Growth Mechanism Of Graphene Research Articles

Atomistic mechanism of graphene growth on a SiC substrate: Large-scale molecular dynamics simulations based on a new charge-transfer bond-order type potential

Thermal decomposition of silicon carbide is a promising approach for the fabrication of graphene. However, the atomistic growth mechanism of graphene remains unclear. This paper describes the development of a new charge-transfer interatomic potential. Carbon bonds with a wide variety of characteristics can be reproduced by the proposed vectorized bond-order term. A large-scale thermal decomposition simulation enables us to observe the continuous growth process of the multiring carbon structure. The annealing simulation reveals the atomistic process by which the multiring carbon structure is transformed to flat graphene involving only six-membered rings. Also, it is found that the surface atoms of the silicon carbide substrate enhance the homogeneous graphene formation.

Controllable Synthesis of Circular Graphene Domains by Atmosphere Pressure Chemical Vapor Deposition

Controlled growth of circular single-crystalline graphene domains has been achieved by atmospheric pressure chemical vapor deposition (APCVD) using solid copper as substrate, thereby demonstrating that the shape of the graphene grains can potentially be precisely tuned by optimizing growth parameters. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the round domains have smooth, clean edges that permit seamless merging of adjacent graphene. Transmission electron microscopy (TEM) and Raman spectra together indicate that the graphene film is mostly monolayer, and electron diffraction reveals that these domains are single crystals. The growth and merging of these circular graphene domains to yield single-crystal graphene films enable us to elucidate the nucleation and growth mechanism of graphene on solid copper foil substrates.

How graphene crosses a grain boundary on the catalyst surface during chemical vapour deposition growth.

The chemical vapour deposition (CVD) growth of graphene is normally an epitaxial process, where the atomic structure of the adlayer should copy the texture of the substrate. However, it has been widely observed that single crystalline graphene grown on metal foil may cross a grain boundary (GB) of the substrate without forming any line defect, a necessary condition to change its crystalline orientation and maintain the structure registry with the substrate on the other side of the GB. Here, we present a comprehensive theoretical study on graphene growth behavior on polycrystalline metal substrates. Our density functional theory (DFT) calculations reveal that for graphene growth on most metal surfaces, the binding energy difference between the epitaxial and non-epitaxial graphene on the substrate is not large enough to compensate for the formation energy of a GB in graphene and therefore, during the CVD process, the growing graphene can pass through a GB on the metal surface without changing its crystalline orientation. Hence, graphene CVD growth cannot be strictly regarded as an epitaxial process; this conclusion is further verified by atomic simulations. The present study shows that the growth of graphene on a metal catalyst surface should be regarded rather as a quasi-epitaxial process, where a graphene domain is aligned only on the single crystalline metal facet on which it nucleates, but this structural registry with the metal substrate may be lost when the graphene crosses a GB on the metal surface.

Catalytic synthesis of few-layer graphene on titania nanowires.

Growth mechanisms of graphitic nanostructures on metal oxides by chemical vapor deposition (CVD) are observed at 750 °C, using titania nanowire aerogel (NWAG) as a three-dimensional substrate and without metal catalysts. We temporally observed catalytic transformation of amorphous carbon into few-layer graphene on the surface of 5-10 nm diameter titania nanowires. The graphitization spontaneously terminates when the titania nanowires are encapsulated by a shell of approximately three graphene layers. Extended CVD time beyond the termination point (>1125 seconds) yields only additional amorphous carbon deposits on top of the few-layer graphene. Furthermore, it was discovered that the islands of amorphous carbon do not graphitize unless they catalytically grow beyond a threshold size of 5-7 nm along the nanowire length, even after an extended thermal treatment. The electrical conductivity of the NWAG increased by four orders of magnitude, indicating that the graphene shell mediated by titania nanowires yielded a network of graphene throughout the three-dimensional nanostructure of the aerogel. Our results help us understand the growth mechanisms of few-layer graphene on nanostructured metal oxides, and inspire facile and controllable processing of metal oxide-nanocarbon fiber-shell composites.

Catalytic activity of pure Ni and Ni-33%Cu for dehydrogenation during graphene growth by chemical vapour deposition

Dissociative chemisorption of CH4/H2 gas mixture during graphene growth was investigated on commercially available Ni and Ni-33wt.% Cu substrates. Catalytic activity of both the substrates was severely decreased by employing very low gas pressure, thereby allowing the examination of very initial stages of dissociative-chemisorption. The chemisorption characteristics of the nickel rich nickel-copper alloy were interestingly found to be similar to those of pure copper, i.e., preferential adsorption of hydrogen over methane. These observations led to an in-depth understanding of the graphene growth mechanism on these substrates.

Catalytic substrates for graphene growth

Abstract

Recent trends in graphene materials synthesized by CVD with various carbon precursors

Graphene is a single layer of carbon atoms arranged in an sp2-hybridized structure with properties far superior compared to other materials. Research and development in graphene synthesis have been rapidly growing the past few years, especially using chemical vapor deposition (CVD) over various types of carbon precursor. The nature and the type of carbon precursor is one important parameter of growth by CVD, especially for graphene production, since they can dramatically impact graphene growth yield and rate. However, effects of the used carbon precursor on graphene growth mechanisms are rarely discussed. In the course of large-scale and low-cost graphene preparation, this review on the recent trends regarding the utilization of diverse carbon precursors used to synthesize graphene via the CVD method is of great interest for development of improved or alternative synthesis methods. The details and the mechanisms involved in graphene synthesis using carbon precursors in the form of gaseous, liquids and solids are compared, analyzed and discussed thoroughly. In this review, we present a thorough overview on the impact and mechanisms of carbon precursors in achieving high-quality graphene with competitive edge in the near future.

(Invited) Electrodeposition of Metals and Alloys for Graphene Growth

Graphene has attracted a lot of attention in the recent days due to its theoretical transport and mechanical properties. In order to step at the industrial level applications, a solid and reliable production process is needed; up to now the quality of the final product is not able to yield the expected characteristics. Distinction must be made between different products on the market: large domain graphene sheets, which are able to retain most of the physical and electrical properties, and graphene nanosheets or platelets. The latter have drawn a lot of interest due to the ease of manufacture, but are not suitable for the kind of application where graphene properties can really push the limit upwards, one above the others, electronics. The more attractive production methods for large domain graphene nowadays include low pressure chemical vapor deposition, mechanical exfoliation, roll to roll processing and many others. From the industrial point of view, thou, the use of vacuum technology raises excessively the production costs and hence should be avoided. This is the reason why graphene chemical vapor deposition is raising in popularity among many research groups, both for transferring graphene after growth of for using it on the very substrate onto which is grown. Polycrystalline transition metal catalysts are well known systems for obtaining single layer graphene and few layers graphene; among the most used Copper and Nickel are playing an important role because of high level of integration these materials have reached in the integrated circuits technology. Many studies have been carried on understanding the differences that underlie graphene growth mechanisms on these two metals; the more obvious but nonetheless important feature is the different Carbon solubility into the two lattices. That is why, on Copper, graphene grows thanks to surface adsorption and segregation of Carbon atoms, while on Nickel it is needed to exploit Carbon atoms supersaturation: in fact, for Copper, Carbon solubility is negligible while for Nickel it’s roughly 0.2 weight percent at high temperatures. Furthermore, due to metals supports fine structure, the crystallites preferential orientation is known to play a relevant role for copper, where the whole process is mainly involving the surface. On the other side for Nickel and Cobalt the crystals preferential orientation role is less known and almost not taken into account at all. Aim of the present work is to carry on an experimental procedure with the precise intent of exploring the effect of different crystalline structures by electrodeposition both on the final quality of the graphene layer and on the transport phenomena that take place in the metal media. The idea is to describe graphene quality evolution while monitoring metal catalyst properties via inspection techniques like X-ray diffraction, atomic force microscopy and scanning electron microscopy, which can give a deep insight into substrate structure. Graphene quality will be assessed by means of Raman spectroscopy, a very useful method to infer graphene quality via its typical fingerprints.

Probing the Gas-Phase Dynamics of Graphene Chemical Vapour Deposition using in-situ UV Absorption Spectroscopy

The processes governing multilayer nucleation in the chemical vapour deposition (CVD) of graphene are important for obtaining high-quality monolayer sheets, but remain poorly understood. Here we show that higher-order carbon species in the gas-phase play a major role in multilayer nucleation, through the use of in-situ ultraviolet (UV) absorption spectroscopy. These species are the volatilized products of reactions between hydrogen and carbon contaminants that have backstreamed into the reaction chamber from downstream system components. Consequently, we observe a dramatic suppression of multilayer nucleation when backstreaming is suppressed. These results point to an important and previously undescribed mechanism for multilayer nucleation, wherein higher-order gas-phase carbon species play an integral role. Our work highlights the importance of gas-phase dynamics in understanding the overall mechanism of graphene growth.

Direct Chemical Vapor Deposition Growth of Graphene Nanosheets on Supported Copper Oxide

A facile chemical vapor deposition method was used to grow multi-layer graphene. A copper-based catalyst was homogeneously deposited on magnesium oxide powder surface by impregnation. The synthesis was conducted under atmospheric pressure without a dedicated reduction step prior to the reaction. The mechanism of multi-layer graphene growth was investigated by high-resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. For the first time, we show that copper under its oxide form could catalyze the growth of multi-layer graphene. Such a simple method leading to produce multi-layer graphene of quite high structural quality could help to develop alternative ways for graphene production by chemical vapor deposition.

Facile growth of vertically-aligned graphene nanosheets via thermal CVD: The experimental and theoretical investigations

Owing to the distinctively morphological and structural features, vertically-aligned graphene nanosheets (VGs) possess many unique properties and hold great promise for applications in various fields. For controllable preparation and wide application of VGs, the establishing reliable growth method and profound understanding of the growth mechanism are of vital significance. Up to date, VGs are normally produced by plasma-enhanced chemical vapor deposition (PECVD) and it's considered that plasma is an indispensible factor for the vertical alignment of graphene sheets. Herein, for the first time, we report the facile and controllable VGs growth via a thermal CVD by precisely tuning growth parameters. Experimental observations in combination with detailed energy calculations reveal that the flow rate of carbon precursor determines the growth dynamics of graphene in CVD. This work offers a novel and reliable technique for VGs preparation and provides new insights into the intrinsic mechanism of vertical graphene growth. Furthermore, benefiting from the ultra-high density of edge sites, thin thickness, and outstanding electrical conductivity of VGs, the as-prepared VGs exhibit excellent field-emission performance such as ultra-low turn-on electric field and threshold field down to 1.07 and 1.65 V μm−1, respectively.

Graphene growth with ‘no’ feedstock

Synthesis of graphene by chemical vapor deposition (CVD) from hydrocarbons on Cu foil substrates can yield high quality and large area graphene films. In a typical CVD process, a hydrocarbon in the gas phase is introduced for graphene growth and hydrogen is usually required to achieve high quality graphene. We have found that in a low pressure CVD system equipped with an oil mechanical vacuum pump located downstream, graphene can be grown without deliberate introduction of a carbon feedstock but with only trace amounts of C present in the system, the origin of which we attribute to the vapor of the pump oil. This finding may help to rationalize the differences in graphene growth reported by different research groups. It should also help to gain an in-depth understanding of graphene growth mechanisms with the aim to improve the reproducibility and structure control in graphene synthesis, e.g. the formation of large area single crystal graphene and uniform bilayer graphene.

Synchronous Growth of High‐Quality Bilayer Bernal Graphene: From Hexagonal Single‐Crystal Domains to Wafer‐Scale Homogeneous Films

The precise control of the domain structure, layer thickness, and stacking order of graphene has attracted intense interest because of its great potential for nanoelectronics applications. Much effort has been devoted to synthesize semiconducting Bernal (AB)‐stacked bilayer graphene because of its tunable band structure and electronic properties that are unavailable to single‐layer graphene. However, fast growth of large‐scale bilayer graphene sheets with a high AB‐stacking ratio and high mobility on copper poses a tremendous challenge, which has to overcome the self‐limiting effect. This study reports a low‐cost but facile method to rapidly synthesize bilayer Bernal graphene by atmospheric pressure chemical vapor deposition using polystyrene as the feedstock. The bilayer graphene grains and continuous film obtained are of high quality and exhibit field‐effect hole mobilities as high as 5700 and 2200 cm2 V−1 s−1 at room temperature, respectively. In addition, a synchronous growth mechanism of bilayer graphene is revealed by monitoring the growth process, resulting in a high surface coverage of nearly 100% for a near‐perfect AB‐stacking order. This new synthesis route is significant for industrial application of bilayer graphene and investigation of the growth mechanism of graphene by the chemical vapor deposition process.

Raman spectroscopy and imaging of Bernal‐stacked bilayer graphene synthesized on copper foil by chemical vapour deposition: growth dependence on temperature

We report on the effect of temperature on the growth of bilayer graphene on a copper foil under atmospheric pressure chemical vapour deposition (AP‐CVD). Before characterization of the AP‐CVD bilayer graphene, a high‐quality graphene flake was obtained from the Kish bulk graphite by micro‐mechanical exfoliation and characterized by using Raman spectroscopy and imaging. The Raman data of the exfoliated, high‐quality graphene flake show monolayer and bilayer graphenes and were compared with the Raman data of AP‐CVD graphene. Raman spectroscopy of AP‐CVD graphene shows bilayer films that exhibit predominantly Bernal stacking with an I2D/IG ratio of ~1. At low growth temperature (~780 °C), Raman disorder‐related peak intensity in the AP‐CVD graphene is high and decreases with an increase in growth temperature to the lowest disorder intensity at ~973 °C. The selected area electron diffraction and atomic force microscopy average step height analysis showed the thickness of the bilayer graphene. The AP‐CVD graphene is uniform at low growth temperatures (~780 °C) with a high disorder and becomes non‐uniform at high growth temperatures (~867–973 °C) with a very low disorder as bilayer graphene evolves to form islands with an average lateral size of <10 μm. Competition between carbon adatoms supply through dehydrogenation of the CHx species, mobility and desorption rate of the carbon‐adatom species for nucleation of the bilayer graphene as a function of temperature is elucidated. This study provides further insight into the growth mechanisms of bilayer graphene by AP‐CVD on Cu. Copyright © 2017 John Wiley & Sons, Ltd.

A molecular dynamics simulation of the graphene growth on Cu(1 1 1) surface

To explore the mechanism of graphene growth on Cu(111) surface by the chemical vapor deposition method, a large scale molecular dynamics simulation was performed. Herein, the self-limiting growth of a single-layer graphene film has been successfully demonstrated. A series of fundamental mechanism steps were identified, where the formation of carbon dimers, trimers, and chains were observed at first stage, followed by coalescence of those carbon species, which give rise to the nucleation of carbon polygons. The detailed processes of graphene growth such as forming rings, healing defects and the combination of graphene nucleuses were revealed as well, and the role of side chains in these processes was studied in depth. Finally, effects of temperature and the carbon deposition rate on quality of graphene films were also discussed.

Direct observation of grain boundaries in chemical vapor deposited graphene

Graphene has received great attention owing to its superior physical properties, making graphene suitable for multiple applications. Numerous graphene growth techniques have been developed in the past decade to provide scalable high quality graphene. Among these techniques, chemical vapor deposition (CVD) on catalytic metal films holds great promises for a large-scale graphene growth. Even though extensive efforts have been devoted to synthesize high quality graphene, formation of defects. In particular, grain boundaries (GBs) have a dominant effect on properties, motivating extensive efforts to tune the CVD growth process to minimize GB. Rapid imaging of GBs will significantly aid in studies of CVD graphene grain structure. Here we report a straightforward technique to optically observe GBs in CVD-grown graphene via optical microscopy, allowing rapid assessment of graphene quality as well as the number of layers. The local oxidation of copper through the damaged GBs induces an optically discernable color change in the underlying copper due to different extend of oxidation between the two copper regions under grains and GBs. Our observation technique for GBs of graphene paves a path for understanding fundamental mechanisms of graphene growth and efficient quality evaluation of large-scale graphene sheet for mass production.

Synthesis of bilayer graphene via chemical vapor deposition and its optoelectronic devices

Due to its unique properties, graphene is a promising two-dimensional material in optoelectronic and energy applications. While the mobility of single layer graphene is extremely high, it has a zero bandgap. This feature restricts various applications of graphene in the field of semiconductor devices. Bilayer graphene, despite the nature of zero bandgap in its pristine form, can be tuned to open bandgap via a dual-gated vertical electrical field in a controlled manner. However, the size and layer number of mechanically exfoliated and liquid phase exfoliated graphene are poorly controlled. Controllable synthesis of large-sized bilayer graphene is an important research direction. This review summarizes a series of work including the controlled synthesis of bilayer graphene by chemical vapor deposition method and bilayer graphene devices. Specifically, growth mechanism of bilayer graphene is dependent on the type of supporting substrate and experimental condition. In the case of Ni substrate, bilayer graphene is grown along the segregation route. On the other hand, graphene growth on Cu is a surface-mediated process due to the extremely low solubility of C in Cu bulk. Depending on the concentration ratio between CH4 and H2, the growth mode of bilayer graphene can be tuned to be similar to Volmer-Weber or Stranski-Krastanov mode, in which the second layer is either grown under or above the first graphene layer. The dynamic growth of bilayer graphene can be further understood by a chemical gate effect and the process in a confined space. Moreover, here in this paper we present several approaches to realize the better control of bilayer graphene growth by modulating the experimental conditions. In terms of device applications for bilayer graphene, in this review we mention two typical applications including field-effect-transistors and hot-electron bolometers. Compared with conventional silicon-based hot-electron bolometer, the bilayer graphene based hot-electron bolometer has a small heat capacity and weak electron-phonon coupling, leading to high sensitivity, fast response, and small thermal noise-equivalent power. Such a bilayer graphene bolometer shows an exceptionally low noise-equivalent power and intrinsic speed three to five orders of magnitude higher than commercial silicon bolometers and superconducting transition-edge sensors at similar temperatures. Finally, the outlook and challenge for future research are also given. While significant progress has been made in the past several years, the controlled growth of bilayer or multi-layer graphene is still a key challenge, and the growth mechanism of bilayer graphene is not yet understood clearly. There is still much room for controlling graphene layer numbers, twisted angles, size, quality, and yield by optimizing the conditions. On the other hand, for the device applications of bilayer graphene, it is highly desired to develop high-performance bilayer graphene-based electronic devices.

Correction: Review of the synthesis, transfer, characterization and growth mechanisms of single and multilayer graphene

Correction for ‘Review of the synthesis, transfer, characterization and growth mechanisms of single and multilayer graphene’ by H. Cheun Lee et al., RSC Adv., 2017, 7, 15644–15693.

Preperetions of bi-layer and multi-layer graphene on copper substrates by atmospheric pressure chemical vapor deposition and their mechanisms

Chemical vapor deposition is widely utilized to synthesize graphene with controlled properties for many applications. And it is one of the most important methods for the preparation of graphene with high quality in large area. Cu substrate is most commonly used for the preparation of graphene in chemical vapor deposition. As is well known, the properties of graphene are greatly affected by the number of layers. However, the syntheses and mechanisms of bi-layer and multi-layer graphene on Cu substrates are still under debate. And how to make a breakthrough in realizing the controllable syntheses of bi-layer and multi-layer graphene on Cu substrates has become a direction for many researchers. In this work, we report bi-layer and multi-layer graphene on Cu substrates prepared by atmospheric pressure chemical vapor deposition. Firstly, the Cu foil is placed on the quartz slides of the tube furnace and heated to 1000℃ with a rate of 15℃/min. After reaching 1000℃, the Cu foilis annealed for 2 h in a gas mixture of hydrogen (20 sccm) and argon (380 sccm). After that, the graphene growth is carried out at 1000℃ under an 80 sccm gas mixture of argon and ethanol. Then, the samples are cooled down to the room temperature with a rate of 100℃/min in a protection gas of hydrogen and argon, and then taken out of the furnace. The graphene is prepared on the Cu foils and finally transferred onto the SiO2/Si substrates. The quality and number of layers of the as-produced graphene are assessed by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical microscopy. By tuning the graphene growth, the monolayer, bi-layer and multi-layer graphene with higer quality and better continuity are obtained. And the growth times of monolayer, bi-layer, and four-layers graphene are respectively 25, 40, and 60 s. And wefind that the graphene layer will be increased in the process of insulation. The growth mechanisms of bi-layer and multi-layer graphene on copper substrates by atmospheric pressure chemical vapor deposition are also discussed. There will be some indiffusible carbon atoms or radicals near the copper foil surface due to the small molecular diffusion mean free path under normal pressure. We suggeste that the bi-layer and multi-layer graphene grown on copper substrates by atmospheric pressure chemical vapor deposition is dominated by van der Waals epitaxial mechanism. This work provides a reference for improving the quality of chemical vapor deposition monolayer, bi-layer and multi-layer graphene.

Review of the synthesis, transfer, characterization and growth mechanisms of single and multilayer graphene

Graphene has emerged as the most popular topic in the active research field since graphene's discovery in 2004 by Andrei Geim and Kostya Novoselov.