| 1. |
- Bafekry, A., et al.
(author)
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A novel two-dimensional boron-carbon-nitride (BCN) monolayer: A first-principles insight
- 2021
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 130:11
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Journal article (peer-reviewed)abstract
- The optical, electronic, and structural properties of a theoretically predicted new boron-carbon-nitride (BCN) two-dimensional monolayer have been explored using density functional theory calculations. The phonon dispersion, molecular dynamics simulation, the cohesive energy, and the Born criteria of elastic constant calculations of the BCN monolayer confirm its stability. The phonon spectrum illustrates an out-of-plane flexure mode with quadratic dispersion in the long-wavelength limit. The BCN monolayer is a semiconductor with a direct bandgap of 0.9 (1.63) eV determined via the Perdew-Burke-Ernzerhof (Heyd-Scuseria-Ernzerhof) functional. The same electron and hole effective masses and mobility values indicate the high recombination rate of electrons and holes. Meanwhile, the BCN monolayer can absorb ultraviolet radiation more effectively than visible light. Due to its interesting physical properties, the novel BCN monolayer could be a rather good candidate material for electro-optical applications.& nbsp;Published under an exclusive license by AIP Publishing
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| 2. |
- Bafekry, A., et al.
(author)
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Ab-initio-driven prediction of puckered penta-like PdPSeX (X=O, S, Te) Janus monolayers : Study on the electronic, optical, mechanical and photocatalytic properties
- 2022
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 582
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Journal article (peer-reviewed)abstract
- A systematic investigation of the structural, mechanical, electronic, and optical properties of puckered penta-like PdPSeX (X=O, S and Te) Janus monolayers has been performed by means of the plane wave density functional theory. It is confirmed that the pentagonal PdPSeX monolayers are dynamically and mechanical stable by means of analysis of their phonon dispersion curves and the Born condition under harmonic approximation, respectively. The PdPSeX Janus monolayers are disclosed as brittle two-dimensional materials (2DMs). The PBE (HSE06)-based calculations exhibit they are indirect semiconductors with bandgap values of 0.65 (1.44) eV, 1.20 (2.02) eV, and 0.98 (1.70) eV for PbPSeO, PbPSeS, and PbPSeTe monolayer, sequentially. The computational results demonstrate the PdPSeTe monolayer as the best suited candidate for visible light absorption and photocatalytic water splitting within the considered pentagonal PdPSeX monolayers. Our ab-initio-based outcomes provide an insight into the fundamental properties of the penta-like PdPSeX Janus structures and surely would motivate further experimental and theoretical studies to reveal the full application potential of this new type of 2DMs.
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| 3. |
- Bafekry, A., et al.
(author)
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Biphenylene monolayer as a two-dimensional nonbenzenoid carbon allotrope: a first-principles study
- 2022
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In: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:1
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Journal article (peer-reviewed)abstract
- In a very recent accomplishment, the two-dimensional form of biphenylene network (BPN) has been fabricated. Motivated by this exciting experimental result on 2D layered BPN structure, herein we perform detailed density-functional theory-based first-principles calculations, in order to gain insight into the structural, mechanical, electronic and optical properties of this promising nanomaterial. Our theoretical results reveal the BPN structure is constructed from three rings of tetragon, hexagon and octagon, meanwhile the electron localization function shows very strong bonds between the C atoms in the structure. The dynamical stability of BPN is verified via the phonon band dispersion calculations. The mechanical properties reveal the brittle behavior of BPN monolayer. The Youngs modulus has been computed as 0.1 TPa, which is smaller than the corresponding value of graphene, while the Poissons ratio determined to be 0.26 is larger than that of graphene. The band structure is evaluated to show the electronic features of the material; determining the BPN monolayer as metallic with a band gap of zero. The optical properties (real and imaginary parts of the dielectric function, and the absorption spectrum) uncover BPN as an insulator along the zz direction, while owning metallic properties in xx and yy directions. We anticipate that our discoveries will pave the way to the successful implementation of this 2D allotrope of carbon in advanced nanoelectronics.
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| 4. |
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| 5. |
- Bafekry, A., et al.
(author)
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Investigation of vacancy defects and substitutional doping in AlSb monolayer with double layer honeycomb structure: a first-principles calculation
- 2022
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In: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:6
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Journal article (peer-reviewed)abstract
- The experimental knowledge of the AlSb monolayer with double layer honeycomb structure is largely based on the recent publication (Le Qin et al 2021 ACS Nano 15 8184), where this monolayer was recently synthesized. Therefore, the aim of our research is to consequently explore the effects of substitutional doping and vacancy point defects on the electronic and magnetic properties of the novel hexagonal AlSb monolayer. Besides experimental reports, the phonon band structure and cohesive energy calculations confirm the stability of the AlSb monolayer. Its direct bandgap has been estimated to be 0.9 eV via the hybrid functional method, which is smaller than the value of 1.6 eV of bulk material. The majority of vacancy defects and substitutional dopants change the electronic properties of the AlSb monolayer from semiconducting to metallic. Moreover, the Mg-Sb impurity has demonstrated the addition of ferromagnetic behavior to the material. It is revealed through the calculation of formation energy that in Al-rich conditions, the vacant site of V-Sb is the most stable, while in Sb-rich circumstances the point defect of V-Al gets the title. The formation energy has also been calculated for the substitutional dopants, showing relative stability of the defected structures. We undertook this theoretical study to inspire many experimentalists to focus their efforts on AlSb monolayer growth incorporating different impurities. It has been shown here that defect engineering is a powerful tool to tune the properties of novel AlSb two-dimensional monolayer for advanced nanoelectronic applications.
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| 6. |
- Bafekry, A., et al.
(author)
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Theoretical prediction of two-dimensional BC2X (X = N, P, As) monolayers: ab initio investigations
- 2022
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In: Scientific Reports. - : NATURE PORTFOLIO. - 2045-2322. ; 12:1
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Journal article (peer-reviewed)abstract
- In this work, novel two-dimensional BC2X (X = N, P, As) monolayers with X atoms out of the B-C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC2X monolayers have been investigated. Stability evaluation of the BC2X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC2N, BC2P and BC2As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC2X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC2N and BC2P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC2X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC2X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.
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| 7. |
- Bafekry, A., et al.
(author)
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Tunable electronic properties of porous graphitic carbon nitride (C6N7) monolayer by atomic doping and embedding: A first-principle study
- 2022
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In: Applied Surface Science. - : ELSEVIER. - 0169-4332 .- 1873-5584. ; 583
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Journal article (peer-reviewed)abstract
- Motivated by the successful synthesis of the porous graphitic carbon nitride (C6N7) monolayer very recently, we investigate the structural and electronic properties of C6N7 with doped and embedded with various atoms by means of spin-polarized density functional theory calculations. C6N7 monolayers doped with B, N, C, and O atoms have been revealed as stable and predicted to be feasible for experimental fabrication as free-standing monolayers based on the energy and thermal stability. Our computations demonstrate that while the C6N7 is a semiconductor, the doped C6N7 monolayers can be metal, dilute-magnetic semiconductor or half-metal. Further, a non magnetic moment is discovered in three of the doped C6N7 models and their electronic properties are disclosed to depend strongly on the spin configurations. The electronic properties of C6N7 depend on the doping atoms and doping sites. Furthermore, the effect of embedding of common nonmetal atoms such as B, C, N, S, O, Al, Si and P as well as transition metal including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn atoms on the electronic and magnetic behavior of the C6N7 are studied. The charge transfer analysis shows that all embedded atoms act as electron donors, expect N, O and S atoms which act as electron acceptors when interacting with C6N7. The modification of the electronic band structure of C6N7 as the underlying mechanism for the changes in its electronic properties has been investigated. The intention is to demonstrate how entering the above mentioned impurities changes the nature of C6N7 into a metal, ferromagnetic-metal or dilute-magnetic semiconductor. These findings give not only an insight into the physical properties of doped and embedded C6N7 monolayer by different atoms, but also can serve as a guide to discover future possible applications of this novel material.
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| 8. |
- Bafekry, A., et al.
(author)
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Two-dimensional FeTe2 and predicted Janus FeXS (X: Te and Se) monolayers with intrinsic half-metallic character: tunable electronic and magnetic properties via strain and electric field
- 2021
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In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 23:42, s. 24336-24343
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Journal article (peer-reviewed)abstract
- Driven by the fabrication of bulk and monolayer FeTe2 (ACS Nano, 2020, 14, 11473-11481), we explore the lattice, dynamic stability, electronic and magnetic properties of FeTeS and FeSeS Janus monolayers using density functional theory calculations. The obtained results validate the dynamic and thermal stability of the FeTeS and FeSeS Janus monolayers examined. The electronic structure shows that the FeTe2 bulk yields a total magnetization higher than the FeTe2 monolayer. FeTeS and FeSeS are categorized as ferromagnetic metals due to their bands crossing the Fermi level. So, they can be a good candidate material for spin filter applications. The biaxial compressive strain on the FeTe2 monolayer tunes the bandgap of the spin-down channel in the half-metal phase. By contrast, for FeTeS, the biaxial strain transforms the ferromagnetic metal into a half-metal. The electric field applied to the FeSeS monolayer in a parallel direction transforms the half-metal to a ferromagnetic metal by closing the gap in the spin-down channel.
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| 9. |
- Bafekry, A., et al.
(author)
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Van der Waals heterostructure of graphene and germanane: tuning the ohmic contact by electrostatic gating and mechanical strain
- 2021
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:37, s. 21196-21206
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Journal article (peer-reviewed)abstract
- Recent exciting developments in synthesis and properties study of the Germanane (GeH) monolayer have inspired us to investigate the structural and electronic properties of the van der Waals GeH/Graphene (Gr) heterostructure by the first-principle approach. The stability of the GeH/Gr heterostructure is verified by calculating the phonon dispersion curves as well as by thermodynamic binding energy calculations. According to the band structure calculation, the GeH/Gr interface is n-type Ohmic. The effects of different interlayer distances and strains between the layers and the applied electric field on the interface have been investigated to gain insight into the van der Waals heterostructure modifications. An interlayer distance of 2.11 angstrom and compressive strain of 6% alter the contact from Ohmic to Schottky status, while the electric field can tune the GeH/Gr contact as p- or n-type, Ohmic, or Schottky. The average electrostatic potential of GeH/Gr and the Bader charge analysis have been used to explain the results obtained. Our theoretical study could provide a promising approach for improving the electronic performance of GeH/Gr-based nano-rectifiers.
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| 10. |
- Delgado Carrascon, Rosalia, 1987-
(author)
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Epitaxy of group III-nitride materials using different nucleation schemes
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Group III-nitride materials, gallium nitride (GaN), aluminum nitride (AlN) and indium nitride (InN) have direct band gaps with band gap energies ranging from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN) wave-lengths, covering the entire spectral range from 0.7 eV to 6.2 eV upon alloying. The invention of the GaN-based blue LEDs, for which the Nobel prize in Physics was awarded in 2014, has opened up avenues for exploration of III-Nitride mate-rial and device technologies, and has inspired generations of researchers in the semiconductor field. Group III-nitrides have also been demonstrated to be among the most promising semiconductors for next generation of efficient high-power, high-temperature and high-frequency electronic devices. The need to build a sustainable and efficient energy system motivates the development of vertical GaN transistors and diodes for applications with power ratings of 50-150 kW, e.g., in electric vehicles and industrial inverters. The key is to grow GaN layers with low concentration of defects (impurities and dislocations), which enables an expansion in both voltage and current ratings and reduction of cost. Despite intense investigations and impressive advances in the field, defects are still a major problem which hinders exploiting the full potential of GaN in power electronics. The aim of this thesis is to perform an in-depth investigation of the growth of GaN and AlGaN under several nucleation mechanisms provided by different underlying substrates. In that regard, four different epitaxial approaches based on different nucleation schemes have been studied: (i) growth of planar GaN layers trough NWs reformation. We investigated GaN layers with different thicknesses on reformed GaN NW templates and highlight this approach as an alternative to the expensive HVPE GaN substrates. The sapphire used as a substrate limits to some extent the reduction of threading dislocations, however, the resulting GaN material presents smooth surfaces and thermal conductivity close to the value for bulk GaN. (ii) Homoepitaxial GaN growth. We developed a hot-wall MOCVD epitaxial approach that enables low surface roughness and appropriate impurity levels for advanced vertical power device architectures. A comprehensive picture of GaN homoepitaxy on different GaN surfaces, GaN templates on SiC and HVPE GaN substrates, is established on the basis of experimental results and thermodynamic considerations. (iii) GaN growth on GaN NWs templates by hot-wall MOCVD resulted in an atomically flat smooth surface with reduction of threading dislocations when the optimum annealing conditions have been employed. (iv) Heteroepitaxial growth of low Al composition n-AlxGa1-xN on SiC substrates revealed 700 nm crack-free epi-layers for an Al composition up to 12%. The highest mobility corresponds to an Al content of 6.5% where we also get a reduction in screw and edge dislocations. The results show the potential application of AlxGa1-xN(x= 0 - 0.12) as the active material for drift layers. Some of the epitaxial approaches developed in this thesis have been already implemented in the growth of power devices such as quasi-vertical GaN FinFETs on SiC substrates and fully-vertical GaN FinFETs on HVPE GaN substrates.
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