 Hydrogen is employed to saturate broken ( " dangling " ) bonds of amorphous silicon and amorphous carbon that helps stabilizing material properties . It is also a potential electron donor in various oxide materials , including ZnO , <unk> , <unk> , MgO , ZrO2 , HfO2 , La2O3 , <unk> , TiO2 , <unk> , <unk> , SiO2 , Al2O3 , ZrSiO4 , <unk> , and <unk> . 
