Scanning tunneling microscopy and spectroscopy of La_0.67Ca_0.33MnO₃ thin films grown on LaAlO₃(100)

Abstract

Thin films of La_0.67Ca_0.33MnO₃ have been deposited at room temperature on LaAlO₃(100) substrates by dc magnetron sputtering. The as-deposited films are amorphous and become polycrystalline on annealing ex situ at 800°C in oxygen ambient. Topographic and tunneling spectroscopic features of annealed films have been studied by a scanning tunneling microscope at room temperature in air. The main microstructural features in these films are the presence of fish-scale or slate like plates, terraces of integer multiple of unit cell or half-unit cell parameter height and oblate shaped grains. Grain boundaries have been identified from the orientation of terraced grains with respect to the substrate plane. Such a planar growth accompanied by grain boundaries may enhance magnetoresistance both at and below ferromagnetic transition temperature. An average barrier height of 4.0 eV of La_0.67Ca_0.33MnO₃ has been obtained from current-voltage measurements. A band gap of 0.2 eV has been found from the existence of states near the Fermi level in the density of states spectrum.