Structure and properties of Langmuir–Blodgett films containing cluster molecules

An approach based on the use of mixed Langmuir–Blodgett (LB) films containing various chemically synthesized nanocluster molecules has been proposed in order to create single-electron transfer model systems functioning at room temperatures. The nanoclusters are shown to form ordered structures (quasilinear chains, two-dimensional arrays, etc.) in such monolayers deposited onto the solid substrates. The tunnel current–bias voltage (I–V) characteristics of isolated cluster molecules Pt5(CO)6(PPh3)4 taken at 300 K exhibit rich structures resulting from the interplay between Coulomb charging effects and discreteness of an electronic spectrum of the cluster. The platinum Pt5(CO)6(PPh3)4 clusters appear to posses surface-active properties and can form stable homogeneous Langmuir monolayers on the water surface. Such monolayers can be effectively transferred onto the solid substrates so that corresponding multilayer LB films are obtained. X-ray difractograms recorded for those films show a number of Bragg peaks caused by the ordered layered structure of the films. Close values of intensity of the second harmonic generation measured for the mono- and 11-layer LB films of the platinum clusters give evidence of the centrosymmetrical Y-type packing of the cluster molecules in multilayer LB films. The pertinent theoretical model of cluster molecule packing in such films has been proposed.