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    Electrical Properties of Silver Impurities and their Annealing Behaviour in p-Type Fz Silicon
    (Journal de Physique III, 1691-12) Adegboyega, G.A; Passari, L; Butturri, Maria Angela; Poggi, Antonella
    The electrical activity of silver as well as its annealing properties in 10 Omega cm p-type Fz silicon substrate are studied by means of the four-point probe and minority carrier lifetime measurements. Silver atom concentration in the range 10^{14} to 10^{15} cm^{-3} consistently showed a donor type behaviour in the material and its presence led to a reduction of up to two orders of magnitude in the lifetime of minority carriers by the formation of deep-level traps. Isochronal annealing of silver contaminated specimens showed some gettering of the Ag impurities with resulting temperature dependent changes in the resistivity as well as the minority carrier lifetime values. Analysis of our results shows that a large fraction of the silver impurity atoms present forms the deep level defects and both the deep- and donor-levels appear to originate from the same source
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    Transport properties of PbSnI4
    (Solid State IonicsA, 1988-10) kuku, titilayo A.; adeosun, O.S; akande, A.R; adiguel, osman
    PbSnI4 has been prepared from equimolar amounts of PbI2 and SnI2. X-ray and DSC measurements show the material to be uniphase in the temperature range 30 to 400°C; it has a tetragonal structure and melts at 379°C. The electrical conductivity is mainly ionic with an ionic transport number greater than 0.99 at 200°C. Conductivity at room temperature is 2.56 × 10−8 Ω−1 cm−1 while the value at 200°C is 1.25 × 10−6 Ω−1 cm−1.
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    Implementable soft decision decoding schemes
    (International Journal of Electronics, 1989-03) Olaniyan, O.O
    An implementable soft decision decoding algorithm is described. The scheme, which can be used to improve the performance of any hard decision decoder, is based on an iterative search method that tests relatively few possible code words from which the code word at nearest minimum distance from the received word is chosen. Computer simulations of the (7, 4) and (15, 7) codes on an additive white gaussian noise channel using the soft decision scheme were undertaken. A coding gain of at least 0-7 dB at an error rate of 10~3 was obtained when compared with that of the hard decision decoder
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    Electrical properties of CuPbBr3
    ( Solid State Ionics, 1989-05) kuku, T.A; Chioba, E.R; Chiodelli, G.
    Electrolyte characterisation of CuPbBr3 has shown the material to be appreciably conductive with a room temperature conductivity of 2.3×10−4(Ω cm)−1, and a value of 1.37×10−2 (Ω cm)−1 at 210°C. Conductivity is mainly by anionic type defects, with ionic transport numbers greater than 0.98 for all temperatures considered in the range from 22 to 215°C. The activation energy for bromine vacancy motion is 0.27 eV. X-ray, DTA and TG analyses also show that the material is characterised by a cubic lattice with lattice parameter a0 = 9.08 Å, melts at 271°C and is thermally stable up to 450°C.
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    Oxidation-induced changes in the electro-optical properties of thin copper films
    (Il Nuovo Cimento D, 1989-07) Adegboyega, G.A
    The room temperature oxidation of vapour deposited copper films has been investigated as a function of film thickness and time by the sheet resistance and optical transmittance measurements. An increase of both sheet resistance and transmittance with a tendency to saturation has been observed. Time variation of the sheet resistance shows that the kinetics of oxidation could be described by a model whereby an initial logarithmic oxide growth changes to an inverse logarithmic one as time progresses; the thicker the film, the longer the change-over time. Absorption coefficients of oxidized films show that the resulting oxide is most probably Cu2O. Evaluation of the oxidized films for possible use as transparent electrode material shows the existence of an optimum thickness value
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    Structural and ionic transport properties of some A2BX4 (A=Cu, B=Pb, Sn, X=Br, I) compounds.
    (1990) Kuku, T.A; Erharhine, P.O; Chiodelli, G.; Akande, A.R.
    The compounds Cu2PbBr4, Cu2SnI4, and Cu2PbI4 have been synthesized as stable phases in the CuBr-PbBr2, CuI-SnI2, or CuI-PbI2 binary systems. Cu2PbBr4 is cubic (a0=9.170 A ̊), whereas Cu2SnI4 and Cu2PbI4 are hexagonal with a=9.050, c =9.706 A ̊, and a=8.064, c=15.128 A ̊, respectively. These materials are characterized mainly by a rather high anionic defect conductivity over the temperature range 20-270°C. The activation energy for the ionic defect mobility is 0.27 eV for Cu2PbBr4, 0.28 eV for Cu2SnI4 and 0.31 eV for Cu2PbI4
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    Some aspects of tropical rainfall and their effect on microwave propagation
    (International Journal of Satellite Communications, 1990-05) Ajayi, G.Olalere
    Some characteristics of tropical rain rate and raindrop size distribution are briefly reported, making use of the data obtained at locations in Nigeria. Models and empirical relations have been obtained for the computation of the effects of tropical rain on radiowave propagation at centimetre and millimetre waves. Results are presented for the effect of integration time on rain rate as well as the rain-rate duration characteristics, rain-induced phase shift, attenuation and depolarization, in addition to the relationship between the rain rate and other rainfall parameters. Comparisons have also been made in many cases with the CCIR reports and results from other locations
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    Intrinsic gettering of Cr impurities in p-type Cz silicon
    ( physica status solidi (a, 1990-09) Adegboyega, G.A; Poggi, Antonella
    The gettering of chromium impurities by means of high temperature oxygen precipitates is studied by means of resistivity, lifetime, and infrared absorption spectroscopy measurements. The results show that the density of interstitial oxygen, following an oxygen precipitation step, is rather low, and the presence of this interstitial oxygen is closely connected with the formation of the so-called new donor defect. Most of the high temperature (T = 1000°C) oxygen precipitates seem to appear in the form of SiO2 and there is a strong evidence of a redissolution of the oxygen precipitates due to Cr diffusion. The presence of this high temperature oxygen precipitate shows a high efficiency in the gettering of Cr impurities.Das Gettern von Chromverunreinigungen mittels Hochtemperatur-Sauerstoffpräzipitaten wird mittels Widerstands-, Lebensdauer- und Infrarotspektroskopiemessungen untersucht. Die Ergebnisse zeigen, daß die Dichte des Zwischengittersauerstoffs nach dem Sauerstoffpräzipitationsschritt ziemlich niedrig ist, und die Anwesenheit dieses Zwischengittersauerstoffs eng verbunden ist mit der Bildung von sogenannten „new-Donor”-Defekten. Die meisten der Hochtemperatursauerstoffpräzipitate (T = 1000°C) scheinen in Form von SiO2 vorzuliegen, und es existiert ein starker Hinweis auf die Wiederauflösung der Sauerstoffpräzipitate infolge der Cr-Diffusion. Die Anwesenheit dieser Hochtemperatursauerstoffpräzipitate zeigen einen hohen Wirkungsgrad für die Getterung der Cr-Verun-reinigungen
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    Precision Measurement of Rotor Angle of a Microsynchronous Alternator
    (IEEE Xplore, 1991) Omoigui, Michael
    A precision instrument used for the measurement of rotor angles of a laboratory microalternator is described. The measurement is performed by integrating digital signals derived from a phase-locked loop (PLL) reference (i.e. laboratory infinite busbar or the terminals of another machine in a multimachine system) and an optical encoder mounted on the shaft of the machine. The integration is executed by synchronous up-down binary counters. A 12-b digital-analog converter enables both transient and dynamic movement of the rotor to be displayed on an oscilloscope or other suitable recorder. When used on a four-pole 3-MVA microalternator, the resolution of the encoder is 0.2 electrical degrees. Relatively slow and fractional movements of the rotor angle arising from dynamic power imbalances as well as fast and large rotor excursions arising from severe transient disturbances, which sometimes result in pole slipping, are reliably and precisely recorded. It is possible to obtain constant information on the stability or lack thereof for the machine under every operating condition. With appropriate transducers, the principle may easily be applied to continuously monitor changes in the rotor angle of large alternators in interconnected power systems
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    The Functions of Language in Herbalist-Client Interaction in Yoruba Traditional Medicine
    (1991) Adegbite, Wale
    A piece of language in use or 'text' can be studied from three vantage points. While sociological, socio-linguistic or socio-psychological approach will be interested in studying the social uses of (parts of) the text or the pragmatic activities of the speaker and interpretant accompanying its production and reception, a textual approach will be more interested in analysing its linguistico-pragmatic features such as the function(s) and message(s), and a linguistic approach will most probably focus the description of form (grammar and lexis) and meaning in the text.
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    Some Features of Language Use in Yoruba Traditional Medicine
    (1993) Adegbite, Wale
    Yoruba traditional medicine (YTM) is a system which basically incorporates a four-square intersection of two pairs of terms in relation to medicine, viz. positive/negative and personal/communal. In the intersection of 'positive personal' medicine which is catered for by the data for this study, the goal is for a herbalist, or a priest of some divinity, to diagnose and treat an illness of a client or patient where the patient is a child, friend or relation of the client. Herbalists deal in various kinds of medicine though many of them may treat cases of different types, they normally have different areas of specialty e.g. gynaecology, paediatrics, traditional midwifery, orthopaedics, psychiatry etc. However, the diviners or priests are well reputed for handling complex cases that are linked to supernatural causation.
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    Photoconductivity of MOCVD CdS thin films
    (Journal of Materials Science Letters, 1995-01) Eleruja, Marcus Adebola; Adedeji, A.U; Azi, samuel; Okulaja, Oluwabukola
    ... [2,3,4] Many techniques have been reported in deposition of CdS thin films. These include evaporation, sputtering, spray pyrolysis, molecular beam epitaxy (MBE) technique, photochemical deposition, successive ionic layer adsorption and reaction (SILAR) method [5][6][7][8][9][10][11][12].In all of these deposition methods there are some problems in each of them, for example , it is difficult to obtain a stiochiometric CdS films by evaporation technique and a high substrate temperature is required in spray deposition. [13] The chemical bath deposition (CBD) method appears to be a relatively simple, in expansion method to prepare a homogenous films with controlled composition [14]. ...
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    Variations in raindrop size distribution and specific attenuation due to rain in Nigeria
    (annals of telecommunications - annales des télécommunications, 1996-01) Adimula, I.A; Ajayi, G.O
    Les distributions des tailles des gouttes de pluie ont été mesurées en trois lieux du Nigéria (Calabar, Ile-Ife et Zaria). Les données collectées pendant trois ans ont servi à obtenir des modèles de ces distributions pour divers types de pluie : bruine, averse, pluie étendue, orage. La distribution lognormale constitue un bon ajustement pour tous les types de pluie en des lieux tropicaux, sauf pour la bruine où le modèle exponentiel convient. On discute aussi les conséquences de ces modèles pour des calculs de l’affaiblissement linéique dû aux pluies tropicales. The raindrop size distributions had been measured at three locations in Nigeria - Calabar, Ile-Ife and Zaria. The data collected over a period of three years have been utilized to obtain models of drop size distributions for drizzle, shower, widespread and thunderstorm rain. The lognormal distribution provides a good fit for all the rain types at these tropical locations except drizzle, where the exponential model is adequate. The implications of the models for specific attenuation calculations for tropical rain are discussed. Mots clésPluie-Zone tropicale-Distribution statistique-Goutte eau-Dimension particule-Ajustement-Loi lognormale-Loi exponentielle-Onde radioélectrique-Affaiblissement Key wordsRain-Tropical zone-Statistical distribution-Water drop-Particle size-Fitting-Lognormal distribution-Exponential distribution-Radio wave-Attenuation
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    The effects of oxygen precipitates on the electrical properties of silver impurities in p-type silicon
    (1996-07) Adegboyega, G.A; Passari, L; Butturri, M.A; Susi, E
    Some characteristics of the silver impurity in silicon with and without oxygen precipitates are studied by means of the four-point probe, minority carrier lifetime, and infra-red absorption spectroscopy measurements. The relative effect of varying contents of oxygen precipitate on the impurity is also investigated. Silver proved to be a donor-type impurity in p-type silicon and its presence led to a reduction, by up to a factor of 21, in the lifetime of the minority carriers by the formation of deep level traps. While the presence of oxygen precipitate in the substrate has little or no effect on the donor-type behaviour, it improved slightly the value of the minority carrier lifetime by gettering some of the Ag impurities and there appears to be a linear dependence of the improved lifetime on the quantity of precipitated oxygen.
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    Deep level transient spectroscopy study of the damage induced in n-type silicon by a gate oxide etching in a CHF3/Ar plasma
    (Journal of vacuum science & technology B, 1997-06) Adegboyega, G.; Perez, I.V; Poggi, Antonella; Susi, E
    Deep level transient spectroscopy was used to detect the presence of deep levels correlated to the defects induced in the Si substrate by a CHF 3 /Ar dry etch of a 550 Å gate oxide as a function of the rf power. Several energy levels were observed; some of them were due to the processing before the dry etching. Three traps produced by the dry etching, with Arrhenius plot activation energies, respectively, E na1 =350  meV , E na2 =220  meV , and E na3 =100  meV , and capture cross sections around 10-20  cm 2 were detected. The correlation with the surface recombination velocity variations and the F and C diffusion in the Si substrate was investigated. © 1997 American Vacuum Society
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    Optical properties of evaporated PbSnS3 thin films
    (Kluwer Academic Publishers, 1998-06) Kuku, T.A; Azi, Samuel
    PbSnS3 is a ternary sulfide semiconductor material which has been relatively little studied in the literature. Thin films of this material were deposited on glass substrates by a thermal evaporation process and their optical properties investigated. The optical parameters were determined from the analysis of measured transmission spectra, at normal incidence, from 400–1500 nm, at room temperature. The fundamental absorption edge is placed at 1.04±0.05 eV and is forbidden in nature. Other absorption edges are obtained at 1.44 and 1.55±0.05 eV, with a nearby direct one at 1.68±0.05 eV. The peaks at 1.44 and 1.55 eV have been independently confirmed by the spectral photocurrent response of the films. © 1998 Kluwer Academic Publishers
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    Optical characterization of pyrolytically deposited ZnxCd1−xS thin films
    ( Optical Materials, 1998-09) Adedeji, A.U; Ojo, I.A.O; Djebah, A
    The precursor bis-(morpholinodithioato-s,s′)–Cd–Zn was prepared and the thin films of ZnxCd1−xS deposited on sodalime glass substrate. A direct optical energy gap of 2.63 eV was obtained from the analysis of the absorption spectrum. The photoluminescence spectrum shows shift in the energy of the primary emission peaks as a function of the excitation energy. The shift was explained as due to the quantum size effect in nanometer thick polycrystalline films. Energy Dispersive X-ray Florescence (EDXRF) confirms the elemental composition of both the precursor and the films
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    Ion transport studies on vacuum deposited PbSnI 4 thin films
    (Thin Solid Films, 1999) Kuku, T.A
    Thin films of the material PbSnI4 have been deposited by vacuum evaporation. The electrical conductivity, its activation energy and dielectric breakdown strength have been found to be film thickness dependent for films ≤5000 Å. Conductivity is by anionic defect motion with an activation energy of 0.320 eV and ionic transference number of 0.995 at room temperature. The ionic transport has been independently verified by an electrochemical cell potential method with the use of the material in an all thin film solid state battery of the configuration M/PbSnI4/(AgI,Ag), (M=Sn,Pb), giving OCV values close to the thermodynamic theoretical maximum for the formation of MI2 at the anode.
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    Theoretical study of the effect of different types of tropical rainfall on microwave and millimeter-wave propagation
    (1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
    In this paper, the effects of tropical rainfall on the propagation of microwave and millimeter-wave signals on terrestrial paths have been investigated. Quantitative evaluation of spheroidal raindrop scattering parameters such as the scattering amplitude functions, total and scattering cross sections, and so on, were carried out for linear polarization (horizontal and vertical), using the least squares fitting method over the frequency range 1–100 GHz. Incident radio signals are assumed plane and arrive normally on the raindrop axis. For the purpose of application to slant paths, two other incident angles, 50° and 70°, were considered. The computed forward scattering amplitude functions were employed to compute the complex effective propagation constant of the radio signals in four tropical rainfall types: drizzle, widespread, shower, and thunderstorm. The corresponding specific attenuation and specific phase shift were computed. Specific attenuation and phase shift due to the rain types for circularly polarized radio signals were also derived. The parameters of the power law relationship between attenuation, phase shift, and rain rate were computed for each rain type and compared with existing temperate and tropical models. The problem of rain-induced depolarization was also investigated by computing the cross polarization discrimination for the four rainfall types over the frequency range 1-50 GHz, which is of immediate importance to system designers
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    Theoretical study of the effect of different types of tropical rainfall on microwave and millimeter-wave propagation
    (Radio Science - RADIO SCI. 34., 1999-09) Ajewole, Oludare; Kolawole, L.B; Ajayi, G.O
    In this paper, the effects of tropical rainfall on the propagation of microwave and millimeter-wave signals on terrestrial paths have been investigated. Quantitative evaluation of spheroidal raindrop scattering parameters such as the scattering amplitude functions, total and scattering cross sections, and so on, were carried out for linear polarization (horizontal and vertical), using the least squares fitting method over the frequency range 1–100 GHz. Incident radio signals are assumed plane and arrive normally on the raindrop axis. For the purpose of application to slant paths, two other incident angles, 50° and 70°, were considered. The computed forward scattering amplitude functions were employed to compute the complex effective propagation constant of the radio signals in four tropical rainfall types: drizzle, widespread, shower, and thunderstorm. The corresponding specific attenuation and specific phase shift were computed. Specific attenuation and phase shift due to the rain types for circularly polarized radio signals were also derived. The parameters of the power law relationship between attenuation, phase shift, and rain rate were computed for each rain type and compared with existing temperate and tropical models. The problem of rain-induced depolarization was also investigated by computing the cross polarization discrimination for the four rainfall types over the frequency range 1-50 GHz, which is of immediate importance to system designers