Search

This work demonstrates the implementation of thioglycolic acid (TGA) functionalized water-soluble NH2–molybdenum disulfide (MoS2) nanosheets as sensitive layers for toxic heavy metal ion sensing in drinking water. The sensor device was tested for several ions commonly found in drinking water, e.g., As (III), Pd (II), Hg (II), and Cd (II). When the sensor was exposed to individual ions, it showed negligible response toward elements such as As (III), Pd (II), and other commonly present metal ions. However, at 25 ppb, some cross sensitivity was observed between Cd (II) and Hg (II) ions. The mathematical analysis was performed to investigate the cross-sensitive behavior, and a model was put forward. It was evident from the higher attachment factor (${N}$) for Cd concerning Hg (II), derived from the model which supported Cd’s higher response when exposed individually (${N}_{\text {Cd}}= 4\times 10^{{16}}$ cm−3/ppb and ${N}_{\text {Hg}}= 1.6\times 10^{{14}}$ cm−3/ppb). Furthermore, the band structure and electron concentration were plotted for individual Cd (II) and Hg (II) ions. Compared to Hg (II), Cd (II) efficiently depleted the amine–MoS2 and TGA junction. To better understand selectivity and response, the device was exposed to Cd (II) and Hg (II) ions simultaneously at different concentrations, which looked into the effect of the two interacting ions. A mathematical model was hence established. It was found that the absorption coefficient (${K}_{\text {Hg}}$) was much higher (63 ppb−1) than Cd (${K}_{\text {Cd}}$) (0.38 ppb−1). The interaction factor (${K}_{\text {Hg-Cd}}$), i.e., the absorption coefficient of Cd in the presence of Hg, was calculated as −0.086 ppb−2, which is lower than ${K}_{\text {Cd-Hg}}{(}-0.013$ ppb−2), which indicated that Hg is more active toward adsorption in competition to the Cd ions. This competitive dominance for Hg (II) adsorption may be attributed to the affinity of thiol groups present in the TGA molecules for Hg (II) over Cd (II) ions. The device was repeatable after testing with five different devices with a standard deviation of 0f 0.5322 and stable up to 50 days with ±3% response variation. Thus, the proposed sensor may be a suitable candidate for low-cost water quality monitors. [ABSTRACT FROM AUTHOR]

Design and analysis of a metal-oxide-metal (MOM) capacitor in 0.18- $\mu \text{m}$ RF CMOS process, suitable for the ${L}$ -, ${S}$ -, and ${C}$ -band integrated circuits, is presented in this article. In order to maximize the flux density per unit area, Moore fractal geometry is chosen for the capacitor plates. The capacitor uses lateral electric fields, in contrast to commonly used vertical electric fields. To further increase the capacitance density, four metal layers of the CMOS process are used by efficient contact of vias. The design strategy makes it possible to achieve a high value of capacitance and ${Q}$ factor, noted as 1.15 pF and 51.6, respectively, at 2.4 GHz, for a silicon area of 65 $\times \,\,65\,\,\mu \text{m}^{{2}}$. The obtained self-resonance frequency is 13.5 GHz. A variability analysis is done and parasitics are extracted using a high-frequency capacitor circuit model. An active, third-order image reject filter (IRF) is subsequently realized as a circuit application for the designed fractal capacitor. The filter provides a notch at 1.8 GHz with more than 35-dB attenuation and a controlled passband centered at 2.4 GHz. [ABSTRACT FROM AUTHOR]