Due to the intriguing optical and electronic properties, 2D materials have attracted a lot of interest for the electronic and optoelectronic applications. Identifying new promising 2D materials will be rewarding toward the development of next generation 2D electronics. Here, palladium diselenide (PdSe ), a noble-transition metal dichalcogenide (TMDC), is introduced as a promising high mobility 2D material into the fast growing 2D community. Field-effect transistors (FETs) based on ultrathin PdSe show intrinsic ambipolar characteristic. The polarity of the FET can be tuned. After vacuum annealing, the authors find PdSe to exhibit electron-dominated transport with high mobility (µ = 216 cm V s ) and on/off ratio up to 10 . Hole-dominated-transport PdSe can be obtained by molecular doping using F -TCNQ. This pioneer work on PdSe will spark interests in the less explored regime of noble-TMDCs.

Honeycomb-like MoS2 nanoarchitectures anchored into 3D graphene foam are successfully fabricated as a high-performance positive electrode for enhanced Li-ion storage. The unique 3D interpenetrating honeycomb-like structure is the key to the high performance. High reversible capacity, superior high-rate capability, and excellent cycling stability are demonstrated.

The development of portable and wearable electronics has promoted increasing demand for high-performance power sources with high energy/power density, low cost, lightweight, as well as ultrathin and flexible features. Here, a new type of flexible Ni/Fe cell is designed and fabricated by employing Ni(OH)2 nanosheets and porous Fe2O3 nanorods grown on lightweight graphene foam (GF)/carbon nanotubes (CNTs) hybrid films as electrodes. The assembled f-Ni/Fe cells are able to deliver high energy/power densities (100.7 Wh/kg at 287 W/kg and 70.9 Wh/kg at 1.4 kW/kg, based on the total mass of active materials) and outstanding cycling stabilities (retention 89.1% after 1000 charge/discharge cycles). Benefiting from the use of ultralight and thin GF/CNTs hybrid films as current collectors, our f-Ni/Fe cell can exhibit a volumetric energy density of 16.6 Wh/l (based on the total volume of full cell), which is comparable to that of thin film battery and better than that of typical commercial supercapacitors. Moreover, the f-Ni/Fe cells can retain the electrochemical performance with repeated bendings. These features endow our f-Ni/Fe cells a highly promising candidate for next generation flexible energy storage systems.

The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibit distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin-orbit coupling (SOC) and interlayer coupling in different structural symmetries. Such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS2 blocks.

Hydrogen bonding exists in all hybrid organic–inorganic lead halide perovskites MAPbX3 (X = Cl, Br, or I). It has a strong influence on the structure, stability, and electronic and optical properties of this perovskite family. The hydrogen-bonding state between the H atoms of the methylammonium (MA) cation and the halide ions is resolved by combining ab initio calculations with temperature-dependent Raman scattering and powder X-ray diffraction measurements on MAPbBr3 hybrid perovskites. When the compounds are cooled, the H-bonding in the NH3 end of the MA group shows sequential changes while the H atoms in the CH3 end form H bonds with only the Br ions in the orthorhombic phase, leading to a decrease in the degree of rotational freedom of MA and a narrowing for MA Raman modes. Hydrogen bonding drives the evolution of temperature-dependent rotations of the MA cation and the concomitant tilting of PbX6 octahedra with the consequent dynamical change in the electronic band structures, from indirect bandgap to direct bandgap along with ∼60-fold PL emission enhancement upon cooling. We experimentally and theoretically reveal the evolution of hydrogen bonding during polymorphic transformations and how the different types of hydrogen bonding lead to specific optoelectronic properties and device applications of hybrid perovskites.