Recently, two-dimensional materials such as molybdenum disulphide (MoS2) have been demonstrated to realize field effect transistors (FET) with a large current on-off ratio. However, the carrier mobility in backgate MoS2 FET is rather low (typically 0.5–20 cm2/V·s). Here, we report a novel field-effect Schottky barrier transistors (FESBT) based on graphene-MoS2 heterojunction (GMH), where the characteristics of high mobility from graphene and high on-off ratio from MoS2 are properly balanced in the novel transistors. Large modulation on the device current (on/off ratio of 105) is achieved by adjusting the backgate (through 300 nm SiO2) voltage to modulate the graphene-MoS2 Schottky barrier. Moreover, the field effective mobility of the FESBT is up to 58.7 cm2/V·s. Our theoretical analysis shows that if the thickness of oxide is further reduced, a subthreshold swing (SS) of 40 mV/decade can be maintained within three orders of drain current at room temperature. This provides an opportunity to overcome the limitation of 60 mV/decade for conventional CMOS devices. The FESBT implemented with a high on-off ratio, a relatively high mobility and a low subthreshold promises low-voltage and low-power applications for future electronics.

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.

Although nitrogen-containing group-directed cyclopalladation reactions have been well-known, Pd(II) insertion into C-H bonds promoted by coordination of an oxygen-only group to the palladium remains rather rare. In the present study, the first cyclopalladation complex formed from a simple phenol ester was characterized by X-ray crystallography. A promising protocol for the ortho C-H activation/aryl-aryl coupling of phenol esters that was not sensitive to moisture or air was then established. The utility of the reaction was demonstrated for the synthesis of useful phenol derivatives.