Fabrication of metal-oxide arrays: mechanism of solvent-mediated metal infiltration into block copolymer nanopatterns

We have studied solvent-mediated infiltration of different oxidation state metal cations selectively inserted into self-assembled block copolymer (BCP) nanopatterns formed from polystyrene-b-poly(4-vinylpyridine) BCP thin films. Work reveals that the stability of the as-obtained metal-pyridine complex is highly influenced by the coordination chemistry of the metal ion and the P4VP group and this impacts the formation of metal oxide patterns. Here, metal cations (Ag+, Ni2+, and In3+) were inserted into the patterns by a solution-mediated infiltration approach followed by an ultraviolet-ozone (UVO) treatment to remove the polymer and oxidize the metallic ions to their oxides. It was found that P4VP/Ag+ pattern was not intact after UVO treatment due to the weak interaction between the silver ions and the pyridine ring; however, Ni2+ and In3+ were able to reproduce the pattern of BCP. The reasons for the observed findings are due to the metal cation oxidation state and ionic sizes as confirmed by the Raman spectroscopy. Metal oxide formation was confirmed by the combination of both AFM and SEM results. XPS analyses confirmed the complete elimination of the BCP template and the presence of the metal oxides. These results provide new insights on metal cation selective infiltration and the formation of metal oxide patterns in polymer templates.