Physics / Fizik

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

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Author: search.filters.author.Şahin, HasanPublisher: search.filters.publisher.American Chemical Society

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Now showing 1 - 3 of 3
  • Article
    Citation - WoS: 15
    Citation - Scopus: 15
    Vertical van der waals heterostructure of single layer InSe and SiGe
    (American Chemical Society, 2019) Eren, İsmail; Şahin, Hasan; Özen, Sercan; Yağmurcukardeş, Mehmet; Sözen, Yiğit; Eren, İsmail; Yağmurcukardeş, Mehmet; Sözen, Yiğit; Şahin, Hasan; 04.05. Department of Pyhsics; 04.04. Department of Photonics; 01. Izmir Institute of Technology; 04. Faculty of Science
    We present a first-principles investigation on the stability, electronic structure, and mechanical response of ultrathin heterostructures composed of single layers of InSe and SiGe. First, by performing total energy optimization and phonon calculations, we show that single layers of InSe and SiGe can form dynamically stable heterostructures in 12 different stacking types. Valence and conduction band edges of the heterobilayers form a type-I heterojunction having a tiny band gap ranging between 0.09 and 0.48 eV. Calculations on elastic-stiffness tensor reveal that two mechanically soft single layers form a heterostructure which is stiffer than the constituent layers because of relatively strong interlayer interaction. Moreover, phonon analysis shows that the bilayer heterostructure has highly Raman active modes at 205.3 and 43.7 cm(-1), stemming from the out-of-plane interlayer mode and layer breathing mode, respectively. Our results show that, as a stable type-I heterojunction, ultrathin heterobilayer of InSe/SiGe holds promise for nanoscale device applications.
  • Article
    Citation - WoS: 17
    Citation - Scopus: 17
    Monitoring the Doping and Diffusion Characteristics of Mn Dopants in Cesium Lead Halide Perovskites
    (American Chemical Society, 2018) Güner, Tuğrul; Şahin, Hasan; Akbalı, Barış; Demir, Mustafa Muammer; Özcan, Mehmet; Topçu, Gökhan; Demir, Mustafa Muammer; Şahin, Hasan; 04.04. Department of Photonics; 03.09. Department of Materials Science and Engineering; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of Technology
    Cesium lead perovskites, in the form of CsPbX3 or Cs4PbX6, have been widely used for various optoelectronic applications due to their exceptionally good optical properties. In this study, the effect of Mn doping on the structural and optical properties of cesium lead halide perovskite crystals are investigated from both experimental and theoretical points of view. It is found that adding MnCl2 during the synthesis not only leads to a Mn-driven structural phase transition from Cs4PbBr6 to CsPbCl3 but also triggers the Br- to Cl- halide exchange. On the other hand, it is observed that, under UV illumination, the color of Mn-doped crystals changes from orange to blue in approximately 195 h. While the intensity of Mn-originated photoluminescence emission exponentially decays in time, the intensity of CsPbCl3-originated emission remains unchanged. In addition, diffusive motion of Mn ions results in both a growing population of MnO2 at the surface and transition of the host into a cesium-rich Cs4PbCl6 phase.
  • Article
    Citation - WoS: 63
    Citation - Scopus: 64
    Vacancy Formation and Oxidation Characteristics of Single Layer Tis3
    (American Chemical Society, 2015) İyikanat, Fadıl; Şahin, Hasan; Senger, Ramazan Tuğrul; Peeters, François M.; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    The structural, electronic, and magnetic properties of pristine, defective, and oxidized monolayer TiS3 are investigated using first-principles calculations in the framework of density functional theory. We found that a single layer of TiS3 is a direct band gap semiconductor, and the bonding nature of the crystal is fundamentally different from other transition metal chalcogenides. The negatively charged surfaces of single layer TiS3 makes this crystal a promising material for lubrication applications. The formation energies of possible vacancies, i.e. S, Ti, TiS, and double S, are investigated via total energy optimization calculations. We found that the formation of a single S vacancy was the most likely one among the considered vacancy types. While a single S vacancy results in a nonmagnetic, semiconducting character with an enhanced band gap, other vacancy types induce metallic behavior with spin polarization of 0.3-0.8 μB. The reactivity of pristine and defective TiS3 crystals against oxidation was investigated using conjugate gradient calculations where we considered the interaction with atomic O, O2, and O3. While O2 has the lowest binding energy with 0.05-0.07 eV, O3 forms strong bonds stable even at moderate temperatures. The strong interaction (3.9-4.0 eV) between atomic O and TiS3 results in dissociative adsorption of some O-containing molecules. In addition, the presence of S-vacancies enhances the reactivity of the surface with atomic O, whereas it had a negative effect on the reactivity with O2 and O3 molecules.