The elaboration and characterization of platinum nanoparticles functionalized with 4-mercaptoaniline is reported. An important point of the synthesis scheme is the use of hexylamine as intermediate labile capping agent. The size and structure of the platinum inner core have been analyzed by X-ray diffraction and TEM microscopy. It is found to be crystalline with a fcc structure and a cell parameter of 0.392 nm very close to the bulk value. The size dispersity is low with an average diameter of ca. 1.5 nm. A well-defined interparticle distance of ca. 3.2 nm is found, corresponding to an organic overlayer thickness of 0.9 nm in good agreement with the estimated molecule length. A rough estimation of the surface per absorbed molecule yields a value of ca. 0.14 nm 2 , pointing to a dense molecular packing. However, IR spectroscopy reveals a very slow degradation process of the organic overlayer, eventually resulting in the formation of sulfate ions onto the platinum surface. A promising perspective is the use of the amine end groups for subsequent overgrafting of the nanoparticles.
The elaboration of Langmuir−Blodgett (LB) films of platinum nanoparticles is described.
In contrast to most of the previously reported studies that concern metallic particles capped
with long alkyl chains, the aggregates involved in this work bear external polar amine
functions. The area per particle is consistent with the formation of essentially monoparticle
thick Langmuir films at low surface pressures. Pure films of these particles are efficiently
transferred horizontally whereas conventional vertical deposition can be used with mixed
films containing added fatty acid. The LB films were characterized by IR spectroscopy, AFM,
STEM, and X-ray diffraction. The electrical properties of the ultrathin materials based on
pure films and mixed films were investigated. The nonmetallic conductivity is characterized
by an activation energy of ≈80 meV and lies in the range 10-2 to 10-3 S·cm-1. The material
exhibits good long-term electrical stability. Finally, it is shown that the fatty acid can be
washed out from mixed films without dramatic effects on the conductivity of the material.
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