Characterization of self-assembled bilayers: Silver-alkanethiolates

Layered materials composed of silver-alkanethiolate units are characterized and compared to self-assembled alkanethiolate monolayers and thiolate-capped nanoparticles. A comprehensive infrared spectroscopy study is presented for silver-alkanethiolate materials having chain lengths varying from 7 to 18 carbon atoms (AgSC7 to AgSC18). The high level of definition in these spectra will make this a benchmark system for comparisons to other metal thiolate systems. An X-ray diffraction study of these same materials is used to determine the tilt angle of the chains (12 +/- 3 degrees), which is very close to that reported for thiolate monolayers on Ag(111). These results are combined with a thorough characterization of the AgSC12 material using X-ray photoelectron spectroscopy, electronic spectroscopy, differential scanning calorimetry, and solid-state NMR. Overall, this provides a detailed description of the structure, the thermal stability, and the high degree of conformational order in these materials, which have not previously been extensively characterized at these chain lengths.