PNNL

Abstract

The high bias behavior of mono- and few-layer WS2 is explored by in situ aberration corrected transmission electron microscopy (AC-TEM). The suspended WS2 devices were found to undergo irreversible breakdown at sufficiently high biases, however simultaneous to the removal of WS2 was the accompanying formation of few-layer graphene decorated with W and WS2 nanoparticles. The breakdown of few-layer WS2 resulted in the formation of facetted 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; 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. The observation of graphene formation, and the role the thin amorphous carbon layer has in the pre-breakdown behavior of the device, demonstrate the importance of employing encapsulated heterostructure device architectures that exclude residues.