Browsing by Subject "Electric discharges"

Now showing 1 - 7 of 7

Open Access
Charging / discharging of thin PS / PMMA films as probed by dynamic x-ray photoelectron spectroscopy
(2007) Sezen, H.; Ertas, G.; Dâna, A.; Süzer, Şefik
Polystyrene / polymethyl methacrylate (PS-PMMA) thin films were analyzed for detecting phase separation as well as probing their electrical responses by XPS. It was also shown that electrical parameters like resistance or capacitance can also be extracted using dynamical XPS measurements. A Kratos ES300 electron spectrometer was used for XPS measurements, and a nearby filament provided low-energy electrons for charge neutralization. The results show that under a positive stress, low-energy electrons are attracted to the sample and yield less positive charge on the sample, due to partial neutralization.
Open Access
Comparison of electron and hole charge-discharge dynamics in germanium nanocrystal flash memories
(AIP Publishing, 2008-02) Akça, İmran B.; Dâna, Aykutlu; Aydınlı, Atilla; Turan, R.
Electron and hole charge and discharge dynamics are studied on plasma enhanced chemical vapor deposition grown metal-oxide-silicon germanium nanocrystal flash memory devices. Electron and hole charge and discharge currents are observed to differ significantly and depend on annealing conditions chosen for the formation of nanocrystals. At low annealing temperatures, holes are seen to charge slower but to escape faster than electrons. They discharge slower than electrons when annealing temperatures are raised. The results suggest that discharge currents are dominated by the interface layer acting as a quantum well for holes and by direct tunneling for elec-trons.
Open Access
Cu doping induced structural and optical properties of bimetallic oxide nanodots by the vertical spark generation
(Polish Academy of Sciences, 2019-05) Güngör, T.; Güngör, E.; Çalışkan, Deniz; Özbay, Ekmel
Undoped ZnO and Cu doped ZnO nanodots (NDs) were synthesized by the modified sparking technique with the Zn and Cu metal electrode pairs such as Zn–Zn, Zn–Cu and Cu–Cu. The effect of deposition geometry on the structural, optical properties and band gap energy were examined. The X-ray diffraction (XRD) analysis demonstrates that the nanodots have the hexagonal wurtzite structure, and visible considerable shift in the peaks position can be linked with the influence of Cu. However, when copper electrode was used, some copper oxide phases, metallic copper and paramelaconite phases were observed. From the results, the average diameters of metal oxide nanodots are about 25 nm and 50 nm which were obtained by using Cu–Cu and for Zn–Zn electrodes respectively from the scanning electron microscopy (SEM) analysis. When the Zn–Cu electrode pairs were used, the mixture of nanorod and nanodots appeared. It was observed that the island growth occurs in the horizontal geometry of electrode pairs and the growth metal oxide species are more strongly bonded to each other than to the substrate. But, these nanodots have more uniform distribution in the vertical geometry of electrodes. Optical studies indicated that the band gap decreased (red shift) when the Cu electrode was used.
Open Access
Mathematical and numerical modeling of the effect of input-parameters on the flushing efficiency of plasma channel in EDM process
(Elsevier Ltd, 2013) Shabgard, M.; Ahmadi, R.; Seyedzavvar, M.; Oliaei, S.N.B.
In the present study, the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process has been simulated using ABAQUS code finite element software. The temperature dependency of material properties and the expanding of plasma channel radius with time have been employed in the simulation stage. The profile of temperature distribution has been utilized to calculate the dimensions of discharge crater. Based on the results of FEM and the experimental observations, a numerical analysis has been developed assessing the contribution of input-parameters on the efficiency of plasma channel in removing the molten material from molten puddles on the surfaces of workpiece and tool at the end of each discharge. The results show that the increase in the pulse current and pulse on-time have converse effects on the plasma flushing efficiency, as it increases by the prior one and decreases by the latter one. Later, the introduced formulas for plasma flushing efficiency based on regression model were utilized to predict the cardinal parameter of recast layer thickness on the electrodes which demands expensive empirical tests to be obtained. © 2012 Elsevier Ltd. All rights reserved.
Open Access
On-machine fabrication of PCD and WC micro end mills using micro electro discharge machining
(Inderscience Enterprises Ltd., 2014) Oliaei, S.N.B.; Özdemir, C.; Karpat, Y.
Micro electro discharge machining (μ -EDM) process can be used to fabricate micro-milling tools of different geometries from tungsten carbide (WC) and polycrystalline diamond (PCD). The non-contact nature of EDM process makes micro tool fabrication a challenging task while offering the advantage of eliminating tool run out and clamping errors since micro tools fabricated on-machine. The tools are fabricated and used on the same spindle. In this study, a combination of block-EDM and wire electro discharge grinding (WEDG) techniques are used to fabricate micro end mills of different geometries. The influences of EDM process parameters on material erosion rate and surface roughness are examined. The performance of the fabricated micro-tools in ductile mode machining of fused silica has been investigated. It is found that micro end mills can be used to fabricate prototypes of microfluidics chips with acceptable quality. © 2014 Inderscience Enterprises Ltd.
Open Access
Synthesis and optical properties of Co and Zn-based metal oxide nanoparticle thin films
(Polish Academy of Sciences, 2017) Gungor, E.; Gungor, T.; Calıskan, D.; Özbay, Ekmel
ZnO, Co doped ZnO (ZnO:Co) and CoO thin films were deposited on glass substrates by using the spark discharge technique with Zn-Zn, Zn-Co and Co-Co metal electrodes (tips). The structural and optical properties of the films were characterized by X-ray diffraction, scanning electron microscopy measurements and UV-Vis spectrometry. Cubic phase reflection of CoO (200) was observed in the samples containing Co. The size of nanoparticles had varied between 38 nm and 200 nm in ZnO thin films. When Co electrode was used, spherical structure had deteriorated and clusters of particles, with smaller radii, were observed. In addition, when Co-Co electrode pairs were used, various cavities with different sizes were formed. Especially, it was observed that the optical transmittance had generally increased with the decreasing spark (charge) voltage, while increasing with the number of sparks. The Co-containing samples were green in color and it was observed that the loss of transmission appears in a specific region in the Co-doped ZnO thin films due to characteristic d-d transition of Co2+ ions. The thickness of the films had decreased with the increasing number of sparks. In addition, the band gap energy, Eg, evaluated by UV-Vis spectroscopy measurements has been shifted to higher wavelengths (red shift) for the ZnO:Co thin films.
Open Access
Zero-free-parameter modeling approach to predict the voltage of batteries of different chemistries and supercapacitors under arbitrary load
(Electrochemical Society, Inc., 2017) Özdemir, E.; Uzundal, C. B.; Ulgut, B.
Performance modeling of electrochemical energy storage systems is gathering increasingly higher attention in recent years. With the ever increasing power demand of mobile applications, predicting voltage behavior under different load profiles is of utmost importance for communications, automotive and consumer electronics. The ideal modelling approach needs not only to accurately predict the response of the battery, but also be robust, easy to implement and have low computational complexity. We will present a new algorithm that is algebraically straightforward, that has no adjustable parameters and that can accurately predict the voltage response of batteries and supercapacitors. The approach works well in a variety of discharge profiles ranging from simple long DC discharge/charge profiles to pulse schemes based on drive schedules published by regulatory bodies. Our approach is based on Electrochemical Impedance Spectroscopy measurements done on the system to be predicted. The spectrum is used in the frequency domain without any further processing to predict the fast moving portion of the voltage in the frequency domain. DC response is added in through a straightforward lookup table. This widely applicable approach can predict the voltage of with less than 1% error, without any adjustable parameters to a large variety of discharge profiles.