Ultrafast nonequilibrium dynamics of strongly coupled resonances in the intrinsic cavity of W S 2 nanotubes

This paper presents a femtosecond optical pump-probe study of the non-equilibrium behavior of the coupled optical resonances in semiconducting WS2. The authors focus on the transient optical response of WS2 nanotubes and show that it arises primarily from the photoinduced shifts of the exciton and trion resonances due to band gap renormalization and screening of the Coulomb interaction providing the exciton and trion binding energy

Charge trapping and coalescence dynamics in few layer MoS2

The optoelectronic properties of a material are determined by the processes following light-matter interaction. Here we use femtosecond optical spectroscopy to systematically study photoexcited carrier relaxation in few-layer MoS2flakes as a function of excitation density and sample thickness. We find bimolecular coalescence of charges into indirect excitons as the dominant relaxation process in two- to three-layer flakes while thicker flakes show a much higher density of defects, which efficiently trap charges before they can coalesce

Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTIC‐HF: baseline characteristics and comparison with contemporary clinical trials

Aims: The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC‐HF) trial. Here we describe the baseline characteristics of participants in GALACTIC‐HF and how these compare with other contemporary trials. Methods and Results: Adults with established HFrEF, New York Heart Association functional class (NYHA) ≥ II, EF ≤35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokinetic‐guided dosing: 25, 37.5 or 50 mg bid). 8256 patients [male (79%), non‐white (22%), mean age 65 years] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NT‐proBNP 1971 pg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTIC‐HF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressure < 100 mmHg (n = 1127), estimated glomerular filtration rate < 30 mL/min/1.73 m2 (n = 528), and treated with sacubitril‐valsartan at baseline (n = 1594). Conclusions: GALACTIC‐HF enrolled a well‐treated, high‐risk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation

Preparation of air-stable expandable MoS2 and rapid expansion by low temperature heating and electron beam irradiation

We report on the intercalation of a quaternary ammonium salt into MoS2 at ambient conditions and the rapid expansion of the resulting intercalated material – an analogue to expandable graphite – both via low temperature heating and via electron beam irradiation in a scanning electron microscope. In both cases the expansion proceeds within seconds and does not alter the material's chemical properties. The range of expansion under the electron beam depends on the energy and incident angle of the electrons. The intercalated material is air-stable and remains expandable for at least a year

Ultrafast nonequilibrium dynamics of strongly coupled resonances in the intrinsic cavity of WS2 nanotubes

Strong coupling of electric transition dipoles with optical or plasmonic resonators modifies their light-matter interaction and, therefore, their optical spectra. Semiconducting WS2 nanotubes intrinsically provide the dipoles through their excitonic resonances, and the optical cavity via their cylindrical shape. We investigate the nonequi- librium light-matter interaction in WS2 nanotubes in the time domain using femtosecond transient extinction spectroscopy. We develop a phenomenological coupled oscillator model with time-dependent parameters to describe the transient extinction spectra, allowing us to extract the underlying nonequilibrium electron dynamics. We find that the exciton and trion resonances shift due to many-body effects of the photogenerated charge carriers and their population dynamics on the femto- and picosecond timescale. Our results show that the time-dependent phenomenological model quantitatively reproduces the nonequilibrium optical response of strongly coupled systems

Femtosecond spectroscopy on MoS2 flakes from liquid exfoliation: surfactant independent exciton dynamics

Ionic surfactants, which are widely used to stabilize nanomaterials in dispersions, can drastically alter the nanomaterial's photophysical properties. Here, we use femtosecond optical spectroscopy to study the dynamics of excitons and charges in few-layer flakes of the two-dimensional semiconductor MoS2. We compare samples obtained via exfoliation in water with different amounts of adsorbed sodium cholate, obtained by repeated washing of the dried flakes. We find that the femtosecond dynamics is remarkably stable against the surfactant adsorption, with a slight increase of the initial exciton quenching occurring during the first few picoseconds as the only appreciable effect. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI

The Effect of Network Formation on the Mechanical Properties of 1D:2D Nano:Nano Composites

Mixtures of 1D carbon nanotubes and 2D nanosheets are important in electrochemical applications where the nanosheets are the active material, while the nanotubes provide electrical conductivity and mechanical reinforcement. While the conductivity of such nano:nano composites has been studied, the mechanical properties have not. Here, we report a detailed study of the structural, electrical, and mechanical properties of composites of MoS₂ nanosheets mixed with carbon nanotubes at various volume fractions, ϕ. Microscopic analysis reveals the nanotube network to evolve from a loosely connected structure for ϕ < 1% to a strongly entangled continuous structure for ϕ > 1%. Significantly, while the network consists of low (∼200) aspect-ratio bundles for ϕ < 1 vol %, above this value, entangled ropes predominate, with the aspect ratio rising sharply with increasing ϕ, reaching ∼4700 for the 6.4 vol % sample. While this transition does not affect the electrical properties, it has a significant effect on the mechanical properties. Below ϕ = 1%, both the modulus and failure strain follow short-fiber composite behavior with the modulus increasing as per the rule of mixtures and failure strain falling with ϕ. However, above ϕ = 1%, both parameters increase with ϕ, consistent with continuous-fiber network behavior. The tensile strength also transitions at 1 vol % from a regime limited by the matrix–fiber interfacial strength (ϕ < 1 vol %) to one limited by the strength of the ropes (ϕ > 1 vol %). Similarly, the toughness is constant at low volume fraction but increases strongly for ϕ > 1 vol %, consistent with a model based on percolation theory

Nanographene-Based Decoration as a Panchromatic Antenna for Metalloporphyrin Conjugates

Porphyrins, a type of heterocyclic aromatic compounds consisting of tetrapyrroles connected by four substituted methine groups, are appealing building blocks for solar energy applications. However, their photosensitization capability is limited by their large optical energy gap, which results in a mismatch in absorption toward efficient harvesting of the solar spectrum. Porphyrin π-extension by edge-fusing with nanographenes can be employed for narrowing their optical energy gap from 2.35 to 1.08&nbsp;eV, enabling the development of porphyrin-based panchromatic dyes with an optimized energy onset for solar energy conversion in dye-sensitized solar fuel and solar cell configurations. By combining time-dependent density functional theory with fs transient absorption spectroscopy, it is found that the primary singlets, which are delocalized across the entire aromatic part, are transferred into metal centred triplets in only 1.2&nbsp;ps; and subsequently, relax toward ligand-delocalized triplets. This observation implies that the decoration of the porphyrin moiety with nanographenes, while having a large impact on the absorption onset of the novel dye, promotes the formation of a ligand-centred lowest triplet state of large spatial extension, potentially interesting for boosting interactions with electron scavengers. These results reveal a design strategy for broadening the applicability of porphyrin-based dyes in optoelectronics

Exciton and charge carrier dynamics in few-layer WS2

Semiconducting transition metal dichalcogenides (TMDs) have been applied as the active layer in photodetectors and solar cells, displaying substantial charge photogeneration yields. However, their large exciton binding energy, which increases with decreasing thickness (number of layers), as well as the strong resonance peaks in the absorption spectra suggest that excitons are the primary photoexcited states. Detailed time-domain studies of the photoexcitation dynamics in TMDs exist mostly for MoS2. Here, we use femtosecond optical spectroscopy to study the exciton and charge dynamics following impulsive photoexcitation in few-layer WS2. We confirm excitons as the primary photoexcitation species and find that they dissociate into charge pairs with a time constant of about 1.3 ps. The better separation of the spectral features compared to MoS2 allows us to resolve a previously undetected process: these charges diffuse through the samples and get trapped at defects, such as flake edges or grain boundaries, causing an appreciable change of their transient absorption spectra. This finding opens the way to further studies of traps in TMD samples with different defect contents