Abstract
The effect of sputtering pressure on the surface/interface microstructure, crystal phase, mechanical properties and electrical characteristics of nanocrystalline W-Mo films is reported. The W-Mo films (≈300 nm) with variable microstructure were deposited under variable argon (Ar) sputtering pressure (PAr), which is varied in the range of 3-19 mTorr. X-ray diffraction analyses indicate that the W-Mo films crystallize in thermodynamically stable α-phase of W. However, the crystal-quality degradation occurs for W-Mo films deposited at higher PAr due to difference in the adatom mobilities. The average grain size (d) of the W-Mo films was in the range of 11-24 nm; grain size decreases with increasing PAr. The effect of PAr and associated microstructure are significant on the mechanical characteristics; the hardness (H) and modulus of elasticity (Er) of W-Mo films deposited at lower PAr were higher but decreases continuously with increasing PAr. The W-Mo films deposited under optimum sputtering pressure exhibit superior mechanical characteristics: H=40 GPa, Er=275 GPa, H/Er=0.8, and H3/Er2=0.145 GPa, which are higher compared to pure, α-phase W-films. The W-Mo films deposited at PAr=3-9 mTorr exhibit high resistivity≈350-400 μΩ-cm, which decreases to 150-200 μΩ-cm for films deposited at higher PAr. Based on the results, structure-mechanical-electrical property correlation in W-Mo films is established.
Highlights
As presented and discussed in this paper, our findings demonstrate that the processing conditions can be tuned to obtain W-Mo films with variable surface and interface microstructure, which enables superior mechanical properties and enhanced electrical resistivity
It is well known that the thermodynamic parameters, namely the temperature and pressure during deposition, influences the growth behavior, crystal structure and grain-size variation, and surface/interface morphology evolution in thin films produced by vapor transport processes.[28,33,40,41,42]
Tungsten-molybdenum (W-Mo) nanocrystalline thin films (≈300 nm) were deposited under variable argon (Ar) sputtering pressure (PAr), which is varied in the range of 3-19 mTorr
Summary
Tungsten (W) and W-based alloys have been the subject of intense research in recent years.[1,2,3,4,5,6,7,8,9,10] W exhibit excellent physical and mechanical properties, such as high melting point, high erosion resistance, reduced long-term activation and radiation tolerance, which makes this material of particular interest for many scientific and technological applications.[3,4,5,6,7,8,9,10] W served the lighting industry (filaments) for decades because of its exceptional strength and stiffness at high temperatures, good thermal conductivity, low thermal expansion (4.43 ppm/◦C), and low resistivity (5.5 Ωcm).[9,10,11] Among the refractory metals, W is a very hard metal. Kim et al presented a new class of gamma radiation shielding materials consisting the nano-W dispersed in polymer nanocomposites
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