a1 Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain
a2 Department of Physics and Optoelectronics Research Centre, University of Southampton, Southampton S017 1BJ, United Kingdom
a3 School of Mathematical and Physical Sciences, University of Sussex, Brighton BN1 9QH, United Kingdom
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 congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) α–Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger.
(Received August 19 1996)
(Accepted March 17 1997)
p1 Present address: Foundation for Research and Technology (F.O.R.T.H.), Hellas, Institute of Electronic Structure and Laser, P.O. Box 1527, Heraklion 711 10, Greece.
a) Permanent address: Centro Internacional de Física, Santa Fé de Bogotá, Apdo. Aéreo 49490, Colombia.
b) Author to whom correspondence should be addressed.