Nanomechanics of Langmuir-Blodgett films

Abstract

The topographical and nanomechanical characterization of molecular films is an important issue due to the increasing interest in this kind of 2-dimensional structure, both from a scientific and technological point of view. In particular, Langmuir and Langmuir-Blodgett (LB) films have been widely studied as it is possible to control the area per molecule in the layer, with the consequent control over the sample nanostructure. Langmuir films can be characterized at the air-water interphase by using surface pressure-area isotherms and Brewster Angle Microscopy (BAM). Surface pressure measurements provide information on the films as a whole and BAM provides optical images of areas in the millimetric range with lateral resolution on the micrometric scale. Langmuir films can be transferred onto an atomically flat substrate and the transferred films (LB films) can be studied in the nanometric range using Scanning Probe Microscopies (SPMs). Of these, Atomic Force Microscopy provides topographical information, while Lateral Force Microscopy and Force Spectroscopy provide information about the nanotribological and nanomechanical properties of the films. These techniques, when applied to the study of mixed films, provide information about miscibility, phase separation, domain structure and mechanical properties. In this respect, SPMs can provide information at a nanometric level that it is not available using BAM. Thanks to the possibility of controlling the film surface pressure, correlation between sample nanostructure and nanomechanics can be established.