PULSED-LASER DEPOSITION OF KNBO3 THIN-FILMS

The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congr uent with the target composition; however, at further distances K-defi cient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic t argets. Best results so far have been obtained with [K]/[Nb] = 2.85 ta rget composition, and crystalline KNbO3 films are formed when heating the substrates to 650 degrees C. Films formed on (100)MgO single cryst als are usually single phase and oriented with the (110) film plane pa rallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 degrees C, nio bium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporat ion from the film. Films formed on (001) alpha-Al2O3 (sapphire) show t he coexistence of (111), (110), and (001) orientations of KNbO3, and t he presence of NbO2 is also observed. KNbO3 films deposited on (001)Li NbO3 crystallize with the (111) plane of the film parallel to the subs trate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration r etained in the film is comparatively larger.