An automatic trough to make alternate layers

Abstract

The Langmuir trough described is specially designed to fabricate alternate multilayers automatically by the Langmuir-Blodgett (LB) technique. Its working principle consists of: (i) making two different films at the surface of a double Langmuir trough; (ii) programming the path of the substrate so that it passes in turn through each film. The apparatus consists principally of a two-compartment Langmuir trough and a system to transfer the substrate from one compartment to the other underneath water. The Langmuir trough contains a single subphase. Its surface is divided into two compartments by a fixed surface barrier located above the central well. Each compartment is equipped with a mobile barrier, so that it can be operated independently for film fabrication and compression. Each compartment is also equipped with an independently programmable dipping arm. Substrate transfer is carried out in the following way: while the two dipping arms are at rest, an auxiliary rotating arm picks up the substrate from one of the arms, transfers it to the other compartment underneath the central barrier and hangs it on the other dipping arm. This sample transferrer is described in detail, together with the way it operates. When the films in the compartments are made of different molecules, this trough builds up alternate LB layers. According to the programme imposed on the substrate transferrer, either centrosymmetric, or non-centrosymmetric, or paired alternate layers can be built. Examples of such alternate layers are given. Their actual structure is discussed: in some cases the films are found to reorganize on or after transfer.