Se Deposition Research Articles

Geochemical characteristics of selenium and its correlation to other elements and minerals in selenium-enriched rocks in Ziyang County, Shaanxi Province, China

Ziyang County, Shaanxi Province, China is a world known selenium (Se)-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990s. This study investigated the geochemical characteristics of Se and its fractions in Se-enriched rocks from Ziyang. Se distribution is uneven, ranging from 0.23 to 57.00 μg/g (17.29±15.52 μg/g). Se content is higher in slate than chert, and even lower in carbonate rocks. Cd, As and V are enriched but Pb is depleted in Se-enriched strata. Se has different correlations both with TS (total sulfur) (R2=0.59 for chert) and TC (total carbon) (R2=0.77 for slate, R2=0.87 for carbonate). Se has significant positive correlations with V (r=0.65), As (r=0.485), Cd (r=0.459) and Pb (r=0.405). The Se level correlates with mineral content, positively with pyrite, chlorite and illite, negatively with albite. Se associated with sulfide/selenide and elemental Se are the predominant fractions of total recovered Se, suggesting that a reducing environment and the formation of sulfides were significant to Se deposition during its geochemical cycle. Although low concentration of bio-available Se (average 5.62%±3.69%) may reduce the risk of Se poisoning in the target area, utilization of Se-rich rock as natural fertilizer should be restricted.

Effects of Different Dietary Selenium Sources on Antioxidant Status and Blood Phagocytic Activity in Sheep.

The objective of this experiment was to investigate the effects of feed supplementation with equivalent doses of selenium from sodium selenite (SS) or selenized yeast (SY) on Se deposition, selenoenzyme activity and lipid peroxidation in tissues as well as in bacterial and protozoal fractions of rumen contents in sheep. The phagocytic activity of monocytes and neutrophils in whole blood was also assessed after 3months of dietary treatment. While animals in the control group were fed with unsupplemented basal diet (BD) containing only background Se (0.16mg/kg DM), the diet of the other two groups (n=6) consisted of identical BD enriched with 0.4mg Se/kg DM either from SS or SY. Concentrations of Se in blood and tissues were found to be significantly increased in both supplemented groups. No response in Se deposition was recorded in the musculus longissimus dorsi of sheep given dietary SS. The intake of SY resulted in a significantly higher Se level in the blood, kidney medulla, skeletal muscles, heart, intestinal and ruminal mucosa than in the case of SS supplementation. No differences appeared between tissue Se contents in the liver and kidney cortex due to the source of added Se. Regardless of source, Se supplementation to feeds significantly increased the glutathione peroxidase (GPx) activity in blood and tissues except the kidney medulla and jejunal mucosa. Supplementation with SY resulted in significantly higher activity of thioredoxin reductase in the liver and ileal mucosa, and also reduced malondialdehyde content in the liver and duodenal mucosa. Dietary Se intake increased Se concentrations in the total rumen contents and bacterial and protozoal fractions. The accumulation of Se in rumen microbiota was associated with increased GPx activity. Phagocytic cell activity was enhanced by Se supplementation. Our results indicate that Se from both sources has beneficial effects on antioxidant status in sheep and can be utilized by rumen microflora.

Distribution of soil selenium in China is potentially controlled by deposition and volatilization?

Elucidating the environmental drivers of selenium (Se) spatial distribution in soils at a continental scale is essential to better understand it’s biogeochemical cycling to improve Se transfer into diets. Through modelling Se biogeochemistry in China we found that deposition and volatilization are key factors controlling distribution in surface soil, rather than bedrock-derived Se (<0.1 mg/kg). Wet deposition associated with the East Asian summer monsoon, and dry deposition associated with the East Asian winter monsoon, are responsible for dominant Se inputs into northwest and southeast China, respectively. In Central China the rate of soil Se volatilization is similar to that of Se deposition, suggesting that Se volatilization offsets it’s deposition, resulting in negligible net Se input in soil. Selenium in surface soil at Central China is roughly equal to low petrogenic Se, which is the main reason for the presence of the Se poor belt. We suggest that both deposition and volatilization of Se could play a key role in Se balance in other terrestrial environments worldwide.

2-Hydroxy-4-Methylselenobutanoic Acid as New Organic Selenium Dietary Supplement to Produce Selenium-Enriched Eggs.

Food-based strategies need to be developed to improve the selenium (Se) status of individuals. The aim of this study was to evaluate the effects of a new organic Se [2-hydroxy-4-methylselenobutanoic acid (HMSeBA)] on selected performance criteria and Se deposition in egg of laying hens. Isa Brown laying hens, 18weeks of age were randomly allocated to two dietary treatments and fed for 10weeks. The hens were fed two corn-soybean meal-based diets comprising a control basal diet without Se supplementation and a test diet supplemented with Se at 0.2mg/kg from HMSeBA. No difference was observed among dietary treatments on feed intake, egg weight and laying rate, whereas egg yolk fatty acid profile and vitamin E content were positively influenced by HMSeBA supplementation. Hens fed Se-supplemented diet exhibited greater (P<0.001) egg yolk total Se contents, which averaged 21.2mg/100g dry matter (DM) compared to control diet (11.7mg/100g DM). Our results suggested that HMSeBA as Se supplement influences positively egg yolk quality without affecting hens' productive traits. Moreover, HMSeBA offers an efficient alternative to fortify eggs with Se, which can consequently lead to greater supply of Se for humans.

Selenium deposition kinetics of different selenium sources in muscle and feathers of broilers

The objective of this study was to determine selenium (Se) deposition kinetics in muscles and feathers of broilers in order to develop a rapid method to compare bioavailability of selenium sources. Different Se sources such as 2-hydroxy-4-methylselenobutanoic acid (HMSeBA, SO), sodium selenite (SS) and seleno-yeast (SY) were compared for their kinetics on Se deposition in muscles and feathers in broiler chicks from 0 to 21 d of age. A total of 576 day-old broilers were divided into four treatments with 8 replicates of 18 birds per pen. The diets used in the experiment were a negative control (NC) not supplemented with Se and 3 diets supplemented with 0.2 mg Se/kg as SS, SY or SO. Total Se content in breast muscle and feathers were assessed on days 0, 7, 14 and 21. At 7 d of age, SO increased muscle Se content compared to D0 (P < 0.05), whereas with the other treatments, muscle Se concentration decreased (P < 0.05). After 21 days, organic Se sources maintained (SY) or increased (SO) (P < 0.05) breast muscle Se concentration compared to hatch value whereas inorganic source (SS) or non-supplemented group (NC) showed a significant decrease in tissue Se concentration (P < 0.05). At D21, Se contents of muscle and feathers were highly correlated (R2 = 0.927; P < 0.0001). To conclude, these results indicate that efficiency of different Se sources can be discriminated through a 7 d using muscle Se content in broiler chickens. Muscle and feathers Se contents were highly correlated after 21 days. Also feather sampling at 21 days of age represents a reliable and non-invasive procedure for Se bioefficacy comparison.

Study of selenium electrodeposition at gold electrode by voltammetric and rotating disc electrode techniques

The electrodeposition process of selenium has been studied by voltammetry (CV) in connection with a rotating disc electrode (RDE) technique. The paper discusses the mechanism and the rate-determining step of Se deposition. It has been determined that the rate of the Se monolayer-forming process observed at ca. 0.6V vs. NHE is diffusion controlled, not surface activation barrier-dependent. It is proposed that this process is an overpotential deposition process (OPD) and not an underpotential deposition process (UPD). The diffusion coefficient for the reacting species was determined as 2.2×10−5cm2s−1. The reacting species are proposed to be identified with HSeO3− ions. The transfer coefficient, α, for this process was calculated as 0.3, exchange current density, jo, as 1.1×10−6Acm−2, and the rate constant, k, as 9.1×10−7cms−1, respectively.Analysis of RDE data recorded for the Se bulk deposition process taking place at ca. −0.1V vs. NHE and fitting them with either the Levich or the Koutecký–Levich equation indicates that this process is a diffusion-dependent one. The calculated diffusion coefficient was determined as 1.1×10−5cm2s. These data, together with experimental condition (pH) allow one to propose H2SeO3 molecules as those being reduced during the formation of the Se bulk deposited layer. The transfer coefficient, α, for this process was calculated as 0.1, exchange-current density, jo, as 7.7×10−6Acm−2, and the rate constant, k, as 1.6×10−4cms−1, respectively. The comparison of kinetic parameters for six-electron and four-electron processes proves that the reaction responsible for building up the Se film is six-electron reaction.

Comparative study of DL-selenomethionine vs sodium selenite and seleno-yeast on antioxidant activity and selenium status in laying hens

The aim of this study was to compare the effect of DL-selenomethionine (SM) with 2 routinely used Se sources, sodium selenite (SS) and seleno-yeast (SY), on relative bioavailability based on antioxidant activity and tissue Se content. Six hundred thirty 131-day-old brown laying hens were randomly assigned to 7 treatments for 168 d (24 wks) with 6 replicates of 15 hens per replicate. The SS and SY animals were supplemented a cornmeal and soybean diet that supplied a total Se 0.3 mg/kg whereas SM was added at 4 different levels to the total Se at 0.1, 0.3, 0.5 and 0.7 mg/kg. All hens fed the Se-supplemented diet showed higher glutathione peroxidase (GSH–Px) activity (P < 0.01), higher superoxide dismutase (SOD) activity (P < 0.05), lower malondialdehyde (MDA) content (P < 0.05) in plasma, and greater Se contents in egg yolks, albumen, leg muscle, breast muscle, liver, and plasma compared with those fed the control diet (P < 0.01). The organic sources (SY and SM) exhibited a greater ability to increase the GSH–Px activity (P < 0.01) and Se content in albumen (P < 0.01), leg, and breast muscles (P = 0.0099 and P = 0.0014, respectively) than the SS that was added at 0.3 mg Se/kg. The higher SM added levels increased the GSH–Px activity until the dose of 0.5mg Se/kg (P < 0.01).The greater Se concentrations in albumen, muscle and liver appeared in the higher SM-added level, as well as above the dose of 0.1 mg Se/kg (P < 0.01). In addition, hens fed the diet with SM accumulated more Se in albumen, leg, and breast muscle than those fed diets with SY (P < 0.05). These results confirmed the higher ability of organic Se sources to increase the antioxidant activity and Se deposition in egg albumen, leg, and breast muscles compared with SS, and demonstrated a significantly better efficiency of SM compared with SY for albumen and muscle Se enrichment.

Biochemical Comparison of Commercial Selenium Yeast Preparations

The trace mineral selenium (Se) is an essential element for human and animal nutrition. The addition of Se to the diet through dietary supplements or fortified food/feed is increasingly common owing to the often sub-optimal content of standard diets of many countries. Se supplements commercially available include the inorganic mineral salts such as sodium selenite or selenate, and organic forms such as Se-enriched yeast. Today, Se yeast is produced by several manufacturers and has become the most widely used source of Se for human supplementation and is also widely employed in animal nutrition where approval in all species has been granted by regulatory bodies such as the European Food Safety Authority (EFSA). Characterisation and comparison of Se-enriched yeast products has traditionally been made by quantifying total selenomethionine (SeMet) content. A disadvantage of this approach, however, is that it does not consider the effects of Se deposition on subsequent digestive availability. In this study, an assessment was made of the water-soluble extracts of commercially available Se-enriched yeast samples for free, peptide-bound and total water-soluble SeMet. Using LC-MS/MS, a total of 62 Se-containing proteins were identified across four Se yeast products, displaying quantitative/qualitative changes in abundance relative to the certified reference material, SELM-1 (P value <0.05; fold change ≥2). Overall, the study indicates that significant differences exist between Se yeast products in terms of SeMet content, Se-containing protein abundance and associated metabolic pathways.

Selenium (Se) Removal from Copper Refinery Wastewater Using a Combination of Zero-Valent Iron (ZVI) and Se(VI)-Reducing Bacterium, &lt;i&gt;Thaurea selenatis&lt;/i&gt;

The copper refinery process produces Se(VI)-bearing wastewater with a high content of Cl− and SO42− ions. To overcome the negative effect caused by Cl− and SO42− ions on Se(VI) reduction and its following removal, this study investigated the possible synergistic effect of the combination of Se(VI)-reducing bacterium, Thaurea (T.) selenatis and zero-valent iron (ZVI). In the presence of SO42− (200 mM) and Cl− (300 mM), the following was observed: (i) ZVI alone was unable to remove Se both under strictly aerobic and micro-aerobic conditions. (ii) Se(VI) reduction by T. selenatis alone was severely inhibited under anaerobic conditions (and thus no microbial growth was observed). (iii) On the other hand, T. selenatis was capable of growth and Se(VI) reduction under micro-aerobic conditions. (iv) Combining T. selenatis and ZVI under micro-aerobic conditions showed a synergistic effect on Se(VI) reduction, readily facilitating Se removal. This synergistic effect was optimized by adjusting the pH to near neutral (optimal for T. selenatis growth), but by adjusting the temperature to 35°C (sub-optimal for T. selenatis growth): Se removal of 55% by T. selenatis alone, was significantly improved to 98% by combining T. selenatis and ZVI. The proposed key process to display the synergistic effect on Se removal under micro-aerobic conditions is as follows: (i) Using the remaining dissolved O2 (DO) during the first hours, T. selenatis can overcome the inhibitory effect of Cl− and SO42− by growing with more energy-gaining aerobic respiration, (ii) ZVI indirectly serves as a reducing agent to maintain low DO levels, consequently readily switching from aerobic to anaerobic Se(VI) respiration by T. selenatis. (iii) ZVI may also be acting directly for Se deposition by reducing microbially-produced intermediate Se(IV), which is more reactive than original Se(VI). The present findings could be used as a basis for developing an economically feasible and environmentally harmless bio-treatment technology for Se(VI) containing copper refinery wastewaters.

Effect of different sources and levels of selenium on performance, meat quality, and tissue characteristics of broilers

The objective of this study was to evaluate the effects of dietary levels of inorganic and organic selenium (Se) on performance, meat physicochemical characteristics, and Se deposition in the tissues of broilers chickens. A total of 2,880 one-day-old broilers (Cobb 500 strain) were divided into 96 experimental pens of 30 birds each. The 12 experimental treatments were arranged in a factorial design of 4 × 3 [selenium levels of 0.15, 0.30, 0.45, and 0.60 ppm, and organic (selenium yeast, SY) or inorganic (sodium selenite, SS) sources of selenium and their association (SY + SS)], with 8 replicates in a completely randomized design. No differences (P > 0.05) among Se levels or sources were detected with regard to any performance parameters. The average values of ADFI, ADG, and FCR were 106 g/bird per day, 63 g/bird per day, and 1.684 kg/kg, respectively. No differences (P > 0.05) were found between treatments regarding pH (5.79) and shear force (30.08 kgf). Those birds receiving 0.15 ppm of Se showed a significantly higher (21.92%) cooking loss of breast meat (P < 0.05). The organic form of Se decreased cooking loss, and the smallest loss was found when the diet was supplemented with 0.60 ppm of Se (15.87%). Deposition of Se in the liver increased from 0.97 (0.15 ppm of Se) to 2.43 mg/kg (0.60 ppm of Se) when using SY. The concentration of Se in the breast meat increased linearly from 0.23 to 1.42 mg/kg with increasing dietary levels of SY. Therefore, dietary supplementation with 0.15 ppm of Se, independent of source, can maintain normal bird performance. The SY was more efficient in depositing Se to the liver and breast muscle than the SS.

Dynamic Selenium Assimilation, Distribution, Efflux, and Maternal Transfer in Japanese Medaka Fed a Diet of Se-enriched Mayflies

Selenium (Se) trafficking in oviparous species remains understudied and a major source of uncertainty in developing sound Se regulations. Here, we utilized (75)Se to follow Se through a simulated natural food chain (water, periphyton, mayflies (Centroptilum triangulifer), fish (Japanese medaka)). We specifically examined Se assimilation efficiency, tissue distribution, efflux rate, and maternal transfer in medaka. Selenium assimilation efficiency (AE) averaged 63.2 ± 8.8% from mayfly diets and was not affected by mayfly [Se] across a dietary range of 5.6-38.7 μg g(-1) (dry wt). However, AE decreased significantly as mayfly larva size increased. Efflux rate constants (ke) were consistent between reproductively inactive (0.066 d(-1)) and spawning females (0.069 d(-1)). Total Se loss rate constant (ke+egg; efflux and egg deposition) was 0.17 d(-1) in spawning females. Interestingly, medaka appeared to rapidly shuttle Se to their eggs directly from their diet via the ovary, as opposed to mobilization from surrounding tissues, resulting in dynamic egg [Se] that was more attributable to recent dietary Se ingestion than female whole body [Se] in this asynchronous spawning fish. Spawning strategy likely plays a large role in the process of fish egg Se deposition and requires further attention to understand risk and toxicity of Se to fish.

2-Hydroxy-4-methylselenobutanoic acid induces additional tissue selenium enrichment in broiler chickens compared with other selenium sources

Two experiments were conducted in broiler chickens to compare the effect of different Se sources on Se tissue enrichment: sodium selenite (SS), seleno-yeast (SY), and a new organic Se source (SO) containing 2-hydroxy-4-methylselenobutanoic acid (HMSeBA) as an active substance. For each experiment, treatments differed only in source or dose of Se additive. Relative efficiency was compared by plasma and tissue [muscle (pectoralis major) and liver] total Se concentrations. The first experiment compared Se sources (SS, SY, and SO) at different concentrations (mg of Se/kg of feed; SS-0.3; SY-0.1 and -0.3; SO-0.1 and -0.3; and a negative control, 0) in broilers between 0 and 42 d of age. Plasma, liver, and muscle Se concentrations were improved by all Se sources at both d 21 and 42 compared with the negative control group. Between Se sources, minor differences were observed for plasma and liver results, whereas a significant dose effect was observed from 0.1 to 0.3 mg of Se/kg of feed (P < 0.05) for each source. Muscle Se concentrations were improved such as SO > SY > SS (P < 0.05). Moreover, the relative muscle Se enrichment comparison, using linear regression slope ratio, indicated an average of 1.48-fold (95% CI 1.38, 1.58) higher Se deposition in muscle for SO compared with SY. In the second experiment, excessive dietary doses of 5 mg of Se/kg of feed from SS and SO showed a lower deleterious effect of SO on BW and feed intake in comparison with standard Se doses (P < 0.05). Seleno amino acid measurements conducted on different tissues of animals fed SO at 0.5 mg/kg of feed showed that HMSeBA is fully converted into selenomethionine and selenocysteine. These results of both experiments demonstrate the higher relative bioavailability of SO compared with SS and SY as determined through tissue Se enrichment.

Evaluation of the efficacy of 2-hydroxy-4-methylselenobutanoic acid on growth performance and tissue selenium retention in growing pigs1

The aim of this study was to compare the efficacy of a new organic Se (2-hydroxy-4-methylselenobutanoic acid [HMSeBA]) source (SO) with sodium selenite (SS) and selenized yeast (SY) at various dietary levels for growth performance and tissue Se deposition in growing pigs. A total of 112 crossbred (Pietrain × [Large White × Landrace]) gilts were allotted at an average body weight of 26.73 kg to 7 dietary treatments with 8 replicate pens of 2 pigs per pen. Pigs were fed basal diets unsupplemented or supplemented either with SS, SY, or SO each at 0.1 or 0.3 mg Se/kg of diet for 32 d. Feed intake and BW were recorded during the experimental period. At the end of the experiment, blood, liver, and psoas major muscle of all gilts were collected for total Se and relative bioavailability determination. No differences were observed on final BW, ADG, ADFI, and G:F among dietary treatments. All Se-supplemented groups exhibited greater total Se contents in plasma (P < 0.01) and liver (P < 0.01) compared with unsupplemented control group. However, Se retention in psoas major muscle was improved only when organic Se source (SY or SO) was added to diets (P < 0.01). Regardless the Se level, the Se deposition in muscle was greater (P < 0.01) in pigs supplemented with SO than those supplemented with SY. Slope ratio assay confirmed the greater bioavailability of Se from organic compared with inorganic Se and also revealed that the relative bioavailability of Se from HMSeBA for plasma, liver, and muscle Se response was 170, 141, and 162%, respectively, for SY. This study shows a potential advantage of HMSeBA supplementation in the increase of Se contents in pig tissues, indicating that this new organic Se source could be an alternative source of Se in swine nutrition.

Electronic parameters and carrier transport mechanism of high-barrier Se Schottky contacts to n-type GaN

The electrical properties and current conduction mechanism of high-barrier Se/n-GaN Schottky diode have been investigated for the first time by current–voltage (I–V) and capacitance–voltage (C–V) measurements. High resolution transmission electron microscopy (HRTEM) results confirmed that no reaction occurs between Se film and the GaN substrate during Se deposition. Investigations reveal that the contact exhibited an excellent rectification behavior. The estimated barrier height of Se/n-GaN Schottky contact is 0.92eV (I–V) and 1.27eV (C–V) with the ideality factor of 1.10. The barrier height and series resistance are extracted by Cheung's functions. It is observed that the series resistance values obtained from Cheung's functions is in good agreement with each other. Further, capacitance–voltage measurements of the Se/n-GaN Schottky diode are carried out at different frequencies. The discrepancy between Schottky barrier heights obtained from I–V and C–V measurements is also explained. The AFM results showed that the surface morphology of the Se Schottky contacts on n-GaN is fairly smooth. The forward bias current transport mechanism of the Se/n-type GaN Schottky diode is determined by the log–log plot of I–V characteristics. Investigations reveal that the Schottky emission mechanism is found to be dominant in the reverse bias region of Se/n-GaN Schottky diode.

Effects of Selenium-Enriched Probiotics on Heat Shock Protein mRNA Levels in Piglet under Heat Stress Conditions

The effects of selenium-enriched probiotics (SP) on tissue selenium (Se) deposition, glutathione peroxidase-1 (GPx1) activity and mRNA level, and heat shock protein (Hsp) mRNA levels of piglets under heat stress conditions were investigated. A total of 48 crossbred ([Landrace × Yorkshire] × Duroc) piglets were randomly divided into 4 groups and fed a basal diet (Con, 0.16 mg Se/kg) or basal diets with added probiotics (P, 0.16 mg Se/kg), sodium selenite (SS, 0.46 mg Se/kg), or SP (0.46 mg Se/kg), respectively, for 42 days. Three piglets were randomly selected from each group for blood sample collection at days 0, 14, 28, and 42 and for liver, kidney, and spleen sample collection at day 42. The results showed that P, SS, and SP could significantly down-regulate the average mRNA levels of Hsp70 (17.3, 23.7, and 40.1%) and Hsp27 (22.4, 24.4, and 44.7%) of the tissues, respectively (P < 0.05), whereas SS and SP could significantly elevate Se concentration, GPx1 activity and mRNA level (P < 0.05). The maximal effects of these parameters were observed in SP. It was concluded that SP is a feasible dietary supplementation of piglets under heat stress conditions during the summer season.

Effect of 2-hydroxy-4-methylselenobutanoic acid as a dietary selenium supplement to improve the selenium concentration of table eggs1

The aim of this study was to compare the effects of a new organic Se [2-hydroxy-4-methylselenobutanoic acid (HMSeBA)] with routinely used mineral and organic Se sources (sodium selenite and selenized yeast) on chosen performance criteria and Se deposition in egg and muscle of laying hens. A total of 240 laying hens (40 wk of age) were randomly assigned to 6 treatments for 56 d with 8 replicates of 5 hens per replicate. The 6 treatments were as follows: control group received basal diet without Se supplementation; the second, fourth, and sixth experimental groups (SS-0.2, SY-0.2, and HMSeBA-0.2, respectively) were fed basal diet supplemented with Se at 0.2 mg/kg from sodium selenite, selenized yeast, and HMSeBA, respectively; and the third and fifth experimental groups (SY-0.1, and HMSeBA-0.1, respectively) were fed basal diet supplemented with Se at 0.1 mg/kg from selenized yeast and HMSeBA, respectively. No difference was observed among dietary treatments on feed intake, egg weight, and laying rate. All hens fed the Se-supplemented diets exhibited greater total Se contents in their eggs compared with control hens (P < 0.01). The egg Se concentrations were greater in hens fed organic Se (HMSeBA-0.2, P < 0.01, and SY-0.2, P < 0.01) than those fed the SS-0.2. In addition, hens fed the diet with HMSeBA-0.2 accumulated more Se in their eggs (+28.78%; P < 0.01) and muscles (+28%; P < 0.01) than those fed the diet supplemented with SY-0.2. These results showed the greater ability of HMSeBA to increase Se deposition in eggs and breast muscle of laying hens, which can subsequently lead to greater supply of Se for humans.

Selenium retention in lambs fed diets supplemented with selenium from inorganic or organic sources

The objective of this study was to compare the effects of feed supplementation with equivalent selenium doses from sodium selenite (SS) and selenised yeast (Se-yeast) on Se absorption, retention, balance, and tissue deposition in young rams. Fifteen male lambs of the Slovak valashka breed (4 months old) were randomly allocated to three dietary treatments consisting of unsupplemented basal diet (BD) containing only background Se (0.07mg/kg dry matter; DM) and two treatments based on identical BD supplemented with 0.3mgSe/kg DM either from SS or from Se-yeast. After 14 weeks, no differences in blood Se levels were observed between rams fed the diet supplemented with SS or Se-yeast (0.30 vs. 0.31mg/L, respectively), while lambs given BD showed significantly lower Se level (0.07mg/L, P<0.001). A similar response was found in the activity of blood glutathione peroxidase (GPx), with mean values for BD, SS and Se-yeast groups of 132.8, 931.7 and 954.4U/g Hb, respectively (P<0.001). The balance measurements carried out in week 12 showed significantly higher relative Se retention (% of Se ingested) in the rams given Se-yeast (58.3%) than in those fed the diet supplemented with SS (45.4%, P<0.05), both differing from the control group (51.6%). The apparent Se absorption rate was significantly higher in the Se-yeast group (62.0%) than in the lambs treated with SS (49.6%) or in those fed the unsupplemented BD (52.9%, P<0.001). Due to lower absorption rate the rams given SS had significantly higher faecal Se excretion than the Se-yeast fed animals, whereas no differences between the supplemented groups appeared in urinary Se excretion. The 14-week intake of Se-yeast resulted in significantly higher Se deposition in liver, muscles, heart, pancreas and spleen than that from SS. The highest tissue Se concentrations in each group were found in the kidney cortex (BD, SS and Se-yeast were 6.0, 12.9 and 11.9mg/kg DM, respectively), whereas the respective levels in the kidney medulla were about four times lower (1.4, 2.7 and 3.1mg/kg DM). The results demonstrate that in sheep the feed supplementation with Se from Se-yeast results in higher absorption of Se from the digestive tract and greater body Se retention than from SS. However, the inorganic source of Se was as effective as the organic one in supplying this essential trace element for the activity of specific selenoprotein GPx in blood.

Successful growth of Cu2Se-free CuGaSe2 by migration-enhanced epitaxy

CuGaSe2 films were grown on GaAs (001) substrates by migration enhanced epitaxy, where Cu + Ga and Se are alternately deposited. The in situ reflection high energy electron diffraction observation during growth revealed that the segregation of Cu2Se on CuGaSe2 can be detected by anomalous diffraction patterns. When the Cu2Se segregation takes place, a distorted pattern appears in both Cu + Ga and Se deposition periods. By optimizing the flux ratios, the anomalous diffraction disappears, and we succeeded in growing high quality CuGaSe2 single crystal layers free from Cu2Se segregation on GaAs (001) substrates. The authors also found that, in the CuGaSe2/GaAs wafers with Cu2Se segregation, a high density of voids is often observed at the substrate surface. These voids disappeared when the Cu2Se-free growth conditions were employed. Ga atoms near the GaAs substrate surface were probably drawn out by excess Cu atoms in the growing layer to form CuGaSe2, leading to the creation of voids with fairly large size.

Electrodeposition of antimony selenide thin films from aqueous acid solutions

Antimony selenide thin films have been prepared onto tin oxide coated glass substrates by potentiostatic electrodeposition from an aqueous acid bath containing K(SbO)C4H4O6⋅0.5H2O and H2SeO3 at 25°C. The electrodeposition mechanism was investigated by cyclic voltammetry. The compositional, morphological, structural, optical, and electrical properties of the deposited films have been studied using energy-dispersive X-ray spectroscopy (EDS), environmental scanning electron microscopy (ESEM), Raman spectroscopy (RS), UV–VIS spectra, and photoelectrochemical tests (PEC), respectively. The formation of antimony selenide was confirmed to proceed via an induced codeposition mechanism: Se deposition occurs first, inducing the deposition of Sb, then, the deposited Sb would further promote the deposition of Se. The influence of deposition potential on the composition, morphology, and structure of the antimony selenide thin films was also explored. Sb2Se3 thin films with homogeneous morphology and near stoichiometric composition can be obtained, and exhibit good optical properties with absorption coefficient of higher than 105cm−1 and band gap of 1.07±0.01eV, as well as electrical properties with p-type conductivity and excellent photoelectrochemical activity.

Growth of CuGaSe2 Layers on Closely Lattice-Matched GaAs Substrates by Migration-Enhanced Epitaxy

CuGaSe2 single-crystal films are grown on the As-stabilized (2×4) surface of (001) GaAs by migration-enhanced epitaxy (MEE), where Cu+Ga and Se are alternately deposited. The growth process is monitored by refraction high-energy electron diffraction (RHEED) in the [110] azimuth. Under the Cu-enriched growth condition, a deformed 4-fold pattern is observed in both Cu+Ga and Se deposition periods. The deformed 4-fold pattern is found to be related to the segregation of Cu2Se on the CuGaSe2 surface as confirmed by the results of X-ray diffraction (XRD) measurement. By reducing the beam equivalent pressure of Cu (Cu-BEP), clear 4-fold patterns appear in both Cu+Ga and Se deposition periods instead of deformed 4-fold patterns. Further reduction of Cu-BEP results in clear 4- and 2-fold patterns for Cu+Ga and Se deposition periods. Under these growth conditions, Cu2Se-segregation-free CGS growth is achieved. Thus, the CuGaSe2 single-crystal layers without Cu2Se-segregation are successfully grown on GaAs(001) substrates by optimizing the Cu-BEP.