Electrical Defect Visualization in Insulating Langmuir-Blodgett Films
Résumé
Direct observation of conducting defects in Langmuir-Blodgett (LB) films by scanning electron microscopy (SEM) is unsuccessful because of defect size (around 50 nm according to literature). In the present paper, a decoration method is described which consists of a local electrochemical deposition of copper on the defects. This technique allows successful, non-destructive SEM observation of the conducting defects. An experimental technique using backscattered electron imaging and X-ray microanalysis is presented for the elimination of substrate artefacts. Typical micrographs are shown. Comparative studies have been worked out on LB films of various molecules: ω-tricosenoic acid, behenic acid, stearic acid, tetracyanoquinodimethane derivatives, amphiphilic pyridino porphyrazine. Results have been obtained on the density and spatial distribution of the defects showing that, among the tested molecules, ω-tricosenoic acid is the best candidate for insulating purposes. Information is also reported concerning the shape of the defects, and the influence of parameters such as transfer speed and number of layers