Scanning tunneling microscopy and spectroscopy of La0.67Ca0.33MnO3 thin films grown on LaAlO3(100)

Thin films of La0.67Ca0.33MnO3 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 La0.67Ca0.33MnO3 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.