A historical overview of the research on TiO2 thin films deposited by atomic layer deposition – Part I: Early Studies

Molecular Layering (ML) or Atomic Layer Epitaxy (ALE) or Atomic Layer Deposition (ALD) technique is a gas-phase layer by layer deposition method which belongs to the general class of Chemical Vapor Deposition (CVD) techniques, and which has become of worldwide importance due to success in down-scaling of microelectronic devices. Among the materials obtained by the technique, titanium dioxide (TiO₂) stands out due to its crystallographic importance and numerous applications ranging from the photovoltaics to self-cleaning surfaces. Here we present an overview of the history of TiO₂ thin films grown by ALD technique organized into three periods: early studies (1960s-1990s), consolidation period (2000s) and current stage (2010-present). First, we report the early material synthesis and characterization studies on ALD TiO₂ thin films during the 4 decades between 1960s to 1990s. Then we address the evolution of the research field from the 2000s until the present day. The purpose of this historical survey is to synthetize the evolution of ALD TiO₂ thin films technology for different applications, which could be useful for students and researchers working in this field. In this manuscript, Part I is presented reporting the first published studies on TiO₂ thin films deposited by ALD.