PubMed İndeksli Yayınlar Koleksiyonu / PubMed Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7645
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Article Citation - WoS: 2Citation - Scopus: 2High-Throughput Analysis of Tetragonal Transition Metal Xenes(Royal Society of Chemistry, 2022) Šabani, Denis; Milošević, Milorad V.; Yorulmaz, Uğur; Yağmurcukardeş, Mehmet; Sevik, CemWe report a high-throughput first-principles characterization of the structural, mechanical, electronic, and vibrational properties of tetragonal single-layer transition metal Xenes (t-TMXs). Our calculations revealed 22 dynamically, mechanically and chemically stable structures among the 96 possible free-standing layers present in the t-TMX family. As a fingerprint for their structural identification, we identified four characteristic Raman active phonon modes, namely three in-plane and one out-of-plane optical branches, with various intensities and frequencies depending on the material in question. Spin-polarized electronic calculations demonstrated that anti-ferromagnetic (AFM) metals, ferromagnetic (FM) metals, AFM semiconductors, and non-magnetic semiconductor materials exist within this family, evidencing the potential of t-TMXs for further use in multifunctional heterostructures.Article Citation - WoS: 6Citation - Scopus: 7Interface-Dependent Phononic and Optical Properties of Geo/Moso Heterostructures(Royal Society of Chemistry, 2022) Yağmurcukardeş, Mehmet; Sözen, Yiğit; Başkurt, Mehmet; Peeters, François M.; Şahin, HasanThe interface-dependent electronic, vibrational, piezoelectric, and optical properties of van der Waals heterobilayers, formed by buckled GeO (b-GeO) and Janus MoSO structures, are investigated by means of first-principles calculations. The electronic band dispersions show that O/Ge and S/O interface formations result in a type-II band alignment with direct and indirect band gaps, respectively. In contrast, O/O and S/Ge interfaces give rise to the formation of a type-I band alignment with an indirect band gap. By considering the Bethe-Salpeter equation (BSE) on top of G0W0 approximation, it is shown that different interfaces can be distinguished from each other by means of the optical absorption spectra as a consequence of the band alignments. Additionally, the low-and high-frequency regimes of the Raman spectra are also different for each interface type. The alignment of the individual dipoles, which is interface-dependent, either weakens or strengthens the net dipole of the heterobilayers and results in tunable piezoelectric coefficients. The results indicate that the possible heterobilayers of b-GeO/MoSO asymmetric structures possess various electronic, optical, and piezoelectric properties arising from the different interface formations and can be distinguished by means of various spectroscopic techniques.Article Citation - WoS: 10Citation - Scopus: 10Vibrational and Optical Identification of Geo2 and Geo Single Layers: a First-Principles Study(Royal Society of Chemistry, 2021) Sözen, Yiğit; Yağmurcukardeş, Mehmet; Şahin, HasanIn the present work, the identification of two hexagonal phases of germanium oxides (namely GeO2 and GeO) through the vibrational and optical properties is reported using density functional theory calculations. While structural optimizations show that single-layer GeO2 and GeO crystallize in 1T and buckled phases, phonon band dispersions reveal the dynamical stability of each structure. First-order off-resonant Raman spectral predictions demonstrate that each free-standing single-layer possesses characteristic peaks that are representative for the identification of the germanium oxide phase. On the other hand, electronic band dispersion analysis shows the insulating and large-gap semiconducting nature of single-layer GeO2 and GeO, respectively. Moreover, optical absorption, reflectance, and transmittance spectra obtained by means of G(0)W(0)-BSE calculations reveal the existence of tightly bound excitons in each phase, displaying strong optical absorption. Furthermore, the excitonic gaps are found to be at deep UV and visible portions of the spectrum, for GeO2 and GeO crystals, with energies of 6.24 and 3.10 eV, respectively. In addition, at the prominent excitonic resonances, single-layers display high reflectivity with a zero transmittance, which is another indication of the strong light-matter interaction inside the crystal medium.Article Citation - WoS: 23Citation - Scopus: 23Bodipy-Vinyl Dibromides as Triplet Sensitisers for Photodynamic Therapy and Triplet-Triplet Annihilation Upconversion(Royal Society of Chemistry, 2021) Dartar, Suay; Üçüncü, Muhammed; Karakuş, Erman; Hou, Yuqi; Zhao, Jianzhang; Emrullahoğlu, MustafaWe devised a new generation of halogen-based triplet sensitisers comprising geminal dibromides at the vinyl backbone of a BODIPY fluorophore. Incorporating geminal dibromides into the pi-conjugation of BODIPY enhanced intersystem crossing due to the heavy atom effect, which in turn improved the extent of excited triplet states.Article Citation - WoS: 2Citation - Scopus: 2Ultra-Thin Structures of Manganese Fluorides: Conversion From Manganese Dichalcogenides by Fluorination(Royal Society of Chemistry, 2021) Başkurt, Mehmet; Nair, Rahul R.; Peeters, François M.; Şahin, HasanIn this study, it is predicted by density functional theory calculations that graphene-like novel ultra-thin phases of manganese fluoride crystals, that have nonlayered structures in their bulk form, can be stabilized by fluorination of manganese dichalcogenide crystals. First, it is shown that substitution of fluorine atoms with chalcogens in the manganese dichalcogenide host lattice is favorable. Among possible crystal formations, three stable ultra-thin structures of manganese fluoride, 1H-MnF2, 1T-MnF2 and MnF3, are found to be stable by total energy optimization calculations. In addition, phonon calculations and Raman activity analysis reveal that predicted novel single-layers are dynamically stable crystal structures displaying distinctive characteristic peaks in their vibrational spectrum enabling experimental determination of the corresponding phases. Differing from 1H-MnF2 antiferromagnetic (AFM) large gap semiconductor, 1T-MnF2 and MnF3 single-layers are semiconductors with ferromagnetic (FM) ground state.Article Citation - WoS: 24Citation - Scopus: 24Defect Tolerant and Dimension Dependent Ferromagnetism in Mnse2(Royal Society of Chemistry, 2019) Eren, İsmail; İyikanat, Fadıl; Şahin, HasanBy 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.Article Citation - WoS: 14Citation - Scopus: 12Octahedrally Coordinated Single Layered Caf2: Robust Insulating Behaviour(Royal Society of Chemistry, 2020) Başkurt, Mehmet; Kang, Jun; Şahin, HasanUsing first-principles calculations, the structural, vibrational, and electronic properties of single-layered calcium fluoride (CaF2) are investigated. The dynamical stability of 1T-CaF2 is confirmed by the phonon dispersions. Raman active vibrational modes of 1T-CaF2 enable its characterization via Raman spectroscopy. In addition, the calculated electronic properties of 1T-CaF2 confirmed insulating behavior with an indirect wide band gap which is larger than that of a well-known single-layered insulator, h-BN. Moreover, one-dimensional nanoribbons of CaF2 are investigated for two main edge orientations, namely zigzag and armchair, and it is revealed that both structures maintain the 1T nature of CaF2 without any structural edge reconstructions. Electronically, both types of CaF2 nanoribbons display robust insulating behavior with respect to the nanoribbon width. The results show that both the 2D and 1D forms of 1T-CaF2 show potential in nanoelectronics as an alternative to the widely-used insulator h-BN with its similar properties and wider electronic band gap.Article Citation - WoS: 67Citation - Scopus: 66Bilayers of Janus Wsse: Monitoring the Stacking Type: Via the Vibrational Spectrum(Royal Society of Chemistry, 2018) Kandemir, Ali; Şahin, HasanMotivated by the recent successful synthesis of Janus type single layers of transition metal dichalcogenides, we investigate the stability, vibrational and electronic properties of the Janus single layer structure of WSSe and its bilayers by means of density functional theory. The structural and vibrational analysis show that the Janus single layer of WSSe forms a dynamically stable structure in the 2H phase. Owing to its non-centrosymmetric structure, the Janus WSSe single layer has two in-plane (E) and two out-of-plane (A) Raman active phonon modes. The eigen-frequencies of the prominent Raman active modes are calculated to be 277 (A) and 322 (E) cm-1. Similar to single layer WS2 and WSe2, Janus WSSe is a direct band gap semiconductor that has two electronically different faces. In addition, the possible bilayer stacking orders of the Janus WSSe single layers are investigated. It is found that there are 3 stacking types of bilayer Janus WSSe and each stacking type has distinctive Raman characteristics in its vibrational spectrum. Our results show that thanks to the vibrational characteristics, which stem from the distinctive interlayer interactions at different sides, the stability and stacking types of the bilayer of WSSe Janus structure can be monitored.Article Citation - WoS: 65Citation - Scopus: 67Angle Resolved Vibrational Properties of Anisotropic Transition Metal Trichalcogenide Nanosheets(Royal Society of Chemistry, 2017) Kong, Wilson; Bacaksız, Cihan; Chen, Bin; Wu, Kedi; Blei, Mark; Fan, Xi; Shen, Yuxia; Şahin, Hasan; Wright, David; Narang, Deepa S.; Tongay, SefaattinLayered transition metal trichalcogenides (TMTCs) are a new class of anisotropic two-dimensional materials that exhibit quasi-1D behavior. This property stems from their unique highly anisotropic crystal structure where vastly different material properties can be attained from different crystal directions. Here, we employ density functional theory predictions, atomic force microscopy, and angle-resolved Raman spectroscopy to investigate their fundamental vibrational properties which differ significantly from other 2D systems and to establish a method in identifying anisotropy direction of different types of TMTCs. We find that the intensity of certain Raman peaks of TiS3, ZrS3, and HfS3 have strong polarization dependence in such a way that intensity is at its maximum when the polarization direction is parallel to the anisotropic b-axis. This allows us to readily identify the Raman peaks that are representative of the vibrations along the b-axis direction. Interestingly, similar angle resolved studies on the novel TiNbS3 TMTC alloy reveal that determination of anisotropy/crystalline direction is rather difficult possibly due to loss of anisotropy by randomization distribution of quasi-1D MX6 chains by the presence of defects which are commonly found in 2D alloys and also due to the complex Raman tensor of TMTC alloys. Overall, the experimental and theoretical results establish non-destructive methods used to identify the direction of anisotropy in TMTCs and reveal their vibrational characteristics which are necessary to gain insight into potential applications that utilize direction dependent thermal response, optical polarization, and linear dichroism.Article Citation - WoS: 68Citation - Scopus: 71Strong Dichroic Emission in the Pseudo One Dimensional Material Zrs3(Royal Society of Chemistry, 2016) Pant, Anupum; Torun, Engin; Chen, Bin; Bhat, Soumya; Fan, Xi; Wu, Kedi; Wright, David P.; Peeters, François M.; Soignard, Emmanuel; Şahin, Hasan; Tongay, SefaattinZirconium trisulphide (ZrS3), a member of the layered transition metal trichalcogenides (TMTCs) family, has been studied by angle-resolved photoluminescence spectroscopy (ARPLS). The synthesized ZrS3 layers possess a pseudo one-dimensional nature where each layer consists of ZrS3 chains extending along the b-lattice direction. Our results show that the optical properties of few-layered ZrS3 are highly anisotropic as evidenced by large PL intensity variation with the polarization direction. Light is efficiently absorbed when the E-field is polarized along the chain (b-axis), but the field is greatly attenuated and absorption is reduced when it is polarized vertical to the 1D-like chains as the wavelength of the exciting light is much longer than the width of each 1D chain. The observed PL variation with polarization is similar to that of conventional 1D materials, i.e., nanowires, and nanotubes, except for the fact that here the 1D chains interact with each other giving rise to a unique linear dichroism response that falls between the 2D (planar) and 1D (chain) limit. These results not only mark the very first demonstration of PL polarization anisotropy in 2D systems, but also provide novel insight into how the interaction between adjacent 1D-like chains and the 2D nature of each layer influences the overall optical anisotropy of pseudo-1D materials. Results are anticipated to have an impact on optical technologies such as polarized detectors, near-field imaging, communication systems, and bio-applications relying on the generation and detection of polarized light.