Search

Assemblies of interacting Rydberg atoms show promise for the quantum simulation of transport phenomena, quantum chemistry and condensed matter systems. Such schemes are typically limited by the finite lifetime of Rydberg states. Circular Rydberg states have the longest lifetimes among Rydberg states but lack the energetic isolation in the spectrum characteristic of low angular momentum states. The latter is required to obtain simple transport models with few electronic states per atom. Simple models can however even be realized with circular states, by exploiting dipole-dipole selection rules or external fields. We show here that this approach can be particularly fruitful for scenarios where quantum transport is coupled to atomic motion, in adiabatic excitation transport or quantum simulations of electron-phonon coupling in light harvesting. Additionally, we explore practical limitations of flexible Rydberg aggregates with circular states and to which extent interactions among circular Rydberg atoms can be described using classical models., 9 Pages, 5 Figures

Zinc cadmium sulfide (Zn x Cd 1 − x S) thin films (0 ≤ x ≤ 1) were deposited by the radio frequency (RF) co-sputtering of cadmium sulfide (CdS) and zinc sulfide (ZnS). The RF powers of CdS and ZnS were varied to control the composition of the films, which was confirmed using energy dispersive X-ray analysis. The structural properties of the films were investigated using X-ray diffraction, which showed that the films have a hexagonal (wurtzite) structure with a strong preferential orientation along the (002) plane. The values of lattice constants ‘a’ and ‘c’ decreased as ‘x’ increased. The surface morphology, topology and optical properties were investigated using field emission scanning electron microscopy (FESEM), atomic force microscopy and ultraviolet spectrophotometry. The FESEM studies revealed an increase in grain size for zinc (Zn) contents up to x = 0.62, followed by a decrease in the grain size until ‘x’ reached 0.81, above which the films were amorphous. The optical band gaps of the films were obtained from optical absorption measurements and shifted to a higher energy as the content of ‘x’ increased. The presence of a small amount of zinc in CdS strongly influenced the optical band gap and transmittance of Zn x Cd 1 − x S thin films. The electrical sheet resistance of the films was also found to be relatively high. Among the range of Zn x Cd 1 − x S compositions tested, the samples with a Zn content of 0.17 to 0.43 showed a better film quality, making them suitable as the window layer in Zn x Cd 1 − x S/CdTe thin film solar cells.

The structural and electrical properties of the magnetron sputtered CdTe thin films with subsequent CdCl 2 solution treatment have been studied with a major focus on the influence of CdCl 2 treatment to achieve high quality thin films. In this study, CdTe films with a thickness of 1.5 to 2 μm have been grown using the magnetron sputtering technique on top of glass substrate at an optimized substrate temperature of 250 °C. Aqueous CdCl 2 concentration varied from 0.3 mol to 1.2 mol with the annealing temperature from 360 °C to 450 °C. The surface roughness of the films increases with the increase of solution concentration, while it fluctuates with the increase of annealing temperature. The density of nucleation centers and the strain increases for the films treated at 360 °C with 0.3 M to1.2 M while the grain growth of the films reduces. However, these strains are released at higher annealing temperatures, resulting in reduced dislocation densities, structural defects as well as increased crystalline property and grain size. The carrier concentration increases with the increase of treated CdCl 2 concentration and subsequent annealing temperature. The highest carrier concentration of 1.05 × 10 14 /cm 3 was found for the CdTe thin films treated with 0.3 M CdCl 2 solution followed by an annealing treatment at 420 °C for 20 min.

Cadmium Telluride (CdTe) thin films with 1 μm thickness were grown by the magnetron sputtering on top of bare glass and glass/FTO/CdS stacks at different substrate temperatures. The crystallographic, morphological, optical and electrical properties of the as-deposited and CdCl 2 immersed with subsequent thermally annealed (also known as CdCl 2 treatment) films were studied through XRD, scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–vis spectrometry and Hall Effect measurements, respectively. It has been revealed that the as-deposited films have poor crystallinity, while CdCl 2 treatments improved crystallinity as well as surface morphology of the films. Increase of the grain size, surface roughness and absorption coefficients were observed in CdCl 2 treated samples. The bulk carrier concentration also increased by a factor 10 in CdCl 2 treated samples. The complete cell was also fabricated by sputtering technique with the configuration of glass/FTO/CdS/CdTe/Cu x Te/Ni/Ag and the performance of the cell with and without CdCl 2 treatment was evaluated under illumination of 1.5 AM. Vivid effects of CdCl 2 treatment are also observed from the cell performances.

Zn x Cd 1-x S thin films at low zinc content have been deposited on bare soda lime glass substrates using RF magnetron co-sputtering of CdS and ZnS for the first time to investigate annealing effect on the structural and optical properties of the thin films. The as-deposited films were annealed in O 2 /N 2 ambient at annealing temperature ranging 200-500 °C. The composition of the films was controlled by varying RF power of CdS and ZnS in such a ratio so that zinc content in the thin films was low. The composition, structural, optical and surface morphological properties of the films was investigated using EDX, XRD, UV-Vis spectrophotometer and FESEM. The annealed films were observed hexagonal wurtzite structure with strong preferential orientation along (002) diffraction peak. Crystallinity of the films increased with increasing annealing temperature below 400 °C whereas beyond 400 °C new peaks were observed along with decreasing trend of (002) diffraction peak. Optical absorption and transmission spectra were recorded within the range 300-900 nm. With increasing annealing temperature, the band gap of the annealed films once decreased and then abruptly increased at around 400 °C. The decreased bandgap may have been due to possible increase in the crystalline nature of the material. From SEM, it was observed that the thin films were formed by different clusters of grains which later changed to isolated grains as the annealing temperature increased. This work confirms that annealing temperature has overbearing influence on the Zn x Cd 1-x S thin film properties deposited by RF magnetron co-sputtering.

In this paper, various factors that affect the solar cell performances are investigated with emphasis given to the window layer (CdS:O) thickness, operating temperature and light intensity as well as the effect of front contact and BSF layers. Various parameters of solar cells such as quantum efficiency, series and shunt resistance associated with the front contact and BSF materials have been investigated also. Two materials ZnO and SnO2were used as front contact and two materials Sb2Te3and ZnTe were used as BSF layers to investigate their effects on ultra-thin cell performances. The results have shown that the BSF layers have no unfavourable effect on cell stability with temperature increase as the cell temperature coefficients with these BSF layers were 0.1% (ZnTe) to 0.3% (Sb2Te3). However, the results of the comparisons demonstrate that the best option is Sb2Te3as BSF material, which exhibits lowest series resistance and behaves as an excellent minority carrier mirror whereas ZnTe showed unexpected series resistance problems because of the adverse heterojunction with CdTe.

Zinc oxide (ZnO) thin films were deposited by RF magnetron sputtering onto ITO coated soda-lime glass substrates. The effects of annealing in temperature range of 250 to 450 °C on the structural and optical properties of the ZnO films have been studied. The crystalline structure, surface topology, morphology, optical properties of the films were determined using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–Visible Spectrometry, respectively. X-ray diffraction measurement showed that the annealed ZnO films were polycrystalline in nature with (002), (101) and (001) oriented crystallites of hexagonal wurtzite structure. Crystalline property and grain size of the films were found to increase after annealing. The optical band gap of ZnO films initially blue shifted (3.1–3.23 eV) when annealed at 400 °C and further red shifted in the range of 3.23 to 3.1 eV being annealed at 250 to 450 °C range. From the UV spectroscopy, the films showed transmittance over 85% in the optical bandgap spectrum. All these results indicate that post deposition annealing improves the film quality with reduced roughness and better crystalline properties that can be utilised as buffer layer in the CIGS or CdTe thin film solar cells.

Cadmium telluride (CdTe) thin film solar cell has long been recognized as a leading photovoltaic candidate for its high efficiency and low cost. A numerical simulation has been performed using AMPS-1D simulator to explore the possibility of higher efficiency and stable CdS/CdTe cell among several cell structures with indium tin oxide (ITO) and cadmium stannate (Cd2SnO4) as front contact material, tin oxide (SnO2), zinc oxide (ZnO) and zinc stannate (Zn2SnO4) as buffer layer, and silver (Ag) or antimony telluride (Sb2Te3) with molybdenum (Mo) or zinc telluride (ZnTe) with aluminium (Al) as back contact material. The cell structure ITO/i-ZnO/CdS/CdSxTe1−x/CdTe/Ag has shown the best conversion efficiency of 16.9% (Voc=0.9 V, Jsc=26.35 mA/cm2, FF=0.783). This analysis has shown that ITO as front contact material, ZnO as buffer layer and ZnTe or Sb2Te3 back surface reflector (BSR) are suitable material system for high efficiency (>15%) and stable CdS/CdTe cells. The cell normalized efficiency linearly decreased at a temperature gradient of −0.25%/°C for ZnTe based cells, and at −0.40%/°C for other cells.

An experimental infection of red fronted gazelles (Gazella rufifrons) with Trypanosoma brucei strain MKAR/84/NITR/6 was carried out. Two waves of parasitaemia which corresponded with a significant decline (p0.05) in packed cell volume (PCV) was encountered in the infected untreated controls and those treated at day 8 post-infection with a sub-optimal dosage of diminazene aceturate (Berenil) at 3.5 mg/kg body weight. At postmortem, hepatomegally, splenomegally, lymphadenopathy, nephritis, myocardial degeneration with pulmonary oedema was observed in the two groups. Similarly, histopathological studies of some organs revealed interstitial haemorrhages, severe degenerative changes with cellular infiltrations. On the other hand, those treated by day 8 post-infection with melarsamine hydrochloride (Cymelarsan) at 0.3 mg/kg, 0.6 mg/kg or diminazene aceturate (Berenil) at 7.0 mg/kg body weight had apparently normal organs at the end of the experiment. These results suggest that, T. brucei can cause severe pathological changes in untreated red fronted gazelles (Gazella rufifrons). However, treatments at the onset of parasitaemia, by day 8 post-infection with melarsamine hydrochloride (Cymelarsan) at 0.3 and 0.6 mg/kg or diminazene aceturate (Berenil) at 7.0 mg/kg body weight ameliorated the deleterious effects of the infection in the gazelles.

In a study to investigate the current status of intramammary mycoplasmosis in caprine udders in Nigeria, a total of 57 and 24 milk samples were collected from udders of goats affected by mastitis and from apparently normal goats' udders, respectively. Acute and chronic mastitis were more commonly observed in goats between 1 and 3 years old. Mycoplasma agalactiae and Mycoplasma capricolum occurred at a significantly higher rate (p

Cadmium Zinc Telluride (CZT) films were deposited by co-sputtering of CdTe and ZnTe targets in an RF magnetron sputtering using various combinations of RF powers, and the effect of sputtering power on the properties of CZT films were studied using SEM, EDX, XRD, AFM and UV-VIS spectrophotometer. The SEM and AFM data shows that as the ratio of the CdTe: ZnTe RF power increases, so does the grains size and surface roughness of the samples. From the EDX results, it was found that the amount of Zn in the ternary reduces with the RF power ratio. The optical analyses of the films indicate that they have good absorption; with shallow absorption edge occurs in the range of 750-850 nm. The energy bandgap of the samples were found to vary between 2.04 eV-2.54 eV, which covers the range of most BSF materials used for CdTe solar cells. The study has thus shown the feasibility of using RF sputtering for the development of both absorber and BSF layer in one monolithic structure, for applications in CdTe thin film solar cells.

Zinc sulphide thin films have been deposited on FTO coated glass substrates using the sputtering and chemical bath deposition techniques. ZnS thin film is at first grown by CBD using a aqueous solution of thioria, ammonia, ammonium chloride and zinc chloride, respectively; whereas ZnS thin film is also grown from sputtering technique at a substrate temperature 300 °C. The grown films from the both processes were annealed in a vacuum furnace of nitrogen ambient with pressure 250–300 mTorr. A comparative study of structural and optical study of these films was carried out by means of XRD, AFM and UV-Vis spectrometry. It has been found that the films in both processes are polycrystalline in nature having the (200) preferential orientation. The crystallite grain size, lattice constant, microstrain and dislocation densities of the films are quite different in both processes as observed from XRD analysis. Surface structure and topography were observed from the AFM images. The higher r.m.s values of surface roughness as well as bigger grains are observed in CBD grown ZnS thin films. The band gap has been found 3.58 and 3.54eV for the films prepared from CBD and sputtering, respectively.

The structural and optical properties of annealed CdS are studied in this work. The CdS films are deposited on ITO coated glasses by sputtering at different substrate temperatures and subsequently annealed in an O 2 /N 2 ambient. It has been observed from XRD diffraction that the films show a trend of conversion from poly crystalline to amorphous or mixed phases after annealing. The films fabricated at room temperature (RT) have been found in complete amorphous form. The surface roughness of the films drastically increased due to thermal annealing observed from AFM images. Optical properties of the films were observed using UV-Vis spectrometer and band gaps of the films were found in the range of 2.80 to 3.08 eV. The annealed films exhibited the blue shift in the direct allowed transition energy band gaps, possibly due to the oxygen incorporation during annealing suggesting the transformation to CdS:O films.

This paper presents the significant role deposition pressure plays in the deposition of high quality ITO films by RF magnetron sputtering. ITO target was sputtered onto bare sodalime glass under various deposition conditions. Particularly, the deposition pressure was varied against several other parameters, until the best film characteristics were obtained. The deposited films were characterized using FESEM, AFM, XRD, UV-Vis and four-point probe. Results indicate that deposition pressure plays significant role in obtaining good quality films. ITO grains change dramatically with pressure, having lower pressure giving better morphology. In addition, lower pressure also produced films with lower resistivity but lower transmittance and poor crystallinity. By separately and collectively optimizing the deposition conditions, ITO films of 160 – 200nm thickness, having resistivity of 7.56×10−5 Ω-cm with 87% transmittance were obtained. To our knowledge, this is the lowest resistivity ITO films produced by magnetron sputtering. This work confirms that even though deposition temperature and RF power have overbearing influence on the film properties, but the deposition pressure also contributes significantly in obtaining good quality films.

The compositional, crystal and microstructural, optical transmission and absorption properties of Zn x Cd 1−x S thin films at low zinc (Zn) content (x=0.2) fabricated by RF co-sputtering using CdS and ZnS were investigated. These ternary compounds were characterized by energy dispersive X-ray analysis (EDX) for composition, X-ray diffraction (XRD) for crystal structure, UV-vis for optical study, forced emission scanning electron microscopy (FESEM) for surface morphology and atomic force microscopy (AFM) for surface topology. XRD patterns of Zn x Cd 1−x S thin films showed the hexagonal structure with a strong reflection peak of (002) plane. From FESEM, the average grain size smaller than 40 nm was observed. Band gap of the films was determined to be 2.6 eV. The average and root mean square roughness of Zn x Cd 1−x S (for x= 0.2) were checked by atomic force microscopy (AFM). The surface of the thin films was found to be smoother, homogenous and densely packed with uniform growth.

This study investigates the key issues in the fabrication of CdTe solar cells on metallic substrates, their trends, and characteristics as well as effects on solar cell performance. Previous research works are reviewed while the successes, potentials, and problems of such technology are highlighted. Flexible solar cells offer several advantages in terms of production, cost, and application over glass-based types. Of all the metals studied as substrates for CdTe solar cells, molybdenum appears the most favorable candidate, while close spaced sublimation (CSS), electrodeposition (ED), magnetic sputtering (MS), and high vacuum thermal evaporation (HVE) have been found to be most common deposition technologies used for CdTe on metal foils. The advantages of these techniques include large grain size (CSS), ease of constituent control (ED), high material incorporation (MS), and low temperature process (MS, HVE, ED). These invert-structured thin film CdTe solar cells, like their superstrate counterparts, suffer from problems of poor ohmic contact at the back electrode. Thus similar strategies are applied to minimize this problem. Despite the challenges faced by flexible structures, efficiencies of up to 13.8% and 7.8% have been achieved in superstrate and substrate cell, respectively. Based on these analyses, new strategies have been proposed for obtaining cheaper, more efficient, and viable flexible CdTe solar cells of the future.

In this work, a numerical analysis on cadmium stannate (Cd 2 SnO 4 ) as front contact, zinc stannate (Zn 2 SnO 4 ) as buffer layer and antimony telluride (Sb 2 Te 3 ) with molybdenum (Mo) as back contact has been conducted in the conventional (SnO 2 /CdS/CdTe/Ag) CdTe cell structures. Here, CdS window layer is replaced by zinc cadmium sulphide (Zn x Cd 1−x S) aiming to improve efficiency and stability utilizing Analysis of Microelectronic and Photonic Structures (AMPS 1D) simulator. Efficiency as high as 17.0% has been found with 80 nm of Zn x Cd 1−x S window layer for x=0.1, 1 μm of CdTe layer and 100 nm Zn 2 SnO 4 buffer layer without Sb2Te 3 back contact. However, ZnO insertion shows lower conversion efficiencies of 11.84% and 14.26%, respectively with and without Sb 2 Te 3 back contact. It has been found that 1 μm of CdTe absorber layer, 70 nm of Zn x Cd 1−x S (x=0.1) window layer, 100 nm of Zn 2 SnO 4 buffer layer and 100 nm Sb 2 Te 3 back contact layer are sufficient for high efficiency (>18.5%) Zn x Cd 1−x S/CdTe cells. Moreover, it has been found that the cell normalized efficiency linearly decreases with the increasing operating temperature at the temperature gradient of −0.3%/°C proving its stability as others.

A numerical analysis has been performed utilizing Analysis of Microelectronic and Photonic Structures (AMPS 1D) simulator to explore the possibility of higher efficiency and stable Zn x Cd 1−x S/CdTe cells. Several cell structures with indium tin oxide (ITO) and cadmium stannate (Cd 2 SnO 4 ) as front contact, zinc stannate (Zn 2 SnO 4 ) and zinc oxide (ZnO) as buffer layer and antimony telluride (Sb 2 Te 3 ) insertion with Nickle (Ni) as back contact has been investigated in the conventional (SnO 2 /CdS/CdTe/Ag) CdTe cell structures in which CdS is replaced by zinc cadmium sulphide (Zn x Cd 1−x S) as window layer. Efficiency as high as 18.0% has been found with 80 nm of Zn x Cd 1−x S window layer for x=0.05, 1 µm of CdTe layer and 100 nm Zn 2 SnO 4 buffer layer without Sb 2 Te 3 back contact. However, ZnO insertion shows low conversion efficiency of 7.84% and 12.26%, respectively with and without Sb 2 Te 3 back contact. It has been found that 1 µm of CdTe absorber layer, 70 nm of Zn x Cd 1−x S (x=0.05) window layer, 100 nm of Zn 2 SnO 4 buffer layer and 100 nm Sb 2 Te 3 back contact layer are sufficient for high efficiency (>17.5%) Zn x Cd 1−x S/CdTe cells. Moreover, it was found that the cell normalized efficiency linearly decreases with the increasing operating temperature at the temperature gradient of −0.25%/°C.

In this work, a conventional structure of CdS/CdTe cells was investigated, where Zn x Cd 1−x S window material that possesses wider bandgap replaced CdS window layer. The effect of composition variation in Zn x Cd 1−x S was analysed for high efficiency cell using AMPS 1D Simulator and the optimal value of x was found to be around 8%. Moreover, to explore the possibility of high efficiency, ultra thin and stable Zn x Cd 1−x S/CdTe cells the CdTe absorber layer thickness was decreased to the extreme limit and 1μm CdTe layer showed reasonable range of efficiency with stability. The thickness of Zn x Cd 1−x S window layer was reduced to 80 nm to increase the overall cell performance with the insertion of ZnO/Zn 2 SnO 4 as the buffer layer. The proposed cell with Zn x Cd 1−x S as window layer showed promising result with an efficiency of 22.42% (Voc = 0.98 V, Jsc = 29.35 mA/cm2, FF = 0.85) using As 2 Te 3 as back surface field (BSF) and copper (Cu) as final back contact. The cell normalized efficiency was found to be decreased linearly at the gradient −0.24/C with the operating temperature that indicated better stability of Zn x Cd 1−x S/CdTe solar cells.

No Abstract.Nigerian Veterinary Journal Vol. 29 (2) 2008: pp. 31-36

Reports on the clinico-pathology and mechanisms of trypanosomosis in free-living and captive wild animals showed that clinical disease and outbreaks occur more commonly among captive than free-living wild animals. This is because the free-living wild animals co-exist with the disease until subjected to captivity. In exceptional cases however, draught, starvation and intercurrent diseases often compromised trypanotolerance leading to overt trypanosomosis in free-living wild animals. Meanwhile, in captivity, space restriction, reduced social interactions, change in social herd structure, reduced specie-to-specie specific behaviors, altered habitat and translocation were the major stressors that precipitated the disease. The cumulative effect of these factors produced severe physiological and somatic stress leading to diminished immune response due to increased blood cortisol output from adrenal cortex. The major symptoms manifested were pyrexia, innapetence, increased respiration, anaemia, cachexia and death. At necropsy, pulmonary oedema, splenomegally, hepatomegally, lympadenopathy and atrophy of body fats were the gross changes encountered. At the ultra-structural level, the tissues manifested degenerative changes, haemorghages, necrosis and mononuclear cellular infiltrations. The mechanisms of cellular and tissue injuries were primarily associated with physical and metabolic activities of the organisms. From the foregoing, it is evident that stress is the underlying mechanism that compromises trypanotolerance in wild animals leading to severe clinico-pathological effects.

The prevalence of parasites and associated packed cell volume (PCV) changes were investigated in captive wild birds maintained in the semi-arid region of north-eastern Nigeria. The results revealed that out of the 126 captive wild birds examined during the period, 98 (77.8%) were infected with at least one parasite species. Arthropod parasites were encountered in 63 (34.1%) birds and the parasites recovered were Echidnophaga gallinacea (27.0%), Argas persicus (18.2%) and Ctnemidocoptes mutans (4.8%). The parasites generally occurred in low numbers. Haemoparasites were recorded in 42 (33.3%) birds and these included Plasmodium (15.9%), Haemoproteus (9.5%) and Leucocytozoon (7.9%) species. The percentage parasitization of the erythrocyte with haemoparasites was generally high (40-90%) and the infected birds had significantly (p Libyostrongylus douglassi in the ostrich and Raillientina echinobothridia in the white stork. Leucocytozoon species are reported for the first time in birds in Nigeria. The presence of this parasite in the study area could be of some epidemiological implications since they are usually known to occur in temperate regions. Their presence in the study area was associated with the annual migration of wild birds between the study area and temperate Europe and Asia. Keywords : parasites, packed cell volume, wild birds, Nigeria. Nigerian Journal of Parasitology Vol. 28 (2) 2007: pp. 109-113

The serological prevalence of antibodies to Mycoplasma mycoides subsp. mycoides SC, the aetiological agent of contagious bovine pleuropneumonia (CBPP), was investigated in Nigerian camels. Fifty-eight serum samples were collected from slaughtered camels and examined by complement fixation (CFT), dot enzyme immunoassay and Western blots. Fourteen of the slaughtered camels examined had pneumonic lesions. All sera examined were negative by CFT but 7 (12.1%) and 4 (6.8%) were positive by dot enzyme immunoassay and Western blots, respectively. The serological evidence of M. mycoides subsp. mycoides SC in camels and its likely implication in the epidemiology of CBPP are discussed.

CdS thin films were deposited by three different processes; close spaced vapour transport (CSVT), chemical bath deposition (CBD), and sputtering technique on ITO coated glasses and their structural and optical properties were investigated through XRD, SEM, EDX and UV-Vis spectrometry, respectively. The as-grown films are annealed at 400°C and 500°C for 30 min in air and the change in structural properties with the thermal stress were also investigated. The crystallite grain size, lattice constant, microstrain and dislocation densities of the films are quite different in these processes as observed from XRD analysis. The highest crystallinity is observed for sputtered CdS thin films. However, the crystalline property of CBD and sputtered CdS increases with the thermal annealing, while CSVT-CdS loses its crystalline form. No significant grain changes are observed for thermally annealed CdS thin films but some cracked lines are observed in CBD and CSVT CdS thin films from SEM images. The absorbance in the visible wavelength decreased for annealed CdS thin films, which might be due to fact that films are becoming denser followed by thermal annealing. Significant blue shifts observed for thermally annealed CdS thin films have been found from all processes. The band gap found for as-grown CSVT-CdS is 2.44 eV, for CBD-CdS is 2.38 eV and for sputtered-CdS is 2.42 eV. The disorder of phonon states in the films are observed from Urbach's tail. The absorption edges due to the exciton–phonon interaction or electron-phonon interaction are also observed from the values of steepness parameter.