Physics / Fizik

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

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Now showing 1 - 20 of 585

Citation - WoS: 3
Citation - Scopus: 3
1/F Noise in Amorphous Silicon and Silicon-Germanium Alloys
(SPIE, 2003) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.
We report measurements of conductance noise of a-Si1-XGeX:H in two different geometries; one where the current flow is transverse to the surface and the other longitudinal to it. Because of the large increase in sample resistance in going from transverse to longitudinal conduction, it was not possible to measure both geometries at the same temperature. However, the temperature trends are compatible with a common noise source. For both geometries, alloying with up to 40% Ge reduces the noise magnitude by a factor of 50 over that found in a-Si:H
Citation - WoS: 10
Citation - Scopus: 7
1/F Noise in Doped and Undoped Amorphous Silicon
(Elsevier Ltd., 2000-05) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.
We measured the spectrum of conductance fluctuations in n-type, p-type, and undoped hydrogenated amorphous silicon (a-Si:H) as a function of temperature. In general, the spectra can be fit to a power law, 1/fα, although in the p-type and undoped samples deviations from a strict power law occur. For n-type and p-type samples, the noise magnitude increases with temperature by approximately a factor of 5 from 295 to 450 K. The slope parameter, α, also increases with temperature in the p-type samples from near unity to 1.4 but not in the n-type sample where it remains near 1.05 independent of temperature. The undoped sample could be measured only over a limited range of elevated temperatures, but α does trend larger. The undoped and lightly doped material have similar noise levels but larger p-type doping reduces the noise by two orders of magnitude. Correlation measurements indicate the 1/f noise is Gaussian for all samples. However, intermittent random-telegraph noise is observed in n-type material.
Citation - WoS: 6
Citation - Scopus: 10
1/F Noise in Hydrogenated Amorphous Silicon-Germanium Alloys
(Institute of Electrical and Electronics Engineers, 2003-08) Johanson, Robert E.; Güneş, Mehmet; Kasap, Safa O.
Measurements were made of conductance noise of a-Si:H and a-Si 1-xGex:H in two different geometries: one where the current flow is transverse to the surface and the other where it is longitudinal to the surface. Because of the large change in sample resistance between the two geometries, it was not possible to measure both geometries at the same temperature. For both geometries, alloyinzg with up to 40% Ge reduces the noise magnitude by several orders of magnitude over that found in a-Si:H. The decrease is incompatible with several popular noise models. Extrapolating the temperature trends for each geometry shows that it is possible that the noise observed in the transverse samples has the same origin as the higher frequency part of the double power law spectra observed in the longitudinal samples.
Citation - WoS: 15
Citation - Scopus: 14
1/F-noise Study of Undoped Intrinsic Hydrogenated Amorphous Silicon Thin Films
(American Physical Society, 1999) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.
Conductance fluctuations in four samples of undoped intrinsic hydrogenated amorphous silicon (a-Si:H) were measured in the temperature range of 450 K to 500 K and for frequencies from 2 Hz to 3 kHz. The noise spectra divide into two regions that each fit a 1/fα power law but with different slope parameters α and different temperature dependences. At low frequencies, α is greater than unity and increases with temperature. At high frequencies, α is near 0.6 and temperature independent, but the noise magnitude decreases rapidly with temperature. We infer from the different dependences on temperature that the noise is generated by two independent mechanisms operating simultaneously in a-Si:H. We also observe that the 1/f noise exhibits a quadratic dependence on bias current and Gaussian statistics.
1/Nc Expansion and Anomaly Cancellation in the Presence of Electroweak Interactions
(IOP Publishing Ltd., 1998-03) Erdem, Recai
We study the question of a consistent formulation of the 1/Nc expansion in the presence of electroweak interactions. We show that in some cases the previous formulation leads to an unrealistic picture. We improve the scheme. We derive the corresponding hypercharge and electric charge values of fermions under the requirement that the standard model in the large-Nc limit should be free of chiral gauge anomalies. We find that the resulting hypercharge and the electric charge values for quarks are the same as for the standard model.
Citation - WoS: 31
Citation - Scopus: 30
Absence of Pseudogap in Heavily Overdoped Bi2sr2cacu2o8+? From Tunneling Spectroscopy of Break Junctions
(Institute of Physics Publishing, 2002-05) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Kendziora, Christopher A.; Miyakawa, Nobuaki
We report tunneling spectroscopy of superconductor-insulator-superconductor break junctions on heavily overdoped Bi2Sr2CaCu2O8+δ with Tc = 56 K. At T ≪ Tc, the junction conductances display well-defined quasiparticle peaks at ±2Δ and in some cases a Josephson current at zero bias. Gap values as small as Δ = 10.5 meV have been observed leading to 2Δ/kTc near the BCS limit for dx2-y2 pairing. Temperature dependence of the gap magnitude, Δ(T), follows the BCS relation and both the quasiparticle gap and Josephson current vanish for T > Tc. Above Tc, the tunneling conductance shows a flat background without any indication of a pseudogap near the Fermi level.
Citation - WoS: 37
Citation - Scopus: 36
Absolute Properties of the Binary System Bb Pegasi
(IOP Publishing, 2007-08) Kalomeni, Belinda; Yakut, Kadri; Keskin, Varol; Değirmenci, Ömer Lütfi; Ulaş, Burak; Köse, Oğuzhan
We present ground-based photometry of the low-temperature contact binary BB Peg. We collected all the times of mid-eclipse available in the literature and combined them with those obtained in this study. Analyses of the data indicate a period increase of (3.0 ± 0.1) × 10-8 days yr -1. This period increase of BB Peg can be interpreted in terms of the mass transfer 2.4 × 10-8 M⊙ yr-1 from the less massive to the more massive component. The physical parameters have been determined as Mc = 1.42M⊙, Mh = 0.53 M⊙, Rc = 1.29 R⊙, Rh, = 0.83 R⊙, Lc = 1.86 L⊙, and L h = 0.94 L⊙ through simultaneous solutions of light and of the radial velocity curves. The orbital parameters of the third body, which orbits the contact system in an eccentric orbit, were obtained from the period variation analysis. The system is compared to the similar binaries in the Hertzsprung-Russell and mass-radius diagrams.
Citation - WoS: 1
Citation - Scopus: 1
Adsorption and Diffusion Characteristics of Lithium on Hydrogenated ?- and Ss-Silicene
(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2017-08) İyikanat, Fadıl; Kandemir, Ali; Bacaksız, Cihan; Şahin, Hasan
Using first-principles density functional theory calculations, we investigate adsorption properties and the diffusion mechanism of a Li atom on hydrogenated single-layer α- and β-silicene on a Ag(111) surface. It is found that a Li atom binds strongly on the surfaces of both α- and β-silicene, and it forms an ionic bond through the transfer of charge from the adsorbed atom to the surface. The binding energies of a Li atom on these surfaces are very similar. However, the diffusion barrier of a Li atom on H-α-Si is much higher than that on H-β-Si. The energy surface calculations show that a Li atom does not prefer to bind in the vicinity of the hydrogenated upper-Si atoms. Strong interaction between Li atoms and hydrogenated silicene phases and low diffusion barriers show that α- and β-silicene are promising platforms for Li-storage applications.
Citation - WoS: 2
Citation - Scopus: 3
Affine Dynamics With Torsion
(Springer Verlag, 2016-03-01) Gültekin, Kemal
In this study, we give a thorough analysis of a general affine gravity with torsion. After a brief exposition of the affine gravities considered by Eddington and Schrödinger, we construct and analyze different affine gravities based on the determinants of the Ricci tensor, the torsion tensor, the Riemann tensor, and their combinations. In each case we reduce equations of motion to their simplest forms and give a detailed analysis of their solutions. Our analyses lead to the construction of the affine connection in terms of the curvature and torsion tensors. Our solutions of the dynamical equations show that the curvature tensors at different points are correlated via non-local, exponential rescaling factors determined by the torsion tensor.
Citation - WoS: 45
Citation - Scopus: 40
Affine Inflation
(American Physical Society, 2017-06) Azri, Hemza; Demir, Durmuş Ali
Affine gravity, a gravity theory based on affine connection with no notion of metric, supports scalar field dynamics only if scalar fields have nonvanishing potential. The nonvanishing vacuum energy ensures that the cosmological constant is nonvanishing. It also ensures that the energy-momentum tensor of vacuum gives the dynamically generated metric tensor. We construct this affine setup and study primordial inflation in it. We study inflationary dynamics in affine gravity and general relativity, comparatively. We show that nonminimally coupled inflaton dynamics can be transformed into minimally coupled ones with a modified potential. We also show that there is one unique frame in affine gravity, as opposed to the Einstein and Jordan frames in general relativity. Future observations with higher accuracy may be able to test affine gravity.
Citation - WoS: 15
Citation - Scopus: 15
Ag and Au Atoms Intercalated in Bilayer Heterostructures of Transition Metal Dichalcogenides and Graphene
(American Institute of Physics, 2014) İyikanat, Fadıl; Şahin, Hasan; Senger, Ramazan Tuğrul; Peeters, François M.
The diffusive motion of metal nanoparticles Au and Ag on monolayer and between bilayer heterostructures of transition metal dichalcogenides and graphene are investigated in the framework of density functional theory. We found that the minimum energy barriers for diffusion and the possibility of cluster formation depend strongly on both the type of nanoparticle and the type of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and Au can be tuned by creating various bilayers. Tunability of the diffusion characteristics of adatoms in van der Waals heterostructures holds promise for controllable growth of nanostructures. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Citation - WoS: 33
Citation - Scopus: 44
Aligning the Cms Muon Chambers With the Muon Alignment System During an Extended Cosmic Ray Run
(IOP Publishing Ltd., 2010) Demir, Durmuş Ali; Karapınar, Güler
The alignment system for the muon spectrometer of the CMS detector comprises three independent subsystems of optical and analog position sensors. It aligns muon chambers with respect to each other and to the central silicon tracker. System commissioning at full magnetic field began in 2008 during an extended cosmic ray run. The system succeeded in tracking muon detector movements of up to 18 mm and rotations of several milliradians under magnetic forces. Depending on coordinate and subsystem, the system achieved chamber alignment precisions of 140-350 μm and 30-200 μrad, close to the precision requirements of the experiment. Systematic errors on absolute positions are estimated to be 340-590 μm based on comparisons with independent photogrammetry measurements. © 2010 IOP Publishing Ltd and SISSA.
Citation - WoS: 35
Citation - Scopus: 53
Alignment of the Cms Muon System With Cosmic-Ray and Beam-Halo Muons
(IOP Publishing Ltd., 2010) Demir, Durmuş Ali; Karapınar, Güler
The CMS muon system has been aligned using cosmic-ray muons collected in 2008 and beam-halo muons from the 2008 LHC circulating beam tests. After alignment, the resolution of the most sensitive coordinate is 80 microns for the relative positions of superlayers in the same barrel chamber and 270 microns for the relative positions of endcap chambers in the same ring structure. The resolution on the position of the central barrel chambers relative to the tracker is comprised between two extreme estimates, 200 and 700 microns, provided by two complementary studies. With minor modifications, the alignment procedures can be applied using muons from LHC collisions, leading to additional significant improvements.
Citation - WoS: 86
Citation - Scopus: 88
Alignment of the Cms Silicon Tracker During Commissioning With Cosmic Rays
(IOP Publishing Ltd., 2010) Demir, Durmuş Ali; Karapınar, Güler
The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3-4 microns RMS in the barrel and 3-14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.
Citation - WoS: 3
Citation - Scopus: 3
Amperometric Detection of Nh3 by Aromatic Sam-Modified Graphene
(IEEE, 2023) Yağmurcukardeş, Nesli; Bayram, Abdullah; Aydın, Hasan; Can, Mustafa; Demiç, Şerafettin; Açıkbaş, Yaşar; Çelebi, Cem
Ammonia (NH3) is a toxic substance resulting in various acute and chronic effects on individuals. NH3 detection, monitoring methods, and detection tools are desperately needed. In this work, we improved the NH3 sensing capabilities of grapheme (GP) films deposited by chemical vapor deposition (CVD) by modifying aromatic self-assembled monolayer (SAM) molecules such as 5-[(3-methylphenyl) (phenyl) amino] isophthalic acid (MeIPA) and 5-(diphenyl)amino] isophthalic acid (PhIPA) on amperometric detection method. Morphological investigations of the films were carried out by optical and scanning electron microscopy (SEM). Surface potential was characterized with Kelvin probe force microscopy (KPFM), and vibrational properties were characterized with Raman spectroscopy. MeIPA modification increased NH3 uptake by two times compared to unmodified GP. The results indicated that the SAM modification enhanced NH3 molecule adsorption and improved its periodic reversible and reproducible response using the amperometric detection system, indicating that SAM molecules might be a feasible probe for NH3. © 2001-2012 IEEE.
Citation - WoS: 44
Citation - Scopus: 42
Analysis of Electronic Parameters and Interface States of Boron Dispersed Triethanolamine/P-si Structure by Afm, I-V, C-V and G/?-v-f Techniques
(Elsevier Ltd., 2010) Yakuphanoğlu, Fahrettin; Okur, Salih
The electronic parameters and interface state properties of boron dispersed triethanolamine/p-Si structure have been investigated by atomic force microscopy, I-V, C-V-f and G/ω-V-f techniques. The surface topography and phase image of the TEA-B film deposited onto p-Si substrate were analyzed by atomic force microscopy. The atomic force microscopy results show a homogenous distribution of boron particles in triethanolamine film. The electronic parameters (barrier height, ideality factor and average series resistance) obtained from I-V characteristics of the diode are 0.81 eV, 2.07 and 5.04 kΩ, respectively. The interface state density of the diode was found to be 2.54 × 1010 eV- cm-2 under Vg = 0. The obtained Dit values obtained from C-V and G/ω measurements are in agreement with each other. The profile of series resistance dependent on voltage and frequency confirms the presence of interface states in boron dispersed triethanolamine/p-Si structure. It is evaluated that the boron dispersed triethanolamine controls the electronic parameters and interface properties of conventional Al/p-Si diode. © 2009 Elsevier B.V. All rights reserved.
Citation - WoS: 16
Citation - Scopus: 17
Analysis of Interface States of the Pentacene Organic Thin-Film Phototransistor by Conductance Technique
(Elsevier Ltd., 2009-02) Okur, Salih; Yakuphanoğlu, Fahrettin
A pentacene thin-film transistor with a channel width of 300 μm and a channel length of 30 μm has been successfully fabricated on n-Si substrate with thermally oxidized SiO2 as a gate insulator. The photovoltaic and interface state density properties of the transistor have been investigated. A pentacene film of 200 nm thickness was deposited on the SiO2 layer with a vacuum thermal evaporator. Atomic force microscopy images of the pentacene film on SiO2 insulating layer show a homogeneous film surface with the rms roughness of 11 nm. The transistor shows p-channel characteristics, as a result of positive carriers generated in the pentacene film for the negative bias voltages applied to the gate. The photosensitivity (Iph/Idark) is measured as 1.45 at an illumination intensity of 3500 lux at the off state. This suggests that the pentacene thin-film transistor shows a phototransistor characteristic. The field-effect mobility of the pentacene OTFT was found to be 0.021 cm2/(V s). The interface state density of the transistor was determined using conductance technique and was found to be about 1.191 × 1010 eV-1 cm-2.
Citation - WoS: 35
Citation - Scopus: 44
Analysis of the Cp Structure of the Yukawa Coupling Between the Higgs Boson and Tau Leptons in Proton-Proton Collisions at Root S=13 Tev
(Springer, 2022) Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Dragicevic, M.; Del Valle, A. Escalante
The first measurement of the CP structure of the Yukawa coupling between the Higgs boson and tau leptons is presented. The measurement is based on data collected in proton-proton collisions at root s = 13 TeV by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb(-1). The analysis uses the angular correlation between the decay planes of tau leptons produced in Higgs boson decays. The effective mixing angle between CP-even and CP-odd tau Yukawa couplings is found to be -1 +/- 19 degrees, compared to an expected value of 0 +/- 21 degrees at the 68.3% confidence level. The data disfavour the pure CP-odd scenario at 3.0 standard deviations. The results are compatible with predictions for the standard model Higgs boson.
Citation - WoS: 3
Citation - Scopus: 4
Analytical Approaches To the Delta-Eddington Model of the Radiative Transfer Through Vertically Inhomogeneous Optical Depths
(Elsevier Ltd., 2008-04) Subaşılar, Bedrettin
Analytical approaches have been developed for one-dimensional monochromatic delta-Eddington radiative transfer equation through a vertically inhomogeneous medium. They are based on the solution of the Riccati equation that arises from the decoupling of the two-stream radiances, and seek to approximate the exponent functions in the solution as opposed to finding the solution as a whole. Depending on the case, Green-Liouville approximation or other techniques presented in this paper are utilized for finding these exponents. Though developed for atmospheric radiative transfer problems applicable to the global climate change modelling, and for non-invasive medical applications on tissue-light interactions, the techniques considered here are quiet general in nature. Hence, they can also be useful in other boundary value problems of the diffusion type that involve linear second order ordinary differential equations with variable coefficients.
Citation - WoS: 2
Citation - Scopus: 2
Analytical Improvement on the Electromagnetic Scattering From Deformed Spherical Conducting Objects
(Institute of Electrical and Electronics Engineers, 2021) Ateş, Barış; Kuştepeli, Alp; Çetin, Zebih
In this paper, electromagnetic scattering from con-ducting deformed spheres is considered analytically by employing the perturbation method and utilizing Debye potentials. To be able to analyze a wide variety of scattering problems, azimuthal variation is indispensable and therefore the geometries of the scatterers considered in this study do not have rotational symmetry, hence they are dependent on the θ and φ angles in spherical coordinates. Analyses are carried up to the second order explicitly to obtain more accurate results and thus scattered fields are obtained with second order corrections. The coefficients used to determine the scattered field are expressed in terms of Clebsch-Gordan coefficients, which enables one to obtain the results for new geometries only by simple algebraic manipulations. Numerical results and their comparisons are also presented for various deformation functions and parameters. IEEE

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