Scanning tunneling microscopy and spectroscopy of La<SUB>0.67</SUB>Ca<SUB>0.33</SUB>MnO<SUB>3</SUB> thin films grown on LaAlO<SUB>3</SUB>(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&#176;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