THERMAL-STABILITY OF SELF-ASSEMBLED MONOLAYERS

Structural changes as function of annealing time and temperature in monolayers of dodecanethiol self-assembled on Au(111) were studied by X-ray photoelectron spectroscopy, contact angle microscopy and high gap impedance scanning tunneling microscopy. Annealing in an oven caused the fusion of small domains into larger ones and the disappearance of gold defects. Small deficiencies (lack of molecules) due to evaporation caused the omission of lines. A slightly lower packing density of the organic chains perpendicular to the missing lines accommodated the mismatch and generated an almost defect-free surface. The shape of sections perpendicular to the missing lines allowed the direction of tilt angles in the domains to be deduced. Higher annealing temperatures eventually led to the oxidation of thiols and to partial desorption of the organic phase. On the way to full desorption and reduced lateral pressure, several metastable crystalline structures of film packing and, in later stages, of amorphous or liquid-like phases could be found.