Layer by Layer Adsorption

The layer-by layer (LbL) adsorption, introduced by G. Decher, is a versatile and inexpensive technique that can be used as a means for fabrication of nanostructured films. The consecutive deposition of layers of two polyelectrolytes, enable the stepwise increase of polyelectrolyte thickness and assemblies with fine control of spatial architecture. To form an LbL film, a substrate is first exposed to a charged polyelectrolyte solution to form the first layer. The treatment of surface with a solution of an oppositely charged polyelectrolyte solution leads to formation of a second layer. The process can then be repeated for film buildup.

Imaging ellipsometry was used for the following measurements:

• Thickness of the different steps and of anchoring layers
• (High sensitivity and accuracy because of four zone nulling and averaging of different regions of interest)
• Time dependency of the adsorption

Thickness maps with high lateral resolution

The consecutive deposition of layers of two polyelectrolytes, polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) onto a tantalum pentoxide substrate was measured by time-resolved ellipsometry in an internal reflection ellipsometry setup. Stepwise increase of polyelectrolyte thickness was shown by time-resolved measurement of the ellipsometric angles, delta and psi. The coated substrate was finally characterized in the dry state.

• The influence of a first (anchoring) layer and film treatment on the structure and properties of polyelectrolyte multilayer (PEM) films obtained from polyallylamine hydrochloride (PAH) and polysodium 4-styrenesulfonate (PSS) was studied by Kolasinska et al (2007). Branched polyethyleneimine (PEI) was used as an anchoring layer. The film thickness was measured by ellipsometry. Complementary X-ray reflectometry and AFM experiments were performed to study the change in the interfacial roughness.

References

Kolasińska M., Krastev R., Warszyński P. (2007) Characteristics of polyelectrolyte multilayers: Effect of PEI anchoring layerand posttreatment after deposition. Journal of Colloid and Interface Science 305, 46-56

Guldi et al (2004) report the fabrication of high quality, robust and photoactive ITO electrodes—in the form of well-defined two- and three-dimensional films. They follow the Langmuir–Schäfer (LS) and the layer-by-layer (LBL) methods. In the LS approach C60-NiP multilayers were transferred from the air–water interface, while the LBL approach utilizes electrostatic and van der Waals interactions for the step-by-step deposition of individual C60-NiP molecules out of solution.

References

Guldi D.M., Zilbermann I., Anderson G.A., Kordatos K., Prato M., Tafuro R., Valli L. (2004) Langmuir-Blodgett and layer-by-layer films of photoactive fullerene- porphyrin dys. Journal of Materials Chemistry 14, 303-309