Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 5Citation - Scopus: 5Differences and Similarities in Biophysical and Biological Characteristics Between U87 Mg Glioblastoma and Astrocyte Cells(Springer, 2023) Özdil, Berrin; Çalık Kocatürk, Duygu; Altunayar Ünsalan, Çisem; Açıkgöz, Eda; Oltulu, Fatih; Görgülü, Volkan; Uysal, Ayşegül; Öktem, Gülperi; Ünsalan, Ozan; Güler, Günnur; Aktuğ, HüseyinCurrent cancer studies focus on molecular-targeting diagnostics and interactions with surroundings; however, there are still gaps in characterization based on topological differences and elemental composition. Glioblastoma (GBM cells; GBMCs) is an astrocytic aggressive brain tumor. At the molecular level, GBMCs and astrocytes may differ, and cell elemental/topological analysis is critical for identifying potential new cancer targets. Here, we used U87 MG cells for GBMCS. U87 MG cell lines, which are frequently used in glioblastoma research, are an important tool for studying the various features and underlying mechanisms of this aggressive brain tumor. For the first time, atomic force microscopy (AFM), scanning electron microscopy (SEM) accompanied by energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) are used to report the topology and chemistry of cancer (U87 MG) and healthy (SVG p12) cells. In addition, F-actin staining and cytoskeleton-based gene expression analyses were performed. The degree of gene expression for genes related to the cytoskeleton was similar; however, the intensity of F-actin, anisotropy values, and invasion-related genes were different. Morphologically, GBMCs were longer and narrower while astrocytes were shorter and more disseminated based on AFM. Furthermore, the roughness values of these cells differed slightly between the two call types. In contrast to the rougher astrocyte surfaces in the lamellipodial area, SEM-EDS analysis showed that elongated GBMCs displayed filopodial protrusions. Our investigation provides considerable further insight into rapid cancer cell characterization in terms of a combinatorial spectroscopic and microscopic approach.Correction Correction To: “curved Space and Particle Physics Effects on the Formation of Bose–einstein Condensation Around a Reissner–nordstrøm Black Hole”(Springer, 2022) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalAfter this correction Fig. 1 in [1] is replaced by Fig. 1 above which is essentially the same as the one in [1]. Figure 2 in [1] now becomes irrelevant. Figure 3 in [1] is replaced by Fig. 2 above which is essentially the same as the one in [1].Article Citation - WoS: 2Citation - Scopus: 2In-Situ Thin Film Copper-Copper Thermocompression Bonding for Quantum Cascade Lasers(Springer, 2021) Rouhi, Sina; Özdemir, Mehtap; Ekmekçioğlu, Merve; Yiğen, Serap; Demirhan, Yasemin; Szerling, Anna; Kosiel, Kamil; Kozubal, Maciej; Kruszka, Renata; Prokaryn, Piotr; Ertuğrul, Mehmet; Reno, John L.; Aygün, Gülnur; Özyüzer, LütfiThe choice of metals, bonding conditions and interface purity are critical parameters for the performance of metal-metal bonding quality for quantum cascade lasers (QCLs). Here, we present a novel approach for the thermocompression bonding of Cu-Cu thin films on GaAs-based waveguides without having any oxide phase, contamination or impurities at the interface. We designed a hybrid system in which magnetron sputtering of Ta, thermal evaporation of Cu and Cu-Cu thermocompression bonding processes can be performed sequentially under high vacuum conditions. GaAs/Ta/Cu and Cu/Ta/GaAs structures were thermocompressionally bonded in our in-situ homebuilt bonding system by optimizing the deposition parameters and bonding conditions. The grown thin film and the obtained interfaces were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) techniques. The optimum Ta and Cu films' thicknesses were found to be about 20 nm and 500 nm, respectively. EDX analysis showed that the Ta thin film interlayer diffused into the Cu structure, providing better adhesivity and rigidity for the bonding. Additionally, no oxidation phases were detected at the interface. The best bonding quality was obtained when heated up to 430 degrees C with an applied pressure of 40 MPa during bonding process.Article Citation - WoS: 2Citation - Scopus: 2Curved Space and Particle Physics Effects on the Formation of Bose-Einstein Condensation Around a Reissner-Nordstrom Black Hole(Springer, 2021) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalWe consider two scalar fields interacting through a chi*chi phi*phi term in the presence of a Reissner-Nordstrom black hole. Initially, only chi particles are present. We find that the produced phi particles are localized in a region around the black hole and have a tendency toward condensation provided that phi particles are much heavier than the chi particles. We also find that such a configuration is phenomenologically viable only if the scalars and the black hole have dark electric charges.Article Citation - WoS: 2Citation - Scopus: 2Particle Physics Processes in Cosmology Through an Effective Minkowski Space Formulation and the Limitations of the Method(Springer, 2021) Erdem, Recai; Gültekin, KemalWe introduce a method where particle physics processes in cosmology may be calculated by the usual perturbative flat space quantum field theory through an effective Minkowski space description at small time intervals provided that the running of the effective particle masses are sufficiently slow. We discuss the necessary conditions for the applicability of this method and illustrate the method through a simple example. This method has the advantage of avoiding the effects of gravitational particle creation in the calculation of rates and cross sections i.e. giving directly the rates and the cross sections due to the scatterings or the decay processes.Article Citation - WoS: 9Citation - Scopus: 7Epitaxial Characteristics of Mbe-Grown Znte Thin Films on Gaas (211)b Substrates(Springer, 2019) Özçeri, Elif; Tarhan, EnverHighly crystalline ZnTe thin films were grown on GaAs (211)B substrates by molecular beam epitaxy (MBE) for potential applications such as MCT detectors and optoelectronic devices. We investigated the effects of Te to Zn (VI/II) flux ratio on the quality of ZnTe films in terms of crystal orientation, elemental composition, surface roughness, and dislocation density. Atomic concentrations of Zn, Te, and oxygen complexes due to oxygen contamination on the film surfaces were analyzed by X-ray photoelectron spectroscopy. X-ray double crystal rocking curve full width half maximum (FWHM) of ZnTe (422) peak was observed as 233 arcseconds for a 1.66 mu m thick film, which indicates high crystallinity. Wet chemical etching was applied to the films to quantify the crystal quality by calculating etch pit densities (EPD) from scanning electron microscope images. A very low EPD value of 1.7 x 10(7) cm(-2) was measured. Additionally, the root mean square roughness values, obtained from atomic force microscopy topography images were in the range of 10-25 nm. These values were supported by FWHM values of red green blue color intensity histograms obtained from Nomarski Microscope images. The results of our analyses indicate that the VI/II flux ratios of 4 and 4.5 produce the best quality ZnTe films on GaAs (211)B substrates.Article Citation - WoS: 13Citation - Scopus: 13Thermodynamics of Regular Black Holes With Cosmic Strings(Springer, 2018) Bayraktar, Ceren H.In this article, the thermodynamics of regular black holes with a cosmic string passing through them is studied. We will observe that the string has no effect on the temperature as well as on the relation between entropy S and horizon area A.Article Citation - WoS: 6Citation - Scopus: 10Effect of Annealing on the Density of Defects in Epitaxial Cdte (211)/Gaas(Springer, 2018) Bakali, Emine; Selamet, Yusuf; Tarhan, EnverCdTe thin films were grown on GaAs (211) wafers by molecular beam epitaxy as the buffer layer for HgCdTe infrared detector applications. We studied the effect of annealing on the density of dislocation of these CdTe thin films under varying annealing parameters such as annealing temperature, annealing duration, and number of cycles. Annealings were carried out using a homemade annealing reactor possessing a special heater element made of a Si wafer for rapid heating. The density of dislocations, which were made observable with a scanning electron microscope after etching with an Everson solution, were calculated by counting the number of dislocations per unit surface area, hence the term etch pit density (EPD). We were able to decrease EPD values by one order of magnitude after annealing. For example, the best EPD value after a 20-min annealing at 400°C was ∼ 2 × 107 cm−2 for a 1.63-μm CdTe thin film which was about 9.5 × 107 cm−2 before annealing. We also employed Raman scattering measurements to see the changes in the structural quality of the samples. From the Raman measurements, we were able to see improvements in the quality of our samples from the annealing by studying the ratio of 2LO/LO phonon mode Raman intensities. We also observed a clear decrease in the intensity of Te precipitations-related modes, indicating a decrease in the size and number of these precipitations.