Report on Two-dimensional material mechanical property without defects

Abstract of Two-dimensional material mechanical property without defects

            In the human history it has been seen that mechanical properties are vital for materials science and engineering and are also essential in different materials applications. The difficult part is the measurement of mechanical properties of 2-dimensional (2D) materials. The study of mechanical properties of 2D materials is lagging despite extensive exploration in recent years. This creates lots of ambiguity and leads to more questions and trials in the research area of these materials.

List of Figures

Figure 1: Atomic structure of graphene and (B) energy bands in graphene. 10

Figure 2: nEt versus the number of layers. 11

Figure 3: monolayer MX2(M = Mo, W; X = S, Se, Te) TMDCs. 14

Figure 4: Force–displacement data from AFM nanoindentation. 17

Figure 5: Linearly elastic properties of monolayer graphene. 19

Figure 6: Schematic illustration of mechanical characterization methods. 21

Figure 7: Schematic of AFM-based methods, including beam bending method. 24

Figure 8: Schematic of pressurized blister method. 25

Family of the 2D materials helps in offering the complete spectrum of all their physical properties starting from the conducting graphene and moving towards the semiconducting MoS2 along with the insulting h-BN, there are many different kind of the 2D crystal structures which condenses the unique combination of all the properties that are associated with mechanics, stiffness as well as the strength of the high in-plane but they are also pretty much low in the flexural rigidity.

Collectively, 2D materials are promising for the different kind of the broad range of applications. We have reviewed the recent experimental as well as the theoretical studies that are being associated with the mechanics and its mechanical properties of all the materials of 2D. Emphasis has been done that how word mechanics has been essential for the study of different kind of the mechanical properties that includes the interfacial properties along with the coupling among the mechanical as well as the physical properties (Novoselov , et al , 2005) .

Out of all the unique properties that are associated with the 2D materials, all the mechanical properties of such ultrathin membranes have been one of the major interest for the scientists and engineers of the different materials, this is due to a reason that 2D materials are the ones that are known to be the most promising candidates for the transparent as well as the flexible electronics along with the composite applications as well. Especially, because of the outstanding intrinsic elastic modulus of the graphene that is (Young’s modulus of 1 TPa and maximum strength over ~100GPa at the breaking strain of ~25%) was being known through a technique called as nanoindentation by the use of atomic force microscopy also called as AFM. Apart from all this, some of the intensive studies have also been made to know more about the mechanical behavior of graphene. Extraordinary mechanical strength along with the stiffness of the graphene has been increased from the expectations of scientists regarding some of the potential roles for the fabrication of strengthening the different components or some of the devices that are electronic in nature or even the sensors as well. Focus upon these studies all of a sudden expanded for the other materials of 2D. Now we are going review some of the theoretical as well as the experimental studies towards the mechanical properties of all the 2D materials. The very first thing which we are going to do here is the introduction of empirical method for the testing of some mechanical properties for the 2D membranes. Some of the fundamental mechanical properties like elastic modulus, strength and friction is being summarized for some of the 2D materials. There are many other factors as well that influence some of the mechanical properties like defects and functionalization are being considered to broaden up the understanding of all the mechanical behaviors of the 2D materials like the composite additives, some of the flexible electronic devices, micro-electromechanical systems also called as MEMS along with some of the substrates called as biocompatible (López et al , 2015). Though some of the significant discrepancies because of the undulations or some other factors that are needed towards the elaborate theoretical models for a much better consistency. Mostly, theoretical framework for the different studies of the mechanics can further be divided into two different forms:

1. Modeling that is based on the conventional continuum along with the structural mechanics.

2. Atomic simulation for which the classical molecular dynamics also termed as MD is being employed most of the times by the empirically known atomic potential.

At the start, Graphene was being modeled as the continuum membrane by the single layer of the atom thickness. Here assumption can be made that response of the graphene towards the small external load is isotropic, elastic or the non-linear and the force-deformation relation can be shown like σ = Eε + Dε2 and D is the third order of the non-linear modulus. Because 2D materials are the ones that have an atom-scale thicknesses, the in-plane behaviors are being dominated specifically and the aforementioned three parameters are considered to be most common for the explanation of mechanical behaviors of the 2D materials (Cadelano et al , 2009). 2D nanomaterials having an atomic thickness can sustain the small radius of curvature, which make them possess a natural advantage for the making of electronics. Such characteristics that are excellent in nature of atomic thickness 2D materials make them great potential applications in the next generation of flexible, slight, and transparent electronic and optoelectronic devices, such as wearable health-monitoring devices, flexible energy storage devices, and collapsible intelligent screens (Jiang et al , 2019).

Chapter 2: Literature review of Two-dimensional material mechanical property without defects

According to the author (Wang et al , 2015) it is conducted that, Graphene is essential in the complete family of the 2D materials and it also leads the research coming towards the sensor technologies, some of the novel electronics and even the experimental realization for all the condensed problems associated with matter physics. It has the honeycomb lattice for the single atom of the thickness of carbon which helps in giving it an appearance like membrane. Therefore all of the electrons in the graphene are known as the massless Dirac fermions. Their band structure consists of the unique character, it has the linear energy dispersion in the vicinity of two nonequivalent symmetric points, called K1 and K2 points, in the Brillouin zone (BZ), in which the valence bands and the conduction bands touch each other as shown below in the figure. That structure is called as the Dirac cone. This structure has the low dimensionality that further lead towards the quantum fluctuations. As the unit cell of the honeycomb lattice have two different nonequivalent sites that further forms the two different sublattices by the name of A and B, low energy electronic states of the graphene is quite near to Fermi energy. Mechanical as well as the electrical properties of all the 2D materials helps in showing of very strong anisotropy when they are being crystallized into the similar structures of the graphite. Elements that fall in the group of IVVII TMDs are mostly layered, while some other groups like VIIIX TMDs falls in the section of structures that are non-layered. Thin layered structures of the 2D materials have some of the extraordinary properties that includes the direct bandgap in a seen range of frequency, coupling of spin-orbit along with the ultra-strong coulomb association that is being related to the valley degree of the freedom. TMD monolayer is the confirmation of X-M-X covalently bonded, hexagonal quasi-2D, just like the graphene in which graphene as well as the valence bands have degenerate extreme that is called as the valleys situated at the K and 2 K points of the hexagonal BZ.

Figure 1: Atomic structure of graphene and (B) energy bands in graphene

Mechanical properties of 2D materials of Two-dimensional material mechanical property without defects
Graphene of Two-dimensional material mechanical property without defects

According to the author Lee et al (2008), it is conducted that Graphene calculated experimentally, the intrinsic elastic modulus (E ~ 1 TPa) along with the ultrahigh breaking strength (σmax ~ 130GPa) of graphene monolayer through AFM nanoindentation, that is in the good terms with the values assumed (E = 1.05 TPa and σmax = 110GPa) by DFT calculation Elastic modulus and fracture strength of the graphene falls by the increasing numbers of layers Related to nanoindentation testing, this means that loading curve starts deviating through the linear elastic regime towards the nonlinear elastic regime at very minute deflections for the graphene that is thicker. Wei et al enlightened the feature in the terms of inhomogeneous strain distribution and stacking nonlinearity. These factors continuously give rise to interlayer slippage and the dissipation of an energy during the loading-unloading cycle. In thicker graphene, inhomogeneous distribution of the strain is accelerated through the out-of-plane direction that results decrease in the elastic properties. Through the use of pressurized blister method, the inplane elastic modulus of monolayer graphene was distinct along with its devotion energy as shown in the figure below. To take the direct measurements for the bending modulus of the 2D materials is really difficult as compared to the indirect methods like Phonon-frequency measurement through the technique of inelastic neurons scattering and the measurement of resonance frequency by the use of AFM have also been used (Lee et al , 2008).

 

 

Figure 2: nEt versus the number of layers

hBN
MoS2 and other TMDCs of Two-dimensional material mechanical property without defects

hBN, is known as the ‘white graphene’ and it is the insulating 2D material having a large gap in the band of 5.8 eV. This has also been used as one of the counterpart of all the graphene for the different electrical applications so it is another reason that all of the mechanical properties are much essential because the available seterostructures of the graphene as well as hBN are useful for the transparent as well as the flexible electronics. Nanoindentation tests on suspended hBN over a µm-scale hole also helped in showing that all of the mechanical properties associated with hBN (elastic modulus of 220–510N m−1 for hBN film with thickness of 1–2nm) can be compared with the graphene. This is due to a reason that the tested mebrane of hBN had different different kind of the serial stacking of the single layer of hBN. Well, the value that has been obtained is much lower as compared to the theoretically assumed value of 270N m−1 for the single layer of hBN. This can be due to a reason that the interlayer of the stacking faults in the samples of hBN have grown by the chemical vapor decision CVD along with some of the unneglectable empirical faults. In the comparison to graphene. Breaking power of the hBN is much low ~8.8N m−1 for 1 nm thick hBN. No doubt that the decrease in the fracture stress along with the elastic modulus have been explained clearly through the defect concentration as well as GBs, the breaking strain (~0.22), that is called as the ratio of maximum stress to the modulus, is being effected negligibly through the availability of different posts. The AFM nanoindentation results of CVD-grown hBN films showed that multilayer hBN film has an elastic modulus of 18000N m−1 , that correspond towards the 3D elastic modulus of ~1.16 TPa. In comparison to graphene, both of the models are not much reliable upon the thickness variation. Certainly, the 3D elastic modulus of graphene falls down from 1.026 ± 0.022 TPa for monolayer to 0.942 ± 0.003 TPa for 8-layer graphene, while the elastic modulus of hBN is between 0.856 ± 0.003 and 0.865 ± 0.073 for 1–9 layers (figure 4(b)). The ab initio DFT calculations showed that the layers of the graphene all of a sudden slides because of the negatively increased energy of the sliding in the AB stacking of the distortion that is being given that large in-plane strain and out-of plane pressure has been given for the surface of conductive graphene. This can also be elaborated through the increased orbitals of 2pz that overlaps between the graphene layers that are conductive in nature. On contrary, more of the polar orbitals in the BN has become localized in each stress level for the increase in the barrier of sliding energy in a positive way. So, in the contrast to graphene, hBN layers and particularly close to the tip of AFM become resistant towards the interlayer sliding (Falin et al , 2017).

Mechanical properties associated with MosS2 considered through the AFM by the suspended structures that are free in nature of the single layer along with the thicker flakes as well. All the results of measurement showed about the elastic modulus for 180 ± 60N m−1 and the breaking strength of 15 ± 3N m−1 , confirming for ~270 and ~23GPa, by the assuming of the thickness of single layer of 0.65 nm. Estimated modulus value is much comparable to that of MoS2 nanotubes (230GPa) and is in good agreement with the value theoretically assumed (262GPa) by MD simulations and a DFT-based TB process. All the mechanical properties of different other TMDCs were also known by the use of first-principles density functional measurements. For the thick MoS2 (5–20 layers), the Young’s modulus is 350 ± 20GPa. Figure 4(c) gives the stress– strain relations of TMDCs for both armchair and zigzag directions. The W-based TMDCs (WX2) have larger elastic moduli and tensile strength as compared to the Mo-based TMDCs (MoX2). Therefore it is very reasonable that the lower elastic modulus along with the strength induce larger anisotropy, that has been shown in the below figure (Castellanos-et al , 2012).

 

Figure 3: monolayer MX2(M = Mo, W; X = S, Se, Te) TMDCs

 Black phosphorous of Two-dimensional material mechanical property without defects

Black phosphorous (even termed as phosphorene) has been ventured theoretically to get the anisotropic elastic modulus along with the maximum strain because of it’s its extraordinary shape. Calculations being obtained from the first principle has been showed that elastic moduli of the single layer of this BP 41.3GPa and 106.4GPa with the zigzag and the armchair directions. Furthermore, single layer of the BP is much flexible and it can even bear the tensile strain up to the limit of 27% having a zigzag direction and 30% for the armchair direction. Author has also resulted that the maximum strain that is allowed reaches up to 30%-32% for the single as well as some different layers of the BP. This high limit of the strain is only because of the structure it has that can get flattened under the tensile strain without getting any change in the structure of the p-p bonds they have. This is another reason that an increased energy strain can be compensated effectivelt through the dihedral angle. Experimentally, Tao et al also measured some of the elastic modulus of suspended few-layer BP by the AFM nanoindentation method for the very first time. High anisotropy under the stress of breaking was also being noticed through the directions of crystalline. For the thick BP, FM nanoindentation studies also showed that the elastic modulus of BP dropped down from 276 ± 32.4GPa for 34 nm to 89.7 ± 26.4GPa for 14.3 nm. The breaking strain got in the range of 8%–17%, having maximum stress of >25GPa. Not like the past results, it got shown that the elastic modulus and breaking strength of BP nanosheets measured in high vacuum were 46 ± 10 and 2.4 ± 1GPa, no matter how much the number of layers were. Opposite to this, severe corrosion of all the mechanical properties associated with BP was being observed when the same test was being done under specific conditions. Same like the findings that were known related to the TMDCs, elastic bond modulus of the single layer of BP (4.8028eV for the armchair direction and 7.9905eV for the zigzag direction), that was achieved analytically was way higher as compared to that of graphene because of the larger thickness of the single layer it shares. (Zhang et al , 2015)

Other materials of Two-dimensional material mechanical property without defects

Silicene has the 2D allotrope of the hexagon in shape that is much same like graphene. No doubt that some of the superior characteristics of silicene have been assumed and they have much high compatibility by the present Si based upon an industry that got expired, high level of reaction of the silicene helps in the induction of the all of the sudden dissociation of the oxygen molecule present on a surface and also makes an Si-O bond. This kind of the instability of the silicene in the given conditions that makes it much difficult to assess the mechanical properties in an empirical way. This is another reason that computational as well as the theoretical approaches have been used for the exploring of properties. Author has also showed that the Poisson ratio and in-plane stiffness of silicene were ν = 0.3 and C = 62 J m−2. Authors have also showed that maximum strength was thought to be to be 5.85N m−1 and 4.78N m−1. Das et  al continued by the comparative study about estimating of an mechanical behavior along with some characteristics of silicon by four different kind of the stimulation methods of MD which are tensile, bending, oscillation and equilibrium as well of the LAMMPS. To get more results, authors have achieved the elastic modulus. For the results, the authors obtained an elastic modulus of silicone that ranges from 0.013 TPa to 5.48 TPa, that depends upon the different kind of the testing techniques. Same like this, the yield strength, the ultimate tensile strength, cohesive energy, and bulk modulus had 18.28GPa, 23.96GPa, 3.72eV/atom, and 3.62 TPa.

 Elastic properties of 2D material of Two-dimensional material mechanical property without defects

            2D materials ma be deformed like thin membranes due to inplane stretching or by twisting out of plane. This results in creating both in-plane and bending moduli properties in 2D materials. A set of coupling moduli may also be defined theoretically by combined stretching and bending, like with graphene being rolled into carbon nanotubes. In this section the focus of study will be experiments of measuring the elastic properties of 2D materials also theoretical estimates from first principles to continuum mechanics modeling.

 Experiments of Two-dimensional material mechanical property without defects

Using an atomic force microscope (AFM) direct measurement of mechanical properties of monolayer graphene was first reported author by nanoindentation of suspended monolayer graphene membranes. The indentation force-displacement behaviour (Fig. 1A) was taken as a result of the nonlinear elastic properties of graphene, with a 2D Young’s modulus of 340 N/m and a third-order elastic stiffness of -690 N/m in the nonlinear regime. A more thorough examination of the nanoindentation trial was performed by Author using the finite element method (FEM) with and anisotropic, nonlinearly elastic constitutive model for graphene as forecasted by density functional theory (DFT) calculations. Identical AFM indentation examinations were later conducted to study the mechanical properties of polycrystalline graphene films with various grain sizes as grown by chemical vapor deposition (CVD). If the post processing stages avoided the damage or rippling it was found that the elastic stiffness of CVD graphene is like that off pristine graphene. The AFM indentation method is appropriate for other 2D materials beyond graphene, like MoS2 and h-BN which is evident.

 

Figure 4: Force–displacement data from AFM nanoindentation

The blister tests or bulge tests which is a technique commonly used for thin film materials can also be applied to 2D materials to measure their properties. Author conducted a series of blister tests applying the remarkable gas impermeability of graphene and found elastic moduli of single and multi-layered graphene membranes. An identical setup was lately employed for single and multi-layered MoS2 to apply large biaxial strains for band gap engineering. The Author (Nicholl et al , 2015) developed an fascinating variation of the blister test where suspended graphene membranes were electrostatically pressurized by applying a voltage between the graphene and gating chip. They realized that the in-plane stiffness of graphene is 20-100 N/m at room temperature, very minor than expected value (∼340 N/m). Additionally, the in-plane stiffness improved moderately when the temperature reduces to 10 K, but it amplified significantly.

 Theoretical predictions of Two-dimensional material mechanical property without defects

To study the elastic and inelastic behaviour of graphene molecular dynamics (MD) simulations are often utilized. Though the correctness of MD simulations relies on parametrization of thee empirical potentials that define the atomic interactions. The reactive empirical bond-order (REBO) potentials have been extensively used in MD simulations of graphene and carbon nanotubes (CNTs). These 8potentials were unfortunately not parametrized to produce accurate elastic properties of graphene (Huang et al , 2006).

 

Figure 5: Linearly elastic properties of monolayer graphene

 

Inelastic properties of 2D material of Two-dimensional material mechanical property without defects
Strength of Two-dimensional material mechanical property without defects

The power of 2D materials can also be inclined by out of plane deformation induced by either external loading or intrinsic topological errors. It has been stated that graphene under heavy loading grows significant out of plane wrinkles, leading to a failure strength about 60 GPa while the pure strength of graphene sample with periodically dispersed disclination quadrupoles showed a strength near 30 GPa, and pronounced out of plane deformation due to grain boundaries can visibly alter the mechanical response of graphene. The opposition among the out of plane and in-plane deformation in an elastic membrane is typically characterized by its flexibility, which is known to be determined by the bending stiffness, in plane stretching modulus and sample size. Meanwhile the active bending stiffness and in-plane stretching modulus display considerable changes for different 2D materials, the out-of-plane effect on fracture is anticipated to vary vastly across diverse 2D materials and deserves more study  (Gao et al , 2016)

Toughness of Two-dimensional material mechanical property without defects

The key property that depicts the strength of material in the presence of an existing crack-like flaw is toughness. Crack like errors (cracks, notches, corners and holes) are inevitable in large scale applications of 2D materials. Some of them are even purposefully introduced to attain specific functions like water desalination, gas separation and DNA sequencing. Utilizing a uniquely designed tension test platform, Zhang et al examined the fracture robustness of graphene as low as 15.9 J/m2 (assuming a thickness of ∼0.335 nm), near to that of preferably brittle materials like glass and silicon. Atomistic simulations are in general agreement with experimental measurements based on the reported robustness and values of pristine single-crystal graphene. For Instance, MD simulations based on the AIRWBO potential forecasted the rigidness of pristine graphene to be around 12 J/m2. Nevertheless, the robustness of polycrystalline graphene shows large scattering and appears to rely on the grain size as well as the thorough distribution of topological defects. There are only limited researches on the fracture robustness of 2D materials beyond graphene, due to a general absence of precise atomistic potentials for MD simulations of 2D materials. Typically, atomistic simulation of fracture needs adequately big samples that surpass the typical capacity of DFT calculations  ( Jiang et al J.-W. , 2015)

Characterization methods of Two-dimensional material mechanical property without defects

During these years, a great amount of effort is going toward the development of effective methods of mechanical characterization based on computational simulations and experiments on it. In experimental methods, two strategies are showing in the figure below; direct testing and indirect testing. On the basis of community hypothesis, indirect testing evaluate that mechanical parameters can produce through dynamic or static deformation of 2D membranes or beams. So, it might be possible to extract mechanical properties of 2DLMs from elastic stiffness. Resonator based methods is division of the indirect testing  (Zhan et al , 2019)

 

Figure 6: Schematic illustration of mechanical characterization methods

A uniform based method or AFM based method is the load where load is basically a point load. On the other side, opportunities for the observation of mechanical behavior in TEM transmission electron microscopy or SEM scanning electron microscopy and direct measurement of mechanical characteristics is given by direct testing. In order to directly map the connection of external strain and lattice deformation in nondestructive pattern, roman spectroscopy is in use. This technique is very useful in order to experiment engineering of strain and other applications related to it. Finite element model FEM is used to solve some issues related to multiscale. But the further application at nanoscale is hinder by continuum mechanics.

 Experimental methods of Two-dimensional material mechanical property without defects

Beam dynamic method of Two-dimensional material mechanical property without defects

The beam dynamic method has been developed in 2007 when vibrations of resonators based on single and multi-layer graphene was studied. But to determine the absolute amplitude of motion it was thought to be non-trivial. Further development has been made on pressurized blister method in 2008. In order to determine the mechanical characteristics of 2DLMs, these methods were in use for experimental purpose. Every method distinguishes from each other according to their criterion in advantages and disadvantages. In beam dynamic method, E and T almost depend completely on spring constant that is denoted as k, therefore it become critical in measurement of amplitudes of motion and resonance of frequencies. Measurement of E in direction of arbitrary crystal orientation is enabled through this method of beam bending. This technique is very practical to use in anisotropic 2D materials. On the other hand, the circular membrane indentation method is used to measure the average mechanical parameters of all directions. So, this technique is more useful in case of 2DMs, like graphene, WS2 and MoS2. The vibrations of resonators are evaluated through this method either electrical (right side of the figure) or optical (left side of the figure down below). In this way we can denote fundamental resonant frequency of resonators as given below;

Whereas where A = 1.03 is denoted for the clamping coefficient of double clamped beam, ρ is the density of the beam, m is the effective mass, thickness is t and length is L for the beam, 12 E is Young’s modulus. Combining with the relation m = 0.735ρwLt and f0 = (1/2π)(k/m) ½. So, k can be solved through given equation;

Figure: Schematic of beam dynamic method

 Beam bending method of Two-dimensional material mechanical property without defects

This method as shown in the given figure is connected to the continuum mechanics, it gives significant measurements on Young’s modulus and pretension of the double clamped beam. Spring stiffness can explain the dependence between displacement and load. It consists of stress, bending and stretching components in case of double clamped beam. Therefore, following equation describe the relationship between deformation and load;

Figure 7: Schematic of AFM-based methods, including beam bending method

Pressurized blister method of Two-dimensional material mechanical property without defects

A micro chamber is used in fabricating as the platform for testing by depositing graphene on substrate having circular or square walls. This is shown in the figure below. By applying pressure inside and outside the chamber, the differences in it generate a uniform pressure on surface of graphene. The relationship between deflection and pressure diff

where Δp is the pressure difference, W is the side length, δ is the central deflection,  T2D is 2D pretension in the membrane, t is the thickness, E is Young’s modulus, ν is Poisson’s ratio, and c1 and c2 are equal to 3.393 and (0.8 + 0.062ν) −3 , respectively (Zhan et al , 2019).

 

                                      Figure 8: Schematic of pressurized blister method                 

To generalize the models for, graphene can be wrapped within a “model material” which represents various kinds of polymer matrices as shown in below figure The model material allows systematic manipulation of influencing factors, and accordingly, it provides a tunable elastic platform to determine the overall performance of GBPNCs. The model material allows methodical variation of material properties beyond the capacity of experimental methods (Atif et al , 2016)

Figure : ANSYS model of graphene

Discussion of Two-dimensional material mechanical property without defects

The section 2 is describing the elastic properties of 2D materials as the very basic mechanical properties. Different methods to measure in plane elastic properties of graphene has been developed [4] and extended to other 2D materials [5,6]. Some experiments performed recently are showing interesting results for in plane graphene stiffness [7], revealing the questions on statistical rippling and effects of defects [8]. Here again, a recent experiment [9] shown the higher magnitudes values than theoretical prediction which make researcher to think abound fundamental mechanics of benign an ultra-membrane with thermal fluctuation effects [10]. To predict linear and nonlinear elastic characteristics of graphene and other 2 D materials density functional theory is used which is based on first principal calculations. While on other side, there is still need of the improvement in accuracy of empirical potentials for molecular dynamics simulation. There is a discussion on effect of thermal rippling of elastic properties of graphene which is basically rely on statistical mechanics of elastic membranes and its MD simulation [11]

This paper is lightening on five sections which describe every single topic respectively and simultaneously. The concept of analyzing 2D materials and their mechanical properties are discussed thoroughly in these chapters. First chapter is introduction where ideas are produced in order to begin the research on particular topics. The explained background of the previous study is here in the section of research study. It is described that how this study will be helpful and is directly related to the literature review. In a section research questions and objectives are conducted that will go for further parts of research study. Theories of several authors are describing in the next chapter of the literature review. Those researchers who worked on challenges for developing the 2D material are described thoroughly. Previous 18-year study in discussed in next chapter. Next section explores 2D material without defects.

Conclusion of Two-dimensional material mechanical property without defects

In this paper, we are summarizing the mechanical properties of 2D materials and materials related to it. 2D material have their own importance now in prominent sciences and technology after the discovery of graphene in 2004. The mechanical properties of graphene are what we can say that the fundamental properties of 2D materials along with their thermal, electrical and optical properties. There is still a large amount of work that can be done in order to explain the properties of 2D materials and dig them deeper. As the development in 2D material is progressing, systematic studies and their mechanical characteristics are lagging behind. Inaccurate experimental characterization is associated with mechanical studies of 2D materials especially when talking about nanoscale defects. As compared to bulk material, 2D materials have better and superior elastic properties. This is the reason that mechanical properties of 2D materials is found to be decreasing with increase in their number of layers. In addition, the mechanical properties and mechanical behavior of graphene, MoS2, h-BN and phosphorene have been investigated systematically, but great deals of other 2DLMs (more than kinds of 2D materials have been synthesized just for TMDs301) are yet to be studied.