Doped Graphene Films Research Articles

Nitrogen doped single layer graphene for CZTS-based thin film solar cells

CdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at ∼336 cm−1 associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I2D/IG ratio and a 25 cm−1 FWHM of the 2D peak, indicating a single-layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a VOC of 0.267 V, JSC of 24.6 mA/cm2, FF of 36.46, and η of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.

Synthesis of N-Doped Graphene Photo-Catalyst for Photo-Assisted Charging of Li-Ion Oxygen Battery.

In this work, nitrogen (N)-doped graphene film is synthesized, as a photo-catalyst, on one side of the copper foam by chemical vapor deposition and the copper foam is directly used as an electrode after porous Pd@rGO cathode loading to the other side of the foam for the photo-assisted charging of the Li-ion oxygen battery. The amount of urea (CO(NH2)2), which is used as N atom source, is optimized to get maximum photo-anodic currents from the n-type graphene films. The optical band gap and the valance band edge potential of the optimized N-doped graphene film are determined as 2.00eV and 3.71VLi+/Li, respectively. X-ray photoelectron spectra provided that the atomic percent of N atoms in the graphene film is 1.34% and the graphitic, pyrrolic and pyridinic N atom percentages are 54.01%, 42.20% and 3.79%, respectively. The photo-assisted charging tests indicated that the N-doped graphene film photo-catalyst reduced the charging potential significantly even at 1000mAg-1 (0.1mAcm-2) current density and improved the cyclic discharge-charge performance of the Li-ion oxygen battery considerably.

(Invited) Defect Engineering in Plasma-Treated Graphene Films

Engineering of defects located in-grain or at grain boundary is central to the development of functional materials and nanomaterials. While there is a recent surge of interest in the formation, migration, and annihilation of defects during ion and plasma irradiation of bulk (3D) materials, the detailed behavior in low-dimensional materials remains most unexplored and especially difficult to assess experimentally. A new hyperspectral Raman imaging scheme providing high selectivity and diffraction-limited spatial resolution is here adapted to examine plasma-induced damage in a polycrystalline graphene film grown by chemical vapor deposition on copper substrates and then transferred on silicon substrates. For experiments realized in nominally pure argon plasmas at low pressure, spatially resolved Raman conducted before and after each plasma treatment shows that the defect generation in graphene films exposed to very low-energy (11 eV) ion bombardment follows a 0D defect curve, while the domain boundaries tend to develop as 1D defects. Surprisingly and contrary to common expectations of plasma-surface interactions, damage generation at grain boundaries is slower than within the grains. Inspired by recent modeling studies, this behavior can be ascribed to a lattice reconstruction mechanism occurring preferentially at domain boundaries and induced by preferential atom migration and adatom-vacancy recombination. Further studies were realized to compare the impact of different plasma environments promoting either positive argon ions, metastable argon species, or VUV-photons on the damage formation dynamics. While most of the defect formation is due to knock-on collisions by 11-eV argon ions, the combination with VUV-photon or metastable atom irradiation is found to have a very different impact. In the former, the photons are mainly thought to clean the films from PMMA residues due to graphene transfer from copper to silicon substrates. On the other hand, in conditions with both ion and metastable atom irradiation, the surface de-excitation of the latter seem to greatly enhance the self-healing of the grain boundaries due to an increase of the local energy deposition. Finally, these experiments were used as building blocks to examine the formation of chemically doped graphene film in such plasmas using argon mixed with either traces of N- or B-bearing gases. While preferential n-type doping was observed in graphene domains in nitrogen-containing plasmas, preferential p-type doping was observed at grain boundaries in boron-containing plasmas.

Highly conductive graphene film with high-temperature stability for electromagnetic interference shielding

Lightweight, flexible and highly conductive electromagnetic interference (EMI) shielding materials are urgently needed to protect the electronic and telecommunication devices from interference failure. Carbon-based films have attracted much interest to provide EMI shielding with minimal thickness in recent years, particularly exemplified by macroscopic graphene film. However, the inferior electrical conductivity to metal or the un-stability of doped graphene film cannot meet the ever-growing demands for harsh environment applications. Here, we prepare highly conductive copper chloride intercalated graphene film (GF-CuCl2) with high-temperature stability up to 400 °C. The intercalation of CuCl2 significantly improves the hole density, and the achieved electrical conductivity (1.09 × 107 S m−1) is nearly 10 times that of pure graphene film. The ultra-low temperature coefficient of resistance (4.31 × 10−4 K−1) makes GF-CuCl2 electrically stable over a broad temperature range. A 35-μm-thick GF-CuCl2 exhibits an average EMI shielding effectiveness of ∼110 dB from 2 to 18 GHz and ∼126 dB from 8.2 to 12.4 GHz, which is the highest among materials of comparable thickness. Moreover, the EMI shielding capability of GF-CuCl2 shows long-term durability under extreme conditions. All these characteristics demonstrate the GF-CuCl2 is suitable for the practical EMI shielding applications.

Substitutional boron doping of graphene using diborane in CVD

This paper reports on a few layer boron doped graphene with high homogeneity, stability and size. To achieve this, we employed diborane to synthesize a boron doped graphene film in a CVD system. During synthesis, we investigated the effect of diborane flow and growth time on copper foil to optimize doped graphene growth conditions. Raman spectroscopy, XPS, EDXS and ellipsometer were employed for the characterization of the doped graphene films. The results of our study enabled the design of a recipe for thin film boron doped graphene growth with optimum optical transmission values. We further found that increasing the flow of diborane from 10 to 30 sccm and growth times from 10 to 30 min leads to the formation of thicker graphene films. However, we discovered that a few layer graphene film with high homogeneity could be obtained for the film that was grown using 10 sccm diborane along with 30-min growth time. The doping was confirmed by observing the shift in the Raman spectra peaks and XPS measurements in comparison to single layer pristine graphene. The study also revealed that boron atoms substituted carbon atoms in the honeycomb structure as confirmed by XPS measurements, which also provide the doping rate to be 2.4%. Our study has significant implications regarding substitutional doping which enables the doping to be stable for a long time, and this is crucial for the doped graphene to be employed in semiconducting technology particularly in optoelectronics.

Preparation of hexagonal boron nitride doped graphene film modified sensor for selective electrochemical detection of nicotine in tobacco sample

The selective detection of nicotine is necessary in biological and biomedical samples to screen the patients who has the neurodegenerative diseases due to tobacco addiction. For this purpose, we have synthesized a hybrid binary composite made of 2D hexagonal boron nitride nanosheets (BN) doped graphene film via a scalable top-down technique for the electrochemical detection of nicotine. Transmission electron microscopy (TEM) images showed that layered graphene sheets bounded with BN nanosheets. Moreover, Fourier-transform infrared (FT-IR), UV–visible (UV–vis), and X-ray photoelectron spectroscopies (XPS) confirmed successful integration of BN within graphene. In addition, the electrical conductivity of the nanocomposite was tested using electrochemical impedance spectroscopy (EIS), which showed high electrical conductivity of BN/graphene coated electrode with low charge transfer resistance. To develop a selective nicotine sensor, glassy carbon electrode (GCE) surface was coated with BN/graphene hybrid film and tested its electro-catalytic activity against nicotine. It was found that BN/graphene/GCE based sensor exhibited excellent electro-catalytic activity for nicotine oxidation at lower potential of +0.97 V in phosphate buffer solution (PBS, pH 7.0) and the linear response was observed from 1 to 1000 μM. The limit of detection (LOD) was estimated as 0.42 μM. The common interferent compounds such as uric acid (UA), paracetamol (PA), glucose (Glu), melamine (Mel), cysteine (Cys) and dopamine (DA) did not interfere on the sensor selectivity. Furthermore, BN/graphene/GCE exhibited high stability and reproducibility. Finally, BN/graphene/GCE-based sensor was successfully applied to detect nicotine in a tobacco sample with high recovery.

(Invited) Defect Engineering in Plasma-Treated Graphene Films

Engineering of defects located in-grain or at grain boundary is central to the development of functional materials and nanomaterials. While there is a recent surge of interest in the formation, migration, and annihilation of defects during ion and plasma irradiation of bulk (3D) materials, the detailed behavior in low-dimensional materials remains most unexplored and especially difficult to assess experimentally. A new hyperspectral Raman imaging scheme providing high selectivity and diffraction-limited spatial resolution is here adapted to examine plasma-induced damage in a polycrystalline graphene film grown by chemical vapor deposition on copper substrates and then transferred on silicon substrates. For experiments realized in nominally pure argon plasmas at low pressure, spatially resolved Raman conducted before and after each plasma treatment shows that the defect generation in graphene films exposed to very low-energy (11 eV) ion bombardment follows a 0D defect curve, while the domain boundaries tend to develop as 1D defects. Surprisingly and contrary to common expectations of plasma-surface interactions, damage generation at grain boundaries is slower than within the grains. Inspired by recent modeling studies, this behavior can be ascribed to a lattice reconstruction mechanism occurring preferentially at domain boundaries and induced by preferential atom migration and adatom-vacancy recombination. Further studies were realized to compare the impact of different plasma environments promoting either positive argon ions, metastable argon species, or VUV-photons on the damage formation dynamics. While most of the defect formation is due to knock-on collisions by 11-eV argon ions, the combination with VUV-photon or metastable atom irradiation is found to have a very different impact. In the former, the photons are mainly thought to clean the films from PMMA residues due to graphene transfer from copper to silicon substrates. On the other hand, in conditions with both ion and metastable atom irradiation, the surface de-excitation of the latter seem to greatly enhance the self-healing of the grain boundaries due to an increase of the local energy deposition. Finally, these experiments were used as building blocks to examine the formation of chemically doped graphene film in such plasmas using argon mixed with either traces of N- or B-bearing gases.

Boron-doped graphene synthesis by pulsed laser co-deposition of carbon and boron

Incorporating dopants, such as boron, in graphene, is crucial for many applications in electrochemistry, sensors, photovoltaics, and catalysis. Many routes have been investigated for the preparation of B-doped graphene (BG) films, including chemical processes. A different way to obtain boron-doped layers to better control the concentration of boron in the doped graphene film, is pulsed laser co-ablation of C and B solid sources followed by rapid thermal heating of the B-doped carbon film deposited on a metal catalyst. Amorphous a-C:B films, containing 2 at. % boron, are synthetized by pulse laser deposition onto a nickel film catalyst. Rapid thermal annealing at 1100 °C leads to the formation of boron-doped graphene films, characterized by Raman, XPS, FEG-SEM, HRTEM and AFM. The results confirm the production of 1–4 layer boron doped graphene films, with a similar 2 at. % boron concentration to that of the a-C:B used as the graphene solid precursor. Boron doping does not modify the nano-architecture of graphene, but increases the concentration of defects in the films. Our results pave a new way for boron doped graphene synthesis using laser processing in a controlled and reproducible way, in particular to achieve designed electrical and chemical properties in various electronic and electrochemical applications.

Seed‐Initiated Synthesis and Tunable Doping Graphene for High‐Performance Photodetectors

AbstractDue to the promising utilizations in nanoelectronics, doping‐tunable graphene is paid extensive attentions. Nevertheless, a harmless approach to dope/co‐dope graphene in a controllable and easy way with low cost is still unattainable. Herein, through seeding of 0D N & S dual‐doped graphene quantum dots (N & S dual‐doped GQDs) on a catalytic substrate and then dynamic chemical vapor deposition (CVD), a monolayered dual‐doped graphene film is demonstrated. The concentrations of dopants in graphene are strictly discerned in accordance with preliminary seeding for dual‐doped GQDs. Through the monitoring of growing process, the research elucidates the growth mechanism of the graphene, and unveils that dual‐doped GQDs can serve as the nucleation centers for creating doped‐graphene films by 2D epitaxial growth and thus graphene with designed dopant concentration can be obtained. Finally, the photodetector built on N & S dual‐doped graphene film is found to perform satisfactorily, accompanying high detectivity (≈1.42 × 1010 cm Hz1/2 W−1) and responsivity (61 mA W−1), at wavelength of 1550 nm. The research proposes a dexterous approach for synthesizing tunably doped graphene films by the combination of locally controlled nucleation seeds and in situ CVD, which lays the foundation for applying graphene in industries of photonic and electronic devices.

Environmentally stable macroscopic graphene films with specific electrical conductivity exceeding metals

Air stable, lightweight, and electrically conductive carbon-based films are highly desired for flexible electronic devices and products. Graphene film, a macroscopic assembly of individual graphene sheets, holds great potential to replace conventional brittle pyrolytic carbon film due to the excellent electrical transport property and flexibility. However, the electrical conductivity of graphene film is still inferior to metallic conductors, usually unstable in air as doped. We chose metal chloride (MoCl5) as air stable dopant and fabricated doped graphene film with well-controlled intercalation structure. The MoCl5 modified graphene film shows record high electrical conductivity of 1.73 × 107 S m−1, record high mobility of 2190.47 cm2 V−1 s−1, remarkable specific electrical conductivity exceeding benchmark metals (e.g., Au, Ag, Cu), and ultralow temperature coefficient of resistance (1.4 × 10−4 K−1). Importantly, the electrical conductivity and overall structure of MoCl5 intercalated films are exceptional stable in atmospheric environment, enabling wide applications in electronic devices, electromagnetic interference, and energy storage.

Free-standing macro-porous nitrogen doped graphene film for high energy density supercapacitor

In this paper, a porous free-standing nitrogen-doped graphene (NG) film for high energy density supercapacitor is prepared via a facile hydrogel strategy. Taking advantage of the hydrogel behavior together with the mechanical stability of GO sheets, an interconnected macro-porous nitrogen-doped free-standing film is constructed. The nitrogen doping structure ensures sufficient pseudocapacitance and conductivity of the film, while the macro-porous structure favors fast ion adsorption. When assembled in a symmetric two-electrode supercapacitor, not any conductive agent or binder is used. The free-standing NG film shows specific capacitance of 455.4 F g−1 based on the mass of whole electrode, while no capacitance loss after 5000 cycles. Furthermore, an asymmetric supercapacitor is assembled with this NG film as negative electrode and a macro-porous graphene/polypyrrole composite film synthesized using the similar strategy as positive electrode. An energy density of 34.51 Wh kg−1 at a power density of 849.77 W kg−1 is obtained, suggesting great potential of this film for application in energy storage field.

Wet-spinning assembly of nitrogen-doped graphene film for stable graphene-polyaniline supercapacitor electrodes with high mass loading

Graphene-polyaniline (GP) composites are promising electrode materials for supercapacitors but possessing unsatisfied stability, especially under high mass loading, due to the low ion transmission efficiency and serious pulverization effect. To address this issue, we propose a scalable method to achieve highly wettable GP electrodes, showing excellent stability. In addition, our results demonstrate that the performance of electrodes is nearly independent of the mass loading, indicating the great potential of such GP electrodes for practical devices. We attribute the remarkable performance of GP to the delicate precursor of nitrogen doped graphene film assembled by wet-spinning technology. This report provides a strategy to promote the ion penetrating efficiency across the electrodes and deter the pulverization effect, aiming at the practical GP supercapacitor electrodes of high mass loading.

Designing Parameters of Surfactant-Free Electrochemical Sensors for Dopamine and Uric Acid on Nitrogen Doped Graphene Films

Electrochemistry studies on the derivatives of graphene have been in the forefront of chemical research in recent years. The large specific surface area, high electrical conductivity, fast electron transfer rate and excellent biocompatibility to biomolecules constitute a few of the underlying reasons for the extensive application of graphene derivatives in modern electrochemistry and related technologies. Much interest in graphene derivatives has been driven by the ease of intentional functionalisation of the carbon backbone of graphene with dopants, such as nitrogen. Doping enhances the electrical conductivity and biocompatibility of nitrogen-doped graphene (NGr) nanomaterials and aids in their potential applications in electrochemical sensing and spectroelectrochemical devices. Despite the application of NGr in electrochemical sensing devices, the major challenge for reproducible industrial application still lies in the use of surfactants and binders and the limited knowledge on the correlation between the N-configurations and the electrocatalytic performance of these NGr-based electrodes. Therefore, the purpose of this short review article is to highlight some recent progress on the application of NGr derivatives for electrochemical detection of biomarkers such as uric acid and dopamine. The paper will also illustrate design parameters for new surfactant-free two-dimensional (2D) N-doped graphene based electrochemical sensors with variable N-functionalities for the detection of dopamine and uric acid.

Formation of environmentally stable hole-doped graphene films with instantaneous and high-density carrier doping via a boron-based oxidant

Large-area graphene films have substantial potential for use as next-generation electrodes because of their good chemical stability, high flexibility, excellent carrier mobility, and lightweight structure. However, various issues remain unsolved. In particular, high-density carrier doping within a short time by a simple method, and air stability of doped graphene films, are highly desirable. Here, we demonstrate a solution-based high-density (>1014 cm−2) hole doping approach that promises to push the performance limit of graphene films. The reaction of graphene films with a tetrakis(pentafluorophenyl)borate salt, containing a two-coordinate boron cation, achieves doping within an extremely short time (4 s), and the doped graphene films are air stable for at least 31 days. X-ray photoelectron spectroscopy reveals that the graphene films are covered by the chemically stable anions, resulting in an improved stability in air. Moreover, the doping reduces the transmittance by only 0.44 ± 0.23%. The simplicity of the doping process offers a viable route to the large-scale production of functional graphene electrodes.

Tuning capacitance of graphene films via a robust routine of adjusting their hierarchical structures

In this work, the nitrogen doped graphene films with hierarchical network structures have been successfully fabricated via a robust routine of adjusting the content of large- and small-sized reduced graphene oxide (RGO) sheets in the graphene films, where the large-sized RGO sheets act as the backbone to form the well-connected network structures and small-sized RGO sheets act as the interlayer and interpore linkers to connect the large-sized RGO sheets and large pores. A maximum capacitance of 429.7 F g−1 is obtained for the optimized RGO electrode with small-sized RGO content of 40 wt%, which is 61.9% improvement compared to the RGO electrodes with pure large-sized RGO sheets. While, the specific surface area and electrical conductivity of the optimized RGO electrode are 36.1% and 26.2% improvement compared to the pure large-sized electrode. Therefore, we attribute the improved capacitance primarily comes from the increasing of specific surface area due to the formation of fine hierarchical structures and the better connection of the network structures (the increasing of electrical conductivity) for the optimized RGO electrode. Besides, the optimized RGO electrode exhibits good cycle, rate performance, power and energy density compared to the previous carbon based supercapacitor. Herein, we can precisely control the specific surface area and electrical conductivity of RGO electrode by simply adjusting the content of large- and small-sized RGO, which may shed useful insight for the design of high performance supercapacitors and Li-ion batteries.

Modification of N-doped graphene films and their applications in heterojunction solar cells

A two-step growth process was developed to synthesis N-doped graphene films by using pentachlorop-yridine as nitrogen source and methane as carbon source. The configuration and compositions of modified graphene films were characterized by X-ray photoelectron spectroscopy (XPS), and its bonding properties were obtained with Raman spectroscopy. The films were found to be N-doped graphene films with the N/C ratio of 2.5%–4%. The electronic properties of the films have been tested by using Hall Effect Measurement System. The nitrogen doped graphene film exhibits lower resistance (7.26 × 10−6 Ω·cm) but smaller mobility (521.8 cm2/V·S). Current density-voltage feature of solar cells with different structures were measured to research the photovoltaic characteristic of Graphene/n-Si solar cells. It was found that solar cells with N-doped graphene layer shown better performance of photovoltaic in illumination. The maximum energy conversion efficiency achieved was 6.24%. The inserted nitrogen atoms can effectively reduce the resistivity of graphene films, thus solve the problem of carrier recombination which caused by slow transmission speed. As a result, N-doped graphene film can highly facilitate the transmission and exportation of current, along with the improvement of short-circuit current density, which further enhance the overall efficiency of the solar cells. This work can promote the development of graphene film in application of transparent conductive electrode fields.

Iodine-steam doped graphene films for high-performance electrochemical capacitive energy storage

Recently, the fabrication of high-performance graphene films as electrode materials become a research tendency for flexible energy-storage devices. Here, we successfully prepare iodine-doped reduced graphene oxide (I-rGO) films with excellent capacitive performance by a simple and versatile technique of iodine steam doping. The iodine as an effective p-type dopant can enhance electrical conductivity of graphene films by charge transfer process, further improving capacitive performance of the devices. The electrochemical properties of as-prepared I-rGO films with different mass loadings are systematically and comprehensively studied. With the change of mass loading (1.5–6.7 mg cm−2), the gravimetric specific capacitance of I-rGO films remains almost invariable at the studied range of current density, and finally can reach ∼150 F g-1 at 0.2 A g−1. With the increasing mass loading, supercapacitors based on the I-rGO films show almost linear growth of areal specific capacitance at any current densities from 1 to 30 mA cm−2 (eventually reach ∼524 mF cm-2 at 1 mA cm−2). Additionally, we fabricate flexible all-solid-state supercapacitors, which also displays excellent areal specific capacitance (∼450 mF cm−2), great cycling stability and favorable electrochemical stability. These results indicate that the fabricated I-rGO films have great advantages as electrode materials for flexible energy-storage devices.

Layer-by-layer hybrid chemical doping for high transmittance uniformity in graphene-polymer flexible transparent conductive nanocomposite

A traditional transparent conducting film (TCF) such as indium tin oxide (ITO) exhibits poor mechanical flexibility and inconsistent transmittance throughout the UV-VIS-NIR spectrum. Recent TCFs like graphene films exhibit high sheet resistance (Rs) due to defect induced carrier scattering. Here we show a unique hybrid chemical doping method that results in high transmittance uniformity in a layered graphene-polymer nanocomposite with suppressed defect-induced carrier scattering. This layer-by-layer hybrid chemical doping results in low Rs (15 Ω/sq at >90% transmittance) and 3.6% transmittance uniformity (300–1000 nm) compared with graphene (17%), polymer (8%) and ITO (46%) films. The weak localization effect in our nanocomposite was reduced to 0.5%, compared with pristine (4.25%) and doped graphene films (1.2%). Furthermore, negligible Rs change (1.2 times compared to 12.6 × 103 times in ITO) and nearly unaltered transmittance spectra were observed up to 24 GPa of applied stress highlighting mechanical flexibility of the nanocomposite film.

One Step Synthesis of Nitrogen-Doped Graphene from Naphthalene and Urea by Atmospheric Chemical Vapor Deposition

Heavy metal pollutants in wastewater are a major environmental concern. In order to fabricate metal organic composite for adsorption of these pollutants, in a first step a pristine and several nitrogen doped graphene films were synthesized by chemical vapor deposition method. Preparation of graphene films was performed through a one-step co-growth of naphthalene and urea mixture as an inexpensive and easy technique to handle solid precursors. This was done over a copper catalyst at different growth temperatures. Different characterization methods including Raman spectroscopy, elemental analysis, and X-ray diffraction confirmed the quality of the pristine and doped graphene. This technique showed an increasing trend of the doping level (nitrogen concentration up to 5.1% overall) as the growth temperature decreased. Results showed that both nitrogen doping, and carrying the synthesis at higher temperatures increase the defects and wrinkles in the graphene. Furthermore, doping introduced a light shift in defect types from vacancy in pristine graphene to boundary type in nitrogen-doped samples, which are favorable for functionalization for environmental applications.

Effect of annealing on doping of graphene with molybdenum oxide

We investigated the effect of post-annealing on the doping of graphene with MoO3 in this study. The as-deposited molybdenum oxide thin film prepared using our method was not completely oxidized; in addition, it was in an amorphous state, due to which its doping effect was not significant. As the post-deposition annealing temperature was increased, the oxidation and crystallization of the molybdenum oxide progressed and the doping effect increased accordingly. After annealing at 350 °C, the holes were the most doped and the sheet resistance was the lowest. The doped graphene film obtained in this study shows higher doping effect and stability compared to other dopants.