Structure and properties of titanium oxide layers deposited by reactive plasma activated electron beam evaporation

Titanium oxide layers were deposited by reactive electron beam evaporation with and without additional plasma activation by spotless arc discharge. The influence of substrate temperature and plasma activation on structure and properties of TiO2 layers are presented. The layers were deposited with very high deposition rates between 40 and 70 nm/s. XRD investigations have revealed that structure of all layers deposited at substrate temperature (TS) below 150 °C is amorphous. Without plasma activation and at substrate temperature above 200 °C layers with anatase phase were deposited. On the other hand with plasma activation the degree of substrate ion bombardment controls the formation of anatase or rutile phase. Furthermore a drastic influence of plasma activation on the properties of the layers could be found. Without plasma activation the refractive index at 550 nm only amounts to between 2.02 and 2.29 depending on substrate temperature. With plasma activation a drastic raise of refractive indexes to values between 2.30 and 2.58 can be reached. In addition the hardness of the layer is obviously influenced by plasma activation. At TS below 150 °C hardness is raised from 2.0 to 6.7 GPa. The formation of the rutile phase in layers deposited with plasma activation is linked with a further increase of hardness up to 12 GPa. Measurements of the contact angle show a promising super hydrophilicity of anatase layers. Therefore these layers should be well-suited as coatings with self-cleaning or antifogging properties. At TS below 150 °C the plasma activation enables the deposition of dense, high-refractive layers at very high deposition rates for applications as optical layers.