Ultra‐Smooth, Chemically Functional Silica Surfaces for Surface Interaction Measurements and Optical/Interferometry‐Based Techniques

Abstract

The study of interfacial phenomena is central to a range of chemical, physical, optical, and electromagnetic systems such as surface imaging, polymer interactions, friction/wear, and ion-transport in batteries. Studying intermolecular forces and processes of interfaces at the sub-nano scale has proven difficult due to limitations in surface preparation methods. Here, we describe a method for fabricating reflective, deformable composite layers that expose an ultrasmooth silica (SiO 2 ) surface (RMS roughness < 0.4 nm) with interferometric applications. The robust design allows for cleaning and reusing the same surfaces for over a week of continuous experimentation without degradation. The electric double-layer forces measured using the composite surfaces are within 10% of the theoretically predicted values. We also demonstrate that standard chemisorption and physisorption procedures on silica can be applied to chemically modify the surfaces; as a demonstration of this, the composite surfaces are successfully modified with octadecyltrichlorosilane (OTS) to study their hydrophobic interactions in water using a surface force apparatus (SFA). These composite surfaces provide a basis for the preparation of a variety of new surfaces, and should be particularly beneficial for the SFA and colloidal probe methods that employ optical/interferometric and electrochemical techniques, enabling characterization of previously unattainable surface and interfacial phenomena.

Multimodal Miniature Surface Forces Apparatus (μSFA) for Interfacial Science Measurements

“…While the measurements shown here demonstrate that clean contact zones can be observed with commercially purchased surfaces, the roughness of the glass surfaces is not ideal for molecular scale force measurements; future efforts will include preparation of smoother surfaces using recent methods. 62 Nonetheless, we have shown here that NR-μSFA enables straightforward sample preparation, accurate force measurements, and facile multi-modality, including Raman spectroscopy.…”

“…Future developments of Raman-μSFA could leverage the roughness to perform surface-enhanced Raman scattering measurements by evaporating gold onto the slightly rough silica surface. Future efforts will also include the preparation of smoother surfaces using recent methods . We have shown here that NR-μSFA enables straightforward sample preparation, accurate force measurements, and facile multimodality, including Raman spectroscopy.…”

“…Future efforts will also include the preparation of smoother surfaces using recent methods. 71 We have shown here that NR-μSFA enables straightforward sample preparation, accurate force measurements, and facile multimodality, including Raman spectroscopy.…”

Polydopamine Ultrathin Film Growth on Mica via In-Situ Polymerization of Dopamine with Applications for Silver-Based Antimicrobial Coatings

“…It is thus compulsory to explore the mechanisms controlling thin film growth of materials on substrate surfaces, especially to achieve the desired control over novel properties of materials. In this context, utilization of an atomically smooth surface is well needed and suitable for exploring the short-range interactions that occur within a separation of less than 3 nm [ 28 ]. Our aim is thus to examine the growth of a PDA thin film in the minimum deposition time necessary for forming a continuous film on a mica surface and simultaneously to establish the physicochemical signatures of the PDA films.…”

Template-Stripped Ultra-Smooth Aluminum Films (0.2 nm RMS) for the Surface Forces Apparatus

“…Mica, however, sees limited use in real-world applications, and it is therefore important to extend the number of substrates viable for roughness-sensitive surface forces studies. A range of alternative systems have been investigated, including Au, Pt, Fe, SiO 2 , and SiN x . − For example, Au has been used as a conductive substrate to study charging dynamics of nanopores . Here, we address the ongoing need for ultra-smooth, contamination-free aluminum for surface forces measurements.…”