Fabrication of ZnO Nanobrushes by H₂–C₂H₂ Plasma Etching for H₂ Sensing Applications

Abstract

Zinc oxide has widespread use in diverse applications due to its distinct properties. Many of these applications benefit from controlling the morphology on the nanoscale, where for example gas sensing is strongly enhanced for high surface-to-volume ratios. In this work the formation of novel ZnO nanobrushes by plasma etching treatment as a new approach is presented. The morphology and structure of the ZnO nanobrushes are studied in detail by transmission and scanning electron microscopy. It is revealed that ZnO nanobrush structures are fabricated by self-patterned preferential etching of ZnO microtetrapods in a hydrogen–acetylene plasma. The etching process was found to be most effective at 1% C2H2 admixture. Nanowire arrays are formed enabled by sidewall passivation due to a-C:H deposition. The nanobrush structures are further stabilized by simultaneous deposition of a SiO x layer from the opposite direction. Highly sensitive (gas response S = 148), selective, and fast (response time 15 s, recovery time 6 s) hydrogen sensors are fabricated from single nanobrushes. Single nanobrush sensors show enhanced sensing performance in increased gas response S of at least 10 times and improved response as well as recovery times when compared to nonporous single ZnO nanorod sensors due to the small diameters (≈50 nm) of the formed nanowires as well as the strongly enhanced surface-to-volume ratio of the nanobrushes by a factor of more than 10.

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Pd decorated ZnO nanosheets for enhanced hydrogen sensing performance

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Al2O3/ZnO Heterostructure-Based Sensors for Volatile Organic Compounds in Safety Applications

“…Volatile organic compounds (VOCs), which originate from multiple sources such as household items, cooking appliances, paint, oil refineries, and vehicle exhaust emissions, are highly hazardous vapors that significantly affect human health and air quality in various industrial environments. − Despite having been investigated extensively over the past few years, the sensing properties toward VOCs need to be improved continuously to meet the most up-to-date requirements for specific applications and to withstand the harsh industrial environments, especially when using heterostructures or heterojunctions of two or more metal oxides. − The selective detection of low concentrations of VOCs is highly important to underpin the continuous monitoring of human health and for environmental safety . Among the various types of materials available, the semiconducting–metal oxide-based chemo-resistive sensors are considered to be promising candidates for the detection of VOCs, , especially those comprising heterostructures/heterojunctions containing two or more different oxides, as these materials show excellent potential for their application in portable solid-state devices because of their low cost, high efficiency, simple preparation method, and good stability. − In the context of real-world applications, the response parameter is influenced by several factors, including the morphology, microstructure, defects, and heterojunctions of the VOC sensors as well as the relative humidity . The response and selectivity performance of solid-state gas sensors can be improved further through control of their properties and, especially, by developing new multilayered or heterostructured oxides with a coating of Al 2 O 3 nanofilms.…”

“…5 Among the various types of materials available, the semiconducting−metal oxide-based chemo-resistive sensors are considered to be promising candidates for the detection of VOCs, 2,6 especially those comprising heterostructures/heterojunctions containing two or more different oxides, as these materials show excellent potential for their application in portable solid-state devices because of their low cost, high efficiency, simple preparation method, and good stability. 1−9 In the context of real-world applications, the response parameter is influenced by several factors, including the morphology, 10 microstructure, defects, and heterojunctions of the VOC sensors as well as the relative humidity. 6 The response and selectivity performance of solidstate gas sensors can be improved further through control of their properties and, especially, by developing new multilayered or heterostructured oxides with a coating of Al nanofilms.…”