Abstract—The influence of silicon surface modification via Si-C18H37 devices on n-type silicon is studied by forming MIS (metal-insulator-silicon) diodes via a mercury-probe. Both the influence of the monolayer molecule (1-octadecene/1-octadecyne) and substrate orientation (<100>/<111>) are investigated. Via multiple J-V and C-V measurements relevant parameters are derived to obtain information on both reproducibility and monolayer and silicon-monolayer interface properties. It was found that 1-alkynes, which are able to make 2 Si-C bonds, have superior insulating properties as compared to 1-alkenes, which are able to make only a single Si-C bond. There was no noticeable influence of substrate orientation, which indicated the broad usability of such monolayers. The ease of fabrication together with the outstanding electrical properties show the potential of these monolayers in creating hybrid molecularsilicon devices.