Direct growth of graphene on vertically standing glass by a metal-free chemical vapor deposition method

A new method to directly grow graphene on quartz glass substrate by atmospheric-pressure chemical vapor deposition (CVD) without using any catalyst was developed. The prime feature of this method is to build a vertical-glass model in the quartz tube to significantly increase the collision probability of the carbon precursors and reactive fragments between each other with the glass surface. The growth rate of high-quality graphene on glass remarkably increases compared with the conventional gas flow CVD technique. The optical transmittance and sheet resistance of the graphene glass can be readily adjusted by regulating growth time. When growth time is 35?min, the graphene glass presents an intriguing sheet resistance of about 1.48 kΩ sq^?1 at a transmittance of 93.08% and exhibits an excellent hydrophobic performance. The method is simple and scalable, and might stimulate various potential applications of transparent and conductive graphene glass in practical fields.     

Direct Growth of Highly Stable Patterned Graphene on Dielectric Insulators using a Surface‐Adhered Solid Carbon Source

A novel method is described for the direct growth of patterned graphene on dielectric substrates by chemical vapor deposition (CVD) in the presence of Cu vapor and using a solid aromatic carbon source, 1,2,3,4‐tetraphenylnapthalene (TPN), as the precursor. The UV/O₃ treatment of the TPN film both crosslinks TPN and results in a strong interaction between the substrate and the TPN that prevents complete sublimation of the carbon source from the substrate during CVD. Substrate‐adhered crosslinked TPN is successfully converted to graphene on the substrate without any organic contamination. The graphene synthesized by this method shows excellent mechanical and chemical stability. This process also enables the simultaneous patterning of graphene materials, which can thus be used as transparent electrodes for electronic devices. The proposed method for the synthesis directly on substrates of patterned graphene is expected to have wide applications in organic and soft hybrid electronics.     

Synthesis of hexagonal graphene on polycrystalline Cu foil from solid camphor by atmospheric pressure chemical vapor deposition

Understanding of graphene nucleation and growth on a metal substrate in chemical vapor deposition (CVD) process is critical to obtain high-quality single crystal graphene. Here, we report synthesis of individual hexagonal graphene and their large cluster on Cu foil using solid camphor as a carbon precursor in the atmospheric pressure CVD (AP-CVD) process. Optical and scanning electron microscopy studies show formation of hexagonal graphene crystals across the grain, grain boundaries and twin boundaries of polycrystalline Cu foil. Electron backscattered diffraction analysis is carried out before and after the growth to identify Cu grain orientation correlating with the graphene formation. The influence of growth conditions and Cu grain structure is explored on individual hexagonal graphene formation in the camphor-based AP-CVD process.     

Layer-by-layer growth of graphene layers on graphene substrates by chemical vapor deposition

We demonstrate a synthesis of graphene layers on graphene templates prepared by the mechanical exfoliation of graphite crystals using a developed chemical vapor deposition (CVD) apparatus that has a furnace with three temperature zones and can regulate the temperatures separately in each zone. This results in individual control over the decomposition reaction of the carbon feedstock and the growth of graphene layers by activated carbon species. CVD growth using multi-temperature zones provides wider temperature windows appropriate to grow graphene layers. We observed that graphene layers proceed by a layer-by-layer growth mode using an optical microscopy, an atomic force microscopy, and Raman spectroscopy. This result suggests that a graphene growth technique using the CVD apparatus is a potential approach for making graphene sheets with precise control of the layer numbers.     

Control of thickness uniformity and grain size in graphene films for transparent conductive electrodes

Large-scale and transferable graphene films grown on metal substrates by chemical vapor deposition (CVD) still hold great promise for future nanotechnology. To realize the promise, one of the key issues is to further improve the quality of graphene, e.g., uniform thickness, large grain size, and low defects. Here we grow graphene films on Cu foils by CVD at ambient pressure, and study the graphene nucleation and growth processes under different concentrations of carbon precursor. On the basis of the results, we develop a two-step ambient pressure CVD process to synthesize continuous single-layer graphene films with large grain size (up to hundreds of square micrometers). Scanning electron microscopy and Raman spectroscopy characterizations confirm the film thickness and uniformity. The transferred graphene films on cover glass slips show high electrical conductivity and high optical transmittance that make them suitable as transparent conductive electrodes. The growth mechanism of CVD graphene on Cu is also discussed, and a growth model has been proposed. Our results provide important guidance toward the synthesis of high quality uniform graphene films, and could offer a great driving force for graphene based applications.     

Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer‐Free Device Fabrication

Graphene is the most broadly discussed and studied two‐dimensional material because of its preeminent physical, mechanical, optical, and thermal properties. Until now, metal‐catalyzed chemical vapor deposition (CVD) has been widely employed for the scalable production of high‐quality graphene. However, in order to incorporate the graphene into electronic devices, a transfer process from metal substrates to targeted substrates is inevitable. This process usually results in contamination, wrinkling, and breakage of graphene samples ‐ undesirable in graphene‐based technology and not compatible with industrial production. Therefore, direct graphene growth on desired semiconductor and dielectric substrates is considered as an effective alternative. Over the past years, there have been intensive investigations to realize direct graphene growth using CVD methods without the catalytic role of metals. Owing to the low catalytic activity of non‐metal substrates for carbon precursor decomposition and graphene growth, several strategies have been designed to facilitate and engineer graphene fabrication on semiconductors and insulators. Here, those developed strategies for direct CVD graphene growth on semiconductors and dielectrics for transfer‐free fabrication of electronic devices are reviewed. By employing these methods, various graphene‐related structures can be directly prepared on desired substrates and exhibit excellent performance, providing versatile routes for varied graphene‐based materials fabrication.     

Copper‐Vapor‐Assisted Growth and Defect‐Healing of Graphene on Copper Surfaces

Although there is significant progress in the chemical vapor deposition (CVD) of graphene on Cu surfaces, the industrial application of graphene is not realized yet. One of the most critical obstacles that limit the commercialization of graphene is that CVD graphene contains too many vacancies or sp³‐type defects. Therefore, further investigation of the growth mechanism is still required to control the defects of graphene. During the growth of graphene, sublimation of the Cu catalyst to produce Cu vapor occurs inevitably because the process temperature is close to the melting point of Cu. However, to date few studies have investigated the effects of Cu vapor on graphene growth. In this study, how the Cu vapor produced by sublimation affects the chemical vapor deposition of graphene on Cu surfaces is investigated. It is found that the presence of Cu vapor enlarges the graphene grains and enhances the efficiency of the defect‐healing of graphene by CH₄. It is elucidated that these effects are due to the removal by Cu vapor of carbon adatoms from the Cu surface and oxygen‐functionalized carbons from graphene. Finally, these insights are used to develop a method for the synthesis of uniform and high‐quality graphene.     

Controllable Growth of Graphene on Liquid Surfaces

Controllable fabrication of graphene is necessary for its practical application. Chemical vapor deposition (CVD) approaches based on solid metal substrates with morphology‐rich surfaces, such as copper (Cu) and nickel (Ni), suffer from the drawbacks of inhomogeneous nucleation and uncontrollable carbon precipitation. Liquid substrates offer a quasiatomically smooth surface, which enables the growth of uniform graphene layers. The fast surface diffusion rates also lead to unique growth and etching kinetics for achieving graphene grains with novel morphologies. The rheological surface endows the graphene grains with self‐adjusted rotation, alignment, and movement that are driven by specific interactions. The intermediary‐free transfer or the direct growth of graphene on insulated substrates is demonstrated using liquid metals. Here, the controllable growth process of graphene on a liquid surface to promote the development of attractive liquid CVD strategies is in focus. The exciting progress in controlled growth, etching, self‐assembly, and delivery of graphene on a liquid surface is presented and discussed in depth. In addition, prospects and further developments in these exciting fields of graphene growth on a liquid surface are discussed.     

Kinetics of Graphene and 2D Materials Growth

During the last 10 years, remarkable achievements on the chemical vapor deposition (CVD) growth of 2D materials have been made, but the understanding of the underlying mechanisms is still relatively limited. Here, the current progress on the understanding of the growth kinetics of 2D materials, especially for their CVD synthesis, is reviewed. In order to present a complete picture of 2D materials' growth kinetics, the following factors are discussed: i) two types of growth modes, namely attachment‐limited growth and diffusion‐limited growth; ii) the etching of 2D materials, which offers an additional degree of freedom for growth control; iii) a number of experimental factors in graphene CVD synthesis, such as structure of the substrate, pressure of hydrogen or oxygen, temperature, etc., which are found to have profound effects on the growth kinetics; iv) double‐layer and few‐layer 2D materials' growth, which has distinct features different from the growth of single‐layer 2D materials; and v) the growth of polycrystalline 2D materials by the coalescence of a few single crystalline domains. Finally, the current challenges and opportunities in future 2D materials' synthesis are summarized.     

H2O‐Etchant‐Promoted Synthesis of High‐Quality Graphene on Glass and Its Application in See‐Through Thermochromic Displays

Direct growth of graphene on glass can bring an innovative revolution by coupling the complementary properties of traditional glass and modern graphene (such as transparency and conductivity), offering brand new daily‐life related applications. However, preparation of high‐quality graphene on nonmetallic glass is still challenging. Herein, the direct route of low sheet resistance graphene on glass is reported by using in situ‐introduced water as a mild etchant and methane as a carbon precursor via chemical vapor deposition. The derived graphene features with large domain sizes and few amorphous carbon impurities. Intriguingly, the sheet resistance of graphene on glass is dramatically lowered down to ≈1170 Ω sq^?1 at the optical transmittance ≈93%, ≈20% of that derived without the water etchant. Based on the highly conductive and optical transparent graphene on glass, a see‐through thermochromic display is thus fabricated with transparent graphene glass as a heater. This work can motivate further investigations of the direct synthesis of high‐quality graphene on functional glass and its versatile applications in transparent electronic devices or displays.     

Remote catalyzation for direct formation of graphene layers on oxides

Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth.     

Synthesis of large area, homogeneous, single layer graphene films by annealing amorphous carbon on Co and Ni

The synthesis of large area, homogenous, single layer graphene on cobalt (Co) and nickel (Ni) is reported. The process involves vacuum annealing of sputtered amorphous carbon (a-C) deposited on Co/sapphire or Ni/sapphire substrates. The improved crystallinity of the metal film, assisted by the sapphire substrate, proves to be the key to the quality of as-grown graphene film. The crystallinity of the Co and Ni metal films was improved by sputtering the metal at elevated temperature as was verified by X-ray diffraction (XRD). After sputtering of a-C and annealing, large area, single layer graphene that occupies almost the entire area of the substrate was produced. With this method, 100 mm²-area single layer graphene can be synthesized and is limited only by the substrate and vacuum chamber size. The homogeneity of the graphene film is not dependent on the cooling rate, in contrast to syntheses using polycrystalline metal films and conventional chemical vapor deposition (CVD) growth. Our facile method of producing single layer graphene on Co and Ni metal films should lead to large scale graphene-based applications.     

氮化碳晶体的研究进展

介绍了氮化碳晶体的合成与表征研究进展，分析了氮化碳晶体合成中存在的主要困难。分析表明：现有的研究结果还没有给出氮化碳晶体合成的确信证据。高温高压法的主要困难在于反应前驱体的选择与制备以及在高压过程中对热力学参数进行有效地控制；等离子体化学气相沉积中，基体原子，主要是硅原子对氮化碳晶体的合成有很大的影响，但目前缺少这方面的系统研究。反应溅射合成时需要解决的困难是在保持较低基片温度的同时如何提高反应气氛中的N原子含量，寻求高比例的sp^3c-N单键的合成条件。电化学方法利用了前驱体中的碳氮单键，能够有效地降低反应能垒和沉积温度，需要解决的问题是如何促进合成产物的晶化和减少副产物。综合运用多种合成技术如在较低的基片温度下，在氮等离子体中通过溅射含有碳氮单键的有机前驱体而引入大量的碳氮单键，控制硅原子在氮化碳晶体生长中的影响程度将是今后氮化碳晶体合成研究的有效途径。     

Graphene on Group‐IV Elementary Semiconductors: The Direct Growth Approach and Its Applications

Since the first development of large‐area graphene synthesis by the chemical vapor deposition (CVD) method in 2009, CVD‐graphene has been considered to be a key material in the future electronics, energy, and display industries, which require transparent, flexible, and stretchable characteristics. Although many graphene‐based prototype applications have been demonstrated, several important issues must be addressed in order for them to be compatible with current complementary metal‐oxide‐semiconductor (CMOS)‐based manufacturing processes. In particular, metal contamination and mechanical damage, caused by the metal catalyst for graphene growth, are known to cause severe and irreversible deterioration in the performance of devices. The most effective way to solve the problems is to grow the graphene directly on the semiconductor substrate. Herein, recent advances in the direct growth of graphene on group‐IV semiconductors are reviewed, focusing mainly on the growth mechanism and initial growth behavior when graphene is synthesized on Si and Ge. Furthermore, recent progress in the device applications of graphene with Si and Ge are presented. Finally, perspectives for future research in graphene with a semiconductor are discussed.     

Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate

Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.     

化学气相沉积制备大面积高质量石墨烯的研究进展

石墨烯是由单层碳原子紧密堆积形成的一种碳质新材料,具有优良的电学、光学、热学及力学等性质。在众多的石墨烯制备方法中,化学气相沉积(Chemical vapor deposition,CVD)最有可能实现大面积、高质量石墨烯的可控制备。综述了CVD方法制备大面积、高质量石墨烯的影响因素,包括衬底、碳源及生长条件(气体流量、生长温度、等离子体功率、生长压强、沉积时间、冷却速率等)。最后展望了CVD方法制备石墨烯的发展方向。     

Single- and few-layer graphene growth on stainless steel substrates by direct thermal chemical vapor deposition

Increasing interest in graphene research in basic sciences and applications emphasizes the need for an economical means of synthesizing it. We report a method for the synthesis of graphene on commercially available stainless steel foils using direct thermal chemical vapor deposition. Our method of synthesis and the use of relatively cheap precursors such as ethanol (CH(3)CH(2)OH) as a source of carbon and SS 304 as the substrate proved to be economically viable. The presence of single- and few-layer graphene was confirmed using confocal Raman microscopy/spectroscopy. X-ray photoelectron spectroscopic measurements were further used to establish the influence of various elemental species present in stainless steel on graphene growth. The role of cooling rate on surface migration of certain chemical species (oxides of Fe, Cr and Mn) that promote or hinder the growth of graphene is probed. Such analysis of the chemical species present on the surface can be promising for graphene based catalytic research.     

3D Graphene Fibers Grown by Thermal Chemical Vapor Deposition

3D assembly of graphene sheets (GSs) is important for preserving the merits of the single‐atomic‐layered structure. Simultaneously, vertical growth of GSs has long been a challenge for thermal chemical vapor deposition (CVD). Here, vertical growth of the GSs is achieved in a thermal CVD reactor and a novel 3D graphene structure, 3D graphene fibers (3DGFs), is developed. The 3DGFs are prepared by carbonizing electrospun polyacrylonitrile fibers in NH₃ and subsequently in situ growing the radially oriented GSs using thermal CVD. The GSs on the 3DGFs are densely arranged and interconnected with the edges fully exposed on the surface, resulting in high performances in multiple aspects such as electrical conductivity (3.4 × 10⁴–1.2 × 10⁵ S m^?1), electromagnetic shielding (60 932 dB cm² g^?1), and superhydrophobicity and superoleophilicity, which are far superior to the existing 3D graphene materials. With the extraordinary properties along with the easy scalability of the simple thermal CVD, the novel 3DGFs are highly promising for many applications such as high‐strength and conducting composites, flexible conductors, electromagnetic shielding, energy storage, catalysis, and separation and purification. Furthermore, this strategy can be widely used to grow the vertical GSs on many other substrates by thermal CVD.     

Graphene Single Crystals: Size and Morphology Engineering

Recently developed chemical vapor deposition (CVD) is considered as an effective way to large‐area and high‐quality graphene preparation due to its ultra‐low cost, high controllability, and high scalability. However, CVD‐grown graphene film is polycrystalline, and composed of numerous grains separated by grain boundaries, which are detrimental to graphene‐based electronics. Intensive investigations have been inspired on the controlled growth of graphene single crystals with the absence of intrinsic defects. As the two most concerned parameters, the size and morphology serve critical roles in affecting properties and understanding the growth mechanism of graphene crystals. Therefore, a precise tuning of the size and morphology will be of great significance in scale‐up graphene production and wide applications. Here, recent advances in the synthesis of graphene single crystals on both metals and dielectric substrates by the CVD method are discussed. The review mainly covers the size and morphology engineering of graphene single crystals. Furthermore, recent progress in the growth mechanism and device applications of graphene single crystals are presented. Finally, the opportunities and challenges are discussed.     

Few-layer graphene direct deposition on Ni and Cu foil by cold-wall chemical vapor deposition

We report an alternative synthesis process, cold-wall thermal chemical vapor deposition (CVD), is replied to directly deposit single-layer and few-layer graphene films on Ar plasma treated Ni and Cu foils using CH4 as carbon source. Through optimizing the process parameters, large scale single-layer graphene grown on Ni foil is comparable to that grown on Cu foil. The graphene films were able to be transferred to other substrates such as SiO2/Si, flexible transparent PET and verified by optical microscopy, Raman microscopy and scanning electron microscopy. The sheet resistance and transmission of the transferred graphene films on PET substrate were also discussed.