Effect of the deposition rate on thin films of CuZnAl obtained by thermal evaporation
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Effect of the deposition rate on thin films of CuZnAl obtained by thermal evaporation L.López-Pavón1, E. López-Cuellar1,2, A. Torres-Castro1,2, C. Ballesteros3, C. José de Araújo4. 1
FIME-UANL, Ave. Universidad S/N. Cd. Universitaria, San Nicolás de los Garza, Nuevo León, México. C.P. 66450 2 CIIDIT, Km. 10 de la Nueva Autopista al Aeropuerto Internacional de Monterrey, Apodaca, Nuevo León, C.P. 66600 3 Departamento de Física, Universidad Carlos III de Madrid, Avda. Universidad 30, 28911 Leganés, Madrid. Spain. 4 Department of Mechanical Engineering, Universidade Federal de Campina Grande, Av. Aprígio Veloso, 882, Bodocongó, Campina Grande - PB, Brazil. Abstract Thermal evaporation is used to deposit thin films of CuZnAl on silicon substrates. For this purpose, a CuZnAl shape memory alloy is used as evaporation source. The chemical composition and the phases present in the films are evaluated at two different deposition rates: 7 and 0.2 Å/s. The thin films are heat treated to promote the diffusion of the elements and characterized by X-ray Diffraction, Energy Dispersive X-ray Spectroscopy and Scanning Transmission Electron Microscopy (STEM). It is shown that the chemical composition of the thin films is significantly different to that of the CuZnAl alloy used as evaporation source. Moreover, the films produced at 7 Å/s show a significant loss of Zn, contrary to the results obtained using a deposition rate of 0.2 Å/s. It is also observed that the composition varies across the thickness of the film, suggesting that the various alloying elements are evaporated at different rates during the deposition process. Finally the predominant phases present in the films belong to the AlxCuy family. Introduction In recent years, the study of nanoparticles or the deposition of thin films of shape memory alloys has become a field of great interest for scientists due to their potential to become a primary actuating mechanism for micro-actuators and biomedical applications [1]. An alloy is considered as a Shape Memory Alloy (SMA) when it can „remember‟ its shape, that is, after a SMA sample has been deformed from its original shape, it regains its original geometry by itself during heating (shape memory effect) or, simply during unloading at a higher ambient temperature (superelasticity) [2]. These properties are associated to a reversible, temperature dependent solid state martensitic phase transformation from a low-symmetry (martensite) to a highly symmetric crystallographic structure (austenite) [3]. SMA has a lot of interesting applications; there are more than 10,000 patents on this matter [4-5]: connectors, thermal or electrics activators, superelastic products, dampers and intelligent materials. Shape memory alloy thin films have been widely used in micro-electro-mechanical systems (micro-actuators) such as micropumps or microvalves [6-13]. The physical vapour deposition (PVD) techniques can be divided into two groups: evaporation and sputtering. In the present study the interest is in thermal evaporation, where the growing
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