Reversible $c$ (4 $\times$ 4) $\leftrightarrow$ (1 $\times$ 2) phase transition on the Ba/Ge(100) surface controlled by oxygen adsorption and desorption

Modified (100) surfaces of group IV semiconductors are successfully used as substrates for growing films of crystalline oxides, in particular, BaO. In this regard, it is important to understand the formation mechanisms and physicochemical properties of surface atomic structures formed on these substrates. In this work, using combined modern experimental methods, we have studied the reversible $c$ (4 $\times$ 4) $\leftrightarrow$ (1 $\times$ 2) phase transition on the Ba/Ge(100) surface, which is due to the presence of oxygen atoms on it. Information about the structural and electronic properties of these surface reconstructions is obtained, and their atomic models are also proposed. The results presented are important, in particular, from the point of view of the integration of germanium into currently used silicon technologies.