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Graphene-based catalysts have been widely applied for catalytic ozonation. However, as it is difficult to obtain graphene with high structural precision, it is currently unfeasible to comprehend the relationships between the intrinsic structure of the layered carbon catalysts with its catalytic activities. Here, an advanced plasma-assisted etch strategy was used to fine tune the ozonation activity of monolayered graphene films by tailoring the defect types. Raman mapping indicated that the defects of the as-prepared monolayered graphene films were predominantly sp3, vacancy, and boundary-type defects, respectively. The roles and contributions of these active defects in manipulating the oxidative potential of monolayered graphene films were revealed by quenching experiments, electron paramagnetic resonance results, and density functional theory calculations. The catalytic results showed that the monolayered graphene films with boundary-like defects exhibited the best catalytic performance toward the degradation of sulfamethoxazole. This work contributes new insights into the design of high-efficiency carbonaceous catalysts by structuring additional defective sites.

The construction of a nonthermal plasma (NTP)-catalysts system is an efficient strategy for purifying organic waste gas. Up to now, developing stable, efficient, and environmental-friendly catalyst...

Instability of rear electrodes undermines the long-term operational durability of efficient perovskite solar cells (PSCs). Here, a composite electrode of copper-nickel (Cu-Ni) alloy stabilized by in situ grown bifacial graphene is designed. The alloying makes the work function of Cu suitable for regular PSCs and Cu-Ni is the ideal substrate for preparing high-quality graphene via chemical vapor deposition, which simultaneously protects the device from oxygen, water and internal components reaction. To rivet the composite electrode with semi-device, a thermoplastic copolymer is employed as an adhesive layer during hot pressing. The resultant device achieved power conversion efficiency of 24.34% with significantly improved stability; the devices without encapsulation retained 97% of their initial efficiency after the damp heat test at 85oC with relative humidity of 85% for 1440 hours and the encapsulated devices maintained 95% of their initial efficiencies after maximum power point tracking under continuous 1 sun illumination for 5000 hours.

Carbon nanotubes (CNTs) have been considered to be an ideal cathode candidate for field emission applications since 1995, and there is always a trade-off between the number of emission tips and the...

Mn3O4-CeO2/holey-graphene nano-composite was fabricated by hydrothermal reaction on the honeycomb-like porous graphene structure. The hybrid materials displayed enhanced capacitive performance (310 F·g−1 at 2 A·g−1). After 1000 cycles, the initial capacitance of the composite still has 92.4% retained. The improved electrochemical performance might be ascribed to the intimate combination of the pesudocapacitance from nanoparticles well-dispersed on graphene sheets and double layer capacitance from excellent conductive graphene scaffold. The investigation presents a promising application of nanoparticles/graphene composites as electrode materials for energy storage.

The Cadmium sulphide/bio-structured carbon composites are synthesized by a novel combination of calcination method and hydrothermal method. The purpose of converting the exposed face of the material from the (101) crystal to the (002) crystal plane is achieved by adding EDTA to the solution system during the hydrothermal process. The results show that the resulting composites retain the special structure of the original templates and the CdS of different exposed surfaces is significantly different in geometry. According to TEM and XRD phase analysis, the method of adding EDTA can effectively control the growth of exposed crystal faces in CdS. Photoluminescence spectroscopy demonstrates that the introduction of bio-structured carbon can improve the efficiency of photogenerated electron-hole pair separation. After 6 h of illumination, the photocatalytic decomposition of the surface-controlled composite material produced about 300 μmol of hydrogen, which is superior to the hydrogen production of the control material. In addition, combined with experimental data analysis and related literature, the mechanism of the combination of materials and the control of crystal growth is proposed, respectively.

In this work, we used acetonitrile a liquid carbon source as precursors to grow nitrogen doped single-crystal graphene by chemical vapor deposition. Faster growth of graphene single crystal with acetonitrile liquid carbon source precursors than that of methane has been realized, and nitrogen was doped in the domain successfully. The growth rate of nitrogen doped single-crystal graphene was up to 20.25 μm min−1. The atomic percentage of N in the sample was about 2.29%. The measured mobility of our samples was found about 644 cm2V−1s−1, which was much higher than many of the N-doped graphene reported previously. We provided a reliable synthetic route for the production of high-quality nitrogen doped single-crystal graphene, which was conducive to its wide applications and commercial productions.

In this paper, the morphology, structure, and magnetic properties of FINEMET/graphene composite ribbons are systematically studied by SEM, Raman and static methods (hysteresis loops) and the dynamic method (giant magneto-impedance effect, GMI) respectively. It is revealed that with the increase of the number of graphene layers, the GMI effect of the FINEMET/graphene composite ribbons decreases, and the anisotropy field and the relaxation frequency of domain wall displacement of FINEMET/graphene composite ribbons increases. The result also confirmed that graphene does regulate the magnetic properties of FINEMET ribbon. Therefore, a comprehensive analysis of the influence of graphene on the magnetic properties of FINEMET ribbon is of important guiding significance in industrial applications.

In this Letter, we found that the growth of graphene on Cu oxide foil is significantly affected by the concentration of oxygen. The grain size of graphene grown on a Cu substrate with a relatively high oxygen concentration is much smaller than that on the substrate with lower oxygen concentration. By controlling the oxidation of the Cu substrate at a proper degree, we can obtain millimeter scale graphene single crystals at a growth temperature of 1050 °C. On the basis of our experimental observations, the dual role of oxygen in the CVD growth of graphene was revealed: (i) Oxygen on a Cu surface can contribute to the decomposition of hydrocarbon feedstock and decrease the graphene growth barrier, resulting in an increased growth rate and a larger grain size of graphene; (ii) excess oxygen in the Cu substrate leads to etching of the graphene edge. Our research provides insights to obtain large-area and single-crystalline graphene by choosing a proper Cu oxide substrate.

High-quality reduced graphene oxide (rGO) sheets can be accessible through Langmuir-Blodgett self-assembly (LBSA) on copper foil and dielectric substrate under high temperature ethanol vapors via chemical vapor deposition (CVD) process. Through the LBSA forming method, a uniform and smooth graphene oxide (GO) film can be obtained on the target substrate, which is more economical and efficient compared to the traditional growth strategy. Moreover, the GO-derived graphene film repaired on copper was nearly defect-free with a negligible defect density (ID/IG ratio of 2/Si, 0.2 kΩ/sq prepared on copper and subsequently transferred to SiO2/Si) that had surpassed other GO-derived graphene ever reported. Meanwhile, we demonstrate that Cu-vapor will degrade the restoration efficiency when introduced remotely, which is quite different from previous studies on graphene growth.

This paper designed and regulated a unique sandwich FINEMET/rGO/FeCo composite ribbons (/F/GFC) with giant magneto-impedance (GMI) effect. The reduced graphene oxide (rGO) was synthesized on the FINEMET ribbons by one-step electroless plating, and FeCo layer was obtained by magnetron sputtering method. The study on morphology, structure, GMI effect and magnetic properties of /F/GFC illustrated that the currents passed through the highly conductive layer of rGO at high frequency, which greatly reducing the skin effect. In addition, the FeCo layer increased the permeability and provided a closed magnetic circuit, which can finally gain a large GMI effect at low frequency. The /F/GFC owned enhanced GMI effect, with the maximum GMI ratio reaching 70.32%, which was 2.1 times of the bare FINEMET ribbon, 1.4 times of the FINEMET/rGO composite ribbon and 1.2 times of the FINEMET/FeCo composite ribbon, respectively. The result can be explained by the regulating effect of magnetic dipole interaction on the magnetic properties of soft magnetic materials.

Electromagnetic interaction in composite structure materials has been a crucial physical mechanism to optimize magnetic property of magnetic devices. In this paper, the composite ribbons of FINEMET coated with reduced graphene oxide (rGO) were successfully prepared by electroless plating method at different pH values. The structure, morphology and magnetic properties of the FINEMET/rGO composite ribbons were characterized by X-Ray diffraction, Raman spectroscopy, scanning electron microscope, giant magneto-impedance (GMI) analysis and vibrating sample magnetometer techniques, respectively. The results showed that the peak position field of composite ribbon first decreases and then increases with the variation of pH value, which indicated that there may be existed electromagnetic interaction and stress between rGO and the FINEMET ribbon. The electromagnetic interaction may lead to the redistribution of current density and the change of skin depth. An interpretation in terms of electromagnetic interaction between rGO and FINEMET ribbon was proposed, which provided a new perspective for analyzing the variation in GMI effect of composite materials.

Growing graphene on copper (Cu) by chemical vapor deposition (CVD) has emerged as a most promising approach to satisfy its practical requirements, but the fast and large-scale characterization of its grown adlayers remains a challenge. Here we present a facile and inexpensive method to directly identify the multilayer graphene stacks on Cu by optical microscopy, using simple ultraviolet and heating treatments. The sharp optical contrast, originating from the variation in Cu oxide thickness underneath graphene, reproduces the stacking geometry with high fidelity to scanning electron microscopy observation, demonstrating the correspondence among the optical contrast, the oxide thickness variation, and the stack of adlayers. The close correlation roots in the throttling effect of graphene grain with discrete structural defects in controlling the rate-determined Cu oxidizing agent supply. We believe that this approach can enable large-scale evaluation of CVD-derived graphene quality, which are critical for op...

We present a three-dimensionally configured cathode with enhanced field-emission performance formed by combining carbon nanotube (CNT) emitters with a nickel foam (NiF) substrate via a conventional screen-printing technique. The CNT/NiF cathode has low turn-on electric field of 0.53 V μm−1 (with current density of 10 μA cm−2) and threshold electric field of 0.87 V μm−1 (with current density of 0.1 mA cm−2), and a very high field enhancement factor of 1.4 × 104. The porous structure of the NiF substrate can greatly improve the field-emission properties due to its large specific surface area that can accommodate more CNTs and increase the emitter density, as well as its high electrical and thermal conductivities that facilitate current transition and heat dissipation in the cathode. Most importantly, the local electric field was also enhanced by the multistage effect resulting from the rough metal surface, which furthermore leads to a high field enhancement factor. We believe that this improved field-emission performance makes such cathodes promising candidates for use in various field-emission applications.

Involving oxygen in the traditional chemical vapor deposition (CVD) process has proven a promising approach to achieve large-scale graphene single crystals (GSCs), but its many relevant fundamental aspects are still not fully understood. Here we report a systematic study on the role of hydrogen in the growth of millimeter-sized GSCs using enclosure-like Cu structures via the oxygen-assisted CVD process. Results show that GSCs have different first layer growth behaviors on the inside and outside surfaces of a Cu enclosure when the H2 environment is varied, and these behaviors will consequently and strongly influence the adlayer formation in these GSCs, leading to two entirely different growth modes. Low H2 partial pressure (PH2) tends to result in fast growth of dendritically shaped GSCs with multiple small adlayers, but high PH2 can modify the GSC shape into hexagons with single large adlayer nuclei. This difference of adlayers is attributed to the different C diffusion paths determined by the shapes of their host GSCs. On the basis of these observations, we developed an isothermal two-step method to obtain GSCs with significantly improved growth rate and sample quality, in which low PH2 is first set to accelerate the growth rate followed by high PH2 to restrict the adlayer nuclei. Our results prove that the growth of GSCs can reach a reasonable optimization between their growth rates and sample quality by simply adjusting the CVD H2 environment, which we believe will lead to more improvements in graphene synthesis and fundamental insight into the related growth mechanisms.

Scalable large graphene single crystals have been synthesized by using a backward faced quartz cuvette in a conventional tube furnace. The effect of the restricted chamber in controlling the graphene single crystal growth has been systematically studied by considering the influence of the flow rate and ratio of H 2 and CH 4 experimentally. Numerical simulations were performed to uncover the underlying mechanism. The convection of CH 4 was substantially suppressed inside the cuvette due to the blocking effect by the close-end geometry. The diffusivity of CH 4 is much lower than that of H 2 , resulting in a slow transportation of CH 4 as well. By using the specific experimental parameters, the mass ratio of H 2 and CH 4 increased about 3 times inside the cuvette, leading to preferential growth of graphene single crystals, as observed in our experiments. Meanwhile, the growth of a second layer can be suppressed by the slower feeding of CH 4 than H 2 . Based on these results, we believe that setup of our restricted chamber can provide another growth approach for scalable graphene single crystals and its analysis can help understand more growth dynamics of graphene single crystal inside other irregular CVD conditions such as rolled-up and enclosed Cu foils.

The photocatalytic potential of large area CVD grown nitrogen doped graphene (NGr) has been explored though the chemical transformation of 4-nitrobenzene thiol into p,p'-dimercaptoazobenzene. Decoration of NGr with Ag nanocubes with rounded edges to form NGr/Ag nanohybrids resulted in a slight increase in the work-function and a decrease in the n-type character of NGr due to ground state transfer of negative charge from NGr to Ag. The Ag nanocubes exhibited a localized surface plasmon resonance (LSPR) at ~425 nm. When the NGr/Ag nanohybrids were illuminated with visible light of wavelength close to the LSPR peak, Kelvin probe force microscopy (KPFM) indicated a dramatic change in surface potential of −225 mV and Raman spectra detected electron accumulation in NGr, which are attributed to a high local field enhancement-mediated hot electron injection into NGr and the formation of long-lived charge separated states. Pristine nitrogen doped graphene and its coupled system with plasmonic Ag nanoparticles showed superior photocatalytic performance compared to bare plasmonic Ag catalyst. While standalone Ag NPs were unable to complete the transformation of 4-NBT into DMAB even at a laser power of 10 mW, NGr/Ag nanohybrids completed this transformation at a laser power of 1 mW, pointing to the high photoreduction strength of NGr/Ag. Density functional theory (DFT) based computational modeling was used to examine the electronic structure of graphene doped with graphitic, pyridinic and pyrrolic nitrogen dopant atoms. DFT results indicated an enhanced chemical reactivity of NGr due to stronger localization of charge at the dopant sites and a pronounced difference in the projected density of states (PDOS) for carbon atoms in proximity to, and distant from, the nitrogen dopant sites.

Simultaneous reduction, repairing and doping of graphene oxide has been realized by the chemical vapor deposition method, using acetonitrile as a nitrogen source. A step-wise increase of acetonitrile partial pressure from 15 to 90 Pa results in nitrogen doped graphene (NG) with gradually tuning N-doping concentration from 0.38 to 0.66 at% and systematically rising graphite-N ratio from 23.25 to 45.39%, which in turn modulates field emission performance and enhance the stability. Raman spectroscopy and X-ray photoelectron spectroscopy suggest pyrrolic-N and pyridinic-N doping bring defects, while defects decrease as N-doping concentration increases due to the rising of graphite-N ratio. Proper defects may increase emission site density and N-doping can reduce work function. When N-doping concentration is controlled at 0.42 at%, NG exhibits the considerable decreasing of turn-on field from 3.35 to 2.18 V/μm at the emission current of 10 μA/cm2 and increasing of field enhancement factor from 1835 to 2967. It also reveals a good field emission stability with no degradation, which is superior to pristine reduced GO emitters. It is suggested the NG with tuning concentration of three type nitrogen emitter is a widely candidate for various field emission devices and applications.

Reduced graphene oxide bundles with sharp tips were fabricated by a simple approach with freeze-drying and hydrothermal reduction, and this approach could modify the surface topography of the field emission cathode and make more graphene bundles sharpen and aligned. This field emission cathode material displayed excellent field emission properties decreased from 2.9 V μm−1 to a low turn-on field of 0.8 V μm−1 at the emission current density of 10 μA cm−2. Sharp graphene emitter arrays have sharp protruded tips in abundance, leading to an enlarged field enhancement factor from 1683 to 10182, which was much better than those films prepared by other methods we adopted. It also revealed a good field emission stability with no degradation in the current for 3 h. We believe that this approach can enhance the field emission performance of graphene emitters, which could be widely candidate for various field emission applications.

Bilayer graphene (BLG) has emerged as a promising candidate for next-generation electronic applications, especially when it exists in the Bernal-stacked form, but its large-scale production remains a challenge. Here we present an experimental and first-principles calculation study of the epitaxial chemical vapor deposition (CVD) nucleation process for Bernal-stacked BLG growth on Cu using ethanol as a precursor. Results show that a carefully adjusted flow rate of ethanol can yield a uniform BLG film with a surface coverage of nearly 90% and a Bernal-stacking ratio of nearly 100% on ordinary flat Cu substrates, and its epitaxial nucleation of the second layer is mainly due to the active CH3 radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this nucleation mechanism will help clarify the formation of BLG by the epitaxial CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.

A field emission from a lateral emitter made by a multiwalled carbon nanotube (MWCNT) yarn was investigated. The lateral emitter showed an excellent field emission performance with a low turn-on electric field of 1.13 V/um at an emission current of 1 uA, high emission current of 0.2 mA at an applied voltage of 700 V, and long-time emission stability for over 20 h without any significant current decay under an initial emission current of about 0.10 mA. The lateral emitter also demonstrated a uniform line emission pattern. It is suggested that the field emission occurs from the outmost MWCNTs which are protruding out from the yarn surface.

In this response, we explain the points mentioned by R. Rani and R. Bhatia in their Comment for our previous paper [AIP Advances 5, 097130 (2015)], that the high value of β obtained in Song et al. [AIP Advances 5, 097130 (2015)] is misleading because it does not corroborate with the obtained Jmax, and the obtained value of Jmax is “low” in the mentioned study as compared to the reported values [J. Appl. Phys. 111, 044307 (2012) & Appl. Phys. Lett. 102, 033102 (2013)]. For the high value of β, the obtained current Jmax is corroborated but such high value is mainly due to the multistage effect when CNTs are deposited on the rough surface of reduced graphene. For the “low” Jmax, although this is true when compared with Sameera et al. [J. Appl. Phys. 111, 044307 (2012) and Appl. Phys. Lett. 102, 033102 (2013)], but we believe that our value is a generally common value when compared with other reports [Diam. Relat. Mater. 47, 1 (2014); J. Alloys Compd. 610, 659 (2014); J. Nanomater. 2013, 5239 (2013)] using the similar method as described in our paper. Therefore, the conclusions from the experimental results on field emission performance of CNT/graphene composite materials in our paper are reliable.

Using ethanol as the carbon source, self-limiting growth of AB-stacked bilayer graphene (BLG) has been achieved on Cu via an equilibrium chemical vapor deposition (CVD) process. We found that during this alcohol catalytic CVD (ACCVD) a source-gas pressure range exists to break the self-limitation of monolayer graphene on Cu, and at a certain equilibrium state it prefers to form uniform BLG with a high surface coverage of ∼94% and AB-stacking ratio of nearly 100%. More importantly, once the BLG is completed, this growth shows a self-limiting manner, and an extended ethanol flow time does not result in additional layers. We investigate the mechanism of this equilibrium BLG growth using isotopically labeled (13)C-ethanol and selective surface aryl functionalization, and results reveal that during the equilibrium ACCVD process a continuous substitution of graphene flakes occurs to the as-formed graphene and the BLG growth follows a layer-by-layer epitaxy mechanism. These phenomena are significantly in contrast to those observed for previously reported BLG growth using methane as precursor.

We demonstrated the fabrication of point-typed field emitters by using carbon nanotube films on graphite rods and investigated their field emission properties. The field emitter showed an increased emission current and an improved long-term emission stability after edge polishing process. The highest emission current of the field emitter was increased from 2.0 mA to 4.3 mA (1.1 A/cm 2 ). The field emitter with edge polishing process indicated a nearly negligible degradation of emission current in 20 h. It is considered that the high field emission performance of the field emitter is caused by the suppressed edge emission after edge polishing process. As a result, the field emitters have the higher emission current, lower field enhancement factor, and higher emission stability compared to the pristine emitter.

Boron nitride (BN) nanomaterials have excellent electrical, chemical and mechanical properties, such as high thermal conductivity, resistant to oxidation, chemical inertness, and negative electron affinity. These unique features make BN a promising cold electron emission material. In this work, we investigated on the field emission properties from BN nanotubes (BNNTs), among the various BN allotropes. BNNT is a tubular structured material like a carbon nanotube. The BN nanomaterial based field emitters were fabricated by a screen printing method. The screen printed BN emitters performed good field emission properties that presented good long-term stability and a high emission current. The detail field emission properties will be discussed.

We demonstrated field emission properties of a CNT point emitter fabricated by using CNTs on a graphite rod. The emitter has the highest current of 6.3 mA; the corresponding current density is 1.6 A/cm2. The emitter is stable at a current of 0.1 mA for 20 hours. It also showed a small and uniform emission pattern at the phosphor coated ITO glass. Our point emitter could be a good candidate for X-ray source applications.

We demonstrated carbon nanotube (CNT) field emitters made by a filtration-transfer method. They showed low turn-on and threshold electric fields, which is attributed to the advantages of this method, such as the high density of emission sites, good electrical contact, strong mechanical adhesion, and low contamination of CNTs tips. In addition, the field emitters showed very stable emission stability for long operation time at the acceleration condition. Moreover, we realized flexible CNT emitters using the fabrication technique.

We fabricated the point emitter using a tip-treated carbon nanotube (CNT) fiber. The CNT point emitter showed the high emission current and good emission stability. It is considered that the excellent field emission properties are attributed to a large field enhancement factor caused by a large aspect ratio of the sharp tip of the point emitter and the tight binding of CNTs.

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm2, and field enhancement factor of ∼1.3 × 104. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

The carbon nanotube (CNT) field emitters have been fabricated by attaching a CNT film on a graphite rod using graphite adhesive material. The CNT field emitters showed much improved field emission properties due to increasing crystallinity and decreasing defects in CNTs after the high temperature thermal annealing at 900 degrees C in vacuum ambient. The CNT field emitters showed the low turn-on electric field of 1.15 V/mu m, the low threshold electric field of 1.62 V/mu m, and the high emission current of 5.9 mA which corresponds to a current density of 8.5 A/cm(2). In addition, the CNT field emitters indicated the enhanced field emission properties due to the multi-stage effect when the length of the graphite rod increases. The CNT field emitter showed good field emission stability after the high temperature thermal annealing. The CNT field emitter revealed a focused electron beam spot without any focusing electrodes and also showed good field emission repeatability. (C) 2014 Author(s).

Carbon nanotube (CNT) emitters with small emission area were fabricated on graphite rods using CNT films. By introducing the edge polishing process, the field emission performance of the CNT emitter was much improved, which showed a very high emission current of 6.34 mA (1.6 A/cm2) under an applied electric field of 5.3 V/μm. It also indicates good long-term emission stability, which reveals no degradation in the emission current for 20 h. The emission patterns demonstrate uniform and well-focused electron beam spots. The enhanced field emission performance is mainly attributed to the suppressed edge emission after the edge polishing process.

Field emission properties of carbon nanotube (CNT) emitters dependent on electrode geometry have been systematically studied using two different types of diode electrode configurations. The experimental and simulation results clearly reveal that field emission properties, such as emission current and long-term emission stability, are strongly influenced by the geometry of the electrode configuration. The enhanced local electric field at the periphery of CNT emitters results in high local edge emissions that severely degrade emission current during long-term emission stability test and reduce the emission current density before electrical breakdown.

Graphite nanoplatelet (GNP) that consists of several tens of layers of graphene sheets is a promising candidate for electron field emission. The GNP emitter shows good field emission properties with a high emission current and a robust long-term stability because of the sharp edges, the high aspect ratio, and the stacked graphene sheets. Most of the electrons are emitted from the sharp edges of GNPs. The GNP emitters fabricated by the screen printing method reveal the turn-on electric field of 1.77 V/μm, the threshold electric field of 4.47 V/μm, the maximum emission current density of 39 mA/cm2, and the good emission stability for 20 h with little degradation rate of the emission current. The GNP field emitters can be a good candidate for several field emission applications such as flat lamps, field emission displays, and x-ray sources.