Electrical Breakdown of Suspended Mono- and Few-Layer Tungsten Disulfide via Sulfur Depletion Identified by in Situ Atomic Imaging

The high-bias and breakdown behavior of suspended mono- and few-layer WS 2 was explored by in situ aberration-corrected transmission electron microscopy. The suspended WS 2 devices were found to undergo irreversible breakdown at sufficiently high biases due to vaporization of the WS 2 . Simultaneous to the removal of WS 2 was the accompanying formation of few-layer graphene decorated with W and WS 2 nanoparticles, with the carbon source attributed to organic residues present on the WS 2 surface. The breakdown of few-layer WS 2 resulted in the formation of faceted S-depleted WS 2 endrils along the vaporization boundary, which were found to exhibit lattice contraction indicative of S depletion, alongside pure W phases incorporated into the structure, with the interfaces imaged at atomic resolution. The combination of observing the graphitization of the amorphous carbon surface residue, W nanoparticles, and S-depleted WS 2 phases following the high-bias WS 2 disintegration all indicate a thermal Joule heating breakdown mechanism over an avalanche process, with WS 2 destruction promoted by preferential S emission. The observation of graphene formation and the role the thin amorphous carbon layer has in the prebreakdown behavior of the device demonstrate the importance of employing encapsulated heterostructure device architectures that exclude residues.