Department of Electrical and Electronics Engineering

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Subject: search.filters.subject.Core-shell nanowire

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    Plasma Oxidized W-WOx Sensor for Sub-ppm H2S Detection
    (MDPI, 2017-08) Benedict, Samatha
    In this work we have fabricated W-WOx core-shell nanowire structure using plasma oxidation, a CMOS compatible process, for sensing H2S gas. For comparison, the sputtered stack structure of W-WOx with different thickness ratios of W to WOx is fabricated and characterized for H2S sensing. The sensor fabricated using plasma oxidation process is found to be significantly better in sensing performance compared to the sensing results obtained from sensor fabricated using sputtering. The response of plasma oxidized sensor is 90.4% for 1 ppm H2S with response and recovery time of 4 s and 46 s respectively. In contrast, the sensor fabricated with sputtered film shows a response of 30.6% at 1 ppm with response and recovery times of 19 s and 84 s respectively. This study clearly indicates that plasma oxidation is an efficient method for development of stable sensors.
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    Nanodisc Decorated W–WO x Suspended Nanowire: A Highly Sensitive and Selective H2S Sensor
    (IEEE, 2019-03) Benedict, Samatha
    In this paper, we report room temperature synthesis of plasma oxidized, suspended tungsten-tungsten oxide (W-WOx) core-shell nanowire for sensing ppb level H 2 S. The electric field modulation at the W-WOx interface of the core-shell nanowire strongly influences the sensing performance and brings down the operating temperature all the way down to 50 °C, compared to completely oxidized (WO x ) nanowire. The optimum interface ratio (W/WOx) of the nanowire shows response of 90.4% (1 ppm) with six months of response stability and excellent selectivity. The limit of detection of 10 ppb with response and recovery time of 4 and 46 s, respectively, is achieved. To enhance the response further, we utilize nanostructuring on top of nanowire, using nanodiscs of 20, 50, and 100 nm diameter and 10 nm height. The nanowire with nanodiscs of 20 nm diameter shows high repeatable response of 12529% (1 ppm) at 150 °C and fast response and recovery times of 12 and 19 s with detection limit of 0.5 ppb. As we switch from unpatterned to patterned nanowire, the observed change in H 2 S sensing characteristics indicates that the core-shell nanowire behavior makes a transition from p-type to n-type. Extensive material characterization is done using UV-Vis spectroscopy, XPS, and TEM.