Herein, we demonstrate that highly sensitive conductometric gas nanosensors for H 2 S can be synthesized by electrodepositing gold nanoparticles on single-walled carbon nanotube (SWNT) networks. Adjusting the electrodeposition conditions allowed for tuning of the size and number of gold nanoparticles deposited. The best H 2 S sensing performance was obtained with discrete gold nanodeposits rather than continuous nanowires. The gas nanosensors could sense H 2 S in air at room temperature with a 3 ppb limit of detection. The sensors were reversible, and increasing the bias voltage reduced the sensor recovery time, probably by local Joule heating. The sensing mechanism is believed to be based on the modulation of the conduction path across the nanotubes emanating from the modulation of electron exchange between the gold and carbon nanotube defect sites when exposed to H 2 S.Sensitive detection and monitoring of gaseous reduced sulfur compounds such as hydrogen sulfide (H 2 S) is important because of toxicity, corrosion, and odor nuisance concerns. H 2 S is generated in large amounts in coal and natural gas processing, petroleum industries, biogas production, and sewage treatment plants. 1 The odor threshold of H 2 S is around 3 ppb in air which is well below any known toxic effects, while the threshold limit value (TLV) was set to 10 ppm; at concentrations exceeding 150 ppm, H 2 S is extremely toxic and hazardous. 2 Hence, it is important to develop sensors that can monitor H 2 S in real time and can detect concentrations from as low as a few parts per billion to the several hundred parts per million in air. A number of H 2 S detection techniques have been developed in the past few decades, with electrochemical detection as the most widely utilized method in compact and portable H 2 S gas monitors. 3,4 These devices often rely on solid state sensors made of semiconducting metal oxides such as tungsten oxide and tin oxide or metals such as gold. H 2 S detection is usually based on determining conductivity changes of thin films upon exposure to H 2 S gas. 4,5 While there are a number of successful devices available commercially, drawbacks of existing H 2 S monitors include high power consumption (e.g., in metal oxide sensors that require high operating temperatures); low sensitivity, making them unsuitable for environmental monitoring; short lifetime (usually less than one year); short linear dynamic range; interference from other gases (e.g., NH 3 , NO x , etc); and high cost. 6 Recently, chemical sensors based on one-dimensional nanostructures such as bare or functionalized semiconducting singlewalled carbon nanotubes (SWNTs), 6,7 metal oxides, and conducting polymer nanowires 8 have attracted a great deal of attention because of their superior sensing performance. In particular, these sensors offer promising perspectives for real-time monitoring of gases or vapors with high sensitivity and low-power consumption and potentially at a low cost. 6 Their small size will also allow future integration with low-pow...

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Ultra-long (>1 cm) polypyrrole (PPy) nanoribbons were batch-synthesized to predetermined locations on 4 inch Si wafers and flexible polyimide film with controlled thicknesses and widths via modified Lithographically Patterned Nanowire Electrodeposition (LPNE), which combines top-down “photolithography” and bottom-up “electrodeposition”. The excessive lengths and lithographic approach enable subsequent patterning of electrodes for direct device fabrication. Electrical transport properties were investigated by temperature-dependent measurements, and back-gated FET measurements were performed to study the properties with respect to the conductivity of PPy nanoribbons. To demonstrate the utility of this approach these nanoribbon devices were interrogated as gas sensors in a conductometric fashion. They displayed excellent sensitivity toward ammonia vapor with a detection limit in the sub ppm. The sensitivity toward ammonia vapor was tuned by the conductivity of the PPy nanoribbons via chemical de/doping.

A Schottky contact-based hydrogen (H2) gas sensor operable at room temperature was constructed by assembling single-walled carbon nanotubes (SWNTs) on a Si/SiO2 substrate bridged by Pd microelectrodes in a chemiresistive/chemical field effect transistor (chemFET) configuration. The Schottky barrier (SB) is formed by exposing the Pd-SWNT interfacial contacts to H2 gas, the analyte it was designed to detect. Because a Schottky barrier height (SBH) acts as an exponential bottleneck to current flow, the electrical response of the sensor can be particularly sensitive to small changes in SBH, yielding an enhanced response to H2 gas. The sensing mechanism was analyzed by I-V and FET properties before and during H2 exposure. I-Vsd characteristics clearly displayed an equivalent back-to-back Schottky diode configuration and demonstrated the formation of a SB during H2 exposure. The I-Vg characteristics revealed a decrease in the carrier mobility without a change in carrier concentration; thus, it corroborates that modulation of a SB via H2 adsorption at the Pd-SWNT interface is the main sensing mechanism.