Portland State University. Department of Physics
Andres H. La Rosa
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Applied Physics
acoustic, confinement, mesoscopic-fluid, shear-force
1 online resource (xviii, 183 pages)
The design, construction, and implementation of Shear-force Acoustic Near-Field Microscopy (SANM), operational from ultrahigh vacuum (UHV) to ambient conditions--offering a pristine environment for more reliable characterization the hydrophobic/hydrophilic wetting properties of surfaces--is presented. SANM capitalizes on its sensitivity to the evanescent near-field acoustic emissions from a mesoscopic fluid (confined between the apex of a laterally oscillating tapered nanosized probe and a flat substrate) when subjected to shear motion. This distinct capability provides direct access to the fluid’s viscoelastic response when subjected to shear interactions, in contrast to indirect measurements performed by other standard probe proximity scanning techniques. The entire in-lab construction of the UHV-SANM has also been accompanied by innovation, including the (patent pending) Load-lock Acoustic-coupling Manipulator (LAM). LAM ensures a mechanical coupling between the sample and the bulky acoustic SANM-sensor (a key aspect to achieve near-field acoustic detection sensitivity,) as well as sample interchange, all under vacuum conditions operation. As a byproduct of this invention, the full microscope system can conveniently be operated remotely. Herein, the UHV-SANM is used to monitor the dynamics of a fluid meniscus--that stochastically forms (or undergoes rupture) when a tapered nanoprobe approaches to (retracts from) a flat surface--at different vacuum conditions. This is relevant to fields in surface science (including scanning probe microscopy), where the eventual presence of a third body material between the probe and the surface is currently the subject of major controversy. UHV-SANM shed light by detecting acoustic emission at 5x10-5 Torr for the first time. The results reveal the important role played by the environment humidity and the effects (enhanced by the vacuum conditions) caused by electrostatic charges. Overall, the scientific relevance of the UHV-SANM system is reflected on the fact that reaching an understanding of the striking properties that mesoscopic fluids display under confinement (namely, enhanced shear viscosity, prolonged relaxation time, confinement-induced phase transformation, hydrophobic effects beyond commonly accepted molecular interaction ranges) remain a major challenge in condensed matter physics.
©2023 Theodore Alex Brockman
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Brockman, Theodore Alex, "UHV-Shear-Force Acoustic Near-Field Microscopy and Its Implementation in the Study of Confined Mesoscopic Fluids" (2023). Dissertations and Theses. Paper 6425.
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