Another way the precursor can diminish selectivity is by reacting with the inhibitor layer. This can either lead directly to unwanted growth nucleation or create defects in the layer which can then be used by further precursor molecules to initiate growth. Very early on, the computational investigations on SAM inhibitor layers focused on the question of decomposition of the tail group by the precursor. Xu and Musgrave found the interaction with the functionalized tail groups to be quite strong but the barriers for decomposition of hydrogen-or methyl-terminated SAMs to be too high to be overcome at ALD conditions in addition to having no thermodynamic driving force. They also showed that the trend of reaction and activation energies for tail groups follows the Hammond postulate (section 1.4.2). The authors concluded from varying the chain length in their model systems, that the interaction is very local and a long tail-group can be modelled with a simple ethyl group. This knowledge has been used many years later in modelling TMA adsorption on an octadecylphosphonic acid (ODPA) SAM modelled by a propyl chain which led to similar findings. For SMI-based inhibitor layers, this research question has then been investigated for alkoxysilanes blocking SiO2 first using a molecular model system. Low barriers of ca. 30 kJ•mol -1 were found for the attachment of TMA and TEA to a hydrolyzed methoxy-group at the TMPS precursor while the direct reaction with the methoxy groups of the SMI showed very high barriers. Interaction with the co-reactant water had been investigated before showing that reaction with Al-CH3 terminated surfaces is possible while high barriers are found for Si-CH3 terminated surfaces. A comprehensive investigation of these decomposition reactions has been conducted later. The different decomposition reactions possible by interaction of the precursor and the co-reactant with the inhibitor layer are summarized in Fig. . Reprint with permission from reference .