Time evolution of the cluster formation rate, J_N (cm⁻³ s⁻¹), for different temperatures and sticking probabilities. Left column: for clusters larger than N = 2, 5, 20 from polymer–monomer cluster growth. Right column: for clusters larger than N = 2, 5, 20 from polymer–polymer cluster growth. Top: early time evolution until t = 10⁷ s for T = 500 K, 1000 K; only J_>2 and J_>5 appear. Middle: intermediate time evolution until t = 10⁹ s for T = 500 K, 1000 K, for J_>2 and J_>5. Bottom: long-term evolution until t = 2 × 10⁹ s for J_>2, J_>5, and also J_>20 for T = 1000 K only. No clusters >20 have yet formed for T = 500 K.