Synthesis of MoS2-Au nanocomposite films by sputter deposition.

Abstract

Molybdenum disulfide based solid lubricants, which are well known for their lubricating behavior in dry and inert atmospheres, oxidize in humid environments. This study focuses on the synthesis of Au doped MoS 2 nanocomposite thin films created by co-sputter deposition at various temperatures for environmental robustness. The ratio of the deposition flux was adjusted to control the composition to about 10% Au by weight. (Scanning) transmission electron microscopy (S)TEM revealed that the room temperature deposited nanocomposite consisted of 2-4 nm size Au particles in a matrix of semi-crystalline MoS 2 . With increasing growth temperatures, the nanocomposite exhibited structural changes: the Au nanoparticles coarsened by diffusion-driven Ostwald ripening to 5-10 nm size and the MoS 2 basal planes encapsulated the Au nanoparticles thereby forming a novel solid Au core MoS 2 nano-onion like structures. In situ TEM heating revealed that Au nanoparticles also coarsened, but unlike heating during film growth, the highly ordered basal planes did not encapsulate the Au. Friction and wear tests confirmed that the MoS 2 -Au nanocomposite films grown at elevated temperatures had significantly longer wear life in air with 50% RH as compared with pure MoS 2 . During frictional contact, exfoliation of the MoS 2 basal planes occurred parallel to the sliding direction, providing a thin blanket of lubrication. All the films were found to be deficient in sulfur. Studies during the final phase of the project indicate that near stoichiometric films can be grown by introducing a small dose of H 2 S gas during sputtering.

On the S/W stoichiometry and triboperformance of WSxC(H) coatings deposited by magnetron sputtering

“…Similar results have been reported for WSeC coatings [20], where WSe 2 deposited by reactive sputtering in CH 4 atmosphere showed a much higher Se/W ratio than that co-sputtered with a graphite target. Dimigen [26] and Goeke [30] pointed out that plasma decomposition of H 2 S even provides a controllable amount of sulfur to the growing film and allows to mitigate substoichiometry.…”

“…The atomic masses of Ar, S and W atom are 40, 32 and 184 respectively, so that the light S atoms (close to Ar) deposited on the substrate are more easily resputtered than W atoms. Also, S has a high vapor pressure (e.g.~3 × 10 −4 Pa at room temperature) [30] and binds weakly to the substrate. On the other hand, the heavier W atoms cannot move far from the target after being sputtered, and this also accounts for the higher content of W in the coatings deposited at shorter target-substrate distances and the enrichment of S in the coatings deposited at longer target-substrate distances.…”

Tribological Properties of New Cu-Al/MoS2 Solid Lubricant Coatings Using Magnetron Sputter Deposition

“…Experimental results reveal that metal doping presents a simple and economical method of improving the comprehensive properties of MoS 2 -based coatings. It is generally believed that doped soft metals, such as Au [8][9][10] and Pb [11,12], can reduce the friction coefficients of coatings due to the synergistic lubrication effects, while such coatings have the disadvantage of poor wear resistance. In contrast, the co-doping of metals such as Ti [13,14], Ni [15], Cr [16,17], Al [10,18], Zr [19], Nb [20] and Mo [21] would be appropriate for reducing the friction coefficient and improving the mechanical properties of the coatings.…”