Amorphous $CaSO_{4}$ nanocrystal deposits for friction and wear reduction at silicon interfaces

When an object is placed on a surface, friction and wear cause uncertainty in its exact position, and thus challenge precision manufacturing. Here, we explore the development of a sacrificial nanocrystal deposit that can suppress friction and wear. Amorphous \ce{CaSO4} nancrystals are deposited through salt solution droplet deposition followed by evaporation. During droplet drying, a precursor film of the aqueous \ce{CaSO4} solution spreads onto a hydrophilic silicon wafer, thus nucleating evenly spread unfaceted amorphous nanocrystals of \ce{CaSO4} on the wafer surface. We used atomic force microscopy to study the extent, topography, and friction and wear behavior of the deposited nanocrystals. We find that the sacrificial layer of nanocrystals is easy to apply and remove, spreads over large (few cm) areas with a constant thickness of about 8 nm, and has favorable friction and wear behavior.