EFFECT OF SURFACE TREATMENT ON CHIRAL AND ACHIRAL SrTiO3 SURFACE MORPHOLOGY AND METAL THIN FILM GROWTH

Pulsed Laser Deposition has been used to grow Pt thin films on single-crystal SrTiO3 substrates, both (100)-oriented (an achiral surface) and (621)-oriented (a chiral surface). Prior to growth, some of the substrates were subjected to chemical and thermal treatments. The impact of these processes on substrate surface quality, as well as the crystalline quality of the resulting Pt films, is investigated. Pt films were deposited over a range of conditions, then characterized for their crystallinity and epitaxy using x-ray diffraction (XRD) and for their surface morphologies using atomic force microscopy (AFM). For the low-index, achiral SrTiO3(100) surface, pretreatment was found to have a substantial positive effect on the substrate surface quality, leading to a well-crystallized “step-terrace” surface structure. However, similar pre-treatments did not produce a discernible step-terrace structure on SrTiO3(621) surfaces, instead leading to formation of large island-like surface defects. The crystallinity and epitaxy of films deposited on pretreated SrTiO3(100) surfaces were much improved compared to films on as-received substrates. Untreated substrates led to polycrystalline, multi-oriented films while films grown on welltreated substrates were epitaxially oriented. These observations are contrasted with the successful epitaxial growth of Pt on untreated SrTiO3(621) substrates. For both types of surfaces, the interface between Pt and SrTiO3 will necessarily play the key role in epitaxial growth. A wellcrystallized, morphologically flat substrate surface is usually considered to be a prerequisite to a low-energy metal-ceramic interface and thus high-quality films. We believe that the differences in the structural nature of the two surfaces may account for the observed differences between chiral and achiral surfaces.