Browsing by Subject "Higher temperatures"
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Item Open Access Electrospinning of functional poly(methyl methacrylate) nanofibers containing cyclodextrin-menthol inclusion complexes(Institute of Physics Publishing, 2009) Uyar, Tamer; Nur, Y.; Hacaloglu, J.; Besenbacher, F.Electrospinning of nanofibers with cyclodextrin inclusion complexes (CD-ICs) is particularly attractive since distinct properties can be obtained by combining the nanofibers with specific functions of the CD-ICs. Here we report on the electrospinning of poly(methyl methacrylate) (PMMA) nanofibers containing cyclodextrin-menthol inclusion complexes (CD-menthol-ICs). These CD-menthol-IC functionalized nanofibers were developed with the purpose of producing functional nanofibers that contain fragrances/flavors with high temperature stability, and menthol was used as a model fragrance/flavor material. The PMMA nanofibers were electrospun with CD-menthol-ICs using three type of CD: α-CD, β-CD, and γ-CD. Direct pyrolysis mass spectrometry (DP-MS) studies showed that the thermal evaporation of menthol occurred over a very high and a broad temperature range (100-355 °C) for PMMA/CDmenthol-IC nanowebs, demonstrating the complexation of menthol with the CD cavity and its high temperature stability. Furthermore, as the size of CD cavity increased in the order α-CD<β-CD<γ-CD, the thermal evolution of menthol shifted to higher temperatures, suggesting that the strength of interaction between menthol and the CD cavity is in the order γ-CD>β-CD>α-CD. © 2009 IOP Publishing Ltd.Item Open Access Preparation of Au and Au-Pt nanoparticles within PMMA matrix using UV and X-ray irradiation(2009) Ozkaraoglu, E.; Tunc, I.; Süzer, ŞefikAu and Au-Pt alloy nanoparticles are prepared and patterned at room temperature within the PMMA polymer matrix by the action of 254 nm UV light or X-rays. The polymer matrix enables us to entangle the kinetics of the photochemical reduction from the nucleation and growth processes, when monitored by UV-vis spectroscopy. Accordingly, increase of the temperature to 50 °C of the reaction medium increases the nucleation and growth rates of the nanoparticle formation by more than one order of magnitude, due to enhanced diffusion and nucleation at the higher temperature, but has no effect on the photochemical reduction process. Presence of Pt ions also increases the same rate, but by a factor two only. Similar photochemical reduction and particle growth take also place within the PMMA matrix, when these metal ions are subjected to prolonged exposure to X-rays, as evidenced by XPS analysis. Both angle-resolved and charge-contrast measurements using XPS reveal that the resultant Au and Pt species are in close proximity to each other, indicating the Au-Pt alloy formation to be the most likely case.Item Open Access Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition(2012) Ozgit, C.; Donmez I.; Alevli, M.; Bıyıklı, NecmiWe report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH 3). At 185 °C, deposition rate saturated for TMA and NH 3 doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH 3 resulted in a constant growth rate of ∼ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≤ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ∼ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum. © 2011 Elsevier B.V. All rights reserved.