Making Nanoflowerbeds: Reaction Pathways Involved in the Selective Chemical Bath Deposition of ZnS on Functionalized Alkanethiolate Self-Assembled Monolayers

Abstract

We have investigated the chemical bath deposition (CBD) of ZnS on functionalized alkanethiolate self-assembled monolayers (SAMs) using time-of-flight secondary ion mass spectrometry and scanning electron microscopy. The reaction mechanism involves both cluster-by-cluster and ion-by-ion growth. The dominant reaction pathway is dependent on both the SAM terminal group and the experimental conditions. On −COOH-terminated SAMs, two types of crystallites are observed: ∼500 nm nanoflowers formed by ion-by-ion growth, and larger ∼2 μm crystallites formed by cluster-by-cluster deposition. The nanoflowers nucleate at Zn²⁺- carboxylate surface complexes. On −OH- and −CH₃-terminated SAMs, only the larger crystallites are formed. These do not adhere strongly to the SAM surface and can be easily removed. Finally, we demonstrate that under appropriate experimental conditions ZnS selectively deposits on the −COOH-terminated SAM regions of −COOH/−CH₃-patterned SAM surfaces, forming nanoscale “flowerbeds”.