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Öğe The electronic transport properties of the [Co2(L)L′(dioxane)2(NO3)2](NO3)2 complex(Elsevier Science Bv, 2003) Yakuphanoglu, F.; Aydogdu, Y.; Gomleksiz, M.; Sekerci, M.; Agan, S.; Alkan, C.The temperature dependence of the electrical conductivity, microstructure and crystal structure properties of the [Co,(L)L'(dioxane)(2)(NO3)(2)](NO3)(2) complex was investigated. The X-ray diffraction showed that the [Co,(L)L'(dioxane)(2) (NO3)(2)](NO3)(2) has a triclinic structure. Temperature dependence of the conductivity curve of the complex exhibited two conduction regions, and while increase of conductivity with temperature in the first region is of hopping conduction which takes place in localized states, the conduction in the second region is of Arrhenius-type. These conduction mechanisms are related to intermolecular and intramolecular conduction progresses. The electrical conductivity of the [Co-2(L)L'(dioxane)(2)(NO3)(2)](NO3)(2) complex was 2.57 x 10(-7) (S/cm) at room temperature with activation energy of 0.46 eV which showed semiconductivity behavior. (C) 2002 Published by Elsevier Science B.V.Öğe Infrared luminescence of annealed germanosilicate layers(Elsevier Science Bv, 2014) Tokay, M. S.; Yasar, E.; Agan, S.; Aydinli, A.In the light of growing importance of semiconductor nanocrystals for photonics, we report on the growth and characterization of annealed germanosilicate layers used for Ge nanocrystal formation. The films are grown using plasma enhanced chemical vapor deposition (PECVD) and post-annealed in nitrogen at temperatures between 600 and 1200 degrees C for as long as 2 h. Transmission electron microscopy (TEM), Raman scattering and photoluminescence spectroscopy (PL) has been used to characterize the samples both structurally and optically. Formation of Ge precipitates in the germanosilicate layers have been observed using Raman spectroscopy for a variety of PECVD growth parameters, annealing temperatures and times. Ge-Ge mode at similar to 300 cm(-1) is clearly observed at temperatures as low as 700 degrees C for annealing durations for 45 min. Raman results indicate that upon annealing for extended periods of time at temperatures above 900 degrees C; nanocrystals of few tens of nanometers in diameter inside the oxide matrix and precipitation and interdiffusion of Ge, forming SiGe alloy at the silicon and oxide interface take place. Low temperature PL spectroscopy has been used to observe luminescence from these samples in the vicinity of 1550 nm, an important wavelength for telecommunications. Observed luminescence quenches at 140 K. The photoluminescence data displays three peaks closely interrelated at approximately 1490,, 1530 and 1610 nm. PL spectra persist even after removing the oxide layer indicating that the origin of the infrared luminescent centers are not related to the Ge nanocrystals in the oxide layer. (C) 2013 Elsevier B.V. All rights reserved.Öğe Low-loss as-grown germanosilicate layers for optical waveguides(Amer Inst Physics, 2003) Ay, F.; Aydinli, A.; Agan, S.We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguide technology. The films were deposited by plasma-enhanced chemical vapor deposition technique using silane, germane, and nitrous oxide as precursor gases. Fourier transform infrared spectroscopy was used to monitor the compositional properties of the samples. It was found that addition of germane leads to decreasing of N-H- and O-H-related bonds. The propagation loss values of the planar waveguides were correlated with the decrease in the hydrogen-related bonds of the as-deposited waveguides and resulted in very low values, eliminating the need for high-temperature annealing as is usually done. (C) 2003 American Institute of Physics.Öğe Raman and TEM studies of Ge nanocrystal formation in SiOx: Ge/SiOx multilayers(Wiley-V C H Verlag Gmbh, 2007) Dana, A.; Agan, S.; Tokay, S.; Aydinh, A.; Finstad, T. G.Alternating germanosilicate-siliconoxide layers of 10-30 nm thickness were grown on Si substrates by plasma enhanced chemically vapor deposition (PECVD). The compositions of the grown films were determined by X-ray photoelectron spectroscopy measurements. The films were annealed at temperatures varying from 670 to 1000 degrees C for 5 to 45 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive X-ray analysis (EDAX) data confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and Transmission Electron Microscopy (TEM). As the annealing temperature is raised to 850 degrees C, single layer of Ge nanocrystals observed at lower annealing temperatures is transformed into a double layer with the smaller sized nanocrystals closer to the substrate SiO2 interface. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
