ALD coating of porous materials and powders Kirill Isakov March 10, 2016

Porous materials and powders Z EYFERT, C AROLINE M., S TEFAN A. P RZYBORSKI, AND N EIL R. C AMERON. Surface functionalized emulsion-templated porous materials for in vitro cell culture in 3D. Abstracts of Papers of the American Chemical Society 238, (2009). T HONGTEM, T ITIPUN, AND S OMCHAI T HONGTEM. Preparation and characterization of Li 1-x Ni 1+ x O 2 powder used as cathode materials, (2005).

ALD coating process Extreme uniformity and thickness control Self-limiting reactions Stepwise manner of growth Independent of topography growth per cycle P UURUNEN, R. L. Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process. Journal of Applied Physics 97, 12 (2005).

ALD = conformal deposition E LAM, J EFFREY W., ET AL. "Atomic layer deposition for the conformal coating of nanoporous materials." Journal of Nanomaterials 2006, (2006). J UNG, Y OON S EOK, ET AL. Ultrathin direct atomic layer deposition on composite electrodes for highly durable and safe Li ‐ ion batteries. Advanced Materials 22, 19 (2010).

Theory of Atomic Layer Deposition The majority of ALD processes include two reactants sequentially introduced to the reactor and separated by purge steps so that excess reactants and by-products are removed before the next reactant pulse. Consequently, ALD process is designed to involve only gas-solid reactions and reactants never meet in the gas-phase. The typical binary ALD process includes four following model steps forming a reaction cycle which also illustrated in the Figure on the Slide 2: 1.Self-terminating gas-solid reaction of reactant A. 2.Purge step to remove excess reactant components and by-products. 3.Self-terminating gas-solid reaction of reactant B. 4.Purge step.

ALD temperature window The ALD process is highly dependent on temperature, experiencing significant disruptions in the growth mechanisms with excessively high or low temperature. This results in the formation of a specific temperature range in which the ALD process is effective in terms of cycle length and gives conformal films. This temperature range is also called the ALD window and it typically spans from 100‰°C to 400°C‰. P ERROS, A. C. P. Thermal and plasma- enhanced atomic layer deposition: the study of and employment in various nanotechnology applications. PhD thesis, Aalto University School of Electrical Engeneering, 2015.

Not really “Atomic Layer” Deposition Growth per cycle (GPC) is usually less than a monolayer thickness of the material growing, due to steric hindrance. Steric hindrance prevents certain chemical reactions to happen as a result of the molecule structure and size, this phenomena is usually observed in molecules with large groups. Growth per cycle also varies with temperature.

ALD of Al 2 O 3 by TMA/H 2 O The ALD of Al2O3 is considered to be a model ALD system and has been continuously used in the semiconductor industry for over two decades. This process is generally implemented using trimethylaluminum (TMA) and H2O as precursors, and produces amorphous alumina films (a- Al2O3). The TMA/H2O process has close to ideal conditions: the reactants are highly reactive and thermally stable; and as methane is the by-product of the reactions it is pumped out of the chamber and does not disrupt the process. The reactions between the surface and the precursors during each half-cycle are described by: 1) ‖ Al–OH + Al(CH 3 ) 3 → Al–O–Al(CH 3 ) 2 + CH 4 2) ‖ Al–CH 3 + H 2 O → ‖ Al–OH + CH 4 where symbol ‖ indicates the surface groups.

Bibliography 1.G EORGE, S. M. Atomic layer deposition: An overview. Chemical Reviews 110, 1 (2010), 111– M IIKKULAINEN, V., L ESKELA, M., R ITALA, M., AND P UURUNEN, R. L. Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends. Journal of Applied Physics 113, 2 (2013). 3.P ERROS, A. C. P. Thermal and plasma-enhanced atomic layer deposition: the study of and employment in various nanotechnology applications. PhD thesis, Aalto University School of Electrical Engeneering, P UURUNEN, R. Growth per cycle in atomic layer deposition: A theoretical model. Chemical Vapor Deposition 9, 5 (2003), 249– P UURUNEN, R. L. Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process. Journal of Applied Physics 97, 12 (2005). 6.W IDJAJA, Y., AND M USGRAVE, C. B. Q UANTUM chemical study of the mechanism of aluminum oxide atomic layer deposition. Applied Physics Letters 80, 18 (2002), 3304–3306.