| 1. |
- Bayani, Amirhossein, et al.
(författare)
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Intercalation of Au Atoms into SiC(0001)/Buffer Interfaces : A First-Principles Density Functional Theory Study
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:24, s. 14842-14846
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Tidskriftsartikel (refereegranskat)abstract
- The process of Au intercalation into a SiC/buffer interface has been theoretically investigated here by using density functional theory (DFT) and the nudged elastic band (NEB) method. Energy barriers were at first calculated (using NEB) for the transfer of an Au atom through a free-standing graphene sheet. The graphene sheet was either of a nondefect character or with a defect in the form of an enlarged hexagonal carbon ring. Defects in the form of single and double vacancies were also considered. Besides giving a qualitative prediction of the relative energy barriers for the corresponding SiC/buffer interfaces, some of the graphene calculations also proved evidence of energy minima close to the graphene sheet. The most stable Au positions within the SiC/buffer interface were, therefore, calculated by performing geometry optimization with Au in the vicinity of the buffer layer. Based on these NEB and DFT calculations, two factors were observed to have a great influence on the Au intercalation process: (i) energy barrier and (ii) preferential bonding of Au to the radical C atoms at the edges of the vacancies. The energy barriers were considerably smaller in the presence of vacancies. However, the Au atoms preferred to bind to the edge atoms of these vacancies when approaching the buffer layer. It can thereby be concluded that the Au intercalation will only occur for a nondefect buffer layer when using high temperature and/or by using high-energy impacts by Au atoms. For this type of Au intercalation, the buffer layer will become completely detached from the SiC surface, forming a single layer of graphene with an intact Dirac point.
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| 2. |
- Bayani, Amirhossein, et al.
(författare)
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The influence by substrate morphology on the Rashba band splitting in graphene
- 2020
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Ingår i: Results in Physics. - : Elsevier. - 2211-3797. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- The influence of substrate morphology on the Rashba band splitting at the Dirac point of graphene, has been theoretically investigated. More specifically, the possibility for this splitting to be caused by spin–orbit coupling (with the heavy metal substrate) was of a special interest to study. The model system consisted of a 4H-SiC (0 0 0 1)/graphene interface, with an intercalated metal layer (Ag and Au, respectively). These intercalating metal layers were built with two different types of morphologies; either flat or buckled (with different buckling positions). The results show that depending on the position of the buckled metal atom, the size of the bandgap and band splitting (at the Dirac point of graphene) will either increase (or decrease). Moreover, the enlargement of the buckling size was also shown to affect the electronic properties of graphene (i.e., by increasing the bandgap). The sizes of the bandgaps and band splitting for the different intercalating metals (Ag and Au), were also found to be different. Spin-projected band structures was also implemented in the present study, with the purpose to show the spin-texture of graphene. It was thereby shown that the spins pined to the x and y spin components for most of the cases.
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| 3. |
- Bayani, Amirhossein, et al.
(författare)
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The morphology of an intercalated Au layer with its effect on the Dirac point of graphene
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- This is a theoretical investigation where Density Functional Theory (DFT) has been used in studying the phenomenon of Au intercalation within the 4H-SiC/graphene interface. The electronic structure of some carefully chosen morphologies of the Au layer has then been of special interest to study. One of these specific Au morphologies is of a more hypothetical nature, whilst the others are, from an experimental point of view, realistic ones. The latter ones were also found to be energetically stable. Band structure calculations showed that intercalated Au layers with morphologies different from a planar Au layer will induce a band gap at the Dirac point of graphene (with up to 174 meV for the morphologies studied in the present work). It should here be mentioned that this bandgap size is four times larger than the energy of thermal motion at room temperature (26 meV). These findings reveal that a wide bandgap at the Dirac point of graphene comes from an inhomogeneous staggered potential on the Au layer, which non-uniformly breaks the sublattice symmetry. The presence of spin-orbit (SO) interactions have also been included in the present study, with the purpose to find out if SO will create a bandgap and/or band splitting of graphene.
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| 4. |
- Kishore, M. R. Ashwin, et al.
(författare)
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Theoretical investigation on BeN2 monolayer for an efficient bifunctional water splitting catalyst
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The search for an active, stable, and abundant semiconductor-based bifunctional catalysts for solar hydrogen production will make a substantial impact on the sustainable development of the society that does not rely on fossil reserves. The photocatalytic water splitting mechanism on a BeN2 monolayer has here been investigated by using state-of-the-art density functional theory calculations. For all possible reaction intermediates, the calculated changes in Gibbs free energy showed that the oxygen evolution reaction will occur at, and above, the potential of 2.06 V (against the NHE) as all elementary steps are exergonic. In the case of the hydrogen evolution reaction, a potential of 0.52 V, or above, was required to make the reaction take place spontaneously. Interestingly, the calculated valence band edge and conduction band edge positions for a BeN2 monolayer are located at the potential of 2.60 V and 0.56 V, respectively. This indicates that the photo-generated holes in the valence band can oxidize water to oxygen, and the photo-generated electrons in the conduction band can spontaneously reduce water to hydrogen. Hence, the results from the present theoretical investigation show that the BeN2 monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.
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| 5. |
- Vali, Mehran, et al.
(författare)
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A Scheme of Quantum Tunnel Field Effect Transistor Based on Armchair Graphene Nano-Ribbon
- 2021
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Ingår i: ECS Journal of Solid State Science and Technology. - : Electrochemical Society. - 2162-8769 .- 2162-8777. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- We proposed a scheme of armchair graphene nanoribbon (AGNR) based tunnel field-effect transistor (TFET). The simulated device consists of two (AGNR) electrodes with zigzag termination that are separated by a narrow gap. The Fermi level of two electrodes is controlled with a common back gate. The main idea is based on taking advantage of the electronic effects of smooth edge atoms of (AGNR) and investigating the effect of applied small uniaxial tensile strain and gate voltage on the output characteristics of simulated TFET. Our analysis shows that the simulated device will have a pronounced negative differential conductance high peak to valley ratio at room temperature. We see that by applying the uniaxial tensile strain, this ratio upgrades to 70 for (AGNR) with width N = 13.
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| 6. |
- Vali, Mehran, et al.
(författare)
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Boron Nitride-Graphene (BN-G) Bilayer as a Channel of Graphene Based Field Effect Transistor
- 2023
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Ingår i: ECS Journal of Solid State Science and Technology. - : Institute of Physics (IOP). - 2162-8769 .- 2162-8777. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- According to the effect of the interlayer interaction of the boron nitride sheet on electronic properties, especially the energy band gap of the graphene sheet in the boron nitride-graphene (BN-G) bilayer, we propose a gapless graphene-based field effect transistor (FET). It is comprised of a boron nitride layer on top of graphene in the channel region. In this study, we investigate the transfer characteristic and output characteristic of the proposed device for different values of the interlayer distance of (BN-G) bilayer. Also, we compare the output results with simulated bilayer graphene channel FET. We find that the I-on/I-off ratio in the proposed device shows a significant promotion compared to graphene bilayer channel FET. Our first-principles calculations show that by decreasing the inter-layer distance of (BN-G) bilayer, the energy gap increase which leads to a dipper I-off current and an increase of I-on/I-off ratio up to 104 for an inter-layer distance of 2.7 angstroms. Moreover, it is found that the proposed device output characteristic displays a very good saturation due to improved pinch-off of the channel.
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