*2.3.4 Substrate oxide evaluation*

X-ray photoelectron spectroscopy (XPS) is a versatile surface analysis technique used for compositional and chemical state analyses. In this study, XPS analysis (ULVAC-PHI, PHI Quantera SXM-CI) using a monochromatic Al Kα source (15 mA, 10 kV) was performed. Wide (0–1000 eV) and narrow scans of Al 2P and O1s for different annealed substrates were collected. The measured binding energies were then corrected with C 1 s at 285.0 eV. When pre-sputtering to clean the surface was performed, the sample surface was reduced and the measurements were affected, so XPS analysis was performed without pre-sputtering. **Table 2** shows the XPS analysis conditions for substrates oxide analysis.

#### *2.3.5 Wipe test*

A CGT Kinetiks 4000 cold-spray system (Cold Gas Technology, Ampfing, Germany) with a custom-made suction nozzle was used to perform the wipe test and coating using TiO2 powder onto the annealed 400°C pure aluminum substrates. The wipe test was conducted to study the deformation behavior of a single particle on this substrate. Prior to deposition, substrate was ground and polished until a mirror finish surface was obtained. The process gas temperature and pressure used were 500°C and 3 MPa, respectively. Nitrogen was used as the process gas. The distance between the exit of the nozzle and the substrate was fixed at 20 mm. The traverse speed of the process was 2000 mm/s. Prior to spraying, the substrates were rinsed with acetone. An FEI Helios Dual Beam 650 field emission SEM (FESEM) and focused ion beam (FIB) microscope was used to investigate the single particle TiO2 deposition onto mirror polish annealed substrate.
