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Inter-dependency between surface morphology and sensitive low RH detection: exploration of an intricate mechanism to extend the lower detection limit

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Abstract

The water vapor molecular dynamics inside a pore structure control both molecular adsorption and desorption processes and the limit of minimum detection (LOD). Pore morphology design, and a higher concentration of electrolyte-driven anions, in accordance with the kinetics of water vapor molecules, is reported here, as the ultimate answer to extremely low relative humidity (RH) detection. In this report, a series of samples were prepared by anodization in different voltage windows, related to specific electrolyte solutions. The sensing attributes comprised: (i) a LOD of ∼3 RH%, (ii) excellent response time (6 s) and recovery time (54 s), and (iii) a hysteresis loss of ∼0.36%, with sustained stability over the period of one year; all these occurring in a sample with a pore diameter ∼5 nm ±3 nm. Interestingly, the LOD extend towards a lower RH% with a decrease in pore diameter; and a suitable explanation is given for the entire range of humidity level, in terms of the molecular mean free path, loss of kinetic energy due to scattering inside the pores, and subsequent overall loss of Brownian energy of the molecules. It is inferred from the sensing response characteristics that pore morphology and lower detection limit are interrelated; therefore, a further extension in LOD from extremely low RH% to trace levels, needs careful engineering of the pore morphology and parameters related to molecular kinetics.

Graphical abstract: Inter-dependency between surface morphology and sensitive low RH detection: exploration of an intricate mechanism to extend the lower detection limit

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Article information


Submitted
17 Jan 2020
Accepted
29 Apr 2020
First published
14 May 2020

This article is Open Access

Nanoscale Adv., 2020, Advance Article
Article type
Paper

Inter-dependency between surface morphology and sensitive low RH detection: exploration of an intricate mechanism to extend the lower detection limit

K. Sharma, N. Alam and S. S. Islam, Nanoscale Adv., 2020, Advance Article , DOI: 10.1039/D0NA00047G

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