Çiğdem Nuhoğlu

An environmentally friendly process; Adsorption of radionuclide Tl-201 on fibrous waste tea

This work presents an investigation of the adsorption of the radionuclide of Tl-201 from waste water on the fibrous tea factory waste. The experimental parameters were chosen as temperature, pH, stirring speed, adsorbent dose and nominal particle size in the ranges of 10.0-40.0 degrees C, 2.0-10.0, 300-720 rpm, 1.0-15.0 g/L and 0.15-0.71 mm, respectively. The most effective parameter on the adsorption yield was found to be pH of the solution. Fourier transforms infrared and electron paramagnetic resonance spectroscopy studies were performed for the characterisation of the adsorption on tea waste. The experimental data were found to be in good agreement with the isotherm models of Freundlich, Halsey, Handerson and Dubinin-Radushkevich. Thermodynamic analysis showed that the values of Delta G and Delta H are negative. It was obtained that the adsorption rate can be represented very well by second-order pseudo homogeneous kinetic model. All the results proved that fibrous tea plant waste makes an excellent adsorbent for Tl-201 radionuclide.

The barrier height inhomogeneity in identically prepared Pb/p-type Si Schottky barrier diodes

We have studied the experimental linear relationship between barrier heights (BHs) and ideality factors for Pb/p-type Si(100) Schottky contacts with a doping density of about 1015 cm−3. The BH for the Pb/p-type Si(100) diodes from the current–voltage (I–V) characteristics varied from 0.686 to 0.735 eV, the ideality factor n varied from 1.054 to 1.191, and from capacitance–voltage (C−2–V) characteristics the BH varied from 0.751 to 0.928 eV. The experimental BH distributions obtained from the I–V and C−2–V characteristics were fitted by a Gaussian function, and their mean BH values were found to be 0.709 and 0.799 eV, respectively. The laterally homogeneous BH value of approximately 0.741 eV for the H-terminated Pb/p-type Si(100) Schottky diodes was obtained from the linear relationship between experimental effective BHs and ideality factors.

Biosorption of Ga-67 radionuclides from aqueous solutions onto waste pomace of an olive oil factory

The aim of this research was to test the removal of Ga-67 radionuclides from aqueous solutions by biosorption onto waste pomace of an olive oil factory (WPOOF). Batch adsorption studies were performed in order to investigate the temperature, the initial pH of the solution, the stirring speed, the biosorbent dose, and the nominal particle size of the biosorbent in the experimental work. The most effective parameter was found to be the initial pH. A high biosorption yield of 98 was obtained. The equilibrium values were fitted to the isotherm models. The values of DeltaG and DeltaH were calculated to be negative. The adsorption kinetics calculations showed that the kinetics of the biosorption process fitted well to the pseudo-second order rate model.

Effect of thermal annealing on Co/n-LEC GaAs (Te) Schottky contacts

The Co/n-GaAs(Te) Schottky barrier diodes have been annealed at temperatures from 100 to 3008C for 5 min and from 350 to 8008C for 1 min in N2 atmosphere. Some expressions have been obtained to interpret the relation between the experiment barrier height F b,o and equilibrium interface charge density Qss(0) depending on annealing temperature. The F b,o value has increased and Qss(0) is decreased with increasing annealing temperature up to 5508C. This increase in the barrier height has been attributed to the value of positive Qss(0), which is responsible for the Fermi level pinning. The relation between the F b,o and Qss(0) depending on annealing temperature is in very good agreement with that of the interface state density distribution especially in the mid-gap. q 2000 Elsevier Science Ltd. All rights reserved.

Cr/- and Fe/n-GaAs Schottky diodes: the stable current-voltage characteristic produced by high-temperature annealing

The electrical characteristics of Cr/- and Fe/liquid-encapsulated Czochralski (LEC)n-GaAs Schottky barrier diodes (SBDs) annealed at temperatures from 100 to C for 5 min and from 350 to C for 1 min have been investigated as a function of annealing temperature, with the use of current-voltage techniques. For Cr/n-GaAs SBDs, the Schottky barrier height and ideality factor n values range from 0.57 eV and 1.10 (for the as-deposited sample) to 0.80 eV and 1.10 (for C annealing). The ideality factor values remain approximately unchanged up to C and increased to 1.28 at C . For Fe/n-GaAs SBDs, the and n values range from 0.60 eV and 1.06 (for the as-deposited sample) to 0.78 eV and 1.08 (for C annealing). After C annealing, while the n values of the Fe/n-GaAs SBDs remain approximately unchanged between 1.10 and 1.12 up to C annealing, the value decreased with increasing temperature and became 0.75 at C (n = 1.11) and 0.73 at C (n = 1.20). It has been seen that the Cr/- and Fe/LECn-GaAs contacts are thermally stable under annealing up to C.

THE EFFECT OF THERMAL ANEALING ON THE SERIES RESISTANCE OF NEARLY IDEAL AND IDEAL TI/N-GAAS SCHOTTKY DIODES

The effect of annealing in the temperature range 100–300°C with steps of 100°C for 5min on characteristic parameters, especially series resistance, of nearly ideal (D1) and ideal (D2) Ti/n-GaAs Schottky barrier diodes (SBDs) has been investigated. Both Ti/n-GaAs SBDs have shown thermal stability up to 300°C annealing. It can be said that the interfacial layer thickness of sample D1 is too thin to hinder thermal stability. The ideality factor and barrier height of samples D1 and D2 have been found to be 1.05 and 0.76eV and 1.06 and 0.75eV at 300°C respectively, while 1.08 and 0.64eV and 1.01 and 0.67eV for their as-deposited samples, respectively. The series resistance values have decreased with increasing annealing temperature. This has been attributed to reduction of the native oxide layer by the metal Ti. It has been concluded that the annealing to a given temperature has improved the electrical characteristics of both Ti/n-GaAs Schottky contacts due to chemical reactions between substrate and the reactive metals and the native oxide.