Browsing by Subject "Materials properties"

Now showing 1 - 5 of 5

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
Fe promoted NOx storage materials: structural properties and NOx uptake
(American Chemical Society, 2010) Kayhan, E.; Andonova, S. M.; Şentürk, G. S.; Chusuei, C. C.; Ozensoy, E.
Fe promoted NOx storage materials were synthesized in the form of FeOx/BaO/Al2O3 ternary oxides with varying BaO (8 and 20 wt %) and Fe (5 and 10 wt %) contents. Synthesized NOx storage materials were investigated via TEM, EELS, BET, FTIR, TPD, XRD, XPS, and Raman spectroscopy, and the results were compared with the conventional BaO/Al2O3 NOx storage system. Our results suggest that the introduction of Fe in the BaO/Al2O3 system leads to the formation of additional NOx storage sites which store NOx mostly in the form of bidentate nitrates. NO2 adsorption experiments at 323 K via FTIR indicate that, particularly in the early stages of the NOx uptake, the NOx storage mechanism is significantly altered in the presence of Fe sites where a set of new surface nitrosyl and nitrite groups were detected on the Fe sites and the surface oxidation of nitrites to nitrates is significantly hindered with respect to the BaO/Al2O3 system. Evidence for the existence of both Fe3+ as well as reduced Fe2+/(3-x)+ sites on the freshly pretreated materials was detected via EELS, FTIR, Raman, and XRD experiments. The influence of the Fe sites on the structural properties of the synthesized materials was also studied by performing ex situ annealing protocols within 323-1273 K followed by XRD and Raman experiments where the temperature dependent changes in the morphology and the composition of the surface domains were analyzed in detail. On the basis of the TPD data, it was found that the relative stability of the stored NOx species is influenced by the morphology of the Ba and Fe containing NOx-storage domains. The relative stabilities of the investigated NOx species were found to increase in the following order: N2O3/NO+ < nitrates on γ-Al2O3 < surface nitrates on BaO < bidentate nitrates on FeOx sites < bulk nitrates on BaO.
Open Access
Methods for probing charging properties of polymeric materials using XPS
(2010) Sezen, H.; Ertas, G.; Süzer, Şefik
Various thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to ±10 V d.c. bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 MΩ resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift due to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger Reff, and conversely the PMMA component shifts are smaller due to the presence of PS domains.
Open Access
Numerical analysis for remote identification of materials with magnetic characteristics
(2011) Ege, Y.; Şensoy, M.G.; Kalender O.; Nazlibilek, S.
There is a variety of methods used for remote sensing of objects such as acoustic, ground penetration radar detection, electromagnetic induction spectroscopy, infrared imaging, thermal neutron activation, core four-pole resonance, neutron backscattering, X-ray backscattering, and magnetic anomaly. The method that has to be used can be determined by the type of material, geographical location (underground or water), etc. Recent studies have been concentrated on the improvement of the criteria such as sensing distances, accuracy, and power consumption. In this paper, anomalies created by materials with magnetic characteristics at the perpendicular component of the Earth magnetic field have been detected by using a KMZ51 anisotropic magnetoresistive sensor with high sensitivity and low power consumption, and also, the effects of physical properties of materials on magnetic anomaly have been investigated. By analyzing the graphics obtained by 2-D motion of the sensor over the material, the most appropriate mathematical curves and formulas have been determined. Based on the physical properties of the magnetic material, the variations of the variables constituting the formulas of the curves have been analyzed. The contribution of this paper is the use of the results of these analyses for the purpose of identification of an unknown magnetic material. This is a new approach for the detection and determination of materials with magnetic characteristics by sensing the variation at the perpendicular component of the Earth magnetic field. The identification process has been explained in detail in this paper. © 2011 IEEE.
Open Access
Saliency for animated meshes with material properties
(ACM, 2010-07) Bülbül, Abdullah; Koca, Çetin; Çapin, Tolga; Güdükbay, Uğur
We propose a technique to calculate the saliency of animated meshes with material properties. The saliency computation considers multiple features of 3D meshes including their geometry, material and motion. Each feature contributes to the final saliency map which is view independent; and therefore, can be used for view dependent and view independent applications. To verify our saliency calculations, we performed an experiment in which we use an eye tracker to compare the saliencies of the regions that the viewers look with the other regions of the models. The results confirm that our saliency computation gives promising results. We also present several applications in which the saliency information is used. © 2010 ACM.