Van Marum colloquium by Prof. Philippe Vereecken from IMEC/KU Leuven.

Abstract
Templated electrodeposition is a common practice for the fabrication of metal nanostructures. The nano-architecture is set by that of the nanoporous template. For complex nano-architectures such as the metal nanomesh (see Figure) which was developed in our group [1,2], templates will remain necessary. Nonetheless, the 3D nanoporous anodized aluminum oxide (AAO) used for the templated electrodeposition, did form by self-assembly. Regular AAO made from pure Al has only vertical pores with a hexagonal arrangement. The additional horizontal pores in the 3D-AAO are formed with regular interval by doping of the aluminum substrate with Cu [1]. Such level of deterministic control on the growth direction is not yet achievable with electrodeposition. Yet, directed growth of pillars and nanowires has been achieved by control of current inhibiting surface layers, either introduced by additives [3] or intrinsic to the metal electrochemistry [4]. One example is found for indium electrodeposition where InCl intermediate adsorbate is believed to form a coating around electrodeposited indium, leading to large single crystalline morphologies and nanowires when guided by a shallow pattern [3].

Conformal deposition of thin-film coatings on high aspect ratio structures is typically claimed by Atomic and Molecular Layer Deposition (ALD and MLD). The nature of the surface limited reactions of these vapor-phase methods allows for the formation of continuous sub-nanometer to a few tens of nanometer thin films with uniform thickness over the most complex architectures. The accuracy of the technique goes at the cost of long deposition cycles especially when very large surface areas with extreme aspect ratios (>100) are involved. In recent years, electrodeposition processes have been found where the metal electrodeposition reaction for e.g., Ni or Pt can be inhibited early on, similarly leading to sub-nanometer to few nanometer thick coatings by cycling [5, 6]. In this paper, we will show examples where this process can be used also to coat nano-architectures such as our nanomesh with very large surface area (100 cm2 per planar cm2) and aspect ratio (100x).

Finally, the electrochemical fabrication of oxide thin-films by electro-precipitation and electrochemically induced sol-gel reactions will be discussed. The poor electronic conductivity of oxides makes that the reaction is maintained by ionic conduction through the films, similar as for oxide formation by anodization. The resistive nature of the layers typically allows also for good conformality over high aspect ratio substrates [7]. Similarly, thin polymer films such as poly-phenylene oxide or PPO can be made conformally [8].

More information found here.

The "Van Marum Colloquia" is a collaborative lecture series between the LION and LIC institutes (Leiden), focusing on fundamental and applied surface science.

References

1. "The Formation Mechanism of 3D Porous Anodized Aluminum Oxide Templates from an Aluminum Film with Copper Impurities" Johannes Vanpaemel, Alaa Abd-Elnaiem, Stefan De Gendt, Philippe M. Vereecken, J. Phys. Chem. C, 119 (4), 2105–2112 (2015)
2. “Combining High Porosity with High Surface Area in Flexible Interconnected Nanowire Meshes for Hydrogen Generation and Beyond" Stanislaw Zankowski and Philippe M. Vereecken, ACS Appl. Mater. Interfaces, 10 (51), pp 44634–44644 (2018)
3. “Electrodeposited free-standing single-crystal indium nanowires" G. Hautier, J. D’Haen, K. Maex and P.M. Vereecken, ESL 11, K49 (2008)
4. “Fabrication of complex architectures using electrodeposition into patterned self-assembled monolayers” N.S.Pesika, A. Radisic, K.J. Stebe, P.C. Searson, Nano Letters. 6, 1023-1026 (2006)
5. "Electro-chemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014)
6. “Self-Terminating Growth of Platinum Films by Electrochemical Deposition” Yihua Liu, Dincer Gokcen, Dincer Gokcen, Ugo Bertocci, Tom Moffat, Science 338(6112):1327-30 (2012)
7. "Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes" Marina Timmermans, Nouha Labyedh, Felix Mattelaer, Stanislaw Zankowski, Stella Deheryan, Christophe Detavernier, and Philippe M. Vereecken, J. Electrochem. Soc. 164, 14, D954-D963 (2017)
8. “Self-limiting electropolymerisation of ultrathin, pinhole free poly(phenylene oxide) film on Carbon Nanosheets” S. Deheryan, D. J. Cott, R. Muller, M. Heyns and P. M. Vereecken, Carbon, 88, 42-50, (2015)