High-order nonlinear mechanical properties of g-SiC

Computational Materials Science, 2010

First principles density functional theory is employed to study the elastic constants and sound velocities in wurtzite-SiC under pressure. The focus is on the behavior of the elastic constants (C ij ) and sound veloc-

Physics of the Solid State, 2004

The pressure dependences of the second-order elastic constants C ij and the velocity of sound in 3 C -SiC and 2 H -SiC crystals are calculated in the framework of the Keating model. The third-order elastic constants C ijk for 3 C -SiC are determined from the dependences of the second-order elastic constants C ij on the pressure p . © 2004 MAIK "Nauka/Interperiodica".

Materials Science Forum, 2005

The pressure dependences of the second-order elastic constants ij C and the velocity of sound in 3C-SiC and 2H-SiC crystals are calculated in the framework of the Keating model with the additional assumption that the central α and the noncentral β force constants are linear functions of external hydrostatic pressure. Grüneisen parameters for the different acoustic modes of 3C-SiC have been also calculated. The third –order elastic constants ijk C for 3C-SiC are determined from the dependences of ij C on the pressure.

Materials Science and Engineering: A, 2004

Direct elastic properties measurements of ␤-SiC films have been made using the interferometric strain gage displacement (ISDG) technique and compared with data acquired by the Brillouin light scattering (BLS) technique. BLS permits to selectively determine the three independent elastic constants (c 11 = 395 GPa; (c 11 − c 12)/2 = 136 GPa and c 44 = 236 GPa) of a ␤-SiC single crystal epitaxial film from the analysis of a number of different surface acoustic modes. The calculated Voigt average values of the elastic constants for the 1 1 1 textured polycrystalline films (C 11 = 500 GPa, C 33 = 534 GPa, C 44 = 166 GPa, C 66 = 201 GPa, C 13 = 62 GPa) using the single crystal constants provides good agreement with experimental results on Young's modulus measured by the ISDG technique. Nevertheless, BLS gave more accurate values of Poisson's ratios.

Journal of Nano- and Electronic Physics

Molecular dynamics simulations using the Tersoff bond-order potential are employed to study the effects of temperature and grain size on mechanical properties of nanocrystalline silicon carbide. In this work, the simulated nanocrystalline SiC samples have a mean grain size varying from 2.5 to 5 nm and contain about 10 5 atoms in the model system. Tension tests with periodic boundary conditions and engineering strain rate of 10 -4 ps -1 are simulated, which result in the stress-strain curves of the single-and nanocrystalline SiC in terms of the average virial stress and true strain. The elastic moduli of the single-and nanocrystalline silicon carbide are determined from fitting the stress-strain curves. In this work, the Young's modulus of nanocrystalline SiC is compared with those of the monocrystalline SiC for different temperatures in the range from 300 K to 3000 K. The numerical results show that the temperature has an obvious effect on Young's modulus, which is attributed to the large volume fraction of grain boundaries in nanocrystalline samples. With increasing temperature, the nanocrystalline SiC shows a brittle-to-ductile transition at temperatures above 600 K. In addition, the reduction in Young's modulus of the nanocrystalline SiC with increasing temperature exhibits a nonlinear trend. It is found that the plasticity of the nanocrystalline SiC samples sharply increases at temperatures above 2000 K. This effect was explained by a decrease in the melting point of the nanocrystalline materials in comparison to monocrystalline solids. The grain size dependence of elastic modulus of nanocrystalline SiC only becomes distinct at high temperatures and at a grain size greater than about 3 nm, while at room temperature elastic properties are almost invariant with the change of grain size. We expect that the quantifications of temperature and grain size dependence of mechanical properties will have implications in the development of nanocrystalline silicon carbide nanostructured materials for high performance structural applications.

Physical Review Letters, 2008

The early stages of epitaxial graphene layer growth on the Si-terminated 6H-SiC(0001) are investigated by Auger electron spectroscopy (AES) and depolarized Raman spectroscopy. The selection of the depolarized component of the scattered light results in a significant increase in the C-C bond signal over the second order SiC Raman signal, which allows to resolve submonolayer growth, including individual, localized C=C dimers in a diamond-like carbon matrix for AES C/Si ratio of ∼3, and a strained graphene layer with delocalized electrons and Dirac single-band dispersion for AES C/Si ratio >6. The linear strain, measured at room temperature, is found to be compressive, which can be attributed to the large difference between the coefficients of thermal expansion of graphene and SiC. The magnitude of the compressive strain can be varied by adjusting the growth time at fixed annealing temperature.

2015

The structural, five different elastic constants and electronic properties of 2H- and 4H-Silicon carbide (SiC) are investigated by using density functional theory (DFT). The total energies of primitive cells of 2H- and 4H-SiC phases are close to each other and moreover satisfy the condition E2H >E4H . Thus, the 4H-SiC structure appears to be more stable than the 2H- one. The analysis of elastic properties also indicates that the 4H-SiC polytype is stiffer than the 2H structures. The electronic energy bands, the total density of states (DOS) are calculated. The fully relaxed and isotropic bulk modulus is also estimated. The implication of the comparison of our results with the existing experimental and theoretical studies is made.

Journal of Applied Physics, 2013

We present results of concomitant measurements of synchrotron x-ray diffraction (XRD), Brillouin, and Raman spectroscopy on the single crystal samples of cubic silicon carbide (3C-SiC) under quasi-hydrostatic pressures up to 65 GPa, as well as x-ray diffraction and Raman spectroscopy up to 75 GPa. We determined the equation of state of 3C-SiC and pressure dependencies of the zone-center phonon, elastic tensor, and mode Gruneisen parameters. Cubic SiC lattice was found to be stable up to 75 GPa, but there is a tendency for destabilization above 40 GPa, based on softening of a transverse sound velocity. By applying the concomitant density and elasticity measurements, we determined the pressure on the SiC sample without referring to any other pressure scale thus establishing a new primary pressure scale with a 2%-4% precision up to 65 GPa. We proposed corrections to the existing ruby and neon pressure scales, and also calibrated cubic SiC as a pressure marker for the x-ray diffraction and Raman experiments. V

Journal of Nepali Physical Society, 2021

Using the first principles calculation, we investigated the structural, electronic, and straindependent optical properties of the two-dimensional hexagonal Silicon Carbide (SiC) Monolayer. We found that the biaxial compressive strain loading gradually changes the direct bandgap SiC into indirect bandgap semiconductor. The compressive strain increases the bandgap but reduces the values of static dielectric constant and refractive index. Conversely, the biaxial tensile strain loading decreases the bandgap but increases the value of static dielectric constant and refractive index. The result shows that the electronic and optical properties of SiC can be engineered to the desired value by applying strain. The large bandgap issue for the SiC monolayer is limiting its uses in different applications which can be overcome with the help of biaxial strain.

Materials Research Society symposia proceedings. Materials Research Society

There is a technological need for hard thin films with high elastic modulus and fracture toughness. Silicon carbide (SiC) fulfills such requirements for a variety of applications at high temperatures and for high-wear MEMS. A detailed study of the mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates was performed by means of nanoindentation using a Berkovich diamond tip. The thickness of both the single and polycrystalline SiC films was around 1-2 µm. Under indentation loads below 500 µN both films exhibit Hertzian elastic contact without plastic deformation. The polycrystalline SiC films have an elastic modulus of 457 + 50 GPa and hardness of 33.5 + 3.3 GPa, while the single crystalline SiC films elastic modulus and hardness were measured to be 433 + 50 GPa and 31.2 + 3.7 GPa, respectively. These results indicate that polycrystalline SiC thin films are more attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since growing single crystal 3C-SiC films is more challenging.