Infrared spectroscopic characterization of [2]rotaxane molecular switch tunnel junction devices.

Langmuir-Blodgett monolayers of a bistable [2]rotaxane were prepared at packing densities of 118, 73, and 54 A(2)/molecule. The monolayers were both characterized via infrared spectroscopy before and after evaporation of a 2 nm film of titanium and incorporated into molecular switch tunnel junction devices. The study suggests that the evaporation process primarily affects portions of the molecule exposed to the metal atom source. Thus, in tightly packed monolayers (73 and 54 A(2)/molecule), only the portions of the [2]rotaxane that are present at the molecule/air interface are clearly affected, leaving key functionality necessary for switching intact. Monolayers transferred at a lower pressure (118 A(2)/molecule) exhibit nonspecific damage and poor switching behavior following Ti deposition. These results indicate that tightly packed monolayers and sacrificial functionality displayed at the molecule/air interface are important design principles for molecular electronic devices.