Memristive Phenomena in Polycrystalline Single Layer MoS$_{2}$

Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, ultrathin transition metal dichalcogenides (e.g. MoS$_{2})$ present a host of attractive features such as high carrier mobility and tunable band-gap. However, available growth methods produce polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions.[1] In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS$_{2}$ transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS$_{2}$. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to \textasciitilde 10$^{3}$.[1] Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Correlated electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism. \textit{Refs: 1. Sangwan et al., Nature Nanotech, 10 403 (2015) }