THIN FILM GAS ADSORPTION MEASUREMENT AND CONTROL
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2024
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The science of interfaces investigates the intermediation among distinctly different phases, enabling the observation of many intriguing phenomena spanning scales from micrometers,
nanometers, and even to the sub-atomic level. The interaction of gaseous molecules with solid
surfaces underlies efforts in understanding and engineering the adsorption and permeation of
gaseous molecules through outer layer(s) of solid phase materials for the applications of sensing,
storing, filtering, etc. This knowledge underlies today’s robust growth of core industrial
technologies such as batteries for electric vehicles, hydrogen storage as a source of clean energy,
gas sensing for wearable devices and safety purposes, and gas filter membranes. In this
dissertation, we expand the use of a well-known gravimetric detection device with high sensitivity
– the Quartz Crystal Microbalance – to detailed examination of the gas-solid interface during
physisorption. The first project presented in this dissertation (Chapter 1): Design of an
environmental chamber for gas adsorption detection with Quartz Crystal Microbalance, helps
create a well-controlled and stable environment around the Quartz Crystal Microbalance as the
adsorption experiment takes place. The chamber’s temperature, pressure, in and out flows were
controlled and thermodynamic information of the cyclohexane adsorption on gold surface of QCM
was successfully collected. This ensures the feasibility of the environmental chamber
encapsulating the QCM for different gas adsorption experiment conditions. The understanding of
gaseous molecule interaction with thin film was elaborated and analytically represented through
the second work (Chapter 2): (II) Analytical study of H2 adsorption on MgB2 thin film. This work
focused on H2 adsorption on MgB2 because MgB2 is a prominent hydrogen storage material listed
by Department of Energy, with interesting its metallic-like and layered structure are interesting to
look into. A parallel effort of chapter 2 is the third project (Chapter 3): (III) Develop an ultrathin
v
film of MgB2 on QCM surface. This project serves as a crucial step for consequential hydrogen
adsorption on MgB2 which is to transfer the MgB2 film onto the QCM surface. Dip coating of
MgB2 in co-solvent proved to provide an ultra-thin film of 5 nm of MgB2 on QCM surface with
negligible coffee ring effect. The final project is presented in Chapter 4: (IV) Study of film
conductivity change at gaseous partial pressure variation. This effort demonstrated joint operation
of electrical conductivity and gravimetric measurements within the QCM environmental chamber,
thereby observing a unique resistivity effect dependent on film composition and adsorption state.
The changes of Au and AuPd thin film resistivity were evaluated under exposure to ethanol and
cyclohexane vapors. A significantly larger change in sheet resistance of ethanol adsorption on
AuPd, as compared with sheet resistance change of ethanol adsorption on Au or Pd films alone,
emphasized the synergistic effect of bimetallic AuPd. Overall, this dissertation provides a
comprehensive experimental and analytical foundation for characterization of sensing and
adsorbing materials. This dissertation prepared the fundamental theory and experimental
techniques for study of adsorption enhancement through external electric field effects, but detailed
study of this topic remains future work. Further interfacing design is needed; first, continuity
testing must be achieved for sequential gas adsorption experiments. The collective goal of the
following research projects, presented below in this report, has been to demonstrate and test the
capabilities of quartz crystal microbalance apparatus as a high-productivity experimental platform
in gas adsorption on thin films, through use of the QCM test platform to deepen the understanding
of surface science as gaseous molecules interact with thin solid films.
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Nanotechnology
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202 pages
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