Browsing by Subject "CdS"

Now showing 1 - 6 of 6

Open Access
CDs have fingerprints too
(Springer, Berlin, Heidelberg, 2009) Hammouri G.; Dana, Aykutlu; Sunar, B.
We introduce a new technique for extracting unique fingerprints from identical CDs. The proposed technique takes advantage of manufacturing variability found in the length of the CD lands and pits. Although the variability measured is on the order of 20 nm, the technique does not require the use of microscopes or any advanced equipment. Instead, we show that the electrical signal produced by the photodetector inside the CD reader is sufficient to measure the desired variability. We investigate the new technique by analyzing data collected from 100 identical CDs and show how to extract a unique fingerprint for each CD. Furthermore, we introduce a technique for utilizing fuzzy extractors over the Lee metric without much change to the standard code offset construction. Finally, we identify specific parameters and a code construction to realize the proposed fuzzy extractor and convert the derived fingerprints into 128-bit cryptographic keys. © 2009 Springer.
Open Access
Charging/discharging dynamics of CdS and CdSe films under photoillumination using dynamic x-ray photoelectron spectroscopy
(A I P Publishing LLC, 2010) Sezen, H.; Süzer, Şefik
Thin films of CdS and CdSe are deposited on HF-cleaned Si O2 /Si substrates containing ∼5 nm thermally grown silicon oxide. x-ray photoelectron spectroscopy (XPS) data of these films are collected in a dynamic mode, which is based on recording the spectrum under modulation with an electrical signal in the form of ±10 V square-wave pulses. Accordingly, all peaks are twined and shifted with respect to the grounded spectrum. The binding energy difference between the twinned peaks of a dielectric system has a strong dependence on the frequency of the electrical stimuli. Therefore, dynamic XPS provides a means to extract additional properties of dielectric materials, such as effective resistance and capacitance. In this work, the authors report a new advancement to the previous method, where they now probe a photodynamic process. For this reason, photoillumination is introduced as an additional form of stimulus and used to investigate the combined optical and electrical response of the photoconductive thin films of CdS and CdSe using dynamic XPS.
Open Access
Dynamical XPS measurements for probing photoinduced voltage changes
(2010) Sezen, H.; Süzer, Şefik
Photoillumination with 405 nm laser causes shifts in XPS peaks of n-Si(100), and CdS. To distinguish between surface photovoltage (SPV), and charging, dynamical measurements are performed, while sample is subjected to square wave pulses of ± 10.00 V amplitude, and 10-3-10 5 Hz frequency. For n-Si, Si2p peaks are twinned at + 10.00 and -10.00, yielding always 20.00 eV difference. Photoillumination shifts the twinned peaks to higher energies, but the difference is always 20.00 eV. However, for CdS, the measured binding difference of Cd3d peaks exhibits strong frequency dependence due to charging, which indicates that both fast SPV and slow charging effects are operative.
Open Access
Encapsulation of vanillin/cyclodextrin inclusion complex in electrospun polyvinyl alcohol (PVA) nanowebs: prolonged shelf-life and high temperature stability of vanillin
(2012-08) Kayaci, F.; Uyar, Tamer
We produced functional nanowebs, containing vanillin, having prolonged shelf-life and high temperature stability facilitated by cyclodextrin (CD) inclusion complexation. Polyvinyl alcohol (PVA) nanowebs incorporating vanillin/cyclodextrin inclusion complex (vanillin/CD-IC) were produced via electrospinning technique. The vanillin/CD-IC was prepared with three types of CDs; α-CD, β-CD and γ-CD to find out the most favourable CD type for the stabilization of vanillin. PVA/vanillin/CD-IC nanofibres, having fibre diameters around ∼200 nm, were successfully electrospun from aqueous mixture of PVA and vanillin/CD-IC. Our results indicated that vanillin with enhanced durability and high temperature stability was achieved for PVA/vanillin/CD-IC nanowebs due to complexation of vanillin with CD, whereas the PVA nanofibres without CD-IC could not effectively preserve the vanillin. Additionally, we observed that PVA/vanillin/γ-CD-IC nanoweb was more effective for the stabilization and slow release of vanillin suggesting that the strength of interaction between vanillin and the γ-CD cavity is stronger when compared to α-CD and β-CD. © 2012 Elsevier Ltd. All rights reserved.
Open Access
Functional electrospun polystyrene nanofibers incorporating α-, β-, and γ-cyclodextrins: Comparison of molecular filter performance
(2010) Uyar, Tamer; Havelund, R.; Hacaloglu, J.; Besenbacher, F.; Kingshott, P.
Electrospinning has been used to successfully create polystyrene (PS) nanofibers containing either of three different types of cyclodextrin (CD); α-CD, β-CD, and γ-CD. These three CDs are chosen because they have different sized cavities that potentially allow for selective inclusion complex (IC) formation with molecules of different size or differences in affinity of IC formation with one type of molecule. The CD containing electrospun PS nanofibers (PS/CD) were initially characterized by scanning electron microscopy (SEM) to determine the uniformity of the fibers and their fiber diameter distributions. X-ray photoelectron spectroscopy (XPS) was used to quantitatively determine the concentration of each CD on the different fiber surfaces. Static time-of-flight secondary ion mass spectrometry (static-ToF-SIMS) showed the presence of each type of CD on the PS nanofibers by the detection of both the CD sodium adduct molecular ions (M + Na+) and lower molecular weight oxygen containing fragment ions. The comparative efficiency of the PS/CD nanofibers/nanoweb for removing phenolphthalein, a model organic compound, from solution was determined by UV-vis spectrometry, and the kinetics of phenolphthalein capture was shown to follow the trend PS/α-CD > PS/β-CD > PS/γ-CD. Direct pyrolysis mass spectrometry (DP-MS) was also performed to ascertain the relative binding strengths of the phenolphthalein for the CD cavities, and the results showed the trend in the interaction strength was β-CD > γ-CD > α-CD. Our results demonstrate that nanofibers produced by electrospinning that incorporate cyclodextrins with different sized cavities can indeed filter organic molecules and can potentially be used for filtration, purification, and/or separation processes. © 2010 American Chemical Society.
Open Access
Synthesis of stable mesostructured coupled semiconductor thin films: meso-CdS-TiO2 and meso-CdSe-TiO2
(2010) Okur, H. İ.; Türker, Y.; Dag, Ö.
Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced self-assembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H20)4] (N03)2, HNO3, and Ti(OC4H 9)4 and then aging the samples under 50% humidity at 30 0C (denoted as meso-xCd(II)-y TiO2). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H 2S (or H2Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H2S (or H2Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H2S or H2Se gas). However, this problem can be overcome by further aging the samples at 130 °C for a few hours before H2S (or H2Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO2. However, the H2Se reaction, additionally, needs to be carried at lower H2Se pressures in an N2 atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-.yTiO2. Otherwise, an excessive number of Se8 particles form in the film samples.