In this approach, a new chemical species is introduced to enhance selectivity: the inhibitor (Fig. .b,c). The core idea of an inhibitor-based approach is to block the NGS, while the GS is not blocked. While approaches using polymer films exist, most current approaches use molecular inhibitors comprised of a surface-anchoring head group and a deposition-blocking tail group (Fig. ). If a long chain is used as tail group, the resulting structures are called self-assembled monolayers (SAMs, often the term is also used for the monomers). If a short chain is used, the term small-molecule inhibitor (SMI) is established in the literature. As is obvious from Fig. ., the two inhibitor classes have strong similarities in their approach to block the surface. Indeed, both classes were proposed in the same seminal work by Chen, Kim, McIntyre and Bent in 2004. Prior to this work, SAMs were only used in microcontact printing for patterned deposition of ZnO and TiO2. Although the term SMI does not yet appear, the concept of varying the chain length to change the blocking property has already been established in this key paper and the methoxy-substituted "short chain SAM" Si(CH3)(OMe)3 proposed was used for successful AS-ALD much later. Also, the major blocking mechanisms (Fig. .) had already been outlined in this study: reactive surface site deactivation (Fig. .b) (here: bonding to HO-Si and Si-O-Si groups) as well as steric blocking (Fig. .c,d). The targeted usage of small molecules (in contrast to SAMs) for the blocking of NGS has been put forward by Mameli et al. inspired by work from Yanguas-Gil, Libera and Elam. The main challenges for computational approaches here are: