Journal of Physical Chemistry B, Vol.109, No.44, 21006-21014, 2005
Evolution of the interface and metal film morphology in the vapor deposition of Ti on hexadecanethiolate hydrocarbon monolayers on Au
The combination of in situ X-ray photoelectron spectroscopy, infrared reflection spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry are used to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a CH3(CH2)(15)S/ Aul I I I I self-assembled monolayer (SAM) at ambient temperature. The results show that for a deposition rate of similar to 0.15 Ti atom center dot nm(-2)center dot s(-1) a highly nonuniform Ti overlayer is produced via a process in which a large fraction of impinging Ti atoms do not stick to the bare SAM surface. The adsorbed atoms form isolated Ti clusters and react with CH3 groups to form carbide products at the cluster-SAM interfaces. Further growth of Ti clusters appears to be concentrated at these scattered reaction centers. The SAM molecules in the local vicinity are subsequently degraded to inorganic products, progressing deeper into the monolayer as the deposition proceeds to give an inorganic/organic nanocomposite. A continuous overlayer does not form until metal coverage approaches similar to 50 Ti atoms per SAM molecule. These data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic, suffering from both a highly nonuniform contact area and the presence of extensive inorganic products such as nonstoichiometric carbides and hydrides.