Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 17Citation - Scopus: 17Monitoring the Doping and Diffusion Characteristics of Mn Dopants in Cesium Lead Halide Perovskites(American Chemical Society, 2018) Güner, Tuğrul; Akbalı, Barış; Özcan, Mehmet; Topçu, Gökhan; Demir, Mustafa Muammer; Şahin, HasanCesium 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: 110Citation - Scopus: 109Structural, 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, HasanThe 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: 12Citation - Scopus: 11Theoretical 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, HasanWe 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: 7Citation - Scopus: 7Stable Ultra-Thin Cdte Crystal: a Robust Direct Gap Semiconductor(IOP Publishing Ltd., 2017) İyikanat, Fadıl; Akbalı, Barış; Kang, J.; Senger, Ramazan Tuğrul; Selamet, Yusuf; Şahin, HasanEmploying density functional theory based calculations, we investigate structural, vibrational and strain-dependent electronic properties of an ultra-thin CdTe crystal structure that can be derived from its bulk counterpart. It is found that this ultra-thin crystal has an 8-atom primitive unit cell with considerable surface reconstructions. Dynamic stability of the structure is predicted based on its calculated vibrational spectrum. Electronic band structure calculations reveal that both electrons and holes in single layer CdTe possess anisotropic in-plane masses and mobilities. Moreover, we show that the ultra-thin CdTe has some interesting electromechanical features, such as strain-dependent anisotropic variation of the band gap value, and its rapid increase under perpendicular compression. The direct band gap semiconducting nature of the ultra-thin CdTe crystal remains unchanged under all types of applied strain. With a robust and moderate direct band gap, single-layer CdTe is a promising material for nanoscale strain dependent device applications.