Due to the safety challenges associated with the use of trimethylaluminum as a metal precursor for the deposition of alumina, different chemicals have been investigated over the years to replace it. The authors have investigated the use of aluminum tri-isopropoxide (TIPA) as an alternative alkoxide precursor for the safe and cost-effective deposition of alumina. In this work, TIPA is used as a stable Al source for atomic layer deposition (ALD) of Al₂O₃ when different oxidizing agents including water, oxygen plasma, water plasma, and ozone are employed. The authors have explored the deposition of Al₂O₃ using TIPA in ALD systems operating in vacuum and atmospheric pressure conditions. For thermal and plasma processes in vacuum ALD, a growth rate of 1.1-2 Å/cycle achieved over a range of 140-300 °C is shown. Film density, roughness, and composition have been tested using various characterization techniques confirming comparable film properties to the thermal ALD of trimethylaluminum and water. The thermal water process at atmospheric pressure ALD (AP-ALD) resulted in a growth rate of up to 1.1 Å/cycle with residual carbon below the XPS detection limit. AP-ALD on nanoparticles shows different growth modes on TiO₂ versus SiO₂ nanoparticle surfaces confirmed by transmission electron microscopy analysis. Using TIPA as an ALD precursor would open up the possibility for a safer and cost-effective process for deposition of Al₂O₃ in various applications.

The aluminum precursor plays a crucial role in the Al₂O₃ ALD process. To date, trimethylaluminum (TMA) is one of the most widely used precursors in experimental and theoretical studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theoretical and experimental investigation is carried out on the Al₂O₃ ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The experimental results pointed out that the thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 Å/cycle at temperatures of 150 to 175 °C. On the basis of the in situ mass spectrometry analysis and DFT calculations, the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissociation occur. Design of heteroleptic precursors containing alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al₂O₃ ALD.

This study reports on the secondary electron emission (SEE) performance of atomic layer deposited MgO films, with thicknesses in the range from 5 to 25 nm, for the application in the Timed Photon Counter. In this novel, photodetector MgO is utilized as a material for the fabrication of ultrathin transmission dynodes (tynodes). Two different types of PECVD silicon oxide films are applied on top of MgO, in order to protect it against etching steps in the fabrication of tynodes and also as a prevention against aging. Applicability of these two materials as capping films is evaluated in terms of achieved secondary electron yield (SEY) of MgO after their removal. Emission of secondary electrons is known to depend on numerous physical and chemical properties of the material, such as surface roughness and chemical composition. On that account, morphological and structural properties of modified MgO are determined by atomic force microscope and x-ray photoelectron spectrometer and linked to the changes in SEE behavior. The authors demonstrate that the application of a suitable capping layer followed by its removal provides an SEY of 6.6, as opposed to the value of 4.8 recorded from the as-deposited MgO film. Furthermore, in a following experiment, they showed that annealing of MgO films at high temperatures (up to 1100 °C) significantly improved the secondary electron emission, elevating the SEY to 7.2.