Graphene Growth Research Articles

Self‐Assembly Growth of Twisted Bilayer Graphene on Liquid Cu

AbstractTwisted bilayer graphene (tBLG) possesses various novel physical properties. Most of tBLG are fabricated by using artificial methods of stacking or folding single‐layer graphene. Chemical vapor deposition (CVD) has been verified that it holds great potential for preparation of large‐size high‐quality graphene. Therefore, it is significant for preparing tBLG in situ by using CVD technology. In this work, a novel approach is developed to directly prepare tBLGs on liquid Cu substrate. When the growth temperature exceeds a certain critical value, the state of aligned high‐quality single‐layer graphene domains grown on liquid Cu will be broken. Then, tBLG with twisted double‐layer regions is prepared in situ by rotating and intercalating between graphene domains. Experimental observations suggest that the liquid phase of Cu substrate and gas flow play a crucial role for the formation of tBLGs. These results demonstrate that the liquid Cu is an ideal potential substrate for preparing tBLGs with a full range of twisted angles and studying the formation mechanism of layer‐stacked materials.

Study of solid carbon source-based graphene growth directly on SiO2 substrate with Cu or Cu/Ni as the sacrificial catalysts

Study of solid carbon source-based graphene growth directly on SiO2 substrate with Cu or Cu/Ni as the sacrificial catalysts

Chemical Vapor Deposition of Graphene on Self-Limited SiC Interfacial Layers Formed on Silicon Substrates for Heterojunction Devices

Direct chemical vapor deposition (CVD) of graphene on any desired substrate is always required to manufacture high-quality heterojunctions with excellent interfacial properties. Herein, the growth of graphene on cubic-silicon carbide (3C-SiC) surfaces using conventional high-temperature direct thermal CVD and plasma-enhanced CVD (PECVD) is explored, which is hardly reported to date. Since 3C-SiC substrates are not available, the controlled self-limited 3C-SiC layers on the Si(100) substrates were grown at different temperatures (900–1200 °C) via thermal-CVD technique to obtain virtual 3C-SiC substrates. The direct production of graphene via thermal CVD could not be achieved on such 3C-SiC surfaces. The density functional theory and molecular dynamics simulations confirm that the carbon atom diffusion over the 3C-SiC surface is extremely low, like over the Si surface, which leads to no graphene growth. A similar growth mechanism may be attributed to their similar crystal structure viz diamond cubic for Si and zinc blend for 3C-SiC. However, graphene nanowalls (GNWs) were successfully grown on both Si and 3C-SiC/Si surfaces at 700 °C via the PECVD technique, where similar surface morphologies were observed because the growth mechanism of GNWs is independent of substrate type. Moreover, I–V characterization was performed for different SiC/Si heterostructures and their corresponding GNWs/SiC/Si heterostructures, respectively. The current conduction improved considerably more for GNW/SiC/Si heterostructures as compared to SiC/Si heterostructures, but the creation of a SiC interfacial layer as well as its quality affected the conductivity of GNWs/SiC/Si heterostructures. The inevitable formation of an interfacial SiC layer during the direct graphene growth via thermal CVD on Si substrates can seriously affect the performance of graphene/Si heterojunction devices. Hence, PECVD growth of graphene is an ideal option to fabricate graphene/Si heterojunction devices with excellent interfacial properties or graphene/3C-SiC/Si heterojunction devices for various electronic/optoelectronic applications such as gas sensors and photovoltaic devices.

Transfer-Free CVD Growth of High-Quality Wafer-Scale Graphene at 300 °C for Device Mass Fabrication.

Direct chemical vapor deposition of graphene on semiconductors and insulators provides high feasibility for integration of graphene devices and semiconductor electronics. However, the current methods typically rely on high temperatures (>1000 °C), which can damage the substrates. Here, a growth method for high-quality large-area graphene at 300 °C is introduced. A multizone furnace with gradient temperature control was designed according to a computational fluid dynamics model. The crucial roles of the chamber pressure in the film continuity and hydrogen composition in the graphene defect density at low temperature were revealed. As a result, a uniform graphene film with the Raman ratio ID/IG = 0.08 was obtained. Furthermore, a technique of laminating single-crystal Cu foil as a sacrificial layer on the substrate was proposed to realize transfer-free growth, and a wafer-scale graphene transistor array was demonstrated with good performance consistency, which paves the way for mass fabrication of graphene devices.

Graphene at Liquid Copper Catalysts: Atomic-Scale Agreement of Experimental and First-Principles Adsorption Height.

Liquid metal catalysts have recently attracted attention for synthesizing high-quality 2D materials facilitated via the catalysts' perfectly smooth surface. However, the microscopic catalytic processes occurring at the surface are still largely unclear because liquid metals escape the accessibility of traditional experimental and computational surface science approaches. Hence, numerous controversies are found regarding different applications, with graphene (Gr) growth on liquid copper (Cu) as a prominent prototype. In this work, novel in situ and in silico techniques are employed to achieve an atomic-level characterization of the graphene adsorption height above liquid Cu, reaching quantitative agreement within 0.1 Å between experiment and theory. The results are obtained via in situ synchrotron X-ray reflectivity (XRR) measurements over wide-range q-vectors and large-scale molecular dynamics simulations based on efficient machine-learning (ML) potentials trained to first-principles density functional theory (DFT) data. The computational insight is demonstrated to be robust against inherent DFT errors and reveals the nature of graphene binding to be highly comparable at liquid Cu and solid Cu(111). Transporting the predictive first-principles quality via ML potentials to the scales required for liquid metal catalysis thus provides a powerful approach to reach microscopic understanding, analogous to the established computational approaches for catalysis at solid surfaces.

Transfer-Free Quasi-Suspended Graphene Grown on a Si Wafer.

The direct growth of graphene affording wafer-scale uniformity on insulators is paramount to electronic and optoelectronic applications; however, it remains a challenge to date, because it entails an entirely different growth mode than that over metals. Herein, the metal-catalyst-free growth of quasi-suspended graphene on a Si wafer is demonstrated using an interface-decoupling chemical vapor deposition strategy. The employment of lower-than-conventional H2 dosage and concurrent introduction of methanol during growth can effectively weaken the interaction between the synthesized graphene and the underlying substrate. The growth mode can be thus fine-tuned, producing a predominantly monolayer graphene film with wafer-level homogeneity. Graphene thus grown on a 4 inch Si wafer enables the transfer-free fabrication of high-performance graphene-based field-effect transistor arrays that exhibit almost no shift in the charge neutral point, indicating a quasi-suspended feature of the graphene. Moreover, a carrier mobility up to 15 000 cm2 V-1 s-1 can be attained. This study is anticipated to offer meaningful insights into the synthesis of wafer-scale high-quality graphene on dielectrics for practical graphene devices.

Using polycyclic aromatic hydrocarbons for graphene growth on Cu(111) under ultra-high vacuum

Ultra-high vacuum deposition of the polycyclic aromatic hydrocarbons azupyrene and pyrene onto a Cu(111) surface held at a temperature of 1000 K is herein shown to result in the formation of graphene. The presence of graphene was proven using scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, Raman spectroscopy, and low energy electron diffraction. The precursors, azupyrene and pyrene, are comparatively large aromatic molecules in contrast to more commonly employed precursors like methane or ethylene. While the formation of the hexagonal graphene lattice could naively be expected when pyrene is used as a precursor, the situation is more complex for azupyrene. In this case, the non-alternant topology of azupyrene with only 5- and 7-membered rings must be altered to form the observed hexagonal graphene lattice. Such a rearrangement, converting a non-alternant topology into an alternant one, is in line with previous reports describing similar topological alterations, including the isomerization of molecular azupyrene to pyrene. The thermal synthesis route to graphene, presented here, is achievable at comparatively low temperatures and under ultra-high vacuum conditions, which may enable further investigations of the growth process in a strictly controlled and clean environment that is not accessible with traditional precursors.

Fast spatially resolved optical characterization of multi-layer CVD graphene

A new quantitative and spatially resolved optical method was developed to quickly analyze the spatial distribution of multilayer graphene grown on large flat substrates, i.e., on one or more 4″ Si wafers. An image processing analysis shows that the background-corrected reflection image of graphene on the flat substrate can be normalized so that the highest image intensity is related to the thinnest or absent layer of graphene. Which of these two most typical cases is in effect for a given sample can be easily determined by a calibration wafer using laser Raman spectroscopy 2D/G peak intensity ratio. We show that the spatial distribution of multilayer graphene can be determined by relating reflected light intensity from an intensity-calibrated reflection image to the layer numbers of a local graphene film. By dividing the greyscale reflection intensity into bins, the spatial multilayer graphene distribution can be visualized with a false-colored contour plot where each graphene layer quantity is represented by a unique color for easy visualization of their spatial distribution regions. The spatial distribution over extended spatial regions of multilayer graphene grown on a flat substrate, for example, a Ni or Cu films on a 4ʺ Si or Ge wafer, can quickly be analyzed and visualized through this non-destructive characterization method by locally sampling and analyzing multiple regions of interest across a full spatially extended large substrate. Selected applications of this method are, for example, process uniformity and quality optimization for one or more large Si wafers grown in a single batch or different batches, as well as for fast and non-destructive automated multilayer graphene growth quality control methods.

Two-step method for growth of adlayer-free large-area monolayer graphene on Cu foil

Chemical vapor deposition is the most promising approach for synthesis of large-area monolayer graphene on Cu foil. However, numerous factors can result in formation of adlayers, such as the morphology of the Cu foil, methane concentration, and growth temperature. Here, we report atmospheric pressure chemical vapor deposition growth of large-area adlayer-free monolayer graphene by the two-step ‘bottom-up-etching’ method. The experimental results showed that a temperature increase in the second step can dramatically accelerate etching of the bottom graphene layer. A growth model for adlayer-free monolayer graphene on Cu foil is proposed.

Evolution of copper step beams during graphene growth by CVD method

Cu step beams (CSBs) are common products obtained when growing graphene by chemical vapor deposition (CVD), which markedly affects the quality of graphene. Although considerable progress has been made in the preparation of large-area graphene on Cu, the growth behavior of CSBs has not been fully understood. This study investigated the main factors influencing the CSBs caused by thermal stress between graphene and Cu foil. The results showed that the copper crystal orientation, number of graphene layers, and surface undulation of the Cu foil influence the morphology of CSBs. It was found that Cu foils with high-index surfaces are more prone to form distinct CSBs, with more than a 50% increase in roughness average (Ra). The orientation of CSBs is closely related to the Cu crystal orientation. Bilayer graphene and trilayer graphene were found to cause deeper and wider CSBs than single-layer graphene, while its Ra increased significantly to about twice that of single-layer graphene. The thermal stress between graphene and Cu foil was studied through Raman spectral analysis. It was confirmed that CSBs are products resulting from the thermal stress released between grown graphene and Cu foil. This study offers new insights for high-quality graphene growth.

Impact of Polymer-Assisted Epitaxial Graphene Growth on Various Types of SiC Substrates.

The growth parameters for epitaxial growth of graphene on silicon carbide (SiC) have been the focus of research over the past few years. However, besides the standard growth parameters, the influence of the substrate pretreatment and properties of the underlying SiC wafer are critical parameters for optimizing the quality of monolayer graphene on SiC. In this systematic study, we show how the surface properties and the pretreatment determine the quality of monolayer graphene using polymer-assisted sublimation growth (PASG) on SiC. Using the spin-on deposition technique of PASG, several polymer concentrations have been investigated to understand the influence of the polymer content on the final monolayer coverage using wafers of different miscut angles and different polytypes. Confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), Raman spectroscopy, and scanning electron microscopy (SEM) were used to characterize these films. The results show that, even for SiC substrates with high miscut angles, high-quality graphene is obtained when an appropriate polymer concentration is applied. This is in excellent agreement with the model understanding that an insufficient carbon supply from SiC step edge decomposition can be compensated by additionally providing carbon from a polymer source. The described methods make the PASG spin-on deposition technique more convenient for commercial use.

Application of Grazing-Incidence X-ray Methods to Study Terrace-Stepped SiC Surface for Graphene Growth.

The synthesis of graphene by the graphitization of SiC surface has been driven by a need to develop a way to produce graphene in large quantities. With the increased use of thermal treatments of commercial SiC substrates, a comprehension of the surface restructuring due to the formation of a terrace-stepped nanorelief is becoming a pressing challenge. The aim of this paper is to evaluate the utility of X-ray reflectometry and grazing-incidence off-specular scattering for a non-destructive estimate of depth-graded and lateral inhomogeneities on SiC wafers annealed in a vacuum at a temperature of 1400-1500 °C. It is shown that the grazing-incidence X-ray method is a powerful tool for the assessment of statistical parameters, such as effective roughness height, average terrace period and dispersion. Moreover, these methods are advantageous to local probe techniques because a broad range of spatial frequencies allows for faster inspection of the whole surface area. We have found that power spectral density functions and in-depth density profiles manifest themselves differently between the probing directions along and across a terrace edge. Finally, the X-ray scattering data demonstrate quantitative agreement with the results of atomic force microscopy.

Growth and Properties of Graphene and Graphene Nanoribbons on Ge

The synthesis of graphene directly on Ge and on Ge deposited on Si provides a scalable route toward integrating graphene onto conventional semiconductors. This presentation will first survey the growth modes of graphene on Ge(001), Ge(011), Ge(111), Ge(112), Ge(001)-6°, and Ge(001)-9° via chemical vapor deposition (CVD), reporting on the effect of Ge surface orientation on graphene island formation and shape, strain in large-area graphene films, and the nanofaceting of the Ge below graphene.[1] We will then focus on the anisotropic growth of semiconducting graphene nanoribbons on Ge(001) and Ge(001)-9° and of nominally single crystal graphene on Ge(110).On Ge(001), we have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics.[2-6] This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are self-orienting, self-defining, and have smooth edges. The ribbons exhibit excellent transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms.On Ge(001), nominally single crystal graphene has been reported in limited cases; however, conflicting studies have evidenced polycrystallinity. Here, the factors affecting the mosaicity of graphene on Ge(110) will be elucidated using low energy electron diffraction and microscopy data.[7][1] R. M. Jacobberger, D. E. Savage, X. Zheng, P. Sookchoo, R. R. Delgado, M. G. Lagally, M. S. Arnold, SUBMITTED (2022).[2] R. M. Jacobberger, M. S. Arnold, et al., Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015).[3] B. Kiraly, M. S. Arnold, M. C. Hersam, N. P. Guisinger et al., Sub-5 nm, Globally Aligned Graphene Nanoribbons on Ge (001), APPLIED PHYSICS LETTERS, 108, 213101 (2016).[4] 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 (2018).[5] V. Saraswat, Y. Yamamoto, H.J. Kim, R.M. Jacobberger, K.R. Jinkins, A.J. Way, N.P. Guisinger, M.S. Arnold Synthesis of armchair graphene nanoribbons on germanium-on-silicon, THE JOURNAL OF PHYSICAL CHEMISTRY C 123 (30), 18445-18454 (2019).[6] A. J. Way, R. M. Jacobberger, N. P. Guisinger, V. Saraswat, X. Zheng, A. Suresh, J. H. Dwyer, P. Gopalan, Michael S. Arnold, SUBMITTED (2022).[7] R. M. Jacobberger, Z. Miao, T. Yu, V. Saraswat, M. G. Lagally, M. S. Altman, M. S. Arnold, SUBMITTED (2022).

High Quality Ge Growth on Si (111) and Si (110) by Using Reduced Pressure Chemical Vapor Deposition

Heteroepitaxial growth of Ge on Si has great interest for various optoelectronic applications such as Ge photodiodes(1). However 4.2% of lattice mismatch causes dislocation formation and island growth. High quality Ge(001) growth techniques are reported in ref.(2-4). Moreover, Ge(111) surface is also interesting because of higher carrier mobility(5). Furthermore, Ge(110) is preferred orientation of virtual substrates for epitaxial graphene growth(6). In the case of the Ge deposition on Si(111) and Si(110) substrates, it seems that the process conditions used for Ge growth on Si(001) are not suitable to realize high crystallinity and smooth surface (7). In this paper, we present a method of high quality and smooth Ge layer growth on Si(111) and Si(110), which is the same level as the Ge growth on Si(001).Epitaxial growth of Ge on Si(111) and Si(110) is carried out using a reduced pressure chemical vapor deposition system. After HF last clean, a wafer is baked at 1000°C and cooled down to 600°C in H2 and further to 300-550°C in N2 to form a hydrogen-free Si surface. Then a 100 nm thick Ge layer is deposited as a seed layer using GeH4 with N2 carrier gas. Afterward the wafer is heated up to 450-650°C in H2 and the main part of Ge is deposited using a H2-GeH4 gas mixture. For threading dislocation density (TDD) reduction, annealing at 800°C in H2 is performed for several times (cyclic annealing) by interrupting the Ge growth. Atomic-force microscopy (AFM) is used for surface roughness analysis. Scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) are used for structural characterization of the Ge layer. Secco defect etching combined with angle view scanning electron microscopy (SEM) or optical microscope is used for TDD evaluation.Figure 1(a,b) summarize the root mean square (RMS) roughness of Ge(111) and Ge(110) seed layers grown at 300-550°C before and after postannealing at 600-800°C. If the growth temperature is lower than 350°C for Ge(111) and 400°C for Ge(110), a significant increase of the surface roughness is observed after postannealing at 700°C and 800°C, respectively. For both crystal orientations, the lowest RMS roughness is observed by depositing at 450°C for as deposited and postannealed samples. The maintained RMS roughness even after postannealing at 800oC may be indicating good crystal quality even at as deposited condition.To confirm the influence of the growth temperature on the crystallinity, cross section TEM images of the Ge(111) and the Ge(110) seed layers deposited at 300°C and 450°C are shown in Fig. 2(a-d). In the case of Ge growth at 300°C (Fig. 2(a,b)), a very high density of stacking faults (SF) and high surface roughness are observed for both crystal orientations. In contrast, by depositing at 450°C (Fig. 2(c,d)), lower SF density in the Ge layer is observed compared to that at 300°C. By postannealing, an improvement of crystallinity is observed for the Ge seed layers deposited at 450°C. However, in the case of 300°C, the crystallinity cannot be improved by the postannealing, because a too high density of dislocations and SF may cause irregular Ge atom migration. As the result, surface roughening occurs.Figure 3(a,b) show AFM surface roughness images after 5 μm-thick Ge(111) and Ge(110) deposited with cyclic annealing at 800°C, respectively. Clear terraces of ~0.3 and ~0.2 nm, whose heights are close to those of Ge(111) bilayer and Ge(110) monolayer, are observed, respectively. RMS roughness of the Ge(111) and the Ge(110) are 0.51 and 0.35 nm, respectively. These RMS roughnesses are comparable to a level reported for Ge (001) in ref.(1).Figure 4 shows TDD of Ge(111) and Ge(110) surfaces as a function of the Ge thickness deposited with cyclic annealing on Si(111) and Si(110) substrates. For both orientations, TDD of ~4×108 cm-2 is obtained for 500 nm-thick samples. With increasing the Ge thickness, the TDD is reduced and levels below TDD of ~5×106 cm-2 are achieved for both Ge (111) and Ge(110) for 5 μm-thick Ge.These methods enable high quality virtual substrate fabrication not only for (001) surfaces but also for (111) and (110) orientation without a chemical mechanical polishing process. References Lischke et al. Nature Photonics15 (2021) 925Yamamoto et al. Solid-State Electron. 60 (2010) 2Yamamoto et al. Semicond. Sci. Technol. 33 (2018) 124007 M. Hartmann et al. J. Appl. Phys. 95 (2004) 5905 H. Lee et al. IEDM Tech. Digest (2009) 09-457J-H. Lee et al. Science 344 6181(2014) 286M. Hartmann et al. J. Cryst. Growth 310 (2008) 5287 Figure 1

Mechanism of crack propagation in penta-graphene

Penta graphene has attracted much attention due to its unique carbon atom topology and novel properties in these years. In this paper, we study the crack growth and material fracture mechanism of penta graphene under uniaxial tension systematically via molecular dynamics simulation. We explore the mechanism of stress field and influencing factors during crack growth on penta graphene. The mechanical properties of penta graphene and graphene are compared and analyzed. The effect of temperature on the mechanical properties of penta graphene is analyzed by comparing the strain-stress curves at various temperatures. The Young's modulus of penta graphene at fracture time are discussed, and we reveal that the temperature influence on Young's modulus before fracture. By designing initial cracks of different lengths on penta graphene, we investigate into the variation of stress field at both crack tips on penta graphene under stress stretching. The mechanism of crack growth and propagation on penta graphene is uncovered with more details from atomic perspective. It is found that the stress fields are concentrated on various parts on penta graphene with the different crack length. During the growth of short cracks, the stress field mainly concentrates on the crack tip during all the process. In the process of the growth of longer cracks, the stress field will first focus on the section of the crack, and then transfer to the crack tip and begin to grow and propagate around. By analyzing the reduced energy release rate during crack growth and fracture, it is suggested that the lower atomic binding energy weakens the fracture strength of penta graphene, and thus affects the mechanical properties of penta graphene.

Controlled growth of large-area monolayer graphene on Ni (110) facet: Insight from molecular dynamics simulation

To achieve the controlled synthesis of high-quality graphene/nickel heterostructure in practice, the study of the atomistic mechanism of graphene growth on the Ni (110) facet whose lattice mismatches with graphene is indispensable. A series of molecular dynamics simulations based on the modified interatomic force field were performed to provide an insightful understanding of the process of graphene growth by chemical vapor deposition. Herein, the dissolution and precipitation mechanism of graphene in the initial stage of growth on Ni (110) has been demonstrated, followed by the dynamic evolution of graphene growth was elucidated. The effects of carbon deposit rate and annealing temperature on graphene growth were investigated in-depth, and the optimum carbon deposit rate and temperature in theory for homogeneous monolayer graphene growth on Ni (110) facet were determined. Furthermore, two self-healing routes of defects of embedded C-chain and C-heptagon for high-temperature catalyzed were analyzed. Lastly, the relevance of the chemical vapor deposition technique was discussed in terms of the actual deposition process. The theoretical investigations and practical discussions can provide an instructive reference for optimizing chemical vapor deposition processing conditions in preparing homogeneous monolayer graphene on the Ni (110) facet.

Conversion of vertical-to-planar graphene by morphing of copper nanostructure during a moderate temperature plasma process

The plasma-enhanced chemical vapor deposition process enables the growth of graphene at a moderate temperature, but it is vertical graphene (VG) with a large number of defects. In this letter, we report a successful method to obtain planar graphene by morphing of Cu nanostructure during a modified Ar/CH4 plasma process at 600 °C. The insertion of meshed metal shields within the plasma region reduces the magnitude of ions bombardment on the substrate. In this circumstance, the evaporated Cu with a thickness of 200 nm on a black Si template is permitted to diffuse and form a planar film. The reduced plasma etching allows the growth of VG leaves and they are converted into planar multilayer graphene during the Cu morphing process. The crystal defect on planar graphene is minimum, where the values of Raman ID/IG and ID’/IG are 1.91 ± 0.06 and 0.20 ± 0.02, respectively.

Multilayer CVD graphene electrodes using a transfer-free process for the next generation of optically transparent and MRI-compatible neural interfaces.

Multimodal platforms combining electrical neural recording and stimulation, optogenetics, optical imaging, and magnetic resonance (MRI) imaging are emerging as a promising platform to enhance the depth of characterization in neuroscientific research. Electrically conductive, optically transparent, and MRI-compatible electrodes can optimally combine all modalities. Graphene as a suitable electrode candidate material can be grown via chemical vapor deposition (CVD) processes and sandwiched between transparent biocompatible polymers. However, due to the high graphene growth temperature (≥ 900 °C) and the presence of polymers, fabrication is commonly based on a manual transfer process of pre-grown graphene sheets, which causes reliability issues. In this paper, we present CVD-based multilayer graphene electrodes fabricated using a wafer-scale transfer-free process for use in optically transparent and MRI-compatible neural interfaces. Our fabricated electrodes feature very low impedances which are comparable to those of noble metal electrodes of the same size and geometry. They also exhibit the highest charge storage capacity (CSC) reported to date among all previously fabricated CVD graphene electrodes. Our graphene electrodes did not reveal any photo-induced artifact during 10-Hz light pulse illumination. Additionally, we show here, for the first time, that CVD graphene electrodes do not cause any image artifact in a 3T MRI scanner. These results demonstrate that multilayer graphene electrodes are excellent candidates for the next generation of neural interfaces and can substitute the standard conventional metal electrodes. Our fabricated graphene electrodes enable multimodal neural recording, electrical and optogenetic stimulation, while allowing for optical imaging, as well as, artifact-free MRI studies.

Preparation and Tribological Properties of Graphene-Based Coatings on Tungsten Carbide

The preparation technology of graphene-based coatings on cobalt-based cemented carbides and the friction properties of graphene-based coatings were researched. Based on cooling rate, growth temperature, and methane flow rate, Raman spectroscopy was used to evaluate the influence of chemical vapor deposition (CVD) on graphene-based coatings. The results show that at the growth temperature of 1000 °C, the cooling rate of 15 °C/min and methane flow rate of 10 sccm are more favorable for the growth of pure graphene coating with fewer layers on a cemented carbide surface. As methane flow boosts, the number of graphene layers increases and amorphous carbon is generated. The resulting tribological properties demonstrate that the friction coefficient of graphene-based coatings decreases as the friction load increases. The above results indicate that the graphene-based coating on a cemented carbide surface can be prepared by regulating its composition and defects through technological parameters, and it is viable to use graphene-based coating as anti-wear coating for cutting tools. The results provide a reference for the preparation and properties of cemented carbide surface graphene.

Carbon clusters on substrate surface for graphene growth- theoretical and experimental approach

Growth morphology of carbon clusters deposited on different substrates were investigated by theoretical and experimental approach. For theoretical approach, molecular dynamics was employed to evaluate an adsorptive stability of different size of carbon clusters placed on different substrates. The adsorptive stability was estimated by the difference of total energy of supercell designed as carbon cluster placed on a certain crystal plane of substrate. Among the simulations of this study, carbon cluster flatly settled down on the surface of SrTiO_{3}(001). The result was experimentally verified with layer by layer growth of graphene by pulsed laser deposition in carbon dioxide atmosphere. The absorptive stability can be useful reference for screening substrate for any target material other than graphene.