Two-dimensional layered semiconductors have recently emerged as attractive building blocks for next-generation low-power non-volatile memories. However, Hongzhou Zhang: hozhang@tcd.ie 1 arXiv:1811.09545v1 [cond-mat.mtrl-sci] 23 Nov 2018 † J.J. and D.K. contributed equally to this project. D.K. performed electrical measurements on samples of different layer thickness and irradiation dose, as well as atomic force microscopy and scanning electron microscopy. CVD growth of MoS 2 monolayers was carried out by C.P.C. Mechanically-exfoliated devices were prepared by J.J. and D.K. Raman and PL spectroscopy was carried out by C.P.C. and analysed by P.M.. J.J and D.K. carried out EBL to fabricate the FET devices. H.S. assisted with fabrication and wirebonding of devices tested in Peking University (PKU). D.K., J.J. and P.M. carried out the HIM irradiations in Trinity College Dublin (TCD) while J.J and Y.Z. conducted the HIM exposures in PKU. J.J carried out the electrical tests (endurance and potentiation) with assistance from H.S and Y.Z in PKU. P.M. performed FIB processing of irradiated devices and carried out TEM of the cross-sectioned lamellae with assistance from C.D.. D.S.F. carried out helium exposures and TEM imaging of the plan-view irradiated devices after J.J. transferred the samples onto TEM grids. Z.L. oversaw the electrical characterisation work in PKU, while R.Z. and J.X. facilitated microscopy experiments in PKU. N.M and G.S.D. oversaw the material growth process and spectroscopic experiments in TCD. J.J.B. and H.Z. conceived the study and supervised the project. The manuscript was written by J.J., D.K. and P.M. All authors agreed with the final version of the paper.

Time-controlled plasma treatment of MoS2 FETs improves carrier transport due to the presence of a two-dimensional oxide phase.

Precise and scalable defect engineering of 2D nanomaterials is acutely sought-after in contemporary materials science. Here we present defect engineering in monolayer graphene and molybdenum disulfide (MoS2) by irradiation with noble gas ions at 30 keV. Two ion species of different masses were used in a gas field ion source microscope: helium (He + ) and neon (Ne + ). A detailed study of the introduced defect sizes and resulting inter-defect distance with escalating ion dose was performed using Raman spectroscopy. Expanding on existing models, we found that the average defect size is considerably smaller for supported than freestanding graphene and that the rate of defect production is larger. We conclude that secondary atoms from the substrate play a significant role in defect production, creating smaller defects relative to those created by the primary ion beam. Furthermore, a similar model was also applied to supported MoS2, another promising member of the 2D material family. Defect yields for both ions were obtained for MoS2, demonstrating their different interaction with the material and facilitating comparison with other irradiation conditions in the literature.