Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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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: 119Citation - Scopus: 119Janus Two-Dimensional Transition Metal Dichalcogenide Oxides: First-Principles Investigation of Wxo Monolayers With X = S, Se, and Te(American Physical Society, 2021) Varjovi, M. Jahangirzadeh; Yağmurcukardeş, Mehmet; Peeters, François M.; Durgun, EnginStructural symmetry breaking in two-dimensional materials can lead to superior physical properties and introduce an additional degree of piezoelectricity. In the present paper, we propose three structural phases (1H, 1T, and 1T') of Janus WXO (X = S, Se, and Te) monolayers and investigate their vibrational, thermal, elastic, piezoelectric, and electronic properties by using first-principles methods. Phonon spectra analysis reveals that while the 1H phase is dynamically stable, the 1T phase exhibits imaginary frequencies and transforms to the distorted 1T' phase. Ab initio molecular dynamics simulations confirm that 1H- and 1T'-WXO monolayers are thermally stable even at high temperatures without any significant structural deformations. Different from binary systems, additional Raman active modes appear upon the formation of Janus monolayers. Although the mechanical properties of 1H-WXO are found to be isotropic, they are orientation dependent for 1T'-WXO. It is also shown that 1H-WXO monolayers are indirect band-gap semiconductors and the band gap narrows down the chalcogen group. Except 1T'-WSO, 1T'-WXO monolayers have a narrow band gap correlated with the Peierls distortion. The effect of spin-orbit coupling on the band structure is also examined for both phases and the alteration in the band gap is estimated. The versatile mechanical and electronic properties of Janus WXO monolayers together with their large piezoelectric response imply that these systems are interesting for several nanoelectronic applications.Article Citation - WoS: 6Citation - Scopus: 6Influence of Buffer Layers on Ni Thin Film Structure and Graphene Growth by Cvd(IOP Publishing Ltd., 2015) Özçeri, Elif; Selamet, YusufBuffer and/or adhesive layers were used to decrease the dewetting of Ni thin film at graphene growth temperatures of around 900 °C. Depositing a thin buffer (Al2O3) layer onto SiO2/Si substrate significantly reduced the dewetting effect and surface roughness of Ni catalyst film. Thin adhesive (Cr) layers with or without Al2O3 buffer layers increased the texturing in (1 1 1) orientation, which was promoted by growing at an elevated temperature (450 °C). The effects of pretreatment and growth temperature on crystal orientation, grain size and surface roughness of Ni film were analyzed. Our results indicated a large positive correlation coefficient between the film thickness and surface roughness for thinner and non-buffered films, and a negative correlation coefficient between the thickness and 900 °C -annealed film roughness for thicker and buffered films. The graphene coverage was greatly improved over the films grown with Al2O3 and/or Cr layers. In summary, we suggest that growing high quality, large area, 1- or 2-layer graphene on polycrystalline Ni transition metal thin film is optimized by using Al2O3 and/or Cr layers to reduce Ni dewetting, surface roughness, and groove depth while controlling grain size and texturing in (1 1 1) orientation by annealing at 900 °C.