Atomic Layer Deposition: from molecular chemistry to nanocoatings
Pengmei Yu1, M. Buyukyazi2, C. Bohr2, M. Scigaj1 S. Mathur2 and Mariona Coll1
1 Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Barcelona, Spain
2 Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, Cologne 50939, Germany
Preparation of functional oxide thin films at low temperatures, over large areas and compatible with low- cost and flexible substrates, offers great industrial potential. The degree of crystal perfection required for these functional oxides varies according to the specific application. Sometimes, high-temperature processing is required for improved functional properties which adds complexity in the materials processing in device integration. Atomic layer deposition (ALD) is a very appealing chemical thin-film deposition method that is unique because ensures excellent large-area uniformity, conformity, and enables simple and atomic layer control of film thickness and composition. Also, ALD offers well controlled interfaces, nanoengineering of smaller and more demanding structures (3D substrates), and uses lower deposition temperatures than traditional vacuum deposition techniques which guarantee low thermal budget and the possibility to use organic or biological substrates. The precursor chemistry is one of the main parameters that determines the processing conditions and ultimately the film properties. In spite of the current variety of commercial precursor for the growth of oxides, there are certain limitations associated with these compounds (stability, volatility, toxicity, handling under inert atmosphere…) therefore, there is an increasing need to develop new or improved precursors for the deposition of functional oxides by ALD. In this work we will present two novel precursors for selected metal oxides. In one case, we demonstrate the use of a cheap, non toxic and easily handling cobalt precursor to prepare Co3O4 thin films and conformal coatings on 3D TiO2/C nanofibers at low temperature (200 ̊C) for more efficient supercapacitors. On the other hand, we present for the first time the use of a single-source heterobimetallic precursor [GdFe(OtBu)6(Py)2] to prepare magnetic GdFeO3, thin films by ALD. The advantages of having the two elements of the final material in a single precursor are threefold: matched stoichiometry, better homogeneity due to the premixed elements and simplified delivery system. To conclude, the combination of novel chemical precursors and ALD opens a plethora of new opportunities to prepare and nanoengineer functional coatings at low temperature with enhanced functionalities.