Electroless Atomic Layer Deposition

Atomic layer deposition (ALD) is a group of methods for the formation of nanofilms of materials, an atomic layer at a time using surface limited reactions.  The majority of those methods are based on use of the vacuum environment.  However there are methods such as sequential ionic layer adsorption reaction (SILAR) which used the condensed phase, that is, aqueous solutions of precursor ions.  In addition, this group has been working on an electrochemical form of ALD for 25 years.   That work is referred to as electrochemical atomic layer deposition (E-ALD) or electrochemical atomic layer epitaxy (EC-ALE), and is based on using underpotential deposition (UPD) for surface limited reactions. The problem with using an electrochemical methodology for the formation of nanofilms is that many substrates are not conductive.   This has stimulated investigations into the growth of materials using an electroless form of ALD (EL-ALD).  An example of an EL-ALD process would be the use of a solution containing H₂ to poise the potential of a Pd surface.  This will result in the adsorption of a layer of hydrogen atoms which can then be exposed to precursors for Pt or Pd, forming an atomic layer of the metal.   That process can then be repeated to grow a nanofilm.  That example takes place on a conducting surface, however.  Work is continuing on development of an EL-ALD method which can start on an insulating surface, and results will be discussed.