Abstract
The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.
Highlights
Atomic force microscopy (AFM)[1] has been extensively applied in numerous applications because it can achieve high spatial resolution and high force sensitivity[2,3]
The dynamic wetting properties of silicon and silicon nitride atomic force microscopy (AFM) tips were investigated at the nanoscale using a nano-Wilhelmy based approach
Geometric models were constructed for the both AFM tips using scanning electron microscopy (SEM) images taken from different viewing angles
Summary
Atomic force microscopy (AFM)[1] has been extensively applied in numerous applications because it can achieve high spatial resolution and high force sensitivity[2,3]. The wetting properties of AFM probe tips are of concern in AFM tip related force measurement, fabrication, and manipulation techniques, such as “dip-pen” nanolithography[4], nano-dispensing[5], micro/nanomanipulation[6,7], and nanotribological investigation[8], and even basic imaging. The wetting properties can be obtained by measuring corresponding capillary forces exerted on them and employing the Wilhelmy balance method with a known solid-liquid-gas (three phase) contact line. This method has been used to study the wetting properties of carbon nanotubes[10,11] and other fibers with constant diameters[11,12,13,14]. Other studies have modified the regular cantilevers through focused ion beam (FIB) milling to achieve probe tips with nearly constant diameters
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