ELSEVIER Physica C 261 (1996) 1-11 PHYSICA ® Growth and etching phenomena observed by STM/AFM on pulsed-laser deposited YBa2fu307_ ~ films B. Dam a,* , N.J. Koeman a, J.H. Rector a, B. St~iuble-Pi~mpin a, U. Poppe b, R. Griessen a a Faculty of Physics and Astronomy, Free University, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands b Forschungszentrum J~lich GmbH, lnstitut fftr Festkfrperforschung, D52425 J~lich, Germany Received 27 October 1995; revised manuscript received 8 January 1996 Abstract The surface morphology of pulsed-laser deposited YBa2Cu30 7_ 8 films is investigated by STM AFM. Instead of spiral growth, a 2D nucleation and growth behaviour is observed. As we find these 2D nuclei also on high-oxygen pressure DC sputtered films grown at a much lower growth rate, we conclude that the supersaturation is not a decisive parameter for the predominance of either growth mode. Instead, we attribute the absence of growth spirals to the non-steady state growth conditions inherent to the pulsed nature of the laser-ablation process. Growth spirals only develop, if a non-vanishing diffusional flow of adatoms towards the step edge is maintained. The number of growth spirals observed on a film is therefore not necessarily a measure for the number of screw dislocations. After wet-etching the films in Br-ethanol, we observe that etch pits are formed consisting of concentric steps. We conclude that these pits are due to repetitive nucleation around linear defects. The etchpit density identified in this way is of the order of 1 per ixm 2. 1. Introduction While growth spirals are routinely observed on crystals grown from solution, the observation of such a surface morphology on vapor-phase deposited YBa2Cu3OT_ 8 came as a surprise [1,2]. For this discovery of spiral steps with a unit-cell step height and a step spacing of around 20 nm the high lateral resolution of scanning tunneling and atomic force microscopy (STM/AFM) was essential. Immedi- ately, it was recognized that the screw dislocations * Corresponding author. Fax: + 31 20 444 7899; e-mail: dam@nat.vu.nl. associated with the growth spirals are important pin- ning sites, which could be responsible for the high critical currents found in these high-T~ superconduct- ing films. Moreover, it turned out that the same type of growth spirals occur on films made by a wide range of other physical vapour deposition (PVD) techniques (see the review in Ref. [3]). Recently, Scheel et al. [4] even found growth spirals on YBa2CU3OT_ 8 films grown by LPE (liquid phase epitaxy), albeit in this case with an interstep distance of several microns. They showed that this larger step spacing (visible by optical microscopy) is related to the fact that in LPE the supersaturation is much lower than in PVD. According to the the spiral- growth theory developed by Burton, Cabrera and 0921-4534/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved PII S0921-4534(96)00121-9