Physical feature exploration of nanocrystalline FeSi2 surface with argon plasma etching under varying power

Nanocrystalline (NC) FeSi2 films were created on Si(111) wafers via direct-current sputtering with facing targets at an ambient temperature, then the films were etched by Ar plasma generated through microwave source at different powers of 50, 100, and 150 W. The surface morphology of the as-coated NC FeSi2 films showed numerous small uniform crystallites and root-mean-square roughness of 4.65 angstrom. The surface for each etched NC FeSi2 film showed appearance of holes and slight increase in the roughness as the power increased. X-ray photoelectron spectra showed that the etching decreased the content of hydrophobic carbon and increased the presence of polar oxide group on the NC FeSi2 films as the power increased. These changes should be the factor behind the shift from hydrophobic state to hydrophilic state. The contact angle of the unetched NC FeSi2 film surface was 100.55 degrees, which is hydrophobic. The NC FeSi2 film's surface reached a minimum contact angle of 35.65 degrees, which belong to hydrophilic state, when the etching power was increased to 150 W. The mechanical properties of NC FeSi2 films rarely affect by Ar plasma. The change in surface state to nearly superhydrophilic after plasma etching indicate possibility to develop NC FeSi2 into a self-cleaning surface coating material.