Elie Albert Moujaes

This study investigates the structural stability and electronic, mechanical, excitonic, and optical properties of 2D-XI₂ (X = Si, Ge, Sn, Pb) monolayers using both first-principles and semiempirical calculations. Our findings reveal that this group has semiconductor characteristics with band gaps from 2.35 to 3.28 eV at the HSE06 level. The excitonic effects are significant with exciton binding energies between 372 and 422 meV. They present a maximum solar harvesting efficiency, at the Shockley–Queisser limit, considering an electron–hole coupling of 16.37%. These findings indicate that these structures are promising for future optoelectronic applications, showing excellent visible and ultraviolet response and enhancing the photovoltaic cell performance.

Designing novel 2D materials is crucial for advancing next-generation optoelectronic technologies. This work introduces and analyzes the 1T'-HfCl₂ monolayer, a novel low-symmetry variant within the 2D transition metal dichloride family. Phonon dispersion calculations reveal no imaginary frequencies, suggesting its dynamical stability. 1T'-HfCl₂ exhibits semiconducting behavior with a direct band gap of 1.52 eV, promising for optoelectronics. Strong excitonic effects with a binding energy of 525 meV highlight significant electron-hole interactions typical of 2D systems. Furthermore, the monolayer achieves total reflection of linearly polarized light along the ŷ direction at photon energies above 2.5 eV, showcasing its potential as an optical polarizing filter. Raman spectra calculations also reveal distinct peaks between 96.72 and 270.38 cm^-1. The tunable excitonic and optical properties of 1T'-HfCl₂ highlight its potential in future functional devices, paving the way for its integration into semiconducting and optoelectronic applications.

We have investigated the Raman spectrum and excitonic effects of the novel 2D Ta₂Ni₃Te₅ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify 10 Raman- and 10 infrared-active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the x direction.

We have investigated the Raman spectrum and excitonic effects of the novel two-dimensional Ta$_2$Ni$_3$Te$_5$ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 eV and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify ten Raman and ten infrared active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and also presents a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the x-direction.

We theoretically investigate the stability of a MoS₂ nanochain, reporting its electronic, mechanical, and optical properties. The nanochain presents a semiconductor structure with a minute band gap of 67m eV compared to the larger gap bulk and monolayer structures. It is more malleable, enduring a maximum compressive (tensile) strain of 6% (6.5%). It is dynamically stable, showing no negative frequencies along its Brillouin zone (BZ) path. The nanochain is thermally stable at 300K, making it possible to synthesize as a freestanding structure. The optical properties of the bulk, monolayer, and 1D MoS₂ materials are evaluated using the time-dependent density functional perturbation theory (TDDFPT) and compared to those determined via the independent particle approximation (IPA). Along the nanochain’s periodic x direction, the reflectivity retains a maximum value of ∼68% in the infrared (IR) region. Furthermore, its optical conductivity also exhibits a peak within the IR regime. These two features make such nanochains suitable as coating materials in applications involving infrared radiation or can even be exploited as conductive substrates in near-IR devices.