Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
Browse
5 results
Search Results
Article Citation - WoS: 3Citation - Scopus: 3Local Vibrational Modes of Natural Isotopes of Substitutional Oxygen in Cdte(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2020) Tarhan, Enver; Ramdas, Anant K.We investigated the localized vibrational modes (LVM) of natural oxygen containing ${}^{16}O,\;{}^{17}O$ and ${}^{18}O$ isotopes at a substitutional tellurium site in cadmium telluride using infrared absorption spectroscopy at cryogenic temperatures. The main absorption peak observed at 350 cm ?1 was formerly attributed to a fundamental LVM mode (?0) of oxygen at a tellurium site. The relatively weak absorption peaks observed at 331 $cm^{-1}$ and 340 $cm^{-1}$ are assigned as the same $\nu_0$ mode of the ${}^{17}O$ and ${}^{18}O$ isotopes, respectively, based on their relative intensities and spectral positions. The spectral positions were confirmed with theoretical calculations using a linear chain model where the peak position at 350$cm^{-1}$ was taken as the reference for the ${}^{16}O$ isotope. From a least square analysis of the observed peak positions we were able to calculate the force constants from perturbation theory. A Lorentzian line shape analysis of each $\nu_0$ absorption peak, considering the effects of isotopic mass and natural abundance variations of the host Cd atoms, was also carried out to further confirm their assignments. Reasonably good line shape fittings were obtained for $\nu_0$ modes of all isotopes of oxygen.Article Citation - WoS: 24Citation - Scopus: 25Investigation of the Structure of Alpha-Lactalbumin Protein Nanotubes Using Optical Spectroscopy(Cambridge University Press, 2014) Tarhan, Özgür; Tarhan, Enver; Harsa, ŞebnemAlpha-lactalbumin (α-la) is one of the major proteins in whey. When partially hydrolysed with Bacillus licheniformis protease, it produces nanotubular structures in the presence of calcium ions by a self-assembly process. This study presents investigation of α-la protein structure during hydrolysis and nanotube formation using optical spectroscopy. Before spectroscopic measurements, nanotubes were examined with microscopy. The observed α-la nanotubes (α-LaNTs) were in the form of regular hollo strands with a diameter of about 20 nm and the average length of 1 μm. Amide and backbone vibration bands of the Raman spectra displayed remarkable conformational changes in α and β domains in the protein structure during nanotube growth. This was confirmed by the Fourier-transform infrared (FTIR) spectroscopy data. Also, FTIR analysis revealed certain bands at calcium (Ca++) binding sites of COO- groups in hydrolysed protein. These sites might be critical in nanotube elongation.Article Citation - WoS: 42Citation - Scopus: 44Growth of Cu2znsns4 Absorber Layer on Flexible Metallic Substrates for Thin Film Solar Cell Applications(Elsevier Ltd., 2015) Yazıcı, Şebnem; Olgar, Mehmet Ali; Akça, Fatime Gülşah; Cantaş, Ayten; Kurt, Metin; Aygün, Gülnur; Tarhan, Enver; Yanmaz, Ekrem; Özyüzer, LütfiIn this work, Cu2ZnSnS4 (CZTS) absorber layers were fabricated using a two-stage process. Sequentially deposited Cu-Zn-Sn thin film layers on metallic foils were annealed in an Ar + S2(g) atmosphere. We aimed to investigate the role of flexible titanium and molybdenum foil substrates in the growth mechanism of CZTS thin films. The Raman spectra and X-ray photoelectron spectroscopy analyses of the sulfurized thin films revealed that, except for the presence of Sn-based secondary phases, nearly pure CZTS thin films were obtained. Additionally, the intense and sharp X-ray diffraction peak from the (112) plane provided evidence of good crystallinity. Electron dispersive spectroscopy analysis indicated sufficient sulfur content but poor Zn atomic weight percentage in the films. Absorption and band-gap energy analyses were carried out to confirm the suitability of CZTS thin films as the absorber layer in solar cell applications. Hall effect measurements showed the p-type semiconductor behavior of the CZTS samples. Moreover, the back contact behavior of these metallic flexible substrates was investigated and compared. We detected formation of cracks in the CZTS layer on the molybdenum foils, which indicates the incompatibility of molybdenum's thermal expansion coefficient with the CZTS structure. We demonstrated the application of the magnetron sputtering technique for the fabrication of CZTS thin films on titanium foils having lightweight, flexible properties and suitable for roll-to-roll manufacturing for high throughput fabrication. Titanium foils are also cost competitive compared to molybdenum foils. © 2015 Elsevier B.V.Article Citation - WoS: 29Citation - Scopus: 30The Structural, Optical and Morphological Properties of Caf2 Thin Films by Using Thermionic Vacuum Arc (tva)(Elsevier Ltd., 2013) Çetin, N. Emre; Korkmaz, Şadan; Elmas, Saliha; Ekem, Naci; Pat, Suat; Balbag, M. Zafer; Tarhan, Enver; Temel, Sinan; Özmumcu, MuratIn this study, calcium fluoride (CaF2) thin films have been prepared by Thermionic Vacuum Arc (TVA) technique on glass substrates. In this technique CaF2 thin films are produced by condensing the plasma of anode material generated in the TVA setup under high vacuum conditions on glass substrates. Crystal structures as well as optical and surface properties of CaF2 antireflective (AR) coated thin films were investigated. X-ray diffraction (XRD) measurements showed that amorphous CaF2 thin films were formed. Optical and surface properties of CaF2 films have been studied based on optical transmittance, reflectance, refractive index and atomic force microscopy imaging (AFM). Our results also show that CaF2 coated samples exhibit lower reflectance (R). From our optical studies, we have observed that CaF2 thin films have high AR properties.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.