College of Biological and Physical Sciences

In this study, Electrophoretic Deposition (EPD) technique was used to fabricate TiO2/Nb2O5 composite
thin films on FTO coated glass for application as photoelectrodes in Dye Sensitized Solar Cells (DSSC). A
TiO2/Nb2O5 ratio of 1:1 was used in a 2-propanol suspension solution with a solid loading of 0.25g/L. Optical
investigations showed that the film with thickness of 5.5 µm deposited at 35.0 V for 90.0 s had the highest
transmittance of 55.0 % at a wavelength (λ) of 1,300 nm. The optical band gap energy (Eg) was 3.884 eV and was
found to be dependent on the annealing time. The solar cell fabricated from this film had an open circuit voltage
(VOC) of 0.66 V, fill factor (FF) of 57.0%, short current density (JSC) of 5.25 mA/cm2 and photo conversion
efficiency (PCE) of 2.0%. Electrochemical Impedance Spectroscopy (EIS) analysis indicate that the DSSC device
with thinner photoelectrodes have more efficient electron transport in the photoanode compared to thicker
photoelectrodes to achieve higher conversion efficiencies.
Keywords: electrophoretic deposition, dye-sensitized solar cell, TiO2/Nb2O5 composite thin films

In this study, electrophoretic deposition (EPD) technique was used to deposit titanium dioxide (TiO2) thin films on
conducting glass substrates for application in water purification from organic contaminants. Phenol was used as a model
pollutant. The EPD suspension related parameters and deposition conditions were first optimized for good quality film
deposits. The suspension stability and deposition conditions that result in good adherence of TiO2 particles to the substrate with
homogeneous film coatings, is ethanol with a pH of 3.0, a TiO2 solid loading of 4.0 wt%, a 0.2 wt% iodine concentration in the
solvent and a deposition voltage of 20.0V in a time of 210.0s. The photocatalytic activity of TiO2 thin films decreases
exponentially with the ultraviolet light (UV) illumination time and it is also dependent on film thickness, sintering temperature
and the intensity of the UV light. Highest rate of photocatalytic activity is observed at an optimal film thickness of 95.0 ±
2.0µm sintered at 300.0°C. The implications of these results are discussed for design of inexpensive waste water purification
systems for light industries before discharge into the ecosystem.
Keywords: Electrophoretic Deposition, Titanium Dioxide, Photocatalysis

The installation of Photovoltaic (PV) solar systems in institutions as well as homesteads in the rural areas in
Kenya is increasing at a high rate; and so is the need for the stake holders to make sure the PV solar systems are professionally designed, sized, installed and maintained. In PV solar system installation, the designing, sizing and the installation are very critical steps. A wrongly designed, sized and installed system will not perform optimally and will underperform (for undersized systems) and waste energy and resources (for oversized systems). Furthermore, undersized systems do not perform to the user’s expectation discouraging the user and eventually a negative customer attitude creeps in which may affect the uptake of solar PV systems. On the other hand, an oversized PV system is extra expense on the side of the client, creating an exaggerated high cost of PV solar systems, again discouraging potential clients from the adoption of the technology. Both scenarios mean loss of business, jobs and the economic and social benefits associated with PV technology. We present a case study of poorly installed PV systemsin Makueni County, Kenya. We observed that the solar modules pecifications at the back of the modules were not clearly done, the batteries were poorly matched and the cables used in the installation were undersized. Due to these issues, even a normal television set was not able to work since the system was installed four years ago (in 2012).The above case emphasizes the need for training in PV solar system design, sizing, installation, and maintenance.
Key words: Photovoltaic (PV), modules, solar system, Installation, training, professional

Aluminium induced crystallization (AIC) was used to crystallize sputtered amorphous silicon
thin films on aluminium-coated glass at annealing temperatures ranging from 250-520° C in
vacuum. Crystalline volume fractions were measured by Raman spectrometry as a function
of annealing temperature. It was shown that the crystallized films had large grains as the
Raman peaks were centred at about 520 cm-1 at and over annealing temperatures of 420°
C. The three-layer sample crystallization resulted in crystallization of the films at lower
temperatures compared to the two-layer sample crystallizations which implied a reduction in
the cost of production of the seedlayer and resulting products. Hall mobilities and hole
densities ranging from 17.0-22.8 cm2V-1s-1and (4.7-9.2)× 1018 cm-3 respectively were
measured. Low hole charge densities for films of the same thickness were achieved at high annealing temperatures which was an indication of less aluminium in seed layers prepared at those temperatures. Having seed layers with sufficiently low hole charge densities is desirable for application of the seed layer in photovoltaic applications.
Key words: microcrystalline, silicon, annealed, raman, crystallinity, hall-effect

A study of structural and properties of pure (undoped) Zinc oxide (ZnO) and phosphorous (P) and Antimony (Sb) doped Zinc Oxide films has been carried out. The films were deposited by an automated spray pyrolysis equipment on both microscope glass at various elevated temperatures (270 oC - 420 oC) and on fluorine doped tin Oxide (FTO) substrates at 420 oC. Structural characterization using Raman spectroscopy showed the presence of the main peak for ZnO at 437 cm-1for all the films. Antimony doped films showed other peaks associated with the doping but phosphorous doping did not show extra peaks. Optical characterization using a UV-VIS-NIR Shimadzu (Model DUV 3700) double beam spectrophotometer provided both reflectance and transmittance data and Scout software was used to compute the band gap. At a wavelength of 600 nm, the average transmittance of the pure ZnO films was ~62 % while it was transmittance was ~85 % and ~80 % for Sb and P doped films respectively, an increase of ~23 % and ~18 % respectively. For the undoped ZnO films, high deposition temperatures led to band gap narrowing from 3.25eV to 3.10eVwhile doping resulted in band gap widening from 3.10 eV to 3.30 eV (for P-doped) and 3.10 eV to 3.33 eV (for Sb-doped),an observation confirmed by the increased transmittance on doping. The band gap narrowing for ZnO films makes the film become a better materials for visible light absorption which is good for photovoltaic applications. The wide gap broadening on doping makes the film more transparent to solar radiation making it suitable for transparent conducting oxide applications.

The installation of Photovoltaic (PV) solar systems in institutions as well as homesteads in the rural areas in
Kenya is increasing at a high rate; and so is the need for the stake holders to make sure the PV solar systems are
professionally designed, sized, installed and maintained. In PV solar system installation, the designing, sizing and the
installation are very critical steps. A wrongly designed, sized and installed system will not perform optimally and will
underperform (for undersized systems) and waste energy and resources (for oversized systems). Furthermore,
undersized systems do not perform to the user’s expectation discouraging the user and eventually a negative customer
attitude creeps in which may affect the uptake of solar PV systems. On the other hand, an oversized PV system is extra
expense on the side of the client, creating an exaggerated high cost of PV solar systems, again discouraging potential
clients from the adoption of the technology. Both scenarios mean loss of business, jobs and the economic and social
benefits associated with PV technology. We present a case study of poorly installed PV systemsin Makueni County,
Kenya. We observed that the solar modules specifications at the back of the modules were not clearly done, the
batteries were poorly matched and the cables used in the installation were undersized. Due to these issues, even a
normal television set was not able to work since the system was installed four years ago (in 2012).The above case
emphasizes the need for training in PV solar system design, sizing, installation, and maintenance

Ultrathin films (50-150nm thick) cuprous oxide (Cu2O) thin films were deposited by low temperature thermal oxidation technique. The structural, optical and photoelectrochemical properties of the thin films were investigated. X-ray diffraction (XRD) and high resolution scanning electron microscope (SEM) was used to study the phase composition and the thin films’ microstructure respectively. XRD results showed that Cu2O was the dominant phase albeit some trace CuO peaks were also observed indicating surface formation of an extremely layer of CuO probably during the cooling process following either deposition or during the annealing steps. SEM showed a highly nanostructure consisting long narrow nanorods with broadening to the surface but with extremely narrow, sharp cylindrical roots standing on the substrate. Photoelectrochemical properties of the films were studied via a standard three electrode using a saturated calomel cell (SCE).

A composite thin film consisting of TiO2 (binder), uniformly mixed CuFeMnO4 paint (solar absorber)
was coated on textured aluminum sheets by dip coating. The film’s elemental analysis was done using energy
dispersive x-ray (EDX) and the surface of the film characterized using scanning electron microscope (SEM). Optical
properties of the TiO2/CuFeMnO4 composite film were also studied using computerized double beam solid-spec
3700 DUV Shimadzu Spectrophotometer. Reflectance was obtained by spectrophotometric measurements, and
thermal emmittance was determined using heat flux- based technique respectively. Reflectance measurement values
less than 0.03 in the solar wavelength (290 nm < λ < 2500 nm) and low thermal emmittance less than 0.016 for
temperatures between 24°C and 100°C were obtained.
Keywords: CuFeMnO4 paint, TiO2- bound, reflectance, thermal emmittance, solar thermal

The sun releases tremendous amount of energy, which if harnessed would provide all energy needs of mankind.
One of the strategies to trap this immense energy is the use of solar modules/panels. However, these solar modules need to be properly sized and installed to be able to function and generate electricity optimally. The successful installation of an off grid Photovoltaic (PV) solar system is a process that begins with a site visit to the area of installation, the determination of the client’s energy needs, installation of the solar PV system,
ommissioning of the installed solar system and ends with user training. Every step is critical for it determines the final performance of the solar system and hence the delicate balance between a satisfied or unsatisfied client. However, the system sizing step tends to attract more attention for it determines the system size and the matching of the balance of system components and so if this is not properly done, then the entire system may not perform as intended. Most documented sizing methods tend to be too complicated and require significant computer knowledge in simulation, modeling and even programming. For practical purposes, many designers
and PV installers, especially in developing countries have basic education may not be well equipped for these complicated sizing methods. Furthermore, very few have been professionally trained in PV solar system Sizing and although there are commercially available sizing software’s, they are too expensive for majority of the people and even if available, they are too complicated for them.In actual sizing therefore, most untrained PV technicians use mere estimates that may not be appropriate for the outcome, more often than not is disappointing. We present a simple sizing method that can easily be learned andapplied in a simple calculation, for example in a simple excels sheet formulas for easier sizing of PV systems.The method is recommended for adoption in developing countries for faster dissemination of professional PV services in system sizing.

Aluminum sheets were polished to reduce ruggedness and then textured in varying acid-ethanol
concentration etchant to form pores. The textured surface was characterized structurally by using
X-ray diffraction (XRD) which revealed aluminum crystallographic planes (1 1 1), (2 0 0), (2 2 0)
and (3 1 1). Its morphology was studied by using energy dispersive X-ray (EDX) and scanning
electron microscope (SEM) that confirmed purity of aluminum sheet to be 99.66% at. Reflectance
of textured and plain aluminum sheet was analyzed by spectrophotometric measurements which
showed that texturing reduced the reflectance of the polished surface by 26% in the UV-VIS-NIR
spectrum of solar radiation. With reduced reflectance of the textured aluminum sheet, it was applicable
for solar radiation absorption.
Keywords
Aluminum, Texturing, Reflectance, Solar Energy, Electro-Polishing

Abstract— This paper reports the results of electrical characterization of TiO2/Nb2O5 composite thin films. Uniform TiO2 and Nb2O5 composites thin films were deposited on FTO coated glass substrate using electrophoretic deposition (EPD) technique. The EPD voltage of 35V (DC) and deposition time of 90s, were used for various volume fractions of Nb2O5 in composites. Uniform and crack free composite films were successfully deposited using the EPD technique as shown by the SEM micrographs. The Hall Effect equipment was used to characterize the films through measurement of current and the Hall voltage. Current against Hall voltage plot for films of various volume fractions of Nb2O5 were used to determine Hall coefficients and majority charge carrier density. The sign of Hall coefficient values revealed that TiO2/Nb2O5 composite thin films had a net n-type polarity indicating electrons were the majority charge carrier in the composite films. The results showed that dye-sensitized solar cells should be fabricated with TiO2/Nb2O5 composites thin films in ratio of 1:1 because such ratio 1:1 for TiO2 and Nb2O5 in composite yielded the highest electron mobility in the films.
Keywords— Electrical characterization, TiO2/Nb2O5 composites, Electrophoretic deposition, thin films, Hall Effect

The effects of niobium doping (for doping concentrations: 0.02 – 0.06 at. % Nb5+) on the crystal structure of
TiO2 prepared by high temperature diffusion method were investigated. The samples were characterized using
energy dispersive X-ray fluorescence (EDXRF) and X- ray diffraction (XRD) spectroscopy to investigate the
chemical compositions, phase compositions and crystallinity of the thin films respectively. Despite the expected
high reutilization at high temperatures (>600oC), XRD results confirmed a significant suppression of anatase to
rutile phase transformation at even a higher synthesis (850oC) temperature. Grain growth retardation was also
observed in niobium doped TiO2, results which were attributed to Nb5+ substitution of lattice Ti4+.
Key words: Anatase, rutile, phase transformation, grain growth

In this study doped SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H2O), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters was done so as to obtain high quality thin films. The effect of varying the Fluorine content on the optoelectronic properties of F: SnO2 thin films was studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was obtained using the solid spec 3700DUV spectrophotometer. Electrical characterization of the thin films was done using the four point probe method at room temperature. Post deposition treatment of the thin films by annealing in air then passivating in nitrogen gas environment was done in a tube furnace at 4500C. Sheet resistivity for the as prepared F: SnO2 was found to be 0.4599 Ωcm and 0.00075 Ωcm being the highest and lowest sheet resistivity at 22.74 at% F and 16.41 at% F doping in SnO2 respectively. Low sheet resistivity of F: SnO2 thin films is due substitutional incorporation of F ions instead of oxygen ions into the crystal lattice of SnO2 thin films which increases free carrier concentration. The effect of annealing generally was found to improve on the electrical conductivity of the thin films which is due to increase in carrier mobility and density. Passivation on the other hand had a slight opposite effect. Effects of annealing and passivation on doped SnO2 thin films band gap energy and their transparency was insignificant, rendering the doped SnO2 thin films good choice for making a transparent thin film gas sensors.
Keywords: Spray Pyrolysis, Fluorine Doping, Palladium Doping, Annealing and Passivation

The effects of niobium doping (for doping concentrations: 0.02 – 0.06 at. % Nb5+) on the crystal structure of
TiO2 prepared by high temperature diffusion method were investigated. The samples were characterized using
energy dispersive X-ray fluorescence (EDXRF) and X- ray diffraction (XRD) spectroscopy to investigate the
chemical compositions, phase compositions and crystallinity of the thin films respectively. Despite the expected
high reutilization at high temperatures (>600oC), XRD results confirmed a significant suppression of anatase to
rutile phase transformation at even a higher synthesis (850oC) temperature. Grain growth retardation was also
observed in niobium doped TiO2, results which were attributed to Nb5+ substitution of lattice Ti4+.
Key words: Anatase, rutile, phase transformation, grain growth

In this study doped SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H2O), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters was done so as to obtain high quality thin films. The effect of varying the fluorine content on the optoelectronic properties of F: SnO2 thin films was studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was obtained using the solid spec 3700DUV spectrophotometer. Electrical characterization of the thin films was done using the four point probe method at room temperature. Post-deposition treatment of the thin films by annealing in air then passivating in nitrogen gas environment was done in a tube furnace at 4500C. Sheet resistivity for the as-prepared F: SnO2 was found to be 0.4599 Ωcm and 0.00075 Ωcm being the highest and lowest sheet resistivity respectively (vague. Needs rephrasing for clarity). The low sheet resistivity of F: SnO2 thin films was attributed to substitutional incorporation of F ions instead of oxygen ions into the crystal lattice of SnO2 thin films, a process which increases free carrier concentration. The effect of annealing generally was found to improve the electrical conductivity of the thin films which is due to increase in carrier mobility and density. Passivation on the other hand had a slight opposite effect. Effects of annealing and passivation on the doped SnO2 thin films’ band gap energy and their transparency was insignificant, rendering the doped SnO2 thin films good choice for making a transparent thin film gas sensors.

Porous clay ceramics are used as thermal insulators in high temperature applications such as kins and chacoal stoves (Jikos).

Nano sized powders of TiO2 (titanium dioxide) and Nb2O5 (Niobium (V) oxide) were used to fabricate TiO2/Nb2O5
composites thin films by EPD (electrophoretic deposition) technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR spectrophotometer spectra. The highest (55%) transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC (direct current) voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM (scanning electron microscope) micrographs of the composite electrode thin films showed that porous films
of high quality with well controlled morphology were deposited by using the EPD technique.
Key words: Electrophoretic deposition, TiO2/Nb2O5 composite electrode thin films.

Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution
consisting of stannic chloride (SnCl4.5H20), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters has been done in order to obtain high quality thin films. The effect of varying the fluorine content on the optical properties of Pd-F:SnO2 thin films were studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was measured using the solid spec 3700DUV spectrophotometer. The calculated optical band gap of the as prepared thin films has been found to range from 3.8eV to 4.11eV. Fluorine incorporation for Pd-F:SnO2 has been found to have a narrowing effect on the band gap, but at its higher concentration the band gap has been seen to increase. The
band gap narrowing is due to the incorporation of F- ions in the crystal lattice therefore giving rise to donor levels in the SnO2 band gap which is an essential characteristic for the gas sensor applications. Both annealing and passivation have been found to have very insignificant change in optical band gap of Pd-F:SnO2.

Keywords: Spray Pyrolysis, Fluorine Doping, Palladium Doping, Co-Doping, Palladium and Fluorine Co-Doping, Annealing, Passivation, Pd and F Co-Doped SnO2 (Pd-F:SnO2)

Abstract: Different thin films samples made of SnO2, F:SnO2, Pd: SnO2 and and co-doped Pd-F: SnO2 were deposited at a substrate temperature of 450oC using optimized doping concentrations of F and Pd, thereafter the samples were annealed and passivated in a tube furnace at 450oC. Optical and electrical methods were used in characterizing the thin film samples: The band gap energy for all samples was extracted from optical data using a proprietary software, Scout™ 98. The calculated band gap energy were found to be 4.1135eV for Pd:SnO2 and 3.8014eV for F:SnO2 being the highest and the lowest calculated band gap energies, respectively. The wide band gap energy has been attributed to the incorporation of Pd ions in crystal lattice of SnO2 thin film for Pd:SnO2 while for F:SnO2 has been due to incorporation of F- ions in the crystal lattice of SnO2 which gives rise to donor levels in the SnO2 band gap. This causes the conduction band to lengthen resulting to a reduction in the band gap energy value. The electrical resistivity was done by measuring the sheet resistance of the SnO2, Pd:SnO2, F:SnO2 and Pd-F:SnO2 thin films. The undoped SnO2 thin film had the highest sheet resistivity of 0.5992 Ωcm while F:SnO2 had the lowest sheet resistivity of 0.0075 Ωcm. The low resistivity of F:SnO2 results from substitution incorporation of F- ions in the crystal lattice of SnO2 thin
films, instead of O- ions which lead to an increase in free carrier concentration. The Pd-F:SnO2 gas sensor device was tested for CO2 gas sensing ability using a lab assembled gas sensing unit. The performance of the gas sensor device was observed that: the as prepared device was more sensitive to CO2 gas than those subjected to annealing and passivation. The decrease in the sensitivity of the annealed Pd-F: SnO2 gas sensor is attributed to decrease in grain boundary potential resulting from grain growth. This causes a decrement in adsorption properties of CO- and O- species by the annealed Pd-F: SnO2 thin film. The sensitivity of passivated Pd-F: SnO2 gas sensor was found to be the lowest. The low sensitivity is due to the effects of nitration and decrement in grain boundary potential resulting from grain growth, nevertheless, the sensitivity of the passivated Pd-F: SnO2 thin film was found to be within the range for gas sensing applications.

Keywords: Spray Pyrolysis, Fluorine doping, Palladium doping, co-doping, Palladium and Fluorine co-doping, Annealing, Passivation, F -co- doped Pd:SnO2 (Pd-F: SnO2)

Abstract
Perception of livestock farmers on the generation of cattle waste-based biogas methane was evaluated in this
study. The study was carried out in Embu West district in Kenya. A random sampling technique was used to
gather information related to farmers’ perception and the data collected with the help of self designed
questionnaires and face to face interviews. In the study, 92.9% of the one hundred and fifty six (156) livestock
farmers practiced zero-grazing and only fourteen (9%) of them had installed biogas digesters in their farms. Chi square tests yielded a value of χ = 0.591, p >0.05 which indicated that there was no significant relationship between uptake of cattle waste-based biogas and farmer’s perception. The hypothesis that low uptake of cattle waste-based biogas technology was due to negative perception of the farmers was found not to hold. Further Chi square tests indicated significant relationship (χ=23.56, p< 0.05) between farmers’ perception and knowledge of cattle waste-based biogas methane. Thus livestock farmers in Embu district had a very positive perception and were quite knowledgeable about biogas technology despite the minimal installation of the cattle waste-based biogas digesters. The research findings indicated that other factors like installation cost contribute to the low uptake of biogas technology. These research findings should assist government and industry understand the reason behind public ‘reservations’ in the adoption of biogas technology as well as develop strategies for enhanced promotion of renewable energy technologies.

Keywords: Biogas methane, perception, renewable energy, Embu west

Abstract
Aluminium induced crystallization (AIC) was used to crystallize sputtered amorphous silicon thin films on aluminium-coated glass at annealing temperatures ranging from 250-520°C in vacuum. Crystalline volume fractions were measured by Raman spectrometry as a function of annealing temperature. It was shown that the crystallized films had large grains as the Raman peaks were centred at about 520 cm-1 at and over annealing temperatures of 420°C. The three-layer sample crystallization resulted in crystallization of the films at lower temperatures compared to the two-layer sample crystallizations which implied a reduction in the
cost of production of the seedlayer and resulting products. Hall mobilities and hole densities ranging from 17.0-22.8 cm2V-1s-1and (4.7-9.2) x 1018 cm-3 respectively were measured. Low hole charge densities for films of the same thickness were achieved at high annealing temperatures which was an indication of less aluminium in seed layers prepared at those temperatures. Having seed layers with sufficiently low hole
charge densities is desirable for application of the seed layer in photovoltaic applications.

Key Words: microcrystalline, silicon, annealed, raman, crystallinity, hall-effect

Abstract: Nano sized powders of TiO2 (titanium dioxide) and Nb2O5 (Niobium (V) oxide) were used to fabricate TiO2/Nb2O5 composites thin films by EPD (electrophoretic deposition) technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR
spectrophotometer spectra. The highest (55%) transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC (direct current) voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM (scanning electron microscope) micrographs of the composite electrode thin films showed that porous films of high quality with well controlled morphology were deposited by using the EPD technique.

Key words: Electrophoretic deposition, TiO2/Nb2O5 composite electrode thin films.

Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H20), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters has been done in order to obtain high quality thin films. The effect of varying the fluorine content on the optical properties of Pd-F:SnO2 thin films were studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was measured using the solid spec 3700DUV spectrophotometer. The calculated optical band gap of the as prepared thin films has been found to range from 3.8eV to 4.11eV. Fluorine incorporation for Pd-F:SnO2 has been found to have a narrowing effect on the band gap, but at its higher concentration the band gap has been seen to increase. The band gap narrowing is due to the incorporation of F- ions in the crystal lattice therefore giving rise to donor levels in the SnO2 band gap which is an essential characteristic for the gas sensor applications. Both annealing and passivation have been found to have very insignificant change in optical band gap of Pd-F:SnO2.

Nano sized powders of TiO2 (titanium dioxide) and Nb2O5 (Niobium (V) oxide) were used to fabricate TiO2/Nb2O5 composites thin films by EPD (electrophoretic deposition) technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR
spectrophotometer spectra. The highest (55%) transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC (direct current) voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM (scanning electron microscope) micrographs of the composite electrode thin films showed that porous films of high quality with well controlled morphology were deposited by using the EPD technique.

Sub-Saharan Africa, and more specifically the East African region, has the lowest rates of access to electricity in the world. On average, at most 15% of the rural population has access to electricity. Rural households and remote institutions use traditional energy sources such as charcoal, firewood, kerosene and diesel for generator sets, batteries and dry cell batteries. On the other hand, the region is one of the most promising in the world in economic development with growth levels being high and market saturation is a far away future problem. This growth has
however been hampered by several factors with lack of energy being one of them. Kenya being one of the countries
in the region faces a similar problem with the traditional sources of hydro facing weather related challenges. The
situation is more wanting in the rural setting having only achieved electrification rates of between 5 and 10%. The rural being where the majority of low-income earning groups reside is further compounded with large geographical imbalance in electricity demand and supply. The main challenge to adopting pv utilization however, is lack of local capacity to handle the uptake all the way from solar home systems to grid connected and hybrid systems. According to Kenya Renewable Energy Association (KEREA), it is estimated that between 800 and 1000 pv technicians have been in practice since this sector started in Kenya in the late eighties, majority of them having the basic skills but no formal training to provide the service. They however have been offering necessary service to end-users and are hence an important aspect in the pv sector as a whole. Currently the pv (mainly SHS) comprise an over the counter trade system which provides loopholes when it comes to quality of products and installation. To safeguard the quality and safety of installations, formal training has to be incorporated in the system.

A simple low cost solar cell characterization experiment has been developed for senior undergraduate students in the Department of Physics, University of Nairobi. Experiments were conducted with 20 W and 40 W power solar modules on different sunny days and times at the open roof top of Physics Department, University of Nairobi. It was observed that the current- voltage (I-V) curves obtained for all the measurements were very similar for each module despite the day or time of measurement. The fill factor (FF), short circuit current (Isc), open circuit voltage (Voc), maximum current (Im) and maximum voltage (Vm) were very similar to those supplied by the manufacturer, an indication of reliability and accuracy of the method. The technique eliminates the need for expensive characterization equipment like solar simulators.

In this work, Titanium Dioxide (TiO2) thin films were prepared by spray pyrolysis and thermally annealed at 400℃. The films were characterized as deposited (no annealing) as well as after annealing. Optical studies showed that the energy band gap of the films was lowered from 3.25 eV to 2.90 eV on Nitrogen (N2) doping. The reduction in energy band gap was attributed to the introduction of N2 impurity states on the bands (conduction band and or valence band). The effect of N2 doping of Titanium Dioxide window layer on the efficiency of the ETA TiO2/In(OH)iSj/Pb(OH)xSy solar cell was investigated using a conventional current-voltage (I-V) technique. The photovoltaic conversion efficiency (η) increased from 1.06% for the solar cell with undoped films to 1.32% for the solar cell with N2-doped films. The increase in photovoltaic conversion efficiency on doping was attributed to increased light absorption due to the Nitrogen doping.

Light soaking characterization on complete SnO2:F/TiO2/ln(OH)xSy/PEDOT:PSS/Au, Pb(OH)xS)pEDOT:PSS/Au, eta solar cell structure
as well as on devices which do not include one or both TiO2 and/or PEDOT:PSS layers has been conducted. Additionally,
studies of SnO2:F/In(OH)xSy/PEDOT:PSS/Au solar cell have been performed. The power conversion
efficiency and the short circuit current density have been found to increase with light soaking duration by a factor of
about 1.6 - 2.7 and 2.1 - 3, respectively. The increase in these two parameters has been attributed to the filling up of trap
states and/or charge-discharge of deep levels found in In(OH)xSy. These effects take place at almost fill factor and open
circuit voltage being unaffected by the light soaking effects.

Transport mechanism studies in Ti02/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS eta solar cell have been carried out. The characterizations have been performed both in the dark and under Varying illumination intensity for temperature range 200 K - 320 K. Calculations from ideality factor have shown that the recombination process of the eta solar cell in the dark to be tunneling enhanced, while under illumination it is thermally activated and takes place through exponentially distributed energy recombination levels. The temperature has been found to influence series resistance of the solar cell. Series resistance has been found to be high at low temperature and low at higher temperature, thus we can conclude that the recombination is thermally activated.

ABSTRACT
Light soaking characterization on complete SnO2:F/TiO2/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au, eta solar cell structure as well as on devices which do not include one or both TiO2 and/or PEDOT:PSS layers has been conducted. Addition- ally, studies of SnO2:F/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au solar cell have been performed. The power conversion efficiency and the short circuit current density have been found to increase with light soaking duration by a factor of about 1.6 - 2.7 and 2.1 - 3, respectively. The increase in these two parameters has been attributed to the filling up of trap states and/or charge-discharge of deep levels found in In(OH)xSy. These effects take place at almost fill factor and open circuit voltage being unaffected by the light soaking effects.

Keywords: Eta Solar Cell; Light Soaking; Conversion Efficiency; TiO2; In(OH)xSy; Pb(OH)xSy

Transport mechanism studies in TiO2/In (OH) xSy/Pb (OH) xSy/PEDOT: PSS eta solar cell have been carried out. The characterizations have been performed both in the dark and under varying illumination intensity for temperature range 200 K–320 K. The recombination process of the eta solar cell in the dark has been found to be tunneling enhanced, while under illumination it is thermally activated and takes place through exponentially distributed energy recombination levels. The illumination intensity and temperature have also been found to have a strong influence on the device conversion efficiency, with the highest efficiency being realized at 200 K

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Undoped and nitrogen-doped titanium dioxide (TiO2) thin films of 400 nm thick deposited by spray pyrolysis were structurally and optically characterized. The effect of substrate temperature on the optical properties of the films was also investigated. Structural studies of the films were undertaken by X-ray diffraction (XRD). Energy dispersive X-ray (EDX) spectrum analysis was used to confirm the presence of nitrogen atoms in the film after doping. The optical properties such as refractive index (n), energy band gap (Eg) and Urbach energy (Eu) were determined from spectrophotometric measurements of reflectance and transmittance for both undoped and doped films. The Undoped films had an energy band gap of 3.25 eV while the doped films had band gap of 2.90 eV. The Urbach energy increased from 1.00 eV for undoped films to 1.04 eV for the nitrogen-doped films. The reduction in energy band gap and increase in Urbach energy was attributed to the introduction of nitrogen impurity tail states on either the conduction band or the valence band of the titanium dioxide.

The study, manipulation and design of materials and devices at level approaching atomic sizes has given rise to nanoscience and nanotechnology, with the former being concerned more with the new properties whereas the latter - nanotechnology focuses on new devices. The nanoscale science and technology involves and cuts across different disciplines. It is now recognized that science founded on the unified concepts on matter at the nanoscale is the new basis for knowledge creation, innovation, and technology integration, and therefore receiving heightened attention world over.

Arising from the current and potential impacts of nanoscience and nanotechnology in all facets of humanity – way of life, health and the environment, it is imperative that any country takes stock of the status of the two intertwined disciplines. For example, it is known that nanotechnology can improve efficiency in manufacturing, energy resources and utilization, reduce environmental impacts of industry and transportation, enhance healthcare, produce better pharmaceuticals, improve agriculture and food production, and expand the capabilities of information technologies. The level of preparedness of a country to create new knowledge, exploit it or absorb such, it will be seen depends on the synergistic relationships amongst all the stakeholders right from the beginning of the research, product development processes, and policy and legislative frameworks that protect the workers producing and consumers of such products.

A study of the Kenya’s situation reveals that so far there minimal understanding or appreciation of what nanoscience and nanotechnology are amongst the key stakeholders, and what their potential benefits are or would be. The teaching of and research in these areas and the accompanying infrastructure are weak and uncoordinated. The regulatory frameworks and policies governing, particularly the manufacturing processes of or nanoscale products are either nonexistent or very weak/inadequate.

Key words: Nanoscience, Nanotechnology, Research, Policies, Kenya

The study, manipulation and design of materials and devices at level approaching atomic sizes has given rise to nanoscience and nanotechnology, with the former being concerned more with the new properties whereas the latter - nanotechnology focuses on new devices. The nanoscale science and technology involves and cuts across different disciplines. It is now recognized that science founded on the unified concepts on matter at the nanoscale is the new basis for knowledge creation, innovation, and technology integration, and therefore receiving heightened attention world over.

Arising from the current and potential impacts of nanoscience and nanotechnology in all facets of humanity – way of life, health and the environment, it is imperative that any country takes stock of the status of the two intertwined disciplines. For example, it is known that nanotechnology can improve efficiency in manufacturing, energy resources and utilization, reduce environmental impacts of industry and transportation, enhance healthcare, produce better pharmaceuticals, improve agriculture and food production, and expand the capabilities of information technologies. The level of preparedness of a country to create new knowledge, exploit it or absorb such, it will be seen depends on the synergistic relationships amongst all the stakeholders right from the beginning of the research, product development processes, and policy and legislative frameworks that protect the workers producing and consumers of such products.

A study of the Kenya’s situation reveals that so far there minimal understanding or appreciation of what nanoscience and nanotechnology are amongst the key stakeholders, and what their potential benefits are or would be. The teaching of and research in these areas and the accompanying infrastructure are weak and uncoordinated. The regulatory frameworks and policies governing, particularly the manufacturing processes of or nanoscale products are either nonexistent or very weak/inadequate.

Electron transport and recombination has been investigated in dye-sensitized electrochemical solar cells at varying TiO2 film thickness using experimental electrochemical potential technique. Photocurrent transients resulting from small-amplitude square wave modulation of the incident light were analyzed, and the effect of illumination intensity and film thickness studied. Photovoltage decay measurements were studied on solar cells when switched from short-circuit and under illumination to open circuit and dark at varying illumination intensity for different film thickness. The analysis was done for varying film thickness at constant illumination intensity and varying illumination intensity at constant film thickness. The varying film thicknesses in this study were 3.0 m, 6.0 m, 12.8 m, 23.5 m and 25.3 m while illumination intensities were 0.5, 1.2, 2.4, 5.1, 9.0 and 15.6 mWcm-2. The voltage decay measured (known as open circuit voltage, Vsc) was seen to first rise to a maximum value then followed by decay. The maximum Vsc (Vsc, max) increased with film thickness at constant prior illumination. On the other hand, Vsc, max was found to depend on the prior illumination and exhibited logarithmic increase with light intensity. The time (tmax) to attain Vsc, max varies exponentially with light intensity and closely matches the electron transport time measured by photocurrent decay measurements.

The thermal shock resistance of porous ceramic materials is often characterized by the Hasselman parameters. However, in other
scenarios, the room-temperature residual strengths after thermal shock are also used to quantify the damage due to thermal shock.
This paper attempts to link the measured residual strengths to the dominant crack features that are introduced due to thermalshock in porous clay ceramics produced by the sintering of clay powders with well-controlled size ranges. Residual strength estimates from bend tests are compared with fracture mechanics predictions. The implications of the residual strength results are then discussed for the characterization of damage due to thermal shock.

This study investigated the effectiveness of three physical-chemical methods namely; pH adjustment, precipitation with alum and the use of polyelectrolytes. In the treatment of diary wastewater from Brookeside milk processing plant. It also investigated the drainability of the sludge produced by each of the three methods. Laboratory tests were carried out in three different batches, one for each of the three methods. In the alum method enough alum was added to the wastewater samples to cause precipitation by sweep floc. In the pH adjustment method, the pH of samples were lowered to the iso-electric point of the casein proteins of approximately pH 4.5 leading to their precipitation as a result of solubility changes. The polyelectrolytes method involved the use of two polyelectrolytes, Sudfloc 3820 and Sudfloc 3860 each of which was used to coagulate the dirty wastewater. For each of the three methods, the samples were taken in one-litre beakers and subjected to Jar tests to determine the optimum dosages. After one hour of settling the supernatants were decanted and subjected to standard Chemical Oxygen Demand (COD) tests, turbidity and pH measurements. The settled sludge was subjected to drainability studies. Results showed the treatment of dairy wastewater by the three physical-chemical methods to be effective. There were COD removals of between 60% and 90% and turbidity reduction of over 90%. The use of the sudfloc polyelectrolytes was found to be the least demanding in terms of effluent quality control as no pH adjustments of either the wastewater or the effluent was required. The use of polyelectolytes produced the least volumes of sludge and also the better drainability and solids concentration. Sudfloc 3820 was found to achieve better results than Sudfloc 3860 in terms of COD reduction and the drainability of sludge produced although both achieved the same drainability studies. This study showed that each of the three physical-chemical methods can be used effectively to remove the white colour of dairy wastewater as well as the bulk of the proteins and fats, hence, enabling the discharge of the effluents into natural waters to be of good assimilative capacity.

Abstract This paper presents the results of a combined experimental and theoretical study of microstructure and thermal shock resistance of an aluminosilicate ceramic. Shock-induced crack growth is studied in sintered structures produced from powders with different particle size ranges. The underlying crack/microstructure interactions and toughening mechanisms are elucidated via scanning electron microscopy (SEM). The resulting crack-tip shielding levels (due to viscoelastic crack bridging) are estimated using fracture mechanics concepts. The implications of the work are discussed for the design of high refractory ceramics against thermal shock.

Keywords Viscoelastic crack bridging . Crack-tip shielding . Thermal shock . Refractory ceramics

Kenya is a developing country aspiring to gain the status of an industrialized country by the year 2030. In pursuit of this political goal various policies and targets are being proposed and pursued. It has thus become very apparent that the stated goal would not be achieved unless there is sufficient exploitable energy available to meet the anticipated demand. To this end various options such as nuclear energy, exploration of oil, exploitation of the geothermal energy reservoirs, building of windmills for energy generation, solar energy, and biofuels are proposed. We discuss Kenya’s present situation and preparedness with respect to the stated goal and how these present and proposed sources of energy have impacted/will impact on the environment and climate and development.

An highly structured TiO2/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au
device has been fabricated. It has been anaylsed for morphological
and optoelectrical properties by scanning electron microscopy,
surface photovoltage spectrscopy and temperature dependent JUT.
The device has been found to undergo thermally activated
recombination at high temperatures while tunneling enhanced
recombination dominates the process at low temperatures

Nanotechnology is the understanding and control of
matter at dimensions between approximately 1 and
100 nanometers, where unique phenomena enable
novel applications. Encompassing nanoscale science,
engineering, and technology, nanotechnology involves
imaging, measuring, modeling, and manipulating
matter at this length scale. Increased energy
efficiency, a cleaner environment, more effective
medical treatment and improved manufacturing
production are just some of the potential benefits of
nanotechnology. Biologists, chemists, physicists and
engineers are all involved in the study of substances at
the nanoscale.

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Nanoscience and nanotechnology deal with the study, manipulation, and the design of materials and devices at the atomic scale. Whereas nanoscience focuses on the new properties, nanotechnology focuses on new devices. The nanoscale science and technology is multidisciplinary and trans-disciplinary. We thus see that nanoscience and nanotechnology bridge the gap between molecular scale and the macroscale. It is now recognized that science founded on the unified concepts on matter at the nanoscale is the new basis for knowledge creation, innovation, and technology integration.
Given the current and anticipated impacts of nanotechnology in work efficiency, ways of life and the environment, national (e.g. Kenya’s) efforts should be focused on how nanotechnology can improve efficiency in manufacturing, energy resources and utilization, reduce environmental impacts of industry and transportation, enhance healthcare, produce better pharmaceuticals, improve agriculture and food production, and expand the capabilities of information technologies. This requires synergistic relationships amongst all the stakeholders right from the beginning of the research and development processes.
A study of the Kenya’s situation reveals minimal understanding of what nanoscience and nanotechnology, and what their potential benefits are. The teaching of and research in these areas and the accompanying infrastructure are weak and disjointed. Moreover, there are almost nonexistent/weak specific regulatory tools and policies governing this important but emerging technology and discipline. Gaps presently exist in our scientific knowledge, and coupled with inadvertent outcomes witnessed in other technological advances there are reasons enough for nanotechnology industries and relevant government agencies to invest in understanding possible risks and neutralize them prior to putting the products into the market.

This study investigated the effectiveness of three physical-chemical methods namely; pH adjustment, precipitation with alum and the use of polyelectrolytes. In the treatment of diary wastewater from Brookeside milk processing plant. It also investigated the drainability of the sludge produced by each of the three methods. Laboratory tests were carried out in three different batches, one for each of the three methods. In the alum method enough alum was added to the wastewater samples to cause precipitation by sweep floc. In the pH adjustment method, the pH of samples were lowered to the iso-electric point of the casein proteins of approximately pH 4.5 leading to their precipitation as a result of solubility changes. The polyelectrolytes method involved the use of two polyelectrolytes, Sudfloc 3820 and Sudfloc 3860 each of which was used to coagulate the dirty wastewater. For each of the three methods, the samples were taken in one-litre beakers and subjected to Jar tests to determine the optimum dosages. After one hour of settling the supernatants were decanted and subjected to standard Chemical Oxygen Demand (COD) tests, turbidity and pH measurements. The settled sludge was subjected to drainability studies. Results showed the treatment of dairy wastewater by the three physical-chemical methods to be effective. There were COD removals of between 60% and 90% and turbidity reduction of over 90%. The use of the sudfloc polyelectrolytes was found to be the least demanding in terms of effluent quality control as no pH adjustments of either the wastewater or the effluent was required. The use of polyelectolytes produced the least volumes of sludge and also the better drainability and solids concentration. Sudfloc 3820 was found to achieve better results than Sudfloc 3860 in terms of COD reduction and the drainability of sludge produced although both achieved the same drainability studies. This study showed that each of the three physical-chemical methods can be used effectively to remove the white colour of dairy wastewater as well as the bulk of the proteins and fats, hence, enabling the discharge of the effluents into natural waters to be of good assimilative capacity.

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A new highly structured In(OH)xSy/Pb(OH)xSy/PEDOT:PSS solar cell has been
developed based on the novel eta concept, and characterized by photovoltage spectroscopy, X-ray
photoelectron spectroscopy, scanning electron spectroscopy, photovoltaic response and quantum
efficiency spectroscopy. In this system, In(OH)xSy, PbS and PEDOT:PSS serve as electron conductor,
light photon absorber material and hole conductor respectively. The electron conductor and absorber
layer were prepared by chemical bath deposition, while the hole conductor was prepared by spin
coating technique. The band gap of as prepared In(OH)xSy has been found to vary with pH of the
solution; furthermore the bandgap of Pb(OH)xSy can be engineered to make it suitable as absorber
material.

The fracture properties of kaolin – based refractories prepared using plant derived binders from okra and
“mrenda” have been investigated. It was observed that okra binder improved the MOR of fired samples from 194.0± 0.1 MPa to 384 ± 0.1 MPa, while the fracture toughness increased from 3.9 ± 0.1 MPa (for binder free samples) to 5.6 ± 0.1 MPa and 5.7 ± 0.1 MPa for okra and ‘mrenda’ plasticized samples respectively. It is concluded that the use of organic binders enhances the reliability and service life of kaolin refractories used in thermally fluctuating environments.

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Dye sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering have been investigated in detail. Electron transport and recombination were studied using intensity-modulated photocurrent and photovoltage spectroscopy. Electron transport time as well as lifetime was found to increase upon lowering of the light intensity and to increase upon increasing the thickness of the TiO2 film. The properties are very similar to those observed for solar cells based on colloidal TiO2 films despite the morphologies being very different. In all cases, films are composed of a porous assembly of TiO2 nanocrystals. Grain boundaries with associated trap and/or energy barriers may explain the observed transport properties.

A new highly structured TiO2/In(OH)xSy/PbS/PEDOT:PSS solar cell has been developed based on the novel eta concept, and characterized by photovoltage spectroscopy, X-ray photoelectron and Auger electron spectroscopies, scanning electron spectroscopy, photovoltaic response and quantum efficiency spectroscopy. In this system, TiO2, In(OH)xSy, PbS and PEDOT: PSS serve as electron conductor, recombination barrier, absorber and hole conductor respectively. The buffer and the absorber layer were prepared by chemical bath deposition, while the electron and hole conductor were prepared by spray pyrolysis/sol-gel and spin coating respectively. The band gap of as prepared In(OH)xSy has been found to vary with PH of the solution, also the band gap of PbS can be engineered to make it suitable as absorber material for solar cell application. At present, a solar cell device has been realized with efficiency up to over 1%, Jsc = 8 mA/cm2 and Voc= 3.0 V.

The fracture characteristics of a kaolin – based refractories prepared using a plant derived binder (from okra) have been investigated. Plasticization with the binder improved the MOR of fired samples by 79.4%, while the fracture toughness increased by 44.3%. Both the Weibull modulus m and the slow crack growth propagation parameter n, also improved in comparison to those plasticized with plain water (no binder). Thus the use of organic binders enhances the reliability and service life of kaolin refractories used in thermally fluctuating environments.

Excitonic solar cells which include organic, hybrid organic–inorganic and dye-sensitized cells (DSSCs) promise inexpensive, large-scale solar energy conversion devices. We report on the charge transport (electron drift mobility) sputter deposited TiO2 and surface photovoltage and photocurrent transients of alumina-passivated TiO2, and on the conversion efficiency of dye-sensitized cells whose photoelectrodes are sputtered.

Electron transport in bare and MgO-coated colloidal TiO2 thin films has been studied using surface photovoltage spectroscopy (SPS), while the charge transport in dye-sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering has been studied by the intensity–modulated photocurrent and photovoltage spectroscopy (IMPS and IMVS). The SPS results obtained showed a dispersive electron transport with strongly retarded photocurrents, and the electron diffusion coefficient measured in a parallel plate capacitor arrangement was observed to be strongly dependent on film thickness. Further, the MgO buffer layer initially enhanced the effective diffusion coefficient but beyond certain MgO concentration the diffusion coefficient decreased. From the IMPS/IMVS studies, the electrons transit more rapidly at higher light intensities whereas the electron lifetime diminishes with increase in light intensity. The electron transit and lifetimes were found to increase with film thickness. Grain boundaries with associated trap and / or energy barriers and their passivation by MgO are proposed to explain the observed transport properties.

In this study, the critical deposition parameters of electrophoretic deposition (EPD) of materials are reviewed and its potential use in the production of thin films for photocatalytic oxidation of organic compounds are analyzed. In a case study, EPD was used to obtain titanium dioxide (TiO2) coatings on glass substrates using colloidal suspensions of TiO2 nanoparticles in ethanol with addition of iodine. The deposit parameters were optimized to obtain homogeneous and strongly adhered TiO2 thin films. The factors that determine the efficiency of TiO2 in the decomposition of organic contaminants are also presented.

In recent years, there has been increasing interest in the use of electrophoretic deposition (EPD) in the production of oxidation and corrosion protective ceramic coatings. In this study, we address the kinetics and dynamics of submonolayer formation during EPD. The effect of constant current and constant voltage deposition conditions on deposition rate are analyzed and experimental data compared to theoretical models.

TiO2 nanofibres have been synthesized by a simple hydrothermal process in 10M NaOH. TEM images have shown that nanofibres measuring average length 500nm and diameter 10nm were formed by this method. XRD analysis indicated strong anatase peaks with crystal orientation in the direction (101) with slight rutile peaks appearing at 5000C calcinations temperature. Thin films prepared from the nanofibres had thickness varying from 4.5 – 5.5μm. The films were used to fabricate complete dye sensitised solar cells with Ruthenium complex dye as sensitizer. I-V characteristics yielded Voc and Jsc of 0.46V – 0.58V and 0.16mA/cm2 – 4.5mA/cm2 respectively under standard illumination of 100mW/cm2 (using a halogen lamp and data acquired using Keithley 2400 Source Meter® controlled by LabVIEW® software).

Temperature dependent current - voltage measurements have been used to characterize an highly structured TiO2/In(OH)xSy/PbS/PEDOT:PSS eta solar cell, which under AM1.5 had the following parameters: Voc = 0.249V, Jsc = 9.24mA/cm2, a fill factor FF = 0.339 and an efficiency of 0.78%. The current voltage characterizations have been done in the dark as well as under illumination. Diode ideality factor A under illumination has been found to be between 1 < A < 2 while in the dark A > 2. Recombination mechanism of the charge carriers has been found to be dominated by tunneling in the dark, while under illumination the charge carrier recombination is thermally activated. In this device, the type and place of the dominant recombination mechanism has been found to depend on illumination.

In this study, electrophoretic deposition (EPD) technique was used to deposit TiO2 thin film on a conducting glass substrate for use in water purification from organic contaminants. The optimum deposition parameters of a good quality film in terms of adherence to the substrate, homogeneity of the film and the extent of microcracking upon drying were: ethanol for obtaining a stable suspension, a pH of 3 for best stability of the suspension and the speed of coating, TiO2 loading concentration of 4 wt %; 0.3wt% iodine dispersant with respect to TiO2 concentration, an applied voltage of 25 volts, and films’ sintering temperature of 573 K for highest photocatalytic activity. The quantitative analysis of phenol by bromination method was used to determine photocatalytic decomposition of phenol in water.

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Nanocrystalline porous titanium oxide films of varying thickness have been deposited in ambient by reactive DC magnetron sputtering at a fixed but high oblique angle of 60o, and then converted to TiO2 by thermal annealing at 450 oC for 4 hours. X-ray diffraction analysis of the films showed that they were predominantly of anatase phase, whereas the as deposited films were amorphous. Top–down scanning electron microscope images of the annealed films showed cauliflower-like surfaces, and exhibited well-defined columns. Atomic force microscope images revealed rough surfaces with larger nodules for thicker films. With the annealed films as the working electrodes in a dye-sensitised solar cell, it was established that the photoelectric conversion efficiency increased with the film thickness. The highest efficiency was ~ 3.3 % at an illumination intensity of 100 W/m2.

In this short article we discuss what Material Science is, its scope, relevance to technological development, its present status in Kenya, and finally propose a way forward. Materials science has been defined as that study that focuses on the material property-structure relationship. It is concerned with how the nano- or micro- or macrostructure determines the various functional properties of the materials desired or of interest. Materials science thus deals with, in an interactive manner, processing, structure, properties, and performance of materials, a relationship which has been summarized as the Materials Science Tetrahedron. It is a multi-and transdisciplinary subject as it is intimately related to basic science subjects like applied physics, chemistry, biology and to various engineering disciplines such as mechanical, electrical, or civil, engineering.

The area of nanostructured materials for dye sensitized solar cells has gained great interest by scientists, especially after a breakthrough by Gratzel and coworkers in developing a solar cell from nanostructured oxide of titania gaining an overall efficiency of about 11%. Since then research has been going on with emphasis on improvement on this achievement.

TiO2 nanofibres measuring average length 500nm and diameter 10nm have been prepared by synthesis method using 10M NaOH and dispersed in alcohol. Thin films prepared from the nanofibres had thickness varying from 4.5 – 5.5μm. The films were used to fabricate complete dye sensitised solar cells with Ruthenium complex dye as sentizer. I-V characteristics yielded Voc and Isc of 0.41V – 0.58V and 0.18mA – to 1.1mA respectively under standard illumination of 100mW/cm2 (using a halogen lamp and data acquired using Keithley 2400 Source Metre® controlled by LabVIEW® software). XRD analysis indicated strong anatase peaks with crystal orientation in the direction (101). This showed that there was no lose of crystalline structure of the TiO2 during the synthesis process. However, as the sintering temperature was raised, the percentage crystal content of anatase reduced as the rutile structure slowly formed.

Nanostructured materials for dye sensitised solar cells (DSSSC) have gained a lot of interest since the breakthrough of 11% solar cell based on TiO2 [1]. A DSSC typically consists of a monolayer of photoactive dye molecules anchored onto the nanoparticles of a wide band gap semiconductor, an electrolyte and a platinised counter electrode.

The focus in our research group are (1) preparation and characterisation of the photoactive electrode (TiO2), (2) nitrogen/metallic oxide doping of the photoactive electrode, (3) identification of natural anthocyanin dye containing plants, extracting and synthesizing and purifying the dye for use as an alternative to the costly ruthenium based dye, (4) improvement on the charge transfer characteristics from the dye to the semiconductor and hence in the whole system, (5) charactrization and optimization of eta solar cell based on TiO2/In(OH)xSy/PbS/PEDOT.PSS/Au and (6) tailoring of semiconductor surface using ultra thin Al2O3 thin film.

TiO2 films were prepared by reactive DC sputtering and from TiO2 nanotubes prepared by synthesis method using 10M NaOH and dispersed in alcohol. XRD, SEM and TEM were used to characterize the electrodes. IPCE and I-V characteristics of the solar cells were obtained and compared with the electrode properties and structures. Some results, discussions and conclusions are presented.

Various studies have revealed that incorporation of cations of valence higher than that of the parent cations e.g., W6+, Ta5+, Nb5+ into the crystal matrix of TiO2 enhances its rate of photoactivity. In the present study, we propose incorporation of Nb5+, pentavalent dopant into TiO2 matrix in order to attempt to establish its optimal concentration for maximum photoactivity. The niobium-doped TiO2 was prepared by high temperature diffusion of the doping cations into the crystal matrix of the parent oxide. The doped samples were found to change from white to light yellow/brown. XRD analysis for anatase-rutile content of the doped samples was performed. At low mol% Nb (0.1197 – 0.2360) in TiO2, the crystalline structure was predominantly rutile at calcinations temperature of 650 oC, but at high mol% Nb (> 1.0000), a relatively higher anatase content was observed at the same calcinations temperature for a period of 2.5 hours.

Energy is important to life, and the amount of energy consumed per capita by a country is indicative of the level of development of that nation. There exist different sources of energy with solar energy as the primary source on our planet. The sun’s energy is inexhaustible, unlimited (by geographical boundaries), and non-polluting. Tapping and utilizing this energy efficiently- even with 10 to 20% efficiency- can solve the threat of climate change caused by the global warming, and also contribute towards the easing of the demand for fossil-fuel. In the developing countries a large proportion of the population is poor and not connected to the national electricity grid. This group of people is weighed down with the high cost, high risks and low benefits of the traditional fuels, candles, paraffin, and dry battery cells. Addressing their energy needs, particularly with clean energy from the renewable sources, will not only result in tangible developmental benefits but also social and environmental benefits. In this article we consider only the direct energy from the sun, and its conversion to heat or electrical forms- the energy carriers of choice.

Nanocrystalline porous titanium oxide films of varying thickness have been deposited in ambient by reactive
DC magnetron sputtering at a fixed but high oblique angle of 60o, and then converted to TiO2 by thermal
annealing at 450 oC for 4 hours. X-ray diffraction analysis of the films showed that they were predominantly of
anatase phase, whereas the as deposited films were amorphous. Top–down scanning electron microscope
images of the annealed films showed cauliflower-like surfaces, and exhibited well-defined columns. Atomic
force microscope images revealed rough surfaces with larger nodules for thicker films. With the annealed films
as the working electrodes in a dye-sensitised solar cell, it was established that the photoelectric conversion
efficiency increased with the film thickness. The highest efficiency was ~ 3.3 % at an illumination intensity of
100 W/m2.

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The effect of quartz and mullite crystalline phases on the strength of triaxial porcelain in the system
quartz-feldspar-kaolin composed of 20%wt silica and feldspar/kaolin ratio of 5:8 has been
investigated. It was found that secondary mullite crystals enhanced both the compressive strength and
elastic properties of porcelain by the interlocking mechanism. Excess glass formation decreased the
fracture strength of porcelain as a result of the combined effect of circumferential cracks around
quartz grains and the microcracks within the quartz grains. The circumferencial cracks due to the
difference in the thermal expansion coefficient mismatch between the glassy and the quartz phases,
whereas the microcracks were due to a- to b- quartz phase inversions.

Thermal conductivity values, in the temperature range 300 – 1200 K, have been measured in air and at
atmospheric pressure for a Kenyan kaolinite refractory with 0% - 50% grog proportions. The experimental
thermal conductivity values were then compared with those calculated using the Zumbrunnen et al [1] and the
Litovsky and Shapiro [2] theoretical models. The experimental values for samples prepared without or low
percentages of grog increased with temperature as predicted by both the theoretical models. On the contrary,
the conductivity values for the sample containing ³ 40% decreased with increase in temperature in a manner
consistent with the Eucken law.

In this study, we have reviewed recently published strength-porosity data of porous
ceramics, and compared these data with those computed from both the minimum contact solid area
(MCA) and the pore stress concentration effect (SCE) models. We observed that the theoretical data
(MCA model) matched better the experimental results of ceramics in the low volume fraction porosity
range (P < 0.25) range, whereas in the volume fraction porosity range (P > 0.25), the SCE model better
predicts the experimental results.

The effect of corchorus olitorius derived binder on the effective thermal conductivity of a kaolinite-based
refractory was investigated. Strong dependence of (effective) thermal conductivity of fired samples on the
binder concentration, temperature and porosity was noted. Comparison of experimental data with Effective
Medium Approximation (EMA) and Geometric Mean Model (GMM) theories showed that predictions from
EMA agreed better with the experimental data than those from GMM. This was attributed to the EMA model
being more rigorous and contained more microstructural information than the simpler GMM.

A review of recently published ultrasonic velocity-porosity data on a variety of porous ceramic materials,
which included information on the pore structure, has been undertaken. These experimental data have been
compared with those calculated using a spheroidal pore model that incorporates information on pore volume
fraction, shape and orientation. Good agreement, especially when fractional porosity is less than ~ 0.25,
between the experimental and calculated values is obtained even when a single ‘effective’ pore shape is
employed in the calculation. The agreement improves if the pore shape at each particular porosity level (the
point-by-point analysis) is used. The predictive ability of the spheroidal pore model is therefore demonstrated.

The effect of corchorus olitorius derived binder on the effective thermal conductivity of a kaolinite-based refractory was investigated. Strong dependence of (effective) thermal conductivity of fired samples on the binder concentration, temperature and porosity was noted. Comparison of experimental data with Effective Medium Approximation (EMA) and Geometric Mean Model (GMM) theories showed that predictions from EMA agreed better with the experimental data than those from GMM. This was attributed to the EMA model being more rigorous and contained more microstructural information than the simpler GMM.

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