MoTe2 is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries; the semiconducting trigonal-prismatic 2H−phase, the semimetallic 1T ′ monoclinic phase, and the semimetallic orthorhombic T d structure 1-4 . The 2H−phase displays a band gap of ∼ 1 eV 5 making it appealing for flexible and transparent optoelectronics. The T d−phase is predicted to possess unique topological properties 6-9 which might lead to topologically protected non-dissipative transport channels 9 . Recently, it was argued that it is possible to locally induce phasetransformations in TMDs 3,10,11,14 , through chemical doping 12 , local heating 13 , or electric-field 14,15 to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements 11 . The combination of semiconducting and topological elements based upon the same compound, might produce a new generation of high performance, low dissipation optoelectronic elements. Here, we show that it is possible to engineer the phases of MoTe2 through W substitution by unveiling the phase-diagram of the Mo1−xWxTe2 solid solution which displays a semiconducting to semimetallic transition as a function of x. We find that only ∼ 8 % of W stabilizes the T d−phase at room temperature. Photoemission spectroscopy, indicates that this phase possesses a Fermi surface akin to that of WTe2 16 .The properties of semiconducting and of semimetallic MoTe 2 are of fundamental interest in their own right, but are also for their potential technological relevance. In the mono-or few-layer limit it is a direct-gap semiconductor, while the bulk has an indirect bandgap 5,17,18 of ∼ 1 eV. The size of the gap is similar to that of Si, making 2H−MoTe 2 particularly appealing for both purely electronic devices 19,20 and optoelectronic applications 21 . Moreover, the existence of different phases opens up the possibility for many novel devices and architectures. For example, controlled conversion of the 1T ′ −MoTe 2 phase to the 2H−phase, as recently reported 22 , could

Two-dimensional lateral heterojunctions based on monolayer transition-metal dichalcogenides (TMDs) have received increasing attention given that their direct band gap makes them very attractive for optoelectronic applications. Although bilayer TMDs present an indirect band gap, their electrical properties are expected to be less susceptible to ambient conditions, with higher mobilities and density of states when compared to monolayers. Bilayers and few-layers single domain devices have already demonstrated higher performance in radio frequency and photosensing applications. Despite these advantages, lateral heterostructures based on bilayer domains have been less explored. Here, we report the controlled synthesis of multi-junction bilayer lateral heterostructures based on MoS 2 -WS 2 and MoSe 2 -WSe 2 monodomains. The heterojunctions are created via sequential lateral edge-epitaxy that happens simultaneously in both the first and the second layers. A phenomenological mechanism is proposed to explain the growth mode with self-limited thickness that happens within a certain window of growth conditions. With respect to their as-grown monolayer counterparts, bilayer lateral heterostructures yield nearly 1 order of magnitude higher rectification currents. They also display a clear photovoltaic response, with short circuit currents ∼10 3 times larger than those extracted from the as-grown monolayers, in addition to room-temperature electroluminescence. The improved performance of bilayer heterostructures significantly expands the potential of two-dimensional materials for optoelectronics.

We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects. In high quality single crystals of both compounds, i.e. displaying carrier mobilities between 10 3 and 10 4 cm 2 /Vs, we observed a large non-saturating magnetoresistivity (MR) which in PtTe2 at a temperature T = 1.3 K, leads to an increase in the resistivity up to 5 × 10 4 % under a magnetic field µ0H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show an excellent agreement with those resulting from band-structure calculations. Surprisingly, this is not the case for PtTe2 whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides a strong support for the existence of a Dirac type-II node in PdTe2 and probably also for PtTe2. Band structure calculations indicate that the topologically non-trivial bands of PtTe2 do not cross the Fermi-level (εF). In contrast, for PdTe2 the Dirac type-II cone does intersect εF , although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to the one of the Dirac type-II node. Therefore it should yield a trivial Berry-phase.