Growth Of Single-layer Graphene Research Articles

Graphene growth from photo-polymerized bi-phenylthiol self-assembled monolayers

We present an enhanced methodology for the synthesis of graphene, from photo-polymerized self-assembled monolayers (SAMs) of 1,1ʹ-biphenyl-4-thiol on both electropolished and oxidized copper substrates. The SAMs were subjected to a two-step process involving light-induced polymerization followed by annealing in a vacuum furnace to yield the two-dimensional solid. Comprehensive characterization using contact angle measurements, X-ray photoelectron spectroscopy, and Raman spectroscopy, as well as scanning electron and transmission electron microscopy, provided conclusive evidence of growth of single-layer graphene. Notably, our findings revealed superior quality graphene on oxidized copper substrates compared to their electropolished counterparts, highlighting the impact of substrate choice on the quality of the resultant material.

The Effect of Pressure on the Growth of Single-Layer Graphene on Copper Sheets by Chemical Vapor Deposition Methods

The Effect of Pressure on the Growth of Single-Layer Graphene on Copper Sheets by Chemical Vapor Deposition Methods

Single-Layer Graphene Coated-Metal Nanoparticles for Water Splitting

Graphene-coated metal nanoparticles (NPs) have attracted great attention owing to their unique structural, photochemical and electrochemical properties based on electron communication between graphene and metal NPs. The development of highly efficient and non-precious metal-based electrocatalysts for water splitting comprising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge. The hybridization of nitrogen (N)-doped carbon and cost-effective transition metals is a promising approach to produce highly active catalysts for HER and OER. Herein, a highly controllable chemical vapor deposition method is designed for large-scale synthesis of nickel nanoparticle wrapped by single-layer N-doped graphene (Ni@SNG), where silica work as molecule sieve to tactfully assist single-layer graphene growth by depressing diffusion of carbon radicals. The Ni@SNG sample synthesized at 800 oC shows excellent activity for HER in alkaline solution with a low overpotential of 100 mV at 10 mA cm-2, which is close to state-of-the-art Pt/C catalyst. Furthermore, the Ni@SNG catalyst supported on nickel foil is developed as a magnetic adsorption binder-free electrode, which exhibits much improved performance on catalytic activity and stability than common Nafion binder-based electrode. Therefore, magnetism adsorption technique, taking full advantages of magnetic catalysts, will be a greatly promising approach to overcome high electron resistance and poor adhesive stability of polymer binder-based electrodes in actual applications.

Significant thermoelectric conversion efficiency enhancement of single layer graphene with substitutional silicon dopants

Graphene was regarded as inappropriate material for practical thermoelectric application due to its low thermoelectric conversion efficiency (ZT) from its superlative thermal conductivity and gapless electronic structure. In this study, for the first time, we experimentally investigate the significant thermoelectric conversion efficiency enhancement in graphene by introducing substitutional Si dopants during the CVD growth of single layer graphene. The thermal conductivity of Si-doped graphene (SiG) shows the significant suppression due to the large molecular weight mismatch between host C atoms and Si dopants in the same group V. On the other hand, the Si dopants do not severely suppress the electrical properties compared to thermal conductivity due to the narrow minimum in the electron transmission spectrum of SiG near Fermi Level. The incorporated Si dopants provide the progressive reduction in Seebeck coefficient due to the increased scattering of charge carriers in SiG, but we found nearly 17 times thermoelectric conversion efficiency enhancement (ZT/ZT 0 ) in the suspended graphene when the 2.59% of Si dopants are incorporated, which is much higher than graphene with other dopants for lattice defects. We believe that substitutional Si dopants can provide a promising method to break the limit in the current graphene based thermoelectric materials. • We demonstrate the enhancement of thermoelectric conversion efficiency (ZT) in Si-doped graphene. • Si-doped graphene shows the significant suppression in thermal conductivity with minimum electrical properties reduction. • Substitutional Si dopants are found to efficiently enhance the ZT of graphene compared to other types of defects. • Si-doped graphene is essential for the practical application of graphene as next-generation thermoelectric materials.

Can a Procedure for the Growth of Single‐layer Graphene on Copper be used in Different Chemical Vapor Deposition Reactors?

In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a "showerhead" cold-wall type, whereas the other represented the popular "tubular" hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm2 -scale SLG growth that differed only by the carrier gas flow rate used in the two reactors.

Role of the Near-Surface Region of a Substrate in a Two-Dimensional Phase Transition Leading to the Growth of Single-Layer Graphene: The Pt–C System

Role of the Near-Surface Region of a Substrate in a Two-Dimensional Phase Transition Leading to the Growth of Single-Layer Graphene: The Pt–C System

Self-Limiting Growth of Single-Layer N-Doped Graphene Encapsulating Nickel Nanoparticles for Efficient Hydrogen Production.

Effective nonprecious metal catalysts are urgently needed for hydrogen evolution reaction (HER). The hybridization of N-doped graphene and a cost-effective metal is expected to be a promising approach for enhanced HER performance but faces bottlenecks in controllable fabrication. Herein, a silica medium-assisted method is developed for the high-efficient synthesis of single-layer N-doped graphene encapsulating nickel nanoparticles (Ni@SNG), where silica nanosheets molecule sieves tactfully assist the self-limiting growth of single-layer graphene over Ni nanoparticles by depressing the diffusion of gaseous carbon radical reactants. The Ni@SNG sample synthesized at 800 °C shows excellent activity for HER in alkaline medium with a low overpotential of 99.8 mV at 10 mA cm-2, which is close to that of the state-of-the-art Pt/C catalyst. Significantly, the Ni@SNG catalyst is also developed as a binder-free electrode in magnetic field, exhibiting much improved performance than the common Nafion binder-based electrode. Therefore, the magnetism adsorption technique will be a greatly promising approach to overcome the high electron resistance and poor adhesive stability of polymer binder-based electrodes in practical applications.

Graphene growth on the textured copper surface

The effect of mechanical processing of copper foil on the single-layer graphene growth is studied. The deformation of the foil in the annealed and unannealed state is carried out by rolling between rollers with varying degrees of roughness. It is shown that the formed single-layer graphene coating on the foil deformed in the unannealed state has a larger number of defects, which is associated with the heterogeneity of the copper texture formed upon annealing. In the case of rolling the copper foil after the annealing stage, the quality of graphene coatings only slightly deteriorates in the deformed areas of foil.

Surfactant-Mediated Epitaxial Growth of Single-Layer Graphene in an Unconventional Orientation on SiC.

We report the use of a surfactant molecule during the epitaxy of graphene on SiC(0001) that leads to the growth in an unconventional orientation, namely R0° rotation with respect to the SiC lattice. It yields a very high-quality single-layer graphene with a uniform orientation with respect to the substrate, on the wafer scale. We find an increased quality and homogeneity compared to the approach based on the use of a preoriented template to induce the unconventional orientation. Using spot profile analysis low-energy electron diffraction, angle-resolved photoelectron spectroscopy, and the normal incidence x-ray standing wave technique, we assess the crystalline quality and coverage of the graphene layer. Combined with the presence of a covalently bound graphene layer in the conventional orientation underneath, our surfactant-mediated growth offers an ideal platform to prepare epitaxial twisted bilayer graphene via intercalation.

Novel Scalable Production of Single-Layer Graphene Coated-Metal Nanoparticles for Water Splitting

Graphene-coated metal nanoparticles (NPs) have attracted great attention owing to their unique structural, photochemical and electrochemical properties based on electron communication between graphene and metal NPs. The development of highly efficient and non-precious metal-based electrocatalysts for water splitting comprising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge. The hybridization of nitrogen (N)-doped carbon and cost-effective transition metals is a promising approach to produce highly active catalysts for HER and OER. Herein, a highly controllable chemical vapor deposition method is designed for large-scale synthesis of nickel nanoparticle wrapped by single-layer N-doped graphene (Ni@SNG), where silica work as molecule sieve to tactfully assist single-layer graphene growth by depressing diffusion of carbon radicals. The Ni@SNG sample synthesized at 800 oC shows excellent activity for HER in alkaline solution with a low overpotential of 100 mV at 10 mA cm-2, which is close to state-of-the-art Pt/C catalyst. Furthermore, the Ni@SNG catalyst supported on nickel foil is developed as a magnetic adsorption binder-free electrode, which exhibits much improved performance on catalytic activity and stability than common Nafion binder-based electrode. Therefore, magnetism adsorption technique, taking full advantages of magnetic catalysts, will be a greatly promising approach to overcome high electron resistance and poor adhesive stability of polymer binder-based electrodes in actual applications. Figure 1

Growth of Single-Layer and Multilayer Graphene on Cu/Ni Alloy Substrates

ConspectusGraphene, a one-atom-thick layer of carbon with a honeycomb lattice, has drawn great attention due to its outstanding properties and its various applications in electronic and photonic devices. Mechanical exfoliation has been used for preparing graphene flakes (from monolayer to multilayer with thick pieces also typically present), but with sizes limited typically to less than millimeters, its usefulness is limited. Chemical vapor deposition (CVD) has been shown to be the most effective technique for the scalable preparation of graphene films with high quality and uniformity. To date, CVD growth of graphene on the most commonly used substrates (Cu and Ni foils) has been demonstrated and intensively studied. However, a survey of the existing literature and earlier work using Cu or Ni substrates for CVD growth indicates that the bilayer and multilayer graphene over a large area, particularly single crystals, have not been obtained.In this Account, we review current progress and development in the CVD growth of graphene and highlight the important challenges that need to be addressed, for example, how to achieve large single crystal graphene films with a controlled number of layers. A single-layer graphene film grown on polycrystalline Cu foil was first reported by our group, and since then various techniques have been devoted to achieving the fast growth of large-area graphene films with high quality. Commercially available Cu/Ni foils, sputtered Cu/Ni thin films, and polycrystalline Cu/Ni foils have been used for the CVD synthesis of bilayer, trilayer, and multilayer graphene. Cu/Ni alloy substrates are particularly interesting due to their greater carbon solubility than pure Cu substrates and this solubility can be finely controlled by changing the alloy composition. These substrates with controlled compositions have shown the potential for the growth of layer-tunable graphene films in addition to providing a much higher growth rate due to their stronger catalytic activity. However, the well-controlled preparation of single crystal graphene with a defined number of layers on Cu/Ni substrates is still challenging.Due to its small lattice mismatch with graphene, a single crystal Cu(111) foil has been shown to be an ideal substrate for the epitaxial growth of graphene. Our group has reported the synthesis of large-size single crystal Cu(111) foils by the contact-free annealing of commercial Cu foils, and single crystal Cu/Ni(111) alloy foils have also been obtained after the heat-treatment of Ni-coated Cu(111) foils. The use of these single crystal foils (especially the Cu/Ni alloy foils) as growth substrates has enabled the fast growth of single crystal single-layer graphene films. By increase of the Ni content, single crystal bilayer, trilayer, and even multilayer graphene films have been synthesized. In addition, we also discuss the wafer-scale growth of single-layer graphene on the single crystalline Cu/Ni(111) thin films.Recent research results on the large-scale preparation of single crystal graphene films with different numbers of layers on various types of Cu/Ni alloy substrates with different compositions are reviewed and discussed in detail. Despite the remarkable progress in this field, further challenges, such as the wafer-scale synthesis of single crystal graphene with a controlled number of layers and a deeper understanding of the growth mechanism of bilayer and multilayer graphene growth on Cu/Ni substrates, still need to be addressed.

Graphene for Si-based solar cells

In this paper, we report on the single layer graphene synthesis to establish the growth conditions and improve the opto-electronic properties that can be employed in silicon based heterojunction solar cells. To do this, the effect of hydrogen and methane flow on the graphene growth on copper foil in a CVD system was investigated. The analyses were conducted by changing either the hydrogen or the methane flow by keeping all the other growth parameters constant. Single layer graphene growth recipe was established in order to have the optimum optical transmission and sheet resistance values via amending the graphene growth conditions. It was found that the sheet resistance values of the single layer graphene should be lowered further to be used as transparent conductive electrode. However, the combination of graphene with indium tin oxide film functioned well as transparent conductive electrode in the silicon based the solar cells. Additionally, the cell efficiency increased by about 10% as a result of incorporating it with the single layer graphene.

Chemical vapor deposition growth of bilayer graphene via altering gas flux geometry

Graphene films with high content of bilayer graphene are obtained by chemical vapor deposition technique on copper (Cu) foil by means of suitably designing the flux geometries of the reactant gases. First single-layer graphene growth is optimized using a preliminary oxygen passivation of the Cu substrate which facilitates the formation of larger graphene grains with low defect density. Then, in order to enhance the transport of reactant species to the catalyst substrate, the gas flux geometry is modified in two ways: (i) fixing a graphite holder next to the Cu substrate perpendicular to the stream of the flux gases or (ii) positioning the Cu foil into a graphite shelter. It is found that both modifications facilitate the growth of a second graphene layer leading to increased formation of bilayer graphene. The obtained graphene layers are characterized by Raman spectroscopy (with special focus on the overtone (2D) of the disorder-induced band), scanning electron microscopy, transmission electron microscopy, atomic force microscope analysis and optical transmission measurements. Narrow symmetric 2D Raman peaks with linewidths ranging down to 22 cm−1 but blue-shifted with respect to that of single-layer graphene are obtained from graphite holder- and shelter-grown samples indicating high-quality bilayer graphene.

Crystal orientation effects of sapphire substrate on graphene direct growth by metal catalyst-free low-pressure CVD

Graphene was directly grown on r-plane (1-102), c-plane (0001), and a-plane (11-20) sapphires by low pressure chemical vapor deposition without the use of a metal catalyst. The growth temperature was systematically changed between 1090 and 1210 °C to investigate the effects of the crystal orientation of sapphire on the graphene growth. It was found that the growth rate of graphene on r-plane sapphire was very fast compared to that of the samples grown on other orientations. The surface catalytic effect of r-plane sapphire promotes the smooth and flat growth of single-layer graphene. The surface of the r-plane sapphire was kept smooth even at a high temperature of 1210 °C because a quick coverage of graphene protects the surface of the sapphire from thermal decomposition and roughening.

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Summary Solid-state Li-metal batteries are promising to improve both safety and energy density compared to conventional Li-ion batteries. However, various high-performance and low-cost solid electrolytes are incompatible with Li, which is indispensable for enhancing energy density. Here, we utilize a chemically inert and mechanically robust boron nitride (BN) film as the interfacial protection to preclude the reduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte by Li, which is validated by in situ transmission electron microscopy. When combined with ∼1–2 μm PEO polymer electrolyte at the Li/BN interface, Li/Li symmetric cells show a cycle life of over 500 h at 0.3 mA·cm−2. In contrast, the same configuration with bare LATP dies after 81 h. The LiFePO4/LATP/BN/PEO/Li solid-state batteries show high capacity retention of 96.6% after 500 cycles. This study offers a general strategy to protect solid electrolytes that are unstable against Li and opens possibilities for adopting them in solid-state Li-metal batteries.

Restoring self-limited growth of single-layer graphene on copper foil via backside coating.

The growth of single-layer graphene (SLG) by chemical vapor deposition (CVD) on copper surfaces is very popular because of the self-limiting effect that, in principle, prevents the growth of few-layer graphene (FLG). However, the reproducibility of the CVD growth of homogeneous SLG remains a major challenge, especially if one wants to avoid heavy surface treatments, monocrystalline substrates and expensive equipment to control the atmosphere inside the growth system. We demonstrate here that backside tungsten coating of copper foils allows for the exclusive growth of SLG with full coverage by atmospheric pressure CVD implemented in a vacuum-free furnace. We show that the absence of FLG patches is related to the suppression of carbon diffusion through copper. In the perspective of large-scale production of graphene, this approach constitutes a significant improvement to the traditional CVD growth process since (1) a tight control of the hydrocarbon flow is no longer required to avoid FLG formation and, consequently, (2) the growth duration necessary to reach full coverage can be drastically shortened.

Formation of graphene on the surface of copper under the conditions of chemical deposition from the gas phase

This work is devoted to experimental studies of the effect of synthesis conditions on formation of single-layer graphene on the copper surface. Under the conditions of formation and growth of single-layer graphene, it is shown that characteristic times of graphite nuclei formation are about 1 min and times of primary layer growth are about 0.5 min. The subsequent layers form in 10 min. It is shown that hydrogen concentration at the initial stage of synthesis affects the growth rate of the second layer significantly.

Growth of single-layer graphene on Ge (1 0 0) by chemical vapor deposition

The integration of graphene into nanoelectronic devices is dependent on the availability of direct deposition processes, which can provide uniform, large-area and high-quality graphene on semiconductor substrates such as Ge or Si. In this work, we synthesised graphene directly on p-type Ge (1 0 0) substrates by chemical vapour deposition. The influence of the CH4:H2 flow ratio on the graphene growth was investigated. Raman Spectroscopy, Raman mapping, Scanning Electron Microscopy, Atomic Force Microscopy and Scanning Tunnelling Microscopy/Scanning Tunnelling Spectroscopy results showed that good quality and homogeneous monolayer graphene over a large area can be achieved on Ge substrates directly with optimal growth conditions.

Simulation of the Dynamics of Isothermal Growth of Single-Layer Graphene on a Copper Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

A new kinetic model of isothermal growth of single-layer graphene on a copper catalyst as a result of the chemical vapor deposition of hydrocarbons on it at a low pressure has been developed on the basis of in situ measurements of the growth of graphene in the process of its synthesis. This model defines the synthesis of graphene with regard for the chemisorption and catalytic decomposition of ethylene on the surface of a copper catalyst, the diffusion of carbon atoms in the radial direction to the nucleation centers within the thin melted near-surface copper layer, and the nucleation and autocatalytic growth of graphene domains. It is shown that the time dependence of the rate of growth of a graphene domain has a characteristic asymmetrical bell-like shape. The dependences of the surface area and size of a graphene domain and the rate of its growth on the time at different synthesis temperatures and ethylene concentrations have been obtained. Time characteristics of the growth of graphene domains depending on the parameters of their synthesis were calculated. The results obtained can be used for determining optimum regimes of synthesis of graphene in the process of chemical vapor deposition of hydrocarbons on different catalysts with a low solubility of carbon.

Chemical etching of copper foils for single-layer graphene growth by chemical vapor deposition

Chemical etching on copper surface is essential as a pre-treatment for single-layer graphene growth by chemical vapor deposition (CVD). Here, we investigated the effect of chemical etching treatment on copper foils for single-layer graphene CVD growth. The chemical etching conditions, such as the type of chemical etchants and the treatment time, were found to strongly influence the graphene domain size. Moreover, a drastic change in the layer structure of graphene sheets, which was attributed to the surface morphology of the etched copper foil, was confirmed by graphene transmittance and Raman mapping measurements.