الفهرس 
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Abstract
Two-dimensional (2D) materials are of great interest due to their unique physical and chemical properties. Graphene is the first discovered 2D material. It has novel properties in different fields such as gas sensing, optical devices and hydrogen storage. Despite its advantages, its zero band gap prevents it from semiconducting properties. Great efforts were made by scientists to open a gap in graphene. One of the most famous methods to open a fractional eV gap is creating periodically pored graphene structure which is called graphene nanomesh. Inspired by graphene, scientists studied several 2D materials such as hexagonal boron nitride, black phos- phorus, MXenes and transition metal dichalcogenides (TMDs). Also inspired by GNM, 2D nanomesh structures were studied and shoowed improvement in the original properties of pristine struc- tures.
2D-TMDs are studied and showed novel properties in different fields such as nanoelectronic devices, solar cells and transistors. They are found in nature in different phases such as 2H and 1T phases. 2H-MoX2 (X=S, Se and Te) are semiconductors with suit- able gaps for transistors but they are nonmagnetic and thus they cannot be uses for magnetic or spintronic applications. On the other hand, 1T-MoX2 are magnetic metals. They can be used for
magnetic applications but they are not suitable for transistors and solar cells.
In this work, as a trial to improve the properties of 2D TMDs, we study the structural, mechanical, electronic and magnetic prop- erties of pristine and nanomesh structures of 2H-MoS2, 2H-MoSe2 and 2H-MoTe2. We study six different nanomeshes for each struc- ture based on the number of Mo and X vacencies where X=S, Se and Te. They form structures with different pore shapes. We study them without and with pore passivation.
We first use the density funcional theory (DFT) as implemented in QUANTUM ESPRESSO code to calculate the wave function and the total energy of each structure. Then, we use them as inputs in the ab-initio moecular dynamic (AIMD) simuations to study the time development of the position vectors and consequently the energy and temperature. We found that the structures are stable and do not change over the time. Also, we calculate the energies of isolated atoms from the DFT to study the cohesive energies by subtracting the sum of the isolated atoms from the total energies and dividing the result by te total number of atoms. It is found that the cohesive energies of all nanomesh structures are negative and close to those of their corresponding pristine structures. This inicates that our studied structures are feasible to be experimen-
tally synthesized.
We apply strain up to ±%2 on the structures and calculated the energy of straines structures from the DFT. The second derivative of the energy per unit unstained volume with respect to the strain defines the Young’s modulus. Young’s moduli of pristine struc- tures are close to previously published results. Young’s moduli of nanomesh structures are less than those of pristine structures and they, generally, decrease by increasing the mean diameters of the pore shapes.
from the DFT, we calculate the band structures, the density of states and the Fermi energy. We plot the DOS as afunction of energy and from it, we determine the electronic type of structures. We calculate the energy gaps from the band structures, Most of nanomesh structures are either semiconductors with different band gaps or half metals. This allow 2D TMD-nanomeshes for spin- tronic and tunable semiconductor applications. Also, we study the magnetic properties. Most of them are magnetic with different magnetizations, allowing for different magnetic applications.
We passivate Mo atoms with O atoms to study the effect of passivation on the electronic and magnetic properties. It is found that passivated structures are nonmagnetic metals.