View source for Physics:Layer by layer

'''Layer-by-layer''' ('''LbL''') deposition is a [[Physics:Thin film|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.<ref name="RICH2015">{{cite journal | doi = 10.1126/science.aaa2491  | title = Technology-driven layer-by-layer assembly of nanofilms | year = 2015 | author = J. J. Richardson| journal = Science | volume = 348 | issue = 6233 | page = 6233|display-authors=0 | pmid=25908826| doi-access = free | hdl = 11343/90861 | hdl-access = free }}</ref>

==Development==
The first implementation of this technique is attributed to J. J. Kirkland and R. K. Iler of [[Company:DuPont|DuPont]], who carried it out using microparticles in 1966.<ref>{{cite journal | doi = 10.1021/ac60231a004 | title = Porous Thin-Layer Modified Glass Bead Supports for Gas Liquid Chromatography | year = 1965 | author = J. J. Kirkland | journal = Analytical Chemistry | volume = 37 | issue = 12 | page = 1458}}{{cite journal | doi = 10.1016/0095-8522(66)90018-3 | title = Multilayers of colloidal particles | year = 1966 | author = R. K. Iler | journal = Journal of Colloid and Interface Science | volume = 21 | issue = 6 | page = 569}}</ref> The method was later revitalized by the discovery of its applicability to a wide range of [[Chemistry:Polyelectrolyte|polyelectrolyte]]s by Gero Decher at [[Organization:University of Mainz|Johannes Gutenberg-Universität Mainz]].<ref>{{cite journal | doi = 10.1002/masy.19910460145 | title = Buildup of ultrathin multilayer films by a self-assembly process, consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces | year = 1991 |author1=Gero Decher |author2=Jong-Dal Hong | journal = Macromolecular Symposia | volume = 46 | page = 321}}</ref>

==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 + - + - + - + - + - .

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.<ref>{{cite journal | doi = 10.1016/S0965-9773(99)00237-8 | title = Layer-by-layer self-assembly: The contribution of hydrophobic interactions | year = 1999 | author = Nicholas A. Kotov | journal = Nanostructured Materials | volume = 12 | issue = 5–8 | page = 789}}</ref> 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,<ref>{{cite journal | doi = 10.1002/chem.19970030107 | title = Molecular Recognition by Hydrogen Bonding in Polyelectrolyte Multilayers | year = 1997 |author1=André Laschewsky |author2=Erik Wischerhoff |author3=Steffen Denzinger |author4=Helmut Ringsdorf |author5=Arnaud Delcorte |author6=Patrick Bertrand | journal = Chemistry: A European Journal | volume = 3 | page = 34}}</ref> nanoparticles,<ref>{{cite journal | doi = 10.1021/j100035a005 | title = Layer-by-Layer Self-Assembly of Polyelectrolyte-Semiconductor Nanoparticle Composite Films | year = 1995 |author1=Nicholas A. Kotov |author2=Imre Dekany |author3=Janos H. Fendler | journal = Journal of Physical Chemistry | volume = 99 | issue = 35 | page = 13065}}</ref> similarly charged polymers,  hydrophobic solvents,<ref>{{cite journal | doi = 10.1021/la9609579 | title = Preparation of the Layer-by-Layer Deposited Ultrathin Film Based on the Charge-Transfer Interaction | year = 1997 |author1=Yuzuru Shimazaki |author2=Masaya Mitsuishi |author3=Shinzaburo Ito |author4=Masahide Yamamoto | journal = Langmuir | volume = 13 | issue = 6 | page = 1385}}</ref> and other unusual systems.<ref>{{cite journal | doi = 10.1021/ja102611q | title = Step-by-step assembly of self-patterning polyelectrolyte films violating (almost) all rules of layer-by-layer deposition | year = 2010 |author1=Nejla Cini |author2=Tülay Tulun |author3=Gero Decher |author4=Vincent Ball | journal = Journal of the American Chemical Society | volume = 132 | issue = 24 | pages = 8264–5 | pmid=20518535}}</ref>

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.<ref name="RICH2015" /> The preparation method distinctly impacts the properties of the resultant films, allowing various applications to be realized.<ref name="RICH2015" /> For example, a whole car has been coated with spray assembly, optically transparent films have been prepared with spin assembly, etc.<ref name="RICH2015" /> Characterization of LbL film deposition is typically done by optical techniques such as dual polarisation interferometry or [[Physics:Ellipsometry|ellipsometry]] or mechanical techniques such as [[Engineering:Quartz crystal microbalance|quartz crystal microbalance]].{{citation needed|date=December 2015}}

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.<ref name="RICH2015" /> By the fact that each bilayer can be as thin as 1&nbsp;nm, this method offers easy control over the thickness with 1&nbsp;nm resolution.

==Applications==
LbL has found applications<ref name="RICH2015" /> in protein purification,<ref>{{cite journal|last1=Liu|first1=Weijing|title=Layer-by-Layer Deposition with Polymers Containing Nitrilotriacetate, A Convenient Route to Fabricate Metal- and Protein-Binding Films|journal=ACS Applied Materials & Interfaces|date=2016|volume=8|issue=16|pages=10164–73|doi=10.1021/acsami.6b00896|pmid=27042860}}</ref> corrosion control, (photo)electrocatalysis,<ref>{{cite journal |last1=Jeon |first1=Dasom |last2=Kim |first2=Hyunwoo |last3=Lee |first3=Cheolmin |last4=Han |first4=Yujin |last5=Gu |first5=Minsu |last6=Kim |first6=Byeong-Su |last7=Ryu |first7=Jungki |title=Layer-by-Layer Assembly of Polyoxometalates for Photoelectrochemical (PEC) Water Splitting: Toward Modular PEC Devices |journal=ACS Applied Materials & Interfaces |date=22 November 2017 |volume=9 |issue=46 |pages=40151–40161 |doi=10.1021/acsami.7b09416}}</ref> biomedical applications,<ref>{{cite journal | doi = 10.1385/CBB:39:1:23 | pmid = 12835527 | title = Biomedical applications of electrostatic layer-by-layer nano-assembly of polymers, enzymes, and nanoparticles | year = 2003 |author1=Hua Ai |author2=Steven A. Jones |author3=Yuri M. Lvov | journal = [[Biology:Cell Biochemistry and Biophysics|Cell Biochemistry and Biophysics]] | volume = 39 | issue = 1 | pages = 23–43 }}</ref> ultrastrong materials,<ref>{{cite journal | doi = 10.1038/nmat906 | title = Nanostructured artificial nacre | year = 2003 |author1=Zhiyong Tang |author2=Nicholas A. Kotov |author3=Sergei Magonov |author4=Birol Ozturk | journal = Nature Materials | volume = 2 | issue = 6 | pages = 413–8 | pmid=12764359}}</ref> and many more.<ref>{{cite book|last=Decher|first=Gero|title=Multilayer thin films -  sequential assembly of nanocomposite materials, vol 2.|year=2012|publisher=Wiley-VCH|location=Weinheim, Germany}}</ref>  LbL composites from graphene oxide harbingered the appearance of numerous graphene and graphene oxide composites later on.<ref>{{Cite journal|last=Kotov|first=Nicholas A.|last2=Dékány|first2=Imre|last3=Fendler|first3=Janos H.|date=1996-08-01|title=Ultrathin graphite oxide-polyelectrolyte composites prepared by self-assembly: Transition between conductive and non-conductive states|journal=Advanced Materials|language=en|volume=8|issue=8|pages=637–641|doi=10.1002/adma.19960080806|issn=1521-4095}}</ref>   The first use of reduced graphene oxide composites for lithium batteries was also demonstrated with LbL multilayers.<ref>{{Cite journal|last=Fendler|first=Janos H.|date=1999-01-01|title=Colloid Chemical Approach to the Construction of High Energy Density Rechargeable Lithium - Ion Batteries|journal=Journal of Dispersion Science and Technology|volume=20|issue=1–2|pages=13–25|doi=10.1080/01932699908943776|issn=0193-2691}}</ref>

== See also ==
* [[Physics:Atomic layer deposition|Atomic layer deposition]]

==References==
{{Reflist}}

[[Category:Thin films]]

{{Sourceattribution|Layer by layer}}