The self-assembly process of alkanethiols of various chain lengths [CH3(CH2)(n-1)SH : n = 10, 15, and 18] on a Au(111) surface in very dilute (< 1 mu M) heptane solutions was monitored in situ by scanning tunneling microscopy in real time. At the initial stage, adsorbed molecules did not arrange in an ordered structure and vacancy islands of the gold surface were created. Gold terraces were then covered with stripe and mesh (p x root 3) structures. An island growth of a densely packed structure [(root 3 x root 3)R30 degrees] was observed after the p x root 3 structures covered the surface.