The use of reactive electropositive metal contacts is proposed to lower contact resistance in MoS2 devices, based on calculations of the sulfur vacancy in MoS2 by the screened exchange (sX) hybrid functional. sX gives band gaps of 1.88 eV and 1.34 eV for monolayer and bulk MoS2. The S vacancy has a formation energy of 2.35 eV in S-rich conditions, while the Mo vacancy has a large formation energy of 8.02 eV in Mo-rich conditions. The S vacancy introduces defect levels 0/−1 at 1.23 eV and −1/−2 at 1.28 eV in the upper gap. Its formation energy becomes small or negative for EF near the conduction band edge, leading to EF pinning near the conduction band for reactive metal contacts and lower contact resistances.

The use of two dimensional (2D) materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academy and industry. While the research on 2D metallic and semiconducting materials is well established, the knowledge and 2 applications of 2D insulators are still very scarce. In this report we study the presence of resistive switching (RS) in multilayer hexagonal boron nitride (h-BN) using different electrode materials, and we engineer a family of h-BN based resistive random access memories with tunable capabilities.The devices show the coexistence of forming-free bipolar and threshold type RS with low operation voltages down to 0.4 V, high current on/off ratios up to 10 6 , long retention times above 10 hours, as well as low variability. The RS is driven by the grain boundaries (GBs) in the polycrystalline h-BN stack, which allow the penetration of metallic ions from adjacent electrodes. This reaction can be boosted by the generation of B vacancies, which is more abundant at the GBs. To the best of our knowledge, h-BN is the first 2D material showing the coexistance of bipolar and threshold RS, which may open the door to additional functionalities and applications.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

The transition metal dichalcogenides (TMDs) are two-dimensional layered solids with van der Waals bonding between layers. We calculate their Schottky barrier heights (SBHs) using supercell models and density functional theory. It is found that the SBHs without defects are quite strongly pinned, with a pinning factor S of about S=0.3, a similar value for both top and edge contact geometries. This arises because there is direct bonding between the contact metal atoms and the TMD chalcogen atoms, for both top and edge contact geometries, despite the weak interlayer bonding in the isolated materials. The Schottky barriers largely follow the metal induced gap state (MIGS) model, like those of three-dimensional semiconductors, despite the bonding in the TMDs being largely constrained within the layers. The pinning energies are found to be lower in the gap for edge contact geometries than for top contact geometries, which might be used to obtain p-type contacts on MoS 2 .

Lead halide perovskites have emerged as low-cost, high-performance optical and optoelectronic materials, however, their material stability has been a limiting factor for broad applications. Here, we demonstrate stable core-shell colloidal perovskite nanocrystals using a novel, facile and low-cost copolymer templated synthesis approach. The block copolymer serves as a confined nanoreactor during perovskite crystallization and passivates the perovskite surface by forming a multidentate capping shell, thus significantly improving its photostability in polar solvents. Meanwhile, the polymer nanoshell provides an additional layer for further surface modifications, paving the way to functional nanodevices that can be self-assembled or lithographically defined.