Approaching the liquid/air interface with scanning force microscopy

Scanning force microscopy at both the air/solid and the liquid/solid interface is very common and understood accurately. Here we demonstrate that the scanning force microscope (SFM) is capable of investigating even at the liquid/air interface, i.e., the surface of a Langmuir film floating on the water subphase. We demonstrate the successful investigation of (a) a solid substrate surface, i.e., a polycrystalline gold sample under water, (b) a mechanically stabilized 2‐docosylamino‐ 5‐nitropyridine Langmuir–Blodgett (LB) film, and (c) a freely floating cadmium‐arachidate (CdA) LB film. The SFM is constructed as a standalone, remote‐controlled, and water‐tight microscope that can be put upside down into the water subphase of a commercial LB trough. The SFM tip therefore approaches the air/water interface from underwater allowing the investigation of the LB chromophores. This force microscope complements our optical techniques (polarization and second‐harmonic microscopy) that have already been set up on top of the LB trough and that achieve monolayer resolution on a floating Langmuir layer. Combined operation of all those techniques will provide correlated information on the optical and structural properties of the LB molecules. © 1996 American Vacuum Society