Humidity Dependence in Silane Monolayer Patterning via Atomic Force Microscopy

The ability to consistently create nanometer-sized patterns is essential for the advancement of biosensing and the development of molecular electronics. Due to their robust nature, silane monolayers are widely used to create uniform surfaces. In order to effectively pattern these surfaces, all the parameters that impact the process must be optimized. Herein, two self-assembled monolayers (SAMs) were formed on a SiO₂/Silicon(100) substrate, octadecyltrichlorosilane (OTS) and octadecyldimethylchlorosilane (ODMS). These SAMS were characterized using goniometry, ellipsometry, and atomic force microscopy (AFM). Due to different binding structures ODMS monolayers are drastically thinner and more disordered than OTS monolayers. This structural difference in the SAMs leads to drastically different results when patterning with an AFM cantilever. In addition to clear dependencies on tip speed, tip sharpness, and applied force, patterns created in both monolayers demonstrate a dependence on the ambient humidity during the patterning process. Both monolayers display and increased ease of removal under higher humidity, indicating that the dependence could stem from a reversal of the dehydration reaction with which the molecules bind to the surface. In addition, humidity extremes, 0% and >90%, can lead to significantly different resulting patterns. These patterns and the precise role of ambient humidity are being investigated.