At 700 K, the oxidation with 1 L O2 of CoGa(001) was investigated by means of high-resolution electron energy loss spectroscopy (EELS), low-energy electron diffraction, Auger electron spectroscopy, and scanning tunneling microscopy (STM). Oxidation with 1 L O2 at 700 K leads to the formation of long, rectangular islands of β-Ga2O3 oriented in the  and  directions of the substrate. EEL spectra of the islands of β-Ga2O3 show intense Fuchs–Kliewer (FK) modes at 305, 455, 645, and 780 cm−1. The β-Ga2O3 islands are well ordered and show a (2×1) structure with two domains, oriented perpendicular to each other. The two-dimensional lattice parameters of β-Ga2O3 are determined to be a = 2.8±0.1 Å and b = 5.8±0.1 Å. © 1998 American Institute of Physics.