Low-temperature Growth Of Graphene Research Articles

Metal dependence of spontaneous graphitization growth at room temperature

The low-temperature graphene growth is a crucial step toward more efficient, cost-effective, productive, cheap, and sustainable energy systems. In this work, we report the effect of transition metal nanoparticles (TMNPs) Ag, Pd, and Cu on the graphitization of amorphous carbon (a-C) deposited onto SiO2 substrates using a one-step magnetron sputtering technique at room temperature (RT). Transmission electron microscopy (TEM), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) were used to examine the structures of TMNP-C films. The a-C around the metallic NPs spontaneously formed a disordered graphitic structure. Moreover, the 2D peak was detected in Raman spectra, and XPS analyses revealed the sp2 graphitization for the Ag-C, Pd-C, and Cu-C films deposited on the SiO2 substrates. These studies suggest that these metals’ graphitization activity is in the sequence of Pd > Cu > Ag. The highest catalytic activity of Pd NPs in graphitization at low temperatures was due to the highest carbon solubility and nano-sized particles. Thus, the control of the particle size of the catalyst to enhance the carbon solubility and decrease the melting point will open up a new strategy to grow high-quality graphene at low- temperatures.

A brief review of low-temperature graphene growth via chemical vapor deposition

Graphene, a one-atom-thick crystal of carbon, has attracted tremendous attention for various electrical and energy applications due to its superior physical and chemical properties. Among various graphene synthetic approaches, the CVD method has been considered a promising way to obtain high-quality graphene in large-scale. However, to obtain high-quality graphene by a typical CVD process, a high temperature of 1000 ℃ or higher should be required to decompose the hydrocarbon precursors, which is a major obstacle to the commercialization of CVD-graphene. Recently, enormous research has been conducted to grow high-quality graphene at a low temperature using various hydrocarbon precursors and external energy sources. Here, we briefly review recent research progress in the low-temperature growth of graphene using CVD methods. In addition, we introduce representative electronic applications based on low-temperature CVD-graphene.

Effect of precursor gas inlet position relative to hot wire cells in HWC-IP-PECVD systems for low-temperature graphene growth

ABSTRACT Graphene growth at low temperatures was investigated by integrating a hot wire cell made from coil-shaped tungsten into a plasma-enhanced chemical vapour deposition (PECVD) system. It was found that the suitable position of the hot wire was such that the precursor gas comes out of the end of the gas pipeline and directly flows into the hot wire along its axis. This position puts the gas pipeline outside of plasma area, yielding uninterrupted plasma. The obtained films, which were grown at a low temperature between 290 °C to 300 °C, showed the presence of sharp G band in Raman spectra, indicating the presence of graphitic carbon structure and was confirmed by X-Ray Diffraction data. Also, sharp D band was detected in Raman spectra, which indicated that the film contains many defects. In addition to the nature of ion bombardment in the PECVD process, the defects were due to the addition of O-H functional groups and the formation of sp3 C-H in the samples, as shown in the FTIR spectra. Due to these defects, the Raman spectra obtained of the films showed very weak 2D bands, suggesting that our samples were in the form of graphene oxide.

Microscopic investigation of Cu-induced crystallization of amorphous carbon at low temperatures

Graphene or graphene-like carbon-reinforced copper matrix composites have gained extensive application prospects in aerospace and electronic fields due to their high electrical, thermal conductivity and excellent machining performance. The preparation of Cu/graphene composites at a relatively low temperature is highly demanded for practical applications. Herein, we develop an approach for synthesizing few-layer graphene (FLG) by contacting amorphous carbon (a-C) with Cu at a low annealing temperature of 300 °C. The mechanism of such low-temperature growth of graphene was discussed by the combined experimental methods of scanning electron microscopy, Auger electron spectroscopy, cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. It is found that the formation of FLG is mediated by the grain-boundary (GB) diffusion, interfacial diffusion and surface diffusion of carbon atoms simultaneously. The high density of Cu GBs can provide a fast diffusion path for “free” C atoms in the a-C sublayer, and the graphene layer was formed at the Cu GBs, at the Cu/a-C interface and on top of the Cu layer where carbon atoms are present. The Cu-induced growth of graphene at low temperatures may provide a promising support for synthesizing Cu/graphene composites in the future.

Low-Temperature Graphene Growth and Shrinkage Dynamics from Petroleum Asphaltene on CuO Nanoparticle

Low-Temperature Graphene Growth and Shrinkage Dynamics from Petroleum Asphaltene on CuO Nanoparticle

Low-Temperature Growth of Graphene on a Semiconductor

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition metal treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around $450-500^\circ\text{C}$. From the chemical reaction between SiC and thin films of Fe or Ru, $\text{sp}^{3}$ carbon is liberated from the SiC crystal and converted to $\text{sp}^{2}$ carbon at the surface. The quality of the graphene is demonstrated using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate is verified using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene based device structures.

Tellurium-assisted and space-confined growth of graphene single crystals

Low-temperature synthesis of large-area graphene films by chemical vapor deposition (CVD) method has attracted extensive research interests owing to their extraordinary potential applications. Current reports on the low-temperature graphene growth usually involve catalytic metal substrates, which exceedingly impedes the direct use of graphene in nanoelectronic fabrications. In this project, we design a space-confined growth chamber utilizing two SiO2/Si chips. The bottom chip loading pre-transferred graphene flakes accommodates the growth of second monolayer graphene, with a tellurium (Te) vapor assisted growth process. Polymethylmethacrylate (PMMA) residues introduced from the transferred graphene substrate is employed as the solid carbon source. Further, the numerical simulation results prove that the high concentration of active carbons in the confined space plays a vital role in this growth process. Density functional theory (DFT) calculations reveal that, Te atoms prefer to bond with the edge carbons of small graphene flakes and serve as an effective catalyst, which helps to grow small graphene flakes by reducing their energy of formation. The successful growth can provide the high-quality monolayer graphene grains at the low temperature (∼350 °C). This facile strategy promises the mass production of graphene at mild conditions and low costs, which contributes to the green chemistry in future.

Very low-temperature growth of few-layer graphene by Ni-induced crystallization of amorphous carbon in vacuum

Graphene of thickness a few atomic layers has been grown in Ni/a-C bilayers at temperatures as low as 300 °C by Ni-induced crystallization of the amorphous carbon (a-C) in high vacuum. The mechanism of such very low-temperature growth of graphene has been investigated by a combinatorial experimental approach including x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy. The growth of this few atomic layer thickness graphene has been found to be mediated by a coupled grain-boundary (GB) diffusion/surface diffusion mechanism. GBs in the top Ni sublayer provide fast diffusion paths for C atoms through the Ni layer, as a result of which graphene layers form above the Ni. The revealed low-temperature growth mechanism of graphene induced by contact with a metal can be applicable in advancing research fields as metal-matrix graphene composites and advanced energy storage devices.

Low Temperature Graphene Growth Effort on Corning Glass Substrate by Using VHF-IP HWC-PECVD

One promising method for growing carbon-based materials, especially for electronics and optoelectronics application, is PECVD (Plasma Enhanced Chemical Vapor Deposition). In addition to the large-area thin film obtained, this method also requires relatively lower growth temperature. By modifying the PECVD reactor through the application of Hot-Wire Cell (HWC) placed between two electrodes (called In Plasma, IP), and plasma generator frequency of 70 MHz which is categorized as Very High Frequency (VHF), graphene flakes have been successfully grown by using methane (CH4) gas as precursor at pressure 300 mTorr and substrate temperature of 275°C on corning glass substrate. This result indicates that this method is potentially to grow graphene at lower temperature by adjusting several growth parameters, especially temperature of hot wire cell that plays important role in the deposition process. It should be noted that important factor that greatly determined the successful of graphene flakes growth was the use of metal catalyst in the form of very thin film. In this research, silver was used as metal catalyst which was prepared by evaporation method and then annealed at 600°C for 30-60 minutes.

Hydrogen sieving from intrinsic defects of benzene-derived single-layer graphene

Single-layer graphene films, crystallized by chemical vapor deposition, host a low density of vacancy defects that are attractive for the size-sieving of molecules. The size and the density of such defects are a function of the growth temperature and the carbon precursor. So far, the studies applying the intrinsic defects of graphene have only used CH4 as the precursor. Since there are reports claiming the synthesis of graphene from benzene at low temperature (up to 100 °C on Cu foil), we systematically studied the crystallization of benzene-derived graphene and the evolution of intrinsic defects. We demonstrate that graphene cannot grow from benzene below 700 °C on Cu. We attribute the reports on low-temperature growth of graphene to the practice of pre-annealing of the Cu foil at 1000 °C and to the unintentional benzene residues in the reactor if the reactor is not purged carefully. Finally, we report that high-quality single-layer-graphene can be synthesized using benzene above 825 °C. The majority of vacancy defects in benzene-derived graphene (900–1000 °C) are smaller than 0.38 nm, leading to an attractive H2 sieving (H2 permeance over 2000 gas permeation units; H2/C3H8 and H2/SF6 selectivities of 12 and 50, respectively).

Temperature dependence of catalytic activity in graphene synthesis for Sn nanoparticles

Graphene synthesis at lower temperatures is quite important for a wider range of practical applications. Sn, which is recently found as a promising catalyst for the low-temperature graphene growth, is taken as the study material in this work. Based on the detailed transmission electron microscopy (TEM) observation, we found that catalytic activity of Sn nano-particles is highly temperature dependent which was observed during graphitization of amorphous carbon. For this study, C–Sn composite nanofibers were prepared on an edge of a carbon foil by the Ar+ ion irradiation with simultaneous supply of Sn. As-fabricated C–Sn composite nanofibers were observed to be the amorphous C nanofibers (CNFs) in which the Sn nanoparticles dispersed. The as-prepared samples were annealed at 180–250 °C in a vacuum and were characterized using Raman spectra and high-resolution TEM to study the graphitization process. The graphitization started to occur at an annealing temperature of 180 °C, which is much lower than the graphitization temperature for bulky Sn. Based on the detailed TEM observation of annealed samples, a model to explain the graphitization mechanism at such a low temperature was proposed.

Low-Temperature Graphene Growth by Forced Convection of Plasma-Excited Radicals.

We developed the forced convection (FC)-PECVD method for the synthesis of graphene, in which a specially designed blowing plasma source is used at moderate gas pressure (1-10 Torr) and the distribution of reactive radicals reaching the substrate surface can be controlled by forced convection. Self-limiting growth of graphene occurs on copper foil, and monolayer graphene growth with a few defects is achieved even at low temperatures (<400 °C). We also demonstrated the enlargement of the growth area using the scalable blowing plasma source. We expect that the FC-PECVD method overcomes the limitations of conventional low-temperature PECVD and provides a breakthrough for the achievement of industrial applications based on graphene.

Switching Vertical to Horizontal Graphene Growth Using Faraday Cage-Assisted PECVD Approach for High-Performance Transparent Heating Device.

Plasma-enhanced chemical vapor deposition (PECVD) is an applicable route to achieve low-temperature growth of graphene, typically shaped like vertical nanowalls. However, for transparent electronic applications, the rich exposed edges and high specific surface area of vertical graphene (VG) nanowalls can enhance the carrier scattering and light absorption, resulting in high sheet resistance and low transmittance. Thus, the synthesis of laid-down graphene (LG) is imperative. Here, a Faraday cage is designed to switch graphene growth in PECVD from the vertical to the horizontal direction by weakening ion bombardment and shielding electric field. Consequently, laid-down graphene is synthesized on low-softening-point soda-lime glass (6 cm × 10 cm) at ≈580 °C. This is hardly realized through the conventional PECVD or the thermal chemical vapor deposition methods with the necessity of high growth temperature (1000 °C-1600 °C). Laid-down graphene glass has higher transparency, lower sheet resistance, and much improved macroscopic uniformity when compare to its vertical graphene counterpart and it performs better in transparent heating devices. This will inspire the next-generation applications in low-cost transparent electronics.

Graphene Growth at Low Temperatures using RF-Plasma Enhanced Chemical Vapour Deposition

The advantage of plasma enhanced chemical vapour deposition (PECVD) method is the ability to deposit thin films at relatively low temperature. Plasma power supports the growth process by decomposing hydrocarbon to carbon radicals which will be deposited later on metal catalyst. In this work, we have successfully synthesis graphene on Ni and Co films at relatively low temperature and optimize the synthesis conditions by adjusting the plasma power. Low temperature growth of graphene was optimized at 600°C after comparing the quality of as-grown graphene at several temperatures from 400 to 800°C and by varying plasma powers in the range of 20 - 100 W. Raman analysis of the as-grown samples showed that graphene prefers lower plasma power of 40 W. The annihilation of graphene formation at higher plasma powers is attributed to the presence of high concentration of hydrogen radical from methane which recombines with carbon elements on thin film surface. The optimum graphene growth conditions were obtained at growth temperature of 600°C, plasma power of 40 W and growth time of 10 min with methane flow rate of 120 sccm.

Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures.

Improved quality of graphene in the absence of hydrogen in a low-temperature growth process using an alcohol precursor

We present the results of low-temperature growth of graphene on polycrystalline copper foil surfaces at 800 °C by using low-pressure chemical-vapor deposition of alcohol precursors. The structural quality of the graphene sample was found to depend significantly on the ambient conditions during the annealing and the growth processes. The improved quality of graphene grown in an oxidizing environment was found to be associated with a lower nucleation density, suggesting that chemisorbed oxygen atoms play a critical role in determining the quality of graphene.

Low-temperature growth of graphene on iron substrate by molecular beam epitaxy

Graphene has attracted a great deal of interest due to its fascinating properties and a wide variety of potential applications. Several methods have been used to achieve high-quality graphene films on different substrates. However, there have been only a few studies on graphene growth on iron (Fe) and the growth mechanism remains unclear. This paper systematically investigates temperature-dependent growth of graphene on Fe substrate by gas-source molecular beam epitaxy. Two-dimensional (2D), large-area graphene samples were grown on Fe thin films, and characterized by Raman, X-ray photoelectron spectroscopy, X-ray diffraction, optical microscopy, transmission electron microscopy and atomic force microscopy. It is found that graphene flakes can be grown on Fe at a growth temperature as low as 400°C and the optimized large-area graphene growth temperature is relatively low between 500°C and 550°C. The graphene growth on Fe that undergoes the formation and decomposition of iron carbide is discussed.

Low temperature growth of graphene using inductively-coupled plasma chemical vapor deposition

Abstract This paper investigates the effect of processing parameters on the growth of graphene at a temperature of 300 °C using an inductively-coupled plasma chemical vapor deposition system. Graphene films were grown on Cu films under CH4/H2/Ar plasma and then subsequently transferred to different substrates. The effects of the plasma power, deposition time and CH4 flow rate on the characteristics of the graphene films were systematically investigated. The results show that AB-stacked bilayer graphene films can be grown at low flow rates of CH4 and low plasma powers for depositions as short as 10 s. The bilayer graphene films exhibited surface enhanced Raman scattering effects and enabled detection of a reporter molecule presenting an example application. Low temperature growth at short processing times may enable realization of the potential uses of graphene in a wide range of applications at practical costs with relaxed constraints on the materials and processes associated with high temperatures.

Matrix assisted low temperature growth of graphene

Single layer graphene has been successfully grown via chemical vapour deposition (CVD) at low temperature by using chlorobenzene trapped in a PMMA polymer matrix as the carbon source. By varying the carbon source temperature, we are able to vary the dominant carbon source from just chlorobenzene to PMMA. Raman spectroscopy and atomic force microscopy (AFM) have been used to characterize the as-grown graphene layer, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to characterize film quality and growth dynamics. Lower source temperatures (corresponding to a chlorobenzene carbon source) result in high quality single layer graphene whereas higher source temperatures (PMMA carbon source) produce disordered multilayered graphene films. SEM imaging reveals that a preferential surface mediated edge growth mechanism for single layer graphene is observed as a function of growth time. This development offers a new methodology for graphene synthesis at low temperatures with implications for the development of printed graphene structures.

Low-temperature growth of graphene using interfacial catalysis of molten gallium and diluted methane chemical vapor deposition

Although the formation of graphene nuclei conventionally requires high temperature of ∼1050 °C in the first growth stage, the presence of the graphene nuclei allowed for low-temperature edge growth, and this peripheral area continued growing even when the temperature was reduced to 300 °C in the second growth stage. The graphene grown at the second stage was a single layer with fewer defects. The Raman map showed high homogeneity with a 2D/G ratio >2 over the entire contact area of molten gallium, and the hole mobility was 600 cm2 V−1 s−1.