Pulsed laser deposition of epitaxial buffer layers on LiNbO 3 F. Sa Ânchez * , N. Domingo, M.V. Garcõ Âa-Cuenca, C. Guerrero, C. Ferrater, M. Varela Departament de Fõ Âsica Aplicada i O Á ptica, Universitat de Barcelona, Avda. Diagonal 647, Barcelona E-08028, Spain Abstract The aim of this work is to obtain ®lms with suitable characteristics for use as buffer layers for YBCO superconducting electrodesinLiNbO 3 -basedelectro-opticdevices.Forthispurpose,anepitaxialbufferwithsingleorientationandlowsurface roughness is required. The possibilities of two oxides, yttria-stabilised zirconia YSZ) and CeO 2 , have been explored. The ®lmsweregrownonX-cutLiNbO 3 single crystals by pulsed laser deposition, and the in¯uence of the processing conditions wasstudied.TheYSZ®lmsareepitaxialwithsingle001)orientationandthesurfaceisappropriateforuseasa®rstlayerin a heterostructure. These were the properties found in ®lms grown under relatively broad ranges of deposition parameters, whichallowsaveryhighreproducibility.However,thelithium-de®cientLiNb 3 O 8 compoundwasfoundattheinterfaceinall the ®lms. This compound was not observed when CeO 2 ®lms were deposited. These ®lms are epitaxial and 0 1 1)-oriented, although they can also contain 0 0 1)-oriented crystals. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Thin ®lms; Epitaxy; LiNbO 3 ; Oxides; YSZ; CeO 2 1. Introduction Theexcellentacousto-opticandelectro-opticprop- ertiesofLiNbO 3 LNO)andtheavailabilityofsingle crystals at a cost-effective price make this material a key factor in the manufacture of acoustic-optic and electro-opticdevices.Theinterestinhigh-speedcom- munications is very high today, and important mod- i®cations in the devices currently in use are under consideration in order to improve their performance. Conductionlossesintheelectrodesareknowntobea potentially limiting factor, and the use of a super- conductor instead of a normal metal has been shown to improve the functional properties in acousto-optic [1±3] and electro-optic [4±6] devices. Most of the published works concern the use of low-temperature superconductors, although interdigital electrodes of the high-temperature superconductor YBa 2 Cu 3 O 7 YBCO) were used in surface acoustic wave ®lters [1,2]. However, the advantages offered by YBCO electrodesareonlyattainablewhentheyareepitaxial and their surface is smooth. The particular character- istics of YBCO and LNO make technological ful®l- ment of these requirements dif®cult. The ordered growth of an YBCO ®lm requires a substrate tem- perature close to 800 8C, high enough to permit the substantialmodi®cationofthesurfaceoftheunstable LNO [7±9]. Also, a high-quality epitaxial growth is not expected because of the discrepancy and complexityofthecrystalstructuresofthetwomateri- als. These technological dif®culties notwithstanding, some groups have reported the epitaxial growth of YBCO on LNO, directly [10±13] or using buffer layers [14±17]. Applied Surface Science 186 2002) 397±402 * Corresponding author. Tel.: 349-3-4021134; fax: 349-3-4021138. E-mail address: fsanchez@fao.ub.es F. Sa Ânchez). 0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-433201)00699-7