Growth Of Few-layer Graphene Research Articles

Ab Initio Molecular Dynamics of the Initial Growth of Few-Layer Graphene on a Cu–Ni(111) Catalyst

Ab Initio Molecular Dynamics of the Initial Growth of Few-Layer Graphene on a Cu–Ni(111) Catalyst

Growth of graphene from solid amorphous carbon: A new geometry for control carbon diffusion barrier

As an alternative strategy to fabricate high-quality graphene over a large area, metal catalysis has been attempted at elevated temperatures with solid carbon sources. However, graphene was generally fabricated on the surface of metal catalysis layer using amorphous carbon as solid carbon sources. In this study, a thin Al2O3 barrier (1 nm) deposited on an amorphous-C/Ni bilayer stack is demonstrated to enable direct growth of few layer graphene (FLG) identified as 3–4 layers on substrate surface at 700 °C and 800 °C. Moreover, the obtained graphene shows a good transmittance (93%) under the light source of 550 nm. The findings provide a way to directly synthesis FLG on the required substrate at low temperature, which may dramatically broaden the applications range of graphene.

Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn-Air Battery.

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn-air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn-air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63V and good electrochemical durability for 83 h at a current density of 10mA cm-2 in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn-air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.

Spiral Growth of Adlayer Graphene.

The morphology of as-grown graphene in chemical vapor deposition (CVD) experiments is sensitive to the reaction environment. Understanding the mechanism of formation of different graphene morphologies is essential to achieve controlled graphene CVD growth. Here the growth and formation mechanism of adlayer graphene spirals are reported. An adlayer graphene spiral is formed by fast propagation of the tips of spiral arms along the edge of the first graphene layer. The driving force to form spirals is the limited availability of carbon diffusing from the Cu surface through the edge of the first graphene layer. In addition, it is found that graphene onions are formed by overlapping graphene spirals with clockwise and anticlockwise arms. Based on these features, a kinetic Monte Carlo (kMC) method is demonstrated using which all the observed graphene spiral structures are successfully reproduced at the atomic level. This study thus unravels the hither-to unresolved mechanism of graphene onion growth and paves the way to the controllable growth of few-layer graphene by increasing the carbon supply at the edge of the first layer graphene.

In-situ growth of few-layer graphene on ZnO with intimate interfacial contact for enhanced photocatalytic CO2 reduction activity

Intimate interfacial contact between semiconductor photocatalysts and cocatalysts is important for the transfer and separation of photogenerated charge carriers. Herein, few-layer graphene, as an efficient cocatalyst, was in-situ deposited on the surface of ZnO. The composite demonstrated improved photocatalytic CO2 reduction performance than pristine ZnO, ascribing to the intimate interfacial contact and Schottky junction between ZnO and graphene. Meanwhile, photothermal effect of graphene and π-π conjugation interaction between graphene and CO2 molecules also contributed to the performance enhancement. This work not only provides a feasible approach for the in-situ growth of graphene, but also develops an efficient photocatalyst for CO2 reduction.

Growth of few-layer graphene on Cu foil by regulating the pressure of reaction gases

A method to grow few-layer graphene in the form of an “inverted pagoda” is proposed by controlling the pressure and the flow rate in a circulating chemical vapor deposition system.

The role of gas-phase dynamics in interfacial phenomena during few-layer graphene growth through atmospheric pressure chemical vapour deposition.

The complicated chemical vapour deposition (CVD) is currently the most viable method of producing graphene. Most studies have extensively focused on chemical aspects either through experiments or computational studies. However, gas-phase dynamics in CVD reportedly plays an important role in improving graphene quality. Given that mass transport is the rate-limiting step for graphene deposition in atmospheric-pressure CVD (APCVD), the interfacial phenomena at the gas-solid interface (i.e., the boundary layer) are a crucial controlling factor. Accordingly, only by understanding and controlling the boundary-layer thickness can uniform full-coverage graphene deposition be achieved. In this study, a simplified computational fluid dynamics analysis of APCVD was performed to investigate gas-phase dynamics during deposition. Boundary-layer thickness was also estimated through the development of a customised homogeneous gas model. Interfacial phenomena, particularly the boundary layer and mass transport within it, were studied. The effects of Reynolds number on these factors were explored and compared with experimentally obtained results of the characterised graphene deposit. We then discussed and elucidated the important relation of fluid dynamics to graphene growth through APCVD.

Very low-temperature growth of few-layer graphene by Ni-induced crystallization of amorphous carbon in vacuum

Graphene of thickness a few atomic layers has been grown in Ni/a-C bilayers at temperatures as low as 300 °C by Ni-induced crystallization of the amorphous carbon (a-C) in high vacuum. The mechanism of such very low-temperature growth of graphene has been investigated by a combinatorial experimental approach including x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy. The growth of this few atomic layer thickness graphene has been found to be mediated by a coupled grain-boundary (GB) diffusion/surface diffusion mechanism. GBs in the top Ni sublayer provide fast diffusion paths for C atoms through the Ni layer, as a result of which graphene layers form above the Ni. The revealed low-temperature growth mechanism of graphene induced by contact with a metal can be applicable in advancing research fields as metal-matrix graphene composites and advanced energy storage devices.

Wafer-scale few-layer graphene growth on Cu/Ni films for gas sensing applications

Pristine, few-layer graphene (FLG)/Si nanopillar assemblies are introduced as gas sensitive chemiresistors showing unprecedented sensitivity towards NO2 when operated at room temperature (25 °C) and in humid air. To achieve this, we first developed wafer-scale (∼50 cm2) FLG growth using sub-micrometer thick films of thermally evaporated Cu/Ni on a SiO2/Si substrate. The Ni film was deposited and annealed to induce the formation of a Cu-rich binary alloy. This alloy formation limited the inter-diffusion of Cu and SiO2, a phenomenon known to take place during the CVD growth of graphene on Cu/SiO2/Si. The as-grown high structural quality FLG was transferred, using a conventional wet chemical method, to lithographically patterned arrays of Si nanopillars (non-flat substrate). Testing of the FLG/Si assembly revealed a NO2 sensitivity that outperforms what is reported in the literature for pristine graphene. Overall, our growth and device fabrication work-flow demonstrate a way to design graphene-based gas sensing systems without incurring inconvenient processing steps such as metal foil etching, surface functionalization or particle loading.

Nickel mediated few-layer graphene growth on glass substrates by pulsed laser deposition

Abstract This article shows the efficacy of transition metal (Ni) as a top layer on glass in the formation of graphene domain. Graphene films were grown on glass substrates from highly ordered pyrolytic graphite by pulsed laser deposition (PLD), with the help of 250 nm thick Ni thin film. The as-synthesized graphene films were characterized by UV–Vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and Optical microscopy. The Raman spectroscopic measurement reveals that catalytic film of Ni enhanced the characteristic 2D-peak of graphene on glass substrate, indicating formation of graphene domain; while similar peaks were not detected in the absence of Ni. Moreover, Raman spectrum has shown less structural disorder in the resulting graphene film with the presence of Ni surfactant. The surface morphology of the as-synthesized graphene film was studied by scanning electron microscopy and optical microscopy. The present study shows an effective and exciting route to obtain high-quality graphene on glass substrates using PLD.

Direct growth of few-layer graphene on AlN-based resonators for high-sensitivity gravimetric biosensors.

We present the successful growth of few-layer graphene on top of AlN-based solidly mounted resonators (SMR) using a low-temperature chemical vapour deposition (CVD) process assisted by Ni catalysts, and its effective bio-functionalization with antibodies. The SMRs are manufactured on top of fully insulating AlN/SiO2 acoustic mirrors able to withstand the temperatures reached during the CVD growth of graphene (up to 650 °C). The active AlN films, purposely grown with the c-axis tilted, effectively excite shear modes displaying excellent in-liquid performance, with electromechanical coupling and quality factors of around 3% and 150, respectively, which barely vary after graphene integration. Raman spectra reveal that the as-grown graphene is composed of less than five weakly coupled layers with a low density of defects. Two functionalization protocols of the graphene are proposed. The first one, based on a covalent binding approach, starts with a low-damage O2 plasma treatment that introduces a controlled density of defects in graphene, including carboxylic groups. After that, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry is used to covalently bind streptavidin molecules to the surface of the sensors. The second functionalization protocol is based on the non-covalent bonding of streptavidin on hydrophobic graphene surfaces. The two protocols end with the effective bonding of biotinylated anti-IgG antibodies to the streptavidin, which leaves the surface of the devices ready for possible IgG detection.

Kinetic studies of few-layer graphene grown by flame deposition from the perspective of gas composition and temperature.

Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth.

Layer-by-Layer Graphene Growth on β-SiC/Si(001).

The mechanism of few-layer graphene growth on the technologically relevant cubic-SiC/Si(001) substrate is uncovered using high-resolution core-level and angle-resolved photoelectron spectroscopy, low-energy electron microscopy, and microspot low-energy electron diffraction. The thickness of the graphitic overlayer supported on the silicon carbide substrate and related changes in the surface structure are precisely controlled by monitoring the progress of the surface graphitization in situ during high-temperature graphene synthesis, using a combination of microspectroscopic techniques. The experimental data reveal gradual changes in the preferential graphene lattice orientations at the initial stages of the few-layer graphene growth on SiC(001) and can act as reference data for controllable growth of single-, double-, and triple-layer graphene on silicon carbide substrates.

Effect of Counterparts and Applied Load on the Tribological Behavior of the Graphene–Nickel Matrix Self-Lubricating Composite

Recently, an in-situ method was proposed to fabricate the graphene–nickel matrix (G–Ni) composite by direct growth of few-layer graphene in bulk nickel, achieving the uniform dispersion of graphene into metal matrix. In this paper, G–Ni composite was prepared by in-situ powder metallurgy method followed by a repressing-annealing process to improve densification of specimen. The tribological behavior of the composite sliding against GCr 15, Si3N4, and ZrO2 balls was comparatively investigated under dry friction condition. The results show that the friction coefficient and wear rate are dependent on the counterparts and the applied load. The G–Ni/ZrO2 tribo-pair exhibits the lowest friction coefficient (0.52) and wear rate (9.58 × 10−5 mm3/Nm) than other tribo-pairs, which can be attributed to good lubrication and protection of the tribofilms formed by tribo-chemical reaction at interface. The friction coefficient for G–Ni/ZrO2 tribo-pair first decreases to a minimum (0.41) at 6 N load and then increases associating quite large fluctuations with increasing load. The formation and breakdown of tribofilms are mainly responsible for the tribological behavior at different loads.

Structural effect of Ni-Cu catalysts for graphene growth by pulsed laser deposition

Pulsed laser deposition was applied to grow few-layers graphene from highly oriented pyloric graphite target on different types of nickel (Ni)-copper (Cu) substrates. The substrates were prepared with two different structures; alloy and composite with different concentration ratios of Ni-Cu bi-metals. X ray diffraction and side view field emission scanning electron microscopy were utilized to analyze and verify the two structures. The catalytic effect of both substrates on graphene growth was studied at different growth temperatures using Raman spectroscopy. The experimental findings yielded unexpected catalytic effect discrepancies of composite than alloy substrates. The composite substrates proved excellent growth ability for unique 2-dimensional (2D) graphene layers over wide range of temperatures, while highly defected graphene was grown on alloy substrates with an appropriate Ni to Cu ratio. Structure of the composite substrates could impose a specific interaction on their surface that enhances the formation of 2D layers. The results suggest a class of highly efficient metallic catalyst for few-layer graphene growth via two steps segregation process and open fundamental insights in understanding graphene growth on complex substrates.

Bi- tri- and few-layer graphene growth by PLD technique using Ni as catalyst

AbstractThe objective of the present research work is to optimize the growth conditions of bi- tri- and few-layer graphene using pulsed laser deposition (PLD) technique. The graphene was grown on n-type silicon (1 0 0) at 530 °C. Raman spectroscopy of the grown films revealed that the growth of low defect tri-layer graphene depended upon Ni content and uniformity of the Ni film. The line profile analysis of the AFM micrographs of the films also confirmed the formation of bi- tri- and a few-layer graphene. The deposited uniform Ni film matrix and carbon/Ni thickness ratio are the controlling factors for the growth of bitri- or few- layer graphene using pulsed laser deposition technique.

High temperature annealing and CVD growth of few-layer graphene on bulk AlN and AlN templates

Graphene and AlN are promising materials, interesting to combine together. In this study, we will present first results for direct growth of graphene on bulk AlN and on AlN templates using chemical vapor deposition, including the annealing of these substrates at high temperatures. Atomic force microscopy (AFM) enabled us to study the evolution of the AlN surface morphology after annealing and growth. Few-layer graphene deposition is demonstrated on the basis of X-ray photoemission and Raman spectroscopy. AFM view of graphene wrinkles on the N-face of bulk AlN.

Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging.

In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene–graphene and graphene–substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.

Optical Relaxation Time Enhancement in Graphene-Passivated Metal Films

Due to the small skin depth in metals at optical frequencies, their plasmonic response is strongly dictated by their surface properties. Copper (Cu) is one of the standard materials of choice for plasmonic applications, because of its high conductivity and CMOS compatibility. However, being a chemically active material, it gets easily oxidized when left in ambient environment, causing an inevitable degradation in its plasmonic resonance. Here, for the first time, we report a strong enhancement in the optical relaxation time in Cu by direct growth of few-layer graphene that is shown to act as an excellent passivation layer protecting Cu surface from any deterioration. Spectroscopic ellipsometry measurements reveal a 40–50% reduction in the total scattering rate in Cu itself, which is attributed to an improvement in its surface properties. We also study the impact of graphene quality and show that high quality graphene leads to an even larger improvement in electron scattering rate. These findings are expected to provide a big push towards graphene-protected Cu plasmonics.

Graphene by one-step chemical vapor deposition from ferrocene vapors: Properties and electrochemical evaluation

Growth of few-layer graphene using ferrocene as precursor by chemical vapor deposition is reported. The growth did not involve any additional carbon or catalyst source or external hydrocarbon gases. Parametric investigation was performed using different conditions, namely, varying growth temperature from 600 to1000 °C, and growth duration from 5 min to 3 h, as well as using fast quenching or gradual cooling after the thermal treatment, in order to examine the effect on the quality of the produced graphene. The growth took place on silicon wafers and resulted, under optimal conditions, in formation of graphene with 2–3 layers and high graphitic quality, as evidenced by Raman spectroscopy, with characteristic full width at half maximum of the 2D band of 49.46 cm−1, and I2D/IG and ID/IG intensity ratios of 1.15 and 0.26, respectively. Atomic force microscopy and X-ray photoelectron spectroscopy were employed to further evaluate graphene characteristics and enlighten growth mechanism. Electrochemical evaluation of the developed material was performed using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge measurements.