Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

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  • Article
    Evaluation of exact quantum query complexities by semidefinite programming
    (Springer Verlag, 2019) Uyanık, Kıvanç
    One of the difficult tasks in quantum computation is inventing efficient exact quantum algorithms, which are the quantum algorithms that output the correct answer with certainty on any input. We improve and generalize the semidefinite programming (SDP) method of Montanaro et al. (Algorithmica 71:775-796, 2015) in order to evaluate exact quantum query complexities of partial functions. We present a more systematical approach to achieve the inspired result by Montanaro et al. for the function EXACT24, which is the Boolean function of 4 bits that output only when 2 of the input bits are equal to 1. The same approach also allows us to reduce the size of the ancilla space used by the algorithms that evaluate symmetric functions like EXACT36. We employ the generalized SDP to verify the complexities of the earliest and best known quantum algorithms in the literature, namely, Deutsch-Jozsa and Grover algorithms for a small number of input bits. We utilized the method to solve the weight decision problem of bit strings with lengths up to 10 bits and observed that the generalized SDP gives better exact quantum query complexities than the known methods. Finally, we test the method on some selected functions and demonstrate that they all exhibit quantum speedup.
  • Article
    Citation - WoS: 56
    Citation - Scopus: 62
    Cross-like terahertz metamaterial absorber for sensing applications
    (Springer Verlag, 2018) Sabah, Cumali; Mulla, Batuhan; Altan, Hakan; Özyüzer, Lütfi
    In this work, a new multiband terahertz metamaterial absorber is designed and characterised by numerical simulation method. In addition, the utilisation of the proposed absorber as a sensor is also investigated. The dielectric and thickness sensing characteristics are analysed. The proposed multiband metamaterial absorber has the ability for utilising the terahertz region up to 2 THz. According to the results, it is found that the proposed absorber is capable of sensing unknown materials and material thickness with any of its five absorption bands. The sensitivity of the proposed sensor is 6.57 GHz / unit sensitivity for dielectric sensing and 7.66GHz/μm for thickness sensing.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 10
    The Influence of Plasma-Based Nitriding and Oxidizing Treatments on the Mechanical and Corrosion Properties of Cocrmo Biomedical Alloy
    (Springer Verlag, 2018) Noli, Fotini; Pichon, Luc; Öztürk, Orhan
    Plasma-based nitriding and/or oxidizing treatments were applied to CoCrMo alloy to improve its surface mechanical properties and corrosion resistance for biomedical applications. Three treatments were performed. A set of CoCrMo samples has been subjected to nitriding at moderate temperatures (~ 400 °C). A second set of CoCrMo samples was oxidized at 395 °C in pure O2. The last set of CoCrMo samples was nitrided and subsequently oxidized under the experimental conditions of previous sets (double treatment). The microstructure and morphology of the layers formed on the CoCrMo alloy were investigated by X-ray diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy. In addition, nitrogen and oxygen profiles were determined by Glow Discharge Optical Emission Spectroscopy, Rutherford Backscattering Spectroscopy, Energy-Dispersive X-ray, and Nuclear Reaction Analysis. Significant improvement of the Vickers hardness of the CoCrMo samples after plasma nitriding was observed due to the supersaturated nitrogen solution and the formation of an expanded FCC γN phase and CrN precipitates. In the case of the oxidized samples, Vickers hardness improvement was minimal. The corrosion behavior of the samples was investigated in simulated body fluid (0.9 pct NaCl solution at 37 °C) using electrochemical techniques (potentiodynamic polarization and cyclic voltammetry). The concentration of metal ions released from the CoCrMo surfaces was determined by Instrumental Neutron Activation Analysis. The experimental results clearly indicate that the CoCrMo surface subjected to the double surface treatment consisting in plasma nitriding and plasma oxidizing exhibited lower deterioration and better resistance to corrosion compared to the nitrided, oxidized, and untreated samples. This enhancement is believed to be due to the formation of a thicker and more stable layer.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Electronic Structure of Cyanocobalamin: Dft+qmc Study
    (Springer Verlag, 2017) Mayda, Selma; Kandemir, Zafer; Bulut, Nejat
    We study the electronic structure and the magnetic correlations of cyanocobalamin (C63H88CoN14O14P) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition metal impurity in a semiconductor host. Here, we first determine the parameters of the Anderson Hamiltonian by performing density functional theory (DFT) calculations. Then, we use the quantum Monte Carlo (QMC) technique to obtain the electronic structure and the magnetic correlation functions for this effective model. We find that new electronic states, which correspond to impurity bound states, form above the lowest unoccupied level of the host semiconductor. These new states derive from the atomic orbitals at the cobalt site and the rest of the molecule. We observe that magnetic moments develop at the Co(3dν) orbitals and over the surrounding sites. We also observe that antiferromagnetic correlations exist between the Co (3dν) orbitals and the surrounding atoms. These antiferromagnetic correlations depend on the filling of the impurity bound states.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Comparative Study of Annealing and Gold Dopant Effect on Dc Sputtered Vanadium Oxide Films for Bolometer Applications
    (Springer Verlag, 2017) Alaboz, Hakan; Demirhan, Yasemin; Yüce, Hürriyet; Aygün, Gülnur; Özyüzer, Lütfi
    Vanadium oxide (VOx) thin film has been widely used for IR detectors and it is one of the promising materials for THz detectors due to its high temperature coefficient of resistance (TCR) values. VOx films with proper TCR values have also high resistance and it restricts bolometer performance especially for uncooled bolometers. To overcome this problem, deposition at elevated temperatures or annealing approach has been accepted and used but gold co-deposition approach has been proposed recently. In this study, vanadium oxide films were fabricated on high resistivity silicon substrates by reactive direct current magnetron sputtering in different O2/Ar atmosphere at room temperature. We investigated influence of oxygen partial pressure during deposition process and fabricated VOx thin films with sufficient TCR values for bolometer applications. In order to decrease resistivity of the deposited films, post annealing and gold doping approaches were performed separately. Effect of both post annealing process and gold doping process on structural and electrical properties of VOx thin films deposited at room temperature were investigated and detailed comparison between these methods were presented. We obtained the best possible approach to obtain optimum conditions for the highly reproducible VOx thin films which have the best resistivity and suitable TCR value for bolometer applications.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Metal Mesh Filters Based on Ti, Ito and Cu Thin Films for Terahertz Waves
    (Springer Verlag, 2016) Demirhan, Yasemin; Alaboz, Hakan; Özyüzer, Lütfi; Nebioğlu, Mehmet Ali; Takan, Taylan; Altan, Hakan; Sabah, Cumali
    In this study, we have investigated the spectral performance of resonant terahertz (THz) bandpass filters which were produced from thin films with a metal-mesh shape. The aforementioned filters were fabricated from titanium, copper and indium tin oxide thin films on fused silica substrates by UV lithography with an array of cross-shaped apertures. Since the mesh period, cross-arm length and its width specify the spectral characteristics of the filters, we were able to reveal the performance of these filters experimentally using both a THz time domain spectrometer and a Fourier transform infrared spectrometer. A commercial electromagnetic simulation software, CST microwave studio, was used to verify the experimental data. The transmission of the filters are in the range 20–55 % at their relevant center frequencies. To our knowledge this study is the first to show that fabricated patterns based on ITO thin films can be used to filter THz radiation.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 7
    Thin Film Like Terahertz Bolometric Detector on Bi2212 Single Crystal
    (Springer Verlag, 2016) Semerci, Tuğçe; Demirhan, Yasemin; Miyakawa, Nobuaki; Wang, Huabing; Özyüzer, Lütfi
    In this study, we developed a microbolometer chip fabricated from high temperature superconducting Bi2Sr2CaCu2O8+δ (Bi2212) single crystals for the terahertz (THz) detection. For the manufacturing of the microbolometer chips, Bi2212 single crystals were transferred on substrate in the thin film like form and electron beam lithography, ion beam etching techniques were used. Resistance versus temperature behavior of the bolometer chips were performed by four probe technique in liquid nitrogen cryostat. Bi2212 microchips were integrated and characterized using in our custom-designed cryogenic bolometer system instead of expensive and massive cooling systems. The fabricated microchips significantly detected signals from the Stefan-Boltzmann lamp which includes a portion of THz radiation. The detected power and response time were studied for Bi2212 thin film like microbolometer chips. Our results demonstrated the feasibility of improved Bi2212 microchips could be used for bolometric detection for THz applications.
  • Other
    Erratum To: Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation
    (Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, Yusuf
  • Article
    Citation - WoS: 6
    Citation - Scopus: 5
    Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation
    (Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, Yusuf
    Molecular beam epitaxy (MBE) growth of thin (∼2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm−2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 12
    Characterization of Cdte Growth on Gaas Using Different Etching Techniques
    (Springer Verlag, 2015) Bilgilisoy, Elif; Özden, Selin; Bakali, Emine; Karakaya, Merve; Selamet, Yusuf
    CdTe buffer layers which were grown on (211)B GaAs by molecular beam epitaxy were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The optical properties and thicknesses of the samples were obtained by ex situ spectroscopic ellipsometry. The surface morphologies of the CdTe epilayers were analyzed by atomic force microscopy, scanning electron microscopy, and Nomarski microscopy before and after chemical etching. We compare the triangle- and trapezoid-shaped etch pits due to the Everson and Nakagawa etch solutions, respectively. Measured etch pit density (EPD) values of triangle etch pits were found in the 8 × 107 cm−2 to 2 × 108 cm−2 range, and trapezoid-shaped etch pits were found in the 1 × 107 cm−2 to 7 × 107 cm−2 range for samples with thicknesses <2 μm.