Browsing by Subject "Ferroelectric"
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Item Open Access Ferroelectric based fractal phononic crystals: wave propagation and band structure(Taylor & Francis, 2020-04) Palaz, S.; Özer, Z.; Mamedov, Amirullah M.; Özbay, EkmelIn this study, the band structure and transmission in multiferroic based Sierpinski carpet phononic crystal are investigated based on finite element simulation. In order to obtain the band structure of the phononic crystal (PnC), the Floquet periodicity conditions were applied to the sides of the unit cell. The square lattice PnC consists of various piezoelectric inclusion in a rubber matrix with square and circular cross section.Item Open Access Ferroelectric Based Photonic Crystal Cavity by Liquid Crystal Infiltration(Taylor & Francis, 2014) Karaomerlioglu, F.; Simsek S.; Mamedov, A. M.; Özbay, EkmelA novel type of two-dimensional photonic crystal is investigated for it optical properties as a core-shell-type ferroelectric nanorod infiltrated with nematic liquid crystals. Using the plane wave expansion method and finite-difference time-domain method, the photonic crystal structure, which is composed of a photonic crystal in a core-shell-type ferroelectric nanorod, is designed for the square lattice and the hexagonal lattice. It has been used 5CB as a photonic crystal core, and LiNbO3 as a ferroelectric material. The photonic crystal with a core-shell-type LiNbO3 nanorod infiltrated with nematic liquid crystals is compared with the photonic crystal with solid LiNbO3 rods and the photonic crystal with hollow LiNbO3 rods.Item Open Access Low temperature growth, characterization and applications of rf-sputtered SrTiO3 and BaSrTiO3 thin films(2016-03) Bayrak, TürkanAmong the several perovskite ferroelectric oxides, SrTiO3 (STO) and BaSrTiO3 (BST) thin lms have attracted signi cant attention due to their potential applications in oxide-based electronics. However, reliability and performance of STO and BST thin lms depend usually on the precise knowledge of microstructure, as well as optical and electrical properties. STO and BST thin lms were deposited at room-temperature on Si (100), UVgrade fused silica, quartz substrates and TiO2 nano bers by radio frequency (RF) magnetron sputtering using di erent plasma power, oxygen mixing ratios (OMRs) and deposition pressure levels. As-deposited thin lms showed amorphous-like nanocrystalline microstructure almost independent of the deposition conditions. In uence of post-deposition annealing at various temperatures of RF sputtered STO thin lms were also investigated. All lms were found to be highly transparent (>75%) in the visible region, and both STO and BST lms exhibited well de ned main absorption edges: the calculated indirect and direct band gaps for STO lms were in the range of 2.32 to 4.55 eV. The refractive index of the STO lms increased with OMR and post-deposition annealing for 3 mTorr deposition for STO, BST and STO annealing study. However, there is no correlation for 5 mTorr deposition. The refractive indices of BST lms were in the range of 1.90-2.07 at 550 nm depending on their deposition conditions. The optical band gap of the BST lms were calculated the ranging in 3.60 to 4.30 eV. Electrical dielectric constant values of the STO thin lms were extracted from frequency or voltage dependent capacitance measurements using micro-fabricated Ag/STO/p-Si device structures. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 C/cm2 charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). Post-deposition annealing at 800oC for 1 h resulted in polycrystalline BST thin lms with increased refractive indices and dielectric constants, along with reduced optical transmission values. Frequency dependent dielectric constants were found to be in the range of 46-72, and the observed leakage current was very small,less than 1 A. Our experimental results show that these low temperature grown STO and BST lms have the potential for various electrical applications.Item Open Access Second harmonic generation in generalized ferroelectric superlattices(Taylor & Francis, 2021-12-01) Ozer, Z.; Palaz, S.; Mamedov, Amirullah M.; Ozbay, EkmelThe goal of the work presented in this investigation is to achieve the efficient parametric interaction of narrow beams (in particular second harmonic generation) using a nonlinear (ferroelectric-LiTaO3) photonic crystal tuned to self-collimation (nondiffractive) regimes. A numerical study of second harmonic generation (SHG) in one-dimensional nonlinear photonic crystals based on a full nonlinear system of equations, implemented by a combination of the method of finite elements and fixed-point iterations, is reported. This model is derived from a nonlinear system of Maxwell’s equations that partly overcomes the known shortcoming of some existing models that rely on the undepleted pump approximation. We derive a general solution of SHG in one-dimensional nonlinear photonic crystals structures. Numerical simulations also show that the conversion efficiency of SHG can be significantly enhanced when the frequencies of the fundamental wave are located at the photonic band edges or are assigned to the designed defect states.Item Open Access Structural, optical, electrical and electrocatalytic activity properties of luminescent organic carbon quantum dots(Wiley-Blackwell, 2018) Karatutlu, Ali; Patil, Bhushan; Şeker, İ.; İstengir, S.; Bolat, A.; Yıldırım, O.; Sevgen, Y. N.; Bakış, Y.; Ortaç, Bülend; Yılmaz, Eda; Sapelkin, A.Carbon is an essential element in human life and recently becoming technologically prominent due to the emerging field of “Carbononics”. We demonstrate organic carbon quantum dots (qdots) containing nitrile bonded (C≡N bond) d-glucose-like traces in various sizes obtained from wheat flour to be promising for imaging applications and to possess a relaxor ferroelectric property and an enhanced electrocatalytic activity that could reduce the cost of energy devices and simple to scale up for the commercialization. The secondary electron microscopy (SEM) imaging shows that the particle size of carbon qdots can be controlled via the sonication exposure time. Elemental analysis and vibrational spectroscopy results show that carbon qdots are sensitive to N2 gas in the atmosphere and could weaken its “carbogenic” property by making a stable C≡N bond at ambient atmosphere. Rietveld analysis and HR-TEM studies demonstrate that the structure of the C qdots was found to fit best with an acentric primitive orthorhombic lattice. The laser scanning confocal microscopy (LSCM) images show enhancement of the light emission when reducing the size and characteristic excitation wavelength-dependent light emission of C qdots. The photoluminescence and UV-Vis absorption spectroscopy techniques show surface dominant emission and absorption upon the nitrile bonding.