DESIGN, FABRICATION, AND TEST OF A SILICATE MICROSENSOR

This work describes a portable microsensor for analyzing the silicate concentration in water. Conventionally adopted silicate analysis methods involve bulky instrumentation that are limited in portability and immediateness. The proposed silicate microsensor consists of a microliquid core waveguide, passive spiral micromixer, and bubble traps that possess excellent signal enhancement properties. The microsensor size is 52 × 26 mm, while each measurement requires only 115 μl of a sample and reagents, thereby reducing the sample requirement for a considerable amount of time and work to collect expensive reagents. The spiral micromixer has a mixing capability superior to that of a premix mixture. Bubble traps have been developed to trap air bubbles formed in the microchannel in order to prevent gas bubbles from interfering with the measurements. As a linear function of silicate concentration, the absorbance response ranges from 0 to 250 nM. Additionally, the linearity is excellent with a linear R value of 0.9985 and the experimental detection limit is 8.9 nM. The proposed portable microsensor significantly contributes to aqueous inspection, subsequently creating a highly value-added technology for chemical sensors and microsystems.

Where Would the Electronic States of a Small Graphite-Like Carbon Island Contribute to the SiC/SiO2 Interface State Density Distribution?

The high density of interface electron traps in the SiC/SiO2 system, near the conduction band of 4H-SiC, is often ascribed to graphitic carbon islands at the interface, although such clusters could not be detected by high resolution microscopy. We have calculated the electronic structure of a model interface containing a small graphite-like precipitate of 19 carbon atoms, with a diameter of ~7 Å, corresponding to the experimental detection limit. The analysis of the density of states shows only occupied states in the band gap of 4H-SiC near the valence band edge, while carbon related unoccupied states appear only well above the conduction band edge.

Large-Volume Liquid Scintillation Counting of Carbon-14

Efforts have been undertaken to further improve the relatively simple technique of low-level liquid scintillation counting of 14C. Two different approaches have been made. By synthesizing more benzene for 14C measurement than usual (with up to 19.5g of carbon) an experimental detection limit of about 0.1 percent modern has been achieved (97.5% confidence level, 1000 min). Absorption of CO2 with up to 5.3g of carbon in 160ml of an absorbent-scintillation solution and counting in a special measuring chamber resulted in an experimental detection limit of about 1 percent modern, with the sample preparation taking only 1 hour. The detection limits achieved by the two techniques correspond to 14C ages of about 55,000 and 35,000 years BP, respectively.