Conformality of atomic layer deposition analysed via experiments and modelling: case study of zinc oxide for catalytic applications

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School of Chemical Technology | Doctoral thesis (article-based) | Defence date: 2024-05-29
Degree programme
73 + app. 127
Aalto University publication series DOCTORAL THESES, 116/2024
Atomic layer deposition (ALD) has been used in various applications including microelectronics and heterogeneous catalysts. Ideally, ALD enables the growth of homogeneously distributed materials on solid supports including high aspect ratio (HAR) structures. However, to ob-tain conformal ALD coatings on HAR structures, process conditions should be optimized. The goals of this work were (i) to develop and apply a zinc oxide ALD process to prepare diverse copper-zinc oxide on zirconia catalysts for carbon dioxide hydrogenation into methanol and (ii) to investigate the effect of various process parameters on ALD conformality. Zinc oxide was added on mesoporous zirconia and alumina particles by the reaction of zinc acetylacetonate in a fixed bed ALD reactor. After the reaction, the remaining acac ligands were oxidatively removed in synthetic air at elevated temperatures. The reaction of zinc acetylacetonate on zirconia showed self-terminating behavior with the areal number density of zinc of approximately two atoms per square nanometer. The steric hindrance of bulky acac ligands was likely a saturation-determining factor for zinc obtained by ALD. Meanwhile, an eggshell-type zinc coating was obtained on alumina, and the zinc loading increased when the reactant dose increased. A diffusion–reaction model adapted to spherical supports was used to simulate the effect of reactant exposure on zinc loading. In the simulation, the zinc loading increased with an increase in the reactant exposure. The simulation results fit well with the experimental results. The zinc-after-copper catalyst was superior compared to other copper-after-zinc or copper-only catalysts for carbon dioxide hydrogenation into methanol. The current research showed the importance of tuning of the interaction of zinc and copper for catalytic performance and demonstrated the potential of zinc acetylacetonate as an ALD reactant. For future ALD conformality studies, a benchmark was proposed using an archetypical trimethylaluminum-water process on lateral HAR microchannels. The effect of process parameters on ALD thickness profiles was investigated using a diffusion–reaction model. For example, penetration depth into microchannels decreased with an increase in the molar mass of ALD reactant and growth per cycle (GPC). The trends of ALD thickness profiles in the free molecular flow regime and transition flow regime were illustrated. This work proposes that the free molecular flow regime and channel filling of less than 5% are the conditions required to obtain fingerprint thickness profile characteristics.
Supervising professor
Puurunen, Riikka L., Assoc. Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland
Thesis advisor
Puurunen, Riikka L., Assoc. Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland
Karinen, Reetta, D.Sc. (Tech.), Aalto University, Department of Chemical and Metallurgical Engineering, Finland
atomic layer deposition, conformality, catalyst, high-aspect-ratio structures
Other note
  • [Publication 1]: Yim, J., Haimi, E., Mäntymäki, M., Kärkäs, V., Bes, R., Arandia, A., Meinander, K., Brüner, P., Grehl, T., Gell, L., Viinikainen, T., Honkala, K., Huotari, S., Karinen, R., Putkonen, M, and Puurunen, R. L., Atomic layer deposition of zinc oxide on mesoporous zirconia using zinc(II) acetylacetonate and air, Chemistry of Materials, 35 (2023) 7915–7930.
    DOI: 10.1021/acs.chemmater.3c00668 View at publisher
  • [Publication 2]: Arandia, A., Yim, J., Warraich, H., Leppäkangas, E., Bes, R., Lempelto, A., Gell, L., Jiang, H., Meinander, K., Viinikainen, T., Huotari, S., Honkala, K., and Puurunen, R. L., Effect of atomic layer deposited zinc promoter on the activity of copper-on-zirconia catalysts in the hydrogenation of carbon dioxide to methanol, Applied Catalysis B: Environmental, 321 (2023) 122046.
    DOI: 10.1016/j.apcatb.2022.122046 View at publisher
  • [Publication 3]: Yim, J., Ylivaara, O. M. E., Ylilammi, M., Korpelainen, V., Haimi, E., Verkama, E., Utriainen, M., and Puurunen, R. L., Saturation profile based conformality analysis for atomic layer deposition: aluminum oxide in lateral high-aspect-ratio channels, Physical Chemistry Chemical Physics, 22 (2020) 23107-23120.
    DOI: 10.1039/D0CP03358H View at publisher
  • [Publication 4]: Yim, J., Verkama, E., Velasco, J.A., Arts, K., and Puurunen, R. L., Conformality of atomic layer deposition in microchannels: impact of process parameters on the simulated thickness profile, Physical Chemistry Chemical Physics, 24 (2022) 8645-8660.
    DOI: 10.1039/D1CP04758B View at publisher