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- Yüksek Lisans TeziAçık Erişim2022Cp-Ti alaşımı üzerine büyütülmüş ZnO ve h-BN ilaveli TiO2 kompozit kaplamaların yapısal ve adhezyon özelliklerinin araştırılması
Ali Kadir Belet
Titanyum ve alaşımları, yüksek mukavemet/ağırlık oranı, oldukça düşük yoğunluk, iyi mekanik davranış, yüksek erime noktası, yüksek korozyon direnci, iyi yorulma mukavemeti ve tokluğu, düşük elastik modülü, mükemmel biyouyumluluk ve anti manyetiklik gibi üstün özelliklerinden dolayı havacılık, kimya, biyomedikal, enerji, otomotiv, askeri ve denizcilik gibi çeşitli endüstrilerde yaygın olarak kullanılmaktadır. Ancak yüksek ve kararsız sürtünme katsayısı, düşük kazımalı aşınma direnci ve güçlü adhezyon eğilimi gibi zayıf tribolojik özellikleri ve şiddetli klorür çözeltisi gibi bazı agresif korozif ortamlarında zayıf korozyon direnci sergilemeleri titanyum ve alaşımlarının bazı mühendislik uygulamalarında kullanımını kısıtlamaktadır. Bu nedenle titanyum ve alaşımlarının yüzey özelliklerini değiştirmek ve/veya geliştirmek oldukça hale gelmiştir. Bu çalışmada mikro ark oksidasyon yöntemi ile Cp-Ti alaşımı üzerine sırasıyla büyütülen TiO2 kaplamaların, ZnO ilaveli TiO2 ve h-BN ilaveli TiO2 büyütülmüş kompozit kaplamaların yapısal özellikleri ve taban malzeme ile kaplamalar arasındaki adhezyon davranışı incelenmiştir.
- MakaleAçık Erişim2021Effect of heating on structure and leaching characteristics of a zinc carbonate ore
Kumas, Cavit; Obut, Abdullah
In this work, the structural changes occurred in a zinc carbonate (smithsonite) ore sample following heating at temperatures between 523 K and 1173 K were investigated in detail using X-ray diffraction (XRD), thermal (TG/DTA) and Fourier-transform infrared (FT-IR) spectroscopy analyses. Afterwards, the leaching characteristics of zinc from the ore sample and the heated ore samples in sodium hydroxide solutions were determined. While heating at 523 K did not cause any structural change in the ore sample, heating at 723 K completely converted smithsonite (ZnCO3) in the ore sample to zinc oxide (ZnO), which resulted lower zinc leaching efficiencies of 40.6% and 62.0% for 3 and 4 mol/dm3 NaOH concentrations, respectively, in comparison to zinc leaching efficiencies (67.2% and 70.7%) obtained for the unheated ore sample. On the other hand, due to neoformation of dissolution resistant ZnFe2O4, Ca2ZnSi2O7 and ZmSiO4 phases during heating and formation of CaZm(OHD2H2O phase during leaching, the leaching efficiency of zinc further decreased to 22.2% and 31.3%, respectively, in 3 and 4 mol/dm3 NaOH solutions for the ore sample heated at 1173 K. The formation of zinc-containing dissolution resistant phases by high-temperature heating was observed to be the only reason for the reduction in the zinc leaching efficiency (49.4% at 1173 K) at the highest NaOH concentration (8 mol/dm3) studied. In this work, the comparative precipitation studies were also conducted and crystalline zinc oxides with different morphologies could be precipitated at considerably high efficiencies from the selected pregnant solutions obtained following leaching.
- MakaleAçık Erişim2019Addressing the sneak-path problem in crossbar RRAM devices using memristor-based one Schottky diode-one resistor array
Gül, Fatih
Resistive random access memories (RRAMs) are favorable contenders in the race towards future technologies. Moreover, the desirable properties of memristor-based RRAM devices make them very good competitors in this field. The sneak paths problem poses one of the main difficulties in the construction of crossbar memory devices. This problem can be effectively suppressed by applying the 1diode-1resistor (1D1R) design structure. The Schottky diode has many advantages compared to the PN junction diode. The low-power (∼1 µW) ZnO active-layered thin-film (60 nm thick) one Schottky diode-one memristor device fabricated in this study included a top Ag electrode and a bottom Al electrode. The material makeup of the device was confirmed via energy dispersive X-ray spectroscopy (EDAX). The memristive and Schottky diode characteristics of the Ag/ZnO/Al device were resolved by measuring the time-dependent voltage/current. The characteristic pinched hysteresis memristive loops were observed at the first quadrant of the current-voltage plane, whereas the diode curves were seen at the third quadrant. Using the current-voltage curves, the height of the Schottky barrier, ideality factor and threshold voltage of the Schottky diode were found to be 0.68 eV, 3.75 and 0.49 V, respectively. After physical implementation and characterization of the one diode-one memristor device, its anti-crosstalk characteristics were investigated. Taking into account the 10% read margin, the maximum crossbar size was found to be 87.
- MakaleYalnız künye2018A novel OTA-based circuit model corroborated by an experimental semiconductor memristor
Gul, Fatih; Babacan, Yunus
A semiconductor memristor device based on a 300-nm ZnO thin film was fabricated by direct-current reactive sputter. The memristive behavior of this device was confirmed by time dependent current–voltage (I-V-t) measurements, and the distinctive pinched hysteresis I-V loops of the memristor were observed. Structural analysis of the ZnO memristor was carried out using both X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). After physical implementation of the memristor, an operational transconductance amplifier (OTA) based memristor circuit was designed to emulate the ZnO-based semiconductor memristor for use in memristor-based circuit applications. All simulations were in good agreement with experimental results. In addition, a comparison of the proposed circuit with other memristor emulators was presented.
- MakaleYalnız künye2017Bipolar resistive switching and conduction mechanism of an Al/ZnO/Al-based memristor
Gul, Fatih; Efeoglu, Hasan
In this study, a direct-current reactive sputtered AliZnO/Al-based memristor device was fabricated and its resistive switching (RS) characteristics investigated. The optical and structural properties were confirmed by using UV vis spectrophotometry and x-ray diffraction, respectively. The memristive and resistive switching characteristics were determined using time dependent current voltage (I-V-t) measurements. The typical pinched hysteresis I-V loops of a memristor were observed. In addition, the device showed forming-free, uniform and bipolar RS behavior. The low electric field region exhibited ohmic conduction, while the Schottky emission (SE) was found to be the dominant conduction mechanism in the high electric field region. A weak Poole-Frenkel (PF) emission also appeared. In conclusion, it was suggested that the SE and PF mechanisms were related to the oxygen vacancies in the ZnO. (C) 2016 Elsevier Ltd. All rights reserved.
- MakaleAçık Erişim2017ZnO and ZnO1−x based thin film memristors: The effects of oxygen deficiency and thickness in resistive switching behavior
Gul, Fatih; Efeoglu, Hasan
In this study, direct-current reactive sputtered ZnO and ZnO1−x based thin film (30 nm and 300 nm in thickness) memristor devices were produced and the effects of oxygen vacancies and thickness on the memristive characteristics were investigated. The oxygen deficiency of the ZnO1−x structure was confirmed by SIMS analyses. The memristive characteristics of both the ZnO and ZnO1−x devices were determined by time dependent current–voltage (I-V-t) measurements. The distinctive pinched hysteresis I-V loops of memristors were observed in all the fabricated devices. The typical homogeneous interface and filamentary types of memristive behaviors were compared. In addition, conduction mechanisms, on/off ratios and the compliance current were analyzed. The 30 nm ZnO based devices with native oxygen vacancies showed the best on/off ratio. All of the devices exhibited dominant Schottky emissions and weaker Poole-Frenkel conduction mechanisms. Results suggested that the oxygen deficiency was responsible for the Schottky emission mechanism. Moreover, the compliance currents of the devices were related to the decreasing power consumption as the oxygen vacancies increased.