Abstract
Recently, high-resolution patterned metal oxide semiconductors (MOS) have gained considerable attention for enhanced gas sensing performance due to their polycrystalline nature, ultrasmall grain size (~5 nm), patternable properties, and high surface-to-volume ratio. Herein, we significantly enhanced the sensing performance of that patterned MOS by galvanic replacement, which allows for selective functionalization on ultrathin Cu2O nanopatterns. Based on the reduction potential energy difference between the base channel material (Cu2O) and the decorated metal ion (Pt2+), Pt could be selectively and precisely decorated onto the desired area of the Cu2O nanochannel array. Overall, the Pt-decorated Cu2O exhibited 11-fold higher NO2 (100 ppm) sensing sensitivity as compared to the non-decorated sensing channel, the while the channel device with excessive Pt doping showed complete loss of sensing properties.
Highlights
IntroductionMetal oxide semiconductors (MOSs) (e.g., n-type [1,2,3,4,5] and p-type [6,7,8,9,10,11,12]) are widely used as gas sensing materials due to their high sensitivity, large specific surface area, applicability to various gases (NO2 , CO2 , H2 , volatile organic compounds (VOCs), etc.), high electron mobility, and good chemical/thermal stability at high operating temperature [13,14,15,16,17,18,19,20]
After the PS residue was removed by oxygen reactive ion etching (RIE) under a low vacuum and O2 (100 standard cubic centimeters per minute) plasma environment, thermal oxidation was performed in a tubular furnace at 450 ◦ C for 3 h to obtain a Cu2 O line channel
Cu2 O nanopatterns and there was no Pt in the substrate area between the Cu2 O channels (Figure 2c–f and Figure S6). These results revealed that the galvanic replacement selectively occurs at the target spots, i.e., the surface of the Cu2 O nanopatterns
Summary
Metal oxide semiconductors (MOSs) (e.g., n-type [1,2,3,4,5] and p-type [6,7,8,9,10,11,12]) are widely used as gas sensing materials due to their high sensitivity, large specific surface area, applicability to various gases (NO2 , CO2 , H2 , volatile organic compounds (VOCs), etc.), high electron mobility, and good chemical/thermal stability at high operating temperature [13,14,15,16,17,18,19,20]. Doping with noble metals such as Pt [21,22], Pd [23], and Ag [2] has been widely used to enhance the sensing performance of the MOS by tuning the gas adsorption or diffusion properties. When metal dopants undergo partial oxidation in air, their oxidation state of the metal additive can be changed into metallic state depending on the environment. This increases the depth of the electron-depleted charge layer due to electron extraction from the metal oxide, thereby changing the electronic state change of the MOS. The chemical sensitization represents a spill-over effect by activating target gas adsorption on the semiconductor surface [24]. The doped promoter facilitates target gas as active state, leading to Sensors 2018, 18, 4438; doi:10.3390/s18124438 www.mdpi.com/journal/sensors
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