Pulsed laser deposition of single phase n- and p-type Cu2O thin films with low resistivity

Low resistivity (~3-24 mOhm.cm) with tunable n- and p-type phase pure Cu2O thin films have been grown by pulsed laser deposition at 25-200 0C by varying the background oxygen partial pressure (O2pp). Capacitance data obtained by electrochemical impedance spectroscopy was used to determine the conductivity (n- or p-type), carrier density, and flat band potentials for samples grown on indium tin oxide (ITO) at 25 0C. The Hall mobility of the n- and p-type Cu2O was estimated to be ~ 0.85 cm2.V-1s-1 and ~ 4.78 cm2.V-1s-1 respectively for samples grown on quartz substrate at 25 0C. An elevated substrate temperature ~ 200 0C with O2pp = 2 - 3 mTorr yielded p-type Cu2O films with six orders of magnitude higher resistivities in the range ~ 9 - 49 kOhm.cm and mobilities in the range ~ 13.5 - 22.2 cm2.V-1s-1. UV-Vis-NIR diffuse reflectance spectroscopy showed optical bandgaps of Cu2O films in the range of 1.76 to 2.15 eV depending on O2pp. Thin films grown at oxygen-rich conditions O2pp > 7 mTorr yielded mixed-phase copper oxide irrespective of the substrate temperatures and upon air annealing at 550 0C for 1 hour completely converted to CuO phase with n-type semiconducting properties (~12 Ohm.cm, ~1.50 cm2.V-1s-1). The as-grown p- and n-type Cu2O showed rectification and a photovoltaic (PV) response in solid junctions with n-ZnO and p-Si electrodes respectively. Our findings may create new opportunities for devising Cu2O based junctions requiring low process temperatures.Comment: 41 pages(including suppl. material), 7 figures (14 suppl. figures

A LED-based Functional Light Source for the Characterization of Thin Film Solar Cells

A light source of selective functionalities of wavelengths, illumination periods, and intensities is desirable for investigating performance parameters as well as the quality of different layers and interfaces of solar cells. Conventional light sources used for these types of research are expensive, space-consuming, cumbersome to work with, and have limited functionalities. We have developed a light source with variable wavelength, intensity, and illumination period to address these issues using an illumination period control unit, voltage regulator, neutral density filter, alterable light emitting diodes, etc. As a proof-of-concept, we employed our constructed light source to investigate the intensity, wavelength, illumination period modulated photovoltaic, and impedance properties of inorganic thin film solar cells such as cadmium telluride (CdTe) and copper zinc tin sulfide (CZTS) using lights of wavelength 410, 520, and 635 nm. We hope to use this light source for photophysical and photochemical studies of metal oxide materials used for renewable energy research.Comment: 4 pages, 7 figure

Effect of Substrate Surface on the Wide Bandgap SnO2 Thin Films Grown by Spin Coating

Tin (IV) oxide (SnO2) sols have been synthesized from SnCl2.2H2O precursor solution by applying two different processing conditions. The prepared sols were then deposited on UV-Ozone treated quartz and soda lime glass (SLG) substrates by spin coating. The as-synthesized film was soft-baked at about 100 deg. C. for 10 min. This process was repeated five times to get a compact film, followed by air-annealing at 250 deg. C. for 2 h. The pristine and annealed films were characterized by UV-Vis-NIR spectroscopy, Grazing Incident X-Ray Diffraction (GIXRD), and Field Emission Scanning Electron Microscope (FESEM). The effect of substrate surface was investigated by measuring the contact angles with De-Ionized (DI) water. UV-Ozone treatment of substrate provides a cleaner surface to grow a homogeneous film. The electrical resistivity of annealed thin films was carried out by a four-point-collinear probe employing the current reversal technique and found in the range of approx. 2x10^3 to 3x10^3 Ohm.cm. Film thickness was found in the range of approx. 137-285 nm, measured by a stylus profilometer. UV-Vis-NIR Transmission data revealed that all the thin film samples showed maximum (82-89) % transmission in the visible range. The optical bandgap of the thin films was estimated to be approx. 3.75 to 4.00 eV and approx. 3.78 to 4.35 eV for the films grown on SLG and quartz substrates, respectively.Comment: 4 pages, 7 figure

Spherical and Rod-shaped Gold Nanoparticles for Surface Enhanced Raman Spectroscopy

Raman Spectroscopy offers an in-situ, rapid, and non-destructive characterization tool for chemical analysis of diverse samples with no or minimal preparation. However, due to the inherent weak signal of conventional Raman spectroscopy, surface plasmon resonance features of noble metal nanoparticles have been utilized to conduct Surface Enhanced Raman Spectroscopy (SERS) in detecting trace label contaminants in foods and foodstuffs. In this effort, we synthesized gold nanoparticles (AuNPs) by reduction of chloroauric acid (HAuCl4) with sodium citrate dehydrate. We prepared different sizes of AuNPs at a fixed temperature (100 oC) but with varying pHs of 4 and 8. The as-synthesized AuNPs were characterized by UV-Vis spectroscopy, dynamic light scattering (DLS), and Field Emission Scanning Electron Microscopy (FE-SEM). FE-SEM micrographs revealed spherical AuNPs with an average diameter of approx. 55 nm and rod-shaped AuNPs with an average length of approx. 170 nm for sample synthesis at pH 8 and 4, respectively. The effectiveness of the as-prepared AuNPs for SERS is tested by detecting Rhodamine 6G diluted at a trace level. This study suggests that plasmonic nanoparticles coupled with SERS have great potential for broad applications in detecting other trace amounts of hazardous chemicals in foods and foodstuffs.Comment: 4 pages, 5 figure

Solid-state Synthesis of Phase Pure CuBi2O4 by Sequential Ball Milling

Bismuth-based metal oxides are an intriguing class of photoelectrode materials that can potentially enable large-scale solar hydrogen production via photoelectrochemical (PEC) water-splitting. For realizing such PEC devices, Kusachiite (copper bismuth oxide) is one of the most promising photocathode materials for high solar to hydrogen efficiency. Here we attempt to synthesize phase pure copper bismuth oxide (CuBi2O4) nanopowders using a facile solid-state reaction technique subsequently sintered at 750 0C for 4 h in air. These CuBi2O4 (CBO) powders have been further sequentially ball milled (SBM) up to 25 h to elucidate the milling duration effect on the optical bandgap of the ball milled CuBi2O4 (SBM-CBO). The structural, optical, and Raman studies suggest that phase pure tetragonal CBO could be grown from raw CuO and Bi2O3 powders. The variations in morphology and chemical composition of CBO with increasing milling hours were examined using field emission scanning electron microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) microanalysis, respectively. The optical bandgap was measured in the range of 1.70 - 1.85 eV from the UV-VIS-NIR Diffuse reflection data of SBM-CBO powders. The CBO photocathode materials with variable structural and optical properties could be a promising candidate for self-sustained PEC generation of hydrogen fuel.Comment: 4 pages, 5 figures, 2022 4th International Conference on Sustainable Technologies for Industry 4.0 (STI

Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017

A double burden of malnutrition occurs when individuals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4% (62.3 (55.1–70.8) million) to 6.4% (58.3 (47.6–70.7) million), but is predicted to remain above the World Health Organization’s Global Nutrition Target of <5% in over half of LMICs by 2025. Prevalence of overweight increased from 5.2% (30 (22.8–38.5) million) in 2000 to 6.0% (55.5 (44.8–67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic

Global burden of 369 diseases and injuries in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019

Background: In an era of shifting global agendas and expanded emphasis on non-communicable diseases and injuries along with communicable diseases, sound evidence on trends by cause at the national level is essential. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) provides a systematic scientific assessment of published, publicly available, and contributed data on incidence, prevalence, and mortality for a mutually exclusive and collectively exhaustive list of diseases and injuries. Methods: GBD estimates incidence, prevalence, mortality, years of life lost (YLLs), years lived with disability (YLDs), and disability-adjusted life-years (DALYs) due to 369 diseases and injuries, for two sexes, and for 204 countries and territories. Input data were extracted from censuses, household surveys, civil registration and vital statistics, disease registries, health service use, air pollution monitors, satellite imaging, disease notifications, and other sources. Cause-specific death rates and cause fractions were calculated using the Cause of Death Ensemble model and spatiotemporal Gaussian process regression. Cause-specific deaths were adjusted to match the total all-cause deaths calculated as part of the GBD population, fertility, and mortality estimates. Deaths were multiplied by standard life expectancy at each age to calculate YLLs. A Bayesian meta-regression modelling tool, DisMod-MR 2.1, was used to ensure consistency between incidence, prevalence, remission, excess mortality, and cause-specific mortality for most causes. Prevalence estimates were multiplied by disability weights for mutually exclusive sequelae of diseases and injuries to calculate YLDs. We considered results in the context of the Socio-demographic Index (SDI), a composite indicator of income per capita, years of schooling, and fertility rate in females younger than 25 years. Uncertainty intervals (UIs) were generated for every metric using the 25th and 975th ordered 1000 draw values of the posterior distribution. Findings: Global health has steadily improved over the past 30 years as measured by age-standardised DALY rates. After taking into account population growth and ageing, the absolute number of DALYs has remained stable. Since 2010, the pace of decline in global age-standardised DALY rates has accelerated in age groups younger than 50 years compared with the 1990–2010 time period, with the greatest annualised rate of decline occurring in the 0–9-year age group. Six infectious diseases were among the top ten causes of DALYs in children younger than 10 years in 2019: lower respiratory infections (ranked second), diarrhoeal diseases (third), malaria (fifth), meningitis (sixth), whooping cough (ninth), and sexually transmitted infections (which, in this age group, is fully accounted for by congenital syphilis; ranked tenth). In adolescents aged 10–24 years, three injury causes were among the top causes of DALYs: road injuries (ranked first), self-harm (third), and interpersonal violence (fifth). Five of the causes that were in the top ten for ages 10–24 years were also in the top ten in the 25–49-year age group: road injuries (ranked first), HIV/AIDS (second), low back pain (fourth), headache disorders (fifth), and depressive disorders (sixth). In 2019, ischaemic heart disease and stroke were the top-ranked causes of DALYs in both the 50–74-year and 75-years-and-older age groups. Since 1990, there has been a marked shift towards a greater proportion of burden due to YLDs from non-communicable diseases and injuries. In 2019, there were 11 countries where non-communicable disease and injury YLDs constituted more than half of all disease burden. Decreases in age-standardised DALY rates have accelerated over the past decade in countries at the lower end of the SDI range, while improvements have started to stagnate or even reverse in countries with higher SDI. Interpretation: As disability becomes an increasingly large component of disease burden and a larger component of health expenditure, greater research and developm nt investment is needed to identify new, more effective intervention strategies. With a rapidly ageing global population, the demands on health services to deal with disabling outcomes, which increase with age, will require policy makers to anticipate these changes. The mix of universal and more geographically specific influences on health reinforces the need for regular reporting on population health in detail and by underlying cause to help decision makers to identify success stories of disease control to emulate, as well as opportunities to improve. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens

Communication—Texture and Bandgap Tuning of Phase Pure Cu2O Thin Films Grown by a Simple Potentiostatic Electrodeposition Technique

Highly textured phase pure Cu _2 O thin films have been grown by a simple electrodeposition technique with varying deposition voltages (−0.3 to −1.0 V). The surface morphology characterized by Scanning Electron Microscopy (SEM) revealed that the deposited thin films coherently carpet the underlying substrate and are composed of sharp faceted well-defined grains of 0.5–1.0 μ m sizes. XRD analyses showed that all films are composed of polycrystalline cubic Cu _2 O phase only and have average crystalline domain size in the range of 30–73 nm. The preferred crystalline orientation of phase pure Cu _2 O films was found to be changing from (200) to (111) with increasing cathodic voltages and showed the highest (111) and (200) crystalline texture coefficient while growing at −1.0 and −0.8 V respectively. The optical bandgap of the as-grown samples was calculated in the range of 1.95–2.20 eV using UV–vis Transmission data. The performance of Cu _2 O/FTO photocathodes was tested by estimating LED “ON/OFF” modulated surface photovoltage into a photoelectrochemical cell at a zero bias

Characterizations of extrinsically doped CZTS thin films for solar cell absorbers fabricated by sol-gel spin coating method

In copper zinc tin sulfide (CZTS) based thin films, copper zinc antisite (CuZn) represents the major p-type acceptor defect with low formation energy. This antisite can create defect-dominated carrier recombination hotspots, which reduces power conversion efficiency. Extrinsic doping in cationic sites of the CZTS thin film during synthesis is an effective way to passivate this defect. It has previously been reported that employing Cd as a dopant can passivate this defect and improve film quality. Injecting toxic Cd into non-toxic CZTS may create more problems than it solves. Simultaneous doping of Cd and other atoms like Mg is hypothesized to accomplish this goal of lowering Cd concentration. For this, it is important to know the effect of doping Cd and Mg separately under analogous experimental conditions. The structural, morphological, and optical properties, as well as the chemical bonding states, of sol-gel spin-coated CZTS thin films were investigated in this study using independent and controlled Cd and Mg doping. The fabrication procedure consisted of two steps: sol-gel spin coating followed by sulfurization. As a solvent for precursors in creating sols for spin coating processes, dimethyl sulfoxide (DMSO) was employed. Each dopant's precursor concentration was chosen to ensure an identical mole percentage of zinc precursor in the solution. The fabricated films were characterized undoped and doped forms using X-ray diffractometry (XRD) with Rietveld refinements, Raman spectroscopy, Field emission scanning electron microscopy (FESEM), 3D profilometry, and Ultraviolet-visible near-infrared (UV-Vis NIR) spectroscopy. The elemental composition ratio and chemical bonding states of the fabricated films were probed by Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), respectively. Fabricated thin films exhibit distinct synergistic features depending on the dopant types used in the fabrication process. The crystal structure of the doped absorber and the chemical valence states of the other elements (Cu, Zn, Sn, and S) were not changed as shown by XRD, Raman, and XPS analyses. The main diffraction peak at the (112) plane is found at Bragg's diffraction angle of 28.6° for an undoped sample. This peak shifts left upon Cd and Mg doping to 28.2° and 28.4° owing to different ionic radii of dopants relative to Zn ions, which indicates the presence of dopants in the fabricated films. Raman spectroscopy probes the Cu-Sn-S secondary phases: cubic Cu2SnS3 at 305 cm−1 in the undoped sample, tetragonal Cu2SnS3 at 296 cm−1 in the Cd-doped sample, and orthorhombic Cu3SnS4 at 291 cm−1 in the Mg-doped sample. From the EDS results, it appears that 45% of the Zn atoms in both the Cd-doped and Mg-doped samples are partially substituted by Cd and Mg, respectively. The optical band gap for Cd-doped samples decreases from 1.61 eV to 1.56 eV when compared to undoped samples. For Mg-doped samples, the optical band gap shrinks even more to 1.1 eV. This corresponds to shifting of absorbance spectra to higher wavelengths known as “redshift”. Urbach energy is determined to be 284 meV and 1072 meV for Cd and Mg doped samples, respectively, to address band tailing issues. Mg doping enhances crystallite size slightly while decreasing microstrain and dislocation density. The RMS surface roughness of Cd and Mg doped samples is 147 nm and 280 nm, respectively. Nevertheless, the primary peaks of Cu, Zn, Sn, S, Cd, Mg, and O, as well as the secondary photoelectron emission lines of these elements, are all found to be present and identified in both the doped samples. These results imply that Cd and Mg doping in the Zn-cationic site of virgin CZTS thin film can be regulated systematically to get appreciated features as a solar cell absorber