Passivation layers to inhibit vapor deposition can be used on reactor surfaces to minimize deposits while depositing on a substrate housed therein, or on particular substrate surfaces, such as metallic surfaces on semiconductor substrates to facilitate selective deposition on adjacent dielectric surfaces. Passivation agents that are smaller than typical self-assembled monolayer precursors can have hydrophobic or non-reactive ends and facilitate more dense passivation layers more quickly than self-assembled monolayers, particularly over complex three-dimensional structures.