GCRIS

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Citation - WoS: 5
Citation - Scopus: 6
Tuning the Structural, Electronic and Dynamical Properties of Janus M4x3y3 (m = Pd, Ni and Co; X,y = S, Se and Te) Monolayers: a Dft Study
(Royal Society of Chemistry, 2021) Eren, İsmail; Akgenç, Berna
Based on density functional theory, the structural, electronic and vibrational properties of two-dimensional transition metal chalcogenides M2X3 and their Janus type M4X3Y3, where M = Pd, Co and Ni and X = Se, S and Te, are investigated. Motivated by the successful synthesis of a 2D Pd2Se3 monolayer and the proof of the dynamical stability of Ni2Se3 and Co2Se3 monolayers, in terms of the phonon band dispersions, we have systemically studied the fundamental physical properties of Janus transition metal chalcogenides, such as their structural, phonon and thermodynamic stability and their electronic and mechanical properties. Our results show that Janus structures of M4X3Y3 are energetically favorable and dynamically stable. The ab initio molecular dynamic simulations (AIMD) results clearly prove that they kept their thermal stability at room temperature. We have demonstrated their structural, electronic and vibrational properties and Raman spectra. The electronic band dispersions show that monolayer Co2Se3 shows half-metal properties with a moderate band gap (1.01 eV), Pd2Se3 has a 1.42 eV direct band gap, while Ni2Se3 has a 1.38 eV indirect band gap. Pd4Se3S3, Pd4Se3Te3 and Pd4S3Te3 are indirect band gap semiconductors with band gaps of 1.22 eV, 1.05 eV and 0.61 eV, respectively. Ni4Se3S3, Ni4Se3Te3 and Ni4S3Te3 are indirect band gap semiconductors with band gaps of 1.61 eV, 0.77 eV and 0.49 eV, respectively. While pristine Co2Se3 is shown to have half-metallicity (HM), the HM behaviour of the Janus Co4Se3Te3 and Co4S3Te3 monolayers disappear and Co4Se3S3 remains a HM with a moderate band gap of 0.85 eV. In addition, the Raman spectra of these Janus materials are shown to exhibit totally distinctive features as compared to those of the pristine materials. This work reveals the important material properties of Janus type M4X3Y3 monolayers, where M = Pd, Co and Ni and X = Se, S and Te, which could have wide applications in new functional devices.
Citation - WoS: 24
Citation - Scopus: 24
Defect Tolerant and Dimension Dependent Ferromagnetism in Mnse2
(Royal Society of Chemistry, 2019) Eren, İsmail; İyikanat, Fadıl; Şahin, Hasan
By performing density functional theory-based calculations, we investigate the structural, vibrational, electronic and magnetic properties of 2D monolayers, nanoribbons and quantum dots of MnSe2. Vibrational spectrum analysis reveals the dynamical stability of not only ferromagnetic but also antiferromagnetic phases of single layer MnSe2 crystal structures. Electronically, calculations show that 1T-MnSe2 is a ferromagnetic structure displaying metallic behavior. It is also found that the structure preserves its dynamical stability and metallic behavior even under the presence of high density Se vacancies. Moreover, it was predicted that, differing from the 2D MnSe2, metal-metal interaction driven reconstructions result in ferromagnetic-to-antiferromagnetic crossover in the ground state of nanoribbons and quantum dots. With its robust ferromagnetic metallic character in the 2D ultra-thin limit and dimension-dependent magnetic properties, MnSe2 is an important candidate for spintronic device applications.
Citation - WoS: 13
Citation - Scopus: 12
Orthorhombic Cspbi3 Perovskites: Thickness-Dependent Structural, Optical and Vibrational Properties
(Elsevier, 2020) Özen, Sercan; İyikanat, Fadıl; Özcan, Mehmet; Tekneci, Gülsüm Efsun; Eren, İsmail; Sözen, Yiğit; Şahin, Hasan
Cesium lead halide perovskites have been subject to intense investigation, mostly because of their potential to be used in optoelectronic device applications. However, regarding the need for nanoscale materials in forthcoming nanotechnology applications, understanding of how the characteristic properties of these perovskite crystals are modified through dimensional crossover is essential. In this study, thickness-dependence of the structural, electronic and vibrational properties of orthorhombic CsPbI3, which is one of the most stable phase at room temperature, is investigated by means of state-of-the-art first-principles calculations. Our results show that (i) bilayers and monolayers of CsPbI3 can be stabilized in orthorhombic crystal symmetry, (ii) among; the possible ultra-thin perovskites only structures with CsI-terminated surface are dynamically stable (iii) electronic band gap increases with decrease in perovskite thickness due to quantum size effect and (iv) reflectivity and transmissivity of the orthorhombic CsPbI3 can be tuned by varying the thickness that modifies the electron confinement. (c) 2019 Elsevier B.V. All rights reserved.

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