Successive Ionic Layer Adsorption and Reaction (SILAR) and Layer-By-Layer (LBL)

Successive Ionic Layer Adsorption And Reaction (SILAR) and Layer-by-Layer (LbL) are thin film fabrication techniques and are increasingly associated with the utilization of silanes and silicones. The films are formed via the deposition of alternating layers of oppositely charged materials with wash steps in between. Silar typically employs solutions of monomeric ionic materials. Layer-by-layer techniques frequently employ polyions in which two oppositely charged polyions are alternately deposited after intermediate wash steps, W. To prepare SILAR or LbL films 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.

SILAR and LbL offer several advantages over other thin film deposition methods. LbL is extremely simple and inexpensive. Another important quality of Silar and LbL is the high degree of control over layer 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 facile control over the thickness with 1 nm resolution. Both LbL and Silar laboratory techniques increasingly use silanes.

Silanes perform important roles in both SILAR and LbL techniques by modifying the substrate in order to control deposition. For example mercaptopropyltrimethoxysilane (SIM6476.0) modified glass and silica substrates allow Silar deposition of CdS thin films with alternating cadmium acetate and sodium sulfide. In other instances cationic silanes such as N-trimethoxysilylpropyl-N,N,N-trimethylammononium chloride (SIT8415.0) and trimethoxysilylpropyl modified polyethyleneimine (SSP-060) or anionic silanes such as carboxyethylsilanetriol, sodium salt (SIC2263.0) and 3-trihydroxypropylmethylphosphonate, sodium salt (SIT8378.5) form a covalently bound ionic layers on a substrate.

Silicones and silsesquioxanes can also be used directly in SILAR and LbL techniques. Most commonly, aminofunctional siloxanes such as AMS-162 or aminofunctional silsesquioxanes such as WSA-70112 are utilized directly in the modification of metal substrates or converted to their cationic form by dispersion or dilution in water followed by the a stoichiometric addition of hydrochloric acid.

Silanes Utilized in Silar Techniques

SIA0608.0

3-AMINOPROPYLSILANETRIOL, 22-25% in water

SIB1500.0

BIS(METHOXYETHYL)-3-TRIMETHOXYSILYLPROPYLAMMONIUM CHLORIDE, 60% in methanol

SIC2263.0

CARBOXYETHYLSILANETRIOL, DISODIUM SALT, 25% in water

SID3392.0

N,N-DIDECYL-N-METHYL-N-(3-TRIMETHOXYSILYLPROPYL)AMMONIUM CHLORIDE, 40-42% in methanol

SIM6476.0

3-MERCAPTOPROPYLTRIMETHOXYSILANE

SIT8378.5

3-(TRIHYDROXYSILYL)PROPYL METHYLPHOSPHONATE, MONOSODIUM SALT, 42% in water

SIT8415.0

N-TRIMETHOXYSILYLPROPYL-N,N,N-TRIMETHYLAMMONIUM CHLORIDE, 50% in methanol

SSP-060

TRIMETHOXYSILYLPROPYL MODIFIED (POLYETHYLENIMINE), 50% in isopropanol

Silicones Utilized in LbL Techniques

AMS-162

(6-7% AMINOPROPYLMETHYLSILOXANE) - DIMETHYLSILOXANE COPOLYMER, 80-120 cSt

SSP-060

TRIMETHOXYSILYLPROPYL MODIFIED (POLYETHYLENIMINE), 50% in isopropanol

WSA-7011

AMINOPROPYLSILSESQUIOXANE IN AQUEOUS SOLUTION

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