Formation and Characterisation of Periodically Structured B2-Aluminides Thin Films by Laser Interference Irradiation
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Formation and Characterisation of Periodically Structured B2-Aluminides Thin Films by Laser Interference Irradiation K.W. Liu and F. Mücklich Functional Materials, Department of Materials Science, Saarland University, Saarbrücken D-66041, Germany ABSTRACT B2-aluminide thin films can be used as protective layers to prevent mechanical, thermal and chemical impact on the main components and as intermediate thermal or diffusion barrier layers for semiconductor contacts. Laser irradiation can induce phase transformation due to thermal interaction with sample surface. Moreover, with laser interference, the laser power can be distributed periodically on interference points or lines. The scale of the pattern, sub-micrometer to dozens of micrometer, can be varied easily to the typical scale of grain sizes. In this work, B2structured NiAl and RuAl thin films with periodic pattern are prepared from corresponding elemental bi-films by laser interference irradiation. The micro-nano-structured surface constitutes of a line-like pattern with a period of about 5 micrometer. There occur melting and re-solidification processes during laser interaction with sample surface. The line-like patterns possess fine grains with a size of about 20 nm in Ni/Al and 5 nm in Ru/Al bi-films. The appearance of B2-structured NiAl and RuAl phases are confirmed by TEM. It is proposed that the phase transformation from initial metastable solid solution to the B2 phases can be induced by laser irradiation. INTRODUCTION B2-aluminide thin films can be used as protective layers to prevent mechanical, thermal and chemical impact on the components and as intermediate thermal or diffusion barrier layers for semiconductor contacts [1]. The aluminides thin films in Ni-Al system can be produced by thermal treatment of the multi-layers of component elements [2-4]. However, to the best knowledge of the authors, there are no reports concerning thin films in the Ru-Al system. Nevertheless nano-RuAl has been synthesized successfully by solid state reaction in mechanical alloying [5, 6]. The mechanical energy induced by the impinging balls has been attributed to the formation of RuAl phase during milling [6, 7]. In this paper the thermal energy induced by laser irradiation is utilized to control the transformation due to the thermal interaction with sample surface. Moreover, with laser interference, the laser power can be distributed periodically on interference points or lines. Laser interference irradiation has been proven to be an immediate approach to produce surface micro-structures with periodicity from micro- to nano-meter scale [8-10]. Due to the short duration of thermal exposure by pulse laser, the phases and morphology of the film can be modified under precise control. In this work, B2-structured NiAl and RuAl thin films with periodic pattern are synthesized from corresponding elemental bi-films by laser interference structuring. EXPERIMENTAL DETAILS
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The elemental thin films with desired composition are prepared by Physical Vapour Deposit
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