First Advisor

Andres La Rosa

Term of Graduation

Summer 2026

Date of Publication

8-20-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Applied Physics

Department

Physics

Language

English

Subjects

Acoustic Microscope with Normal Force, Near-field Acoustic Microscope

Physical Description

1 online resource (xxiii, 195 pages)

Abstract

This dissertation introduces quartz tuning fork (QTF) based Shear-force Near-field Acoustic Microscopy (SANM) and Whispering Gallery Acoustic Microscopy (WGAS) systems, upgraded this time with Atomic Force Microscopy (AFM) capability to also monitor the vertical force component involved in shear force interactions. This enhanced system aims at studying nano-sized confined fluids under shear, with an emphasis on finding correlations between the fluid's a) viscoelastic properties and b) near-field acoustic wave emission capability. In the current SANM/WGAS/AFM system addressed here, the confined fluid is constituted by the water meniscus that bridges the gap between the apex of a laterally oscillating tapered probe and a stationary solid flat substrate. The studies in this thesis are relevant not only to fundamental scientific research of fluids confined in nanosized spaces (whose properties depart in many aspects from its bulk properties, namely enhanced shear viscosity, prolonged relaxation time, confinement-induced phase transformation), but also to technological areas (like adhesion, wetting processes, and interfacial friction phenomena, including the considerable effort for developing thin-film coatings to eliminate capillary adhesion between components to reduce corrosion and wear).

This thesis places emphasis on the integration of AFM into the SANM/WGAS system: i) To characterize the dynamic response of the water meniscus at different size confinements, approach-retraction cycles (ARC) are performed sequentially. During these cycles, a laterally oscillating probe (attached to an electrically driven QTF) first approaches and subsequently retracts from the substrate. We provide conclusive evidence that, during the probe's approach, unstable finger-like water bridges (unable to emit sound) are formed prior to their coalescence into a water meniscus across the probe-substrate gap. ii) The acoustic wave emitted by the suddenly formed water meniscus (laterally driven by the oscillating probe) is detected in the near-field region by an acoustic transducer attached to the back side of the (~ 1 mm thick) substrate, which constitutes the distinctive metrology capability of the SANM technique. iii) Frequency modulation (FM) feedback, tracking of the probe's lateral oscillations amplitude (using either the acoustic WGAS or the QTF piezoelectric current as input control signals), is used to monitor the changes in both the lateral oscillation amplitude and the resonance frequency of the probe during an ARC. FM near-field acoustic measurements, using variable driving voltage while maintaining the QTF's oscillation amplitude constant during ARCs, have been accomplished in this thesis. iv) An AFM cantilever probe (attached to one of the QTF tines) is used to monitor the vertical force acting on the laterally oscillating probe.

The probe-fluid-substrate interactions have been systematically tested a) using probes of different (slender and chubby) apex geometry, b) using substrates of different wetting (hydrophobic, hydrophilic) properties, and c) performing the experiments under different environment relative humidity (RH) conditions (40% and 60% RH). SANM and frequency modulation (FM) feedback control was integrated into a commercial atomic force Microscope system. FM allows discriminating the elastic and inelastic components of the probe-fluid-substrate interfacial interactions. The incorporation of AFM aimed at helping identify the actual position of the substrate during an ARC. To further gain information about the position of the substrate surface, a contact current setting was implemented using a metallic probe and sample. Lastly, with PID control in contact mode from a commercial AFM system (integrated with SANM capability), topography images are obtained concurrently monitoring the SANM signal for comparison purposes.

A simple harmonic oscillator model (SHO) model is presented, which allows to extract effective values of the meniscus fluid's elastic kfluid and damping ?fluid parameters. A thermodynamic argument based on the grand potential Φ (T, V, μ) = –PV is used to justify the stochastic formation of a water meniscus when the probe is placed at nanometer-sized distances from the surface. Efforts to obtain numerical solutions of the Young-Laplace equation that govern the shape of the meniscus are also initiated, aiming to correlate the curvature of the meniscus with the intensity of the acoustic wave it emits. Altogether, from the measurements and models outlined above, a plausible understanding of the genealogy of the meniscus formation and the ARC traces appears to emerge when testing hydrophilic surfaces: First, a water film appears to form on the substrate and the probe surfaces. As these two films approach each other, multiple unstable water bridge filaments start to appear between probe and sample prior to their coalescence into meniscus (tests using a blunt tip allowed to demonstrate this behavior more clearly). ARC displayed hysteresis only at ambient humidity greater than 55% ambient humidity. On the other hand, implementing SANM with an AFM probe was challenging to interpret, which can be attributed to the weaker spring constant (40N/m) compared to the 2000 N/m when using a stylus attached to a QTF. An analysis in the context of elastohydrodynamic interactions suggests that the motion of the AFM pyramid probe inside a viscous fluid and in the vicinity of a surface induces a hydrodynamic stress field that may affect the pyramid's motion drastically.

Rights

© 2026 Kacharat Supichayanggoon

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/45145

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