Journal of Crystal Growth 197 (1999) 523—528 Scanning force microscopy and electron microscopy studies of pulsed laser deposited ZnO thin films: application to the bulk acoustic waves (BAW) devices P. Verardi*, N. Nastase, C. Gherasim, C. Ghica, M. Dinescu, R. Dinu, C. Flueraru  CNR, Istituto di Acustica **O.M. Corbino++, Area di Ricerca Tor Vergata, Via del Fosso del Cavaliere, I-00133 Rome, Italy  National Institute for Microtechnology, Bucharest, Romania  INFM, P.O. Box MG-36, RO-76900 Bucharest, Romania  Laser Department, INFPLR, P.O. Box MG-16, RO-76900 Bucharest, Romania Abstract New results concerning high crystalline ZnO thin films deposited on Si and sapphire substrates by laser ablation of Zn targets in oxygen reactive atmosphere are reported. Cross-section scanning electron microscopy (SEM) studies clearly evidenced a columnar structure of the layer. As a result of the preparation technique for TEM studies, the film is breaking into separate columnar groups: the ZnO columns observed are 100—500 nm thick, depending on the deposition conditions. The diffraction patterns taken on a large selected area reveal the crystalline hexagonal structure of the ZnO film with a"0.324 nm and c"0.5205 nm. The (0 0 2) diffraction spot is elongated due to the slope of the diffraction object, that is a confirmation of the fact that the columns are grown along the c-hexagonal axis. Scanning force microscopy evidenced the sharp boundaries of different domains from the uniform granular distribution on the surface. Characterization of the films was also conducted to establish their performance as piezoelectric layers in transducers for bulk acoustic wave devices in the GHz range. The insertion and conversion losses and the electromechanical coupling constant were measured using an appropriate set-up.  1999 Elsevier Science B.V. All rights reserved. Keywords: ZnO; Thin film; Scanning force microscopy; Piezoelectric properties 1. Introduction Pulsed laser deposition (PLD) technique has been applied to the synthesis and deposition of many compound films [1]. Zinc oxide is one of the * Corresponding author. Tel.: #39 6 30365765; fax: #39 6 30365341. materials reported to be deposited by this tech- nique starting from a sintered ZnO target [2]. The possibility of combining in PLD the synthesis and deposition of the compound has been applied in our case. A solid target of pure Zn was ablated in a reactive oxygen atmosphere. The resulting ZnO was collected on the substrate facing the target at a given distance. The aim of the present paper is to study the crystalline structure of zinc oxide films 0022-0248/99/$ — see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 9 8 ) 0 0 8 0 8 - 2