We describe a versatile bottom-up approach to covalently and rapidly graft hydroxyl terminated poly (2-vinyl pyridine) (P2VP-OH) polymers in 60 seconds that can subsequently be used to fabricate high quality TiO2 films on silicon substrates. A facile strategy based upon room temperature titanium vapor phase infiltration of the grafted P2VP-OH polymer brushes produces TiO2 nanofilms of 2-4 nm thickness. In order to fabricate coherent inorganic films with precise thickness control, it is critical to generate a high-quality polymer brush film i.e. a complete monolayer. Definition of precise and regular polymer monolayers is straightforwardly achieved for polymers which are weakly interacting with one another and the substrate (apart from the reactive terminal group used for grafting). However this is much more challenging for reactive systems. Crucial parameters are explored including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with very high coverage and uniformity across wafer scale areas. Additionally, we compare the P2VP-OH polymer system with another reactive polymer PMMA-OH and a relatively non-reactive polymer PS-OH, the latter we prove to be extremely effective for surface blocking and deactivation. Our methodology provides new insight into the grafting of polymer brushes and their ability to form dense TiO2 films. We believe the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area selective deposition, solar cell absorber layers and antimicrobial surface coatings.

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This work identifies the critical factors when developing a polymer brush vapor phase infiltration process, while also demonstrating the use of novel pyridines for area selective purposes.

Due to its low cost and suitable band gap, silicon has been studied as a photoanode material for some time. However, as a result of poor stability during the oxygen evolution reaction (OER), Si still remains unsuitable for any extended use. Ultra-thin titanium dioxide (TiO2) films have been used as protective coatings and are shown to enhance Si photoanode lifetime with added solar to hydrogen performance improvements through distancing the oxidation reaction away from the Si photoanode surface and improved charge transport through the anode. This study details the nucleation, growth chemistry, and performance of TiO2 thin films prepared via thermal and plasma enhanced atomic layer deposition (ALD) using both titanium isopropoxide and tetrakis(dimethylamido)titanium as the precursor material. The effect of post ALD treatments of plasma and air annealing was also studied. Films were investigated using photoelectrochemical cell testing to evaluate photoelectrochemical performance, and in-vacuum cycle-by-cycle x-ray photoelectron spectroscopy was used as the primary characterisation technique to study nucleation mechanisms and film properties contributing to improvements in cell performance. TiO2 grown by plasma enhanced ALD results in cleaner films with reduced carbon incorporation. However, despite increased carbon incorporation, thermally grown films showed improved photocurrent as a result of oxygen vacancies in these films. Post deposition annealing in a H2 ambient is shown to further improve photocurrent in all cases, while annealing in atmosphere leads to uniform film chemistry and enhanced photocurrent stability in all cases.