Suppression of the lateral diffusion under the gate of an MOS transistor by argon implantation
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A new technique for eliminating the overlap diffusion of the source and drain in MOS devices is reported. This technique involves the implantation of argon in the source and drain regions following the arsenic implant, using the same auto-aligned gate. The results show that, compared to the conventional process, a reduction in the lateral diffusion of arsenic is observed, which results in negligible gate-junction overlap encroachment and a consequent gain in device speed. Furthermore, improvements in source-drain breakdown voltages, punchthrough voltages, and substrate currents are also seen.Arsenic poisoning
Arsenobetaine
Arsenic toxicity
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The arsenic-removing capacity of some low-cost materials was tested by passing aqueous arsenic solutions (16 and 57 ppb) of pH 7 through materials packed in plastic buckets. It was found that the initial concentration of arsenic solutions and their retention time in adsorbents greatly affected the removal of arsenic from the aqueous solution. Maximum arsenic removal was observed when the packed materials were exposed to 16 ppb of arsenic solution. With 57 ppb of arsenic solution, arsenic removal was reduced on that of 16 ppb; however, the reduced arsenic concentration was close to the recommendations of the World Health Organization drinking water quality guidelines.
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Arsenic contamination of drinking water poses serious health risks to millions of people worldwide. Current technologies used to clean arsenic-contaminated water have significant drawbacks, such as high cost and generation of large volumes of toxic waste. In this study, we investigated the potential of using recently identified arsenic-hyperaccumulating ferns to remove arsenic from drinking water. Hydroponically cultivated, two arsenic-hyperac cumulating fern species (Pteris vittata and Pteris cretica cv. Mayii) and a nonaccumulating fern species (Nephrolepis exaltata) were suspended in water containing 73As-labeled arsenic with initial arsenic concentrations ranging from 20 to 500 μg L-1. The efficiency of arsenic phytofiltration by these fern species was determined by continuously monitoring the depletion of 73As-labeled arsenic concentration in the water. With an initial water arsenic concentration of 200 μg L-1, P. vittata reduced the arsenic concentration by 98.6% to 2.8 μg L-1 in 24 h. When the initial water arsenic was 20 μg L-1, P. vittata reduced the arsenic concentration to 7.2 μg L-1 in 6 h and to 0.4 μg L-1 in 24 h. At similar plant ages, both P. vittata and P. cretica had similar arsenic phytofiltration efficiency and were able to rapidly remove arsenic from water to achieve arsenic levels below the new drinking water limit of 10 μg L-1. However, N. exaltata failed to reduce water arsenic to achieve the limit under the same experimental conditions. The significantly higher efficiency of arsenic phytofiltration by arsenic-hyperaccumulating fern species is associated with their ability to rapidly translocate absorbed arsenic from roots to shoots. The nonaccumulating fern N. exaltata was unable to translocate the absorbed arsenic to the shoots. Our results demonstrate that the arsenic-phytofiltration technique may provide the basis for a solar-powered hydroponic technique that enables small-scale cleanup of arsenic-contaminated drinking water.
Pteris vittata
Arsenic poisoning
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This review will describe method for biological monitoring of inorganic arsenic exposure, that delineates the chemical species of arsenic measured in urine. The studies established a method for exposure-level-dependent biological monitoring of inorganic arsenic exposure. Low-level exposure could be monitored only by determining the urinary inorganic arsenic concentration. High-level exposures clearly produced increased urinary inorganic arsenic, methylated arsenic (MA), dimethylated arsenic (DMA) and the sum of urinary inorganic arsenic and its metabolites (inorganic arsenic+ MA+ DMA) could be determined. Urinary arsenobetaine proved to be specifically seafood-derived arsenic, which could be distinguished from occupational arsenic exposure.There is increased use of gallium arsenide and indium arsenide in the semiconductor industry today. The determination of arsenic in ambient air is difficult to carry out in semiconductor factories. Monitoring arsenic exposure by determining the arsenic in the hair appeared to be of value only when used for environmental monitoring of arsenic rather than for biological monitoring.
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Threshold voltages for ion implanted GaAs MESFETs are measured and shown to have good coincidence with calculated results. The effect of implantation energy on threshold voltage is discussed. The optimum implantation energy is about 45 ∼ 60 keV.
MESFET
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Arsenic (V) is separated from arsenic (III) by coprecipitation with MgNH4PO4·6H2O at pH 9.0. The precipitate is dissolved in H2SO4 (1 + 5) and HCl(1 + 1) and analyzed for arsenic by silver diethyldithiocarbamate spectrophotometric method. The amount of arsenic (V) is calculated by subtracting arsenic (V) from the total arsenic determined on a separate portion of sample. Large amounts of iron (III) and manganese (II) interfered with the determination of arsenic (V). The oxidation number of arsenic in some typical samples was found to be five.
Coprecipitation
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Abstract The effect of arsenite [arsenic(III)], arsenate [arsenic(V)] and dimethylarsinic acid (DMA) on the growth of radish and the concentration of arsenic compounds in the roots and leaves of radish were investigated. Radish was grown in pots on Luvisols individually amended with arsenic concentrations of 20 mg kg −1 in the form of arsenic(III), arsenic(V), and DMA. In untreated soil, arsenate was the dominant arsenic compound; arsenite and DMA were also present. Arsenic(III) added to the soil was oxidized to arsenic(V), so that no differences between arsenic(III) and arsenic(V) soil treatments were observed. On DMA treatment, this compound remained in soil in high concentration in soluble and plant‐available states, and the sum of arsenic(III), arsenic(V) and methylarsonic acid (MA) reached only 30% of water‐extractable arsenic content. A low portion of soil arsenic added as DMA was immobilized, via adsorption, compared with inorganic compounds. Arsenic(III) was the dominant compound in radish roots planted in the untreated soil, whereas in leaves most of the arsenic present was arsenic(V). DMA was also detected in both plant tissues. A similar distribution of arsenic compounds was also found on arsenic(III) and arsenic(V) treatments. On DMA treatment, this compound showed high stability and the DMA concentration exceeded the sum of the remaining arsenic compounds [arsenic(III), arsenic(V) and MA] in both roots and leaves of radish. Copyright © 2002 John Wiley & Sons, Ltd.
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This study was carried out to determine the accumulation rate of arsenic by Blyxxa malayana and also to assess the potential of this plant as bio-indicator. The Blyxxa malayana was transplanted in different arsenic concentrations solution ; no arsenic contains 0.2 ppm arsenic, 0.6 ppm arsenic and 1.2 ppm arsenic. The concentration of arsenic in Blyxxa malayana, soil sample and water sample was analyzed every 2 weeks for 8 weeks using Voltammetry (757 VA Computrace). The results indicated that there are relationships between the amount of arsenic accumulated by Blyxxa malayana to the arsenic soil concentration and arsenic solution concentration. There are increasing in amount of arsenic accumulated in Blyxxa malayana due to the increasing arsenic soil and arsenic solution concentration. Overall, Blyxxa malayana was a plant with potential arsenic accumulator properties and it can be applied as bio-indicator for the arsenic contaminated condition.
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Ion implantation has been widely employed to adjust the threshold voltage of MOS transistors made on low-conductivity substrates. However, the temperature variation of device characteristics associated with the ion implantation has not been fully understood. In this paper, an analysis of the effect of the ion implantation on the threshold-voltage drift is presented, and simple but accurate design equations for predicting the temperature coefficients of the threshold voltages of implanted devices relative to those of unimplanted devices are given. Experimental results from four basic types of devices exhibit close agreement with theory. The analysis presented here is directly applicable to the design of an on-chip NMOS voltage reference based on the threshold voltage difference due to the ion implantation.
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