Investigation of the crystal structure on the nanomechanical properties of pulsed laser deposited niobium nitride thin f
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Ashraf Hassan Farha Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529; and Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606
Yüksel Ufuktepe Department of Physics, Cukurova University, Adana, 01330, Turkey
Hani E. Elsayed-Ali Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529; and Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606
Abdelmageed A. Elmustafaa) Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529; and Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606 (Received 30 December 2011; accepted 3 May 2012)
NbN thin films grown on Nb using pulsed laser deposition (PLD) were investigated for film crystal structures. The nanomechanical properties of NbN on Nb were examined as a function of the film/substrate crystal structure. X-ray diffraction (XRD) reveals peaks that correspond to d-NbN cubic and b-Nb2N hexagonal phases in addition to d9-NbN phase. Samples of various crystal structures were tested for phase characterization, microstructure, and surface morphology using XRD analysis, scanning electron microscopy, and atomic force microscopy. The nanomechanical properties were investigated using nanoindentation. The results indicate that there are clear effects of the crystal structure on the hardness of the PLD-grown NbNx films. I. INTRODUCTION
Most of the niobium nitride (NbNx) studies were focused on their superconducting properties.1,2 Besides their excellent superconducting properties, interests have recently grown in studies related to their mechanical properties.3 NbNx films exist in many crystal structures, including c-Nb4N3 (tetragonal), d-NbN (face-centered cubic), d9-NbN (hexagonal), e-NbN (hexagonal), g-NbN (hexagonal), and b-Nb2N (hexagonal). NbNx films could be found in any of these phases and/or in most cases present a mixed phase composition.4 The cubic phases of NbNx are softer than the hexagonal phases (b-Nb2N, d9-NbN).5 Several deposition techniques were used to fabricate NbNx thin films such as ion beam assisted deposition,6 reactive magnetron sputtering,7 and pulsed laser deposition (PLD).8,9 In PLD, experimental parameters can easily be modified, making it a highly flexible thin-film growth technique suitable for fabrication of many types of oxides, nitrides, carbides, and complex compounds. For NbNx films deposited by PLD, the composition and structural a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.167 J. Mater. Res., Vol. 27, No. 13, Jul 14, 2012
properties of the films are mainly influenced by nitrogen pressure, laser power, and substrate deposition temperature. Many researchers reported on the influence of PLD deposition parameters, such as background gas pressure and substrate temperature on the structure of NbNx thin films deposited on MgO and Si substrates.3–10 The importa
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