Surface Energy Change of Atomic-Scale Metal Oxide Thin Films by Phase Transformation

Abstract

Fine-tuning of the surface free energy (SFE) of a solid material facilitates its use in a wide range of applications requiring precise control of the ubiquitous presence of liquid on the surface. In this study, we found that the SFE of rare-earth oxide (REO) thin films deposited by atomic layer deposition (ALD) gradually decreased with increasing film thickness; however, these changes could not be understood by classical interaction models. Herein, the mechanism underlying the aforesaid decrease was systematically studied by measuring contact angles, surface potential, adhesion force, crystalline structures, chemical compositions, and morphologies of the REO films. A growth mode of the REO films was observed: layer-by-layer growth at the initial stage with an amorphous phase and subsequent crystalline island growth, accompanied by a change in the crystalline structure and orientation that affects the SFE. The portion of the surface crystalline facets terminated with (222) and (440) planes evolved with an increase in ALD cycles and film thickness, as an amorphous phase was transformed. Based on this information, we demonstrated an SFE-tuned liquid tweezer with selectivity to target liquid droplets. We believe that the results of this fundamental and practical study, with excellent selectivity to liquids, will have significant impacts on coating technology.

Surface Zeta Potential of ALD-Grown Metal-Oxide Films

“…Among these films, most of the materials exhibit hydrophilic properties, whereas In 2 O 3 presents the highest WCA, revealing its hydrophobicity. SnO 2 has a highly hydrophilic surface, retaining a tightly bound hydration layer, which can passively repel foulants such as hydrophobic organic molecules and oils. , A previous study of ALD Y 2 O 3 found that the WCA increased with increasing film thickness from ∼42° at 3 nm to 100° at 50 nm due to the evolution in film crystallinity with thickness . Our finding of WCA = 57.3° at 10 nm Y 2 O 3 is consistent with this previous study.…”

“…Figure S19 shows that 7.1 and 15.6 nm ZrO 2 films, for example, have similar surface-charge properties. A previous study found a distinct correlation between the WCA and thickness of ALD Y 2 O 3 films and attributed this variation in surface properties to changes in the crystallinity of the ALD Y 2 O 3 coatings . The Si native oxide and the ALD SiO 2 coatings are amorphous as-deposited, so the crystallinity does not change with thickness.…”

Self-Formation of Superhydrophobic Surfaces through Interfacial Energy Engineering between Liquids and Particles

“…12 Common protocols, however, need complex and expensive processes to fabricate microstructures. Also, to coat with low-surface-energy materials, processes such as chemical vapor deposition, 13 atomic layer deposition, 14,15 electrodeposition, 16 calcination, 17 and so forth have been adopted, 18 but these are complex for practical applications where a hydrophobic function is required. On the other hand, several industrial-friendly techniques have been also introduced such as in-liquid functionalization 19 and spray coating, 20,21 offering the expansion of applicability.…”

How the surface state of nickel/gadolinium-doped ceria cathodes influences the electrochemical performance in direct CO2 electrolysis

“…The depth profile measurements (figure S7) highlighted that under the aforementioned conditions, a new steady state has been established, having higher degree of oxidation in subsurface layers than on the Ni/NiO surface. This runs counter to the expected trend in which oxide species in vacuum diffuse and accumulate on the surface of the metal due to their lower surface free energy [50,51]. This result can be rationalized by considering that the stronger interaction of CO 2 with Ni 0 species establish a new equilibrium that inhibits the diffusion of oxygen from the inner layers to the outer shell.…”