A study of positive charge effect on AFM anodization lithography using metal phosphate monolayers

Monolayer films of metal phosphate were prepared by sequential adsorption of phosphoric acid (PA) and metal ions (Zr4+ or Ca2+). The monolayer formation was confirmed and characterized by ellipsometry and atomic force microscopy (AFM). Nanometer-scale patterning on the self-assembled metal phosphate films has been achieved using AFM. The difference in AFM lithography on positively charged surfaces in the case of Zr4+ and Ca2+ ions was investigated and summarized. Since the presence of the positive charges allows electrons to move from a tip to a layer easily, the lithographic process initiates at a lower voltage in the layer of Zr2+ phosphate than in the layer of Ca phosphate or PA. Other lithographic results on metal phosphate layers were compared with those on a monolayer of PA.