We report ambipolar charge transport in α-molybdenum ditelluride (MoTe2 ) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (Vbg) and drain-source voltage (Vds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications.

Two-dimensional layered crystals could show phonon properties that are markedly distinct from those of their bulk counterparts, because of the loss of periodicities along the c-axis directions. Here we investigate the phonon properties of bulk and atomically thin α-MoTe2 using Raman spectroscopy. The Raman spectrum of α-MoTe2 shows a prominent peak of the in-plane E(1)2g mode, with its frequency upshifting with decreasing thickness down to the atomic scale, similar to other dichalcogenides. Furthermore, we find large enhancement of the Raman scattering from the out-of-plane B(1)2g mode in the atomically thin layers. The B(1)2g mode is Raman inactive in the bulk, but is observed to become active in the few-layer films. The intensity ratio of the B(1)2g to E(1)2g peaks evolves significantly with decreasing thickness, in contrast with other dichalcogenides. Our observations point to strong effects of dimensionality on the phonon properties of MoTe2.

graphene in 2004, diverse layered transition metal dichalcogenides with tunable band gaps have been shown to exhibit extraordinary electrical and optical properties in logic circuits, photodetectors, light-emitting diodes, gas sensors, and energy storage devices. [7][8][9][10][11][12][13][14] However, owing to their low mobility ceiling of a few hundred cm 2 V −1 s −1 , 2D-based fieldeffect transistors (FETs) still encounter a bottleneck for their application in highfrequency electronic devices. In this regard, indium selenide (InSe), with ultrahigh mobility near 1000 cm 2 V −1 s −1 at room temperature, has successfully attracted attention as one of the burgeoning III-VI group layered metal chalcogenides. The van der Waals layered Se-In-In-Se stacked structure, with a smooth surface and narrow band gap (1.26 eV), exhibits a perfect photoresponse to the visible spectrum. [15][16][17][18] Recent studies, which have focused on gating engineering with graphene, a passivation layer with hexagonal boron nitride or a self-assembled monolayer, and contact engineering with low work-function electrodes, have demonstrated that layered InSe possesses an intrinsically excellent charge transport and optoelectronic performance that are comparable with majority of 2D materials. [19][20][21][22][23][24][25] For instance, Wang Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm 2 V −1 s −1 at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices. InSe TransistorsBecause of the down scaling limit of silicon-based devices, 2D materials with prominent mechanical flexibility and carrier transport performance have provided significant potential for their use in the new generation atomic electronic devices. [1][2][3][4][5][6] Following in the footsteps of the discovery of monolayer