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.     

Synthesis of large-area, few-layer graphene on iron foil by chemical vapor deposition

We demonstrate a simple and controllable way to synthesize large-area, few-layer graphene on iron substrates by an optimized chemical vapor deposition (CVD) method using a mixture of methane and hydrogen. Based on an analysis of the Fe-C phase diagram, a suitable procedure for the successful synthesis of graphene on Fe surfaces was designed. An appropriate temperature and cooling process were found to be very important in the synthesis of highly crystalline few-layer graphene. Graphene-based field-effect transistor (FET) devices were fabricated using the resulting few-layer graphene, and showed good quality with extracted mobilities of 300–1150 cm²/(V·s).      

系统压强对微波等离子体化学气相沉积金刚石成核的影响

为了在氧化铝上制备（100）定向织构的金刚石薄膜,必须先提高金刚石的成核密度,在微波等离子体化学气相沉积（MPCVD）系统中,采用低压成核的方法,在氧化铝陶瓷上沉积出高成核密度的金刚石薄膜,扫描电镜显示其成核密度可达10^8cm^-2。在此基础上,沉积出（100）织构的金刚石薄膜。     

石墨烯的化学气相沉积法制备

化学气相沉积(CVD)法是近年来发展起来的制备石墨烯的新方法,具有产物质量高、生长面积大等优点,逐渐成为制备高质量石墨烯的主要方法.通过简要分析石墨烯的几种主要制备方法(胶带剥离法、化学剥离法、SiC外延生长法和CVD方法)的原理和特点,重点从结构控制、质量提高以及大面积生长等方面评述了CVD法制备石墨烯及其转移技术的研究进展,并展望了未来CVD法制备石墨烯的可能发展方向,如大面积单晶石墨烯、石墨烯带和石墨烯宏观体的制备与无损转移等.     

石墨烯薄膜的前驱气体预热化学气相沉积快速制备方法

石墨烯具有优异的光学、电学和力学等性能而备受人们关注,但是目前石墨烯材料受产量、尺寸和均匀性等因素的限制,以至于在终端产品上还没有形成真正的应用。主要阐述了一种利用前驱气体预热化学气相沉积法(PT-CVD)快速制备大面积单层石墨烯薄膜方法,实现石墨烯薄膜批量制备和大面积转移在300mm×300 mm面积的聚对苯二甲酸乙二醇酯衬底上,并获得在400~800nm光波段下大于95%的光透过率和(146±15)Ω/sq的方块电阻。分别利用扫描电镜、共聚焦拉曼光谱仪、紫外-可见分光光度计和四探针设备等检测了前驱气体预热化学气相沉积法制备的石墨烯薄膜的均匀性、透过率和方块电阻等参数特性。最后,通过解决了石墨烯微纳米线路结构和真空贴合等关键技术实现了石墨烯真实多点电容式触控面板,并成功运用在5.5寸手机终端产品应用上。     

Effect of copper foil annealing process on large graphene domain growth by solid source-based chemical vapor deposition

Controlling the metal catalyst surface structure is a critical factor to achieve growth of large graphene domains. In this prospect, we explored the annealing process to create an oxide layer and subsequent recrystallization of Cu foil for growth of large graphene domain by the atmospheric pressure chemical vapor deposition (AP-CVD) technique. We revealed the transformation of Cu surface crystallographic structures in every step of annealing process by electron back-scattered diffraction analysis. Initially, electroless polished Cu foils are annealed in Ar and then in H₂ atmosphere to obtain a smoother surface with reduced graphene nucleation sites. The transformation of Cu grain structures at various annealing steps was confirmed, where the gas atmosphere and annealing duration have significant influence. Graphene domains with the size more than 560 µm are obtained on the processed Cu surface using polystyrene as solid precursor. It is obtained that the oxidation and recrystallization process of Cu foil surface significantly influence the nucleation density, which enable growth of larger graphene domain in the developed CVD process.     

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.     

Electrochemically grown Pd nanoparticles used for synthesis of carbon nanotube by microwave plasma enhanced chemical vapor deposition

Pd nanoparticles of well-defined shapes with face centered cubic structure were grown electrochemically on silicon substrates with high degree of reproducibility. As direct application of these electrochemically grown Pd nanostructures they have been used as catalyst for the growth of multi wall carbon nanotube (MWCNT). It is observed that the MWCNTs are filled with a Pd based material during growth by microwave plasma enhanced chemical vapor deposition (MPECVD) technique. High-resolution transmission electron microscopy, used to study the material inside MWCNT suggests the formation of PdH0.649 or Pd2Si during the growth of carbon nanotube. Raman spectroscopy has been used to study the structure of the MPECVD grown carbon nanotubes.     

The effect of argon dilution on deposition of microcrystalline silicon by microwave plasma enhanced chemical vapor deposition

Microwave plasma-enhanced chemical vapor deposition (PECVD) is a very promising method for industrial scale fabrication of microcrystalline silicon solar cells since the technique is well applicable for large areas, and high deposition rates can be obtained. We have investigated the effect of Ar dilution on the growth process and the material properties of microcrystalline silicon. The major benefit of Ar addition in the MWPECVD process, using H₂ and SiH₄ as reactant gases, is an improved stabilization of the plasma, in particular at low pressure and MW power. We show, however, that material properties of the microcrystalline silicon layers deteriorate if we partly substitute H₂ by Ar during the deposition. The density of the layers - as expressed by the refractive index - decreases, and the defect density (measured by Fourier transform photocurrent spectroscopy) increases with increasing Ar flow. Investigation of the plasma by optical emission study shows that Ar atoms play a very active role in the dissociation processes of H₂ and SiH₄. Substitution of H₂ by Ar decreases the SiH^? emission and increases the Si^? emission. On the other hand, the H_α/H_β ratio increases upon substitution of H₂ by Ar. The latter effect shows that Ar addition does not lead to higher electron temperatures and we conclude that the changes of SiH^? and Si^? emissions are due to dissociation of SiH₄ by Ar^? (quenching reactions). The precise role of Ar in MWPECVD of microcrystalline silicon needs further investigation, but we conclude that the usage of this gas should be minimized in order to maximize the quality of the silicon layers.     

Comprehensive study of graphene grown by chemical vapor deposition

Graphene was grown on Cu foil by chemical vapor deposition with CH₄ as carbon source, and then was transferred onto various substrates for device applications. The structural and optical properties of graphene were investigated, comprehensively. Raman spectra indicate as-grown and transferred graphene films are homogenous monolayer graphene. Optical microscopy and scanning electron microscopy images reveal wrinkle-free and smooth surface of transferred graphene, confirming the high quality of graphene. In addition, the transferred graphene on glass exhibits excellent transmittances in the visible region (89.3 % at ~500 nm). Therefore, the results present the controllable approaches to achieve as-grown and transferred high quality graphene for the fabrication of multiple nanoelectronic devices.     

Coating of diamond-like carbon nanofilm on alumina by microwave plasma enhanced chemical vapor deposition process

Diamond-like carbon (DLC) nanofilms with thickness varied from under one hundred to a few hundred nanometers have been successfully deposited on alumina substrates by microwave plasma enhanced chemical vapor deposition (MW-PECVD) process. To obtain dense continuous DLC nanofilm coating over the entire sample surface, alumina substrates were pre-treated to enhance the nucleation density. Raman spectra of DLC films on samples showed distinct diamond peak at around 1332 cm(-1), and the broad band of amorphous carbon phase at around 1550 cm(-1). Full width at half maximum height (FWHM) values indicated good formation of diamond phase in all films. The result of nano-indentation test show that the hardness of alumina samples increase from 7.3 +/- 2.0 GPa in uncoated samples to 15.8 +/- 4.5-52.2 +/- 2.1 GPa in samples coated with DLC depending on the process conditions. It is observed that the hardness values are still in good range although the thickness of the films is less than a hundred nanometer.     

Direct synthesis of large-area Al-doped graphene by chemical vapor deposition:Advancing the substitutionally doped graphene family

Graphene doping continues to gather momentum because it enables graphene properties to be tuned,thereby affording new properties to,improve the performance of,and expand the application potential of graphene.Graphene can be chemically doped using various methods such as surface functionalization,hybrid composites(e.g.,nanoparticle decoration),and substitution doping,wherein C atoms are replaced by foreign ones in the graphene lattice.Theoretical works have predicted that graphene could be substitutionally doped by aluminum(Al)atoms,which could hold promise for exciting applications,including hydrogen storage and evolution,and supercapacitors.Other theoretical predictions suggest that Al substitutionally doped graphene(AIG)could serve as a material for gas sensors and the catalytic decomposition of undesirable materials.However,fabricating Al substitutionally doped graphene has proven challenging until now.Herein,we demonstrate how controlled-flow chemical vapor deposition(CVD)implementing a simple solid precursor can yield high-quality and large-area monolayer AIG,and this synthesis is unequivocally confirmed using various characterization methods including local electron energy-loss spectroscopy(EELS).Detailed high-resolution transmission electron microscopy(HRTEM)shows numerous bonding configurations between the Al atoms and the graphene lattice,some of which are not theoretically predicted.Furthermore,the produced AIG shows a CO₂ capturability superior to those of other substitutionally doped graphenes.     

Low-temperature synthesis of thin graphite sheets using plasma-assisted thermal chemical vapor deposition system

We report the low-temperature synthesis of thin graphite sheets using a hybrid chemical vapor deposition (HCVD) system that combines plasma and thermal CVD (TCVD). Electron beam deposited Ni films were used as catalytic substrates, and methane was used as a carbon feedstock. The quartz tube was into two regions: core plasma region for efficient dissociation of methane and a TCVD region for thermal synthesis, respectively. After the syntheses at different TCVD temperatures from 550 °C to 900 °C, as-grown films were transferred to transparent polymeric substrates to apply as flexible conductive electrodes. Finally, it was found that thin graphite sheets consisting of ~ 15 graphene layers were synthesized at 600 °C using the HCVD system and could be applicable as transparent conductive films.     

Shear modulus of monolayer graphene prepared by chemical vapor deposition

We report shear modulus (G) and internal friction (Q(-1)) measurements of large-area monolayer graphene films grown by chemical vapor deposition on copper foil and transferred onto high-Q silicon mechanical oscillators. The shear modulus, extracted from a resonance frequency shift at 0.4 K where the apparatus is most sensitive, averages 280 GPa. This is five times larger than those of the multilayered graphene-based films measured previously. The internal friction is unmeasurable within the sensitivity of our experiment and thus bounded above by Q(-1) ≤ 3 × 10(-5), which is orders-of-magnitude smaller than that of multilayered graphene-based films. Neither annealing nor interface modification has a measurable effect on G or Q(-1). Our results on G are consistent with recent theoretical evaluations and simulations carried out in this work, showing that the shear restoring force transitions from interlayer to intralayer interactions as the film thickness approaches one monolayer.     

Gas sensing properties of graphene synthesized by chemical vapor deposition

The gas sensing properties of graphene synthesized by a chemical vapor deposition (CVD) method are investigated. Synthesis of graphene is carried out on a copper substrate using a methane and hydrogen gas mixture by a CVD process at the atmospheric pressure. The graphene films are transferred to different substrates after wet etching of the copper substrates. The Raman spectra reveal that the graphene films made on SiO₂/Si substrates are of high quality. The reflectance spectra of graphene were measured in UV/Visible region of the spectrum. Theoretically calculated reflectance spectra based on Fresnel's approach indicates that the CVD graphene has a single layer. The gas sensing properties of graphene were tested for different reducing gasses as a function of measurement temperature and gas concentration. It is found that the gas sensing characteristics such as response time, recovery time, and sensitivity depend on the target gas, gas concentration, test temperature, and the ambient gas composition. The cross sensitivity of few combinations of reducing gasses such as, NH₃, CH_4, and H₂ was also investigated.     

Wafer scale homogeneous bilayer graphene films by chemical vapor deposition

The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. However, bilayer graphene samples have been limited to μm(2) size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. × 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.     

Low-temperature plasma-enhanced chemical vapor deposition of hard carbon films

Carbon films were prepared by the plasma-enhanced chemical vapor deposition method from methane gas under different regimes of a growing film surface ion bombardment. Ion energy and ion flux was measured for different deposition regimes and were controllably and independently varied for deposition of different film samples. The structure of the films deposited was studied by Raman scattering spectroscopy. It was found that ion bombardment of the growing film surface is a key factor in hard carbon films deposition. A correlation between the sp³ hybridized carbon fraction content with both ion energy and ion flux was found. The maximum sp³ hybridized carbon fraction content was achieved for films deposited under maximum ion energy and ion flux conditions. Additionally, a dependence of the film properties on the substrate material and on the final film thickness was observed.