A polystyrenebased polymeric diazonium salt (PS-DAS) was used to demonstrate that its ultrathin films could be prepared through a sequential growth manner.The films were prepared by dipping the substrates in the PSDAS solution

washing with deionized water

and drying repeatedly.The growing process of untrathin films was monitored by UV-Vis spectroscopy and ellipsometry.The surface morphology and wettability of the films were characterized by AFM and water contact angle measurements.Results showed that PS-DAS could form thin films through uniformly layer-by-layered growth manner by a repeated dipping-coating- drying process.The UV-Vis and ellipsometry results showed that the amount of PS-DAS adsorbed in each dipping cycle was almost the same.In the dipping-washing-drying cycles

the drying step after each deposition was critical for growth of the PS-DAS ultrathin film.After heating treatment

cross-linking occurred in the thin films.The water contact angle changed from 77° to 90.7° after heating

which indicated the decomposition of the diazonium functional groups.The solvent resistance of the PSDAS ultrathin films was also greatly enhanced by cross-linking.The observations are helpful for understanding the unique self-assembling properties of polymeric diazonium salt which could be used to prepare ultrathin films.