scholarly journals Effect of the External Velocity on the Exfoliation Properties of Graphene from Amorphous SiO2 Surface

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 454
Author(s):  
Qi Zhang ◽  
Xing Pang ◽  
Yulong Zhao
Keyword(s):  
External Action ◽  
Atomic Scale ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Amorphous Sio2 ◽  
Sio2 Substrate ◽  
Graphene Layers ◽  
Upward Velocity ◽  
Topmost Layer ◽  
Critical Velocities

External action has a significant influence on the formation of high-quality graphene and the adhesion of graphene on the surface of the MEMS/NEMS device. The atomic-scale simulation and calculation can further study the exfoliation process of graphene by external actions. In multilayer graphene systems where graphene layers were simulated weakly contacted with SiO2 substrate, a constant vertical upward velocity (Vup) was applied to the topmost layer. Then two critical velocities were found, and three kinds of distinct exfoliation processes determined by critical upward velocities were observed in multilayer graphene systems. The first critical velocities are in the range of 0.5 Å/ps–3.18 Å/ps, and the second critical velocities are in the range of 9.5 Å/ps–12.1 Å/ps. When the Vup is less than the first critical velocity, all graphene layers will not be exfoliated. When Vup is between the first and second critical Vup, all layers can be exfoliated almost synchronously at last. When Vup is larger than the second critical Vup, the topmost layer can be exfoliated alone, transferring energy to the underlying layers, and the underlying layers are slowly exfoliated. The maximum exfoliation force to exfoliate the topmost layer of graphene is 3200 times larger than that of all graphene layers. Moreover, it is required 149.26 mJ/m2 to get monolayer graphene from multilayers, while peeling off all layers without effort. This study explains the difficulty to get monolayer graphene and why graphene falls off easily during the transfer process.

scholarly journals Estimation of Number of Graphene Layers Using Different Methods: A Focused Review

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4590
Author(s):  
Vineet Kumar ◽  
Anuj Kumar ◽  
Dong-Joo Lee ◽  
Sang-Shin Park
Keyword(s):  
Electron Microscopy ◽  
Raman Spectra ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Characterization Methods ◽  
Graphene Layers ◽  
Force Microscopy ◽  
Stacking Order ◽  
Transmission Electron ◽  
Few Layer Graphene

Graphene, a two-dimensional nanosheet, is composed of carbon species (sp2 hybridized carbon atoms) and is the center of attention for researchers due to its extraordinary physicochemical (e.g., optical transparency, electrical, thermal conductivity, and mechanical) properties. Graphene can be synthesized using top-down or bottom-up approaches and is used in the electronics and medical (e.g., drug delivery, tissue engineering, biosensors) fields as well as in photovoltaic systems. However, the mass production of graphene and the means of transferring monolayer graphene for commercial purposes are still under investigation. When graphene layers are stacked as flakes, they have substantial impacts on the properties of graphene-based materials, and the layering of graphene obtained using different approaches varies. The determination of number of graphene layers is very important since the properties exhibited by monolayer graphene decrease as the number of graphene layer per flake increases to 5 as few-layer graphene, 10 as multilayer graphene, and more than 10 layers, when it behaves like bulk graphite. Thus, this review summarizes graphene developments and production. In addition, the efficacies of determining the number of graphene layers using various characterization methods (e.g., transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and mapping, and spin hall effect-based methods) are compared. Among these methods, TEM and Raman spectra were found to be most promising to determine number of graphene layers and their stacking order.

scholarly journals Growth Phase Diagram of Graphene Grown Through Chemical Vapor Deposition on Copper

NANO ◽  
2020 ◽  
Vol 15 (10) ◽  
pp. 2050137 ◽  
Author(s):  
Qinke Wu ◽  
Sangjun Jeon ◽  
Young Jae Song
Keyword(s):  
Electron Microscopy ◽  
Phase Diagram ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Copper Surface ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Graphene Growth ◽  
Graphene Layers

The phase diagram for graphene growth was obtained to understand the physics of the growth mechanism and control the layer number or coverage of graphene deposited on copper via low-pressure chemical vapor deposition (LPCVD). Management of the number of graphene layers and vacancies is essential for producing defect-free monolayer graphene and engineering multilayered functionalized graphene. In this work, the effects of the CH4 and H2 flow rates were investigated to establish the phase diagram for graphene growth. Using this phase diagram, we selectively obtained fully covered and partially grown monolayer graphene, graphene islands through Volmer–Weber growth, and multilayer graphene through Stranski–Krastanov-like growth. The layer numbers and coverage were determined using optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. The growth modes were determined by the competition between catalytic growth with CH4 and catalytic etching with H2 on the copper surface during CVD growth. Intriguingly, this phase diagram showed that multilayer graphene flakes can be grown via LPCVD even with low CH4 and H2 flows.

scholarly journals Adhesion Behavior between Multilayer Graphene and Semiconductor Substrates

2018 ◽  
Vol 8 (11) ◽  
pp. 2107 ◽  
Author(s):  
Qi Zhang ◽  
Xin Ma ◽  
Yulong Zhao
Keyword(s):  
Critical Velocity ◽  
Bonding Strength ◽  
Energy Levels ◽  
Mechanical Systems ◽  
Semiconductor Surface ◽  
Multilayer Graphene ◽  
Adhesion Forces ◽  
Micro Electro Mechanical Systems ◽  
Graphene Layers ◽  
Topmost Layer

A high bonding strength between graphene and a semiconductor surface is significant to the performance of graphene-based Micro-Electro Mechanical Systems/Nano-Electro Mechanical Systems (MEMS/NEMS) devices. In this paper, by applying a series of constant vertical upward velocities (Vup) to the topmost layer of graphene, the exfoliation processes of multilayer graphene (one to ten layers) from an Si semiconductor substrate were simulated using the molecular dynamics method, and the bonding strength was calculated. The critical exfoliation velocities, adhesion forces, and adhesion energies to exfoliate graphene were obtained. In a system where the number of graphene layers is two or three, there are two critical exfoliation velocities. Graphene cannot be exfoliated when the Vup is lower than the first critical velocity, although the total number of graphene layers can be exfoliated when the Vup is in the range between the first critical velocity and second critical velocity. Only the topmost layer can be exfoliated to be free from the Si surface if the applied Vup is greater than the second critical velocity. In systems where the number of graphene layers is four to ten, only the topmost layer can be free and exfoliated if the exfoliation velocity is greater than the critical velocity. It was found that a relatively low applied Vup resulted in entire graphene layers peeling off from the substrate. The adhesion forces of one-layer to ten-layer graphene systems were in the range of 25.04 nN–74.75 nN, and the adhesion energy levels were in the range of 73.5 mJ/m2–188.45 mJ/m2. These values are consistent with previous experimental results, indicating a reliable bond strength between graphene and Si semiconductor surfaces.

Vibrational Analysis of a Single-Layered Nanoporous Graphene Membrane

NANO ◽  
2016 ◽  
Vol 11 (04) ◽  
pp. 1650043 ◽  
Author(s):  
Haw-Long Lee ◽  
Win-Jin Chang
Keyword(s):  
Boundary Conditions ◽  
Vibrational Analysis ◽  
Atomic Scale ◽  
Good Correspondence ◽  
Graphene Layers ◽  
Simply Supported ◽  
Vibrational Behavior ◽  
Fundamental Frequencies ◽  
Nanoporous Graphene ◽  
New Applications

In this study, we use the atomic-scale finite element method to investigate the vibrational behavior of the armchair- and zigzag-structured nanoporous graphene layers with simply supported-free-simply supported-free (SFSF) and clamped-free-free-free (CFFF) boundary conditions. The fundamental frequencies computed for the graphene layers without pores are compared with the results of previous studies. We observe very good correspondence of our results with that of the other studies in all the considered cases. For the armchair- and zigzag-structured nanoporous graphenes with SFSF and CFFF boundary conditions, the frequencies decrease with increasing porosity. When the positions of the pores are symmetric with respect to the center of the graphene, the frequency of the zigzag nanoporous graphene is higher than that of the armchair one. To the best of our knowledge, this is first study investigating the relation between the vibrational behavior and porosity of nanoporous graphene layers, which is essential for tuning the material/structural design and exploring new applications for nanoporous graphenes.

scholarly journals A Comparative Study of the ZnO Growth on Graphene and Graphene Oxide: The Role of the Initial Oxidation State of Carbon

2020 ◽  
Vol 6 (2) ◽  
pp. 41
Author(s):  
Miguel Angel Gomez-Alvarez ◽  
Carlos Morales ◽  
Javier Méndez ◽  
Adolfo del Campo ◽  
Fernando J. Urbanos ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Oxidation State ◽  
Atomic Ratio ◽  
Quasi Equilibrium ◽  
Initial Oxidation ◽  
Sio2 Substrate ◽  
Graphene Layers ◽  
Stages Of Growth ◽  
Early Stages

The role of the oxidation state of carbon on the early stages of growth of metal oxides was studied for the particular case of ZnO deposition on graphene and graphene oxide on SiO2 (G/SiO2 and GO/SiO2, respectively) substrates. The growth was carried out by thermal evaporation of metallic Zn under an oxygen atmosphere at room temperature. This technique permits quasi-equilibrium conditions during the oxide growth, allowing the characterization of the fundamental interaction between ZnO and the graphene-based substrates. Although in both cases ZnO follows a Volmer–Weber growth mode controlled by nucleation at defects, the details are different. In the case of the GO/SiO2 substrate, the nucleation process acts as a bottleneck, limiting the coverage of the complete surface and allowing the growth of very large ZnO structures in comparison to G/SiO2. Moreover, by studying the Zn-LMM Auger spectra, it is shown how the initial nature of the substrate influences the composition of the ZnO deposit during the very early stages of growth in terms of Zn/O atomic ratio. These results are compared to those previously reported regarding ZnO growth on graphite and graphene on Cu (G/Cu). This comparison allows us to understand the role of different characteristics of graphene-based substrates in terms of number of defects, oxidation state, graphene support substrate and number of graphene layers.

Simulation of the thermomechanical behavior of graphene/PMMA nanocomposites via continuum mechanics

2019 ◽  
Vol 11 (5) ◽  
pp. 655-669
Author(s):  
Androniki Tsiamaki ◽  
Nicolaos Anifantis
Keyword(s):  
Mechanical Properties ◽  
Accurate Method ◽  
Thermomechanical Properties ◽  
Van Der Waals Interactions ◽  
Monolayer Graphene ◽  
Graphene Sheets ◽  
Temperature Dependent ◽  
Content Type ◽  
Graphene Layers ◽  
Derived Properties

Purpose The purpose of this paper is to simulate and investigate the thermomechanical properties of graphene-reinforced nanocomposites. Design/methodology/approach The analysis proposed consists of two stages. In the first stage, the temperature-dependent mechanical properties of graphene are estimated while in the second stage, using the previously derived properties, the temperature-dependent properties of graphene-reinforced PMMA nanocomposites are investigated. In the first stage of the analysis, graphene is modeled discretely using molecular mechanics theory where the interatomic interactions are simulated by spring elements of temperature-dependent stiffness. The graphene sheets are composed of either one or more (up to five) monolayer graphene sheets connected via van der Waals interactions. However, in the second analysis stage, graphene is modeled equivalently as continuum medium and is positioned between two layers of PMMA. Also, the interphase between two materials is modeled as a medium with mechanical properties defined and bounded by the two materials. Findings The mechanical properties including Young’s modulus, shear modulus and Poisson’s ratio due to temperature changes are estimated. The numerical results show that the temperature rise and the multiplicity of graphene layers considered lead to a decrease of the mechanical properties. Originality/value The present analysis proposes an easy and accurate method for the estimation of the temperature-dependent mechanical properties of graphene-reinforced nanocomposites.

Plasmon spectrum of graphene monolayer on substrate

2019 ◽  
Vol 33 (09) ◽  
pp. 1950102
Author(s):  
I. N. Askerzade ◽  
R. T. Askerbeyli
Keyword(s):  
Substrate Material ◽  
Plasmon Mode ◽  
Monolayer Graphene ◽  
Graphene Monolayer ◽  
Multilayer Graphene ◽  
Linear Dispersion ◽  
Long Wavelength ◽  
Theoretical Considerations ◽  
Plasmon Spectrum ◽  
Good Agreement

Plasmon modes in monolayer graphene on substrate are analyzed taking into account the thickness of graphene and substrate material layer in the evaluation of Coulomb potential. It is shown that plasmon mode in graphene monolayer has linear dispersion in contrast to multilayer graphene in long-wavelength limit. The slope of plasmon spectrum is determined by the thickness and dielectric constant of substrate. Obtained results are in good agreement with experimental data and other theoretical considerations.

scholarly journals Investigating the Integrity of Graphene towards the Electrochemical Hydrogen Evolution Reaction (HER)

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Alejandro García-Miranda Ferrari ◽  
Dale A. C. Brownson ◽  
Craig E. Banks
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Plane Surface ◽  
Linear Sweep Voltammetry ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Linear Sweep ◽  
Electrochemical Reversibility ◽  
Physicochemical Characterisation ◽  
Few Layer Graphene

Abstract Mono-, few-, and multilayer graphene is explored towards the electrochemical Hydrogen Evolution Reaction (HER). Careful physicochemical characterisation is undertaken during electrochemical perturbation revealing that the integrity of graphene is structurally compromised. Electrochemical perturbation, in the form of electrochemical potential scanning (linear sweep voltammetry), as induced when exploring the HER using monolayer graphene, creates defects upon the basal plane surface that increases the coverage of edge plane sites/defects resulting in an increase in the electrochemical reversibility of the HER process. This process of improved HER performance occurs up to a threshold, where substantial break-up of the basal sheet occurs, after which the electrochemical response decreases; this is due to the destruction of the sheet integrity and lack of electrical conductive pathways. Importantly, the severity of these changes is structurally dependent on the graphene variant utilised. This work indicates that multilayer graphene has more potential as an electrochemical platform for the HER, rather than that of mono- and few-layer graphene. There is huge potential for this knowledge to be usefully exploited within the energy sector and beyond.

Multilayer Graphene-Based Carbon Interconnect

2012 ◽  
Vol 1407 ◽  
Author(s):  
Tianhua Yu ◽  
Edwin Kim ◽  
Nikhil Jain ◽  
Bin Yu
Keyword(s):  
Performance Metrics ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Large Area ◽  
Electrical Stress ◽  
Oxygen Plasma Etching ◽  
Doping Technique ◽  
System Breakdown ◽  
Grown Graphene ◽  
On Chip

ABSTRACT3D stacked (or uncorrelated) multilayer graphene (s-MLG) is investigated as a potential material platform for carbon-based on-chip interconnects. S-MLG samples are prepared by repeatedly transferring and stacking the large-area CVD-grown graphene monolayers, followed by wire patterning and oxygen plasma etching of graphene. We observed superior wire conduction of s-MLG over that of monolayer graphene or ABAB-stacked multilayer graphene. Further reduction of s-MLG resistivity is anticipated with increasing number of stacked layers. Electrical stress-induced doping technique is used to engineer the Dirac point, as well as to reduce graphene-to-metal contact resistance, improving the overall performance metrics of the s-MLG system. Breakdown experiments show that the current-carrying capacity of s-MLG is significantly enhanced as compared with that of monolayer graphene.

scholarly journals Imaging of local structures affecting electrical transport properties of large graphene sheets by lock-in thermography

2019 ◽  
Vol 5 (2) ◽  
pp. eaau3407 ◽  
Author(s):  
H. Nakajima ◽  
T. Morimoto ◽  
Y. Okigawa ◽  
T. Yamada ◽  
Y. Ikuta ◽  
...  
Keyword(s):  
Transport Properties ◽  
Electrical Transport ◽  
Chemical Vapor ◽  
Atomic Scale ◽  
Electrical Transport Properties ◽  
Large Area ◽  
Graphene Layers ◽  
Device Applications ◽  
Chemical Vapor Deposition Graphene ◽  
Lock In

The distribution of defects and dislocations in graphene layers has become a very important concern with regard to the electrical and electronic transport properties of device applications. Although several experiments have shown the influence of defects on the electrical properties of graphene, these studies were limited to measuring microscopic areas because of their long measurement times. Here, we successfully imaged various local defects in a large area of chemical vapor deposition graphene within a reasonable amount of time by using lock-in thermography (LIT). The differences in electrical resistance caused by the micrometer-scale defects, such as cracks and wrinkles, and atomic-scale domain boundaries were apparent as nonuniform Joule heating on polycrystalline and epitaxially grown graphene. The present results indicate that LIT can serve as a fast and effective method of evaluating the quality and uniformity of large graphene films for device applications.

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