Differential friction force spectroscopy of micropatterned organosilane self-assembled monolayers

Abstract.

Frictional properties of organosilane self-assembled monolayers (SAMs) and hydrated silicon oxide (SiOH) surfaces on a single sample substrate were studied; the frictional force difference between the surfaces was measured by employing one as a standard. Using a lateral force microscope (LFM), differential frictional force microscopic data were obtained by measuring the difference in the friction forces of the two surfaces with respect to the vertical load force applied to the LFM probe. The SAMs were prepared from n-octadecyltrimethoxysilane [ODS, H₃C(CH₂)₁₇Si(OCH₃)₃], n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS, H₂N(CH₂)₆NH(CH₂)₃Si(OCH₃)₃], 3,3,3-trifluoropropyltrimethoxysilane [FAS3, F₃C(CH₂)₂Si(OCH₃)₃] and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS17, F₃C(CF₂)₇(CH₂)₂Si(OCH₃)₃] by chemical vapor deposition. In the vertical force range of 0 to 600 nN, the SAMs showed no damage at all, and frictional force on the SAM surfaces increased linearly with the vertical force. The order of the frictional force magnitudes determined with the SiOH-terminated probe was SiOH > AHAPS > FAS3 > FAS17 > ODS. In addition, the frictional force difference did not become zero even at a vertical force of 0 nN, that is, the frictional differences could even be imaged by LFM through probe–sample adhesion.