Selenium Environment Research Articles

Cu(In,Ga)Se 2 thin films and devices sputtered from a single target without additional selenization

Typically, Cu(In,Ga)Se 2 (CIGS) thin films for photovoltaic devices are deposited by co-evaporation or, alternately, by deposition of the metals with or followed by treatment in a selenium environment. In this article, we describe CIGS films that are instead deposited by RF magnetron sputtering from a single quaternary target without any additional selenization. Devices built with these films exhibit efficiencies as high as 8.9%. We demonstrate that deposition power can be varied in order to change the film morphology and improve device performance.

Se activity and its effect on Cu(In,Ga)Se2 photovoltaic thin films

AbstractWe study some physical properties of CuIn1–x Gax Se2 thin‐films fabricated by evaporation from elemental sources under various Selenium environments. Specifically, thin‐films were fabricated under growth conditions such as Se deficiency, near stoichiometry and excess Se during coevaporation to investigate the impact of the Se environment on absorber film properties and ultimately the device performance. We determine the chemical activity of Se in the evaporation process has a strong influence on film macrostructure (prefered orientation) and microstructure, particularly at the grain and grain boundary level. It is shown that the optoelectronic properties at grain boundaries are affected by the Se environment used resulting in absorber thin‐films with distictive defect distribution and defect density. Consequently, the performance of the solar cells fabricated from those films is also affected by the Se environment. These effects on solar cell performance and absorber properties are reported in a (i) structural analysis of the CuIn1–x Gax Se2/Mo/glass samples by X‐ray and electron backscattering techniques; (ii) optolectronic radiative characteristics of the absorbers by cathode luminescence and photoluminescence studies and (iii) current–voltage, quantum efficiency and capacitance–voltage measurements for the solar cells made from the absorbers fabricated under the pre prescribed Se growth conditions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High Efficiency Copper Indium Gallium DiSelenide (CIGS) by High Power Impulse Magnetron Sputtering (HIPIMS): A Promising and Scalable Application in Thin-film Photovoltaics

AbstractA novel method to deposit Copper Indium Gallium Diselenide (CIGS) using High Power Impulse Magnetron Sputtering (HIPIMS) was demonstrated and compared to the existing DC magnetron sputtering process. The metal-ion assisted thin-film growth inherent to a HIPIMS deposition process was used to advantage in depositing CIGS films. The HIPIMS plasma was characterized by measuring ion currents on a Langmuir probe placed into the plasma sufficiently close to the substrate. The high density plasma consisting of both metal and metal ions resulted in CIGS thin-film solar cells of superior conversion efficiencies (˜13%) as compared to conventional DC magnetron sputtering (˜10%). The efficiency enhancement was attributed to the improvement in the shunt resistance of the solar cell which corresponds to the increase in the density of the CIGS layer. Furthermore, it was also possible to grow large grained CIGS (˜1 micron) with high mobility metal-ions from the HIPIMS process. The scalability potential of the HIPIMS CIGS process was also demonstrated by running a 1.5 m long Copper-Indium-Gallium rotatable in a selenium environment using a HIPIMS power supply. The cylindrical magnetron was run at an average power of 7.8 KW and peak powers of as much as 300 KW with controlled arcing. The existence of a HIPIMS plasma was confirmed by the ion currents on the Langmuir probe and the metal signals from a Plasma Emission Monitor (PEM).

Does selenium deficiency unmask mercury toxicity in motor neurons?

Objective Inorganic mercury enters in particular motor neurons and has been implicated in motor neuron diseases. One way that cells protect themselves from mercury toxicity is via selenium, so we sought to determine whether the motor neurons of mice on a low selenium diet would be more susceptible to mercury toxicity. Methods Recently weaned mouse pups were placed on diets containing either low, normal or high levels of selenium. Twenty days later, half were exposed to mercury vapor. Ninety days after exposure, their spinal motor neurons and phrenic motor axons were examined histologically. Mercury in the spinal cord was sought using autometallography. Results Neither low nor high selenium diets combined with mercury vapor had any clinical effect on the mice. Mercury was seen within the spinal motor neurons of all exposed mice. Spinal motor neurons and phrenic motor axons however appeared normal in morphology and size across the groups. Conclusion Diets low or high in selenium did not damage motor neurons with or without mercury. This suggests that changes in the selenium environment are unlikely to precipitate mercury toxicity in motor neurons.

Preparation of selenium-enriched sprouts and identification of their selenium species by high-performance liquid chromatography-inductively coupled plasma mass spectrometry.

Sprouts of several plants (10 families and 28 species) were cultivated in a high selenium environment, and the chemical species of selenium in these selenium-enriched sprouts were identified by using high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS). Cultivation of sprouts of kaiware daikon (type of radish) with 5.0 microg/ml or 10.0 microg/ml of selenium as selenite inhibited the growth. However, no abnormalities in the shape or color were apparent even in the sprouts exposed to 10.0 microg/ml of selenium. The selenium concentration in the sprouts of most plants examined was higher than that from environmental exposure. Among the types of selenium that were accumulated, a large part (69-98%) was extractable in 0.2 M HCl. Chemical analysis of selenium in the HCl extract showed that the main selenium species in all the sprouts examined was Se-methylselenocysteine. In addition to Se-methylselenocysteine, selenomethionine, non-metabolized selenite, gamma-glutamyl-Se-methylselenocysteine and an unknown selenium compound were also detected in several high-selenium sprouts. Since higher anticarcinogenic activities of these monomethylated selenoamino acids have been observed, it is anticipated that such selenium-enriched sprouts will be used as a foodstuff for cancer prevention.

Detection of Crystalline Phases in CuInSe2 Films Grown by Selenisation Process

CuInSe 2 thin films have been prepared using a two-step process. The process involved the deposition of alternate layers of Cu and In onto molybdenum coated glass substrates using magnetron sputtering resulting in a Cu 11 In 9 precursor phase, free from inhomogeneous secondary phases, followed by annealing in an excess selenium environment at various temperatures ranging from 250 to 450 °C to synthesis the compound. This method results in densely packed, randomly oriented polycrystalline CuInSe 2 films with the chalcopyrite crystal structure with grain size larger than 2.0 μm for annealing temperatures of 500 °C. The layers annealed at 500 °C showed nearly stoichiometric composition with a direct energy band gap of 1.01 eV.

EXAFS studies of Cu + ion conducting and semiconducting copper chalcogenide and chalcohalide glasses

The short-range order in semiconducting xCu 2Se · (1 − x)As 2Se 3 and mixed conducting xCuI · (1 − x)As 2Se 3 glasses has been investigated using Extended X-ray Absorption Fine Structure (EXAFS) measurements at the Cu, As and Se K-edges. A non-tetrahedral local coordination of copper, either by Se or by Se and I, has been found in these glassy systems. The pyramidal AsSe 3 units remain essentially intact on introducing Cu 2Se or CuI. However, the average selenium coordination number, N Se–Y, where Y=As or Cu, increases with x from 2.0 to 2.5–2.6. Simple stoichiometric relationships account for the observed changes in N Se–Y for the Cu 2Se–As 2Se 3 glasses, which suggest that, at a nearest neighbour level, the average selenium environment consists of two relatively weakly interacting components coming from vitreous As 2Se 3 and a hypothetical glassy Cu 2Se. On the contrary, the EXAFS results indicate that CuI is dispersed in the glass network on a molecular level and interacts with the host matrix. Favourable conductivity pathways, associated with CuI, are suggested to appear in the glass structure, which explain the improved Cu + ion conduction and copper diffusion.

X-ray and high resolution selenium-77 solid state NMR spectroscopy as complementary probes to structural studies of organophosphorus diselenides

77 Se high resolution solid state NMR spectroscopy was employed to study structural properties of bis(diisopropoxyphosphorothioyl) diselenide 1 and bis(dineopentoxyphosphorothioyl) diselenide 2. The principal elements T ii of 77 Se effective dipolar/chemical shift tensor were calculated from spinning sideband intensities employing the WIN-MAS program. The values of anisotropy and asymmetry parameters reflect the distortion of the selenium environment. It was found that the T 33 component mostly contributes to changes in the isotropic chemical shifts. 77 Se CP/MAS experiments were used to decide the assignment of space group by counting the number of crystallographically unique selenium centers in the unit cell. Crystals of diselenide 1 are triclinic, space group P1̄ with a=8.485(3) Å, b=8.508(1) Å, c=8.511(2) Å, α=98.835(15)°, β=111.653(24)°, γ=93.524(21)°, V=559.5(3) Å 3, D c=1.544(2) g/cm 3 and Z=1. Refinement using 2222 reflections for 157 variables gives R=0.037. Crystals of diselenide 2 are triclinic, space group P1 with a=9.1418(8) Å, b=9.1465(8) Å, c=9.9200(9) Å, α=74.751(8)°, β=74.629(7)°, γ=82.216(7)°, V=769.7(1) Å 3, D c=1.365(2) g/cm 3 and Z=1. Refinement using 3316 reflections for 297 variables gives R=0.0272.

Atomic structure of selenium inserted in zeolites of the Na-mordenite type

The atomic structure of Se incorporated with various amounts in both small and large pore zeolites of the Na-mordenite type is investigated by X-ray absorption spectroscopy (XAS). The results of the EXAFS analysis are compared to those obtained for hexagonal selenium. The distances of Se to its first and second Se neighbors are found to be 2.33 and 3.61 A, respectively, and attributed to intrachain distances, which are reduced with respect to those of hexagonal selenium. The lack of the Se-Se distance at 3.44 A confirms the loss of the first interchain bonds present in hexagonal Se and confirms the incorporation of single chains of Se in the channels of the mordenite in agreement with previous results given in the literature. Only small differences in the selenium environment are observed for the various contents of Se in mordenite. The presence of a peak around 4 A in the Fourier transforms of the EXAFS data of all the analyzed compounds is attributed to the partial overlap of the single Se chains present inside the mordenite channels.

Growth and Characterization of Copper Indium Diselenide Thin Films by Molecular Beam Deposition

AbstractCuInSe2 thin films grown on Corning 7059 glass substrates were prepared by molecular beam deposition method with various Cu/In ratios in order to study the relationship between composition and material properties. Under a fixed copper beam flux intensity and overpressure selenium environments, the composition of films was modulated by changing the indium beam flux: intensity to obtain Cu-rich or In-rich films. The X-ray diffraction patterns show that the epitaxy films grown onto glass substrates are the polycrystalline structure. The grain size of polycrystalline films indicate that the surface morphology of the films are varied as a function of Cu/In ratio.

Temporal and spatial monitoring of soil selenium at Kesterson Reservoir, California

The selenium and salt content of the top 15 cm of the soil profile at Kesterson Reservoir (Merced County, California) have been monitored annually to develop a data set that provides a foundation for: (1) evaluating the status of the selenium inventory and biological hazards at Kesterson Reservoir; (2) understanding selenium fluxes near the soil surface; and (3) making long-term predictions of the selenium concentrations available for plant uptake and dissolution into rainwater ephemeral pools. Results of this monitoring program indicate that the soil selenium inventory at Kesterson may be categorized in terms of three main patterns: (1) spatial trends associated with historic Reservoir operations; (2) temporal trends due to the oxidation and remobilization of the selenium inventory and; (3) temporal trends due to seasonal cycles. It is evident that the selenium inventory and distribution within the soil profile will evolve slowly whereby the fraction of the total inventory that is now immobile (est. at 93%) will oxidize to more mobile and bioavailable forms. Two major issues with broad importance were raised concerning sampling the surface soil selenium environment at Kesterson which may be helpful to others conducting investigations of similar nature. These issues include: (1) the recognition that variations in surface soil contaminant concentrations due to seasonal redistribution may obscure long term trends and; (2) large spatial variability in soil contaminant concentrations make it difficult to obtain large enough data sets to detect statistically significant changes in the contaminant inventory until large changes have already taken place. A combination of both process-oriented and synoptic type sampling are recommended to better define time trends.

Selenium Content of Bison, Elk and Mule Deer

ABSTRACTSelenium (Se) content of elk, mule deer, bison and beef skeletal muscle was measured and compared. Selenium content was determined by graphite furnace after wet nitric acid digestion. Game samples did not differ in Se content but contained more Se than beef (wet weight) (P<0.05). On dry weight basis, deer contained more Se than elk, bison or beef (P<0.05). Within samples from male elk and deer, and elk and bison of both genders, there were interactions between species and muscles (P<0.05). Type of muscle and gender did not influence Se content (P<0.05). Selenium toxicity from consuming game that foraged in high selenium environments is remote.

Amyotrophic lateral sclerosis and selenium

<h3>To the Editor.—</h3> In the article "Amyotrophic Lateral Sclerosis in a High Selenium Environment" by Kilness and Hochberg (237:2843,1977) and in a subsequent publicity release by the American Medical Association, it was implied that excessive toxic amounts of selenium were the cause for a cluster of four cases of amyotrophic lateral sclerosis (ALS), which occurred in a highly seleniferous, sparsely populated region of South Dakota within a ten-mile radius from each other. I would like to point out that clusters of ALS occur elsewhere in areas with normal or low selenium levels in the geochemical environment. It cannot be concluded from the available evidence that a high intake of selenium is a cause or<i>the</i>cause of ALS. The most frequently occurring error in scientific logic is the assumption that two phenomena that occur side by side may be, or must be, connected with each other as cause and effect.

Amyotrophic Lateral Sclerosis and Selenium

ABSTRACT To the Editor.— In the article Amyotrophic Lateral Sclerosis in a High Selenium Environment by Kilness and Hochberg (237:2843,1977) and in a subsequent publicity release by the American Medical Association, it was implied that excessive toxic amounts of selenium were the cause for a cluster of four cases of amyotrophic lateral sclerosis (ALS), which occurred in a highly seleniferous, sparsely populated region of South Dakota within a ten-mile radius from each other. I would like to point out that clusters of ALS occur elsewhere in areas with normal or low selenium levels in the geochemical environment. It cannot be concluded from the available evidence that a high intake of selenium is a cause or the cause of ALS. The most frequently occurring error in scientific logic is the assumption that two phenomena that occur side by side may be, or must be, connected with each other as cause and effect.

Amyotrophic Lateral Sclerosis in a High Selenium Environment

During a ten-year period, four cases of amyotrophic lateral sclerosis have been found in a sparsely populated county (population 4,000) in west-central South Dakota. The patients were unrelated male farmer-ranchers between 57 and 66 years of age, living within a 15-km radius of each other. The cases occurred in a region where naturally occurring selenium toxication is endemic in farm animals.

Amyotrophic lateral sclerosis in a high selenium environment

Amyotrophic lateral sclerosis in a high selenium environment

TISSUE SELENIUM CONTENT OF THE GROWING PIG

Selenium retention studies were made on a group of 86 pigs, ranging in weight from 10 to 132 kg. The animals were raised under a natural selenium environment in which the creep ration contained 0.69, grower–finisher ration 0.34, and the sow ration 0.46 ppm of Se on an air-dry basis. The Se content of the drinking water was 0.41 ppb. Selenium was determined in two body compartments: the offal, comprising internal organs, feet and head; and the second compartment, the dressed carcass. The average Se content per kg of offal was 189.4 ± 8.05 μg (SE), 142.2 ± 5.50 μg per kg of dressed carcass and 152.1 ± 5.30 μg per kg of warm empty body. On the basis of total protein in the empty body, (comparable to fat-free dry muscle) the Se content was 1,029.8 ± 36.0 μg per kg. On a fat-free basis, (comparable to fat-free fresh muscle) the Se content was 214.4 ± 7.60 μg per kg. Sex differences in Se content were not significant. Based on present National Research Council–National Academy of Sciences estimated requirements, the natural Se environment in this study represents a nontoxic nutritional level which is surplus to physiological requirements. The selenium levels reported are considered to represent "normal" physiological levels, resulting from an adequate, natural Se environment.