band shift. This might be explained by an increased screening of the atomic core potential due to the higher number of charge carriers per C atom in the graphene layer. Furthermore, charge transfer into the SiC substrate leads to a change in band bending at the SiC/QFMLG interface, which saturates into a flat band scenario at higher Cs coverage. An analysis of the Fermi surfaces suggests an increasing electron-phonon-coupling in strongly doped QFMLG. In monolayer graphene (MLG), which is intrinsically n-type doped due to the presence of the buffer layer at the SiC interface, n-type doping can be enhanced by Cs evaporation in a similar fashion. In contrast to QFMLG, core level spectra and Dirac cone position in MLG apparently show a rigid band shift even for very high doping, emphasizing the importance of the substrate.

A hybrid quantum-classical theory for predicting terahertz charge-transfer plasmons in metal nanoparticles on graphene.

Metal nanoparticle (NP) complexes lying on a single-layer graphene surface are studied with a developed original hybrid quantum-classical theory using the Finite Element Method (FEM) that is computationally cheap. Our theory is based on the motivated assumption that the carrier charge density in the doped graphene does not vary significantly during the plasmon oscillations. Charge transfer plasmon (CTP) frequencies, eigenvectors, quality factors, energy loss in the NPs and in graphene, and the absorption power are aspects that are theoretically studied and numerically calculated. It is shown the CTP frequencies reside in the terahertz range and can be represented as a product of two factors: the Fermi level of graphene and the geometry of the NP complex. The energy losses in the NPs are predicted to be inversely dependent on the radius R of the nanoparticle, while the loss in graphene is proportional to R and the interparticle distance. The CTP quality factors are predicted to be in the range ∼10-100. The absorption power under CTP excitation is proportional to the scalar product of the CTP dipole moment and the external electromagnetic field. The developed theory makes it possible to simulate different properties of CTPs 3-4 orders of magnitude faster compared to the original FEM or the finite-difference time domain method, providing possibilities for predicting the plasmonic properties of very large systems for different applications.

Significantly enhanced thermoelectric performance of interstitial N-doped graphene: A density functional theory study

The thermoelectric characteristics of interstitial nitrogen (N)-doped graphene have been studied using the first principles calculations combined with the semi-classical Boltzmann theory. We found that the Seebeck coefficient of N-doped graphene is 3 and 5.5 times higher compared to pristine graphene, along with ZT values. At room temperature, for pristine graphene, the ZT value stands at 0.81, whereas it rises to 0.98 and 1.00 for N-doped graphene with 6.25 % and 50 % nitrogen doping, respectively. The increase in the Seebeck coefficient of N-doped graphene is due to the increase in the effective mass band as the chemical potential rises above the conduction band minimum. We observed that N-doped graphene exhibits the highest ZT value in the positive energy range, indicating a p-type character. Our findings suggest that N-doped graphene has promising potential for thermoelectric applications and provides insights into the underlying physics governing the thermoelectric properties of doped graphene materials.

Exploring Spin Distribution and Electronic Properties in FeN4-Graphene Catalysts with Edge Terminations.

Understanding the spin distribution in FeN4-doped graphene nanoribbons with zigzag and armchair terminations is crucial for tuning the electronic properties of graphene-supported non-platinum catalysts. Since the spin-polarized carbon and iron electronic states may act together to change the electronic properties of the doped graphene, we provide in this work a systematic evaluation using a periodic density-functional theory-based method of the variation of spin-moment distribution and electronic properties with the position and orientation of the FeN4 defects, and the edge terminations of the graphene nanoribbons. Antiferromagnetic and ferromagnetic spin ordering of the zigzag edges were considered. We reveal that the electronic structures in both zigzag and armchair geometries are very sensitive to the location of FeN4 defects, changing from semi-conducting (in-plane defect location) to half-metallic (at-edge defect location). The introduction of FeN4 defects at edge positions cancels the known dependence of the magnetic and electronic proper-ties of undoped graphene nanoribbons on their edge geometries. The implications of the reported results for catalysis are also discussed in view of the presented electronic and magnetic properties.

A Path towards Timely VAP Diagnosis: Proof-of-Concept Study on Pyocyanin Sensing with Cu-Mg Doped Graphene Oxide.

In response to the urgent requirement for rapid, precise, and cost-effective detection in intensive care units (ICUs) for ventilated patients, as well as the need to overcome the limitations of traditional detection methods, researchers have turned their attention towards advancing novel technologies. Among these, biosensors have emerged as a reliable platform for achieving accurate and early diagnoses. In this study, we explore the possibility of using Pyocyanin analysis for early detection of pathogens in ventilator-associated pneumonia (VAP) and lower respiratory tract infections in ventilated patients. To achieve this, we developed an electrochemical sensor utilizing a graphene oxide-copper oxide-doped MgO (GO - Cu - Mgo) (GCM) catalyst for Pyocyanin detection. Pyocyanin is a virulence factor in the phenazine group that is produced by Pseudomonas aeruginosa strains, leading to infections such as pneumonia, urinary tract infections, and cystic fibrosis. We additionally investigated the use of DNA aptamers for detecting Pyocyanin as a biomarker of Pseudomonas aeruginosa, a common causative agent of VAP. The results of this study indicated that electrochemical detection of Pyocyanin using a GCM catalyst shows promising potential for various applications, including clinical diagnostics and drug discovery.

Controlled doping rates of graphene oxide in aluminum for high electrical performance and oxygen reduction reaction

The brush coating method allows the advantage of being able to produce thin films simply and quickly. This study introduces a method for thin-film production by brushing a solution containing graphene doped in Al2O3 using the sol–gel method. Graphene oxide (GO) is suitable for semiconductors with bandgap values of about 1.7 eV at room temperature, and the characteristics of the thin films were analyzed according to the doping ratio. First, X-ray photoelectron spectroscopy measurements were obtained to analyze the chemical composition of the thin-film surface. Since graphene is a carbon isomer, the characteristic of oxygen vacancies was confirmed by the increasing C–C bond intensity with increasing GO doping concentration. In addition, Raman analysis was performed to analyze the concentration of molecular groups of compounds for defects in graphene. Thereafter, through atomic force microscopy measurements, as the graphene doping ratio increased, the average roughness increased from 1.785 to 33.67, the residual DC voltage also increased by about 48.42 %, and the polar anchoring energy also increased by about 16.33 %. In addition, response-time–transmittance measurements were performed to measure the electro-optical properties of the thin film, and excellent Vth and stable response speed were obtained. Additionally, the validity of the results was supported through bandgap analysis. Finally, the degree of alignment of liquid–crystal molecules on the film surface was confirmed by polarized optical microscopy and pretilt angle measurements, and the suitability of the thin film for display devices was shown via transmittance measurements. As a result, GO:Al2O3 hybrid thin film is an excellent candidate for use as an alignment film for solar energy, secondary batteries, and next-generation liquid crystal displays.

Analysis of p-Type Doping in Graphene Induced by Monolayer-Oxidized TMDs.

Doping is one of the most difficult technological challenges for realizing reliable two-dimensional (2D) material-based semiconductor devices, arising from their ultrathinness. Here, we systematically investigate the impact of different types of nonstoichiometric solid MOx (M are W or Mo) dopants obtained by oxidizing transition metal dichalcogenides (TMDs: WSe2 or MoS2) formed on graphene FETs, which results in p-type doping along with disorders. From the results obtained in this study, we were able to suggest an analytical technique to optimize the optimal UV-ozone (UVO) treatment to achieve high p-type doping concentration in graphene FETs (∼2.5 × 1013 cm-2 in this study) without generating defects, mainly by analyzing the time dependency of D and D' peaks measured by Raman spectroscopy. Furthermore, an analysis of the structure of graphene sheets using TEM indicates that WOx plays a better protective role in graphene, compared to MoOx, suggesting that WOx is more effective for preventing the degradation of graphene during UVO treatment. To enhance the practical application aspect of our work, we have fabricated a graphene photodetector by selectively doping the graphene through oxidized TMDs, creating a p-n junction, which resulted in improved photoresponsivity compared to the intrinsic graphene device. Our results offer a practical guideline for the utilization of surface charge transfer doping of graphene toward CMOS applications.

Tunable gas absorption capability for graphene doped silica aerogel by wrinkle structure: Effects of gas absorption, mechanical properties and thermal insulation

Gas absorption capability of material proposes a dominant role in the energy storage, selective gas absorption/capture. Aerogels with ultra-high porosity, ultra-low thermal conductivity have been widely used in gas absorption. However, a persistent limitation of these materials is their static and unalterable gas absorption capacity. In this work, a wrinkled graphene structure is proposed to adjust the gas capability. A series of molecular dynamics (MD) simulations are carried out to propose an atomic-level understanding of the effects of wrinkled structure, including effects of pressure, surface wettability, number of gas molecules, thermal insulation, and mechanical properties. It is found that the gas capability can be reduced by 20% with wrinkle structure. Notably, the linear response between pressure and gas absorption capability is observed. Moreover, wrinkle structure functions as a thermal resistance to restrict solid heat transfer. The mechanical property of the aerogel composite is improved by a doped graphene sheet with a high wrinkle degree. This work will pave the way for the development of aerogel with high and selective gas absorption capability.

Green, Solvent-Free Mechanochemical Synthesis of Nano Ag2O/MnO2/N-Doped Graphene Nanocomposites: An Efficient Catalyst for Additive-Base-Free Aerial Oxidation of Various Kinds of Alcohols.

Herein, we report a solvent-less, straightforward, and facile mechanochemical technique to synthesize nanocomposites of Ag2O nanoparticles-doped MnO2, which is further codoped with nitrogen-doped graphene (N-DG) [i.e., (X %)N-DG/MnO2-(1% Ag2O)] using physical milling of separately prepared N-DG and Ag2O NPs-MnO2 annealed at 400 °C over an eco-friendly ball-mill process. To assess the efficiency in terms of catalytic performance of the nanocomposites, selective oxidation of benzyl alcohol (BlOH) to benzaldehyde (BlCHO) is selected as a substrate model with an eco-friendly oxidizing agent (O2 molecule) and without any requirements for the addition of any harmful additives or bases. Various nanocomposites were prepared by varying the amount of N-DG in the composite, and the results obtained highlighted the function of N-DG in the catalyst system when they are compared with the catalyst MnO2-(1% Ag2O) [i.e., undoped catalyst] and MnO2-(1% Ag2O) codoped with different graphene dopants such as GRO and H-RG for alcohol oxidation transformation. The effects of various catalytic factors are systematically evaluated to optimize reaction conditions. The N-DG/MnO2-(1% Ag2O) catalyst exhibits premium specific activity (16.0 mmol/h/g) with 100% BlOH conversion and <99.9% BlCHO selectivity within a very short interval. The mechanochemically prepared N-DG-based nanocomposite displayed higher catalytic efficacy than that of the MnO2-(1% Ag2O) catalyst without the graphene dopant, which is N-DG in this study. A wide array of aromatic, heterocyclic, allylic, primary, secondary, and aliphatic alcohols have been selectively converted to respective ketones and aldehydes with full convertibility without further oxidation to acids over N-DG/MnO2-(1% Ag2O). Interestingly, it is also found that the N-DG/MnO2-(1% Ag2O) can be efficiently reused up to six times without a noteworthy decline in its effectiveness. The prepared nanocomposites were characterized using various analytical, microscopic, and spectroscopic techniques such as X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman, field emission scanning electron microscopy, and Brunauer-Emmett-Teller.

Facile synthesis of β-Ga2O3 based high-performance electronic devices via direct oxidation of solution-processed transition metal dichalcogenides

Gallium oxide (Ga2O3) is a promising wide bandgap semiconductor that is viewed as a contender for the next generation of high-power electronics due to its high theoretical breakdown electric field and large Baliga’s figure of merit. Here, we report a facile route of synthesizing β-Ga2O3 via direct oxidation conversion using solution-processed two-dimensional (2D) GaS semiconducting nanomaterial. Higher order of crystallinity in x-ray diffraction patterns and full surface coverage formation in scanning electron microscopy images after annealing were achieved. A direct and wide bandgap of 5 eV was calculated, and the synthesized β-Ga2O3 was fabricated as thin film transistors (TFT). The β-Ga2O3 TFT fabricated exhibits remarkable electron mobility (1.28 cm2 Vs−1) and a good current ratio (I on/I off) of 2.06 × 105. To further boost the electrical performance and solve the structural imperfections resulting from the exfoliation process of the 2D nanoflakes, we also introduced and doped graphene in β-Ga2O3 TFT devices, increasing the electrical device mobility by ∼8-fold and thereby promoting percolation pathways for the charge transport. We found that electron mobility and conductivity increase directly with the graphene doping concentration. From these results, it can be proved that the β-Ga2O3 networks have excellent carrier transport properties. The facile and convenient synthesis method successfully developed in this paper makes an outstanding contribution to applying 2D oxide materials in different and emerging optoelectronic applications.

Recent Advances in Functional Materials for Optical Data Storage.

In the current data age, the fundamental research related to optical applications has been rapidly developed. Countless new-born materials equipped with distinct optical properties have been widely explored, exhibiting tremendous values in practical applications. The optical data storage technique is one of the most significant topics of the optical applications, which is considered as the prominent solution for conquering the challenge of the explosive increase in mass data, to achieve the long-life, low-energy, and super high-capacity data storage. On this basis, our review outlines the representative reports for mainly introducing the functional systems based on the newly established materials applied in the optical storage field. According to the material categories, the representative functional systems are divided into rare-earth doped nanoparticles, graphene, and diarylethene. In terms of the difference of structural features and delicate properties among the three materials, the application in optical storage is comprehensively illustrated in the review. Meanwhile, the potential opportunities and critical challenges of optical storage are also discussed in detail.

Theoretical calculation study on enhancing the sensitivity and optical properties of graphene adsorption of nitrogen dioxide via doping

In order to study the adsorption of NO&lt;sub&gt;2&lt;/sub&gt; on pristine graphene and doped graphene (N-doped, Zn-doped, and N-Zn co-doped), we simulate the adsorption process by applying the first-principles plane-wave ultrasoft pseudopotentials of the density-functional theory in this work. The adsorption energy, Mulliken distribution, differential charge density, density of states, and optical properties of NO&lt;sub&gt;2&lt;/sub&gt; molecules adsorbed on the graphene surface are calculated. The results show that the doped graphene surface exhibits higher sensitivity to the adsorption of NO&lt;sub&gt;2&lt;/sub&gt; compared with the pristine graphene surface, and the order of adsorption energy is as follows: N-Zn co-doped surface &gt; Zn-doped surface &gt; N-doped surface &gt; pristine surface. Pristine graphene surface and N-doped graphene surface have weak interactions with and physical adsorption of NO&lt;sub&gt;2&lt;/sub&gt;. Zn-doped graphene surfac and N-Zn co-doped graphene surface form chemical bonds with NO&lt;sub&gt;2&lt;/sub&gt; and are chemisorbed. In the visible range, among the three doping modes, the N-Zn co-doped surface is the most effective for improving the optical properties of graphene, with the peak absorption and reflection coefficients improved by about 1.12 and 3.42 times, respectively, compared with pristine graphene. The N-Zn co-doped graphene not only enhances the interaction between the surface and NO&lt;sub&gt;2&lt;/sub&gt;, but also improves the optical properties of the material, which provides theoretical support and experimental guidance for NO&lt;sub&gt;2&lt;/sub&gt; gas detection and sensing based on graphene substrate.

Defect healing and doping of CVD graphene by thermal sulfurization

Selective healing action of morphological defects in CVD graphene by sulfur leaves unchanged chemical defects that are potentially useful for subsequent chemical functionalization.

High density electron doping in boron-doped twisted bilayer graphene: a ladder to extended flat-band

Realizing Von Hove singularity (VHS) and extended flat bands of graphene near the Fermi level (EF) to explore many-body interactions with a high tendency towards superconductivity.