Crystallization through vapor deposition is ubiquitous and is inevitably influenced by impurities that often impact the local structure. Interestingly, the effect of immobilizing some of the depositing particles themselves, which would preserve local structural symmetry, remains largely unexplored. Herein, we perform colloidal vapor deposition on a substrate with a few pinned adcolloids, termed “mobility impurities.” Through thermodynamic and kinematic measurements, we demonstrate that these pinned adcolloids, even though they share identical geometry and interaction with depositing particles, are disfavored as nucleation centers. Our experimental findings, supported by molecular dynamics simulations and a simple theoretical model, reveal that entropic contributions, rather than energetic ones, govern nucleation physics in the presence of mobility impurities. Moreover, tuning the mobility of colloids on the substrate adjusts the nucleation likelihood at pinned sites. In later stages of growth, pinning induces mode localization and alters the thin film's vibrational spectrum. Our work thus underscores the potential of strategically incorporating mobility impurities to engineer material properties.

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• Crystal growth
• Nucleation on surfaces
• Colloidal crystal
• Crystal phenomena