Low-temperature Synthesis Of Graphene Research Articles

Characteristics of Graphene Growth at Different Temperatures from the Benzene Ring Structure in Coal Tar

A large number of aromatic substances can be found in so-called coal tar (containing >10,000 individual compounds), which is a mixture of heavy liquid fractions (dense viscous black liquor, tended to solidification) obtained after the pyrolysis of coal (solid product—coke, gas products, and light liquid products are also produced during the process). Volatile monocyclic aromatic hydrocarbons, which are naturally occurring in coal tar, can be exploited as premium raw materials for the production of graphene by chemical vapor deposition (CVD). Moreover, aromatic chemicals (compounds with benzene rings) can produce graphene at lower temperatures than other small-molecule gas feedstocks (for graphene growth via methane gas, the temperature must be at least 900 °C). The intermediate reaction mechanism involved in the creation of graphene from various temperature ranges of monocyclic aromatic hydrocarbons in benzene ring structures has long been a fascinating enigma. Accordingly, in this paper, we analyze the graphene growth pattern of benzene at different temperatures from 300 to 900 °C. For graphene synthesis in the lower temperature range (300~600 °C), analytical experiments show that benzene rings (almost) do not crack during the gas phase process. Thus, the structure of the benzene ring is directly coupled into graphene in the above temperature range. When benzene is more thoroughly transformed into tiny molecules that are deposited on the surface of copper foil at higher temperatures (700~900 °C), graphene is formed by a complex mixture of carbon sources, including gaseous small molecules (methane and ethane) and benzene. Based on the process above, we provide an alternative solution for the large-scale industrial preparation of graphene, with low energy consumption, via low-temperature synthesis of graphene by the CVD method using the coal tar carbon source at 500 °C, which is the optimal growth temperature of the benzene ring.

Porous Silicon Skeleton as Catalysts for Hydrocarbon Decomposition at Low Temperature Synthesis of Graphene Nanocomposites

The energy of low-temperature synthesis of graphene on the surface of nanoporous silicon (nc-PS) is considered. It was shown that the energy of low-temperature synthesis of graphene on nc-PS is due to the excess energies of the nanocrystal surface, the interfaces of the nanocrystal nc-Si/c-Si monocrystal matrix, and the free dangling bonds of silicon atoms of nanoscale silicon grains in the skeleton of porous silicon. This opens up a new perspective for the development of methods for the low-temperature synthesis of graphene without metal catalysts for the decomposition of carbon precursors, including the use of the ALD (atomic layer deposition) method.

Qualitative Analysis of Growth Parameters for PECVD Based Low Temperature Synthesis of Graphene Using Design of Experiments

Determination of key factors and parameters is necessary to design any process when number of factors are large. Design of Experiments technique is an important statistical tool to serve the purpose. This work demonstrates a method to perform qualitative analysis in order to determine cardinal control factors for Graphene growth at low temperature values using Fractional Factorial design. Graphene is synthesized using Plasma Enhanced Chemical Vapor Deposition (PECVD) method in this work. Attribute Response Analysis suggests that Graphene growth temperature, deposition time and RF power are important controlling factors. This is verified by Graphene growth using the predicted recipe.

One pot low temperature synthesis of graphene coupled Gd-doped ZnFe2O4 nanocomposite for effective removal of antibiotic levofloxacin drug

Nanocomposites of reduced graphene oxide (rGO) coupled gadolinium doped ZnFe2O4 (GZFG) have been successfully one pot in-situ synthesized adopting low temperature solution process from zinc nitrate, iron nitrate, gadolinium acetate and graphene oxide with varying concentrations of gadolinium (upto 10% Gd with respect to Zn) in the precursor medium. X-ray diffraction and transmission electron microscopy studies confirm the presence of single phase cubic spinel structure of ZnFe2O4 that uniformly distributed over the rGO layers. With increasing Gd doping concentration in precursor medium, the average crystallite size of ZnFe2O4 diminishes gradually from ~11 to ~5.5 nm. Raman and X-ray photoelectron spectral analyses confirm an existence of interaction between rGO and ZnFe2O4 in GZFG samples. Using antibiotic levofloxacin in water, the drug removal capacity (DRC) of GZFG has been performed by optimization of parameters such as gadolinium doping concentration in precursor medium, solution pH, etc. However, the gadolinium doping leads to an improvement in DRC of the nanocomposite and the 5% Gd doped sample shows about 86% DRC at the optimized condition. This simple strategy can be utilized in the synthesis of rGO coupled Gd doped other metal oxide nanocomposites for DRC application.

Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst

Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to 50–100 °C. Our results represent a significant progress in reducing graphene synthesis temperature and understanding its mechanism.

Low temperature synthesis of graphene hybridized surface defective hierarchical core–shell structured ZnO hollow microspheres with long-term stable and enhanced photoelectrochemical activity

Time dependent structural change (solid → core–shell → hollow) of in situ formed ZnO–graphene (ZG) microspheres by low temperature solution process and their photoelectrochemical stability.

Direct low-temperature synthesis of graphene on various glasses by plasma-enhanced chemical vapor deposition for versatile, cost-effective electrodes

Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400–600 °C. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.

Characterization of low temperature graphene synthesis in inductively coupled plasma chemical vapor deposition process with optical emission spectroscopy.

Low-temperature graphene was synthesized at 400 degrees C with inductively coupled plasma chemical vapor deposition (PECVD) process. The effects of plasma power and flow rate of various carbon containing precursors and hydrogen on graphene properties were investigated with optical emission spectroscopy (OES). Various radicals monitored by OES were correlated with graphene film properties such as sheet resistance, I(D)/I(G) ratio of Raman spectra and transparency. C2H2 was used as a main precursor and the increase of plasma power enhanced intensity of carbon (C2) radical OES intensity in plasma, reduced sheet resistance and increased transparency of graphene films. The reduced flow rate of C2H2 decreased sheet resistance and increased transparency of graphene films in the range of this study. H2 addition was found to increase sheet resistance, transparency and attributed to reduction of graphene grain and etching graphene layers. OES analysis showed that C2 radicals contribute to graphite networking and sheet resistance reduction. TEM and AFM were applied to provide credible information that graphene had been successfully grown at low temperature.

Synthesis of graphene on Co/SiC structure

Bi-layer graphene sheets have been prepared on the basis of a reaction of cobalt with silicon carbide at temperatures around 1,000 °C. This is a type of viable low temperature graphene synthesis. Preparation of graphene was carried out with various thicknesses of the Co layer deposited onto the SiC surface and parameters of the annealing process (temperature, annealing time) were varied. Number of carbon mono-layers in the prepared graphene and its crystallinity were determined from the results of Raman spectroscopy. The best results have been obtained for a structure with Cobalt layer of 300 nm thickness, annealed at 1,080 °C for the period of 120 s. When using shorter annealing times, significantly non-homogenous reaction of Co with SiC has been observed, forming two different phases on the surface.

Three step fabrication of graphene at low temperature by remote plasma enhanced chemical vapor deposition

In this report, we systematically studied low temperature fabrication of graphene from precursors containing cyclobenzene groups by remote plasma enhanced chemical vapor deposition. A new three-step growth procedure was developed with good control of the nucleation, domain growth and domain connection stages. Based on this growth procedure, high quality continuous graphene films could be obtained using naphthalene as the graphene precursor at temperatures lower than 600 °C. A transmittance of ∼96.4% and continuous optical images confirmed the successful fabrication of uniform single-layer graphene films with desirable quality at temperatures lower than 400 °C. Carrier mobility of graphene synthesized at 400 °C reached ∼682 cm2 V−1 s−1, indicating the samples are of reasonable quality. Low temperature graphene synthesis may pave the way for low cost large scale graphene fabrication, and for production of flexible substrates, especially polymer substrates.

Low-temperature synthesis of graphene on Fe2O3 using inductively coupled plasma chemical vapor deposition

Graphene was directly synthesized at as low as 700°C on Fe2O3/Si substrate using inductively coupled plasma (ICP) chemical vapor deposition. By contrast, nanographene film was synthesized on SiO2 and sapphire even at 1000°C, suggesting that catalytic Fe elements on Fe2O3 played a critical role in graphene formation. Another key factor in results was the assistance of ICP, which significantly affected the growth kinetics. With increasing ICP power, the thickness of graphene was controllably reduced and ultimately self-limited to a single layer. Moreover, the crystal quality of graphene was constantly enhanced.

Low-temperature synthesis of graphene on nickel foil by microwave plasma chemical vapor deposition

Microwave plasma chemical vapor deposition (MPCVD) was employed to synthesize high quality centimeter scale graphene film at low temperatures. Monolayer graphene was obtained by varying the gas mixing ratio of hydrogen and methane to 80:1. Using advantages of MPCVD, the synthesis temperature was decreased from 750 °C down to 450 °C. Optical microscopy and Raman mapping images exhibited that a large area monolayer graphene was synthesized regardless of the temperatures. Since the overall transparency of 89% and low sheet resistances ranging from 590 to 1855 Ω∕sq of graphene films were achieved at considerably low synthesis temperatures, MPCVD can be adopted in manufacturing future large-area electronic devices based on graphene film.

Low-temperature synthesis of graphene

A new method is proposed for the low-temperature production of graphene with high yield. The method is based on the low-temperature synthesis and decomposition of graphite intercalation compounds with sodium ammoniates. The proposed technology retains high efficiency, which is typical of graphene synthesis via graphite oxidation and thermal expansion, and offers new advantages by ensuring high purity and structural perfection of the product.

Relatively low temperature synthesis of graphene by radio frequency plasma enhanced chemical vapor deposition

We present a simple, low-cost and high-effective method for synthesizing high-quality, large-area graphene using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) on SiO 2/Si substrate covered with Ni thin film at relatively low temperatures (650 °C). During deposition, the trace amount of carbon (CH 4 gas flow rate of 2 sccm) is introduced into PECVD chamber and the deposition time is only 30 s, in which the carbon atoms diffuse into the Ni film and then segregate on its surface, forming single-layer or few-layer graphene. After deposition, Ni is removed by wet etching, and the obtained single continuous graphene film can easily be transferred to other substrates. This investigation provides a large-area, low temperature and low-cost synthesis method for graphene as a practical electronic material.