Design And Preparation Of TiO₂-based Anti-reflection Films

Antireflection （AR） film is one of the most important optical films and it hasbeen widely used in the fields of medicine, building, military and so on. In order toachieve the broadband, omnibearing and efficient antireflection, which desired bymodern optical devices, the TiO₂-based AR films have been explored intensively. Onthe baseis of technical study towards refractive index （RI） and homogeneity of TiO₂films, TiO₂-based single, double, multilayer broadband AR films and gradient RI filmhave been designed respectively using the classic spectral theory and TFCalc software.Electron beam evaporation （E-beam） and double-source co-evaporation were electedto fabricate these AR films. Relevant structural features and optical performanceswere discussed.According to the preparation investigations on the RI and homogeneity of TiO₂films, it’s found that, by the processes of E-beam, ion assistant deposition andglancing angle deposition, the RI of TiO₂films can be regulated in the range of1.7to2.4. Besides, the RI of TiO₂films prepared by E-beam process have positivenon-uniformity and the film thicknesses also exhibited inhomogeneity. Thesenon-uniformities can be decreased by selecting the substrate materials with lowsurface roughness, using the right cleaning process, rotating the substrate orconducting annealing appropriately. This work has provided many useful directions toacquire AR films with steady performances.Utilizing the spectral theory and TFCalc software, TiO₂-based single, double andmultilayer broadband AR films have been designed and were prepared by E-beamprocess. It’s found that the TiO₂single layer couldn’t achieve AR effect. It can beimproved by depositing an incremental layer with low RI. The MgF2/TiO₂filmperformed good broadband AR property and its maximum transmittance was94.3%. Abetter broadband AR effect would be acquired if the layer of middle RI takes the placeof TiO₂. And the lower the RI of top layer is, the better the AR effect would become.The mean reflectance and the maximum transmittance of the designed and preparedmultilayer broadband AR film, made up by eight alternating layers of SiO₂and TiO₂,were6.33%and95.3%respectively, which was much better than the single anddouble AR films.Using mixture medium theoretical model and TFCalc software, the MgF2-TiO₂ mixed gradient RI AR film was designed. And it was prepared by double-sourceco-evaporation process. With the increasing film thickness, the RI profile decreasedin an exponential way from2.18to1.59. So it exhibited excellent antireflectionperformance. Its mean reflectance in the range of400nm to800nm was just5.56%and it nearly eliminated the Fresnel reflections at the central wavelength. What’smore, the MgF2-TiO₂mixed gradient film performed omnibearing AR property at thewavelength of550nm. It’s suitable to work for the oblique incidence light for all theday.