Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

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Subject: search.filters.subject.Monolayer structures

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  • Article
    Citation - WoS: 12
    Citation - Scopus: 12
    Ultra-Thin Znse: Anisotropic and Flexible Crystal Structure
    (Elsevier Ltd., 2017) Bacaksız, Cihan; Şenger, Ramazan Tuğrul; Şahin, Hasan
    By performing density functional theory-based calculations, we investigate the structural, electronic, and mechanical properties of the thinnest ever ZnSe crystal [11]. The vibrational spectrum analysis reveals that the monolayer ZnSe is dynamically stable and has flexible nature with its soft phonon modes. In addition, a direct electronic band gap is found at the gamma point for the monolayer structure of ZnSe. We also elucidate that the monolayer ZnSe has angle dependent in-plane elastic parameters. In particular, the in-plane stiffness values are found to be 2.07 and 6.89 N/m for the arm-chair and zig-zag directions, respectively. The angle dependency is also valid for the Poisson ratio of the monolayer ZnSe. More significantly, the in-plane stiffness of the monolayer ZnSe is the one-tenth of Young modulus of bulk zb-ZnSe which indicates that the monolayer ZnSe is a quite flexible single layer crystal. With its flexible nature and in-plane anisotropic mechanical properties, the monolayer ZnSe is a good candidate for nanoscale mechanical applications.
  • 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.