Author ORCID Identifier
https://orcid.org/0009-0008-6795-8084
Date Available
7-20-2026
Year of Publication
2025
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Engineering
Department/School/Program
Electrical Engineering
Faculty
Professor Dr. Zhi David Chen
Faculty
Professor Dr. Yuan Liao
Abstract
Relative humidity sensors are used for high-humidity measurement. Moisture sensors, or dew point sensors are used for low-humidity measurement (< 1 ppmv). The dissertation contains two parts of studies. In the first part, the effect of surface morphology on the response speed of moisture sensors is studied. Moisture sensors using α-Al2O3 films as porous dielectric materials deposited by anodic spark deposition are studied. In this part of the study, a variety of small pores have been studied to investigate the response speed of moisture sensors. Three different surface morphologies have been studied using scanning electron microscopy. One sample has the maximum number of small pores, one sample has the medium number of small pores, and the last sample has the minimum number of small pores. Small pores are defined as pore size ranging from 40 nm to 200 nm. We found that the sensor made as porous material with the maximum number of small pores has the fastest response speed, and that from the minimum number of small pores has the slowest response speed either from high humidity to low humidity or from low humidity to high humidity.
In the second part, research is focused on moisture adsorption and desorption, and various processes of humidity/moisture sensors, which are essential for various environmental and industrial applications. Unlike the relative humidity sensors, moisture sensors require very high sensitivity for detecting moisture levels below 0.5 ppmv (-80°C dew point) or even at 13 ppbv (-100°C dewpoint). For the extremely low moisture levels, chemical absorption and desorption of hydroxyl groups plays a key role in the sensor’s sensitivity and stability. We designed a series of experiments to study adsorption and desorption of hydroxyl groups. The hydroxyl groups were driven out by heating the sensor at low humidity and at a series of temperatures ranging from 80°C to 145°C.We studied the desorption characteristics of the hydroxyl groups through heating at a low moisture level (10 ppmv or -60°C dew point). The desorption of hydroxyl groups was saturated after heating the sensor above 124°C, suggesting that all hydroxyl groups were driven out. The hydroxyl groups can also be driven into sensing materials (SiO2) through heating at high humidity and at a series of temperatures ranging from 70°C to 145°C. We observed that the hydroxyl groups returned to the sensing material (SiO2).
Therefore, the experiments provided insight into the mechanism and kinetics of the moisture adsorption and desorption on the SiO2 sensing material.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2025.279
Funding Information
This study was supported by Fulbright Foreign Student Program (January 2022 to May 2025). And, Valvoline Global Operations, Lexington, Kentucky, United States of America also supported this study for one year from August 2023 to July 2024. Moreover, ZDC Tech Limited & Company also supported this study for two years from March 2022 to February 2024.
Recommended Citation
Ali, Ronak, "SURFACE MORPHOLOGY AND MOISTURE ADSORPTION/DESORPTION CHARACTERISTICS OF HYBRID-DIELECTRIC MOISTURE SENSORS" (2025). Theses and Dissertations--Electrical and Computer Engineering. 217.
https://uknowledge.uky.edu/ece_etds/217
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