Photonics / Fotonik

Permanent URI for this collectionhttps://hdl.handle.net/11147/2590

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2017 - 20184

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Department: search.filters.department.İzmir Institute of Technology. Materials Science and EngineeringInstitution Author: search.filters.institutionAuthor.Akbalı, Barış

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Now showing 1 - 4 of 4
  • Article
    Citation - WoS: 89
    Citation - Scopus: 85
    Cspbbr3 Perovskites: Theoretical and Experimental Investigation on Water-Assisted Transition From Nanowire Formation To Degradation
    (American Physical Society, 2018) Akbalı, Barış; Topçu, Gökhan; Güner, Tuğrul; Özcan, Mehmet; Demir, Mustafa Muammer; Şahin, Hasan
    Recent advances in colloidal synthesis methods have led to an increased research focus on halide perovskites. Due to the highly ionic crystal structure of perovskite materials, a stability issue pops up, especially against polar solvents such as water. In this study, we investigate water-driven structural evolution of CsPbBr3 by performing experiments and state-of-the-art first-principles calculations. It is seen that while an optical image shows the gradual degradation of the yellowish CsPbBr3 structure under daylight, UV illumination reveals that the degradation of crystals takes place in two steps: transition from a blue-emitting to green-emitting structure and and then a transition from a green-emitting phase to complete degradation. We found that as-synthesized CsPbBr3 nanowires (NWs) emit blue light under a 254 nm UV source. Before the degradation, first, CsPbBr3 NWs undergo a water-driven structural transition to form large bundles. It is also seen that formation of such bundles provides longer-term environmental stability. In addition theoretical calculations revealed the strength of the interaction of water molecules with ligands and surfaces of CsPbBr3 and provide an atomistic-level explanation to a transition from ligand-covered NWs to bundle formation. Further interaction of green-light-emitting bundles with water causes complete degradation of CsPbBr3 and the photoluminescence signal is entirely quenched. Moreover, Raman and x-ray-diffraction measurements revealed that completely degraded regions are decomposed to PbBr2 and CsBr precursors. We believe that the findings of this study may provide further insight into the degradation mechanism of CsPbBr3 perovskite by water.
  • Article
    Citation - WoS: 110
    Citation - Scopus: 109
    Structural, Electronic and Phononic Properties of Ptse2: From Monolayer To Bulk
    (IOP Publishing Ltd., 2018) Kandemir, Ali; Akbalı, Barış; Kahraman, Z.; Badalov, S. V.; Özcan, Mehmet; İyikanat, Fadıl; Şahin, Hasan
    The layer dependent structural, electronic and vibrational properties of the 1T phase of two dimensional (2D) platinum diselenide are investigated by means of state-of-the-art first-principles calculations. The main findings of the study are: (i) monolayer platinum diselenide has a dynamically stable 2D octahedral structure with 1.66 eV indirect band gap, (ii) the semiconducting nature of 1T-PtSe2 monolayers remains unaffected even at high biaxial strains, (iii) top-to-top (AA) arrangement is found to be energetically the most favorable stacking of 1T-PtSe2 layers, (iv) the lattice constant (layer-layer distance) increases (decreases) with increasing number of layers, (v) while monolayer and bilayer 1T-PtSe2 are indirect semiconductors, bulk and few-layered 1T-PtSe2 are metals, (vi) Raman intensity and peak positions of the A1g and Eg modes are found to be highly dependent on the layer thickness of the material, hence; the number of layers of the material can be determined via Raman measurements.
  • Article
    Citation - WoS: 12
    Citation - Scopus: 11
    Theoretical and Experimental Investigation of Conjugation of 1,6-Hexanedithiol on Mos2
    (IOP Publishing Ltd., 2018) Gül, Aytaç; Bacaksız, Cihan; Ünsal, Emre; Akbalı, Barış; Tomak, Aysel; Zareie, Hadi M.; Şahin, Hasan
    We report an experimental and theoretical investigation of conjugation of 1,6-Hexaneditihiol (HDT) on MoS2 which is prepared by mixing MoS2 structure and HDT molecules in proper solvent. Raman spectra and the calculated phonon bands reveal that the HDT molecules bind covalently to MoS2. Surface morphology of MoS2/HDT structure is changed upon conjugation of HDT on MoS2 and characterized by using Scanning Electron Microscope (SEM). Density Functional Theory (DFT) based calculations show that HOMO-LUMO band gap of HDT is altered after the conjugation and two-S binding (handle-like) configuration is energetically most favorable among three different structures. This study displays that the facile thiol functionalization process of MoS2 is promising strategy for obtaining solution processable MoS2.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Few-Layer Mos2 as Nitrogen Protective Barrier
    (IOP Publishing Ltd., 2017) Akbalı, Barış; Yanılmaz, Alper; Tomak, Aysel; Tongay, Sefaattin; Çelebi, Cem; Şahin, Hasan
    We report experimental and theoretical investigations of the observed barrier behavior of few-layer MoS2 against nitrogenation. Owing to its low-strength shearing, low friction coefficient, and high lubricity, MoS2 exhibits the demeanor of a natural N-resistant coating material. Raman spectroscopy is done to determine the coating capability of MoS2 on graphene. Surface morphology of our MoS2/graphene heterostructure is characterized by using optical microscopy, scanning electron microscopy, and atomic force microscopy. In addition, density functional theory-based calculations are performed to understand the energy barrier performance of MoS2 against nitrogenation. The penetration of nitrogen atoms through a defect-free MoS2 layer is prevented by a very high vertical diffusion barrier, indicating that MoS2 can serve as a protective layer for the nitrogenation of graphene. Our experimental and theoretical results show that MoS2 material can be used both as an efficient nanocoating material and as a nanoscale mask for selective nitrogenation of graphene layer.