Symmetry Breaking and Spin-Orbit Coupling for Individual Vacancy-Induced In-Gap States in MoS Monolayers.

Spins confined to point defects in atomically thin semiconductors constitute well-defined atomic-scale quantum systems that are being explored as single-photon emitters and spin qubits. Here, we investigate the in-gap electronic structure of individual sulfur vacancies in molybdenum disulfide (MoS) monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb blockade regime. Spectroscopic mapping of defect wave functions reveals an interplay of local symmetry breaking by a charge-state-dependent Jahn-Teller lattice distortion that, when combined with strong (≃100 meV) spin-orbit coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the lattice at low temperature, susceptible to lattice strain.

Near-Unity Emitting, Widely Tailorable, and Stable Exciton Concentrators Built from Doubly Gradient 2D Semiconductor Nanoplatelets.

The strength of electrostatic interactions (EIs) between electrons and holes within semiconductor nanocrystals profoundly affects the performance of their optoelectronic systems, and different optoelectronic devices demand distinct EI strength of the active medium. However, achieving a broad range and fine-tuning of the EI strength for specific optoelectronic applications is a daunting challenge, especially in quasi two-dimensional core-shell semiconductor nanoplatelets (NPLs), as the epitaxial growth of the inorganic shell along the direction of the thickness that solely contributes to the quantum confined effect significantly undermines the strength of the EI. Herein we propose and demonstrate a doubly gradient (DG) core-shell architecture of semiconductor NPLs for on-demand tailoring of the EI strength by controlling the localized exciton concentration via in-plane architectural modulation, demonstrated by a wide tuning of radiative recombination rate and exciton binding energy.

Thermopressure Coupling Effect Mimicking Natural Graphite Formation to Enhance the Storage K-Ion Performance of Carbonaceous Heterostructures.

Borrowing from natural mechanisms for material design can lead to functional mimicry and improvement. Inspired by graphite formation, a thermopressure coupling strategy under micropressure (<400 Pa) is applied to prepare carbon anodes. A thermopressure response is discovered based on the cellulose precursor.

2D Material Infrared Photonics and Plasmonics.

Two-dimensional (2D) materials including graphene, transition metal dichalcogenides, black phosphorus, MXenes, and semimetals have attracted extensive and widespread interest over the past years for their many intriguing properties and phenomena, underlying physics, and great potential for applications. The vast library of 2D materials and their heterostructures provides a diverse range of electrical, photonic, mechanical, and chemical properties with boundless opportunities for photonics and plasmonic devices. The infrared (IR) regime, with wavelengths across 0.

Pressure driven rotational isomerism in 2D hybrid perovskites.

Multilayers consisting of alternating soft and hard layers offer enhanced toughness compared to all-hard structures. However, shear instability usually exists in physically sputtered multilayers because of deformation incompatibility among hard and soft layers. Here, we demonstrate that 2D hybrid organic-inorganic perovskites (HOIP) provide an interesting platform to study the stress-strain behavior of hard and soft layers undulating with molecular scale periodicity.

Reversible Photochromism in ⟨110⟩ Oriented Layered Halide Perovskite.

Extending halide perovskites' optoelectronic properties to stimuli-responsive chromism enables switchable optoelectronics, information display, and smart window applications. Here, we demonstrate a band gap tunability (chromism) via crystal structure transformation from three-dimensional FAPbBr to a ⟨110⟩ oriented FAPbBr structure using a mono-halide/cation composition (FA/Pb) tuning. Furthermore, we illustrate reversible photochromism in halide perovskite by modulating the intermediate phase in the FAPbBr structure, enabling greater control of the optical band gap and luminescence of a ⟨110⟩ oriented mono-halide/cation perovskite.

Layered P3-Type KFeMnTiO as a Low-Cost and Zero-Strain Electrode Material for both Potassium and Sodium Storage.

Layered transition metal oxides are ideal Na/K host materials due to their high theoretical capacities and appropriate working potentials, and the pursuit of cost-effective and environmentally friendly alternatives with high energy density and structural stability has remained a hot topic. Herein, we design and synthesize a low-cost and zero-strain cathode material, P3-type KFeMnTiO, which demonstrates superior properties for both potassium and sodium storage. The cathode delivers a reversible potassium storage capacity of 117 mA h g at 20 mA g and a fast rate capability of 71 mA h g at 1000 mA g.

Formation of Corrugated = 1 2D Tin Iodide Perovskites and Their Use as Lead-Free Solar Absorbers.

Major strides have been made in the development of materials and devices based around low-dimensional hybrid group 14 metal halide perovskites. Thus far, this work has mostly focused on compounds containing highly toxic Pb, with the analogous less toxic Sn materials being comparatively poorly evolved. In response, the study herein aims to (i) provide insight into the impact of templating cations upon the structure of = 1 2D tin iodide perovskites (where refers to the number of contiguous two-dimensional (2D) inorganic layers, , not separated by organic cations) and (ii) examine their potential as light absorbers for photovoltaic (PV) cells.

Strong self-trapping by deformation potential limits photovoltaic performance in bismuth double perovskite.

Bismuth-based double perovskite CsAgBiBr is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.

Electronic States Modulation by Coherent Optical Phonons in 2D Halide Perovskites.

Excitonic effects underpin the fascinating optoelectronic properties of 2D perovskites that are highly favorable for photovoltaics and light-emitting devices. Analogous to switching in transistors, manipulating these excitonic properties in 2D perovskites using coherent phonons could unlock new applications. Presently, a detailed understanding of this underlying mechanism remains modest.

In-plane optical anisotropy in ReS flakes determined by angle-resolved polarized optical contrast spectroscopy.

Various in-plane anisotropic properties are observed for the layered semiconducting transition metal dichalcogenide (TMD), rhenium disulfide (ReS) due to its reduced symmetry. The understanding of these unique anisotropic behaviors in ReS will promote its applications in optoelectronics. In this work, angle-resolved polarized optical contrast spectroscopy has proved to be an efficient, quantitative, and non-destructive method to probe the optical anisotropy in ReS flakes with different thicknesses.

New Metallic Ordered Phase of Perovskite CsPbI under Pressure.

Pressure-induced electronic structure transition from insulating phase to metal state is a potential new paradigm for halide perovskites. The metallization based on these materials may afford a novel motif toward realizing new electronic properties even superconductivity phenomenon. Herein, how static compression modulates the crystal and electronic structure of typical perovskite semiconductors cesium lead iodine (CsPbI) by both experimental and theoretical studies is reported.

Improving Polysulfides Adsorption and Redox Kinetics by the Co N Nanoparticle/N-Doped Carbon Composites for Lithium-Sulfur Batteries.

Improved conductivity and suppressed dissolution of lithium polysulfides is highly desirable for high-performance lithium-sulfur (Li-S) batteries. Herein, by a facile solvent method followed by nitridation with NH , a 2D nitrogen-doped carbon structure is designed with homogeneously embedded Co N nanoparticles derived from metal organic framework (MOF), grown on the carbon cloth (MOF-Co N). Experimental results and theoretical simulations reveal that Co N nanoparticles act as strong chemical adsorption hosts and catalysts that not only improve the cycling performance of Li-S batteries via chemical bonding to trap polysulfides but also improve the rate performance through accelerating the conversion reactions by decreasing the polarization of the electrode.

Double-Shelled Phosphorus and Nitrogen Codoped Carbon Nanospheres as Efficient Polysulfide Mediator for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries are regarded as very promising energy storage devices due to their high energy density, low cost, and environmental friendliness; however, their insulating properties and the instability of sulfur-based electrodes impede the practical applications of Li-S batteries. Here, a versatile strategy to synthesize double-shelled nitrogen and phosphorus codoped carbon spheres (NPDSCS) as an efficient sulfur host for Li-S batteries is reported. With strong trapping, good affinity, high adsorption for polysulfides, and the bifunctional catalyzing for sulfur redox processes, the developed NPDSCS cathodes with a high S loading of 72.

Coherent Spin and Quasiparticle Dynamics in Solution-Processed Layered 2D Lead Halide Perovskites.

Layered 2D halide perovskites with their alternating organic and inorganic atomic layers that form a self-assembled quantum well system are analogues of the purely inorganic 2D transition metal dichalcogenides. Within their periodic structures lie a hotbed of photophysical phenomena such as dielectric confinement effect, optical Stark effect, strong exciton-photon coupling, etc. Detailed understanding into the strong light-matter interactions in these hybrid organic-inorganic semiconductor systems remains modest.

Advanced Energy Storage Devices: Basic Principles, Analytical Methods, and Rational Materials Design.

Tremendous efforts have been dedicated into the development of high-performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery-like behavior depending on the electrode design and the charge storage guest ions.

High-Pressure-Induced Comminution and Recrystallization of CH NH PbBr Nanocrystals as Large Thin Nanoplates.

High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane.

Pressure-Induced Phase Transition in Weyl Semimetallic WTe.

Tungsten ditelluride (WTe ) is a semimetal with orthorhombic T phase that possesses some unique properties such as Weyl semimetal states, pressure-induced superconductivity, and giant magnetoresistance. Here, the high-pressure properties of WTe single crystals are investigated by Raman microspectroscopy and ab initio calculations. WTe shows strong plane-parallel/plane-vertical vibrational anisotropy, stemming from its intrinsic Raman tensor.

Ordered and Atomically Perfect Fragmentation of Layered Transition Metal Dichalcogenides via Mechanical Instabilities.

Thermoplastic polymers subjected to a continuous tensile stress experience a state of mechanical instabilities, resulting in neck formation and propagation. The necking process with strong localized strain enables the transformation of initially brittle polymeric materials into robust, flexible, and oriented forms. Here we harness the polymer-based mechanical instabilities to control the fragmentation of atomically thin transition metal dichalcogenides (TMDs).

Phase evolution of lithium intercalation dynamics in 2H-MoS.

Due to the easy intralayer gliding and weak interlayer van der Waals interaction in transition metal dichalcogenides (TMDs), ion (particularly Li) intercalation has been used to modify and tune their atomic structures to obtain the desired optical, electronic and chemical properties for future optoelectronics and energy storage applications. A good understanding of the transformative structures during intercalation is critical. In this paper, we investigate the structural transformation dynamics of 2H-MoS using electrochemical Li intercalation for 2H-MoS.

"Electron/Ion Sponge"-Like V-Based Polyoxometalate: Toward High-Performance Cathode for Rechargeable Sodium Ion Batteries.

One key challenge facing room temperature Na-ion batteries lies in identifying earth-abundant, environmentally friendly and safe materials that can provide efficient Na storage sites in Na-ion batteries. Herein, we report such a material, polyoxometalate NaH[MnVO] (NMV), with entirely different composition and structure from those cathode compounds reported before. Ex-situ XPS and FTIR analyses reveal that NMV cathode behaves like an "electron/Na-ion sponge", with 11 electrons/Na acceptability per mole, which has a decisive contribution to the high capacity.

Water-Responsive Shape Recovery Induced Buckling in Biodegradable Photo-Cross-Linked Poly(ethylene glycol) (PEG) Hydrogel.

The phenomenon of recovering the permanent shape from a severely deformed temporary shape, but only in the presence of the right stimulus, is known as the shape memory effect (SME). Materials with such an interesting effect are known as shape memory materials (SMMs). Typical stimuli to trigger shape recovery include temperature (heating or cooling), chemical (including water/moisture and pH value), and light.