Capacitive humidity sensors based on large diameter porous alumina prepared by high current anodization

Kashi, M. Almasi; Ramazani, A.; Abbasian, Hamed; Khayyatian, A.

doi:10.1016/j.sna.2011.11.033

Cited by 57 publications

(20 citation statements)

References 19 publications

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“…In a solid state configuration, EIS has also been applied for the detection of water vapor in moisture sensors − and resulted in commercially available devices . An exhaustive and recent review on the subject can be found in ref .…”

Section: Introductionmentioning

confidence: 99%

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy

Perrotta

García

Michels

et al. 2015

ACS Appl. Mater. Interfaces

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Water permeation in inorganic moisture permeation barriers occurs through macroscale defects/pinholes and nanopores, the latter with size approaching the water kinetic diameter (0.27 nm). Both permeation paths can be identified by the calcium test, i.e., a time-consuming and expensive optical method for determining the water vapor transmission rate (WVTR) through barrier layers. Recently, we have shown that ellipsometric porosimetry (i.e., a combination of spectroscopic ellipsometry and isothermal adsorption studies) is a valid method to classify and quantify the nanoporosity and correlate it with the WVTR values. Nevertheless, no information is obtained about the macroscale defects or the kinetics of water permeation through the barrier, both essential in assessing the quality of the barrier layer. In this study, electrochemical impedance spectroscopy (EIS) is shown as a sensitive and versatile method to obtain information on nanoporosity and macroscale defects, water permeation, and diffusivity of moisture barrier layers, complementing the barrier property characterization obtained by means of EP and calcium test. EIS is performed on thin SiO2 barrier layers deposited by plasma enhanced-CVD. It allows the determination of the relative water uptake in the SiO2 layers, found to be in agreement with the nanoporosity content inferred by EP. Furthermore, the kinetics of water permeation is followed by EIS, and the diffusivity (D) is determined and found to be in accordance with literature values. Moreover, differently from EP, EIS data are shown to be sensitive to the presence of local macrodefects, correlated with the barrier failure during the calcium test.

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Section: Introductionmentioning

confidence: 99%

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy

Perrotta

García

Michels

et al. 2015

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

show abstract

“…Among the various types of existing sensors (resistive, mass-sensitive, electromagnetic, etc. ), capacitive-type sensors are the most popular and of commercial interest because they present a higher sensitivity than the others and have as a competitive advantage their fabrication process, which is simpler [24]. Several techniques exist to produce porous alumina, such as chemical vapour deposition (CVD), sputtering and sol-gel processes [25].…”

Section: Introductionmentioning

confidence: 99%

Development of Capacitive-Type Sensors by Electrochemical Anodization: Humidity and Touch Sensing Applications

Carneiro

Ribeiro

Miranda

et al. 2021

Sensors

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This work describes the development of a capacitive-type sensor created from nanoporous anodic aluminium oxide (NP-AAO) prepared by the one-step anodization method conducted in potentiostatic mode and performed in a low-cost homemade system. A series of samples were prepared via an anodization campaign carried out on different acid electrolytes, in which the anodization parameters were adjusted to investigate the effect of pore size and porosity on the capacitive sensing performance. Two sensor test cases are investigated. The first case explores the use of highly uniform NP-AAO structures for humidity sensing applications while the second analyses the use of NP-AAO as a capacitive touch sensor for biological applications, namely, to detect the presence of small “objects” such as bacterial colonies of Escherichia Coli. A mathematical model based on equivalent electrical circuits was developed to evaluate the effect of humidity condensation (inside the pores) on the sensor capacitance and also to estimate the capacitance change of the sensor due to pore blocking by the presence of a certain number of bacterial microorganisms. Regarding the humidity sensing test cases, it was found that the sensitivity of the sensor fabricated in a phosphoric acid solution reaches up to 39 (pF/RH%), which is almost three times higher than the sensor fabricated in oxalic acid and about eight times higher than the sensor fabricated in sulfuric acid. Its improved sensitivity is explained in terms of the pore size effect on the mean free path and the loss of Brownian energy of the water vapour molecules. Concerning the touch sensing test case, it is demonstrated that the NP-AAO structures can be used as capacitive touch sensors because the magnitude of the capacitance change directly depends on the number of bacteria that cover the nanopores; the fraction of the electrode area activated by bacterial pore blocking is about 4.4% and 30.2% for B1 (E. Coli OD600nm = 0.1) and B2 (E. Coli OD600nm = 1) sensors, respectively.

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“…Electrochemical anodizing is one of the most important surface finishing processes for aluminum and its alloys and is widely employed for dielectric film coating [20,21,22], coloring [23,24,25], hardening [26,27,28], corrosion resistance improvements [29,30,31], and novel nanomaterial fabrication [32,33,34,35,36,37,38,39,40,41,42,43]. So far, processes combining traditional anodizing in sulfuric, oxalic, and phosphoric acids with self-assembled monolayer (SAM) coatings have been reported by several research groups for superhydrophilic and superhydrophobic aluminum surfaces [44,45].…”

Section: Introductionmentioning

confidence: 99%

A Superhydrophilic Aluminum Surface with Fast Water Evaporation Based on Anodic Alumina Bundle Structures via Anodizing in Pyrophosphoric Acid

et al. 2019

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A superhydrophilic aluminum surface with fast water evaporation based on nanostructured aluminum oxide was fabricated via anodizing in pyrophosphoric acid. Anodizing aluminum in pyrophosphoric acid caused the successive formation of a barrier oxide film, a porous oxide film, pyramidal bundle structures with alumina nanofibers, and completely bent nanofibers. During the water contact angle measurements at 1 s after the water droplet was placed on the anodized surface, the contact angle rapidly decreased to less than 10°, and superhydrophilic behavior with the lowest contact angle measuring 2.0° was exhibited on the surface covered with the pyramidal bundle structures. As the measurement time of the contact angle decreased to 200–33 ms after the water placement, although the contact angle slightly increased in the initial stage due to the formation of porous alumina, at 33 ms after the water placement, the contact angle was 9.8°, indicating that superhydrophilicity with fast water evaporation was successfully obtained on the surface covered with the pyramidal bundle structures. We found that the shape of the pyramidal bundle structures was maintained in water without separation by in situ high-speed atomic force microscopy measurements.

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Capacitive humidity sensors based on large diameter porous alumina prepared by high current anodization

Cited by 57 publications

References 19 publications

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy

Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy

Development of Capacitive-Type Sensors by Electrochemical Anodization: Humidity and Touch Sensing Applications

A Superhydrophilic Aluminum Surface with Fast Water Evaporation Based on Anodic Alumina Bundle Structures via Anodizing in Pyrophosphoric Acid

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