Ten Nanometer Scale WO₃/CuO Heterojunction Nanochannel for an Ultrasensitive Chemical Sensor

Abstract

The fabrication of p–n heterostructures of a metal oxide semiconductor (MOS) showed that a large amount of heterojunction interfaces is one of the key issues in MOS gas sensor research, since it could significantly enhance the sensing performance. Despite considerable progress in this area, fabrication of an ideal p–n heterojunction sensing channel has been challenging because of morphological limitations of synthetic methods in the conventional bottom-up fabrication based on precursor reductions. In this study, a 10 nm scale p–n heterojunction nanochannel was fabricated with ultrasmall grained WO3/CuO nanopatterns in a large area (centimeter scale) through unique one-step top-down lithographic approaches. The fabricated p–n heterostructure nanochannel showed ultrathinness (20 nm thickness) and high aspect ratio (>10) and consisted of highly dispersed p-type dopants and n-type channel materials. This facile heterojunction nanostructure could induce a high degree of extended depletion layer and efficient catalytic properties within its single-nanochannel surfaces. Accordingly, the WO3/CuO nanochannel exhibited ultrasensitive detection performance toward ethanol (C2H5OH) (R a/R g = 224 at100 ppb), 12 times higher than that of a pristine WO3 nanochannel. The limit of detection of the sensors was calculated to be below parts per billion levels (0.094 ppb) with significant response amplitudes (R a/R g = 75), which is the best ethanol-sensing performance among previously reported MOS-based sensors. Our unique lithographic approach for the p–n heterojunction nanochannel is expected to be universally applicable to various heteronanostructures such as the n–n junction, p–p junction, and metal–semiconductor junction without combinatorial limitations.

Ion Selective Nanochannels: From Critical Principles to Sensing and Biosensing Applications

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Sensors Based Upon Nanowires, Nanotubes, and Nanoribbons: 2016–2020

“…A depletion layer forms at the surface of an n-type metal oxide NW surface, depleting the concentration of electrons and increasing the NW resistance . When the sensor is exposed to reducing gases (H 2 , CO, and H 2 S), the reaction between the reducing gas molecules and oxygen anions releases those electrons back into the CB, restoring the NW’s resistance to its baseline value . However, the exposure of n-type metal oxide NWs to oxidizing gases (CO 2 , NO 2 , and Cl 2 ) increases the width of the depletion layer and further increases the sensor’s resistance …”

Ultrasensitive Photoelectrochemical Biosensor Based on Novel Z-Scheme Heterojunctions of Zn-Defective CdS/ZnS for MicroRNA Assay

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