Desorption of neutral molecules from self-assembled monolayers subjected to keV ion bombardment

Laser postionization in combination with mass spectrometry was used to detect neutral molecules desorbed from self-assembled monolayers of phenethyl mercaptan and benzyl mercaptan on gold upon 8 keV Ar ⁺ bombardment. From experimentally obtained time distributions, it was determined that the majority of the desorbed neutral molecules leave the surface with low translational energies of about 0.03 eV. As the substrate temperature is reduced, the distributions become broader and shift to longer flight times. In combination with mass distributions, these results indicate that the thermal desorption process is initiated by chemical reactions in the organic layer, creating fragments of the original molecule weakly bound to the surface, prior to release.