The impact of solution agglomeration on the deposition of self-assembled monolayers

Self-assembled monolayers (SAMs) are commonly produced by immersing substra tes in organic solutions containing trichlorosilane coupling agents. Unfort unately, such deposition solutions can also form alternate structures, incl uding inverse micelles and lamellar phases. The formation of alternate phas es is one reason for the sensitivity of SAM depositions to factors such as the water content of the deposition solvent. if such phases are present, th e performance of thin films used for applications such as the minimization of friction and stiction in micromachines can be seriously compromised. Inv erse micelle formation has been studied in detail for depositions involving 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) in isooctane, Nuclear mag netic resonance experiments have been used to monitor the kinetics of hydro lysis and condensation reactions between water and FDTS. Light-scattering e xperiments show that there is a burst of nucleation at a critical concentra tion of hydrolyzed FDTS to form high concentrations of spherical agglomerat es. Atomic force microscopy results show that the agglomerates then deposit on substrate surfaces. Deposition conditions leading to monolayer formatio n involve using deposition times that are short relative to the induction t ime for agglomeration. After deposition, inverse micelles can be converted into lamellar or monolayer structures with appropriate heat treatments if s urface concentrations are relatively low.