(Invited) Templated Electrodeposition By Molecular Assemblies: Exploring Limits

Abstract

Organic molecules play a vital role in deposition processes, both as randomly adsorbed entities to control kinetics and as organized layers in area selective deposition. Applications of the latter include deposition from the gas phase such as atomic layer deposition as well as from solution in processes ranging from electrochemical and electroless deposition of patterned metal films to the growth of layers of metal-organic frameworks. While self-assembled monolayers (SAMs) offer a convenient way to templated deposition down to the scale of tens of nanometers, the move towards the bottom end of the nanoscale poses increasingly stringent requirements on their structure and properties. This encompasses both the precision at which SAM patterns can be defined and the extent to which these layers can direct nucleation and control growth.As far as electrodeposition is concerned, SAMs have been employed to generate metal patterns by harnessing their versatility and modifying a combination of interfacial properties such as adhesion and charge transfer. Typically, chemically passive molecules are used and the process is based on defects present in a SAM. Thus limiting resolution due to the statistical distribution of defects as regards their size and location, a complementary strategy where the deposition process can be actively controlled by a molecular property seems more promising to advance templated electrodeposition to the ultrasmall length scale. A scheme which affords such an active control is based on functionalized SAMs. As illustrated in the cartoon, metal ions are coordinated at the outer interface of the SAM (step 1) and reduced in a subsequent electrochemical step (2). Yielding deposits on top of the SAM, these can act as seeds for the deposition from the bulk electrolyte (3), thereby enabling the generation of ultrathin layers and the combination of different metals. Due to weak adhesion between the deposit and the SAM, structures can be lifted off and transferred to other substrates, thus offering a replicate generation of patterns.The presentation addresses issues which are key to achieving ultrahigh resolution. Strategies aimed at overcoming current limitations as regards variability in dimensions are discussed, arguably one of the most pressing problems in the move towards ever smaller features. This involves topics ranging from the factors controlling coordination chemistry of SAMs to their design beyond single component systems. Figure 1