You should check methods related to NSL (Nanosphere Litography). I advice You to check papers published by Prof. Michael Giersig. He put much impressive contribution in the field You are interested!
Hi Wojciech. check this http://pubs.rsc.org/en/content/articlelanding/2014/nr/c4nr00254g#!divAbstract
Any way I found that adding chloride ions to silver precursor solution (to make bigger nanoparticles) when preparing nanoparticles according to the method proposed by Metraux the tips tends to be sharper