Layer by layer
Layer-by-Layer (LbL) deposition is a thin film fabrication technique. The films are formed by depositing alternating layers of oppositely charged materials with wash steps in between. A simple representation can be made by defining two oppositely charged polyions as + and -, and defining the wash step as W. To make an LbL film with 5 bilayers one would deposit W+W-W+W-W+W-W+W-W+W-W, which would lead to a film with 5 bilayers, specifically +-+-+-+-+-. The bilayers and wash steps can be performed in many different ways including dip coating, spin-coating, spray-coating and flow based techniques. Characterisation of LbL film deposition is typically done by optical techniques such as dual polarisation interferometry or ellipsometry or mechanical techniques such as QCM or QCMD.
LbL offers several advantages over other thin film deposition methods. LbL is extremely simple and cheap. There are a wide variety of materials that can be deposited by LbL including polyions, metals, ceramics, nanoparticles, and biological molecules. Another important quality of LbL is the high degree of control over thickness, which arises due to the linear growth of the films with the number of bilayers. By the fact that each bilayer can be as thin as 1 nm, this method offers easy control over the thickness with 1 nm resolution.
LbL has found applications in corrosion control, biomedical applications, and many more.
- Decher, Gero (2012). Multilayer thin films - sequential assembly of nanocomposite materials, vol 2. Weinheim, Germany: Wiley-VCH.