Vibrational properties of ultrathin Ga2O3 films grown on Ni(1 0 0)

Growth and vibrational properties of ultrathin films of Ga2O3 on Ni(1 0 0) were investigated in the temperature range of 80–1200 K by using electron energy loss spectroscopy (EELS), Auger electron spectroscopy, and low energy electron diffraction (LEED). At 80 K, a 30 Å thick Ga layer was deposited on the c(2×2)-oxygen structure prepared on Ni(1 0 0). Afterwards, the Ga layer was oxidized with oxygen until saturation. At 80 K, both the Ga layer and the oxidized Ga layer are amorphous. After annealing to room temperature a energy loss at ∼640 cm−1 occurs. This loss is assigned to a vibrational excitation of Ga–O bonds in the Ga-oxide structure. Further annealing up to 700 K leads to the characteristic Fuchs–Kliever phonons of Ga2O3 at 305, 470 and 745 cm−1 in the EEL spectrum and the LEED pattern of Ga oxide shows a weak diffuse ring structure of domains with long-range order but random orientation with respect to the substrate. The lattice constant is determined to be 2.8 Å which corresponds to the distance between two O2− ions in the oxide lattice.