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- Chafai, A., et al.
(författare)
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First-principles insights into the optical and electronic characteristics of barium intercalated AB-stacked bilayer graphene
- 2023
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Ingår i: The European Physical Journal Plus. - : Springer Nature. - 2190-5444. ; 138:8
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Tidskriftsartikel (refereegranskat)abstract
- The present study describes the electronic and optical characteristics of barium atoms (an alkaline earth metal) intercalated within AB-stacked bilayer graphene (AB-2LG). Using state-of-the-art first-principles computations and taking into account the dispersion forces between the diverse nanosheets, we determined that the intercalation of barium atoms (Ba) into AB-2LG increases the interlayer distance from 3.357 to 5.584 degrees A, and no C-Ba bond formation has been observed. In addition, our findings reveal that the presence of Ba atoms inside the AB-2LG induces a change in the Space group number from 164 (pure AB-2LG) to 156 (Ba-intercalated AB-2LG). Concurrently, we observed that the AB-2LG band structure exhibits a Dirac cone at the K-point, which is a characteristic signature of a semi-metallic character. By contrast, the electronic behavior of the barium-intercaled AB-2LG is found to be metallic. Also, we noticed that the confinement of Ba atoms into the AB-2LG shifts the Dirac point under the Fermi level. Additionally, upon examining the optical properties under the 001 and 100-polarization of the incident light, we found that all optical parameters of both under-investigated bidimensional materials exhibit an anisotropic character. Interestingly, under the 001-polarization, we observed that the intercalation of AB-2LG with Ba atoms reduces the optical absorption to zero in the visible region, and blueshifts are the absorption peak observed in the infrared region. Furthermore, in the case of 001-polarization, the presence of Ba atoms enhances the optical absorption in the 7-9 eV spectral range. However, the obtained data exhibit a remarkable decrease in the refractive index after the Ba intercalation process, for both considered polarization directions.
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- Chafai, A., et al.
(författare)
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External electric field modulation of single-layer MoSe2 electronic and optical properties : A first-principles investigation
- 2023
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Ingår i: MICRO AND NANOSTRUCTURES. - : Elsevier. - 2773-0123. ; 182
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Tidskriftsartikel (refereegranskat)abstract
- A wisely applied external electric field could effectively develop the optoelectronic properties of single-layer materials. The optical and electronic characteristics of monolayer molybdenum diselenide (ML-MoSe2) are deeply studied by means of density functional computations (DFT) to pinpoint the effect of the out-of-plane applied electric field (F//Oz). In fact, variations in the applied electric field strength gradually increase the energy of the electronic band gap (Eg) from 1.44 eV at 0V/& ANGS; to 1.51 eV at & PLUSMN;0.6V/& ANGS;. We also probed a sharp drop in the energy gap at high intensities. However, dielectric function, reflectivity, and loss function are studied for unpolarized and polarized incident light. Interestingly, the 001-polarization of the incident light affects the dielectric function's magnitude and position; this effect is more emphasized in the presence of an electric field with positive strengths. Furthermore, we found that the applied negative/positive electric field enhances the UV-visible reflectivity. Also, blue shifts of the ML-MoSe2 optical properties spectrum appear when subjected to the 001-polarized incident light. However, the loss function exhibits a weak response to the applied F. Additionally, we obtain that the 001-light polarization improves a plasmonic peak around 100 nm. Our results will provide a new view to understanding the controllable optical and electronic properties of MoSe2 monolayer, which is valuable for the design of new optoelectronic and plasmonic devices under development.
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- Chafai, A., et al.
(författare)
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Linear and nonlinear optical properties of donors inside a CdSe/ZnTe core/shell nanodot : Role of size modulation
- 2019
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Ingår i: RESULTS IN PHYSICS. - : ELSEVIER. - 2211-3797. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- The optical absorption coefficient (OAC) and the refractive index (RI), related to a confined donor, were theoretically investigated by the mean of the density matrix formalism. In order to obtain the 1s - 1p donor transition energy a variational calculation, within the context of the effective-mass approach, was deployed. Our numerical results exhibit the possibility to modulate the electronic and optical properties of confined donors by tailoring the inner and outer radii of the core/shell heterodot. Further, we have obtained that the nanodot size shrinking leads, for very small values of core radius, to reduce the magnitude of the total absorption coefficient resonance peak. It was also obtained that the resonance peak position of the absorption coefficient is redshifted with increasing the core radius for a fixed shell thickness. The same situation occurs when reducing the thickness of the shell material for a fixed core size.
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- Chafai, A., et al.
(författare)
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Nonlinear optical characteristics of an exciton in a GaSb-capped InSb heterodot : role of size control
- 2020
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Ingår i: The European Physical Journal Plus. - : SPRINGER HEIDELBERG. - 2190-5444. ; 135:2
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Tidskriftsartikel (refereegranskat)abstract
- The optical characteristics of a bound electron-hole quasiparticle inside a GaSb-capped InSb nanodot were investigated using a combination between a density-matrix approach and variational calculations. Our theoretical model considers the electric permittivity mismatch between the core and shell materials via the self-energy term obtained by the means of an image charge approach. Furthermore, the core-to-shell conduction and valence band offsets were modeled by finite-depth confinement potentials. To elucidate the impact of the nanoheterodot spatial parameters on the confined exciton optical properties, we have investigated the change of the refractive index, the optical absorption coefficient, and the 1p-1s exciton transition energy with respect to the nanodot shape. Our numerical results exhibit the great potential for the improvement of the exciton optical properties by tailoring the nanodot size. It was also obtained that, for a fixed core radius, the resonance peak position of the optical absorption coefficient was still constant after a certain shell thickness value. Otherwise, decreasing the shell thickness leads to blue-shifting the 1p-1s transition energy.
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| 7. |
- Chafai, A., et al.
(författare)
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Recombination energy for negatively charged excitons inside type-II core/shell spherical quantum dots
- 2018
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : ELSEVIER SCIENCE BV. - 1386-9477 .- 1873-1759. ; 101, s. 125-130
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Tidskriftsartikel (refereegranskat)abstract
- The recombination energy of isolated neutral exciton and that of isolated negatively charged exciton inside a type-II core/shell spherical quantum dot are studied. Our investigation considers the charge-carriers effective mass discontinuity at the surface contact between the core and shell materials. Although our model omits the effect of the surface polarization, the dielectric-constant mismatch at the nanodot boundaries was taken into account. In order to achieve the exciton and negative trion energies, we proceed by a variational calculation in the framework of the envelope approximation. Our results reveal a strong correlation between the nanodot morphology and the energy spectrum of the neutral and negatively charged exciton.
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| 8. |
- Chafai, A., et al.
(författare)
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Role of a uniform magnetic field on the energy spectrum of a single donor in a core/shell spherical quantum dot
- 2019
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Ingår i: Zhongguó wùli xuékan. - : ELSEVIER SCIENCE BV. - 0577-9073. ; 57, s. 189-194
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Tidskriftsartikel (refereegranskat)abstract
- Using the variational approach within the framework of the effective-mass approximation (EMA), the binding energy of a centred hydrogenic donor impurity in a CdSe/ZnTe core/shell spherical quantum dot (CSSQD) in the presence of an external magnetic field was investigated. In this model, we have taken into account the effect of the radial dependence of the dielectric constant and of the electron effective mass. Our numerical results show a remarkable influence of the nanodot spatial parameters and of the external magnetic field strength on the shallow donor binding energy.
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| 9. |
- Chafai, A., et al.
(författare)
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Shallow donor inside core/shell spherical nanodot : Effect of nanostructure size and dielectric environment on energy spectrum
- 2017
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 111, s. 976-982
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Tidskriftsartikel (refereegranskat)abstract
- We have reported the impact of the core and shell radii on the energy spectrum of centered shallow donor confined inside CdSe/ZnTe core/shell quantum dot and ZnTe/CdSe inverted core/shell quantum dot. The dielectric discontinuity between the nanosystems and their surrounding medium was considered. In order to examine the behavior of the donor binding energy as a function of the spatial parameters a variational approach within the framework of the effective-mass approximation was deployed. Our model shows that for a fixed shell radius the increase of the core radius value blue-shifts the binding energy of the donor inside inverted core/shell quantum dot only if the value of the core to shell radii ratio is between 0.9 and 1, otherwise it is red-shifted. By contrast, for core/shell quantum dot system the binding energy is red-shifted by increasing the core radius for a fixed nanostructure size and for all values of the core to shell radii ratio. We have also found that the donor binding energy values are more important in a core/shell nanodot than in an inverted core/shell quantum dot.
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| 10. |
- Chafai, A., et al.
(författare)
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Tuning the binding energy of on-center donor in CdSe/ZnTe core/shell quantum dot by spatial parameters and magnetic field strength
- 2017
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 94, s. 96-99
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of the electron ground state and of the ground state binding energy of an on-center donor confined in a CdSe/ZnTe core/shell spherical nanodot was examined theoretically within the framework of the effectivemass approximation and using a variational calculation. The radial dependence of the dielectric constant and of the electron effective mass as well as the effect of the polarization charge were considered. Our results highlight the large impact of the magnetic field strength and the spatial parameters on the energy behavior for both the electron and the donor. Our study points out also the fact that the magnetic confinement may be eclipsed by the spatial confinement in heteronanostructures with small size and expected to be dominant in the opposite case.
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