Direct synthesis of graphene on 3D-printed arbitrary shaped CoCrMo alloy substrates using double-tube chemical vapor deposition

Direct synthesis of graphene with well-defined nanoscale pores over large areas can transform the fabrication of nanoporous atomically thin membranes (NATMs) and greatly enhance their potential for practical applications. However, scalable bottom-up synthesis of continuous sheets of nanoporous graphene that maintain integrity over large areas has not been demonstrated. Here, it is shown that a simple reduction in temperature during chemical vapor deposition (CVD) on Cu induces in-situ formation of nanoscale defects (≤2-3 nm) in the graphene lattice, enabling direct and scalable synthesis of nanoporous monolayer graphene. By solution-casting of hierarchically porous polyether sulfone supports on the as-grown nanoporous CVD graphene, large-area (>5 cm2 ) NATMs for dialysis applications are demonstrated. The synthesized NATMs show size-selective diffusive transport and effective separation of small molecules and salts from a model protein, with ≈2-100× increase in permeance along with selectivity better than or comparable to state-of-the-art commercially available polymeric dialysis membranes. The membranes constitute the largest fully functional NATMs fabricated via bottom-up nanopore formation, and can be easily scaled up to larger sizes permitted by CVD synthesis. The results highlight synergistic benefits in blending traditional membrane casting with bottom-up pore creation during graphene CVD for advancing NATMs toward practical applications.

化学气相沉积法(CVD)在制备高质量、大尺寸石墨烯方面显示出巨大 的优势 [11~13] , 该方法成本低廉, 更能够和目前的集 成 电 路 工 艺 相 兼 容 .

A facile approach to direct growth of layer-tunable graphene on Ge substrates

<p indent=0mm>In 2004, graphene was successfully prepared by micromechanical exfoliation of graphite, which attracts wide attention in the scientific research community. After that, related research of two-dimensional (2D) materials has received continuous exploration. In particular, academia and industry have paid tremendous attention and high expectations on graphene, owing to its remarkable and tunable physical, electrical, optical, magnetic properties and its potential applications in various fields. These practical applications include high performance electronics and optoelectronics, such as field effect transistors, transparent and flexible electrodes, spintronic devices, solar cells and so on. However, as is well-known, the practical commercial applications are based on mature and repeatable preparation of materials. Great achievements have been made in developing synthesis techniques, including micromechanical exfoliation, epitaxial growth, chemical vapor deposition (CVD), chemical exfoliation, arc discharge, segregation growth and bottom-up synthesis and so on. Among these methods, CVD method is regarded as the most versatile platform to obtain high quality, large area, and controllable number of layers with good repeatability and low cost for real commercial applications. Up to now, the past decade has witnessed significant developments in the field of CVD graphene synthesis. Herein, we present the development of this field by firstly introducing the origin of graphene and the background of CVD method. Then, the main achievements in the development of graphene since 2008 are presented from the point of view of controllable preparation. The CVD synthesis of graphene is focused mainly on four aspects: the selection and modification of catalytic substrates, the manipulation of reaction conditions, bandgap engineering and clean transfer. The selection of catalytic substrate plays a critical role in the controllable preparation of graphene by CVD method. The representative catalytic mechanisms of different substrates for growing graphene are introduced, followed by various modifications of catalytic metal substrates. Besides, surface morphology and microstructure of substrates have a great impact on the quality and uniformity of as-grown graphene. Thus, due to the disadvantages of non-uniform surface energy, defects, wrinkles and impurities on the surface of solid metal, the introduction of liquid copper catalytic system helps to better control the nucleation uniformity and optimize the graphene growth. Moreover, the preparation of large-area monocrystalline metal foils for obtaining large-scale single-crystal graphene was also reviewed. In order to avoid the disadvantages such as the damage, wrinkle and polymer pollution of graphene associated with transfer process occurred in the cases of using metal substrates to grow graphene, direct synthesis of graphene on dielectric substrates is presented with focuses on two basic controls of nucleation density and growth rate. A series of techniques such as reaction medium regulation, substrate surface modification, and plasma-assisted growth, the introduction of gaseous metals and direct preparation of graphene on liquid glass are introduced. The development of graphene vertical and planar heterostructures with hexagonal boron nitride is also presented. Moreover, the disadvantage of graphene limits its application in logic circuits due to its zero bandgap without an acceptable on/off ratio, and three main ways to open graphene bandgap are discussed including doping, the preparation of a large area of AB stacking bilayer graphene and engineering graphene nanoribbons. After that, a brief introduction of transfer method used in graphene post-processing is given. Finally, we summarize the problems existing in the field, and the future opportunities and challenges are discussed.

Direct graphene synthesis on substrates via chemical vapor deposition (CVD) is an attractive approach for manufacturing flexible electronic devices. The temperature for graphene synthesis must be below ∼200 °C to prevent substrate deformation while fabricating flexible devices on plastic substrates. Herein, we report a process whereby defect-free graphene is directly synthesized on a variety of substrates via the introduction of an ultrathin Ti catalytic layer, due to the strong affinity of Ti to carbon. Ti with a thickness of 10 nm was naturally oxidized by exposure to air before and after the graphene synthesis, and the various functions of neither the substrates nor the graphene were influenced. This report offers experimental evidence of high-quality graphene synthesis on Ti-coated substrates at 150 °C via CVD. The proposed methodology was applied to the fabrication of flexible and transparent thin-film capacitors with top electrodes of high-quality graphene.

Direct synthesis and characterization of graphene layers on silica glass substrates

The direct synthesis of graphene on dielectric substrates has attracted growing interest due to its potential for scalable, transfer-free integration in electronic and photonic applications. However, graphene grown on dielectrics typically exhibits lower carrier mobility compared to copper-grown counterparts, limiting its performance. Here, we report the synthesis of large-area graphene on Al-rich reconstructed c-plane sapphire (0001) via chemical vapor deposition (CVD) and reveal that, over time and under ambient storage conditions, a spontaneous decoupling occurs at the graphene-sapphire interface. Raman spectroscopy reveals a reduction in both strain and doping in the aged samples, consistent with electrical transport measurements showing a twofold increase in carrier mobility. X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (cross-sectional TEM) identify the intercalation of oxygen-containing species at the interface as the mechanism responsible for the decoupling. These findings uncover a previously unrecognized pathway to enhance the electronic performance of directly grown graphene on sapphire, reinforcing the viability of this platform for future scalable graphene-based technologies.

As one of the most appealing materials, graphene possesses remarkable electric, thermal, photoelectric and mechanic characteristics, which make it extremely valuable both for fundamental researches and practical applications. Nowadays the synthesis of graphene is commonly achieved by growing on metal substrate via chemical vapor deposition. For the integration in micro-electric device, the as-grown graphene needs to be transferred onto target dielectric layer. However, wrinkles, cracks, damages, and chemical residues from the metal substrate and the auxiliary polymer are inevitably introduced to graphene during such a transfer process, which are greatly detrimental to the performances of the graphene devices. Therefore, the direct synthesis of graphene on dielectric layer is of great importance. Many researches about this subject have been carried out in the last few years. While only few papers have systematically reviewed the direct growth of graphene on dielectric layer. For the in-depth understanding and further research of it, a detailed overview is required. In this paper, we summarize the recent research progress of the direct syntheses of graphene on dielectric layers, and expatiate upon different growth methods, including metal assisted growth, plasma enhanced growth, thermodynamics versus kinetics tailored growth, et al. Then differences in property between graphenes grown on various dielectric and insulating layers which serve as growth substrates in the direct growing process are discussed, such as SiO2/Si, Al2O3, SrTiO3, h-BN, SiC, Si3N4 and glass. Some kinds of mechanisms for graphene to be directly grown on dielectric layers have been proposed in different reports. Here in this paper, we review the possible growth mechanisms and divide them into van der Waals epitaxial growth and catalytic growth by SiC nanoparticles or oxygen atoms. Detailed data including Raman signals, sheet resistances, transmittances, carrier motilities are listed for the direct comparison of the quality among the graphenes grown on dielectric layers. The research focus and major problems existing in this field are presented in the last part of this paper. We also prospect the possible developing trend in the direct syntheses of high quality graphenes on dielectric layers in the future.

Direct synthesis of graphene nanoribbons on dielectric or semiconducting substrates offers a scalable route for integration of graphene-based devices into a conventional silicon-based technology.(1) So-far, wafer-scale synthesis of armchair graphene nanoribbons has been demonstrated on Ge (001) using chemical vapor deposition.(2) However, direct synthesis of graphene or graphene nanoribbons has not yet been achieved on CMOS compatible Si(001) due to formation of stable SiC at temperatures > 1000 K, which are needed to achieve synthesis of nanoribbons with smooth, armchair edges. A promising and realistic way to overcome this challenge is to synthesize graphene nanoribbons on CMOS compatible Ge(001)/Si(001) substrates. So far the synthesis of monolayer graphene on Ge(001)/Si(001) substrates has been demonstrated by CVD.(3, 4) In this study, we synthesized graphene nanoribbons on 3 µm epitaxial Ge(001)/Si(001) substrates, by ambient pressure CVD using methane as the carbon precursor. We show that growth kinetics of graphene nanoribbons on Ge(001)/Si(001) are comparable to that on Ge(001). By tuning the methane flow and growth time we are able to synthesize graphene nanoribbons ranging from 100 nm to 1 µm in length with high aspect ratios, whilst avoiding Si diffusion from the bulk. For instance, by restricting methane to < 6000 ppm and growth time to < 3h, graphene nanoribbons with widths < 10 nm can be synthesized with aspect ratios as high as 70. Such nanoribbons grown on Ge(001) have been shown to exhibit technologically relevant band-gaps as well as exceptional charge transport properties.(5) Furthermore, we also investigated the possible role of threading dislocations in Ge epilayer on nucleation or growth of nanoribbons and show that nanoribbons readily grow over the threading dislocations. Lastly, we studied the evolution of surface roughness with the nucleation density of nanoribbons. Our study provides valuable insight into the mechanism of graphene nanoribbon growth on Ge(001)/Si(001) substrates. From this information, it is expected that unidirectional graphene nanoribbons with rational placement and control over width poly-dispersity can be synthesized on Ge(001)/Si(001) platform akin to Ge(001), which has been demonstrated recently using seed-mediated growth.(6) This provides a scalable way for wafer scale integration of graphene nanoribbon arrays on Si and provides motivation for further research into this direction. References A. Khan et al., Direct CVD Growth of Graphene on Technologically Important Dielectric and Semiconducting Substrates. Advanced Science 5, (2018).R. M. Jacobberger et al., Direct oriented growth of armchair graphene nanoribbons on germanium. Nature Communications 6, (2015).I. Pasternak et al., Graphene growth on Ge(100)/Si(100) substrates by CVD method. Scientific Reports 6, (2016).M. Lukosius et al., Metal-Free CVD Graphene Synthesis on 200 mm Ge/Si(001) Substrates. Acs Applied Materials & Interfaces 8, 33786-33793 (2016).R. M. Jacobberger, M. S. Arnold, High-Performance Charge Transport in Semiconducting Armchair Graphene Nanoribbons Grown Directly on Germanium. Acs Nano 11, 8924-8929 (2017).A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium. Nano Letters 18, 898-906 (2018). Figure 1

The synthesis of transfer-free graphene is necessary for expanding its industrial applications. Although the direct synthesis of graphene on the insulating substrate via a metal sacrificial film was reported, the growth mechanism of transfer-free graphene still remains to be studied. Herein, a detailed synthesis model of graphene grown from different carbon sources has been established to help in selecting the growth conditions for high-quality graphene. A detailed discussion on the critical influence of dissolution and the diffusion rate of carbon atoms on the growth process has also been presented. The high decomposition temperature carbon sources promote the formation of high-quality monolayers of graphene. The carbon diffusion rate of the Cu film is significantly higher than that of Ni. This promotes the synthesis of graphene from methane and diamond-like carbon. However, adverse effects are exerted on polymethyl methacrylate. Ion implantation technology and different components of the Ni–Cu alloy were used to understand this growth mechanism. This work could guide the growth conditions of transfer-free, large-scale, and high-quality graphene that can be potentially used for the fabrication of a semiconductor or an insulation substrate in theory. The reported method can generate interest in the field and increase the industrial applications of graphene-based devices that exhibit rough or patterned surfaces.

Direct synthesis of high-quality graphene on dielectric substrates is of great importance for the application of graphene-based electronics and optoelectronics. However, high-quality and uniform graphene film growth on dielectric substrates has proven challenging due to limited catalytic ability of dielectric substrates. Here, by employing a Cu ion implantation assisted method, high-quality and uniform graphene can be directly formed on various dielectric substrates including SiO2/Si, quartz glass, and sapphire substrates. The growth rate of graphene on the dielectric substrates was significantly improved due to the catalysis of Cu. Moreover, during the graphene growth process, the Cu atoms gradually evaporated away without involving any metal contamination. Furthermore, an interesting growth behavior of graphene on sapphire substrate was observed, and the results show the graphene domains growth tends to grow along the sapphire flat terraces. The ion implantation assisted approach could open up a new pathway for the direct synthesis of graphene and promote the potential application of graphene in electronics.

We report the direct synthesis of graphene on Si/SiO2 substrates by a simple annealing process. An amorphous carbon layer and a Ni/Au layer were deposited on a Si/SiO2 substrate, and then the sample was annealed under an H2/Ar atmosphere. The Au layer suppressed the formation of Ni islands and graphene was synthesized at the interface between the metal and SiO2 layers. The graphene had an effective mobility similar to that of graphene synthesized by chemical vapor deposition. The technique does not require reactive carbon source gasses and transfer processes, which makes it a practical method of graphene synthesis.

Non-metal catalytic synthesis of graphene from a polythiophene monolayer on silicon dioxide

Many applications of graphene especially for the fabrication of electrical devices require physical placement of graphene on dielectric substrates. Several strategies developed for the graphene device fabrication include 1) mechanical exfoliation of graphene on a dielectric substrate followed by fabrication, 2) graphene growth on metal catalysts by chemical vapor deposition (CVD) process followed by transferring it onto dielectric substrates and fabrication, 3) dispersion of reduced graphene oxides (RGOs) on dielectric substrates followed by fabrication, etc. To utilize the intrinsic high charge carrier mobility of graphene, however, a direct synthesis of graphene by CVD on dielectric substrates is highly demanding. In this presentation, I will introduce our recent experimental results demonstrating successful direct growth of graphene on various dielectric substrates, such as hexagonal boron nitride (h-BN), sapphire, quartz, and amorphous SiO2/Si, thus excluding complex transfer process to secure the quality of graphene by excluding impurities that are accompanied during the transfer process. The detailed growth mechanism involved in graphene nucleation and growth propagation on various substrates will be also discussed.

Controllable preparation of graphene glass fiber fabric towards mass production and its application in self-adaptive thermal management