Mechanical properties of nanocrystalline and epitaxial TiN films on (100) silicon
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Q. Wei North Carolina A&T State University, Greensboro, North Carolina 27411
X. Zhang, C.C. Koch, and J. Narayan Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916 (Received 26 February 2001; accepted to July 2001)
We investigated mechanical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25 to 700 °C during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having a uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using x-ray diffraction and high-resolution transmission electron microscopy. Hardness measurements were made using nanoindentation techniques. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant at less than 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size. This behavior was modeled recently involving grain boundary sliding, which is particularly relevant in the case of hard materials such as TiN. I. INTRODUCTION
High-temperature ceramics constitute a very useful class of materials due to their high melting point, strength, and stability at elevated temperatures. For example, TiN films are successfully applied as wearprotection coatings for tools and mechanical components1–5 decoration coatings,6–8 electrical contacts, and diffusion barriers in electronic devices,9,10 because of their excellent corrosion and erosion resistance, high hardness, high thermal stability and desirable optical, and electrical properties. However, there are disadvantages associated with these materials in terms of poor toughness and ductility that severely limit their applications. Poor toughness and ductility result from the lack of dislocations and mobility. To alleviate some of these problems, reduction of grain size can enhance grain-boundary sliding and grain boundary diffusion related creep phenomena. In the nanoscale regime, we envisage that grainboundary sliding and creep phenomena may dominate and control the mechanical properties of TiN nanocrystalline films. Polycrystalline TiN films have been formed by a variety of techniques such as ion beam assisted deposition,11 plasma immersion ion implantation,12 reactive J. Mater. Res., Vol. 16, No. 9, Sep 2001
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magnetron deposition,13 laser assisted chemical vapor deposition,14 metalorganic chemical vapor deposition,15 and pulsed laser deposition (PLD).16 Compared to other techniques, PLD offers a unique advantage in terms of low-temperature deposition, where the grain size can be varied from nano (nm), to micro (m), to epitaxial single crysta
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