Electronic and magnetic properties of graphene quantum dots doped with alkali metals
| Autor: | N.H. Teleb, Medhat Ibrahim, Hazem Abdelsalam, Mohammed Eid M. Ali, Qinfang Zhang, Waleed Osman, I.S. Yahia |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Spin polarization
lcsh:TN1-997 Materials science Alkali metals Spin states Binding energy 02 engineering and technology DFT 01 natural sciences law.invention Biomaterials law 0103 physical sciences Doping Singlet state lcsh:Mining engineering. Metallurgy 010302 applied physics Condensed matter physics Spintronics Graphene quantum dots Graphene Metals and Alloys 021001 nanoscience & nanotechnology Surfaces Coatings and Films Electronic and magnetic properties Quantum dot Ceramics and Composites Condensed Matter::Strongly Correlated Electrons 0210 nano-technology Ground state |
| Zdroj: | Journal of Materials Research and Technology, Vol 11, Iss, Pp 1517-1533 (2021) |
| ISSN: | 2238-7854 |
| Popis: | The electronic and magnetic properties of armchair-hexagonal (AHEX) and zigzag-triangular (ZTRI) graphene quantum dots doped with alkali metals are investigated using density functional theory. The binding energy confirms the stability of the undoped systems. Although doping decreases stability of single layer structures, in bilayer ones the binding energy between the layers increases. The former is due to the broken bonds and the deformation at the surface, while the later is due to the chemical bonds formation between the layers. We found that the lowest ground state energy for AHEX/AHEX-doped is the singlet/quadruplet spin state. Therefore, AHEX dots experience transformation from diamagnetic to ferromagnetic state after doping. In addition, the optimized spin state for ZTRI/ZTRI-doped is the quintet/sextet spin-polarized state. In few cases, the doped AHEX/ZTRI dots have doublet/quadruplet spin state due to the strong interaction between the flake atoms that passivates some unpaired electrons. Magnetic properties depend also on stacking, for instance pristine bilayer triangular flakes become antiferromagnetic due to pairing between edge states. The energy gap significantly affected by doping, for instance the gap decreases from ~3.7 eV in hexagonal flakes to 1.5 eV when it is doped with Na in the upper position. Electrons from the broken bonds around the doped metal form orbitals loosely bound to the flake consequently decreasing the energy gap. On the other hand, stacking increases the energy gap in bilayer triangular flakes due to the mutual passivation of the reactive edge states from both the layers. The calculated spin up/down density ratio is high in hexagonal flakes leading to high spin polarization (P), for instance P = 0.64 in hexagonal flakes doped with K atom. The found enhanced spin polarization, in addition to the tunable magnetic properties, makes doped graphene flakes promising candidates for spintronic devices. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|