Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 4Citation - Scopus: 4Photonic Crystal Textiles for Heat Insulation(American Institute of Physics, 2023) Çetin, Zebih; Tunçtürk, Yiğit; Sözüer, Hüseyin SamiIn this work, we have studied transmission properties of a photonic crystal-like structure that can be woven into fabrics. An interesting possibility emerges when considering the potential energy savings through suppression of radiation. It is a well-established fact that every object at a finite temperature inherently emits electromagnetic waves. Within the specific context of the human body, radiation takes on a crucial role as a fundamental mechanism governing heat dissipation. Thus, exploring ways to manage or mitigate this radiation could offer innovative approaches to optimize energy consumption and enhance heat regulation. It is well known that a photonic crystal can block electromagnetic energy with a specific frequency that is falling into a photonic bandgap. By using the numerical method called a finite-difference time domain, we have shown that this property of a periodic structure can be used to make textiles to save energy that is used to heat a human body environment. Numerical calculations have shown that by using the proposed photonic crystal structure, 53 % of electromagnetic energy is reflected. Although we mainly focused on textiles, it is worth highlighting that the same fundamental principle can be extended to diverse fields; for example, this structure can be integrated with construction materials and effectively function as a radiation heat insulator. © 2023 Author(s).Article Citation - WoS: 25Citation - Scopus: 26Structural and Optical Characteristics of Tantalum Oxide Grown by Pulsed Nd:yag Laser Oxidation(AVS Science and Technology Society, 2006) Atanassova, Elenada A.; Aygün, Gülnur; Turan, Raşit; Babeva, T.Tantalum pentoxide (Ta2 O5) thin films (20-50 nm) have been grown by 1064 nm Nd:YAG laser oxidation of Ta film deposited on Si. The chemical bonding, structure, and optical properties of the films have been studied by Fourier transform infrared spectroscopy, x-ray diffraction, and reflectance measurements at normal light incidence in the spectral range of 350-800 nm. The effect of the substrate temperature (250-400 °C) during oxidation and its optimization with respect to the used laser beam energy density (3.2-3.4 J cm2 per pulse) is discussed. It is established that the substrate temperature is a critical factor for the effectiveness of the oxidation process and can be used to control the composition and amorphous status of the films. The film density explored by refractive index is improved with increasing film thickness. The refractive index of the layers grown under the higher laser beam energy density and at substrate temperature of 350-400 °C was found to be close to the value of bulk Ta2 O5. The films are amorphous at substrate temperature below 350 °C and possessed an orthorhombic (Β- Ta2 O5) crystal structure at higher temperatures. The thinner layers crystallize at a little higher temperature.Article Citation - WoS: 2Citation - Scopus: 2Origin of a Localized Vibrational Mode in a Gasb Substrate With a Mbe-Grown Znte Epilayer(IOP Publishing Ltd., 2006) Kim, Hyunjung; Tarhan, Enver; Chen, G.; Ramdas, A. K.; Sciacca, M. D.; Gunshor, R. L.A localized vibrational mode (LVM) with a remarkable fine structure is observed in the infrared transmission spectrum of a ZnTe epilayer grown with molecular beam epitaxy (MBE) on a GaSb substrate. On the basis of the Zn and Te deposited on the GaSb substrate during the MBE growth of ZnTe, and assuming diffusion of Zn and Te into GaSb, the LVM is attributed to Zn, substitutionally replacing either the cation, Ga (ZnGa), or the anion, Sb (Zn Sb). The frequency of the LVM and its fine structure can then be interpreted in terms of the infrared active modes of 64Zn substituting for Sb as an anti-site impurity and treating the centre as an XY4 quasimolecule. With X≡64Zn and Y≡ 69Ga and 71Ga, occupying the nearest-neighbour sites reflecting all the possible combinations and permutations as well as the natural isotopic abundance of Ga, the fine structure of the LVM can be accounted for quantitatively.Article Developing a Trilayer Processing Technique for Superconducting Yba 2cu3o7-? Thin Films by Using Ge Ion Implantation(IOP Publishing Ltd., 2005) Avcı, İlbeyi; Tepe, Mustafa; Öktem, Bülent; Serincan, Uğur; Turan, Raşit; Abukay, DoğanFor making trilayer superconducting devices based on YBa2Cu 3O7-δ (YBCO) thin film processing, we developed a new technique by employing Ge ion implantation. A YBCO thin film of 150 nm thickness having high c-axis orientation and a transition temperature, T c, of 90 K was implanted with 80 keV, 1 × 1016 Ge ions cm-2 at room temperature. By the result of TRIM calculation, Ge ions were found to penetrate into the YBCO thin film approximately 60 nm below the surface of the film, thus leaving the lower part of the film as a superconductor. Upon implantation with Ge ions, the implanted upper part of the sample lost its electrical conductivity and diamagnetism while its original crystalline structure was preserved. The implanted ions we found did not alter the overall crystal structure of the YBCO thin film; this allowed us to grow an epitaxial superconducting upper layer of YBCO on top of the implanted area, leaving no need to use any buffer layer. The superconducting properties of the upper layer were similar to those of the pure YBCO base layer with an increased room temperature resistivity and a lowered Tc (88 K). This process provides an effective method for fabrication of a trilayer HTS device structure.