Pulsed Laser Deposition of Metal Dichalcogenides on Stainless Steel
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PULSED LASER DEPOSITION OF METAL DICHALCOGENIDES ON STAINLESS STEEL
P. J. John*, V. J. Dyhouse*, N. T. McDevitt***, A. Safriet*, J. S. Zabinski**, and M. S. Donley** *University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0168 **WRDC/MLBT, Materials Laboratory, Wright-Patterson AFB, Ohio 45433 ***RamSpec Research, 4399 E. Mohave Dr., Dayton, OH 45431 ABSTRACT Films of MoS 2 have been successfully deposited on 440C stainless steel using an excimer laser. A comparison was made of films ablated with the laser operating at 193 nm and at 248 nm. The effects of substrate temperature were also studied. X-ray Photoelectron Spectroscopy (XPS) measurements indicated that the films were sulphur rich as compared to single crystal MoS 2 . Laser Raman measurements indicated that annealing was necessary to obtain crystalline films. All films exhibited coefficients of friction in the neighborhood of 0.03 in a dry nitrogen environment. Coefficients of friction in laboratory air were significantly higher. INTRODUCTION Molybdenum disulfide thin films are useful as solid lubricating coatings for space bearing applications. In addition, since MoS 2 has a broader temperature range than existing oils or greases, MoS 2 films show promise for use as high temperature lubricants. Some of the techniques that are currently used to generate thin films of MoS, and other transitional metal dichalcogenides include radio frequency (RF) sputtering [1,2], DC sputtering [3,5], and magnetron sputtering [3,4]. This work is directed at developing pulsed laser ablation (PLA) as an additional technique for depositing thin films of metal dichalcogenides. Previously, a frequency doubled Nd:YAG laser (A=530 nm) was used to deposit MoS 2 films on 440C stainless steel [6,7]. XPS analysis indicated that the substrate temperature played a very important role in the chemistry of the films with higher temperatures resulting in better films. Time-of-flight measurements indicated that this evaporation process was more thermal than ablative. For this work, higher energy photons (x=248 nm and A=193 nm) were used to deposit the MoS 2 films. The experiments here were designed to examine how film chemistry and friction characteristics are affected by laser wavelength, substrate temperature, and light fluence on the target. EXPERIMENT MoS 2 films were grown using an excimer laser operating with either KrF (248 nm) or ArF (193 nm). For both wavelengths, laser pulse energies of 100 mJ and 200 mJ were used. The substrates were 30 mm diameter polished 440C disks. The depositions were accomplished in an ultra high vacuum environment with base pressure on the order of Ix1O- torr. The laser was focused down to a spot approximately 3 mm x 6 mm on a 25 mm diameter MoS 2 target in the deposition chamber. Targets were produced by pressing MoS 2 powder at 70 MPA. Subsequent analysis indicated that targets pressed at a temperature of 1000C were no different than targets pressed at room temperature. The target was rotated and the laser beam was rastered across the
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