Bio

Publications


2018

Nguu, J, Nyongesa F, Robinson Musembi, Aduda B.  2018.  Electrophoretic Deposition and Characterization of TiO2/Nb2O5 Composite Thin Films for Dye Sensitized Solar Cells. AbstractJournal article website

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

2017

Nyarige, JS, WAITA SEBASTIAN, Simiyu J, Mureramanzi S, Aduda B.  2017.  Structural and Optical Properties of Phosphorous and Antimony doped ZnO thin films Deposited by Spray Pyrolysis: A Comparative Study. International Advanced Research Journal in Science, Engineering and Technology. 4(11) Abstract

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.

Nyongesa, F, Aduda BO.  2017.  Electrophoretic Deposition of Titanium Dioxide Thin Films for Photocatalytic water purification systems. ResearchGate/publication/319331243. Abstract
n/a
Mulati, DM, Nyang'onda TN, Aduda BO.  2017.  Raman Crystallinity and Hall Effect Studies of Microcrystalline Silicon Seed Layers. Journal of Agricultural Science and Technology. 16(1):106-118. AbstractJournal Website Link

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

WAITA, SEBASTIAN, Aduda B.  2017.  Emphasis on Photovoltaic (PV) Solar System Installation Training: A Case Study of a PV Solar System Installed in Makueni County, Kenya. International Advanced Research Journal in Science, Engineering and Technology. 3(8):31-37. AbstractJournal Article Website

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

Nyongesa, F, Aduda BO.  2017.  Electrophoretic Deposition of Titanium Dioxide Thin Films for Photocatalytic water purification systems. Advances in Materials. 6(4):31-37. AbstractJournal Article Website

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

2016

WAITA, SEBASTIAN, Aduda B.  2016.  PHOTOVOLTAIC (PV) SOLARSYSTEM SIZING FOR OFF GRID SOLAR HOME SYSTEMS. International Journal of Applied and Natural Sciences (IJANS). 5(5):2319-4022. Abstract

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.

Ayieko, CO, Musembi RJ, Ogacho AA, Aduda BO, Muthoka BM, Jain PK.  2016.  Optical Characterization of TiO2-bound (CuFeMnO4) Absorber Paint for Solar Thermal Applications. American Journal of Energy Research. 4(1):11-15. AbstractJournal Article Website

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

Ogacho, A, Aduda BO.  2016.  Structural, Optical and Photoelectrochemical Properties of Cuprous Oxide Synthesized by Low Temperature Thermal Oxidation. Material Science Research India. 13(1):01-06. AbstractJournal Article Website

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).

WAITA, SEBASTIAN.  2016.   Emphasis on Photovoltaic (PV) Solar System Installation training: A case study of a PV Solar System Installed in Makueni County, Kenya . International Advanced Research Journal in Science, Engineering and Technology . 3(8) Abstract

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

2015

Nyongesa, FW, B. O. Aduda, Agacho AA.  2015.  Organic Binders to Enhance Efficiency of Charcoal Stoves (Jikos) & Water Filters, 6-11 December. 8th International Conference of the Africa Materials Resecrah Society (A-MRS). , Accrea, Ghana Abstract

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

Mwathe, PM, Robinson Musembi, Munji M, Nyongesa F, Odari B, Njoroge W, Aduda B, Muthoka B.  2015.  Effect of Annealing and Surface Passivation on doped SnO2 thin filmsPrepared by Spray Pyrolysis Technique. Elservier. Abstract

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.

Alex Awuor Ogacho, Ajuoga P, Aduda BO.  2015.  Suppression of Anatase to Rutile Phase Transformation of Niobium doped TiO2 Synthesized by High Temperature Diffusion Technique. International Educative Research Foundation and Publisher. 3(6):140-146. AbstractJournal Website Link

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

Mwathe, PM, Robinson Musembi, Munji M, Nyongesa F, Odari B, Njoroge W, Aduda B, Muthoka B.  2015.  Effect of Annealing and Surface Passivation on Doped SnO2 Thin Films Prepared by Spray Pyrolysis Technique . Advances in Materials. 4(3):51-58. AbstractJournal Website Link

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

Alex Awuor Ogacho, Ajuoga P, Aduda BO.  2015.  International Journal for Innovation Education and Research. International Journal for Innovation Education and Research. 3(6):140-146. AbstractJournal Article Website

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

Nguu, JN, Aduda BO, Nyongesa FW, Njogu SM, Mwathe PM.  2015.  Electrical Characterization of Nano-TiO2/Nb2O5 Composite Thin Films Deposited Using Electrophoretic Deposition. International Journal of Innovative Research in Advanced Engineering. 2(2):192-198. AbstractJournal Article Website

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

Ayieko, CO, Musembi RJ, Ogacho AA, Aduda BO, Muthoka BM, Jain PK.  2015.  Controlled Texturing of Aluminum Sheet for Solar Energy Applications. Advances in Materials Physics and Chemistry,. 5:458-466. Abstractjournal article website

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

2014

WAITA, SEBASTIAN, Simiyu J, Kiragu AN, Imali V, Aduda B.  2014.  A Simple Low Cost Solar Cell Characterization Laboratory Experiment for Senior Undergraduate Students. AbstractFull text link

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.

Simiyu, J, WAITA SEBASTIAN, Robinson Musembi, Ogacho A, Aduda B.  2014.  Promotion of PV Uptake and Sector Growth in Kenya through Value Added Training in PV Sizing, Installation and Maintenance. Energy Procedia. 57:817–825. Abstract

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.

Nguu, JN, Aduda BO, Nyongesa FW, Musembi RJ.  2014.  Electrophoretic Deposition of TiO2/Nb2O5 Composite Electrode Thin Films for Photovoltaic Application. Journal of Energy and Power Engineering . 8:757-764. 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.

Munguti, LK, Mwathe PM, Robinson Musembi, Munji M, Odari B, Ntilakigwa AA, Nguu J, Aduda B, Muthoka B.  2014.  EFFECT OF PROCESS-RELATED PARAMETERS ON BAND GAP OF ELECTROPHORETICALLY DEPOSITED TIO2NB2O5 COMPOSITE THIN FILMS. Science Publishing Group. 1 AbstractFull text Link

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.

Nguu, JN, Aduda BO, Nyongesa FW, Musembi RJ.  2014.  Electrophoretic Deposition of TiO2/Nb2O5 Composite Electrode Thin Films for Photovoltaic Application. Journal of Energy and Power Engineering. 8 (2014):757-764. Abstract

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.

Nyang'onda, TN, Mulati DM, Aduda BO.  2014.  Raman Crystallinity and Hall Effect Studies of Microcrystalline Silicon Seed Layers. Silicon seed layers. 16(1):106-117. AbstractJournal article website

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

Nguu, J, Ndivo S, Aduda B, Nyongesa F, Robinson Musembi.  2014.  Livestock Farmers’ Perception on Generation of Cattle Wastebased Biogas Methane: the Case of Embu West District, Kenya. Journal of Energy Technologies and Policy. No.8(Vol.4) Abstract

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

Mwathe, PM, Robinson Musembi, Munji M, Odari B, Munguti L, Ntilakigwa AA, Mwabora J, Njoroge W, Aduda B, Muthoka B.  2014.  Surface passivation effect on CO2 sensitivity of spray pyrolysis deposited Pd-F: SnO2 thin film gas sensor. 2014; 3(5):38-44. Abstract

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)

Mwathe, PM, Robinson Musembi, Munji M, Odari B, Munguti L, Ntilakigwa AA, Nguu J, Aduda B, Muthoka B.  2014.  Influence of surface passivation on optical properties of spray pyrolysis deposited Pd-F:SnO2. International Journal of Materials Science and Applications. 2014; 3(5):137-142. Abstract

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)

Nguu, JN, Aduda BO, Nyongesa FW, and Musembi RJ.  2014.  Electrophoretic Deposition of TiO2/Nb2O5 Composite Electrode Thin Films for Photovoltaic Application. Journal of Energy and Power Engineering. 8 (2014) 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.

2013

Musembi, RJ, Aduda BO, Mwabora JM, Rusu M, Fostiropoulos K, Lux-Steiner MC.  2013.  Transport Mechanism in TiO2/In (OH) xSy/Pb (OH) xSy/PEDOT: PSS eta Solar Cell. Researchgate. Abstract

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

Robinson Musembi, Aduda B, Mwabora J, Rusu M, Fostiropoulos K, Lux-Steiner M.  2013.  Light Soaking Induced Increase in Conversion Efficiency in Solar Cells Based on In(OH)xSy/Pb(OH)xSy. Materials Sciences and Applications. 4,2013:718-722. Abstract

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

Musembi, R;, Aduda B;, Mwabora J;, Rusu M;, Fostiropoulos K;, Lux-Steiner M.  2013.  Effect of Recombination on Series Resistance in eta Solar Cell Modified with In(OH)xSy Buffer Layer. Internatio n al J ournal of Ene r g y En gi nee ri ng 20 1 3. Abstract

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.

Aduda, B, Robinson Musembi, Mwabora J, Rusu M, Fostiropoulos K, Martha L-S.  2013.  Light Soaking Induced Increase in Conversion Efficiency in Solar Cells Based on In(OH)xSy/Pb(OH)xSy. Material Sciences and Applications. Abstract

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.

Aduda, BO, Jain PK, Ayieko CO, Musembi RJ, Waita SM.  2013.  Performance of TiO2/In(OH)iSj/Pb(OH)xSy Composite ETA Solar Cell Fabricated from Nitrogen Doped TiO2 Thin Film Window Layer. International Journal of Materials Engineering. 3(2):11-16. Abstractpublished_paper21.pdf

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.

2012

Ayieko, CO, Musembi RJ, Waita SM, Aduda BO.  2012.  Structural and Optical Characterization of Nitrogen-doped TiO2 Thin Films Deposited by Spray Pyrolysis on Fluorine Doped Tin Oxide (FTO) Coated Glass Slides. International Journal of Energy Engineering. 2(3):67-72. Abstract

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.

2011

F.W. Nyongesa, Rahbar N, Obwoya SK, Zimba J, Aduda BO, Soboyejo WO.  2011.  An Investigation of Thermal Shock in Porous Clay Ceramics. International Scholarly Research Network. :9. Abstract

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.

Simiyu, J, Aduda B, Mwabora J.  2011.  Electron Transport and Recombination Studies on TiO2 Dye Sensitized Solar Cells Employing Electrochemical Potential Techniques: the Effect of Film Thickness, 12th - 16th Dec. 5th International Conference on Electroceramics, 2011 (ICE 2011) . , University of New South Wales, Sydney, Australia Abstract

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.

Aduda, BO.  2011.  REVIEW OF THE CURRENT STATE OF NANOTECHNOLOGIES RESEARCH AND POLICY MAKING IN KENYA, 12 – 13 December. Nanotechnologies for Kenya’s Development: Questions of Knowledge Brokerage and Risk Governance Workshop. , Silversprings Hotel, Nairobi Abstract

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.

Aduda, BO.  2011.  Nanotechnologies for Kenya’s Development. Nanotechnologies for Kenya’s Development. , Silversprings Hotel, Nairobi Abstract

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

2010

Padh, H, Aduda BO, Alwis ADP.  2010.  NANOTECHNOLOGY: PRESENT STATUS AND FUTURE PROSPECTS IN DEVELOPING COUNTRIES/NAM S&T CENTRE. Nanotechnology. Abstract

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.

Musembi, RJ, Mwabora JM, Aduda BO.  2010.  TRANSPORT MECHANISM CHARACTERIZATION IN ETA SOLAR CELL. Condensed Matter Research Group. Abstract

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

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