Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 3Citation - Scopus: 4Lipid Bilayer on Wrinkled-Interfaced Graphene Field Effect Transistor(Elsevier Ltd., 2021) Özkendir İnanç, Dilce; Çelebi, Cem; Yıldız, Ümit HakanThis study describes lipid bilayer-based sensor interface on SiO2 encapsulated graphene field effect transistors (GFET). The SiO2 layer was utilized as a lipid compatible surface that drives bilayer formation. The two types of surface morphologies i) wrinkled morphology by thermal evaporation (TE) and ii) flat morphology by pulsed electron deposition (PED) were obtained. The sensing performance of wrinkled and flat interfaced-GFETs were investigated, pH sensitivity of wrinkled interfaced-GFETs were found to be ten fold larger than the flat ones. The enhanced sensitivity is attributed to thinning of the oxide layer by formation of wrinkles thereby facilitating electrostatic gating on graphene. We foresee that described wrinkled SiO2 interfaced-GFET holds promise as a cell membrane mimicking sensing platform for novel bioelectronic applications. © 2020Article Citation - WoS: 12Citation - Scopus: 16Humidity Adsorption Kinetics of a Trypsin Gel Film(Elsevier Ltd., 2012) Okur, Salih; Ceylan, Çağatay; Çulcular, EvrenThis study focuses on the humidity adsorption kinetics of an isopropanol-induced and pH-triggered bovine pancreatic trypsin gel (BPTG). The BPTG was adsorbed on a gold coated Quartz Crystal Microbalance (QCM) substrate with a thickness of 376nm. The morphology of the film was characterized using Atomic Force Microscopy (AFM). QCM was used to investigate the humidity sensing properties of the BPTG film. The response of the humidity sensor was explained using the Langmuir model. The average values of adsorption and desorption rates between 11% RH (relative humidity) and 97% RH were calculated as 2482.5M -1s -1 and 0.02s -1, respectively. The equilibrium constant and average Gibbs Free Energy of humidity adsorption and desorption cycles were obtained as 133,000 and -11.8kJ/mol, respectively. © 2011 Elsevier Inc..Article Citation - WoS: 82Citation - Scopus: 92Metal Ion Release From Nitrogen Ion Implanted Cocrmo Orthopedic Implant Material(Elsevier Ltd., 2006) Öztürk, Orhan; Türkan, Uğur; Eroğlu, Ahmet EminCoCrMo alloys are used as orthopedic implant materials because of their excellent mechanical and corrosion properties. However, when placed in vivo, these alloys release Co, Cr, Mo ions to host tissues, which may give rise to significant health concerns over time. Nitrogen ion implantation can be used to form protective layers on the surface of CoCrMo orthopedic alloys by modifying the near surface layers of these materials. In this study, medical grade CoCrMo alloy (IS0 5832-12) was ion implanted with 60 keV nitrogen ions to a high dose of 1.9 × 10 18 ions/cm 2 at substrate temperatures of 100, 200 and 400 °C. The N implanted layer microstructures, implanted layer phases, and thicknesses were studied by a combination of Bragg-Brentano (θ/2θ) and grazing incidence (Seeman-Bohlin) X-ray diffraction (XRD and GIXRD) and cross-sectional scanning electron microscopy (SEM). Atomic force microscopy (AFM) was used for roughness analysis of N implanted as well as as-polished surfaces. Static immersion tests were performed to investigate metal ion release into simulated body fluid (SBF) by electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma optical emission spectrometry (ICP-OES). XRD and SEM analyses indicated that the N implanted layers were ∼ 150-450 nm thick and composed of the (Co,Cr,Mo) 2+xN nitride phase and a high N concentration Co-based FCC phase, γ N depending on the substrate temperature. ETAAS analysis results showed that in vitro exposure of the N implanted surfaces resulted in higher levels of cobalt ion release into the simulated body fluid compared to the untreated, polished alloy. The higher Co release from the N implanted specimens is attributed to the nature of the implanted layer phases as well as to the rougher surfaces associated with the N implanted specimens compared to the relatively smooth surface of the untreated material. SEM analysis of N implanted and untreated specimens after immersion tests clearly indicated calcium phosphate formation on the as-polished CoCrMo alloy, indicating a degree of bioactivity of the untreated metal surface which is absent in the N implanted specimens.