Area-selective atomic layer deposition of TiO₂ on ZnO using stearic acid monolayers: insights into selectivity loss using friction force microscopy for growth inhibition studies

In this work, we present a detailed kinetic analysis of stearic acid (SA) self-assembled monolayer (SAM) formation, thermal stability on ZnO surfaces and its role as a growth inhibitor during TiO₂ atomic layer deposition (ALD). Additionally, we performed an extensive friction force microscopy (FFM) study to establish a relationship between tribological behavior and X-ray photoelectron spectroscopy (XPS) quantification of Ti atomic percentages. The results revealed that a highly ordered and densely packed SA SAM was successfully formed on ZnO after 48 hours of deposition. Infrared spectroscopy showed monolayer order up to 160°C, indicating thermal suitability for ALD conditions. The growth inhibition study indicated that the SA SAM effectively blocked TiO₂ nucleation, preventing growth for at least 50 ALD cycles. This inhibition capability highlights the potential of the SA SAM system for ALD processes requiring selective deposition. Furthermore, FFM analysis provided a nanoscale view of surface changes, confirming chemical nucleation trends observed through XPS and ellipsometry; the comparison between slight friction changes in SAM-treated samples and XPS atomic quantification revealed Ti caused a significant impact on friction at this point, giving insight into selectivity loss. The FFM results also emphasized the value of this technique for qualitatively analyzing surface modifications in nanoscale systems. These findings demonstrate the viability of SA SAM on the ZnO system as thermally stable, effective growth inhibitors in area-selective atomic layer deposition processes.