Structural- and chemical-phase-separation on single crystalline sapphire (0001) surfaces

Atomic force microscopy (AFM) was used to characterize morphology and chemistry on step-controlled single crystalline sapphire (0001) surfaces. Hydrophilicity on the surface can be evaluated using frictional force imaging. A sapphire surface that is covered with bunched steps accompanied with crossing steps clearly exhibits the phase-separation into two domains with different hydrophilicity, where an almost hydrophobic domain forms inside a hydrophilic area. By analyzing the histogram of the step height, we concluded that the difference in the hydrophilicity is associated with the surface reconstruction. We found that the phase-separation characterized by the hydrophilicity and charge potential self-organizes on the sapphire surface with specific step arrangements. We demonstrated selective adsorption of biomolecules on step-controlled surfaces as an example of the application.