Tribological Behavior of Few-Nanometer-Thick Mos2 Prepared by Low-Temperature Conversion of Atomic Layer Deposited Moox Films

Abstract

Molybdenum disulfide (MoS2) is a popular lamellar material with desirable properties who’s form, and function can vary widely, from particles to monolayer/micron thick films and applications in semiconductors to aerospace lubricants and many more.  Physical vapor deposition (PVD) is commonly used to produce dense, conformal micron thick MoS2 coatings, but lacks the ability to coat more complex geometries due to line-of-sight constraints and typically exhibit amorphous or nanocrystalline microstructures.  Atomic layer deposition (ALD) has also been employed to deposit monolayer to 10’s of nanometers thick lamellar solids like MoS2 & WS2 in transistor, sensors or electrocatalyst applications but not commonly for applications as solid lubricants in aerospace like their PVD counterparts. While recent work has shown that ALD MoS2 can exhibit favorable microstructures for solid lubricant applications and allows for non-line of sight deposition on complex geometries, it has not been widely adopted due to high deposition temperatures (>500 ⁰C) that can lead to softening of steel substrates. In this work, we show one of the first applications highlighting the use of ultra-thin (5-10 nm) low temperature (~250 ⁰C) MoS2 coatings as a promising solid lubricant for macroscale mechanical interfaces. Post-deposition chemical conversion of ALD MoOx to MoS2 by annealing in H2S at temperatures ranging from 200 – 550 ⁰C resulted in highly-ordered basally-oriented surface microstructures. The results from this work suggest that converted-ALD MoS2 coatings can serve as viable solid lubricants for aerospace applications requiring low-temperature processing, including those with complex geometries.

Keywords: MoS2, Atomic Layer Deposition, Low Friction, Low Temperature Conversion