Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 2Citation - Scopus: 2The Effect of Thickness of Silver Thin Film on Structural and Optical Properties of Porous Silicon(World Scientific Publishing Co. Pte Ltd, 2017) Çetinel, A.; Özdoğan, M.; Utlu, G.; Artunç, N.; Şahin, G.; Tarhan, EnverIn this study, porous silicon (PS) samples were prepared on n-type silicon (100) wafers by electrochemical etching method, varying the current density from 20 to 100mA/cm2 and keeping constant HF concentration (10%) and etching time of 15min. Then, Ag thin films, which have 10, 50 and 100nm film thicknesses, were deposited on PS layers by using thermal evaporation to investigate the influence of Ag film thickness on structural and optical properties of PS. The structural and optical properties of PS and Ag deposited PS layers have been investigated by XRD, FE-SEM, Raman and photoluminescence (PL) spectroscopy. FE-SEM XRD and Raman analyzes indicate that average pore size and porosity of PS layers increase with the increasing current density. Further, Ag nanoparticles have embedded in pore channel. PL measurement reveals that higher porosity of PS would be better to form the Ag-PS nano-composite material leading to stronger PL band. The PL spectra of PS and Ag-PS samples indicate that PL bands show blue shift with increasing current density and film thickness. Consequently, it has been found that the structural and optical properties of PS depend on current density and Ag film thickness individually.Conference Object Citation - WoS: 36Citation - Scopus: 40Thermal Management in Large Bi2212 Mesas Used for Terahertz Sources(Institute of Electrical and Electronics Engineers Inc., 2009) Kurter, Cihan; Gray, Kenneth E.; Zasadzinski, John F.; Özyüzer, Lütfi; Koshelev, A. E.; Li, Q.; Yamamoto, T.; Kadowaki, K.; Kwok, W. K.; Tachiki, M.; Welp, U.We present a thermal analysis of a patterned mesa on a Bi 2Sr2CaCu2O8 (Bi2212) single crystal that is based on tunneling characteristics of the c-axis stack of ∼800 intrinsic Josephson junctions in the mesa. Despite the large mesa volume (e.g., 40 × 300 × 1.2 μm3) and power dissipation that result in self-heating and backbending of the current-voltage curve (I-V), there are accessible bias conditions for which significant polarized THz-wave emission can be observed. We estimate the mesa temperature by equating the quasiparticle resistance, Rqp(T), to the ratio V/I over the entire I-V including the backbending region. These temperatures are used to predict the unpolarized black-body radiation reaching our bolometer and there is substantial agreement over the entire I-V. As such, backbending results from the particular R qp (T) for Bi2212, as first discussed by Fenton, rather than a significant suppression of the energy gap. This model also correctly predicts the observed disappearance of backbending above ∼60 K.Conference Object Citation - WoS: 3Citation - Scopus: 3Low-Field Behavior of Ti-Added Mgb2/Cu Superconducting Wires(Institute of Electrical and Electronics Engineers Inc., 2005) Gençer, Ali; Kılıç, Ahmet; Okur, Salih; Güçlü, Nusret; Özyüzer, Lütfi; Belenli, İbrahimWe report on low-field magnetic properties of Ti-added (0-20 wt.% of Ti) Cu-clad MgB2 superconducting wires. Wires were produced by mixing appropriate amount of Ti and reacted MgB2 powder which was then placed inside Cu tubes with a diameter of 6 mm. The tubes were then cold worked by rolling or drawing to smaller diameters and then annealed at various temperatures to enhance the grain connectivity. XRD studies show that Ti addition results in new but minor phases. We have then measured ac susceptibilities in the temperature range between 20 K and 40 K in ac fields of 20-1600 A/m. The data show that an additional loss mechanism is established with Ti-addition. The calculated ac losses are increasing with increasing Ti-content in the main superconducting matrix.Article Citation - WoS: 49Citation - Scopus: 51Voc Sensors Based on a Metal Oxide Nanofibrous Membrane/Qcm System Prepared by Electrospinning(Royal Society of Chemistry, 2014) Horzum Polat, Nesrin; Taşçıoğlu, Didem; Özbek, Cebrail; Okur, Salih; Demir, Mustafa MuammerWe report a simple synthetic route to fabricate crystalline ZnO and CeO2/ZnO nanofibrous mats and their sensing characteristics against volatile organic compounds (VOCs) such as benzene, propanol, ethanol, and dichloromethane. Precursor fibers were fabricated by electrospinning of poly(vinyl alcohol) and metal salt(s) at 2.5 kV cm-1 in aqueous solution. The fibers were directly deposited on the crystal surface of a quartz crystal microbalance (QCM). The crystal, which was coated by nanostructured PVA/metal precursor(s) fibers, was subjected to calcination in air at 500 °C for 5 h. The formation of an oxide based nanofiber mat was revealed by scanning electron microscopy and X-ray diffraction. Upon exposure of the nanofiber mats to the VOCs, the compounds adsorbed onto the surface of oxidic fibers. The physisorption of the compounds was confirmed by FTIR and QCM. Both systems showed sensitivity to the VOCs and they hold a broad promise particularly for sensing applications of volatile alcoholic compounds. The introduction of CeO2 into the ZnO structure reduced the sensitivity of ZnO most probably due to the decrement of oxygen vacancies.