Grafting of ‘push-pull’ systems on germanium: towards the electric passivation Greffage de molécules 'push-pull' sur germanium: vers la passivation diélectrique

Germanium is well-known for its good electronic properties, but also for the poor passivationquality of its natural or thermally-grown oxide layer. The robust passivation of Ge surfaces isthus a crucial step on the way to its integration in electronics at nanoscale. Before passivation,the natural oxide layer must be removed from the surface. Different methods wereinvestigated and compared. The surfaces were analysed by X-ray photoelectron spectroscopyand by atomic force microscopy to determine the impact of the etching on the roughness.Oxide-free Cl-terminated surfaces were chosen and functionalized with variousarenediazonium salts. The grafting is a fast reaction (less than 30 minutes) and proceeds insoft conditions (room temperature in acetonitrile solutions). The functionalization was foundto proceed even at low temperature (-18°C). The modified surfaces were mainly studied byXPS and AFM. The morphology of the organic layer was influenced by the temperature andduration of the grafting as well as by the presence of substituents on the aromatic ring. Wedemonstrated that smooth oxide-free Ge surfaces could be prepared by a cyclic oxidation-rinsingetching procedure and could be functionalized with various arenediazonium salts.The stability of the organic layer was compared to the stability of a self-assembled monolayerof alkanethiolates. The absolute coverage was also determined. This constitutes a first steptowards Ge crystal passivation by organic thin films.