  Noncontact Atomic Force Microscopy and synchrotron x-ray scattering
measurements on dotriacontane (n-C32H66 or C32) films adsorbed on SiO2-coated
Si(100) wafers reveal a narrow temperature range near the bulk C32 melting
point Tb in which a monolayer phase of C32 molecules oriented perpendicular to
surface is stable. This monolayer phase undergoes a delayering transition to a
three-dimensional (3D) fluid phase on heating to just above Tb and to a solid
3D phase on cooling below Tb. An equilibrium phase diagram provides a useful
framework for interpreting the unusual spreading and receding of the monolayer
observed in transitions to and from the respective 3D phases.
