Structural factors determining the nanomechanical performance of transition metal nitride films
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Structural factors determining the nanomechanical performance of transition metal nitride films K. Sarakinos, S. Kassavetis, P. Patsalas and S. Logothetidis Aristotle University of Thessaloniki, Department of Physics, GR-54124, Thessaloniki, Greece ABSTRACT Chromium nitride (CrN) and Titanium nitride (TiN) thin films were deposited employing unbalanced magnetron sputtering (UBMS) for various values of substrate bias voltage (Vb). The structural characterization of the films in terms of phase identification and the density determination was achieved utilizing X-Ray techniques (XRD and XRR respectively), while the internal stresses were calculated by the change of the substrate’s curvature using Stoney’s equation. The nanomecahnical properties of the films (hardness and elastic modulus) were investigated using the Nanoindentation (NI) technique in the Continuous Stiffness Measurement (CSM) configuration. According to the NI results the hardness of the films ranges between between 15-25 GPa while the elastic modulus between 180-250 GPa. The analysis revealed that the hardness of the films is maximum when their orientation is pure (either [111] or [100]), while it is minimized under mixed orientation regime. Furthermore, the hardness of the films increases as the internal compressive stresses and the mass density increase. The latter can be validated through the comparison of the results concerning the above films to reported results for TiN films prepared by balanced magnetron sputtering (BMS) INTRODUCTION Transition metal nitrides have been established as a category of very important technological materials since they exhibit exceptional mechanical properties and find a vast range of optical properties [1]. In specific, the mononitrides of the group IVb-VIb of the transition metals form fcc crystals (rocksalt type) and they exhibit or not electronic conductivity depending on the position of the Fermi level in respect to the 3-d band of the constituent metal [1]. Among them TiN is the most widely investigated due to its refractory character and gold-like color. On the other hand CrN gains scientific and research interest during the last years due to its increased resistance to severe environments where TiN is not functional [2-5]. In this work we present a thorough study of the structural properties, which determine the nanomechanical properties of unbalanced magnetron sputtered (UBMS) CrN and TiN thin films. The effect of substrate bias voltage (Vb) on the nanomechanical response (i.e. hardness and elastic modulus) of the above thin films is presented in more detail. Taking into account the established correlation between the structural features of films and Vb [6], the effect of structural factors to the nanomechanical performance can be also investigated. The results revealed that the hardness is maximized in the case of clear growth orientation (either [111] or [100]). The above results are compared to results concerning TiN grown with balanced magnetron sputtering [7] in order to support the related analys
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