Characterization of self-assembled monolayers of alkanethiol on GaAs surface by contact angle and angle-resolved XPS measurements

Self-assembled monolayers (SAMs) of alkanethiol molecules (CnH2n + 1SH, n=4, 8, 12, 18) have been constructed on a GaAs(1 0 0) surface in 5 mM alkanethiol/ethanol solutions with addition of ammonia (NH4OH). The contact angles of the GaAs surface modified by alkanethiol with longer chain (n⩾12) were higher than 100° when the concentration of NH4OH in the modification solution was higher than 5%, showing a hydrophobic GaAs surface, which was covered by a well-ordered organic monolayer, was formed. Furthermore, the angle-resolved X-ray photoelectron spectroscopy measurements were carried out to determine chemical bonding, thickness and the tilt angle of the SAMs on the GaAs surface.