Mahmut Kus

A detailed analysis of current-voltage characteristics of Au/perylene-monoimide/n-Si Schottky barrier diodes over a wide temperature range

The current-voltage characteristics of Au/perylene-monoimide (PMI)/n-Si Schottky device have been investigated at a wide temperature range between 75 and 300 K in detail. The measured current-voltage (I-V) characteristics of the device show a good rectification behavior at all temperatures. The electronic parameters such as the ideality factor and the barrier height are determined from the experimental data using standard current-voltage analysis method and also temperature dependence of these parameters is analyzed. In addition to the standard analysis, using the Cheung and Cheung method, the series resistance and some other electrical properties are calculated for the device, and a good agreement is obtained between relevant diode parameters. It was observed that Au/PMI/n-Si Schottky diodes exhibit space charge limited (SCL) conduction at all temperatures. Therefore, we have analyzed this SCL current mechanism in more detail. From this analysis, several electronic parameters related with the SCL mechani...

Inkjet printing and low temperature sintering of CuO and CdS as functional electronic layers and Schottky diodes

Here we report on inkjet printing of a conductive amorphous copper oxide (CuO) ink and of semiconducting cadmium sulfide (CdS) quantum dots under ambient conditions and at low temperature to form functional thin films, which were used for the fabrication of Schottky diodes. Inkjet printed CuO features were sintered using a commercial photonic sintering tool in order to form the diode rectifying contacts. This was accomplished by using the tools proprietary high-intensity flash lamp at very short pulse durations, ensuring a low processing temperature that favors the usage of low-cost substrates. The photonic sintering method was also used for sintering CdS films, resulting in a more efficient removal of the organic moieties around the CdS nanoparticles than a wet chemical KOH treatment. The here reported process allows the deployment of a low-cost polyethylene terephthalate (PET) polymer foil as the substrate material. The initial results showed modest performance of the fabricated Schottky diode. Nevertheless, the general approaches demonstrate new routes for low temperature manufacturing methods for functional electronic layers based on accordingly developed functional materials utilising amorphous metal oxides and quantum dots.

Preparation of MIP-based QCM nanosensor for detection of caffeic acid.

In the present work, a new caffeic acid imprinted quartz crystal microbalance (QCM) nanosensor has been designed for selective assignation of caffeic acid in plant materials. Methacrylamidoantipyrine-iron(III) [MAAP-Fe(III)] as metal-chelating monomer has been used to prepare selective molecular imprinted polymer (MIP). MIP film for detection of caffeic acid has been developed on QCM electrode and selectivity experiments and analytical performance of caffeic acid imprinted QCM nanosensor has been studied. The caffeic acid imprinted QCM nanosensor has been characterized by AFM. After the characterization studies, imprinted and non-imprinted nanosensors was connected to QCM system for studies of connection of the target molecule, selectivity and the detection of amount of target molecule in real samples. The detection limit was found to be 7.8 nM. The value of Langmuir constant (b) (4.06 × 10(6)) that was acquired using Langmuir graph demonstrated that the affinity of binding sites was strong. Also, selectivity of prepared caffeic acid imprinted nanosensor was found as being high compared to chlorogenic acid. Finally, the caffeic acid levels in plant materials was determined by the prepared QCM nanosensor.

Adsorption of dyes on Sahara desert sand.

Sahara desert sand (SaDeS) was employed as a mineral sorbent for retaining organic dyes from aqueous solutions. Natural sand has demonstrated a strong affinity for organic dyes but significantly lost its adsorption capacity when it was washed with water. Therefore, characterization of both natural and water washed sand was performed by XRD, BET, SEM and FTIR techniques. It was found that water-soluble kyanite, which is detected in natural sand, is the dominant factor affecting adsorbance of cationic dyes. The sand adsorbs over 75% of cationic dyes but less than 21% for anionic ones. Among the dyes studied, Methylene Blue (MB) demonstrated the strongest affinity for Sahara desert sand (Q(e)=11.98 mg/g, for initial dye solution concentration 3.5 x 10(-5)mol/L). The effects of initial dye concentration, the amount of the adsorbent, the temperature and the pH of the solution on adsorption capacity were tested by using Methylene Blue as model dye. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied. It was concluded that adsorption of Methylene Blue on Sahara desert sand followed pseudo-second order kinetics. Gibbs free energy, enthalpy change and entropy change were calculated and found -6411 J/mol, -30360 J/mol and -76.58 J/mol K, respectively. These values indicate that the adsorption is an exothermic process and has a spontaneous nature at low temperatures.

The modification of Schottky barrier height of Au/p-Si Schottky devices by perylene-diimide

Perylene-diimide (PDI) thin film was fabricated by spin coating method on p-Si single-crystal substrate to prepare Au/PDI/p-Si Schottky device. The electrical properties of the Au/PDI/p-Si Schottky device were investigated by current-voltage (I–V) measurements in the temperature range 80–300 K and room temperature capacitance-voltage (C–V) measurement. Results showed a rectification behavior. Junction parameters such as ideality factor (n), barrier height (ϕB0), series resistance (Rs) interface state density (Nss), built-in potential (Vbi), carrier concentration (NA), and the width of the depletion layer (WD) were obtained from the I–V and C–V measurements. The values of ideality factor (n) and barrier height (BH) for the Au/PDI/p-Si structure from the I–V measurements were obtained as 1.77 and 0.584 eV at 300 K, 7.78 and 0.176 eV at 80 K, respectively. It was seen that the BH value of 0.584 eV calculated for the Au/PDI/p-Si structure was significantly larger than the value of 0.34 eV of conventional Au/p...

Penternary chalcogenides nanocrystals as catalytic materials for efficient counter electrodes in dye-synthesized solar cells

The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method, and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV–Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18–25 nm particle sizes which are forming nanospheres, and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that of Cu2ZnSn(SeS)4 nanocrystals and conventional platinum (Pt). The photovoltaic results demonstrated that DSSC with a Cu2CoSn(SeS)4 nanocrystals-based counter electrode achieved the best efficiency of 6.47%, which is higher than the same photoanode employing a Cu2ZnSn(SeS)4 nanocrystals (3.18%) and Pt (5.41%) counter electrodes. These promising results highlight the potential application of penternary chalcogen Cu2CoSn(SeS)4 nanocrystals in low-cost, high-efficiency, Pt-free DSSCs.

Humidity adsorption kinetics of calix[4]arene derivatives measured using QCM technique

This study focuses on the characterization of sulphonated calix[4]arene derivative films coated on a quartz substrate with a thickness of 40 nm by spin coating method for humidity detection. The humidity adsorption kinetics of the sulphonated calix[4]arene films was investigated by quartz crystal microbalance (QCM) technique. The Langmuir model was used to determine the adsorption rates and Gibbs free energy for various relative humidities between 11% and 97%. Our reproducible experimental results show that suphonated calix[4]arene films have a great potential for humidity sensing applications at room temperature operations.

Solvent washing with toluene enhances efficiency and increases reproducibility in perovskite solar cells

We report a simple process for reproducibly fabricating perovskite solar cells. We emphasize that the solvent washing technique is the most practical method for successful uniform crystallization so it facilitates highly efficient reproducible perovskite solar cells. The critical parameter for tuning crystallinity is determined to be the type of washing solvent and the quantity dispensed. The amount of washing solvent strongly affects the particle size distribution resulting in better or worse interconnection between the crystal grains. We discovered that 20 µl of toluene is the best washing solvent for device reproducibility. Our proposed parameters result in 90% reproducible perovskite solar cells with an average efficiency around 8%.

A Comparative Study of Supported TiO2 as Photocatalyst in Water Decontamination at Solar Pilot Plant Scale

The degradation of gallic acid and imidacloprid with supported Millennium PC500 and Degussa P25 TiO2 is reported. TiO2 particles were immobilized using a titanium sol-solution and direct deposition on glass supports. The film characterization was done by x-ray diffraction, scanning electron microscopy, and atomic force microscopy, and degradation of organic compounds was monitored by high-performance liquid chromatography, total organic carbon analyzer, and ion chromatography. The experiments were performed under sunlight in compound parabolic collector plants with flat supports inside the glass tubes. Photocatalytic activity of the films was compared and identified. Although sol-gel coatings had better mechanical properties, mineralization was observed to be approximately five times slower than paste-deposited films. Photoactivity of the films decreased with silver deposition due to the nature of the organic compounds. The rate constants were calculated to be between 2×10–1 and 6×10–2 mg m2/kJ for organic compounds, and 6×10–2 and 6×10–3 for total organic carbon.

Luminescence Enhancement of Oled Performance by Doping Colloidal Magnetic FE 3 O 4 Nanoparticles

We report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Poly∞uorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5{10nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence e-ciency increases by doping with MNPs into emissive layer. Difierent dopant concentrations varied from 0,4% to 2% were monitored. It was observed that the electroluminescence increases up to 1%w/v doping ratio. The luminance of OLEDs increased from 15.000cd/m 2 to 24.000cd/m 2 in comparison pristine device with 1% MNP doped device.