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Physical properties of structured high Tc thin films by laser ablation on SrTiO3, ZrO2 and Si substrates

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PII: 0921-5107(92)90106-J Materials Science and Engineering, B I 3 (1992) 67-74 67 High T c thin films prepared by laser ablation: material distribution and droplet problem D. H. A. Blank, R. P. J. IJsselsteijn, P. G. Out, H. J. H. Kuiper, J. F lokst ra and H. Rogal la University of Twente, Faculty of Applied Physics, P.O. Box 217, 7500 AE Enschede (Netherlands) Abstract The lateral material distribution of laser-deposited YBa2Cu307_ ,~ films and the density of droplets coming from the target were studied by varying the laser pulse energy, the laser spot size and the target-to-substrate distance. Silicon wafers at ambient temperature were used as substrates to guarantee a large sticking coefficient of the particles. The deposition rate is found to depend linearly on the laser energy density E and quadratically on the spot size S at the target, whereas the droplet density is slightly dependent on E and increases linearly with l/S, yielding a threshold energy of 0.9 J cm -2. With a laser spot size of 7.15 mm 2 and a laser energy density of 1.2 J cm- 2, we were able to reduce the number of droplets to one to two per 500/zm 2 for a high quality high T~ film with a typical thickness of 100 nm. 1. Introduction In this paper a study about the laser-induced plasma of the high Tc material YBa2Cu30 7_0 is presented. In detail the shape of the plasma, the particle distribution and the occurrence of droplets have been investigated. Despite the number of advantages of laser ablation compared with other deposition techniques, it has one drawback: occurrence of droplets. These droplets are small spherical particles, with a typical diameter of 0.5-2/zm, coming from the target and leading to rough surfaces. In the literature some attention is paid to the reduction in the number of particles by using a high density target [1] or a second laser beam parallel to the substrate, which interferes with the plume of the ablated material [2]. We report on the influence of the

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