Browsing by Author "Kasırga, Talip Serkan"
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Item Open AccessChemical vapor transport synthesis of a selenium-based two-dimensional material(TÜBITAK, 2018) Kasırga, Talip Serkan; Kasırga, Talip SerkanSelenium-based layered materials, and in particular transition-metal diselenides (TMDSs), have intriguing properties in the monolayer limit. Materials such as MoSe2, WSe2, and NbSe2 display striking features such as spin-valley coupling at the valence-band edges and offer great potential for optoelectronics applications. Although a dozen of other TMDSs have been realized or proposed, whether two-dimensional chalcogens are possible or not is still an open challenge. In this work, we show the chemical vapor transport synthesis of a novel, atomically thin selenium-based material on oxidized silicon substrates. This new member of the two-dimensional materials family has a unique Raman spectrum similar to that of bulk selenium and has an optical gap of ∼1.57 eV at room temperature determined by the photoluminescence. No transition metals are found in the stoichiometry of the crystals. Analysis of high-resolution transmission electron micrographs of the monolayers reveals a distinctive set of hexagonal spots indicating a sixfold symmetry of the lattice. Atomic force microscopy measurements show the monolayer thickness to be ∼0.75 nm. Item Open AccessElectric-field-induced reversible phase transitions in a spontaneously ion-Intercalated 2D metal oxide(American Chemical Society, 2021-05-12) Rasouli, Hamid Reza; Kim, J.; Mehmood, Naveed; Sheraz, Ali; Jo, M. K.; Song, Seungwoo; Kang, K.; Kasırga, Talip Serkan; Rasouli, Hamid Reza; Mehmood, Naveed; Sheraz, Ali; Kasırga, Talip SerkanElectric field driven reversible phase transitions in two-dimensional (2D) materials are appealing for their potential in switching applications. Here, we introduce potassium intercalated MnO2 as an exemplary case. We demonstrate the synthesis of large-area single-crystal layered MnO2 via chemical vapor deposition as thin as 5 nm. These crystals are spontaneously intercalated by potassium ions during the synthesis. We showed that the charge transport in 2D K-MnO2 is dominated by motion of hydrated potassium ions in the interlayer space. Under a few volts bias, separation of potassium and the structural water leads to formation of different phases at the opposite terminals, and at larger biases K-MnO2 crystals exhibit reversible layered-to-spinel phase transition. These phase transitions are accompanied by electrical and optical changes in the material. We used the electric field driven ionic motion in K-MnO2 based devices to demonstrate the memristive capabilities of two terminal devices. Item Open AccessHigh elasticity and strength of ultra-thin metallic transition metal dichalcogenides(Royal Society of Chemistry, 2021-05-24) Sheraz, Ali; Mehmood, Naveed; Çiçek, M. M.; Ergün, İ.; Rasouli, H. R.; Durgun, Engin; Kasırga, Talip Serkan; Sheraz, Ali; Mehmood, Naveed; Durgun, Engin; Kasırga, Talip SerkanMechanical properties of transition metal dichalcogenides (TMDCs) are relevant to their prospective applications in flexible electronics. So far, the focus has been on the semiconducting TMDCs, mostly MoX2 and WX2 (X = S, Se) due to their potential in optoelectronics. A comprehensive understanding of the elastic properties of metallic TMDCs is needed to complement the semiconducting TMDCs in flexible optoelectronics. Thus, mechanical testing of metallic TMDCs is pertinent to the realization of the applications. Here, we report on the atomic force microscopy-based nano-indentation measurements on ultra-thin 2H-TaS2 crystals to elucidate the stretching and breaking of the metallic TMDCs. We explored the elastic properties of 2H-TaS2 at different thicknesses ranging from 3.5 nm to 12.6 nm and find that the Young's modulus is independent of the thickness at a value of 85.9 ± 10.6 GPa, which is lower than the semiconducting TMDCs reported so far. We determined the breaking strength as 5.07 ± 0.10 GPa which is 6% of the Young's modulus. This value is comparable to that of other TMDCs. We used ab initio calculations to provide an insight into the high elasticity measured in 2H-TaS2. We also performed measurements on a small number of 1T-TaTe2, 3R-NbS2 and 1T-NbTe2 samples and extended our ab initio calculations to these materials to gain a deeper understanding on the elastic and breaking properties of metallic TMDCs. This work illustrates that the studied metallic TMDCs are suitable candidates to be used as additives in composites as functional and structural elements and for flexible conductive electronic devices.