Browsing by Author "İpek, S."
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Item Open Access Antioxidant electrospun zein nanofibrous web encapsulating quercetin/cyclodextrin inclusion complex(Springer, 2018) Aytaç, Zeynep; İpek, S.; Durgun, Engin; Uyar, TamerQuercetin/gamma-cyclodextrin inclusion complex (quercetin/γ-CD-IC)-encapsulated electrospun zein nanofibers were designed as a quick and an efficient antioxidant nanofibrous material via electrospinning. Structural and thermal analyses along with the solubility enhancement as observed in phase-solubility diagram support the successful formation of the inclusion complexation between quercetin and γ-CD. The molar ratio of quercetin and γ-CD was found 1:1 in quercetin/γ-CD-IC which was confirmed with experimental (phase solubility and 1H-NMR) and computational modeling studies. Computational modeling was also useful to indicate that B orientation is more favorable when quercetin is forming host-guest inclusion complexation with γ-CD from the narrow rim. This result was also consistent with the calculations of the experimental studies performed by 1H-NMR. The successful electrospinning of zein nanofiber encapsulating quercetin/γ-CD-IC (zein-quercetin/γ-CD-IC-NF) yielded bead-free nanofiber morphology having 750 ± 255 nm fiber diameter. For comparative studies, pristine zein nanofibers (zein-NF, 695 ± 290 nm) and zein nanofibers encapsulating quercetin only (zein-quercetin-NF, 750 ± 310 nm) were also electrospun. The antioxidant (AO) characteristics of zein-quercetin/γ-CD-IC-NF were studied by the concentration-dependent AO activity tests.Item Open Access Boron-pnictogens: Highly anisotropic two-dimensional semiconductors for nanoelectronics and optoelectronics(American Physical Society, 2022-06-16) Kılıç, M. E.; Rad, Soheil Ershad; İpek, S.; Jahangirov, SeymurTwo-dimensional materials open up tremendous opportunities for nanoelectronics and optoelectronics. Using first-principles density functional methods, we predict a family of two-dimensional boron-pnictogen materials. Our results show that these materials have excellent energetic, dynamical, thermal, mechanical, and chemical stabilities. The intrinsic structural anisotropy found in these materials leads to highly direction-dependent mechanical, electronic, and optical properties. They possess highly anisotropic Young's modulus and Poisson's ratio. The tensile strength under uniaxial and biaxial deformations is found to be very high for these materials. Electronically, they are all semiconductors with narrow band gaps. The band gap energies can be tuned by alloying, strain engineering, and chemical functionalization. They exhibit anisotropic and high carrier mobility. All these electronic properties make them promising candidates for nanoelectronic device applications. Using state-of-the-art GW- Bethe-Salpeter equation approach, taking the electron-hole effect into account, the prominent optical absorption structure with strong anisotropy in the visible light region endow the boron-pnictogen materials with great potential in optoelectronics.Item Open Access Semiconducting defect-free polymorph of borophene: peierls distortion in two dimensions(American Physical Society, 2018) İpek, S.; Kılıç, M. E.; Moğulkoç, A.; Cahangirov, S.; Durgun, EnginIn contrast to the well-defined lattices of various two-dimensional (2D) systems, the atomic structure of borophene is sensitive to growth conditions and type of the substrate which results in rich polymorphism. By employing ab initio methods, we reveal a thermodynamically stable borophene polymorph without vacancies which is a semiconductor unlike the other known boron sheets, in the form of an asymmetric centered-washboard structure. Our results indicate that asymmetric distortion is induced due to Peierls instability which transforms a symmetric metallic system into a semiconductor. We also show that applying uniaxial or biaxial strain gradually lowers the obtained band gap and the symmetric configuration is restored following the closure of the band gap. Furthermore, while the Poisson's ratio is calculated to be high and positive in the semiconducting regime, it switches to negative once the metallicity is retrieved. The realization of semiconducting borophene polymorphs without defects and tunability of its electronic and mechanical response can extend the usage of boron sheets in a variety of nanoelectronic applications.