A Janus MoSSe monolayer, synthesized recently though the chemical vapor deposition method [A. Y. Lu, H. Zhu, J. Xiao, C. P. Chuu, Y. Han, M. H. Chiu, C. C. Cheng, C. W. Yang, K. H. Wei Y. Yang, Y. Wang, D. Sokaras, D. Nordlund, P. Yang, D. A. Muller, M. Y. Chou, X. Zhang and L. J. Li, Nat. Nanotechnol., 2017, 12, 744-749], has drawn considerable attention as a new two-dimensional (2D) material owing to its fascinating electronic and optical properties. In this study, based on first-principles calculations, we systematically explore for the first time the performance of Janus MoSSe monolayers as a channel material contacting with graphene to form van der Waals (vdW) heterostructures. Our calculations show that the intrinsic electronic properties of both the graphene and MoSSe monolayer are preserved well in our proposed two graphene/MoSSe heterostructures (i.e. G/SMoSe and G/SeMoS heterostructures), and n-type Schottky contacts with a small Schottky barrier height (SBH) are formed at their respective interfaces. An analytical model is presented for the barrier heights. Moreover, the n-type Schottky barrier at the G/SMoSe heterostructure interface can be reduced by increasing the interlayer distance and can even be changed to an Ohmic contact by applying a negative electric field. More interestingly, varying the interlayer distance or applying an external electric field can effectively modulate the Schottky barrier and the Schottky contact (n-type and p-type) of the G/SeMoS heterostructure interface. These theoretical findings not only provide insights into the fundamental properties of the graphene/MoSSe interfaces but also open the possibility of designing high-performance field-effect transistors (FETs) based on the graphene/MoSSe heterostructures.

In this work, the core‐shelled Sb@Sb2O3 heterostructure encapsulated in 3D N‐doped carbon hollow‐spheres is fabricated by spray‐drying combined with heat treatment. The novel core‐shelled heterostructures of Sb@Sb2O3 possess a mass of heterointerfaces, which formed spontaneously at the core‐shell contact via annealing oxidation and can promote the rapid Na+/K+ transfer. The density functional theory calculations revealed the mechanism and significance of Na/K‐storage for the core‐shelled Sb@Sb2O3 heterostructure, which validated that the coupling between the high‐conductivity of Sb and the stability of Sb2O3 can relieve the shortcomings of the individual building blocks, thereby enhancing the Na/K‐storage capacity. Furthermore, the core‐shell structure embedded in the 3D carbon framework with robust structure can further increase the electrode mechanical strength and thus buffer the severe volume changes upon cycling. As a result, such composite architecture exhibited a high specific capacity of ≈573 mA h g−1 for sodium‐ion battery (SIB) anode and ≈474 mA h g−1 for potassium‐ion battery (PIB) anode at 100 mA g−1, and superior rate performance (302 mA h g−1 at 30 A g−1 for SIB anode, while 239 mA h g−1 at 5 A g−1 for PIB anode).

Schematic of the WS2/MnO2 heterostructure for valleytronic devices and the diagram of the anomalous valley Hall effect.

The surface potential (SP) variations in mono and multilayer molybdenum disulfide (MoS) are visualized in situ and detected using Kelvin probe force microscopy (KPFM) in different humidity conditions for the first time. N-type doping, which originates from the SiO substrate, is discovered in the exfoliated MoS and is accompanied by a screening length of five layers. The influence of water, which serves as an environmental gating for MoS, is investigated by controlling the relative humidities (RHs) in the environmental chamber. A monotonic decrease in the SP is observed when the threshold concentration is achieved. This corresponds to the Fermi level variation, which is dominated by different processes. The results also indicate that water adsorption could result in MoS p-type doping and provide compensation that partially counteracts the substrate effect. Under this condition, the interlayer screening effect is influenced because of the water dipole-induced electric field. Density functional theory calculations are performed to determine the band structure variations and the interactions between water molecules and between water molecules and the MoS surface in mono and trilayer MoS under different RHs. The calculations are in excellent agreement with the experimental results. We propose that in situ measurements of the SP using KPFM under different environmental regimes is a noninvasive and effective method to provide real-time visualization and detection of electronic property variations in two-dimensional materials.

Both synaptic emulators and brain-like calculation demand an energy-efficient and bio-realistic device where two-dimensional materials have been proven as a promising competitor. Lateral memristors based on transfer-free single-crystal MoS 2 with single layer grown by chemical vapor deposition (CVD) were fabricated. Here the MoS 2 memristor successfully emulates typical biological synaptic behaviors including excitatory/inhibitory post-synaptic current (EPSC/IPSC), spike timing-dependent plasticity (STDP), spike rate-dependent plasticity (SRDP) and long-term plasticity (LTP). Moreover, an interesting multi-state LTP and a low consumption of 1.8 pJ after LTP process are achieved which is attributed to the high resistance of transfer-free single-crystal monolayer MoS 2 , representing a low value among previous MoS 2 devices. The migration of Sulfur vacancies lead the conductance modulation by changing the Schottky barrier instead of forming a filament. Our work demonstrates that MoS 2 memristors can more flexibly satisfy the demands of complex artificial synaptic/neuron applications.