Re-evaluating the stability of nanoscale aluminium oxide barrier layers in electrochemical conditions Andrew J. Bagnall, Ziwen Zhao, Mun Hon Cheah, Alina Sekretareva Department of Chemistry – Ångström Laboratory, Uppsala University, 75120 Uppsala, Sweden Nanoscale insulating barriers based on metal oxides have been widely used to control the flow of electrons and/or as protective layers in a diverse array of systems, including microelectronics, 1 photovoltaics, 2 analytical electrochemistry, 3 electrocatalysis, 4 and photoelectrocatalysis. 5 Atomic layer deposition (ALD) allows the deposition of such films with an exceptional degree of control, uniformity, conformality and pinholefreeness. 6 Aluminium oxide (Al 2 O 3 ) grown from trimethylaluminium and water has long been considered a model ALD process for its reliability under relatively mild conditions. 6 Along with its highly insulating electronic structure, the thermodynamic stability of Al 2 O 3 across a wide range of potentials at neutral pH make it a key candidate for tunnelling barriers in photoelectrodes, but this has thus far been hindered by underexplored stability issues, attributed to surface restructuring, with specific ionic species suspected to play a role. 7,8
A systematic study into the stability and insulation of Al 2 O 3 films in various buffers across the pH scale is therefore presented, assessing their viability for shorter-term applications and fundamental studies of photoelectrocatalysis, where high barriers to both oxidation and reduction may be required to control the flow of non-thermal photoexcited carriers. References 1. R. Goul et al., AIP Advances , 2019 , 9 , 025018. 2. J. Zhang et al., ChemSusChem , 2017 , 10 , 3810–3817. 3. J. Kim et al., Proc. Natl. Acad. Sci. U.S.A. , 2013 , 110 , 20918–20922. 4. A. K. Vannucci et al., Proc. Natl. Acad. Sci. U.S.A. , 2013 , 110 , 20918–20922. 5. A. M. Lapides et al., Chem. Sci. , 2015 , 6 , 6398–6406.
6. S. M. George, Chem. Rev. , 2010 , 110 , 111–131. 7. S. A. Willis et al., Langmuir , 2021 , 37 , 14509–14519. 8. G. Kim et al., J. Electroanal. Chem , 2020 , 877 , 114550.
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