Total effective surface area principle for enhancement of capacitive humidity sensor of thick-film nanoporous alumina

Chung, Chen-Kuei; Khor, O. K.; Kuo, E. H.; Ku, Chin-An

doi:10.1016/j.matlet.2019.126921

Cited by 16 publications

(9 citation statements)

References 11 publications

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“…Anodization is a typical electrochemical deposition technology. Among many humidity-sensor materials, it is mostly used in the preparation of Al 2 O 3 [ 51 , 55 , 56 , 57 , 58 , 59 ] and TiO 2 [ 60 ]. This method will be described below in terms of the mechanism of anodic aluminum oxide (AAO) [ 61 , 62 ].…”

Section: Materials and Methods For Nanosensor Synthesismentioning

confidence: 99%

“…The recent advances of several studies into ceramic humidity nanosensors are listed in Table 1 for comparison [ 10 , 51 , 55 , 56 , 57 , 58 , 59 , 78 , 79 , 80 , 81 ]. The ceramic sensors are mainly manufactured using solution methods [ 10 , 78 , 81 ], anodization [ 51 , 55 , 56 , 57 , 58 , 59 ] or the PVD [ 80 ] process. Due to the poor conductivity of ceramics, the measurement type is divided into two types: capacitance and resistance, or current or voltage types.…”

Section: Humidity Nanosensorsmentioning

confidence: 99%

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Advances in Humidity Nanosensors and Their Application: Review

Chung

2023

Sensors

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As the technology revolution and industrialization have flourished in the last few decades, the development of humidity nanosensors has become more important for the detection and control of humidity in the industry production line, food preservation, chemistry, agriculture and environmental monitoring. The new nanostructured materials and fabrication in nanosensors are linked to better sensor performance, especially for superior humidity sensing, following the intensive research into the design and synthesis of nanomaterials in the last few years. Various nanomaterials, such as ceramics, polymers, semiconductor and sulfide, carbon-based, triboelectrical nanogenerator (TENG), and MXene, have been studied for their potential ability to sense humidity with structures of nanowires, nanotubes, nanopores, and monolayers. These nanosensors have been synthesized via a wide range of processes, including solution synthesis, anodization, physical vapor deposition (PVD), or chemical vapor deposition (CVD). The sensing mechanism, process improvement and nanostructure modulation of different types of materials are mostly inexhaustible, but they are all inseparable from the goals of the effective response, high sensitivity and low response–recovery time of humidity sensors. In this review, we focus on the sensing mechanism of direct and indirect sensing, various fabrication methods, nanomaterial geometry and recent advances in humidity nanosensors. Various types of capacitive, resistive and optical humidity nanosensors are introduced, alongside illustration of the properties and nanostructures of various materials. The similarities and differences of the humidity-sensitive mechanisms of different types of materials are summarized. Applications such as IoT, and the environmental and human-body monitoring of nanosensors are the development trends for futures advancements.

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Section: Materials and Methods For Nanosensor Synthesismentioning

confidence: 99%

Section: Humidity Nanosensorsmentioning

confidence: 99%

Advances in Humidity Nanosensors and Their Application: Review

Chung

2023

Sensors

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“…In addition, aluminum is the most commonly used metal in production lines, and its processing has a high degree of industrial compatibility. Furthermore, the highly specific surface area [ 23 ] of AAO structure leads to good sensing performance, especially as a humidity sensor [ 23 , 24 , 25 , 26 , 27 , 28 ]. In 1987, Khanna and Nahar [ 29 ] published the first paper on measuring atmospheric humidity using AAO.…”

Section: Introductionmentioning

confidence: 99%

An Effective Resistive-Type Alcohol Vapor Sensor Using One-Step Facile Nanoporous Anodic Alumina

Chung

2023

Micromachines

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With the increases in work environment regulations restricting alcohol to 1000 ppm, and in drink-driving laws, testing for alcohol with a simple method is a crucial issue. Conventional alcohol sensors based on sulfide, metal oxide, boron nitride or graphene oxide have a detection limit in the range of 50–1000 ppm but have disadvantages of complicated manufacture and longer processing times. A recent portable alcohol meter based on semiconductor material using conductivity or chemistry measurements still has the problem of a complex and lengthy manufacturing process. In this paper, a simple and effective resistive-type alcohol vapor sensor using one-step anodic aluminum oxide (AAO) is proposed. The nanoporous AAO was produced in one-step by anodizing low-purity AA1050 at room temperature of 25 °C, which overcame the traditional high-cost and lengthy process at low temperature of anodization and etching from high-purity aluminum. The highly specific surface area of AAO has benefits for good sensing performance, especially as a humidity or alcohol vapor sensor. With the resistance measurement method, alcohol vapor concentration of 0, 100, 300, 500, 700 and 1000 ppm correspond to mean resistances of 8524 Ω, 8672 Ω, 9121 Ω, 9568 Ω, 10,243 Ω, and 11,045 Ω, respectively, in a linear relationship. Compared with other materials for detecting alcohol vapor, the AAO resistive sensor has advantages of fast and simple manufacturing with good detection limits for practical applications. The resistive-type alcohol vapor-sensing mechanism is described with respect to the resistivity of the test substance and the pore morphology of AAO. In a human breath test, the AAO sensor can quickly distinguish whether the subject is drinking, with normal breath response of −30% to −40% and −20% to −30% response after drinking 50 mL of wine of 25% alcohol.

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“…These sensors have the advantage of reacting with molecules down to the level of a single molecular layer, ensuring high sensitivity and excellent response and recovery times [ 9 , 10 , 11 ]. Capacitance-based gas sensors have certain advantages over other types of sensors, such as low-temperature dependence, excellent thermal stability, linear response, and low power consumption [ 12 , 13 , 14 ]. In particular, a capacitive gas sensor was selected in this study, owing to its advantageous characteristics of possessing a simple structure, miniaturizability, and ability to allow continuous observation.…”

Section: Introductionmentioning

confidence: 99%

Anodic Aluminum Oxide-Based Chemi-Capacitive Sensor for Ethanol Gas

Lim,

Kim,

Park

et al. 2023

Nanomaterials

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Alcohol ingested by humans can be analyzed via breath tests; however, approximately 1% can be excreted via the skin. In this paper, we present a capacitive sensor using hydrophobically treated anodic aluminum oxide (AAO) capable of detecting alcohol excreted through the epidermis. The degree of hydrophobicity based on the duration of exposure to 3-aminopropyltriethoxysilane vapor comprising a small number of Si–NH2 functional groups on the AAO surface was confirmed and the optimal exposure time was confirmed to be 60 min. The hydrophobized AAO showed a 4.8% reduction in sensitivity to moisture. Simultaneously, the sensitivity of the sensor to ethanol decreased by only 12%. Lastly, the fabricated sensor was successfully operated by attaching it to an ankle-type breathalyzer.

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Total effective surface area principle for enhancement of capacitive humidity sensor of thick-film nanoporous alumina

Cited by 16 publications

References 11 publications

Advances in Humidity Nanosensors and Their Application: Review

Advances in Humidity Nanosensors and Their Application: Review

An Effective Resistive-Type Alcohol Vapor Sensor Using One-Step Facile Nanoporous Anodic Alumina

Anodic Aluminum Oxide-Based Chemi-Capacitive Sensor for Ethanol Gas

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