We report here the results of investigations using a scanning tunneling microscope (STM) and a scanning force microscope (STM) on YBa2Cu3Oy/PrBa2Cu3Oy (YBCO/PrBCO) superlattices and YBCO thin films. STM and SFM measurements were performed in air at 295 K while the tunneling spectroscopy was carried out in vacuum (< 10-3 Torr) at 4.3 K. STM images were observed to exhibit the atomic structure of [(YBCO)n/(PrBCOm)]l superlattices where the subscripts n and m refer to the numbers of unit cells of the individual YBCO or PrBCo layers respectively and l is the number of repetitions of the (YBCO)n/(PrBCO)m cell. The STM images of a [(YBCO)l/(PrBCO)l]40 superlattice show atoms aligned with a lattice parameter of 3.81 Å along the crystal a-axis and 3.89 Å along the crystal b-axis. SFM images show a periodic variation on the YBCO surface. In the tunneling spectra, the current-voltage characteristics at 4.3 K show Coulomb staircases. The tunneling conductance at 4.3 K reveals conductance peaks at 2 Δ = 3.5, 17.0; 23.5 and 41 meV and the curve dI/dV versus V has a zero bias conductance. The tunneling spectra of YBCO thin films showed semiconducting or superconducting behaviors depending on the tip-sample distance.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering