MgO Monolayer Research Articles

Buckling strain effects on the electron and the phonon spectra, the stability, thermal, and optical characteristics of an MgO nanosheet using PBE/GGA and HSE06

The stability, the electronic, the phonon, the thermal, and the optical properties of a buckled MgO monolayer are investigated using DFT with the PBE/GGA and the HSE06 functionals. Model calculations for a buckled MgO monolayer indicate a more interesting behavior than for its flat phase. The band gap decreases from 4.9 to 2.83 eV within the HSE06 approach due to increased electron density of states in the conduction band in the direction of the buckling. Both phonon dispersion and molecular dynamic calculations confirm the dynamic and the thermal stability of the buckled MgO monolayer. The heat capacity of a buckled monolayer is higher than for the flat one in a high temperature range due to a higher phonon density of states caused by the buckling effects. Furthermore, the buckled MgO monolayer has a higher static dielectric function leading to an increased ability to store electrical energy. The buckling creates wrinkles at the surface of the MgO monolayer that can localize collective electron oscillations, resulting in suppression of the plasmon frequency. The main intensity peak in the optical conductivity is red-shifted from the near-ultraviolet to the visible light region in the presence of buckling which may be beneficial for optoelectronic devices.

Thermoelectric Properties of BeO and MgO Monolayers from First-Principles Calculations

Thermoelectric Properties of BeO and MgO Monolayers from First-Principles Calculations

Site dependent strategy for B/C/N homo and heteroatom co-doping in governing the optoelectronic behavior of MgO monolayers

Density functional theory calculations are carried out to investigate the effects of homo- and hetero-type co-doping of B, C and N on structural and electronic properties of MgO monolayers (MLs). The co-doping sites considered here are the possible equivalent and non-equivalent positions of a hexagon in a pristine MgO ML. The planarity of the monolayers is found to be governed by the site selectivity of the dopant atoms as well as the positions of doping. Planar monolayers have a higher likelihood of formation than the non-planar monolayers. In case of non-equivalent doping, the doping atoms always prefer positions that are closer. Stepwise substitution is more likely to occur than simultaneous substitution in formation of the co-doped monolayers. Most of the co-doping combinations introduce magnetism to the pristine MgO ML. Hetero-type monolayers prefer to be in magnetic states and even exhibit higher magnetic moments than homo-type MLs, with a maximum value of 4 μB for B–N co-doping. Almost all the monolayers are semiconducting with significantly reduced band gaps, while few hetero-type monolayers are metallic in nature. The electronic energy band gaps of the monolayers are compatible with the IR and visible regions of the electromagnetic spectrum. The overall tuning of the electronic properties renders the co-doped MgO monolayers effective for applications in spintronics and optoelectronics.

Optical conductivity enhancement and thermal reduction of BN-codoped MgO nanosheet: Significant effects of B-N atomic interaction

We investigate the electronic, the thermal, and the optical properties of BN-codoped MgO monolayers taking into account the interaction effects between the B and the N dopant atoms. The relatively wide indirect band gap of a pure MgO nanosheet can be changed to a narrow direct band gap by tuning the B-N attractive interaction. The band gap reduction does not only enhance the optical properties, including the absorption spectra and the optical conductivity, but also the most intense peak is shifted from the Deep-UV to the visible light region. The red shifting of the absorption spectra and the optical conductivity are caused by the attractive interaction. In addition, both isotropic and anisotropic characteristics are seen in the optical properties depending on the strength of the B-N attractive interaction. The heat capacity is reduced for the BN-doped MgO monolayer, which can be referred to changes in the bond dissociation energy. The bond dissociation energy decreases as the difference in the electronegativities of the bonded atoms decreases. The lower difference in the electronegativities leads to a weaker endothermic process resulting in reduction of the heat capacity. An ab initio molecular dynamics, AIMD, calculation is utilized to check the thermodynamic stability of the pure and the BN-codoped MgO monolayers. We thus confirm that the BN-codopant atoms can be used to gain control of the properties of MgO monolayers for thermo- and opto-electronic devices.

Electronic structure alteration in MgO monolayer through alkali metal doping

We have studied the structural and electronic properties of MgO monolayer (ML) by substituting one of its Mg sites with alkali metal atoms (Li, Na, K) using DFT calculations in Quantum ESPRESSO. All the planar-doped monolayers are structurally stable shown by the computed binding energy per atom values. Formation energies suggest that Li exhibits the strongest binding with MgO ML. Doping turns the non-magnetic semiconducting MgO MLs into half-metallic magnets with magnetic moment of ∼ 1μB. The corresponding magnetic states are contributed by the valence orbitals of O atoms near the doping sites. Thus, Li, Na, K substitution introduces huge changes in electronic structure and properties of MgO ML.

Exploring electronic, optical, and phononic properties of MgX (X = C, N, and O) monolayers using first principle calculations

The electronic, the thermal, and the optical properties of hexagonal MgX monolayers (where [Formula: see text] = [Formula: see text], [Formula: see text], and [Formula: see text]) are investigated via first principles studies. Ab-initio molecular dynamic, AIMD, simulations using NVT ensembles are performed to check the thermodynamic stability of the monolayers. We find that an MgO monolayer has semiconductor properties with a good thermodynamic stability, while the MgC and the MgN monolayers have metallic characters. The calculated phonon band structures of all the three considered monolayers show no imaginary nonphysical frequencies, thus indicating that they all have excellent dynamic stability. The MgO monolayer has a larger heat capacity then the MgC and the MgN monolayers. The metallic monolayers demonstrate optical response in the IR as a consequence of the metal properties, whereas the semiconducting MgO monolayer demonstrates an active optical response in the near-UV region. The optical response in the near-UV is beneficial for nanoelectronics and photoelectric applications. A semiconducting monolayer is a great choice for thermal management applications since its thermal properties are more attractive than those of the metallic monolayer in terms of heat capacity, which is related to the change in the internal energy of the system.

Site selective behaviour of B, C and N doping in MgO monolayers towards spintronic and optoelectronic applications

The electronic, magnetic and optical properties of graphene-like MgO monolayers doped with B, C and N atoms in both Mg and O sites are investigated in the framework of density functional theory. The impurity atoms induce magnetism in the host material irrespective of the sites of substitution. The HSE based hybrid DFT calculations show that the wide electronic band gap semiconducting pristine MgO monolayer becomes metallic due to B and C doping in the Mg site of MgO monolayer system (BMg and CMg). However, rests of the doped monolayers remain semiconducting with appearance of impurity states that lowers their energy band gaps compared to the pristine value. Accordingly, the optical behaviour of the doped systems get tuned making them optically active for a wide spectral range in electromagnetic spectrum starting from infrared to UV region. Therefore, such site selective modulation of electronic and optical properties achieved through substitutional doping in MgO monolayers may be effective for desirable moulding of these materials for spintronic and optoelectronic applications.

Tuning the electronic and magnetic properties of MgO monolayer by nonmetal doping: A first-principles investigation

Tuning the electronic and magnetic properties of MgO monolayer by nonmetal doping: A first-principles investigation

Two-dimensional heterostructures formed by graphenelike ZnO and MgO monolayers for optoelectronic applications

Two-dimensional heterostructures are an emerging class of materials for novel applications because of extensive engineering potential by tailoring intriguing properties of different layers as well as the ones arising from their interface. A systematic investigation of mechanical, electronic, and optical properties of possible heterostructures formed by bilayer structures graphenelike ZnO and MgO monolayers is presented. Different functionality of each layer makes these heterostructures very appealing for device applications. ZnO layer is convenient for electron transport in these structures, while MgO layer improves electron collection. At the outset, all of the four possible stacking configurations across the heterostructure are mechanically stable. In addition, stability analysis using phonon dispersion reveals that the AB stacking formed by placing the Mg atom on top of the O atom of the ZnO layer is also dynamically stable at zero temperature. Henceforth, we have investigated the optical properties of these stable heterostructures by applying many-body perturbation theory within the framework of GW approximation and solving the Bethe-Salpeter equation. It is demonstrated that strong excitonic effects reduce the optical band gap to the visible light spectrum range. These results show that this new two-dimensional form of ZnO/MgO heterostructures open an avenue for novel optoelectronic device applications.

Effect of oxygen vacancy defects on electronic and optical properties of MgO monolayers: First principles study

The optoelectronic properties induced by oxygen vacancy defects in MgO (111) monolayers have been studied using hybrid level of DFT method. HSE calculations show significant reduction in electronic band gap of MgO monolayer as a result of introduction of oxygen vacancies. The pristine monolayer has a wide band gap (4.84 eV, indirect) semiconducting behaviour, which changes to 2.97 eV (indirect) and 2.28 eV (direct) with increment in oxygen vacancy defect concentrations of 6.25 % and 12.5 %, respectively. Consequently, presence of oxygen vacancies leads to energy red shift of the observed optical phenomena with reference to the pristine monolayer. Most importantly, the di-vacancy system with two consecutive vacancy sites displays the strongest optical absorption and also becomes optically responsive over the spectral range from visible to ultraviolet region in the electromagnetic spectrum. Thus creation of oxygen vacancies in MgO monolayers may be a fruitful technique for achieving a suitable solar energy material.

Two-dimensional quantum confinement effects on thermoelectric properties of MgO monolayers: A first principle study

In this paper, the thermoelectric properties of magnesium oxide in the bulk and monolayer (ML) phases in the two facets of (100) and (111) have been calculated and compared by using density functional theory (DFT) and Boltzmann theory. The electronic band structure calculations of bulk and monolayers of MgO indicate that the band gap for bulk and MgO(100) ML is direct, and indirect for MgO(111) ML Κ-to Γ-point. The estimated band gaps are in good agreement with other theoretical and experimental works. Due to the quantum confinement effects, two small peaks are observed in the n-doping region of the room temperature Seebeck coefficients of the monolayers which are not present in the bulk structure. In addition, we demonstrate that the room temperature figure of merit of MgO(100) ML has a remarkable peak at μ ​= ​2.71 ​eV with the value of about 1.5 which is attributed to its corresponding Seebeck coefficient peak. Beside, with increasing temperature, this peak shifts to the lower chemical potentials and reaches to 1.8 ​at ​T ​= ​800 ​K and μ ​= ​2.4 ​eV. Our findings show that a proper n-doping MgO(100) ML is a promising material for future thermoelectric applications at room and even high temperatures.

High tensile strength and thermal conductivity in BeO monolayer: A first-principles study

In a latest experimental advance, graphene-like and insulating BeO monolayer was successfully grown over silver surface by molecular beam epitaxy (ACS Nano 15(2021), 2497). Inspired by this accomplishment, in this work we conduct first-principles based simulations to explore the electronic, mechanical properties and thermal conductivity of graphene-like BeO, MgO and CaO monolayers. The considered nanosheets are found to show desirable thermal and dynamical stability. BeO monolayer is found to show remarkably high elastic modulus and tensile strength of 408 and 53.3 GPa, respectively. The electronic band gap of BeO, MgO and CaO monolayers are predicted to be 6.72, 4.79, and 3.80 eV, respectively, using the HSE06 functional. On the basis of iterative solution of the Boltzmann transport equation, the room temperature lattice thermal conductivity of BeO, MgO and CaO monolayers are predicted to be 385, 64 and 15 W/mK, respectively. Our results reveal substantial decline in the electronic band gap, mechanical strength and thermal conductivity by increasing the weight of metal atoms. This work highlights outstandingly high thermal conductivity, carrier mobility and mechanical strength of insulating BeO nanosheets and suggest them as promising candidates to design strong and insulating components with high thermal conductivities.

Stability and thermoelectric properties of the MgO monolayers under tensile and compressive strain

In this study, the stability and thermoelectric properties of MgO (111) and (100) monolayers under compressive and tensile strain were investigated by density functional theory. The flat MgO (111) revealed to be stable against a biaxial and uniaxial tensile strain of up to ε = 15% and compressive strain of up to ε = −2% for biaxial strain and −5% for uniaxial strain. The rumbled MgO (100) showed stability for the only tensile strain of up to 8%. The thermoelectric properties of the MgO monolayers predict the figure of merit of about unity in both n- and p-type doping regions which found to be promising for practical application of MgO monolayers in thermoelectric devices.

Structural, electronic and optical properties of pristine and functionalized MgO monolayers: a first principles study.

In this paper, we present a detailed investigation of the structural, electronic, and optical properties of pristine, nitrogenated, and fluorinated MgO monolayers using ab initio calculations. The two dimensional (2D) material stability is confirmed by the phonon dispersion curves and binding energies. Full functionalization causes notable changes in the monolayer structure and slightly reduces the chemical stability. The simulations predict that the MgO single layer is an indirect semiconductor with an energy gap of 3.481 (4.693) eV as determined by the GGA-PBE (HSE06) functional. The electronic structure of the MgO monolayer exhibits high sensitivity to chemical functionalization. Specifically, nitrogenation induces metallization of the MgO monolayer, while an indirect–direct band gap transition and band gap reduction of 81.34 (59.96)% are achieved by means of fluorination. Consequently, the functionalized single layers display strong optical absorption in the infrared and visible regimes. The results suggest that full nitrogenation and fluorination may be a quite effective approach to enhance the optoelectronic properties of the MgO monolayer for application in nano-devices.

ZnO/(Zn)MgO polar and nonpolar superlattices

The bandgaps of short period ZnO/(Zn)MgO superlattices deposited on c-, m-, and a-ZnO substrates were examined both theoretically and experimentally. Ab initio calculations showed that the bandgaps of c-oriented polar superlattices are smaller than those of nonpolar ones; however, this is mainly due to different geometric configurations, because the influence of internal electric fields existing in polar superlattices is not very significant. The calculations revealed that for 5–6 MgO monolayers in the barriers, the bandgap values become independent of the barrier thickness, which suggests that such superlattices can be treated as sets of isolated ZnO wells. In the experimental part of this work, it is demonstrated that short period ZnO/MgO and ZnO/ZnMgO superlattices can be grown successfully on differently oriented crystalline bulk ZnO substrates using molecular beam epitaxy. The bandgaps of the superlattices were determined from low temperature photoluminescence measurements. It is shown that they agree well with the theoretical results.

First-principle Calculations to Investigate Electronic And Optical Properties of MgO Monolayer

First-principle Calculations to Investigate Electronic And Optical Properties of MgO Monolayer

The electronic and optical properties of MgO mono-layer: Based on GGA-mBJ

Abstract The electronic and optical properties of MgO mono-layer were calculated based on the density functional theory (DFT) with FP-LAPW method using PBE-GGA and GGA-mBJ approximations. The electronic calculations of MgO mono-layer show a more interesting behavior than its bulk phase such as decreasing the band gap from 7.8 eV to 3.1 eV (for GGA) and 4.2 eV (for GGA-mBJ). Also, the MgO mono-layer has a direct band gap at Γ point in the Brillion Zone, and the effective masses of electrons are very greater than the effective mass of holes in this point. The optical coefficients such as dielectric parameters, energy loss functions, Refractions, Extinction and Absorption of this graphene-like (G-L) were calculated by RPA method which indicates the semiconducting properties of this mono-layer at the in-plane and perpendicular directions to emitting light.

Electronic, magnetic and optical properties of B, C, N and F doped MgO monolayer

MgO as one of the alkaline earth oxides has various applications in industry. In this work, we aim to investigate the electronic, optical and magnetic properties of MgO monolayers. Furthermore, monolayer structures with substituted B, N, C and F atoms instead of O atom are studied. These results indicate that MgO layer has possessed potential application in optoelectronic and spintronic nano-devices.

CH3Br adsorption on MgO/Mo ultrathin films: A DFT study

The adsorption of methyl bromide on MgO ultrathin films supported on Mo(100) was studied by means of density functional theory calculations, in comparison to the MgO(100) and Mo(100) surfaces. The adsorption energy and geometry were shown to depend on the thickness of the supported oxide film. MgO films as thick as 2ML (or more) display adsorptive properties similar to MgO(100), i.e. the adsorption of CH3Br is mostly due to dispersion and the molecule lies in a tilted geometry almost parallel to the surface. The CH3Br HOMO-LUMO gap is almost unaltered with respect to the gas phase. On metallic Mo(100) surfaces the bonding is completely different with the CH3Br molecule strongly bound and the C–Br bond axis almost vertical with respect to the metal surface. The MgO monolayer supported on Mo exhibits somehow intermediate properties: the tilt angle is larger and the bonding is stronger than on MgO(100), due to the effect of the supporting metal. In this case, a small reduction of the HOMO-LUMO gap of the adsorbed molecule is reported. The results help to rationalize the observed behavior in photodissociation of CH3Br supported on different substrates.

MgO monolayer epitaxy on Ni (100)

The growth of two-dimensional oxide films with accurate control of their structural and electronic properties is considered challenging for engineering nanotechnological applications. We address here the particular case of MgO ultrathin films grown on Ni (100), a system for which neither crystallization nor extended surface ordering has been established previously in the monolayer range. Using Scanning Tunneling Microscopy and Auger Electron Spectroscopy, we report on experiments showing MgO monolayer (ML) epitaxy on a ferromagnetic nickel surface, down to the limit of atomic thickness. Alternate steps of Mg ML deposition, O2 gas exposure, and ultrahigh vacuum thermal treatment enable the production of a textured film of ordered MgO nano-domains. This study could open interesting prospects for controlled epitaxy of ultrathin oxide films with a high magneto-resistance ratio on ferromagnetic substrates, enabling improvement in high-efficiency spintronics and magnetic tunnel junction devices.