Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 28Search for a Heavy Bottom-Like Quark in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA search for pair-produced bottom-like quarks in pp collisions at root s = 7 TeV is conducted with the CMS experiment at the LHC. The decay b' -> tW is considered in this search. The b'(b) over bar' tW-(t) over barW(+) process can be identified by the distinctive signature of trileptons and same-sign dileptons. With a data sample corresponding to an integrated luminosity of 34 pb(-1), no excess above the standard model background predictions is observed and a b' quark with a mass between 255 and 361 GeV/c(2) is excluded at the 95% confidence level. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 21Measurement of the Ratio of the 3-Jet To 2-Jet Cross Sections in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA measurement of the ratio of the inclusive 3-jet to 2-jet cross sections as a function of the total jet transverse momentum. HT, in the range 0.2 < H-T < 2.5 TeV is presented. The data have been collected at a proton-proton centre-of-mass energy of 7 TeV with the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb(-1). Comparisons are made between the data and the predictions of different QCD-based Monte Carlo models for multijet production. All models considered in this study are consistent with the data for H-T > 0.5 TeV. This measurement extends to an H-T range that has not been explored before. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 33Search for Physics Beyond the Standard Model Using Multilepton Signatures in Pp Collisions at Root S=7 Tev(Elsevier Ltd., 2011) Demir, Durmuş Ali; Karapınar, GülerA search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb(-1) of integrated luminosity in pp collisions at root s = 7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 24Effect of Defects and Secondary Phases in Cu2znsns4 Absorber Material on the Performance of Zn(o,s) Buffered Devices(Elsevier Ltd., 2019) Türkoğlu, Fulya; Köseoğlu, Hasan; Cantaş, Ayten; Akça, Fatime Gülşah; Meriç, Ece; Buldu, Dilara Gökçen; Aygün, GülnurCopper zinc fin sulfide (CZTS) absorber layer attracts so much attention in photovoltaic industry since it contains earth abundant, low cost and non-toxic elements contrary to other chalcogenide based solar cells. In the present work, CZTS absorber layers were prepared following a two-stage process: firstly, a stack of metal precursors (Copper (Cu)/Tin (Sn)/Zinc (Zn)/Copper (Cu)) were deposited on molybdenum (Mo) substrate by magnetron sputtering, then this stack was annealed under S atmosphere inside a tubular furnace. CZTS thin films were investigated using energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The effect of sulfurization time and the thickness of top and bottom Cu layer in precursors on the properties of CZTS thin films were investigated. The importance of Cu thickness adjacent to Sn to avoid detrimental phases was addressed. The significance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as fin dioxide and zinc oxide, and formation of molybdenum disulfide and voids between Mo/CZTS interface was also addressed. Moreover, cadmium sulfide buffer layer, which is conventionally used in CZTS solar cells, is replaced by an environmentally friendly alternative zinc oxysulfide buffer layer.Article Citation - WoS: 2Citation - Scopus: 2Tuning Thermal Transport in Graphene Via Combinations of Molecular Antiresonances(Elsevier Ltd., 2018) Sevim, Koray; Sevinçli, HaldunWe propose a method to engineer the phonon thermal transport properties of low dimensional systems. The method relies on introducing a predetermined combination of molecular adsorbates, which give rise to antiresonances at frequencies specific to the molecular species. Despite their dissimilar transmission spectra, thermal resistances due to individual molecules remain almost the same for all species. On the other hand, thermal resistance due to combinations of different species are not additive and show large differences depending on the species. Using a toy model, the physics underlying the violation of resistance summation rule is investigated. It is demonstrated that equivalent resistance of two scatterers having the same resistances can be close to the sum of the constituents or ∼ 70% of it depending on the relative positions of the antiresonances. The relative positions of the antiresonances determine the net change in transmission, therefore the equivalent resistance. Since the entire spectrum is involved in phonon spectrum changes in different parts of the spectrum become important. Performing extensive first-principles based computations, we show that these distinctive attributes of phonon transport can be useful to tailor the thermal transport through low dimensional materials, especially for thermoelectric and thermal management applications.Article Citation - WoS: 8Citation - Scopus: 10Experimental and Computational Investigation of Graphene/Sams Schottky Diodes(Elsevier Ltd., 2018) Aydın, Hasan; Bacaksız, Cihan; Yağmurcukardeş, Nesli; Karakaya, Caner; Mermer, Ömer; Can, Mustafa; Senger, Ramazan Tuğrul; Şahin, Hasan; Selamet, YusufWe have investigated the effect of two different self-assembled monolayers (SAMs) on electrical characteristics of bilayer graphene (BLG)/n-Si Schottky diodes. Novel 4″bis(diphenylamino)-1, 1′:3″-terphenyl-5′ carboxylic acids (TPA) and 4,4-di-9H-carbazol-9-yl-1,1′:3′1′-terphenyl-5′ carboxylic acid (CAR) aromatic SAMs have been used to modify n-Si surfaces. Cyclic voltammetry (CV) and Kelvin probe force microscopy (KPFM) results have been evaluated to verify the modification of n-Si surface. The current–voltage (I–V) characteristics of bare and SAMs modified devices show rectification behaviour verifying a Schottky junction at the interface. The ideality factors (n) from ln(I)–V dependences were determined as 2.13, 1.96 and 2.07 for BLG/n-Si, BLG/TPA/n-Si and BLG/CAR/n-Si Schottky diodes, respectively. In addition, Schottky barrier height (SBH) and series resistance (R s ) of SAMs modified diodes were decreased compared to bare diode due to the formation of a compatible interface between graphene and Si as well as π–π interaction between aromatic SAMs and graphene. The CAR-based device exhibits better diode characteristic compared to the TPA-based device. Computational simulations show that the BLG/CAR system exhibits smaller energy-level-differences than the BLG/TPA, which supports the experimental findings of a lower Schottky barrier and series resistance in BLG/CAR diode.Article Citation - WoS: 6Citation - Scopus: 7Thermally and Optically Tunable Sub-Terahertz Superconducting Fishnet Metamaterial(Elsevier Ltd., 2018) Sabah, Cumali; Mulla, Batuhan; Altan, Hakan; Özyüzer, LütfiIn this paper, a novel fishnet metamaterial structure is designed and analyzed under different material combinations and under different active controlling techniques. The results indicate that, the proposed fishnet metamaterial has a single resonance with double negativity at 0.39 THz when quartz substrate and aluminum is utilized in the design. Moreover, when the metallic parts are replaced with YBCO, the proposed design also exhibits double negativity with a stronger resonance and can be used as a switch between the double negative and single negative modes if the temperature is altered. In addition to these, when substrate (quartz) is replaced with MgO, the resonance shifts from 0.39 THz to 0.26 THz and shows double negativity. Moreover, switching properties under illumination can also be obtained when the silicon is utilized in the design (MgO-YBCO combination). According to these results, it is found that, in the case that the conductivity of silicon exceeds a certain value, the character of the resonance changes from double negative to the single negative mode.Article Citation - WoS: 4Citation - Scopus: 5Conductance Fluctuations in Undoped Hydrogenated Amorphous Silicon-Germanium Alloy Thin Films(Elsevier Ltd., 2002) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.; Yang, Jeffrey C.; Guha, SubhenduWe report coplanar conductance fluctuations of device quality, undoped hydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) measured from 430 to 490 K. The a-SiGe:H alloys produce noise power spectra similar to coplanar undoped a-Si:H films in the same temperature range. The noise power spectrum S(n) does not fit a single 1/fα power law but rather has two distinct regions, each accurately fitted by a power law, but with different slopes. The low frequency slope α1 is similar to that observed in undoped a-Si:H films varying from 1.30 to 1.46 for different Ge concentrations and shows a slight temperature dependence. At higher frequencies, the slope α2 is less than unity and temperature independent but depends on the Ge content of the film. α2 decreases from 0.60 for no Ge (pure a-Si:H) to 0.15 for 40 at.% Ge. The noise power at lower frequencies increases and at higher frequencies decreases substantially as the temperature increases from 430 to 490 K. We infer that similar noise mechanisms are operating in undoped a-SiGe:H and a-Si:H films but that the Ge content is influencing the noise, particularly the slope at higher frequencies. In addition, the noise has the expected quadratic dependence on bias current and obeys Gaussian statistics.Editorial Preface(Elsevier Ltd., 2017) Özyüzer, Lütfi; Kosiel, Kamil; Reno, John L.; Basa, Deekpak KumarIt is our pleasure to publish the proceedings of selected papers from the Science and Applications of Thin Films, Conference & Exhibition (SATF2016) in a Special Issue of Thin Solid Films. SATF2016 was held at the Ilica Hotel Spa & Wellness Thermal Resort, Cesme, Izmir, Turkey, from September 19 to 23, 2016. It was a very successful conference with over 241 abstracts submitted from33 countries, including 30 invited talks, 61 contributed talks, and over 150 poster presentations. More information about the conference can be found at http://www. satf2016.org/Article Citation - WoS: 12Citation - Scopus: 12Ultra-Thin Znse: Anisotropic and Flexible Crystal Structure(Elsevier Ltd., 2017) Bacaksız, Cihan; Şenger, Ramazan Tuğrul; Şahin, HasanBy performing density functional theory-based calculations, we investigate the structural, electronic, and mechanical properties of the thinnest ever ZnSe crystal [11]. The vibrational spectrum analysis reveals that the monolayer ZnSe is dynamically stable and has flexible nature with its soft phonon modes. In addition, a direct electronic band gap is found at the gamma point for the monolayer structure of ZnSe. We also elucidate that the monolayer ZnSe has angle dependent in-plane elastic parameters. In particular, the in-plane stiffness values are found to be 2.07 and 6.89 N/m for the arm-chair and zig-zag directions, respectively. The angle dependency is also valid for the Poisson ratio of the monolayer ZnSe. More significantly, the in-plane stiffness of the monolayer ZnSe is the one-tenth of Young modulus of bulk zb-ZnSe which indicates that the monolayer ZnSe is a quite flexible single layer crystal. With its flexible nature and in-plane anisotropic mechanical properties, the monolayer ZnSe is a good candidate for nanoscale mechanical applications.