Thermal Expansion Of Graphene Research Articles

A Roadmap for the Chalcogenide-graphene Composites Formation Under a Glassy Regime

Background: Nano-composite is an innovative material having nano in which fillers dispersed in a matrix. Typ-ically, the structure is a matrix- filler combination, where the fillers like particles, fibers, or fragments are surrounded and bound together as discrete units by the matrix. The term nano-composite encompasses a wide range of materials right from three dimensional metal matrix composites to two dimensional lamellar composites. Therefore, the physical, chemical and biological properties of nano materials differ from the properties of individual atoms and molecules or bulk matter. The chalcogenide – graphene composites in glassy regime is the growing novel research topic in the area of composite material science. It is obvious to interpret such materials different physicochemical mechanism. Objective: The key objective of this research work to explore the internal physicochemical mechanism of the chalcogenide – graphene composites under the glassy regime. Including the prime chalcogen alloying element selenium amorphous atomic structure and their fullerene like bonding nature. By accommodating the essential properties of the stacked layers of bilayer graphene. The diffusion, compression and dispersion of the bilayer graphene in selenium rich ternary (X(1-x-y)-Y(x)- Z(y) + GF (bilayer graphene); X = Se, Y = Semimetal or metalloid, Z = None metal) alloys under the complex regime on and after thermal melting process are addressed. Materials and Methods: To synthesize the composite materials the well-known melt quenched method had adopted. More-over, to interpret the amorphous selenium (Se8) chains and rings molecular structures we had used vista software with an available CIF data file. While to show the armchair and zig-zag bonds with bilayer graphene structure the nanotube modeler simulation software has used. Results: Outcomes of this study reveals the chalcogenide -graphene nano composite formation under a glassy regime changes the individual materials structural and other physical properties that is reflecting in different experimental evi-dences, therefore, the modified theoretical concepts for the different properties of such composite materials are interpreted in this study. Discussion: The dispersion and diffusion of the high stiff graphene bonds in low dimension chalcogen rich alloys has been interpreted based on their quadric thermal expansion behaviour. In addition to this, a possible bond angle modification in the formation of X(1-x-y)-Y(x)- Z(y) + GF composites are also addressed. To interpret the distinct optical property behavior of the formed X(1-x-y)-Y(x)- Z(y) + GF composites and parent chalcogenide glassy alloys a schematic model of the energy levels is also addressed. Conclusion: To make a better understating on the formation mechanism such composites, the diffusion and deformation of high stiff graphene σ and π bonds in a low dimension chalcogenide alloy basic mechanism are discussed on basis of novel “thermonic energy tunneling effect” concept, which could result in quadratic thermal expansion of graphene. Moreover, the structural unit modifications of such composite materials are described in terms of their bond angle modifications and in-fluence of the coordination defects. The energy levels suppression and creation of addition sub energy levels in such com-posite materials are discussed by adopting the viewpoint impact of the foreign alloying elements and surface π-plasmonic resonance between the graphene layers in the honeycomb band structure. Thus, this study has described various basic aspects of the chalcogenide system – bilayer graphene composites formation under a glassy regime.

Comment on “A novel approach to calculate thermal expansion of graphene: Molecular dynamics study” by Hamid Ghasemi, Ali Rajabpour

Comment on “A novel approach to calculate thermal expansion of graphene: Molecular dynamics study” by Hamid Ghasemi, Ali Rajabpour

Reply to the Comment by Carlos P. Herrero et al. on “A novel approach to calculate thermal expansion of graphene: Molecular dynamics study”

Reply to the Comment by Carlos P. Herrero et al. on “A novel approach to calculate thermal expansion of graphene: Molecular dynamics study”

Young's modulus and thermal expansion of tensioned graphene membranes

Tensioned graphene membranes are of interest both for fundamental physics and for applications ranging from water filtration to nanomechanical resonators. It is generally assumed that these membranes have a stretching modulus of about 340 N/m and a negative, temperature-independent thermal expansion coefficient due to transverse phonon modes. In this paper, we study the two-dimensional Young's modulus and thermal expansion of graphene as functions of temperature by using laser interferometry to detect the static displacement of the membrane in a cryostat. Surprisingly, we find that the modulus decreases strongly with increasing temperature, which leads to a positive temperature-dependent thermal expansion coefficient. We show that the thermally rippled membrane theory is not consistent with our data, while the effects of surface contaminants typically present on these membranes may explain the observed behavior. Our experiments undermine long-standing assumptions about tensioned two-dimensional membranes, but are consistent with puzzling behavior observed in previous experiments on graphene resonators.

Bending mode and thermal expansion of graphene

Proceeding from the model of a two-dimensional elastic continuum, we describe the characteristic features of thermal expansion of graphene using an approach that goes beyond the quasi-harmonic approximation. The negative value of the thermal expansion coefficient of graphene at low temperatures and its sign reversal at T about 1000 K are established. It is shown that the bending vibrational mode plays a decisive role in peculiarities of the thermal contraction/expansion of graphene and that the contribution of this mode to the thermal expansion coefficient does not depend on the sample size, due to the "sound" nature of the bending mode long-wave dispersion. The obtained results allow giving a quantitative description of the known data of numerical experiments on the thermal expansion of graphene in the entire interval of the MD simulations.

Comparative study of phonon spectrum and thermal expansion of graphene, silicene, germanene, and blue phosphorene

Based on first-principles calculation using density functional theory, we study the vibrational properties and thermal expansion of mono-atomic two-dimensional honeycomb lattices: graphene, silicene, germanene and blue phosphorene. We focus on the similarities and differences of their properties, and try to understand them from their lattice structures. We illustrate that, from graphene to blue phosphorene, phonon bandgap develops due to large buckling-induced mixing of the in-plane and out-of-plane phonon modes. This mixing also influences their thermal properties. Using quasi-harmonic approximation, we find that all of them show negative thermal expansion at room temperature.

Erratum: Effect of preparation on the commensurabilities and thermal expansion of graphene on Ir(111) between 10 and 1300 K [Phys. Rev. B88, 165406 (2013)

Received 23 October 2014DOI:https://doi.org/10.1103/PhysRevB.90.239901©2014 American Physical Society

Effect of preparation on the commensurabilities and thermal expansion of graphene on Ir(111) between 10 and 1300 K

The effects of the temperature on the structure of a single layer of graphene on Ir(111) have been investigated in situ in the growth chamber by grazing incidence x-ray diffraction between 10 and 1300 K. In addition, the effect of two growth temperatures has been studied. The graphene lattice parameter of the main, nonrotated phase displays a characteristic hysteresis whose lower and upper branches correspond to phases in which integer numbers ($m$,$n$)${}_{\mathrm{Ir}}$ of the Ir lattice parameters match integer numbers ($p$,$q$)${}_{\mathrm{Gr}}$ of the graphene lattice parameters, i.e., commensurate phases, (19,0)${}_{\mathrm{Ir}}$\ifmmode\times\else\texttimes\fi{}(21,0)${}_{\mathrm{Gr}}$ and (9,0)${}_{\mathrm{Ir}}$\ifmmode\times\else\texttimes\fi{}(10,0)${}_{\mathrm{Gr}}$, respectively. With a higher growth temperature, graphene presents, in addition to a main nonrotated, incommensurate phase, domains with a small rotation (2.37\ifmmode^\circ\else\textdegree\fi{}) relative to the substrate, corresponding to a (7,2)${}_{\mathrm{Ir}}$\ifmmode\times\else\texttimes\fi{}(8,2)${}_{\mathrm{Gr}}$ commensurate phase. Despite the weak interaction between graphene and iridium, the thermal expansion coefficient of graphene is positive at all temperatures, even at liquid helium temperature contrary to free-standing graphene. It is also close to the iridium thermal expansion because of the tendency to form commensurate phases, which creates a strong link between the graphene and substrate lattices and decreases the elastic energy.