Oxygen plasma induced solvent resistance of polystyrene particles enables the fabrication of ultra-thin free-standing crosslinked polymer films

Plasma-treated polystyrene particles (PSP) are key building blocks in the fabrication of two- dimensional nanostructure arrays. Oxygen plasma etching can shrink PS particles and is a widespread tool in fundamental research and applications, but its effect has not been well understood. Here, we show that oxygen plasma induces an ultra-thin cross-linking layer on the surface of the PSPs, which increases their solvent resistance . We found in X-ray photoelectron spectroscopy (XPS) fine structure and valence band probing that the polymer C C bonds are breaking and recombining to form oxygenated functional groups. Our results explain, why oxygen plasma etched PS particles are more difficult to dissolve in nanofabrication procedures. Further, we used the ultra-thin cross-linked polymer layer to construct novel substrate-base microcavity arrays.