Atomic/molecular layer deposition of hybrid inorganic-organic thin films

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Pia Sundberg Name of the doctoral dissertation Atomic/molecular layer deposition of hybrid inorganic-organic thin films Publisher School of Chemical Technology Unit Department of Chemistry Series Aalto University publication series DOCTORAL DISSERTATIONS 201/2014 Field of research Inorganic Chemistry Manuscript submitted 11 September 2014 Date of the defence 12 December 2014 Permission to publish granted (date) 18 November 2014 Language English Monograph Article dissertation (summary + original articles) Abstract The possibility to combine the best properties of the two constituents makes inorganicorganic hybrid materials as intriguing candidates for many high-end applications. However, the distinctly different material properties of the inorganic and organic constituents make the fabrication of hybrid materials challenging. For example when using solution deposition techniques, a solvent which works for the organic constituent does not necessarily work well for the inorganic one. Also when considering the potential applications for hybrids, many require the use of high-quality thin films. Atomic and molecular layer deposition (ALD and MLD) techniques are gas-phase deposition methods based on sequential surface-saturated reactions. By combining the two techniques it is possible to deposit high-quality hybrid thin films with accurate thickness and composition control. In this thesis novel inorganic-organic hybrid thin films were deposited using the combination of ALD and MLD. One of the main challenges when growing hybrid materials using the combined ALD/MLD technique is finding suitable precursors. When flexible linear organic precursors are used in ALD/MLD they may bend and hinder the growth process. In this work rigid aromatic amines, 4,4'-oxydianiline (ODA) and 4-aminophenol (AP) were used to improve the growth rates. Diethyl zinc (DEZ) and TiCl4, precursors commonly used in ALD, were selected as the inorganic precursors. Successful film growth was observed for all possible precursor combinations, but the growth rates achieved using AP as organic precursor were higher than those obtained using ODA, Ti-AP hybrid exhibiting almost ideal growth. As AP has two different functional groups, more control is achieved in the growth process whereas the ether bond in ODA allows the molecule to bend. From the inorganic precursors TiCl4, which is stronger Lewis acid and has more ligands than DEZ, catalyzed the deposition reaction better. The cyclic growth process characteristic to ALD and MLD was utilized to make nanostructures consisting of oxides and hybrid materials. The material pairs investigated were TiCl4+ODA hybrid and TiO2, DEZ+AP hybrid and ZnO, and trimethylaluminum (TMA) + ethylene-1,2-diol (EG) and Al2O3. By varying the hybrid and oxide content in the Tiand Zncontaining mixtures, it was possible to tune the degree of crystallinity, surface roughness, refractive index, mechanical properties and density in the formed films. The TMA-EG and Al2O3 nanolaminates were grown on polylactic acid substrates in order to fabricate a film more suitable for coating biomaterials in packaging applications. When compared to coatings made from pure Al2O3 or TMA+EG hybrid, the nanolaminate consisting of TMA+EG and Al2O3 layers withstood straining better. The strained nanolaminate was also better oxygen barrier than the strained pure coatings.