Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

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

Browse

Filters

20153

Settings

Author: search.filters.author.Senger, Ramazan TugrulScopus Q: search.filters.scopusQuartile.N/A

Search Results

Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 149
    Citation - Scopus: 149
    Hexagonal Aln: Dimensional-Crossover Band-Gap Transition
    (American Physical Society, 2015) Bacaksız, Cihan; Şahin, Hasan; Özaydın, H. Duygu; Horzum, Şeyda; Senger, Ramazan Tugrul; Peeters, François M.
    Motivated by a recent experiment that reported the successful synthesis of hexagonal (h) AlN [Tsipas, Appl. Phys. Lett. 103, 251605 (2013)APPLAB0003-695110.1063/1.4851239], we investigate structural, electronic, and vibrational properties of bulk, bilayer, and monolayer structures of h-AlN by using first-principles calculations. We show that the hexagonal phase of the bulk h-AlN is a stable direct-band-gap semiconductor. The calculated phonon spectrum displays a rigid-layer shear mode at 274 cm-1 and an Eg mode at 703 cm-1, which are observable by Raman measurements. In addition, single-layer h-AlN is an indirect-band-gap semiconductor with a nonmagnetic ground state. For the bilayer structure, AA′-type stacking is found to be the most favorable one, and interlayer interaction is strong. While N-layered h-AlN is an indirect-band-gap semiconductor for N=1-9, we predict that thicker structures (N≥10) have a direct band gap at the Γ point. The number-of-layer-dependent band-gap transitions in h-AlN is interesting in that it is significantly different from the indirect-to-direct crossover obtained in the transition-metal dichalcogenides.
  • Article
    Citation - WoS: 35
    Citation - Scopus: 33
    Portlandite Crystal: Bulk, Bilayer, and Monolayer Structures
    (American Physical Society, 2015) Aierken, Y.; Şahin, Hasan; İyikanat, Fadıl; Horzum, Şeyda; Süslü, A.; Chen, B.; Senger, Ramazan Tugrul; Tongay, S.; Peeters, François M.
    Ca(OH)2 crystals, well known as portlandite, are grown in layered form, and we found that they can be exfoliated on different substrates. We performed first principles calculations to investigate the structural, electronic, vibrational, and mechanical properties of bulk, bilayer, and monolayer structures of this material. Different from other lamellar structures such as graphite and transition-metal dichalcogenides, intralayer bonding in Ca(OH)2 is mainly ionic, while the interlayer interaction remains a weak dispersion-type force. Unlike well-known transition-metal dichalcogenides that exhibit an indirect-to-direct band gap crossover when going from bulk to a single layer, Ca(OH)2 is a direct band gap semiconductor independent of the number layers. The in-plane Young's modulus and the in-plane shear modulus of monolayer Ca(OH)2 are predicted to be quite low while the in-plane Poisson ratio is larger in comparison to those in the monolayer of ionic crystal BN. We measured the Raman spectrum of bulk Ca(OH)2 and identified the high-frequency OH stretching mode A1g at 3620cm-1. In this study, bilayer and monolayer portlandite [Ca(OH)2] are predicted to be stable and their characteristics are analyzed in detail. Our results can guide further research on ultrathin hydroxites.
  • Article
    Citation - WoS: 45
    Citation - Scopus: 43
    Tuning the Magnetic Anisotropy in Single-Layer Crystal Structures
    (American Physical Society, 2015) Torun, Engin; Şahin, Hasan; Bacaksız, Cihan; Senger, Ramazan Tugrul; Peeters, François M.
    The effect of an applied electric field and the effect of charging are investigated on the magnetic anisotropy (MA) of various stable two-dimensional (2D) crystals such as graphene, FeCl2, graphone, fluorographene, and MoTe2 using first-principles calculations. We found that the magnetocrystalline anisotropy energy of Co-on-graphene and Os-doped-MoTe2 systems change linearly with electric field, opening the possibility of electric field tuning MA of these compounds. In addition, charging can rotate the easy-axis direction of Co-on-graphene and Os-doped-MoTe2 systems from the out-of-plane (in-plane) to in-plane (out-of-plane) direction. The tunable MA of the studied materials is crucial for nanoscale electronic technologies such as data storage and spintronics devices. Our results show that controlling the MA of the mentioned 2D crystal structures can be realized in various ways, and this can lead to the emergence of a wide range of potential applications where the tuning and switching of magnetic functionalities are important.