Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Access Right: Open AccessAuthor: search.filters.author.Yagmurcukardes, Mehmet

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  • Article
    Dimensionality Effects in Anisotropic Single Layers TiSe5 and TiTe5: a Comparative Study of 2D Sheets and 1D Nanochains
    (IOP Publishing Ltd, 2026) Can Dogan, Kadir; Kutay Tamdogan, Omer; Bozkurt, Yagmur; Cetin, Zebih; Yagmurcukardes, Mehmet
    In this study, we present a comprehensive first-principles investigation of the structural, vibrational, and electronic properties of titanium pentachalcogenide structures in both two-dimensional (2D) and one-dimensional (1D) nanochain (NC) forms. Total energy and geometry optimizations reveal that the 2D TiX5 (X = Se, Te) structures exhibit in-plane anisotropy arising from the trigonal prismatic TiX3 units interconnected via the chalcogenide chains. Phonon band dispersions and elastic tensor elements confirm the dynamical and mechanical stability of the 2D layers, respectively. Electronically, while TiTe5 is a metal, TiSe5 possesses direct band gap semiconducting behavior. In addition, free-standing 1D NC counterparts, which are sub-units of the 2D structures, are investigated by means of their stability. Three stable 1D NCs, namely TiTe5-NC, TiSe7-NC, and TiTe7-NC, are found to be composed of edge-sharing TiX6-like units with either five- or seven-fold coordination. The dynamically stable 1D NCs are shown to be semiconductors with relatively larger band gaps as compared to 2D layers. Predicted Raman spectra reveal clear signatures of vibrational mode evaluations as a result of quantum confinement from the 2D layer to the 1D NC. Moreover, finite-temperature ab-initio quantum molecular dynamics simulations at 300 K confirm the thermal stability of both the 2D TiX5 layers and 1D NC derivatives, showing that the Ti-based systems retain their structural integrity under ambient conditions and are feasible candidates for experimental synthesis. Our findings highlight the formation of stable semiconducting 1D NCs of Ti-pentachalcogenides from their 2D counterparts.
  • Article
    Citation - Scopus: 1
    Magnetism in Twisted Triangular Bilayer Graphene Quantum Dots
    (Amer Physical Soc, 2025) Mirzakhani, Mohammad; Cetin, Zebih; Yagmurcukardes, Mehmet; Park, Hee Chul; Peeters, Francois M.; da Costa, Diego R.
    Using a tight-binding model along with the mean-field Hubbard method, we investigate the effect of twisting angle on the magnetic properties of twisted bilayer graphene (tBLG) quantum dots (QDs) with triangular shape and zigzag edges. We consider such QDs in two configurations: when their initial untwisted structure is a perfect AA- or AB-stacked BLG, referred to as AA- or AB-like dots. We find that AA-like dots exhibit an antiferromagnetic spin polarization for small twist angles, which transits to a ferromagnetic spin polarization beyond a critical twisting angle theta c. Our analysis shows that theta c decreases as the dot size increases, obeying a criterion, according to which once the maximum energy difference between electron and hole edge states (in the single-particle picture) is less than (U/gamma 0) t0, the spin-polarized energy levels are aligned ferromagnetically [U is the Hubbard parameter and gamma 0 (t0) the graphene intralayer (interlayer) hopping]. Unlike AA-like dots, AB-like dots exhibit finite magnetization for any twist angle. Furthermore, in the ferromagnetic polarization state, the ground net spin for both dot configurations agrees with the prediction from Lieb's theorem.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Anisotropic Single-Layer Tilted Α-Bi: Identification of Uniaxial Strain Via Raman Spectrum
    (Amer Chemical Soc, 2024) Dogan, Kadir Can; Yagmurcukardes, Mehmet
    In the present study, the structural, vibrational, electronic, and elastic properties of single-layer alpha-Bi are investigated by performing density functional theory-based first-principles calculations. Structural optimizations show that free-standing alpha-Bi possesses a tilted black phosphorus-like anisotropic structure. The phonon band dispersions and linear-elastic parameters reveal the dynamical and mechanical stability of the alpha-Bi structure, respectively. In addition, quantum molecular dynamics simulations indicate the thermal stability of the single layer at room temperature. Electronically, it is found that alpha-Bi exhibits an indirect band gap semiconducting behavior, whose hole and electron effective masses are shown to be orientation-dependent with the latter being more anisotropic. Such anisotropic effective masses reveal orientation-dependent transport properties in single-layer alpha-Bi. Moreover, the orientation-dependent elastic features of alpha-Bi show that at an angle of 45 degrees with respect to the zigzag (ZZ) orientation, an auxetic behavior is predicted for the structure. Furthermore, the impact of uniaxial strains along the two main orientations (ZZ and armchair directions) is investigated on the vibrational properties of single-layer alpha-Bi. The phononic stability of the structure is first predicted at the strain limits (+/- 5) for both directions, and the results reveal the preserved stability of the single layer under both compressive and tensile strains. The calculated Raman spectra under uniaxial strains show that the type (compressive or tensile) and the direction of the applied strain can be deduced from the Raman spectra analysis. Overall, strain-induced modifications in the Raman spectrum of 2D alpha-Bi in terms of the peak positions may be useful tools for the characterization of induced strain in experimental studies.