Wyniki wyszukiwania - Biblioteka Nauki

1

Modeling a Bandwidth of a Two-Level Independent Quantum Laser System States

100%

Mosiori C. O.

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tom 3

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nr 12

2012-2018

EN

An electromagnetic radiation is basically considered to be a transverse wave propagating through an accessible media whether it is an optical fibre or a thin film depending on its propagating conditions. In analyzing its propagation, utilized specific cross-section areas have become an important base of understanding its extinction parameters. The term cross-section in this work applies only to boundary conditions within which particles interact within electromagnetic spectra through absorption or scattering. In such small volume contextual framework, nanotechnology reconsiders scattering cross-section coefficients. In this work, two different degenerate states were modeled and analyzed using a developed model of a laser cavity containing a media of length, L, with a gain of, k, per unit length which were mirrored to represent the upper and a lower level manifolds inhomogeneous broadening Stark levels respectively. The model developed created an impression that a laser medium is a coherent ensemble of particles or atoms whose bandwidth depends on how a laser is constructed.

2

TiO2 Thin Films by Solution Technique for Solar Cells

63%

Mogunde C. , Mosiori C. O.

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nr 8

6001-6007

EN

Titanium dioxide has a number of applications in solar cells. In this study, TiO2 thin films were synthesized using a simple but less expensive, low temperature and large area deposition method referred to as chemical bath deposition. Their electrical and optical properties were examined at various temperatures where it was observed that the films exhibited low reflectance which increased with increase in wavelength with refractive indices of 2.2–2.5 in the visible spectra. Sheet resistivity ranged between 13.54±0.095 Ω/m to 17.27±0.209 Ω/m. They were use to fabricate photovoltaic cell which exhibited the following parameters: a short circuit current, Isc=0.002445 A, open voltage, Voc = 0.04731 V, a fill factor, FF=0.551 and an efficiency, η=0.531 %. They were recommended for diode applications.

3

Studies on Cd1Se0.6Te0.4 Thin Films by Spectroscopic and Diffractometer Characterization

63%

Mosiori C. O. , Oeba D. A.

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nr 9

2001-2006

EN

Cadmium selenide tellurium is a compound containing cadmium, tellurium and selenium elements forming a combined solid. Hall measurements suggest that it is an n-type semiconductor. Related optical studies indicate that is transparent to infra-red radiation. Structural studies clearly show that it has a wurtzite, sphalerite crystalline forms. Cadmium is a toxic heavy metal, and selenium is only toxic in large amounts or doses. By this toxicity, cadmium selenide is a known to be carcinogen to humans; however, this does not stop investigating it for optoelectronic applications. Current research has narrowed down to investigating cadmium selenide when in the form of nanoparticles. Cadmium selenide finds applications has found applications in opto-electronic devices like laser diodes, biomedical imaging, nano-sensing, high-efficiency solar cells and thin-film transistors. By chemical bath deposition, Cd1Se0.6Te0.4 thin films were grown onto glass. Tellurium was gradually introduced as an impurity and its crystalline structure and optical properties were investigated by XRD and UV-VIS spectroscopy. The main Cd1Se0.6Te0.4/glass characteristics were correlated with the conditions of growing and post-growth treatment and it was found out that films were homogeneous films with controllable thickness onto the glass substrate and suitable for n-type “sandwich” heterostructures applications. Comparison of the intensities of equivalent reflexions provided a test for the internal consistency of the measurements. Equivalent reflexions in two specimens differed on average by 1.4 % and 0.6% from the mean measured intensity, attesting to the high internal consistency of measurements from extended-face crystals. By comparison from data obtained from all samples showed their average deviation from the mean to be 0.9 %.

4

Determination of Planck’s Constant using Light Emitting Diodes

51%

Mosiori C. O. , Oeba D. A. , Shikambe R.

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tom 3

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nr 10

2007-2012

EN

Planck’s constant is named after Max Planck, a nineteenth-century physicist who first described it by relating it as E=h where symbols have their usual meanings. It is a relationship used when comparing a quantum of energy absorbed to that emitted during electron transitions which can be extended to emission by light-emitting diodes. The purpose of this study was to determine Planck’s constant using the energy needed to excite free electrons in a light emitting diode. When a light-emitting diode is switched on, electrons recombine with holes within and release energy in the form of photons which can be determined using energy band gaps of the semiconductor composite material used to fabricate the LED. Therefore, LEDs consist of a chip of doped semiconducting layers to create a p-n junction. In LEDs, current flows easily from the p-side to the n-side but not in the reverse from electrodes with different voltages. When an electron meets a hole, it is inhaled and it falls into lower energy level releasing energy in the form of a photon. Photon emissions take place when electrons return to a lower energy state. Therefore, electrons within a LED crystal are excited to a higher energy state and any radiation emitted depends on the p-n junction direct band gap. Depending on the materials used, LEDs emit radiation with energies corresponding to either near-infrared, visible, or near-ultraviolet light. In reality, a LED is designed to have a small area (approximately less than 1 mm2). In this work, an electric current was used to excite electrons and the corresponding energy was measured using a voltmeter. Planck’s constant was calculated by substituting the obtained frequency and energy from the voltmeter in the relationship, E = hw.

5

Electrical Behavior of Cd0.3Zn1.1x S0.7 Thin Films for Non-Heat Light Emitting Diodes

51%

Mosiori C. O. , Maera J. , Shikambe R. , Magare R.

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tom 3

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nr 6

2.8-2.16

EN

In developing countries like Kenya, solution processing technique is the cheapest and simplest technique to grow inorganic composites thin films. This method was used to grow thin films of Cd0.3Zn1.1xS0.7 on ordinary microscope Perspex substrate slides from aqueous solutions of Zinc chloride and cadmium chloride in ammonia solution. A solution of triethanalomine was used as a complexing agent while thiourea was used as source of sulphide ions. Electrical properties as a function of their thicknesses were obtained by varying deposition time while all other parameters were maintained constant. Using a resistance measurement device and a Gauss meter, resistivity and the conductivity of the films were found to be thickness dependent with semiconductor nature.

6

Impact of Annealing Thin Films In(OH)xSy Growth By Solution Technique

51%

Mosiori C. O. , Magare R. , Munji M.

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tom 3

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nr 7

3.1-3.8

EN

Indium Hydroxy Sulphide has demonstrated abundance in resources, low prices, nontoxic characteristics, radiation resistance, high temperature resistance, and chemical stability, and therefore it has become an extremely important photoelectric, photovoltaic, and light sensing thin film material. Some treatment on this material include thermal annealing which is a process used for intrinsic stress liberation, structural improving, and surface roughness to control its electro-optical properties. In a qualitative way, annealing modifies surface morphology, intrinsic parameters, and electron mobility with temperature and time. In this work, an explanation on the surface modification of In(OH)xSy thin films when subjected to an annealing process is discussed. Both electrical and optical effects caused by annealing were carried out and characterizations were performed at different annealing temperatures in nitrogen in the temperature range 373–573 K. Using optical measurements data and simulated data, Scout software was employed and the results showed that increasing annealing temperature causes a slight decrease in transmittance with a consequence of modifying the energy band gaps values between 2.79–3.32 eV. It was concluded that annealing influence optical transmittance and resistance of the film make the thin films potential for photovoltaic, and light sensing applications.

7

Optical Analysis of Ag-NPs Containing Methyl Ammonium Lead Tri-Iodide Thin Films

51%

Mosiori C. O. , Njoroge W. K. , Ochoo L. O.

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nr 9

2007-2015

EN

Methyl ammonium lead tri-iodide hybrid thin films were grown using solution technique. They were doped with silver nano-particles at different concentrations at concentrations of 0.05, 0.06, 0.07, 0.08, and 0.09 mM. Their reflectance and transmittance were recorded in the wavelength range 300–900 using UV-Vis double - beam spectrophotometer. Using these measurements, other optical parameters were simulated using scout software. The effect of silver nanoparticles was investigated. Results revealed that the thin films had highest transmittance of about 79 % as their band gap varied from 1.921–1.832 eV. Electrical conductivity varied from 1.4–1.6×105 S cm–1 while optical conductivity varied in the range of 0.3–0.6×1010 sec-1. They had a significantly low refractive index, suitable for optical applications within the range of 1.6–1.8. The extinction coefficient varied in the range as 1.0–1.7×10-5 while the absorption coefficient varied varies in the range of 2.1-4.2 cm- 1. It was concluded that the thin films were suitable for photonic device applications.