Layer by layer

This article is about the thin film fabrication technique. For the Rubik's Cube method, see 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. This can be accomplished by using various techniques such as immersion, spin, spray, electromagnetism, or fluidics.[1]

Development

The first implementation of this technique is attributed to J. J. Kirkland and R. K. Iler of DuPont, who carried it out using microparticles in 1966.[2] The method was later revitalized by the discovery of its applicability to a wide range of polyelectrolytes by Prof. Gero Decher at Johannes Gutenberg-Universität Mainz.[3]

Implementation

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 + - + - + - + - + - .

It is important to note that the representation of the LbL technique as a multilayer build-up based solely on electrostatic attraction is a simplification. Other interactions are involved in this process, including hydrophobic attraction.[4] Multilayer build-up is enabled by multiple attractive forces acting cooperatively, typical for high-molecular weight building blocks, while electrostatic repulsion provides self-limitation of the absorption of individual layers. This range of interactions makes it possible to extend the LbL technique to hydrogen-bonded films,[5] nanoparticles,[6] similarly charged polymers, hydrophobic solvents,[7] and other unusual systems.[8]

The bilayers and wash steps can be performed in many different ways including dip coating, spin-coating, spray-coating, flow based techniques and electro-magnetic techniques.[1] The preparation method distinctly impacts the properties of the resultant films, allowing various applications to be realized.[1] For example, a whole car has been coated with spray assembly, optically transparent films have been prepared with spin assembly, etc.[1] Characterization of LbL film deposition is typically done by optical techniques such as dual polarisation interferometry or ellipsometry or mechanical techniques such as quartz crystal microbalance.

LbL offers several advantages over other thin film deposition methods. LbL is simple and can be inexpensive. 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 variable growth profile of the films, which directly correlates to the materials used, the number of bilayers, and the assembly technique.[1] 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.

Applications

LbL has found applications[1] in corrosion control, biomedical applications,[9] ultrastrong materials,[10] and many more.[11]

See also

References

  1. 1 2 3 4 5 6 J. J. Richardson; et al. (2015). "Technology-driven layer-by-layer assembly of nanofilms". Science. 348: 6233. doi:10.1126/science.aaa2491.
  2. ↑ J. J. Kirkland (1965). "Porous Thin-Layer Modified Glass Bead Supports for Gas Liquid Chromatography". Analytical Chemistry. 37: 1458. doi:10.1021/ac60231a004.R. K. Iler (1966). "Multilayers of colloidal particles". Journal of Colloid and Interface Science. 21: 569. doi:10.1016/0095-8522(66)90018-3.
  3. ↑ Gero Decher; Jong-Dal Hong (1991). "Buildup of ultrathin multilayer films by a self-assembly process, consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces". Macromolecular Symposia. 46: 321. doi:10.1002/masy.19910460145.
  4. ↑ Nicholas A. Kotov (1999). "Layer-by-layer self-assembly: The contribution of hydrophobic interactions". Nanostructured Materials. 12: 789. doi:10.1016/S0965-9773(99)00237-8.
  5. ↑ André Laschewsky; Erik Wischerhoff; Steffen Denzinger; Helmut Ringsdorf; Arnaud Delcorte; Patrick Bertrand (1997). "Molecular Recognition by Hydrogen Bonding in Polyelectrolyte Multilayers". Chemistry: A European Journal. 3: 34. doi:10.1002/chem.19970030107.
  6. ↑ Nicholas A. Kotov; Imre Dekany; Janos H. Fendler (1995). "Layer-by-Layer Self-Assembly of Polyelectrolyte-Semiconductor Nanoparticle Composite Films". Journal of Physical Chemistry. 99: 13065. doi:10.1021/j100035a005.
  7. ↑ Yuzuru Shimazaki; Masaya Mitsuishi; Shinzaburo Ito; Masahide Yamamoto (1997). "Preparation of the Layer-by-Layer Deposited Ultrathin Film Based on the Charge-Transfer Interaction". Langmuir. 13: 1385. doi:10.1021/la9609579.
  8. ↑ Nejla Cini; Tülay Tulun; Gero Decher; Vincent Ball (2010). "Step-by-step assembly of self-patterning polyelectrolyte films violating (almost) all rules of layer-by-layer deposition". Journal of the American Chemical Society. 132: 8264. doi:10.1021/ja102611q.
  9. ↑ Hua Ai; Steven A. Jones; Yuri M. Lvov (2003). "Biomedical applications of electrostatic layer-by-layer nano-assembly of polymers, enzymes, and nanoparticles". Cell Biochemistry and Biophysics. 39: 23. doi:10.1385/CBB:39:1:23.
  10. ↑ Zhiyong Tang; Nicholas A. Kotov; Sergei Magonov; Birol Ozturk (2003). "Nanostructured artificial nacre". Nature Materials. 2: 413. doi:10.1038/nmat906.
  11. ↑ Decher, Gero (2012). Multilayer thin films - sequential assembly of nanocomposite materials, vol 2. Weinheim, Germany: Wiley-VCH.
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