Deposition (LB)

(find LB deposition devices here)

Definition:

Deposition is the controlled transfer process of an insoluble spread monolayer of atoms or molecules floating at the gas/liquid interface onto a solid substrate.

Summary/Description:

The deposition of an insoluble spread monolayer of atoms or molecules floating at the gas/liquid interface onto a solid substrate is accomplished by successively dipping a solid substrate up and down through the monolayer, while simultaneously keeping the molecular density or surface pressure constant by a computer controlled feedback system between the electrobalance measuring the surface pressure and a barrier moving mechanism controlling the available area for the monolayer molecules. Consequently the floating monolayer with precisely controlled properties is adsorbed to the solid substrate. In this way multilayer structures of hundreds of layers can be produced. These multilayer structures are commonly called Langmuir-Blodgett or simply LB films.

The quantity and the quality of the deposited monolayer on a solid support is measured by a so called transfer ratio, t.r. This is defined as the ration between the decrease in monolayer area during a deposition stroke, A_l, and the area of the substrate, A_s. For ideal transfer the t.r. is equal to 1. Depending on the behaviour of the molecule the solid substrate can be dipped through the film until the desired thickness of the film is achieved.

The production of so called alternating layers which consist of two different kind of molecules is also possible by using highly sophisticated instruments. In such an instrument there is a trough with two separate compartments both possessing a floating monolayer of a different molecule. These monolayers can then be alternatingly deposited on one solid substrate.

An alternative way to deposit the monolayer is the Langmuir-Schaeffer (LS) technique. This technique differs from the vertical technique described above only in the sense that the solid substrate is horizontally lowered in contact with the monolayer.