Abstract
We report the electrical detection of captured gases through measurement of the quantum tunneling characteristics of gas-mediated molecular junctions formed across nanogaps. The gas-sensing nanogap device consists of a pair of vertically stacked gold electrodes separated by an insulating 6 nm spacer (~1.5 nm of sputtered α-Si and ~4.5 nm ALD SiO2), which is notched ~10 nm into the stack between the gold electrodes. The exposed gold surface is functionalized with a self-assembled monolayer (SAM) of conjugated thiol linker molecules. When the device is exposed to a target gas (1,5-diaminopentane), the SAM layer electrostatically captures the target gas molecules, forming a molecular bridge across the nanogap. The gas capture lowers the barrier potential for electron tunneling across the notched edge region, from ~5 eV to ~0.9 eV and establishes additional conducting paths for charge transport between the gold electrodes, leading to a substantial decrease in junction resistance. We demonstrated an output resistance change of >108 times upon exposure to 80 ppm diamine target gas as well as ultralow standby power consumption of <15 pW, confirming electron tunneling through molecular bridges for ultralow-power gas sensing.
Highlights
The development of low-power Internet-of-Things (IoT) sensor systems has been rigorously pursued by an increasing number of scientific communities to enable continuous access to various information around the globe
Similar gas sensors have been deployed for remote and continuous environmental monitoring to detect the presence of toxic gases such as Correspondence: Aishwaryadev Banerjee 1Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT 84112, USA 2Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA Full list of author information is available at the end of the article volatile organic compounds (VOCs), CO, SO2, H2S, and O32
We previously introduced the concept for quantum tunneling-based gas sensing with preliminary results[15,16,17,18,19,20,21,22,23,24,25]
Summary
The development of low-power Internet-of-Things (IoT) sensor systems has been rigorously pursued by an increasing number of scientific communities to enable continuous access to various information around the globe. Some low-power (sub-10 μW) gas sensors have been demonstrated; they displayed only limited output signal changes of less than a few orders of magnitude, being limited in the minimum detection amount when utilizing ~μWatt level of power These sensors achieved low-power operation by utilizing self-heating under a bias voltage or by minimizing electrical leakage paths within the device, such as self-heating carbon nanotubes[4], Si-nanowire/TiO2 core–shell heterojunctions[5], chemically gated Si nanowire/SnO2 thin film FETs6 and Pd-based Si nanomembrane sensors[7]. They were limited in the output signal
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