Optical properties of ultrathin PbO layers grown on Pb films

The optical properties of ultrathin (2-7 nm) oxide layers grown on Pb films have been measured by spectroscopic ellipsometry over the 1.4-5.4-eV photon energy range. The shape of the dielectric function resembles published measurements made on much thicker evaporated layers of orthorhombic PbO, but with the absorption edge shifted downward in energy by about 0.6 eV. The band gap in our case is estimated to be 2.8 eV from the theory of direct allowed transitions.