Çırak, Burcu Bozkurt

A Cr-decorated TiO2 nanoporous transparent electrode was fabricated by DC sputtering, anodization, and thermal evaporation methods, respectively. Ti films were deposited on fluorine-doped tin oxide (FTO) coated glass and anodized to obtain a transparent TiO2 nanoporous film (TN). The fabricated electrodes were characterized using a field emission scanning electron microscope (FESEM), atomic force microscope (AFM) and X-Ray diffraction (XRD). Photoelectrochemical activity of prepared films was investigated by photo-electrocatalytic degradation of RhB dye under constant voltage and UVA light irradiation. The Cr-decorated TiO2 nanoporous film (CTN) served as an electrode and exhibited better photo-electrocatalytic performance than a TN electrode. Results show that Cr decoration increased photoelectrochemical activity significantly due to more efficient charge separation and lower recombination rate.

Çayır Taşdemirci, Tuba

Nickel Oxide (NiO) thin films have been grown by Successive Ionic Layer Adsorption and Reaction (SILAR) method on glass substrates at room temperature. Grown NiO thin films subsequently annealed from 200 °C to 400 °C for 0.5 h. The effect of annealing temperature on the structural, morfological, molecular and optical properties were analyzed. NiO thin films were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), fouirer transform infrared spektrofotometre (FTIR) and UV–vis spectrophotometer respectively. The crystal and surface properties of NiO thin films developed with annealing temperature. The energy band gap values were reduced from 3.3 to 3.11 eV depending with annealing temperature.

Ekinci, Huseyin; Kuryatkov, Vladimir V.; Forgey, Chris; Dabiran, Amir; Jorgenson, Robert; Nikishin, Sergey A.

Two types of 3-period In14Ga86N/GaN multiple quantum well light-emitting diodes (LEDs) were studied, differing only in the conditions under which their p-GaN layers were grown by metalorganic chemical vapor deposition. The p-GaN of one type of LED was grown with a carrier gas mixture of N2/H2. A carrier gas of only N2 was used to grow the p-GaN of the second type of LED at a relatively elevated temperature, making the entire structure grown in pure N2 alone. Subsequently the growth, fabrication and characterization of each type of LED were methodologically studied. Based on the XRD analysis, the thickness of the well, barrier and In composition of the LED structures were estimated to be 2.5 nm, 8.5 nm and x = 14%, respectively. Finally, the electroluminescence output of these devices was evaluated at a current of 20 mA at room temperature. It was observed that the LED structure grown with nitrogen-only carrier gas had approximately 25% superior electroluminescence.

Özdokur, Kemal Volkan; Çırak, Burcu Bozkurt; Caglar, Bulent; Çırak, Çağrı; Karadeniz, Sibel Morkoç; Kılınç, Tuba; Erdoğan, Yaşar; Ekinci, Ali Ercan

Platinum decorated heterogeneous catalysts for methanol oxidation reaction have crucial importance for the commercial sustainability of Direct Methanol Fuel Cells (DMFC). In this study, TiO2/ZnO/Pt nanocomposite film was fabricated as a promising electrocatalytic surface to enhance methanol oxidation in alkaline medium. Firstly, an TiO2/ZnO layer was prepared via DC sputtering followed by electrodeposition techniques on FTO electrode and then platinum nanoparticles were decorated onto the obtained nanocomposite film for the first time. The characterization of the developed transparent films was performed by using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cycling voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The XRD, FESEM and XPS results showed that metallic Pt nanoparticles were uniformly distributed onto the TiO2/ZnO film consisting of anatase TiO2 and wurtzite ZnO layers with a thickness of ca. 370 and 320 nm, respectively. Five cycles of deposition of ZnO and Pt nanoparticles showed best catalytic activity after optimization. The oxidation peak of 0.5 M methanol at TiO2/ZnO/Pt was located at −0.17 V and the corresponding peak current increased about 10- and 5-fold in comparison to FTO/Pt and FTO/TiO2/Pt electrodes, respectively.

Bozkurt Çırak, Burcu; Karadeniz, Sibel Morkoç; Kılınç, Tuba; Caglar, Bulent; Ekinci, Ali Ercan; Yelgin, Hüseyin; Kürekçi, Mehmet; Çırak, Çağrı

In this study, anodic TiO2 nanotube (TNT) arrays with average nanotube diameter from 26 nm to 115 nm and length from 1.3 μm to 6.4 μm were grown by electrochemical method. Anodization process were performed under different voltages from 10 to 50 V in ethylene glycol – ammonium fluoride – water electrolyte. Formation mechanism of TNTs was summarized. Surface morphology, crystal structure, roughness, wettability and elasticity of TNT arrays were characterized by using field emission scanning electron microscope (FESEM), X-Ray diffraction (XRD), atomic force microscope (AFM), optical tensiometer and universal mechanical tester, respectively. Water contact angle measurements and nanoindentation tests proved that water contact angle and elastic modulus of TNT arrays decrease with increasing anodization voltage. Photocurrent-photovoltage curves and electrochemical impedance spectroscopy (EIS) measurements of dye sensitized solar cells (DSSC) were made to investigate the effects of anodization voltages on photoanode performance. The light conversion efficiency and photocurrent density of TNT photoanodes was increased with increasing anodization voltage due to larger nanotube length and surface area. The results show that anodization voltage is significant parameter for the surface properties and dye sensitized solar cell (DSSC) performance TNT arrays.