(705c) Development of New Chemistries for Molecular Layer Deposition

High quality nanoscale polymer films fabricated with molecular precision are seeing increasing importance in applications such as microelectronics, sensors, biomedical devices, and energy technologies. Most deposition methods, such as dip-coating, spin-coating, and surface initiated-polymerizations, are solution based and lack nanoscale control. Molecular layer deposition (MLD) is an emerging vapor-phase technique that offers excellent control at the nanoscale. This powerful method creates conformal polymer films with molecular precision by sequentially depositing organic bifunctional precursors in a self-limiting layer-by-layer fashion. However, MLD proceeds in absence of solvent, pH cannot be varied, and catalysts cannot easily be employed, and this has so far limited the number of linking chemistries applicable to MLD, and hence also its applications.

Here our search for new linking chemistries compatible with the solid-gas phase nature of MLD will be presented. Our effort can be divided into three very different reaction types. Firstly, we have examined nucleophilic substitutions of alkyl iodides with different nucleophilic precursors, to e.g. enable controlled growth of nanoscale polyethylenimine. This reaction type is so far unexplored for MLD, but it is similar in nature to the nucleophilic acyl substation which is the most common MLD linking chemistry. The second reaction type is the pericyclic Diels Alder reaction. This reaction creates new carbon-carbon bonds without the need for a catalyst, and it is therefore a powerful addendum to the existing toolbox of MLD chemistries. The third reaction class is photo-activated MLD, in which the direct input of energy from UV-light is utilized to overcome otherwise infeasible reaction barriers. Photo-activated MLD may also result in new carbon-carbon bond forming reactions. We will present our successful and unsuccessful results pertaining to these new classes of MLD chemistries, including XPS, ellipsometry and IR analysis of the nanoscale polymer thin films. Additionally, the challenges we have encountered with each of these new chemistries will be discussed.