We examine the capabilities of the ab-initio calculations within density functional theory (DFT) on the 2D monolayer MoS 2 , graphene, and Gr-MoS 2 heterostructure.The stability, elastic properties, acoustics, electronic and optical properties of the three hexagonal MoS 2 , graphene, and Gr-MoS 2 heterostructure is presented. The energy bandgap and both Total and partial density of states are calculated within the PBE functional and are enhanced by the HSE06 functional. Gr-MoS 2 hold an indirect bandgap (0.294 ev) while MoS 2 is a direct bandgap (1.83 eV); moreover, graphene is used in its metal form in our calculations. The geometrically optimized relaxed structural parameters are (a = b = 3.308 Å, c = 11.961 Å), (a = b = 3.156 Å, c = 12.440 Å), and (a = b = 2.450 Å, c = 7.286 Å) for Gr-MoS 2 , MoS 2 , and Gr, respectively. The energy bandgap of the three hexagonal crystals is induced in the pressure limit (0-40) GPa. Pressure give rise to bandgap in Gr, and does not affect the MoS 2 bandgap significantly, whereas the minimal bandgap for Gr-MoS 2 changes drastically under pressure. The pressure-dependent elastic moduli and related mechanical characteristics are reported. The optical properties are calculated throughout incident photon energies (0-40 eV). Most of the reported propertiesshow a relative agreement with the cited literature. However, there are no experimental nor reliable theoretical results for the Gr-MoS 2 heterostructure, and to the best of the author's knowledge many of the results of Gr-MoS 2 are reported first in this work.
Plasma sputtering was used to deposit carbon layer from pure graphite with thicknesses (20, 54, 63 nm) on a p-type silicon wafer substrate for the preparation of a Si-CNT (Silicon-Carbon Nano Tubes) junction without any catalyst. The I-V characteristics of the junction were found to be similar to that of the diode, which confirm that the carbon layer or, in other words, that the carbon nanotubes are acting as an n-type semiconductor. The effect of heat and light illumination on the I-V characteristics is studied. At temperatures (32, 40, 50 and 60 o C), the I-V characteristics shows increase in conductivity with increasing the temperature for a certain thickness. The effect of light on I-V characteristics has also been studied showing an increase in current flow, the effect of both heat and light illumination is more pronounced at low values of the thickness of the CNT layer due to their low resistivity.
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