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 WS₂ was explored by in situ aberration-corrected transmission electron microscopy. The suspended WS₂ devices were found to undergo irreversible breakdown at sufficiently high biases due to vaporization of the WS₂. Simultaneous to the removal of WS₂ was the accompanying formation of few-layer graphene decorated with W and WS₂ nanoparticles, with the carbon source attributed to organic residues present on the WS₂ surface. The breakdown of few-layer WS₂ resulted in the formation of faceted S-depleted WS₂ tendrils 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 WS₂ phases following the high-bias WS₂ disintegration all indicate a thermal Joule heating breakdown mechanism over an avalanche process, with WS₂ 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.