The solar-assisted oxidation of water is an essential half reaction for achieving a complete cycle of water splitting. nanosheets results in a 10-fold increase in incident-photon-to-current-efficiency compared to the individual constituents. This proves that charge carrier lifetime is tailorable in atomically thin crystals by creating heterojunctions of different compositions and architectures. Our results suggest that the MoS 2 and WS 2 nanosheets and their bulk heterojunction blend are interesting photocatalytic systems for water oxidation, which can be coupled with different reduction processes for solar-fuel production.

We demonstrate strong anisotropic spin-orbit interaction (SOI) in graphene induced by monolayer WS_{2}. Direct comparison between graphene-monolayer WS_{2} and graphene-bulk WS_{2} systems in magnetotransport measurements reveals that monolayer transition metal dichalcogenide can induce much stronger SOI than bulk. Detailed theoretical analysis of the weak antilocalization curves gives an estimated spin-orbit energy (E_{so}) higher than 10 meV. The symmetry of the induced SOI is also discussed, and the dominant z→-z symmetric SOI can only explain the experimental results. Spin relaxation by the Elliot-Yafet mechanism and anomalous resistance increase with temperature close to the Dirac point indicates Kane-Mele SOI induced in graphene.

The rise of atomically thin materials has the potential to enable a paradigm shift in modern technologies by introducing multi-functional materials in the semiconductor industry. To date the growth of high quality atomically thin semiconductors (e.g. WS2) is one of the most pressing challenges to unleash the potential of these materials and the growth of mono- or bi-layers with high crystal quality is yet to see its full realization. Here, we show that the novel use of molecular precursors in the controlled synthesis of mono- and bi-layer WS2 leads to superior material quality compared to the widely used direct sulfidization of WO3-based precursors. Record high room temperature charge carrier mobility up to 52 cm2/Vs and ultra-sharp photoluminescence linewidth of just 36 meV over submillimeter areas demonstrate that the quality of this material supersedes also that of naturally occurring materials. By exploiting surface diffusion kinetics of W and S species adsorbed onto a substrate, a deterministic layer thickness control has also been achieved promoting the design of scalable synthesis routes.

We report a systematic study on strong enhancement of spin-orbit interaction (SOI) in graphene induced by transition-metal dichalcogenides (TMDs). Low temperature magnetotoransport measurements of graphene proximitized to different TMDs (monolayer and bulk WSe2, WS2 and monolayer MoS2) all exhibit weak antilocalization peaks, a signature of strong SOI induced in graphene. The amplitudes of the induced SOI are different for different materials and thickness, and we find that monolayer WSe2 and WS2 can induce much stronger SOI than bulk WSe2, WS2 and monolayer MoS2. The estimated spin-orbit (SO) scattering strength for graphene/monolayer WSe2 and graphene/monolayer WS2 reaches ∼ 10 meV whereas for graphene/bulk WSe2, graphene/bulk WS2 and graphene/monolayer MoS2 it is around 1 meV or less. We also discuss the symmetry and type of the induced SOI in detail, especially focusing on the identification of intrinsic (Kane-Mele) and valley-Zeeman (VZ) SOI by determining the dominant spin relaxation mechanism. Our findings pave the way for realizing the quantum spin Hall (QSH) state in graphene.

The emerging family of atomically thin materials is fueling the development of conceptually new technologies [1] in highly efficient optoelectronics [2,3] and photonic applications, [4] to name a few. The large variety of bandgap values found in layered transition-metal dichalcogenides (TMDCs) [5,6] make these materials especially suited for transistor applications. TMDCs are compounds with the general formula MX 2 , where M is a transition metal, e.g., Mo and W, and X is an element of the chalcogen group, S, Se, and Te. They appear in a layered structure where the metal forms a hexagonal plane and the chalcogenides are positioned over and under this plane in either a trigonal prismatic (2H), as shown in Figure 1a, or octahedral (1T) stacking configuration. [7] In the semiconducting 2H systems, the compounds show a transition from indirect bandgap in bulk materials to direct bandgap in single layers. [8] Transient currents in atomically thin MoTe 2 field-effect transistors (FETs) are measured during cycles of pulses through the gate electrode. The curves of the transient currents are analyzed in light of a newly proposed model for charge-trapping dynamics that renders a time-dependent change in the threshold voltage as the dominant effect on the channel hysteretic behavior over emission currents from the charge traps. The proposed model is expected to be instrumental in understanding the fundamental physics that governs the performance of atomically thin FETs and is applicable to the entire class of atomically thin-based devices. Hence, the model is vital to the intelligent design of fast and highly efficient optoelectronic devices.Single-and few-layered TMDCs have been implemented in a wide range of applications, ranging from thin film transistors, [9] digital electronics and optoelectronics, [2,10,11] flexible electronics, [12] and up to energy conversion and storage devices. [13] However, the defect states in TMDCs have an ambivalent nature and can have a major positive or negative impact on the performance of atomically thin devices. The presence of defects in photodetectors can be beneficial since it has been shown to immobilize charges at the channel which improves the gain in photodetectors [14] and produces nonvolatile memory mechanisms. [15] On the other hand, large hysteresis caused, for example, by charge traps [2] and significant Schottky barriers [16] at the metal-semiconductor interface are still a major design challenge for the realization of novel device architectures. They have been shown to cause degradation in the performance of transistors [17] and generate high levels of flicker noise. [18,19] To overcome these challenges, hysteresis is usually avoided by encapsulation [20,21] or operation under high vacuum. [22,23] Most of the current research into surface states of TMDCs has focused on the chemical origins of charge trapping. A full understanding of their effect on the electrical properties is still lacking, hindering the optimization of functional components. While hysteresis has been sho...