A method of forming a film on a substrate includes depositing first and second evaporating source materials respective from first and second evaporating sources onto the substrate while moving the evaporating sources together with respect to the substrate, the first and second evaporating source materials being different from each other and positioned to provide a non-overlapping deposition region of the first evaporating source material, an overlapping deposition region of the first and second evaporating source materials and a non-overlapping deposition region of the second source material such that when the evaporating sources are moved, a film is formed to include a first layer that is a deposition of only the first evaporating source material, a second layer that is a deposition of a mixture of the first evaporating source material and the second evaporating source material and a third layer that is a deposition of only the second source material.