Excess Se Research Articles

Selenization of Cu and In thin films for the preparation of selenide photo-absorber layers in solar cells using Se vapour source

Abstract Gas phase selenization of vacuum deposited Cu and In thin films employing an elemental Se vapour source is demonstrated as an essential first step in the search for optimized process parameters for the formation of single phase CuInSe2 materials suitable for solar cell applications. The selenization was accomplished in Se vapour, derived from an elemental Se source, held at 240–260°C. This source was placed in a flow of nitrogen gas at 500 Torr to transport the Se vapour to the metal films. The selenization reaction readily occurs at Cu and In films kept at 340–400°C. Lower selenization temperatures invariably lead to the formation of Cu and In selenides with well defined crystalline microstructures. Hexagonal CuSe with an excess of Se in the matrix is the equilibrium growth phase, while the cubic Cu2−xSe phase evolves under conditions of excess Se flux. Selenization of the In films consistently led to the formation of the β-form of hexagonal In2Se3. At high selenization temperatures (400°C), while the β-form still emerges as the major component, traces of the α-form of In2Se3 are also detected. Detailed X-ray diffraction, electron probe analysis and microstructure data are presented.

Urinary selenium concentrations

Urinary selenium concentrations are used as an indicator of selenium status. A strong correlation has been established between dietary selenium and daily urinary selenium excretion in a wide range of populations from all over the world with different dietary selenium intake. Data on urinary selenium concentrations in healthy individuals and patients with different pathological conditions are reviewed. Selenium excretion rates of 20-200 micrograms/day are not associated with deficiency or toxicity problems. Urinary Se excretion is decreased in children, elderly people, and pregnant women. Workers exposed to heavy metals, and cancer patients, have higher and lower urinary Se concentrations, respectively, than control groups. The trimethylselenonium ion, a minor metabolite of Se in urine, assumes a significant role only in the detoxification of excess Se intake. Studies of bioavailability and balance show the important role of the kidneys in homeostatic regulation of Se.

Thermodynamic Excess Quantities of Solid Ternary FexNixCo1-2x Alloys by Computeraided Knudsen Cell Mass Spectrometry

Computer-aided Knudsen cell mass spectrometry is used for thermodynamic investigations on solid ternary Fe 2 Ni 2 Co 1-2x alloys. The «Digital Intensity Ratio» method has been applied for the evaluation of the thermodynamic mixing functions, Ternary thermodynamically adapted power series are used for the algebraic representation of the thermodynamic excess properties. The values of the molar heats of mixing HE, of the molar excess entropies SE, and of the molar excess Gibbs energies G E along a section with constant ratio of the mole fractions x N /x Fe =1 are presented

The chemistry of the initial stages of the growth of ZnSe on GaAs(100) using diethylzinc and diethylselenium precursors

The adsorption and reaction of molecular and cracked diethylselenium on clean GaAs(100)-4×1 and in the presence of coadsorbed diethylzinc were studied using temperature programmed desorption, X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy. Diethylselenium was found to adsorb only molecularly on the GaAs(100)-4×1 surface and was unreactive toward coadsorbed diethylzinc. Cracking of the diethylselenium prior to adsorption resulted in the deposition of selenium on the surface. Heating the adsorbed selenium layer to 800 K produced a Ga2Se3 surface compound. Diethylzinc adsorbed dissociatively on the selenium-covered surface resulting in the formation of ZnSe and adsorbed ethyl groups. For submonolayer Se coverages, the adsorbed ethyl groups reacted to form gaseous ethylene, ethane and hydrogen near 570 K, while Se in excess of one monolayer reacted with adsorbed ethyl groups at 435 K to form gaseous diethylselenium. The mechanisms and stable surface species involved in these reactions and their implications for the metalorganic chemical vapor deposition (MOCVD) growth of ZnSe thin films are discussed.

Effects of aurothioglucose and dietary Se on glutathione S-transferase activities and glutathione concentrations in chick tissues.

Experiments were conducted to determine whether the increased glutathione S-transferase (GSH-T) activity associated with selenium (Se) deficiency is necessarily related to losses in the activity of Se-dependent glutathione peroxidase (SeGSHpx) in chicks. Nutritional Se status was altered in two ways: by treatment with an antagonist of Se utilization, aurothioglucose (AuTG), and by feeding diets containing excess Se. Chicks given AuTG (10-30 mg AU/kg, sc) had growth rates and hepatic GSH concentrations that were comparable to those of saline-treated controls; however, their plasma GSH levels exceeded those of either Se-deficient (6-fold) or -adequate (3-fold) saline-treated chicks. Hepatic SeGSHpx activities of AuTG-treated chicks were half those of controls under conditions of Se-adequacy; however, this effect was not detected when Se was deficient. Hepatic GSH-TCDNB (assayed with 1-chloro-2,4-dinitrobenzene) activities of AuTG-treated chicks were significantly greater than those of controls when Se was deficient (i.e., when SeGSHpx activity was 12% of the Se-adequate level); however, deprivation of Se did not affect GSH-TCDNB activity in the absence of AuTG. Chicks fed excess Se (6-20 ppm as Na2SeO3) in diets containing either low (2 IU/kg) or adequate (100 IU/kg) VE, showed hepatic GSH-TCDNB activities and GSH concentrations greater than those of Se-adequate (0.2 ppm Se) chicks by 100% and 40%, respectively. That increased hepatic GSH-TCDNB activity can occur because of either AuTG or excess Se status under conditions wherein SeGSHpx activity is not affected indicates that the transferase response is not directly related to changes in the peroxidase.

Computerunterstützte Thermodynamik fester Ni-Pd Legierungen über die Knudsenzellen-Massenspektrometrie und Berechnung des Zustandsdiagrammes

Solid Ni–Pd alloys have been investigated thermodynamically by means of the computer-aided Knudsen cell mass spectrometry. Thermodynamic evaluation has been performed by applying the enlarged “Algebraic Intensity-Ratio”-method (A.I.R.). The thermodynamic excess properties can be described algebraically by means of T.A.P.-series (Thermodynamically adapted power series) with three adjustable parameters (C = [8757.5–11.2810 T/K] J/mol; C = [–18573.3 + 5.1073 T/K] J/mol; C = [3908.0–0.4558] J/mol). – At higher temperatures solid Ni–Pd alloys are characterised by negative molar excess Gibbs energies GE, and slightly positive molar excess entropies SE. At 1500 K the minimum GE-value is –3270 J/mol (57 at.% Pd), and the maximum SE-value is 2.25 J/mol·K (43.7 at.% Pd). Ni–Pd alloys with Pd contents with less than 50 at.% Pd show endothermic molar heats of mixing HE (maximum value: 835 J/mol at 21.5 at.% Pd), whereas Ni–Pd alloys with more than 50 at.% Pd show slightly exothermic HE-values (minimum value: –575 J/mol at 79.5 at.% Pd). The thermodynamic Pd-activities aPd exhibit at 1500 K over the whole concentration range slightly negative deviations from Raoult's law. The thermodynamic Ni-activities aNi of the Ni-rich solid alloys (xPD < 0.25) show at 1500 K nearly ideality, Ni–Pd alloys with higher Pd contents than 25 at.% Pd were found to show slightly negative deviations from ideality. – The phase diagram has been computed by means of a generally applicable procedure for the calculation of the equilibrium compositions of coexisting phases. The calculations were based upon the results of this work, the thermodynamic data from mass spectrometric studies on the liquid phase, and literature data for the heat capacities and enthalpies of Ni and Pd.

Some aspects of selenium relationships in soils and plants

Abstract The variation in the Se amounts in plants reflects differences in the texture of the soil in which plants are grown. In the La Roche‐Posay region of France, kaolinite soils produce crops with excessive Se. Leaching may contribute to Se accumulation in drainage water, raising Se concentrations in plants grown in soils low in available Se, such as sandy or chalky soils. Also, various plant species differ in their capacity to concentrate Se and other elements. For instance, Helminthia echioides accumulates Se at rates ranging from 2.05 to 7.9 ppm and shows positive correlations with P, Mn, Zn, Ni, Co and Cd. For Trifolium repens, values ranging from 2 to 32.5 ppm of Se are positively correlated with the levels of K, Co and Mo. Conversely, absorption of Se is inhibited by Fe, Al, Ni and As.

Type I Iodothyronine Deiodinase Activity after High Selenium Intake, and Relations between Selenium and Iodine Metabolism in Rats

Type I iodothyronine deiodinase (I-D), which catalyzes the production of the thyroid hormone 3,3´,5-triiodothyronine from thyroxine, has recently been identified as a selenoenzyme. It is therefore of interest to investigate the relationships between selenium and iodine metabolism. In the livers of Se-deficient rats I-D activity was inhibited; the production of 3,3´,5-triiodothyronine and 3,3´-diiodothyronine from added thyroxine was decreased by >95% relative to Se-adequate controls. The hepatic I-D activity was also reduced in rats fed a diet with a low iodine concentration. Unaltered glutathione peroxidase activities in liver and plasma of these rats suggest, however, that with normal Se intake this metabolic pathway of Se is not affected by iodine depletion. When rats were administered 75Se-labeled selenium at levels equal to the amounts ingested from diets with Se concentrations of 0.3 or 2 mg Se/kg, greater Se concentrations were found in the thyroid and liver of the animals receiving the higher dosage. The thyroidal 3,3´,5-triiodothyronine and thyroxine concentrations, however, were comparable in rats fed diets with 0.3 mg Se/kg diet as selenite and 2 mg Se/kg as selenite or L-selenomethionine. The measurement of the hepatic I-D and glutathione peroxidase activities in these animals showed that excessive Se supply does not elevate the activities of the two enzymes but might even have the opposite effect. At high Se intake tissue Se concentration cannot therefore be used as indicator of the selenoenzyme activities.

Distribution of selenium in erythrocytes, plasma, and urine of Chinese men of different selenium status

Blood and urine were collected from Chinese men living in areas of China with deficient, adequate, and excessive levels of selenium (Se). Se content and glutathione peroxidase (GSH-Px) activity were determined on blood fractions and total Se and trimethylselenium (TMSe) determined in the urine. There was an increase of erythrocyte and plasma Se concentration with each increase of Se status. In contrast, this was not true for the GSH-Px activity. Both erythrocyte and plasma GSH-Px activity were higher in men with adequate Se intake than in those with deficient intakes of this element, but this activity was not any higher in men with excessive Se intake than those with adequate intake. The percentage of Se associated with GSH-Px in both plasma and erythrocytes was inversely related to the Se status of the men. Gel filtration of erythrocyte lysates revealed basically one major Se peak from all men, but the amounts of Se in this peak differed greatly among the three groups. Most of this Se was associated with hemoglobin. In contrast, different patterns were obtained in the plasma from the various men. One main peak was obtained with plasma from Se-deficient men, but two Se peaks were obtained with plasma from men with adequate Se status, and up to four peaks were obtained with plasma from men with excessive Se status. The excretion of Se in urine increased proportionally with the Se status and TMSe increased from none detectable in deficient men, to 2% of total Se in men with adequate status to 7% of total Se from men with excessive Se intake.

Plant and animal species composition and heavy metal content in fly ash ecosystems

Plant and animal species present on a coal fly ash slurry pond site and a dry deposit site were surveyed and sampled during a two-day period in October. Elemental analyses were determined for most of the species encountered. A total of 48 plant species were observed on the two sites, with 35 species on the wet site, and 20 on the dry site. Eighteen terrestrial and 7 aquatic animal species were found on the wet site, exclusive of vertebrates which were not studied with the exception of a carp (Cyprinus carpio). Eleven terrestrial invertebrates and one aquatic species were observed on the dry site. Neutron activation analysis was carried out for: Se, Hg, Cr, Ni, Zn, Co, Sb, Cd, and As. Using literature values for phytotoxicity, we conclude that, in general, plants did not accumulate toxic levels of metals. Only one plant (Impatiens biflora Willd.) showed a significant level of Cd. Of 20 plants analyzed on the wet site, 10 had excessive Se concentrations (>5 ppm); on the dry site 6 out of 18 had high Se values. In animals (Gryllus sp.; Melanoplus sp.; Trachelipus sp.; Lumbricus terrestris; Physa integra; Cyprinus carpio) the trace metal concentration was generally in between that of control animals and that of the fly ash itself. One exception included Zn, which, although the most variable element examined, was concentrated in all the terrestrial animals to levels higher than in fly ash. Crickets are the most consistent bioconcentrators with Cr, Se, and Zn at higher levels than for control animals. All animal species studied accumulated Se compared to controls.

Selenium and glutathione peroxidase tissue distribution in rats: Effect of dietary intake and total body burden of selenium

A series of experiments was performed to determine theeffects of individual variability and dietary selenium (Se) concentration on tissue distribution of Se in rats. Experiment one used mature rats selected for high or low concentrations of Se in blood. Rats selected for high concentrations of Se in blood tended to have greater concentrations and amounts of Se in liver and erythrocytes than rats selected for low blood Se. Experiment two examined the distribution of Se in rats fed diets deficient, adequate or high (but not toxic) in Se. Kidney and liver accumulated Se in excess of dietary Se concentration at all dietary Se concentrations. Selenium concentrations in the muscle and vesicular gland reflected dietary Se concentrations, while the testes had the same amount of Se regardless of dietary intake. The largest Se pool in rats fed the deficient diet was the testes, whereas the muscle was the largest pool in rats fed a high Se diet. Changes in tissue distribution of Se suggest that some tissues have priority for Se when it is limiting. Other tissue pools of Se become saturated at high dietary intakes, and genetic differences may cause individual variation in deposition of Se into proteins other than GSH-Px.

Excess compressibility and excess dielectric constant for a morpholine-n-butyl alcohol liquid mixture

The variation in excess compressibility beta SE and excess dielectric constant in 'E as a function of mole fraction x at room temperature have been determined for a liquid mixture of morpholine (as the solute) with n-butyl alcohol (as the solvent). The excess compressibility was found to be negative for this liquid mixture and is explained in terms of solute-solvent interactions. The excess dielectric constant was found to be abnormally positive for this liquid mixture at a mole fraction of around 0.25 and is explained in terms of the alignment of dipoles.

Arsenic doped ZnSe grown by molecular-beam epitaxy

We have been able to incorporate As into molecular-beam epitaxy (MBE) grown ZnSe in the range of 1017–1021 atoms/cm3 using Zn3As2 as the As source. This contrasts with very low As levels we obtained using an As cracker cell. The As incorporation is highly nonlinear with Zn3As2 flux and depends on the excess Se used. Several samples doped with Zn3As2 show low temperature photoluminescence with near band edge emission dominated by shallow acceptor levels. We will describe the details of several growth variations studied and their influence on As incorporation.

Computerunterstützte Knudsenzellen‐Massenspektrometrie: Die thermodynamischen Mischungsfunktionen flüssiger Gold‐Palladium‐Legierungen

AbstractThermodynamic investigations on liquid Au—Pd alloys have been performed by means of a computer‐aided mass spectrometer in combination with a high temperature Knudsen cell unit with improved temperature measurement. A further development of the “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been applied for determining the thermodynamic excess functions. T.A.P.‐series (Thermodynamically adapted power series) with three adjustable parameters are used for the algebraic representation of the thermodynamic excess properties. At 1850 K the molar excess Gibbs energy GE is negative (minimum: — 1300 J/mol at 33.9 at.% Pd) nearly over the whole range of concentration, only the alloys with more than 85 at.% Pd show slight positive GE‐values (maximum: 78 J/mol at 93.2 at.% Pd). The molar heats of mixing HE, and the molar excess entropies SE show at 1850 K a similar behaviour. These quantities are mainly negative; slightly positive values occur only for alloys with more than 70 at.% Pd. The minimum HE‐value is —8220 J/mol (28.7 at.% Pd), and the minimum SE‐value is —3.8 J/mol · K (28 at.% Pd). The maximum HE‐value is 1390 J/mol at 88.15 at.% Pd. and the maximum SE‐value is 0.7 J/mol · K (87.5 at.% Pd). At 1850 K the thermodynamic Au‐activities aAu are found to show slight negative deviations from ideality over the whole concentration range. The same behaviour is observed for the Pd‐activities for Pd‐concentrations less than 50 at.‐% Pd. The Pd‐activities of alloys with more than 50 at.‐% Pd show slight positive deviations from Result's law.

Hepatic glutathione metabolism and lipid peroxidation in response to excess dietary selenomethionine and selenite in mallard ducklings

Studies were conducted with mallard (Anas platyrhynchos) ducklings to determine the effects of excess dietary selenium (Se) on hepatic glutathione concentration and associated enzymes, and lipid peroxidation. Day-old ducklings were fed 0.1, 10, 20, or 40 ppm Se as seleno-DL-methionine or sodium selenite for 6 wk. Selenium from selenomethionine accumulated in a dose-dependent manner in the liver, resulting in a decrease in the concentration of hepatic-reduced glutathione (GSH) and total hepatic thiols (SH). These effects were accompanied by a dose-dependent increase in the ratio of oxidized glutathione (GSSG) to GSH, and an increase in malondialdehyde concentration as evidence of lipid peroxidation. Hepatic and plasma GSH peroxidase activity was initially elevated at 10 ppm Se as selenomethionine, whereas GSSG reductase activity was elevated at higher dietary concentrations of Se. Selenium from sodium selenite accumulated in the liver to an apparent maximum at 10 ppm in the diet, resulting in an increase in hepatic GSH and GSSG accompanied by a small decrease in total hepatic SH. Sodium selenite resulted in an increase in hepatic GSSG reductase activity at 10 ppm and in plasma GSSG reductase activity at 40 ppm. A small increase in lipid peroxidation occurred at 40 ppm. These findings indicate that excess dietary Se as selenomethionine has a more pronounced effect on hepatic glutathione metabolism and lipid peroxidation in ducklings than does selenite, which may be related to the pattern of accumulation. Effects of Se as selenite appear to be less pronounced in ducklings than reported in laboratory rodents. The effects of selenomethionine, which occurs in vegetation, are of particular interest with respect to the health of wild aquatic birds in seleniferous locations.

Effect of Laser Irradiation on Low‐Temperature Photoconductivity and Photoluminescence Spectra of Gallium Selenide

AbstractFeatures of photoluminescence (PL) and photoconductivity (PC) spectra, taken at 4.2 to 60 K, of GaSe crystals of stoichiometric composition and grown with an excess and with a lack of Ga atoms are analyzed. It is shown that the presence of excessive Se atoms in the matrix of GaSe crystals results in the formation of centres where triplet excitons are bound. Excessive Ga atoms formed in a crystal both, in the process of its growth and under the effect of laser irradiation give rise to regions with another polytype composition (γ‐modification). The presence of such (γ‐polytype) regions is shown to produce packing defects whre localization of excited electron states (n &gt; 1) occurs. An effect of PC signal increase with increasing exposure dose is found, which is attributed to the formation of acceptor centres.

Preparation of CuGaSe 2 crystals from Te solutions

The growth conditions of CuGaSe 2 chalcopyrite crystals from Te solutions have been studied. The crystals, grown from the solutions containing solutes with the composition of the stoichiometric CuGaSe 2, have a zincblende structure. But from the solutions with excess Cu or with both excess Cu and excess Se, chalcopyrite-structure crystals CuGa(Se xTe 1−x) 2 are obtained. It is confirmed that the introduction of Te atoms in the crystals is reduced by using Te solutions containing excess Cu and Se solute.

Thermodynamik fester Fe ‐Ni Legierungen: Massenspektrometrische Bestimmung der thermodynamischen Mischungseffekte und Berechnung des Schmelzdiagramms

AbstractThermodynamic investigations on solid Fe‐Ni alloys (f.c.c.‐phase) have been performed by means of a mass spectrometer in combination with a high temperature Knudsen cell unit. The “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been applied for determing the thermodynamic excess functions. The molar excess Gibbs energies GE, the molar heats of mixing HE, and the molar excess entropies SE are negative over the whole range of composition. At 1623 K the minimum value of GE is ‐2350 J/mol (57.6 at % Ni), the minimum value of HE is ‐3950 J/mol (63.6 at % Ni), and the minimum value of SE is ‐1.04 J/mol K (70.2 at % Ni). The thermodynamic activities aj show slight negative deviations from Raoult's law. Using the results of this work, the thermodynamic results from mass spectrometric studies on liquid Fe ‐Ni alloys, and literature data for the enthalpies and heat capacities of Fe and Ni the phase diagram has been redetermined, using a generally applicable procedure for the calculation of the equilibrium compositions of coexisting phases. The applied procedure is based upon the generalized Newton method for the numerical solution of equations.

Thermodynamics of Solid Cu—Ni Alloys by Knudsen Cell Mass Spectrometry and Re‐Calculation of the Phase Diagram

AbstractSolid Cu—Ni alloys have been investigated thermodynamically within the whole range of composition by Knudsen Cell Mass Spectrometry. The “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been used for the determination of the thermodynamic mixing behavior. The thermodynamic activities aj show positive deviations from Raoult's law. The molar enthalpies of mixing HE and the molar excess Gibbs energies GE are positive over the whole range of composition. At 1350 K the maximum value of HE is 2420 J/mol (59.48 at‐% Ni), and the maximum value of GE is 3220 J/mol (53 at‐% Ni). The excess entropies SE are negative over the whole range of composition with a minimum value of — 0.719 J/mol · K at 36.71 at‐% Ni. The phase diagram has been re‐evaluated by using an analytical procedure which is based on the generalized Newton method for the numerical solution of equations. The calculations are based on the thermodynamic data obtained in this study, on the thermodynamic results from mass spectrometric studies on liquid Cu—Ni alloys, and on literature data for the heat capacities and the heats of melting of Cu and Ni.

Adaptive Changes in Hepatic Glutathione Metabolism in Response to Excess Selenium in Rats

Experiments were conducted with rats to determine if administration of excess selenium (Se) alters hepatic glutathione (GSH) metabolism. Se was fed, 6 ppm as Na2SeO3, for 6 weeks in a 15% casein, tocopherol-free diet and compared to 0.1 ppm Se. High Se significantly increased the concentrations of hepatic nonprotein sulfhydryls (NPSH) and oxidized glutathione (GSSG) as well as the GSSG:NPSH ratio. Of the NPSH, 94.1 ± 1.7% was shown to be GSH. Similar increases in NPSH, GSSG and GSSG:NPSH due to high Se were seen when the diet was supplemented with methionine (0.3%) and/or vitamin E (100 IU/kg diet) although methionine independently increased NPSH and GSSG. Hepatic glucose-6-P dehydrogenase, glutathione reductase and γ-glutamyl-transpeptidase activities were significantly increased by high Se but cysteine dioxygenase activity was unaffected. An i.p. injection of Na2SeO3 (15 µmol Se/kg body weight) significantly increased hepatic GSSG, which was followed by an increase in NPSH(GSH) compared to saline controls. These results indicate that excess Se causes a shift in hepatic GSH toward a more oxidized state. Increases in NPSH(GSH) and in the enzyme activities observed appeared to be adaptive changes initiated in an attempt to maintain a normal GSSG:GSH ratio. Elevated GSSG or the increased GSSG:GSH ratio caused by Se may initiate these adaptations.