Identify a precursor that reacts with GS but does not decompose or penetrate the inhibitor layer (iii) Understand the factors governing stability of the inhibitor layer Chemically, this is the most complex approach but its tunability to various material combinations (including the possibility to block several NGSs with one inhibitor or the usage of precursors as inhibitors ) lead to strong research activity here. Given the major role of surface chemistry in determining selectivity in this approach, computational approaches are especially useful for these inhibitor-based approaches (section 3.4).