Oxide (R m 0 n ) films are grown by evaporation from separate sources of element (R) and an oxide (M r O s ) which serves as the oxygen source. The oxide (M r O s ) should sublimate congruently; i.e., without decomposing into oxygen and its constituent element (M). On the growth surface this oxide (M r O s ) can react with the element (R) to form another oxide (R m O n ) that is thermodynamically more stable:
Using this technique, films of Al z O 3 , MgO, Si0 2 and MgAl 2 O 4 have been grown using As 2 0 3 or Sb 2 0 3 as the oxygen source.