Pulsed Laser Deposition of Thin Metallic Multilayers and Amorphous Films
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PULSED LASER DEPOSITION OF THIN METALLIC MULTILAYERS AND AMORPHOUS FILMS HANS-ULRICH KREBS AND OLAF BREMERT Institut fUr Metallphysik, University of Gittingen, HospitalstraBe 3-7, 3400 G~ttingen, and Sonderforschungsbereich 345, F. R. Germany
ABSTRACT The method of pulsed excimer laser ablation using KrF radiation was applied for the deposition of thin metallic elementary multilayers. Above an ablation threshold of about 5 J/cm an 'explosive' evaporation of the metallic targets occurs leading to high deposition rates of up to S nm/s. For different metals, the ablation threshold slightly varies leading at the same laser fluence to different growth rates as shown for Ag, Fe, Zr and Nb. By using two elementary targets and adjusting the dwelling times on both targets, Fe/Ag, Fe/Zr and Fe/Nb multilayers of different bilayer thicknesses were deposited. While Fe/Ag superstructures show crystalline phases down to a periodicity of I nm, Fe/Zr and Fe/Nb films are amorphous at such wavelengths. On the other side, Fe/Nb multilayers can also be amorphized by a solid state interdiffusion reaction of the elementary multilayers. The surfaces of the grown films are smooth except for a small number of droplets on the film surface. INTRODUCTION Since many years, the laser ablation technique has been successfully applied for the thin film deposition of semiconductors, insulators and high temperature superconductors.1-S But recently, for the first time also the preparation of thin 6 metallic alloys by this laser deposition technique was systematically investigated. It was high deposition rates can be obtained shown in about 30 metallic alloy systems that 2 above an ablation threshold of about S J/cm . Furthermore, a stoichiometry transfer between the target and the deposited film exists. This was explained by an 'explosive' evaporation of the target material due to a superheating of the target surface. In this letter we report on our results applying this technique of pulsed laser deposition for the first time on the preparation of metallic elementary multilayers. First, we report on our studies on the ablation thresholds and deposition rates of pure elements, before we discuss some results on artificially produced Fe/Ag, Fe/Zr and Fe/Nb superlattices with different lattice mismatch. The Fe-Ag system has a positive heat of mixing, while a negative heat of mixing exists in the Fe-Zr and Fe-Nb system, as can be determined, for instance, by so-called CALPHAD calculations. 7 The question arises, whether also in laser deposited films amorphous phases can be formed by a deposition of superstructures with small layer periodicities as observed in sputtered systems.a On the other hand, it is of interest whether solid state interdiffusion reactions of laser deposited multilayers with larger bilayer
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Fig. 1. Schematic diagram of the pulsed laser deposition setup with two elementary foils in oscillating mode.
Mat. Res. Soc. Symp. Proc. Vol. 285. 01993 Materials Research Society
528
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