SCANNING FORCE MICROSCOPY STUDY OF SINGLE-CRYSTAL SUBSTRATES USED FOR THIN-FILM GROWTH OF HIGH-TEMPERATURE SUPERCONDUCTORS

Scanning force microscopy (SFM) is applied to study the surface morphology of polished single-crystalline substrates such as SrTiO3 (100), LaAlO3 (100), NdGaO3 (001) and MgO (100), which are used for thin-film growth of high-temperature superconductors. SFM reveals the misorientation of the substrate surface showing terraces with steps of a unit cell in height. The polishing leads to irregular shape of the step ledges. Oxygen anneal initiates partial regrowth of the surface. The average terrace width compares well to the surface misorientation. On SrTiO3 substrate surfaces cross-shaped features are observed indicating extended defects in the crystal. LaAlO3 substrates exhibit twin domains which cause severe surface roughening resulting in height variations of over 20 nm. MgO surface reacts with the ambient as demonstrated by comparing a freshly cleaved clean MgO surface to the same sample stored for several weeks under ambient conditions. Micron-sized particles appear on aging.