Atomic force microscopy of thin organic films on silicon in ultrahigh vacuum and under ambient conditions

In this paper we investigate thin organic films on silicon oxide by different atomic force microscopy (AFM) techniques. For the preparation of the organic films we chose octadecyltrichlorosilane (OTS), which shows a strong tendency for self-assembly. As substrates we use silicon covered with a native silicon oxide. The self-assembled monolayers are deposited in solution to give octadecylsiloxane (ODS) islands. Island density and size vary, among other things, with the solution age, its concentration and the deposition time. Growth and structure are investigated in air as well as in ultrahigh vacuum (UHV) with AFM. The measurements are performed in contact, non-contact or tapping mode. We found that the ODS islands are 1.6 nm in height in UHV as well as under ambient conditions. From the length of the OTS molecules a height of 2.6 nm should be expected. We attribute the reduced height to a tilt of the alkyl chains. Damping maps show that the energy dissipation on the ODS islands is less than on the silicon oxide substrate. Copyright © 2002 John Wiley & Sons, Ltd.