Studies of Nanomechanical Properties of Pulsed Laser Deposited NbN films on Si Using Nanoindentation
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Studies of Nanomechanical Properties of Pulsed Laser Deposited NbN films on Si Using Nanoindentation M. A. Mamun1,4, A. H. Farha2,4, Y. Ufuktepe3, H. E. Elsayed-Ali2,4, and A. A. Elmustafa1,4 1 Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529, USA 2 Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529, USA 3 Department of Physics, Cukurova University, Adana, 01330, TURKEY 4 Applied Research Center, Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA ABSTRACT Nanomechanical and structural properties of pulsed laser deposited niobium nitride thin films were investigated using X-ray diffraction, atomic force microscopy, and nanoindentation. NbN film reveals cubic į-NbN structure with the corresponding diffraction peaks from the (111), (200), and (220) planes. The NbN thin films depict highly granular structure, with a wide range of grain sizes that range from 15-40 nm with an average surface roughness of 6 nm. The average modulus of the film is 420±60 GPa, whereas for the substrate the average modulus is 180 GPa, which is considered higher than the average modulus for Si reported in the literature due to pileup. The hardness of the film increases from an average of 12 GPa for deep indents (Si substrate) measured using XP CSM and load control (LC) modes to an average of 25 GPa measured using the DCM II head in CSM and LC modules. The average hardness of the Si substrate is 12 GPa. INTRODUCTION Niobium nitride grown on Si(100) substrate interests optoelectronic community because the films can be integrated in devices. For example, NbN grown on sapphire has been demonstrated as a single-photon optical photodetector to detect photons in the far infrared with temporal response of few ps, and that makes these devices most attractive for optical quantum applications [1]. It is well documented that the majority of the studies related to NbN are related to its superconducting properties [2-4]. Other excellent properties are high hardness and toughness compared to pure Nb, which makes it a suitable material for protective-wear coatings [5-9]. Kneisel et al., 2009 adopted the Conflat design with Nb and concluded that RF measurements on single-cell cavities indicated Nb-1Zr and NbN are good candidates for the flanges [5]. Nanomechanical properties of NbN films with different structures have been reported on different type of substrates. According to Benkahoul et al., (2004) the hardness reached 40 GPa for a crystalline NbN and drops to ∼ 25 GPa for the δ-NbN thin films prepared using reactive magnetron sputtering of Nb metal target in an Ar/N2 atmosphere [7]. Other study on NbN films prepared by magnetron sputtering showed that the appearance of İ-NbN phase in the films causes decrease in the hardness and modulus of NbN films from their peak values of 36.6 GPa and 457 GPa, respectively that they observed for the fcc į-NbN cubic phase [10]. Wen et al., (2009) concluded that the structure for NbN layers is a crit
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