Abstract
As a main optical thin-film material, SiO2 has a low refractive index in the UV-visible wavelength region. It is used widely for optical coatings with superior environmental resistance. In contrast, Nb2O5 is a high refractive index material. To improve their mechanical properties, SiO2 and Nb2O5 single-layer thin films were prepared using high-density plasma assisted vapor deposition. Plasma conditions were varied by changing the coil current related to energy intensity, and the oxygen gas flow rate related to ionization. Analyses of SiO2 and Nb2O5 thin films using XRD revealed amorphous composition irrespective of the assist. However, cross-sectional SEM images showed that thin film densification differed according to the assist. Furthermore, XPS showed differences in SiO2 thin films from the bonding state according to the assist. The Nb2O5 thin films exhibited slight differences according to the assist. Surface roughness measurements and abrasion resistance tests were done for thin films deposited under various plasma conditions. The plasma-assisted deposited SiO2 films were much more durable than non-assist films. The refractive indexes of the films were measured using optical transmission spectra and ellipsometry. Results show correlation between the durability and the refractive indexes. The film packing density was related to the durability. No difference was found in the durability for Nb2O5 between plasma-assisted deposited films and non-assisted deposited ones. However, a difference was found in the refractive index between the films of two types. The film hardness was measured using nanoindentation. The Nb2O5 films were harder than the SiO2 films. The Nb2O5 film stiffness was also three times greater than that of SiO2 films. However, the damage to plasma-assisted SiO2 films was less than that to plasma-assisted Nb2O5 films. This high stiffness is expected to cause plastic deformation. Future investigations must examine the relations among film packing density, durability, hardness, and stiffness.
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