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6 pages, 195 KiB

Open AccessEditorial

Graphene Mechanics

by Qing Peng

Crystals 2019, 9(12), 636; https://doi.org/10.3390/cryst9120636 - 29 Nov 2019

Viewed by 2367

Abstract

Graphene might be one of the most important materials in human history [...] Full article

(This article belongs to the Special Issue Graphene Mechanics)

Research

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14 pages, 6483 KiB

Open AccessArticle

Graphene Adhesion Mechanics on Iron Substrates: Insight from Molecular Dynamic Simulations

by Lu Wang, Jianfeng Jin, Peijun Yang, Yaping Zong and Qing Peng

Crystals 2019, 9(11), 579; https://doi.org/10.3390/cryst9110579 - 6 Nov 2019

Cited by 17 | Viewed by 3953

Abstract

The adhesion feature of graphene on metal substrates is important in graphene synthesis, transfer and applications, as well as for graphene-reinforced metal matrix composites. We investigate the adhesion energy of graphene nanosheets (GNs) on iron substrate using molecular dynamic (MD) simulations. Two Fe–C [...] Read more.

The adhesion feature of graphene on metal substrates is important in graphene synthesis, transfer and applications, as well as for graphene-reinforced metal matrix composites. We investigate the adhesion energy of graphene nanosheets (GNs) on iron substrate using molecular dynamic (MD) simulations. Two Fe–C potentials are examined as Lennard–Jones (LJ) pair potential and embedded-atom method (EAM) potential. For LJ potential, the adhesion energies of monolayer GN are 0.47, 0.62, 0.70 and 0.74 J/m² on the iron {110}, {111}, {112} and {100} surfaces, respectively, compared to the values of 26.83, 24.87, 25.13 and 25.01 J/m² from EAM potential. When the number of GN layers increases from one to three, the adhesion energy from EAM potential increases. Such a trend is not captured by LJ potential. The iron {110} surface is the most adhesive surface for monolayer, bilayer and trilayer GNs from EAM potential. The results suggest that the LJ potential describes a weak bond of Fe–C, opposed to a hybrid chemical and strong bond from EAM potential. The average vertical distances between monolayer GN and four iron surfaces are 2.0–2.2 Å from LJ potential and 1.3–1.4 Å from EAM potential. These separations are nearly unchanged with an increasing number of layers. The ABA-stacked GN is likely to form on lower-index {110} and {100} surfaces, while the ABC-stacked GN is preferred on higher-index {111} surface. Our insights of the graphene adhesion mechanics might be beneficial in graphene growing, surface engineering and enhancement of iron using graphene sheets. Full article

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13 pages, 3101 KiB

Open AccessArticle

A Grain Boundary Regulates the Friction Behaviors between Graphene and a Gold Substrate

by Pinxuan He, Qiang Cao, Pengjie Wang, Huaipeng Wang, Shaolong Zheng, Shuting Lei, Sheng Liu and Qing Peng

Crystals 2019, 9(8), 418; https://doi.org/10.3390/cryst9080418 - 13 Aug 2019

Cited by 8 | Viewed by 4008

Abstract

The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of graphene by means of molecular [...] Read more.

The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of graphene by means of molecular dynamics simulations. We have systematically examined the coupling effects of the grain boundary with different mechanical pressures, velocities, temperatures, contact areas, and relative rotation angles on nanofriction. It is revealed that grain boundaries could reduce the friction between graphene and the gold substrate with a small deformation of the latter. Large lateral forces were observed under severe deformation around the grain boundary. The fluctuation of lateral forces was bigger on surfaces with grain boundaries than that on single-crystal surfaces. Friction forces induced by the armchair grain boundaries was smaller than those by the zigzag grain boundaries. Full article

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8 pages, 1858 KiB

Open AccessEditor’s ChoiceArticle

Optical Transport Properties of Graphene Surface Plasmon Polaritons in Mid-Infrared Band

by Yindi Wang, Hongxia Liu, Shulong Wang, Ming Cai and Lan Ma

Crystals 2019, 9(7), 354; https://doi.org/10.3390/cryst9070354 - 12 Jul 2019

Cited by 26 | Viewed by 4289

Abstract

The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation [...] Read more.

The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation results indicate that graphene SPPs show unique properties in the mid-infrared region including ultra-compact mode confinement and dynamic tunability, which allow these SPPs to overcome the defects of metal SPPs and traditional silicon-based optoelectronic devices. Thus, they can be used to manufacture subwavelength devices. The work in this paper lays a theoretical foundation for the application of graphene SPPs in the mid-infrared region. Full article

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10 pages, 3282 KiB

Open AccessArticle

Effect of Angle, Temperature and Vacancy Defects on Mechanical Properties of PSI-Graphene

by Lu Xie, Tingwei Sun, Chenwei He, Haojie An, Qin Qin and Qing Peng

Crystals 2019, 9(5), 238; https://doi.org/10.3390/cryst9050238 - 6 May 2019

Cited by 25 | Viewed by 3750

Abstract

The PSI-graphene, a two-dimensional structure, was a novel carbon allotrope. In this paper, based on molecular dynamics simulation, the effects of stretching direction, temperature and vacancy defects on the mechanical properties of PSI-graphene were studied. We found that when PSI-graphene was stretched along [...] Read more.

The PSI-graphene, a two-dimensional structure, was a novel carbon allotrope. In this paper, based on molecular dynamics simulation, the effects of stretching direction, temperature and vacancy defects on the mechanical properties of PSI-graphene were studied. We found that when PSI-graphene was stretched along 0° and 90° at 300 K, the ultimate strength reached a maximum of about 65 GPa. And when stretched along 54.2° and 155.2° at 300 K, the Young’s modulus had peaks, which were 1105 GPa and 2082 GPa, respectively. In addition, when the temperature was raised from 300 K to 900 K, the ultimate strength in all directions was reduced. The fracture morphology of PSI-graphene stretched at different angles was also shown in the text. In addition, the number of points removed from PSI-graphene sheet also seriously affected the tensile properties of the material. It was found that, compared with graphene, PSI-graphene didn’t have the negative Poisson’s ratio phenomenon when it was stretched along the direction of 0°, 11.2°, 24.8° and 34.7°. Our results provided a reference for studying the multi-angle stretching of other carbon structures at various temperatures. Full article

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13 pages, 4656 KiB

Open AccessArticle

Preparation of Few-Layer Graphene by Pulsed Discharge in Graphite Micro-Flake Suspension

by Xin Gao, Naoaki Yokota, Hayato Oda, Shigeru Tanaka, Kazuyuki Hokamoto, Pengwan Chen and Meng Xu

Crystals 2019, 9(3), 150; https://doi.org/10.3390/cryst9030150 - 13 Mar 2019

Cited by 10 | Viewed by 4237

Abstract

Few-layer graphene nanosheets were produced by pulsed discharge in graphite micro-flake suspension at room temperature. In this study, the discharging current and voltage data were recorded for the analysis of the pulsed discharge processes. The as-prepared samples were recovered and characterized by various [...] Read more.

Few-layer graphene nanosheets were produced by pulsed discharge in graphite micro-flake suspension at room temperature. In this study, the discharging current and voltage data were recorded for the analysis of the pulsed discharge processes. The as-prepared samples were recovered and characterized by various techniques, such as TEM, SEM, Raman, XRD, XPS, FT-IR, etc. The presence of few-layer graphene (3–9 L) in micrometer scale was confirmed. In addition, it is investigated that the size of recovered graphene nanosheets are influenced by the initial size of utilized graphite micro-flake powder. Based on the process of pulsed discharge and our experimental results, the formation mechanism of few-layer graphene was discussed. The influence of charging voltage on as-prepared samples is also investigated. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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8 pages, 2378 KiB

Open AccessArticle

The Mechanical Properties of Defective Graphyne

by Shuting Lei, Qiang Cao, Xiao Geng, Yang Yang, Sheng Liu and Qing Peng

Crystals 2018, 8(12), 465; https://doi.org/10.3390/cryst8120465 - 12 Dec 2018

Cited by 20 | Viewed by 4604

Abstract

Graphyne is a two-dimensional carbon allotrope with superior one-dimensional electronic properties to the “wonder material” graphene. In this study, via molecular dynamics simulations, we investigated the mechanical properties of α-, β-, δ-, and γ-graphynes with various type of point defects and cracks with [...] Read more.

Graphyne is a two-dimensional carbon allotrope with superior one-dimensional electronic properties to the “wonder material” graphene. In this study, via molecular dynamics simulations, we investigated the mechanical properties of α-, β-, δ-, and γ-graphynes with various type of point defects and cracks with regard to their promising applications in carbon-based electronic devices. The Young’s modulus and the tensile strength of the four kinds of graphyne were remarkably high, though still lower than graphene. Their Young’s moduli were insensitive to various types of point defects, in contrast to the tensile strength. When a crack slit was present, both the Young’s modulus and tensile strength dropped significantly. Furthermore, the Young’s modulus was hardly affected by the strain rate, indicating potential applications in some contexts where the strain rate is unstable, such as the installation of membranes. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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8 pages, 3844 KiB

Open AccessArticle

Large-Scale Assembly and Mask-Free Fabrication of Graphene Transistors via Optically Induced Electrodeposition

by Yu Zhang, Yong Yang, Na Liu, Fanhua Yu, Haibo Yu and Niandong Jiao

Crystals 2018, 8(6), 239; https://doi.org/10.3390/cryst8060239 - 7 Jun 2018

Cited by 2 | Viewed by 3849

Abstract

Graphene, known as an alternative for silicon, has significant potential in microelectronic applications. The assembly of graphene on well-defined metal electrodes is a critical step in the fabrication of microelectronic devices. Herein, we present a convenient, rapid, and large-scale assembly method for deposition [...] Read more.

Graphene, known as an alternative for silicon, has significant potential in microelectronic applications. The assembly of graphene on well-defined metal electrodes is a critical step in the fabrication of microelectronic devices. Herein, we present a convenient, rapid, and large-scale assembly method for deposition of Ag electrodes, namely optically induced electrodeposition (OIED). This technique enables us to achieve custom-designed and mask-free fabrication of graphene transistors. The entire assembly process can be completed within a few tens of seconds. Our results show that graphene-based transistors fabricated with Ag electrodes function as a p-type semiconductor. Transfer curves of different samples reveal similar trends of slightly p-type characteristics, which shows that this method is reliable and repeatable. Full article

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7 pages, 5351 KiB

Open AccessArticle

The Influence of Hydroxyl Groups on Friction of Graphene at Atomic Scale

by Rui Li and Chenggang Song

Crystals 2018, 8(4), 167; https://doi.org/10.3390/cryst8040167 - 16 Apr 2018

Cited by 12 | Viewed by 5062

Abstract

Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising [...] Read more.

Hydroxyl groups play an important role in friction of graphene oxides. In this paper, the influence of hydroxyl groups on friction of graphene is investigated by molecular dynamics simulation. The results show that the friction does not always go up with the rising of hydroxyl groups ratio, and reaches the maximum when the hydroxyl groups ratio between interfaces is about 10%. The reason is that hydrogen bonds tend to form in interlayers when the hydroxyl groups ratio is high. The formed hydrogen bonds between interfaces are closely related to the friction. However, the analysis of the component of van der Waals, Coulomb’s forces and hydrogen bonds interaction between interfaces indicates that van der Waals forces are dominant in friction, which can be attributed to the influence of interface distance on friction. Full article

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8 pages, 24653 KiB

Open AccessArticle

High-Density Hydrogen Storage in a 2D-Matrix from Graphene Nanoblisters: A Prospective Nanomaterial for Environmentally Friendly Technologies

by Michael M. Slepchenkov, Pavel V. Barkov and Olga E. Glukhova

Crystals 2018, 8(4), 161; https://doi.org/10.3390/cryst8040161 - 6 Apr 2018

Cited by 5 | Viewed by 5520

Abstract

In this paper, the atomic structure and mechanical stability of a new structural graphene modification—a 2D matrix of nanoscale cells in the form of a few-layer graphene substrate and nanoblister of a graphene monolayer—were studied for the first time. It is shown that [...] Read more.

In this paper, the atomic structure and mechanical stability of a new structural graphene modification—a 2D matrix of nanoscale cells in the form of a few-layer graphene substrate and nanoblister of a graphene monolayer—were studied for the first time. It is shown that such matrices are mechanically stable and are promising for environmentally friendly technologies. The calculated local atomic stress fields demonstrate that the atomic framework is not destroyed, even in the presence of defects in the atomic network of graphene nanoblister (Stone-Wales defect, double vacancies defect, ad-dimmer defect, and their combination). However, it was established that the presence of one or more SW defects leads to the appearance of critical stresses. These critical stresses can induce local bond breaking in the atomic network with an increase in temperature or external pressure. It was found that graphene nanoblister can store molecular hydrogen with a maximum density of 6.6 wt % for 1158 m²/g at 77 K under normal pressure. Full article

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10 pages, 29360 KiB

Open AccessArticle

Interaction of Edge Dislocations with Graphene Nanosheets in Graphene/Fe Composites

by Lu Wang, Jianfeng Jin, Jingyi Cao, Peijun Yang and Qing Peng

Crystals 2018, 8(4), 160; https://doi.org/10.3390/cryst8040160 - 4 Apr 2018

Cited by 44 | Viewed by 5885

Abstract

Graphene is an ideal reinforcement material for metal-matrix composites owing to its exceptional mechanical properties. However, as a 2D layered material, graphene shows highly anisotropic behavior, which greatly affects the mechanical properties of graphene-based composites. In this study, the interaction between an edge [...] Read more.

Graphene is an ideal reinforcement material for metal-matrix composites owing to its exceptional mechanical properties. However, as a 2D layered material, graphene shows highly anisotropic behavior, which greatly affects the mechanical properties of graphene-based composites. In this study, the interaction between an edge dislocation (b = 1/2 (111)) and a pair of graphene nanosheets (GNSs) in GNS reinforced iron matrix composite (GNS/Fe) was investigated using molecular dynamic simulations under simple shearing conditions. We studied the cases wherein the GNS pair was parallel to the (1

\bar{1}

0), (11

\bar{2}

), and (111) planes, respectively. The results showed that the GNS reinforcement can effectively hinder dislocation motion, which improves the yield strength. The interaction between the edge dislocation and the GNS pair parallel to the (11

\bar{2}

) plane showed the strongest effect of blocking dislocations among the three cases, resulting in increases in the shear modulus and yield stress of 107% and 1400%, respectively. This remarkable enhancement was attributed to the Orowan “by-passing” strengthening mechanism, whereas cross-slip of dislocation segments was observed during looping around GNSs. Our results might contribute to the development of high-strength iron matrix composites. Full article

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14 pages, 1788 KiB

Open AccessArticle

Sliding Dynamics of Parallel Graphene Sheets: Effect of Geometry and Van Der Waals Interactions on Nano-Spring Behavior

by Alessandro Crisafulli, Ali Khodayari, Shahin Mohammadnejad and Matteo Fasano

Crystals 2018, 8(4), 149; https://doi.org/10.3390/cryst8040149 - 28 Mar 2018

Cited by 19 | Viewed by 5680

Abstract

Graphene and carbon nanotubes are promising materials for nanoelectromechanical systems. Among other aspects, a proper understanding of the sliding dynamics of parallel graphene sheets or concentric nanotubes is of crucial importance for the design of nano-springs. Here, we analytically investigate the sliding dynamics [...] Read more.

Graphene and carbon nanotubes are promising materials for nanoelectromechanical systems. Among other aspects, a proper understanding of the sliding dynamics of parallel graphene sheets or concentric nanotubes is of crucial importance for the design of nano-springs. Here, we analytically investigate the sliding dynamics between two parallel, rigid graphene sheets. In particular, the analysis focuses on configurations in which the distance between the sheets is kept constant and lower than the equilibrium interlayer spacing of graphite (unstable configurations). The aim is to understand how the interlayer force due to van der Waals interactions along the sliding direction changes with the geometrical characteristics of the configuration, namely size and interlayer spacing. Results show metastable equilibrium positions with completely faced sheets, namely a null force along the sliding direction, whereas net negative/positive forces arise when the sheets are approaching/leaving each other. This behavior resembles a molecular spring, being able to convert kinetic into potential energy (van der Waals potential), and viceversa. The amplitude of both storable energy and entrance/exit forces is found to be proportional to the sheet size, and inversely proportional to their interlayer spacing. This model could also be generalized to describe the behavior of configurations made of concentric carbon nanotubes, therefore allowing a rational design of some elements of carbon-based nanoelectromechanical systems. Full article

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7 pages, 1422 KiB

Open AccessArticle

The Influence of Vertical Vibration on Nanoscale Friction: A Molecular Dynamics Simulation Study

by Yang Cheng, Pengzhe Zhu and Rui Li

Crystals 2018, 8(3), 129; https://doi.org/10.3390/cryst8030129 - 9 Mar 2018

Cited by 15 | Viewed by 7385

Abstract

The influence of vibration on friction at the nanoscale was studied via molecular dynamics (MD) simulations. The results show that average friction increases in a high-frequency range. This can be attributed to the vibration of the tip following vibration excitation, which results in [...] Read more.

The influence of vibration on friction at the nanoscale was studied via molecular dynamics (MD) simulations. The results show that average friction increases in a high-frequency range. This can be attributed to the vibration of the tip following vibration excitation, which results in peaks of repulsive interaction between tip and substrate and leads to higher friction. However, when the frequency is lower than a certain value, friction decreases. This is because vibration excitation results not in an obvious vibration of the tip but in a slightly larger interface distance, which leads to a decrease in friction. Full article

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14 pages, 7487 KiB

Open AccessArticle

Effect of Thermally Reduced Graphene Oxide on Mechanical Properties of Woven Carbon Fiber/Epoxy Composite

by Nitai Chandra Adak, Suman Chhetri, Naresh Chandra Murmu, Pranab Samanta and Tapas Kuila

Crystals 2018, 8(3), 111; https://doi.org/10.3390/cryst8030111 - 27 Feb 2018

Cited by 26 | Viewed by 5870

Abstract

Thermally reduced graphene oxide (TRGO) was incorporated as a reinforcing filler in the epoxy resin to investigate the effect on the mechanical properties of carbon fiber (CF)/epoxy composites. At first, the epoxy matrix was modified by adding different wt % of TRGO from [...] Read more.

Thermally reduced graphene oxide (TRGO) was incorporated as a reinforcing filler in the epoxy resin to investigate the effect on the mechanical properties of carbon fiber (CF)/epoxy composites. At first, the epoxy matrix was modified by adding different wt % of TRGO from 0.05 to 0.4 wt % followed by the preparation of TRGO/CF/epoxy composites througha vacuum-assisted resin transfer molding process. The prepared TRGO was characterized by using Fourier transform infrared spectroscopy, Raman Spectroscopy and field emission scanning electron microscopy (FE-SEM) techniques. It was observed that the wrinkled structure of synthesized TRGO may be helpful to interlock with the epoxy resin and CF.The inter-laminar shear strength, in-plane fracture toughness and impact strength increased by ~67%, 62% and 93% at 0.2 wt % of TRGO loading in the CF/epoxy composites as compared to the CF reinforced epoxy. The mechanical properties of the hybrid composites decreased beyond the 0.2 wt % of TRGO incorporation in the epoxy resin. The fracture surfaces of the hybrid composites were studied by FE-SEM image analysis to investigate the synergistic effect of TRGO in the CF/epoxy composite. This study suggested that TRGO could be used asgood nanofiller to resist the matrix and fiber fracture. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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12 pages, 5292 KiB

Open AccessArticle

Mechanically Robust 3D Graphene–Hydroxyapatite Hybrid Bioscaffolds with Enhanced Osteoconductive and Biocompatible Performance

by Weibo Xie, Fuxiang Song, Rui Wang, Shenglin Sun, Miao Li, Zengjie Fan, Bin Liu, Qiangqiang Zhang and Jizeng Wang

Crystals 2018, 8(2), 105; https://doi.org/10.3390/cryst8020105 - 23 Feb 2018

Cited by 20 | Viewed by 4710

Abstract

In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature [...] Read more.

In this paper, we describe three-dimensional (3D) hierarchical graphene–hydroxyapatite hybrid bioscaffolds (GHBs) with a calcium phosphate salt electrochemically deposited onto the framework of graphene foam (GF). The morphology of the hydroxyapatite (HA) coverage over GF was controlled by the deposition conditions, including temperature and voltage. The HA obtained at the higher temperature demonstrates the more uniformly distributed crystal grain with the smaller size. The as-prepared GHBs show a high elasticity with recoverable compressive strain up to 80%, and significantly enhanced strength with Young’s modulus up to 0.933 MPa compared with that of pure GF template (~7.5 kPa). Moreover, co-culture with MC3T3-E1 cells reveals that the GHBs can more effectively promote the proliferation of MC3T3-E1 osteoblasts with good biocompatibility than pure GF and the control group. The superior performance of GHBs suggests their promising applications as multifunctional materials for the repair and regeneration of bone defects. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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10 pages, 17514 KiB

Open AccessArticle

One Step Preparation of Fe–FeO–Graphene Nanocomposite through Pulsed Wire Discharge

by Xin Gao, Naoaki Yokota, Hayato Oda, Shigeru Tanaka, Kazuyuki Hokamoto and Pengwan Chen

Crystals 2018, 8(2), 104; https://doi.org/10.3390/cryst8020104 - 23 Feb 2018

Cited by 29 | Viewed by 7324

Abstract

The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded [...] Read more.

The Fe–FeO–graphene nanocomposite material was produced successfully by pulsed wire discharge in graphene oxide (GO) suspension. Pure iron wires with a diameter of 0.25 mm and a length of 100 mm were used in the experiments. The discharge current and voltage were recorded to analyze the process of the pulsed wire discharge. The as-prepared samples—under different charging voltages—were recovered and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM). Curved and loose graphene films that were anchored with spherical Fe and FeO nanoparticles were obtained at the charging voltage of 8–10 kV. The present study discusses the mechanism by which the Fe–FeO–graphene nanocomposite material was formed during the pulsed wire discharge process. Full article

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10 pages, 1786 KiB

Open AccessArticle

Atomic-Site-Specific Analysis on Out-of-Plane Elasticity of Convexly Curved Graphene and Its Relationship to s p 2 to s p 3 Re-Hybridization

by Makoto Ashino and Roland Wiesendanger

Crystals 2018, 8(2), 102; https://doi.org/10.3390/cryst8020102 - 20 Feb 2018

Cited by 4 | Viewed by 4284

Abstract

The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties [...] Read more.

The geometry of two-dimensional crystalline membranes is of interest given its unique synergistic interplay with their mechanical, chemical, and electronic properties. For one-atom-thick graphene, these properties can be substantially modified by bending at the nanometer scale. So far variations of the electronic properties of graphene under compressing and stretching deformations have been exclusively investigated by local-probe techniques. Here we report that the interatomic attractive force introduced by atomic force microscopy triggers “single”-atom displacement and consequently enables us to determine out-of-plane elasticities of convexly curved graphene including its atomic-site-specific variation. We have quantitatively evaluated the relationship between the out-of-plane displacement and elasticity of convexly curved graphene by three-dimensional force field spectroscopy on a side-wall of a hollow tube with a well-defined curvature. The substantially small intrinsic modulus that complies with continuum mechanics has been found to increase significantly at atomically specific locations, where

s p^{2}

to

s p^{3}

re-hybridization would certainly take place. Full article

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12 pages, 3037 KiB

Open AccessArticle

Strain Effects in Gallium Nitride Adsorption on Defective and Doped Graphene: First-Principles Calculations

by Han Yan, Pei-Cheng Ku, Zhi-Yin Gan, Sheng Liu and Peng Li

Crystals 2018, 8(2), 58; https://doi.org/10.3390/cryst8020058 - 26 Jan 2018

Cited by 9 | Viewed by 5311

Abstract

Transferable, low-stress gallium nitride grown on graphene for flexible lighting or display applications may enable next-generation optoelectronic devices. However, the growth of gallium nitride on graphene is challenging. In this study, the adsorptions of initial nucleation process of gallium nitride on graphene were [...] Read more.

Transferable, low-stress gallium nitride grown on graphene for flexible lighting or display applications may enable next-generation optoelectronic devices. However, the growth of gallium nitride on graphene is challenging. In this study, the adsorptions of initial nucleation process of gallium nitride on graphene were investigated using first-principles calculations based on density functional theory. The adsorption energies and the role of in-plane strains were calculated for different possible configurations of the adatoms on the surfaces of vacancy defect and doped graphene. Compared with the results of the gallium adatom, adsorption of the nitrogen atom on graphene was found to exhibit greater stability. The calculations reveal that the vacancy defect core enhanced the adsorption stability of the adatom on graphene, whereas the incorporation of oxygen impurity greatly reduced the stable adsorption of the gallium and nitrogen adatoms. Furthermore, the calculations of strain showed that the lattice expansion led to increased stability for all adsorption sites and configuration surfaces, except for the nitrogen adatom adsorbed over the gallium atom in Ga-doped graphene. The study presented in this paper may have important implications in understanding gallium nitride growth on graphene. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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12 pages, 2870 KiB

Open AccessArticle

The Influence of Epitaxial Crystallization on the Mechanical Properties of Polyamide 66/Reduced Graphene Oxide Nanocomposite Injection Bar

by Enyi Chi, Minfang An, Guibin Yao, Feng Tian and Zongbao Wang

Crystals 2017, 7(12), 384; https://doi.org/10.3390/cryst7120384 - 20 Dec 2017

Cited by 15 | Viewed by 4703

Abstract

Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the [...] Read more.

Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the two-dimensional small angle X-ray scattering technique, were used to research the crystallization behavior in PA66/RGO nanocomposites. The results indicated that RGO was an effective nucleation agent for PA66. The presence of RGO could enhance the orientation degree of the PA66 crystals and did not influence the crystal structure of the PA66. The non-epitaxial crystals and the epitaxial crystals existed in PA66/RGO nanocomposites. The size of epitaxial crystals was much greater than that of the non-epitaxial crystals. Tensile test results showed that the presence of fewer epitaxial crystals can improve the mechanical properties of a polymer. Full article

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Review

Jump to: Editorial, Research

28 pages, 19453 KiB

Open AccessReview

Basic Concepts and Recent Advances of Crystallographic Orientation Determination of Graphene by Raman Spectroscopy

by Yucheng Lan, Mobolaji Zondode, Hua Deng, Jia-An Yan, Marieme Ndaw, Abdellah Lisfi, Chundong Wang and Yong-Le Pan

Crystals 2018, 8(10), 375; https://doi.org/10.3390/cryst8100375 - 21 Sep 2018

Cited by 29 | Viewed by 11779

Abstract

Graphene is a kind of typical two-dimensional material consisting of pure carbon element. The unique material shows many interesting properties which are dependent on crystallographic orientations. Therefore, it is critical to determine their crystallographic orientations when their orientation-dependent properties are investigated. Raman spectroscopy [...] Read more.

Graphene is a kind of typical two-dimensional material consisting of pure carbon element. The unique material shows many interesting properties which are dependent on crystallographic orientations. Therefore, it is critical to determine their crystallographic orientations when their orientation-dependent properties are investigated. Raman spectroscopy has been developed recently to determine crystallographic orientations of two-dimensional materials and has become one of the most powerful tools to characterize graphene nondestructively. This paper summarizes basic aspects of Raman spectroscopy in crystallographic orientation of graphene nanosheets, determination principles, the determination methods, and the latest achievements in the related studies. Full article

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30 pages, 6272 KiB

Open AccessReview

A Review of Current Development of Graphene Mechanics

by Qiang Cao, Xiao Geng, Huaipeng Wang, Pengjie Wang, Aaron Liu, Yucheng Lan and Qing Peng

Crystals 2018, 8(9), 357; https://doi.org/10.3390/cryst8090357 - 6 Sep 2018

Cited by 78 | Viewed by 11802

Abstract

Graphene, a two-dimensional carbon in honeycomb crystal with single-atom thickness, possesses extraordinary properties and fascinating applications. Graphene mechanics is very important, as it relates to the integrity and various nanomechanical behaviors including flexing, moving, rotating, vibrating, and even twisting of graphene. The relationship [...] Read more.

Graphene, a two-dimensional carbon in honeycomb crystal with single-atom thickness, possesses extraordinary properties and fascinating applications. Graphene mechanics is very important, as it relates to the integrity and various nanomechanical behaviors including flexing, moving, rotating, vibrating, and even twisting of graphene. The relationship between the strain and stress plays an essential role in graphene mechanics. Strain can dramatically influence the electronic and optical properties, and could be utilized to engineering those properties. Furthermore, graphene with specific kinds of defects exhibit mechanical enhancements and thus the electronic enhancements. In this short review, we focus on the current development of graphene mechanics, including tension and compression, fracture, shearing, bending, friction, and dynamics properties of graphene from both experiments and numerical simulations. We also touch graphene derivatives, including graphane, graphone, graphyne, fluorographene, and graphene oxide, which carve some fancy mechanical properties out from graphene. Our review summarizes the current achievements of graphene mechanics, and then shows the future prospects. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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27 pages, 1986 KiB

Open AccessReview

Optoelectronics Based Dynamic Advancement of Graphene: Characteristics and Applications

by Himadri Shekhar Mondal, Md. Mahbub Hossain, Md. Ekhlasur Rahaman, Sheikh Mohammed Boni Amin, Md. Bellal Hossain, Md. Mehadi Hasan Mahasin and Pankoj Kumar Mondal

Crystals 2018, 8(4), 171; https://doi.org/10.3390/cryst8040171 - 17 Apr 2018

Cited by 12 | Viewed by 5794

Abstract

Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing [...] Read more.

Graphene has impressive features that make it an exceptional material for sophisticated applications in next generation electronics and opto-electronics devices. This peremptory material has attracted researchers’ attention in various fields of recent advancement since its discovery in 2004. Its applied fields are increasing day by day. This two-dimensional material (2D) is using mellifluously for the development in different types of devices in the field of optics, photonics, light emitting diode (LED), medical diagnosis, sensing, and so on. In this review, the relevant optical properties and the applications areas with available results in various fields are discussed. Again, the optical conductivity of strained graphene is reviewed in a wavelength related regime that depends on strain modulus and position with field arrangements. Graphene shows a saturation and reverse saturation process due to the increase of light intensity. In addition, strong absorption is observed from the visible to mid-infrared (MIR) wavelength range. Moreover, the application areas of graphene including optics, photonics, plasmonics, mode-locked laser, optical modulator, etc., and the comparison of various results obtained from different sources are presented. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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