Generic substrate for the surface forces apparatus: deposition and characterization of silicon nitride surfaces

We introduce a novel substrate for direct normal and lateral force measurements in the surface forces apparatus (SFA). While most SFA experiments are typically carried out using molecularly smooth mica surfaces, the new layered structure allows the use of just about any material which can be deposited as a thin film using evaporation or chemical vapor deposition. In this work, we demonstrate the use of this method for preparing plasma enhanced chemical vapor deposited silicon nitride substrates. Chemical, structural, optical and mechanical characterization of the substrates was carried out using secondary ion mass spectroscopy, atomic force microscopy, transmission electron microscopy, ellipsometry, multiple beam interferometry and SFA force measurements. The latter showed an extremely low adhesion energy (γ < μJ/m²) between silicon nitride surfaces prepared using this method, which is attributed to the surface roughness (ca. 2.2 nm rms).