Nanoscale Observation of Alkane Delayering

TL;DR

This study uses advanced microscopy and x-ray techniques to observe nanoscale phase transitions of alkane films on silicon, revealing a narrow temperature window where monolayer and 3D phases coexist and transition.

Contribution

It provides the first nanoscale observation of alkane delayering and phase behavior near the melting point using combined microscopy and scattering methods.

Findings

Identification of a stable monolayer phase near the melting point.

Observation of a delayering transition to a 3D fluid phase.

Development of an equilibrium phase diagram for the system.

Abstract

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.