Results and Discussion

1. Sputter Deposition of Thin Film CompositesJack Stransky1, Sriram Sundararajan21 Deparment of Chemistry University of Wisconsin - Stout2Department of Mechanical Engineering, Iowa Sate University Results and Discussion • According to previous research1 these settings would deposit a coating of 100nm • Sputter deposition typically produces even films • Atomic Force Microscope –Thin film thickness analysis • Profilometer – Thin film thickness analysis • Tribometer • Frictional and wear force testing of planar thin films • 100 nN minimum normal force • Contact profilometry step height results • Step heights of thin films showed high variance between trials using this method • Showed film thicknesses of hundreds of nanometers with hundred nanometer standard deviation between step heights taken of the same sample • Measurements not considered accurate because it may have measured a buildup of material cause by creation of the step making it not representative of the sample itself Introduction and Motivation Objectives Materials • Ever-growing need for superior coatings able to withstand severe operating conditions, including high temperatures, to have low friction, and to last longer. • Multicomponent coatings can combine desired properties from different components • Multilayer coating • Multiphase coating • Thin films can be produced using various methods such sputter deposition which allows for deposition of layers of different materials. • Depositmultilayer thin films using sputter coating • Titanium Nitride (TiN)3 • Tungsten Disulfide (WS2)1 • Investigate optimal sputter deposition parameters for samples • Perform friction and wear analysis on planar samples and atomic surface analysis of needle samples • Sputtering targets • Titanium Nitride (TiN) - strong, wear resistant, high melting point 3 • Tungsten Disulfide (WS2) - solid state lubricant (low coefficient of friction), high melting point 1 • Methods • Electropolisher – Needle sample preparation • Etches wire to microscale sharpness using an electrolyte • Voltage is applied to electrolyte and wire • Sputter Coater – Thin film deposition • WS2 and TiN targets deposited on glass substrate • Deposition rate unknown • Sputter coater power settings from 100-200 W, argon partial pressure was from 8-16 mTorr, and sputter coating was done for 15 minutes. Figure 3: AFM images of a few nm step in a thin film of WS2 • AFM step height results • Found thin film heights to be~5nm • Growth rate would then be ~1/3 nm/min • Non contact Laser profilometry step height results • Laser profilometer showed much lower step heights as well. • Samples heights found to be ~10nm • Atom probe needle sample preparation • Tips were prepared by etching tungsten wire in 5% NaOH electrolyte while 4V DC was applied for around 15 minutes. 20 tips were made using this method. • Tribometer tests at normal loads of 100,300,500, and 700nN destroyed the probe • Tips intended for atom probe use are unusable for friction and wear testing on the tribometer • Very thin layers of tungsten disulfide were produced • Growth rate was <1nm/min meaning that the thin film thickness of tungsten disulfide can be well controlled through sputter coating. • 1 Scharf, T.W.; Rajendran A.; Banerjee. B.; Sequeda, F. Growth structure and friction behavior of titanium doped tungsten disulphide (Ti-WS2) nanocomposite thin films. Thin Solid Films. 2009,517, 5666-5675. • 2 Miller, M.K Atom Probe Tomography: Analysis at the Atomic Level;Kluwer Academic/Plenum: New York, 2000 • 3 Stone, D. S.; K. B. Yoder; W. D. Sproul "Hardness and elastic modulus of TiN based on continuous indentation technique and new correlation". Journal of Vacuum Science and Technology, 1991,9 2543–2547. Figure 1: Electropolishing schematic 2 Figure 2: Sputter Coating system Figure 4:Atom probe tip at 500x magnification Conclusions References Table 1: Contact profilometer data. Ra and step size are in angstroms