A direct atomic layer deposition method for growth of ultra-thin lubricant tungsten disulfide films

We describe a direct atomic layer deposition method to grow lubricant tungsten disulfide (WS2) films. The WS2 films were deposited on a Si (100) substrate and a zinc sulfide (ZnS) film coated the Si (100) substrate using tungsten hexacarbonyl and hydrogen sulfide as precursors. The ZnS film served as an intermediate layer to facilitate the nucleation and growth of the WS2 films. The thickness of the WS2 films was measured via scanning electron microscope, the microstructure was probed with an X-ray diffractometer and a transmission electron microscope. The friction coefficient was measured with a ball-on-disk tester under dry nitrogen. The results reveal that the WS2 films deposited on both substrates are similar to 175 nm and have (002) and (101) crystal orientations. The WS2 film deposited on the ZnS coated Si substrate exhibits a stronger (002) orientation and a denser crystal structure than that deposited on the Si substrate. The WS2 films on both substrates have low friction coefficients. However, due to the stronger (002) orientation and denser crystal structure, the friction coefficient of the WS2 film deposited on ZnS coated Si substrate is smaller with longer wear life.