Molecular bridge-mediated ultralow-power gas sensing

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 sputteredα-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.