Substrates for ALD were washed with Acetone, Methanol/Ethanol, then deionized water and blow dried with N2 before deposition. Depositions were performed with a Picosun R-200 Advanced ALD tool attached to an MBraun glovebox. At a chamber base pressure of approx. 12 hPa the substrates were heated to 150°C. Trimethylaluminum (TMAl, EpiValence Ltd, Electronic grade) was used as precursor gas, DI water as reactant and N2 as purging gas. For each cycle, corresponding to one layer, the substrates were first exposed to precursor gas (flow = 150 sccm), purged, then reactant gas (flow = 200 sccm) and finally the chamber was purged again which completes a cycle. Pulse and purge durations were 0.1 s and 10 s, respectively.