The band gap of ultrathin amorphous and well-ordered Al2O3 films on CoAl(100) measured by scanning tunneling spectroscopy

The structural and electronic properties of ultrathin insulator Al2O3 films on CoAl(100) have been studied using a combination of scanning tunneling spectroscopy and microscopy. The analysis of the differential conductance yields a band gap of 2.6-2.9 eV for amorphous Al2O3. In the case of a well-ordered alumina film, the band gap is increased to 4.5 eV. On each of the oxide phases, the barrier height is to a large extent independent of local variations such as the surface corrugations or oxide steps. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056577]