Physics Commons^™

Binding Energies Of Excitons In Symmetric And Asymmetric Coupled Double-Quantum Well Structures In A Magnetic Field, Esi̇n Kasapoğlu, Hüseyi̇n Sari, Yüksel Ergün, Sezai̇ Elagöz, Naci̇ Balkan, İsmai̇l Sökmen

Turkish Journal of Physics

The binding energy of excitons in the symmetric and asymmetric coupled double GaAs/Ga_{1-x}Al_xAs quantum wells is calculated by using variational approach. Results have been obtained as a function of the potential symmetry, the size of the quantum well, and the coupling parameter of the wells in the presence of a magnetic field applied parallel to the growth direction. The role of the asymmetric barriers, magnetic field, barrier and well width in determining the tunability of the excitonic binding parameters of the GaAs/Ga_{1-x}Al_xAs system is discussed.

Stability Of Quasi-Two-Dimensional Bipolarons, R. Tuğrul Senger, Ati̇lla Erçelebi̇

Turkish Journal of Physics

The stability criteria of quasi-two-dimensional dimensional bipolarons have been studied within the framework of strong coupling and path-integral theories. It is shown that the critical values of the electron-phonon coupling constant (\alpha), and the ratio of dielectric constants (\eta = \epsilon_{\infty}/\epsilon_{0}) exhibit some non-trivial features as the effective dimensionality is tuned from three to two.

Band-Gap Renormalization In Quantum Wires, K. Güven, C. R. Bennett, B. Tanatar

Turkish Journal of Physics

Improved techniques in semiconductor fabrication increased the interest in quantum wire structures, because of their opto-electronic device application possibilities. Many-body interactions among the electrons and holes in the wire lead to the band-gap renormalization (BGR), which in turn affect the optical properties of the system. We study the BGR within the random-phase approximation incorporating the dynamical effects, and investigate the density dependence.

Light Emission From Travelling Space Charge Domains, M. Hostut, N. Balkan

Turkish Journal of Physics

We report light emission from n-doped GaAs epilayers associated with impact ionization when the device is biased in the negative difference resistance (NDR) regime (F > 3.5 kV cm^{-1}). Spectral distribution of the emitted light (electroluminescence) has been measured to identify the energy distribution of the recombining electron-hole pairs. Electron temperatures, calculated from the high energy tail of the electroluminescence spectra, show that the light emission is due to the recombination of the impact ionized holes with the background, channel, and the travelling space charge electrons. The range of the electron temperatures obtained indicate that the contribution to the light emission …

The Orbit Center Dependence Of The Energy Levels In A Multiple Quantum Wells Under External Tilted Magnetic And Electric Fields, R. Amca, Y. Ergün, H. Sari, S. Elagöz, İ. Sökmen

Turkish Journal of Physics

An analytical solution to the Schrödinger equation for a multiple quantum well system subjected to an externally applied electric field the growth direction and an externally applied tilted magnetic field are obtained and the results are discussed. The energy dependence energy spectrum of the system as a function of the external electric field and the orbit center is also discussed.

Carrier Transport And Band Offsets In Two Dimensional Heterostructures, Hi̇lmi̇ Ünlü

Turkish Journal of Physics

Advances in the low dimensional heterojunction device technology cannot be complete without adequate and reliable analytic model for determining interface properties such as band offsets needed to study the carrier transport and to evaluate the device performance at high temperatures and pressures. In this article, using the extended universal tight binding model of semiconductors, a new way of determining the band offsets in heterostructures is presented. In this model the band offsets are first determined by aligning the vacuum level, defined relative to valence band maximum which is screened by optical dielectric constant of semiconductors, at the interface at absolute …

Bands Of Localized Electromagnetic Waves In Random Collections Of Dielectric Particles, Marian Rusek, Arkadiusz Orlowski

Turkish Journal of Physics

Anderson localization of electromagnetic waves in random arrays of dielectric cylinders is studied. An effective theoretical approach based on the finite size scaling analysis of transmission is developed. The disordered dielectric medium is modeled by a system of randomly distributed 2D electric dipoles. The appearance of the band of localized waves emerging in the limit of an infinite medium is discovered. It suggests deeper insight into existing experimental and theoretical results.

Feasibility Of Fabrication Of Heteroepitaxial Ge_X Si_{1-X}/Si(111) Structure By Pulsed Nd: Yag Laser, R. N. Al-Rawi, R. A. Ismail, R. N. Mousis

Turkish Journal of Physics

Heteroepitaxial Ge_x Si_{1-x} alloy layers have been formed by 10 ms and 300 \mu s laser pulse induced mixing of pure germanium films and Si(111) substrates where Ge films of thickness (500-1250) Å are thermally evaporated onto Si(111) under vacuum pressure \sim 10^{-5} Torr. The near surface of the sample then undergoes rapid melting and regrowth processes during each pulse from a free running Nd; YAG laser. The alloy layers are (4.6-6.5) \mum thick and have a Ge fraction of x = 6-8.2%.

Electrical Switching In Potassium-Boro-Vanadate-Iron Glasses, H. R. Panchal, D. K. Kanchan

Turkish Journal of Physics

Electrical switching has been observed in 20K_2O : (75-y)V_2O_5 : yB_2O_3 : 5Fe_2O_3 glasses which were prepared by a splat quenching method. To investigate switching phenomenon, glass samples of the same dimension from as quenched material were examined for their I-V characteristics at various ambient temperatures. The exponential decrease of switching voltage is observed with increasing ambient temperature indicating the cause of switching due to Joule's heating. It is also observed that the switching voltage can be controlled by varying the ambient temperature and switching temperature by changing the voltage. The dependence of switching temperature on the amount of V_2O_5 …

Electronic And Lattice Thermal Conductivity Of Bi_{1-X} Sb_X And Ag-Sb-Te Systems, Sabi̇r Ali̇yev, Agami̇rza Movsum-Zadeh, Sadiyar Ragimov, Eldar Zulfigarov

Turkish Journal of Physics

An investigation of the electronic (\aleph_e) and lattice (\aleph_L) parts of the thermal conductivity for samples of Bi_{1-x} Sb_x (0,02 < X < 0,12) and system of Ag-Sb-Te was carried out in the temperature interval 6-300K. Separation of \aleph_L and \aleph_e has been made by suppressing \aleph_e in magnetic field. The experimental data of \aleph_L and \aleph_e have been compared, respectively, with Gallaway's theory and with a theory which takes into account the inelastic character of scattering. It is observed that the Lorentz number L calculated by using the experimental values of \aleph_e and thermomagnetic coefficients is smaller than its Zommerfeld's value L_0 in high doping Bi_{0.88}Sb_{0.12}. A satisfactory agreement between the theory and the experiment allows to conclude that besides the normal and U-processes in Bi_{1-x}Sb_x the defects of mass also plays a considerable role in scattering. It is observed that \aleph_L of single phase samples Ag_{0.82}Sb_{1.18}Te_{2.18} is smaller than AgSbTe_2 samples. It is shown that this is due to the presence of p-Ag_2 Te in AgSbTe_2. It is established that the high concentration of intrinsic defects plays a considerable role in scattering for Ag-Sb-Te as well.

The Peculiarities Of The Electrical And Thermoelectrical Properties Of P-Type Ag_2te, Ali̇ İhsan Demi̇rel, S. A. Aliev, F. F. Aliev, F. Z. Guseynov, Sali̇m Orak

Turkish Journal of Physics

The electrical and thermoelectrical properties of p-type Ag_2Te have been investigated. Various peculiarities were observed: the minimum (at T \approx 65 K) and maximum (at T \approx 200 K) on the temperature dependence of conductivity \sigma (T); the weak dependence of Hall coefficient R(T) (in 200-300 K range) and the maximum (at T \approx 100 K and 250 K) on the temperature dependence of thermal power \alpha_0 (T). The investigation results were interpreted by two-bands model. It is shown that mentioned peculiarities have been stimulated by the narrow gap of Ag_2Te and its temperature dependence.

Relative L X-Ray Fluorescene Cross-Sections In Heavy Elements In The Energy Region Of 16-122 Kev, Oğuz Doğan, Mehmet Ertuğrul, Önder Şi̇mşek, Ümi̇t Turgut, Hasan Erdoğan

Turkish Journal of Physics

Relative L1, L\alpha, L\beta and L\gamma x-ray fluorescence cross-sections were observed in Ta, W, Re, Au, Hg, T1, Pb, Bi, Th and U of 16.03, 17.78, 22.58, 25.77, 32.89, 38.18, 43.94, 50.21, 59,5 and 122 keV energies. In this study, L X-ray fluorescence cross-sections were measured at 59.5 and 122 keV and measured values of the other energies were taken from tables by Mann et. al. (1). The experimental relative fluorescene cross-sections were computed for the excitation energies 16.03, 17.78, 22.58, 25.77, 32.89, 38.18, 43.94, 50.21, 59.5 and 122 keV, compared with the theoretically calculated values by Scofield(11). The experimental …

Confined Bipolarons In The Strong Coupling Limit, R. Tuğrul Senger, Ati̇lla Erçelebi̇

Turkish Journal of Physics

Within the framework of the strong-coupling polaron theory and the bulk phonon approximation we report the possibility and criteria in achieving stable bipolaron states in confined media. We use a simple model of two electrons constrained within an anisotropic three dimensional parabolic potential box of tunable barrier slopes. Conforming the confining potential from one geometry to the other, we obtain an explicit tracking of the stability criteria as a function of the degree of confinement uncovering all low dimensional major geometric configurations of common interest.

Electroweak Symmetry Breaking In Low-Scale Quantum Gravity, M. Boz, A. Demi̇r, Namik Kemal Pak

Turkish Journal of Physics

We discuss the implications of low-scale quantum gravity on electroweak symmetry breaking by computing one-loop gravitational corrections to the Higgs potential. We conclude that these radiative corrections are quite large after summing over the graviton and dilaton Kaluza-Klein towers, and there is no possibility of electroweak symmetry breaking unless one allows for the complex vacuum expectation value for the Higgs field.

Projectile Fragmentation In Emulsion At (4.1-4.5) A Gev/C, A. El-Naghy, S. A. H. Abou-Steit, M. Mohery

Turkish Journal of Physics

The fragmentation process has been investigated for 4.5A GeV/c^{28}Si nuclei in emulsion and compared with the results of 4.5A GeV/c^{24}Mg and 4.1A GeV/c^{22}Ne in order to test the validity of the different theoretical models. It has been found that a single parameter distribution is insufficient to explain exactly the fragmentation process. Correlation studies have shown to be necessary for distinguishing between the different theoretical models for the fragmentation. The impact parameter, which defines the nature of the collision, has been found to influence considerably the shape of the charge yield distribution. The angular distributions of the projectile fragments can be …

Stellar Observations Made At The Malatya Danjon Astrolabe Station, Orhan Gölbaşi, Hüseyi̇n Kiliç, Fernand Chollet

Turkish Journal of Physics

We give here the first results of astrometric stellar observations made at the Malatya Station with the modified astrolabe of Paris observatory. This campaign is conducted as part of a cooperation between Inönü University and the Paris Observatory. The astrolabe, which is strictly similar to that of Santiago de Chile, can use two reflecting prisms instead of the trnsparent prism of the Danjon Astrolabe. Consequently, it is possible to observe at the two zenith distances of 30° and 60°. The time is supplied by a GPS receiver which gives UTC with the necessary precision. As the station is a new …

Canonical Treatment Of Regular Lagrangians With Holonomic Constraints As Singular Systems, Eqab M. Rabei

Turkish Journal of Physics

Regular Lagrangians with holomonic constraints are treated as singular systems using the canonical method. The Lagrange multipliers are introduced as generalized coordinates. The regular Lagrangians are extended to be singular and the Hamiltonian formulation is obtained. The equations of motion are written as total differential equations in terms of the time t and the Lagrange multipliers. It is also shown that Lagrange multipliers can be determined from the integrability conditions.

Magnetisation In Two-Dimensions, Bengü Kaplan

Turkish Journal of Physics

We discuss the magnetisation deviation in two-dimensions (2d) for an iron film for which the anisotropy is much smaller and hence the magnetisation is a stronger function of temperature. The magnetisation deviation can be adequately described by an RPA (random phase approximation) approach. Our results fit the experimental data at high fields and hence can be used to estimate the value of the effective exchange interaction (J_{2d}) for monolayer (ML) films.

Low-Magnetic Field Microwave Absorption In Superconductors And Conducting Polymers, I. L. Khairullin, P. K. Khabibullaev, V. Yu. Sokolov, A. A. Zakhidov

Turkish Journal of Physics

Low-magnetic field microwave absorption (MA) in superconductors and conducting polymers is analysed in a low-field signal (LFS) version of the MA detecting method. The temperature dependences, hysteretic benavior and other properties of a LFS are compared in superconducting versus non-superonducting systems. Spin selective hopping processes between polarons and bipolarons is proposed to be one of the possible mechanisms of a LFS in non-degenarate conducting polymers.

Direct Current Glow Discharges In Atmospheric Air, Robert H. Stark, Karl H. Schoenbach

Bioelectrics Publications

Direct current glow discharges have been operated in atmospheric air by using 100 μm microhollow cathode discharges as plasma cathodes. The glow discharges were operated at currents of up to 22 mA, corresponding to current densities of 3.8 A/cm² and at average electric fields of 1.2 kV/cm. Electron densities in the glow are in the range from 10¹² to 10¹³  cm⁻³. Varying the current of the microhollow cathode discharge allows us to control the current in the atmospheric pressure glow discharge. Large volume atmospheric pressure air plasmas can be generated by operating microhollow cathode discharges …

Time-Resolved Reflection High-Energy Electron Diffraction Study Of The Ge(111)-C(2×8)-(1×1) Phase Transition, Xinglin Zeng, Bo Lin, Ibrahim El-Kholy, Hani E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The dynamics of the Ge(111)-c(2×8)-(1×1) phase transition is investigated by 100-ps time-resolved reflection high-energy electron diffraction. A laser pulse heats the surface while a synchronized electron pulse is used to obtain the surface diffraction pattern. Slow heating shows that the adatoms in Ge(111)-c(2×8) start to disorder at ∼510 K and are converted to a disordered adatom arrangement at 573 K. For heating with 100-ps laser pulses, the Ge(111)-c(2×8) reconstructed adatom arrangement starts to disorder at 584±16K, well above the onset temperature of ∼510 K for the disordering of Ge(111)-c(2×8) observed for slow …

Room-Temperature Blue Luminescence Of Thermally Oxidized Si1-X-YGeXCY Thin Films On Si (100) Substrates, Xuemei Cheng, Youdou Zheng, Xiabing Liu, Lan Zang, Zhiyun Lo, Shunming Zhu, Ping Han, Ruolian Jiang

Physics Faculty Research and Scholarship

We measured at room temperature the photoluminescence spectra of the thermally oxidized Si_1-x-yGe_xC_y thin films which were grown on silicon substrates by plasma-enhanced chemical vapor deposition and the wet oxidized at 1100 °C for 20 min. The photoluminescence band with a peak at ~393 nm under the exciting radiation of λ = 241 nm was observed. Possible mechanism of this photoluminescence is discussed.

Population Trapping In Extremely Highly Excited States In Microwave Ionization, Michael W. Noel, W. M. Griffith, T. F. Gallagher

Physics Faculty Research and Scholarship

When a lithium atom in a Rydberg state (n 􏰟 80) is exposed to a short, intense microwave pulse we find that substantial population is left in extremely highly excited states (n . 120), in spite of the fact that the microwave field amplitude is more than 40 times larger than required to classically ionize these states.

The Atomic Force Microscope In The Elucidation Of Leukocyte Abnormality, Derbrenn O'Connor

Theses

The aim of this project was to investigate the novel use of the atomic force microscope (AFM) as a technique in the elucidation of leukocyte abnormality. To this end, comparative AFM imaging and elasticity studies were performed on normal and myeloid leukaemic leukocytes.

Initially, an evaluation of techniques for the isolation of specific leukocyte (e.g. lymphocytes, granulocytes, etc.) populations from whole blood or leukocyte concentrates, was carried out. It was found that a silanised glass surface failed to select and immobilise a leukocyte population. However, centrifugation of whole blood in an Isopaque-ficoll gradient solution yielded a viable mixed leukocyte population …

Computer Based Methodologies For On-Line Scanning Force Microscopic Detection Of Immunological Binding Events, Patrick Joseph O'Mahony

Theses

The overall aim of this work was to develop computer based methodologies for the on-line scanning force microscopic detection of immunological binding events. To achieve this aim it was necessary to develop a rapid, high-resolution data acquisition system to digitise scanning force microscope (SFM) data on-line and then to develop an effective method for extracting the scanner induced background curvature from this data to reveal the nanoscale height binding events. Four techniques were investigated in terms of operational speed and performance accuracy; namely, polynomial interpolation; least squares approximation; real-time recursive least squares approximation; and wavelet approximation.

It was found that …

Thermal Plasmaspheric Morphology: Effect Of Geomagnetic And Solar Activity, Mark Anthony Reynolds, G. Ganguli, J.A. Fedder, J. Lemaire, R.R. Meier, D.J. Melendez-Alvira

Publications

A multispecies kinetic model of the thermal plasma in the plasmasphere is used to predict the spatial dependence of the hydrogen ion and helium ion density and temperature for different levels of geomagnetic and solar activity. The particular convection electric field model chosen is intended for the time intervals between substorms. The plasma density and temperature in the equatorial plane are found to exhibit a local-time variation that is sensitive to the details of the convection electric field. In particular, the parallel temperature increases with altitude and the perpendicular temperature decreases with altitude, except in the postmidnight sector, features that …

Observational Limit On Gravitational Waves From Binary Neutron Stars In The Galaxy, B. Allen, J. K. Blackburn, J. D. Creighton, Teviet Creighton

Physics & Astronomy Faculty Publications

Using optimal matched filtering, we search 25 hours of data from the LIGO 40-m prototype laser interferometric gravitational-wave detector for gravitational-wave chirps emitted by coalescing binary systems within our Galaxy. This is the first test of this filtering technique on real interferometric data. An upper limit on the rate R of neutron star binary inspirals in our Galaxy is obtained: with 90% confidence, R<0.5h−1. Similar experiments with LIGO interferometers will provide constraints on the population of tight binary neutron star systems in the Universe.

Mössbauer Effect Determination Of Relative Recoilless Fractions For Iron Oxides, Sei J. Oh, Desmond C. Cook

Physics Faculty Publications

The relative recoilless fraction (F-value) of each of six iron oxides, defined as the ratio of the recoil-free fractions of two different materials, was experimentally determined relative to hematite at 300 K and 77 K by Mössbauer spectroscopy. Using the relative recoil-free fractions compared to that of hematite, the relative recoilless fractions between all pairs of the seven iron oxides were determined. The F-values can allow conversion of Mössbauer subspectral areas to the relative atomic, molecular, or weight fractions of each iron oxide present in a mixed oxide phase sample.

Design And Optimization Of Chromophores For Liquid Crystal And Photorefractive Applications, Kenneth D. Singer, V. Ostoverkhov, Rolfe G. Petschek

Faculty Scholarship

Organic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.

Surface Resistance Measurements Of Superconducting Niobium Samples With A Triaxial Cavity, Paul Martin Boccard

Physics Theses & Dissertations

This experimental study has revealed and investigated many of the physical issues that affect accurate measurement of the surface resistance for small samples consisting of superconducting niobium films on copper substrates. It is believed that this work provides the groundwork for future research directed towards solving this important problem. Accurate measurement of surface resistance for such samples is needed to allow the rapid evaluation and optimization of the deposition parameters necessary for manufacturing low-loss superconducting niobium films.

A superconducting niobium triaxial cavity was investigated to determine its suitability for measuring the residual surface resistance of copper samples that were sputter-coated …