Crystal Orientation Effects on the Nanotribological, Mechanical and Electrical Properties of Atomically Flat SrTiO3 Surfaces

Abstract

Research on perovskite oxides offers opportunities to explore diverse scientific phenomena at the nano- and atomic scales, along with their promising technological potential. In particular, strontium titanate (SrTiO₃) has attracted substantial research attention not only as a model system, but also for its ability to provide good interfacial compatibility with other hetero-oxide materials. However, the role of crystal orientation remains relatively unexplored. In this study, three SrTiO₃ single-crystalline substrates with different crystal orientations ((001), (110), and (111)) were investigated. Scanning probe microscopy (SPM) revealed that all three surfaces are atomically flat with well-defined terraces, and the measured step heights match the theoretical lattice spacing for each direction. Simultaneously acquired friction measurements unveiled marked variations in friction depending on the crystal orientation. Additional SPM studies on local mechanical properties revealed that the (110) and (111) samples exhibit reduced modulus and increased adhesion, ultimately enhancing energy dissipation and friction. Even after normalizing by modulus-dependent contact area, the pressure–shear relations in (110) and (111) were found to be strongly modulated by surface orientation-dependent structure and chemistry compared with the (001). Furthermore, surface potential mapping showed that the TiO₂-induced work function in (001) is significantly reduced by the presence of SrO in (110) and oxygen-deficient Ti sites in (111). These results provide new insights into the interplay between orientation-dependent intrinsic surface features of SrTiO₃ and offer valuable guidelines for characterizing other metal oxides.