Ultrahigh-pressure isostructural electronic transitions in hydrogen.

High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal1, which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate2,3. Therefore, understanding such transitions remains an important objective in condensed matter physics4,5. However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions. Here we present a single-crystal X-ray diffraction study of solid hydrogen at pressures of up to 254 gigapascals that reveals the crystallographic nature of the transitions from phase I to phases III and IV. Under compression, hydrogen molecules remain in the hexagonal close-packed (hcp) crystal lattice structure, accompanied by a monotonic increase in anisotropy. In addition, the pressure-dependent decrease of the unit cell volume exhibits a slope change when entering phase IV, suggesting a second-order isostructural phase transition. Our results indicate that the precursor to the exotic two-component atomic hydrogen may consist of electronic transitions caused by a highly distorted hcp Brillouin zone and molecular-symmetry breaking.

Interventions for postburn pruritus.

BACKGROUND: Postburn pruritus (itch) is a common and distressing symptom experienced on healing or healed burn or donor site wounds. Topical, systemic, and physical treatments are available to control postburn pruritus; however, it remains unclear how effective these are. OBJECTIVES: To assess the effects of interventions for treating postburn pruritus in any care setting. SEARCH METHODS: In September 2022, we searched the Cochrane Wounds Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE (including In-Process & Other Non-Indexed Citations), Ovid Embase, and EBSCO CINAHL Plus. We also searched clinical trials registries and scanned references of relevant publications to identify eligible trials. There were no restrictions with respect to language, publication date, or study setting. SELECTION CRITERIA: Randomised controlled trials (RCTs) that enrolled people with postburn pruritus to compare an intervention for postburn pruritus with any other intervention, placebo or sham intervention, or no intervention. DATA COLLECTION AND ANALYSIS: We used the standard methodological procedures expected by Cochrane. We used GRADE to assess the certainty of the evidence. MAIN RESULTS: We included 25 RCTs assessing 21 interventions with 1166 randomised participants. These 21 interventions can be grouped into six categories: neuromodulatory agents (such as doxepin, gabapentin, pregabalin, ondansetron), topical therapies (such as CQ-01 hydrogel, silicone gel, enalapril ointment, Provase moisturiser, beeswax and herbal oil cream), physical modalities (such as massage therapy, therapeutic touch, extracorporeal shock wave therapy, enhanced education about silicone gel sheeting), laser scar revision (pulsed dye laser, pulsed high-intensity laser, fractional CO2 laser), electrical stimulation (transcutaneous electrical nerve stimulation, transcranial direct current stimulation), and other therapies (cetirizine/cimetidine combination, lemon balm tea). Most RCTs were conducted at academic hospitals and were at a high risk of performance, attrition, and detection bias. While 24 out of 25 included studies reported change in burn-related pruritus, secondary outcomes such as cost-effectiveness, pain, patient perception, wound healing, and participant health-related quality of life were not reported or were reported incompletely. Neuromodulatory agents versus antihistamines or placebo There is low-certainty evidence that doxepin cream may reduce burn-related pruritus compared with oral antihistamine (mean difference (MD) -2.60 on a 0 to 10 visual analogue scale (VAS), 95% confidence interval (CI) -3.79 to -1.42; 2 studies, 49 participants). A change of 2 points represents a minimal clinically important difference (MCID). Due to very low-certainty evidence, it is uncertain whether doxepin cream impacts the incidence of somnolence as an adverse event compared to oral antihistamine (risk ratio (RR) 0.64, 95% CI 0.32 to 1.25; 1 study, 24 participants). No data were reported on pain in the included study. There is low-certainty evidence that gabapentin may reduce burn-related pruritus compared with cetirizine (MD -2.40 VAS, 95% CI -4.14 to -0.66; 1 study, 40 participants). A change of 2 points represents a MCID. There is low-certainty evidence that gabapentin reduces the incidence of somnolence compared to cetirizine (RR 0.02, 95% CI 0.00 to 0.38; 1 study, 40 participants). No data were reported on pain in the included study. There is low-certainty evidence that pregabalin may result in a reduction in burn-related pruritus intensity compared with cetirizine with pheniramine maleate (MD -0.80 VAS, 95% CI -1.24 to -0.36; 1 study, 40 participants). A change of 2 points represents a MCID. There is low-certainty evidence that pregabalin reduces the incidence of somnolence compared to cetirizine (RR 0.04, 95% CI 0.00 to 0.69; 1 study, 40 participants). No data were reported on pain in the included study. There is moderate-certainty evidence that ondansetron probably results in a reduction in burn-related pruritus intensity compared with diphenhydramine (MD -0.76 on a 0 to 10 numeric analogue scale (NAS), 95% CI -1.50 to -0.02; 1 study, 38 participants). A change of 2 points represents a MCID. No data were reported on pain and adverse events in the included study. Topical therapies versus relevant comparators There is moderate-certainty evidence that enalapril ointment probably decreases mean burn-related pruritus compared with placebo control (MD -0.70 on a 0 to 4 scoring table for itching, 95% CI -1.04 to -0.36; 1 study, 60 participants). No data were reported on pain and adverse events in the included study. Physical modalities versus relevant comparators Compared with standard care, there is low-certainty evidence that massage may reduce burn-related pruritus (standardised mean difference (SMD) -0.86, 95% CI -1.45 to -0.27; 2 studies, 166 participants) and pain (SMD -1.32, 95% CI -1.66 to -0.98). These SMDs equate to a 4.60-point reduction in pruritus and a 3.74-point reduction in pain on a 10-point VAS. A change of 2 VAS points in itch represents a MCID. No data were reported on adverse events in the included studies. There is low-certainty evidence that extracorporeal shock wave therapy (ESWT) may reduce burn-related pruritus compared with sham stimulation (SMD -1.20, 95% CI -1.65 to -0.75; 2 studies, 91 participants). This equates to a 5.93-point reduction in pruritus on a 22-point 12-item Pruritus Severity Scale. There is low-certainty evidence that ESWT may reduce pain compared with sham stimulation (MD 2.96 on a 0 to 25 pressure pain threshold (PPT), 95% CI 1.76 to 4.16; 1 study, 45 participants). No data were reported on adverse events in the included studies. Laser scar revision versus untreated or placebo controls There is moderate-certainty evidence that pulsed high-intensity laser probably results in a reduction in burn-related pruritus intensity compared with placebo laser (MD -0.51 on a 0 to 1 Itch Severity Scale (ISS), 95% CI -0.64 to -0.38; 1 study, 49 participants). There is moderate-certainty evidence that pulsed high-intensity laser probably reduces pain compared with placebo laser (MD -3.23 VAS, 95% CI -5.41 to -1.05; 1 study, 49 participants). No data were reported on adverse events in the included studies. AUTHORS' CONCLUSIONS: There is moderate to low-certainty evidence on the effects of 21 interventions. Most studies were small and at a high risk of bias related to blinding and incomplete outcome data. Where there is moderate-certainty evidence, practitioners should consider the applicability of the evidence for their patients.

Incorporation of Th4+ and Sr2+ into Rhabdophane/Monazite by Wet Chemistry: Structure and Phase Stability.

Rhabdophane is an important permeable reactive barrier to enrich radionuclides from groundwater and has been envisaged to host radionuclides in the backend of the nuclear fuel cycle. However, understanding of how An4+ and Sr2+ precipitate into rhabdophane by wet chemistry has not been resolved. In this work, Th4+ and Sr2+ incorporation in the rhabdophane/monazite structure as La1-2xSrxThxPO4·nH2O solid solutions is successfully achieved in the acid solution at 90 °C. Some specific issues such as lattice occupation of Th4+ and Sr2+, precipitation reaction kinetics, and crystal growth affected by starting stoichiometry are discussed in detail, along with investigating the chemical stability of La1-2xSrxThxPO4·nH2O precipitations and associated La1-2xSrxThxPO4 monazite. The results reveal that the excess of Sr2+ appears to be a prevailing factor with a suggested initial Sr: Th ≥ 2 to obtain the stability domain of La1-2xSrxThxPO4·nH2O (x = 0∼ 0.1). A rapid ion removal associated with a nucleation process has been observed within 8 h, and Th4+ can be removed more than 98% after 24 h in 0.01 mol/L solutions. From structural energetics based on density functional theory, the lattice occupation of Th4+ and Sr2+ is energetically favorable in nonhydrated lattice sites of [LaO8], although two-thirds of lattice sites are associated with [LaO8·H2O] hydrated sites. Intriguingly, the crystal transformation from rhabdophane to monazite associated with the transformation from [SrO8] to [SrO9] polyhedra can greatly improve the leaching stability of Sr2+.

Hoop compression driven instabilities in spontaneously formed multilayer graphene blisters over a polymeric substrate.

The blistering of elastic membranes is prone to elastic-solid as well as substrate-based mechanical instabilities. The solid-based instabilities have been well-explored in the mechanically indented blisters of elastic membranes over the rigid/solid substrates, but an integrated study illustrating the underlying mechanism for the onset of solid as well as substrate-based instabilities in the spontaneous blistering of a 2D material is still lacking in the literature. In this article, an extensive experimental as well as analytical analysis of the spontaneous blister-formation in the multilayer graphene (MLG) flakes over a polymeric substrate is reported, which elucidates the involved mechanism and the governing parameters behind the development of elastic-solid as well as viscoelastic-substrate based instabilities. Herein, a 'blister-collapse model' is proposed, which infers that the suppression of the hoop compression, resulting from the phase-transition of the confined matter, plays a crucial role in the development of the instabilities. The ratio of blister-height to flake-thickness is a direct consequence of the taper-angle of the MLG blister and the thickness-dependent elasticity of the upper-bounding MLG flake, which shows a significant impact on the growth-dynamics of the viscous fingering pattern (viscoelastic-substrate based instability) under the MLG blister.

Progress and challenges in layered two-dimensional hybrid perovskites.

Dimensionality is the game-changer property of a material. The optical and electronic properties of a compound get dramatically influenced by confining dimensions from 3D to 2D. The bulk 3D perovskite materials have shown remarkable up-gradation in the power conversion efficiency, hence grabbing worldwide attention. But instability against moisture, temperature, and ion migration are the factors constantly back-stabbing and hindering from full-scale commercialization. 2D perovskite material has emerged as an excellent bridging entity between structural-chemical stability, and viable commercialization. Organic-inorganic 2D perovskite materials come with a layered structure in which a large organic cation layer as a spacer is sandwiched between two inorganic metal halide octahedra layers. Moreover, hydrophobic spacer cations are employed which isolate inorganic octahedral layers from water molecules. Hydrophobic spacer cations protect the authentic structure from being degraded. These layered structures occur in two phases namely the Ruddlesden-Popper phase and Dion-Jacobson phase, depending on the spacer cation types. Alternating inorganic and organic layers form multiple quantum wells naturally, along with spin-orbit-coupling gives Rashba splitting. 2D perovskite materials are coming up with interesting chemical, physical properties like exciton dynamics, charge carrier transport, and electron-phonon coupling as a result of the quantum confinement effect. Despite appreciable stability, limited charge transport and large bandgap are limiting the application of 2D perovskite materials in solar cells. These limitations can be overcome by using the concept of 2D/3D multidimensional hybrid perovskites, which includes the long-term stability of 2D perovskite and the high performance of 3D perovskite at the same time. Here in this perspective, we have given brief insight on structural versatility, synthesis techniques, some of the unique photophysical properties, potential device fabrication, and recent advancements in the 2D structure to stand against degradation. Certain shortcomings and future outlooks are also discussed to make the perspective more informative.

Biaxial stress and functional groups (T = O, F, and Cl) tuning the structural, mechanical, and electronic properties of monolayer molybdenum carbide.

MXenes are a family of novel two-dimensional (2D) materials attracting intensive interest because of the rich chemistry rooted from the highly diversified surface functional groups. This enables the chemical optimization suitable for versatile applications, including energy conversion and storage, sensors, and catalysis. This work reports the ab initio study of the crystal energetics, electronic properties, and mechanical properties, and the impacts of strain on the electronic properties of tetragonal (1T) and hexagonal (2H) phases of Mo2C as well as the surface-terminated Mo2CT2 (T = O, F, and Cl). Our findings indicate that 2H-Mo2C is energetically more stabilized than the 1T counterpart, and the 1T-to-2H transition requires a substantial energy of 210 meV per atom. The presence of surface termination T atoms on Mo2C intrinsically induces variations in the atomic structure. The calculated structures were selected based on the energetic and thermodynamic stabilities (400 K). The O atom prefers to be terminated on 2H-Mo2C, whereas the Cl atom energetically stabilizes on 1T-Mo2C. Meanwhile, with certain configurations, 2H-Mo2CF2 and 1T-Mo2CF2 with slightly different energies could exist simultaneously. The Mo2CO2 possesses the highest mechanical strength and elastic modulus (σmax = 52 GPa at εb = 20% and E = 507 GPa). The nature of the ordered centrosymmetric layer and the strong bonding between 4 d-Mo and 2 p-O of 2H-Mo2CO2 are responsible for its promising mechanical properties. Interestingly, the topological properties of 2H-Mo2CO2 at a wide range of strains (-10% to 12%) are reported. Moreover, 2H-Mo2CF2 is metallic through the range of calculation. Meanwhile, originally semiconducting 1T-Mo2CF2 and 1T-Mo2CCl2 preserve their features under the ranges of the strain of -2% to 10% and -1% to 5%, respectively, beyond which they undergo the semiconductor-to-metal transitions. These findings would guide the potential applications in modern 2D straintronic devices.

Relativistic Effects in Platinum Nanocluster Catalysis: A Statistical Ensemble-Based Analysis.

Nanoclusters are materials of paramount catalytic importance. Among various unique properties featured by nanoclusters, a pronounced relativistic effect can be a decisive parameter in governing their catalytic activity. A concise study delineating the role of relativistic effects in nanocluster catalysis is carried by investigating the oxygen reduction reaction (ORR) activity of a Pt7 subnanometer cluster. Global optimization analysis shows the critical role of spin-orbit coupling (SOC) in regulating the relative stability between structural isomers of the cluster. An overall improved ORR adsorption energetics and differently scaled adsorption-induced structural changes are identified with SOC compared to a non-SOC scenario. Ab initio atomistic thermodynamics analysis predicted nearly identical phase diagrams with significant structural differences for high coverage oxygenated clusters under realistic conditions. Though inclusion of SOC does not bring about drastic changes in the overall catalytic activity of the cluster, it is having a crucial role in governing the rate-determining step, transition-state configuration, and energetics of elementary reaction pathways. Furthermore, a statistical ensemble-based approach illustrates the strong contribution of low-energy local minimum structural isomers to the total ORR activity, which is significantly scaled up along the activity improving direction within the SOC framework. The study provides critical insights toward the importance of relativistic effects in determining various catalytic activity relevant features of nanoclusters.

Role of atomicity in the oxygen reduction reaction activity of platinum sub nanometer clusters: A global optimization study.

Metal nanoclusters are an important class of materials for catalytic applications. Sub nanometer clusters are relatively less explored for their catalytic activity on account of undercoordinated surface structure. Taking this into account, we studied platinum-based sub nanometer clusters for their catalytic activity for oxygen reduction reaction (ORR). A comprehensive analysis with global optimization is carried out for structural prediction of the platinum clusters. The energetic and electronic properties of interactions of clusters with reaction intermediates are investigated. The role of structural sensitivity in the dynamics of clusters is unraveled, and unique intermediate specific interactions are identified. ORR energetics is examined, and exceptional activity for sub nanometer clusters are observed. An inverse size versus activity relationship is identified, challenging the conventional trends followed by larger nanoclusters. The principal role of atomicity in governing the catalytic activity of nanoclusters is illustrated. The structural norms governing the sub nanometer cluster activity are shown to be markedly different from larger nanoclusters.

Catalyzing Bond-Dissociation in Graphene via Alkali-Iodide Molecules.

Atomic design of a 2D-material such as graphene can be substantially influenced by etching, deliberately induced in a transmission electron microscope. It is achieved primarily by overcoming the threshold energy for defect formation by controlling the kinetic energy and current density of the fast electrons. Recent studies have demonstrated that the presence of certain species of atoms can catalyze atomic bond dissociation processes under the electron beam by reducing their threshold energy. Most of the reported catalytic atom species are single atoms, which have strong interaction with single-layer graphene (SLG). Yet, no such behavior has been reported for molecular species. This work shows by experimentally comparing the interaction of alkali and halide species separately and conjointly with SLG, that in the presence of electron irradiation, etching of SLG is drastically enhanced by the simultaneous presence of alkali and iodine atoms. Density functional theory and first principles molecular dynamics calculations reveal that due to charge-transfer phenomena the CC bonds weaken close to the alkali-iodide species, which increases the carbon displacement cross-section. This study ascribes pronounced etching activity observed in SLG to the catalytic behavior of the alkali-iodide species in the presence of electron irradiation.

Large-Scale Fabrication of Wettability-Controllable Coatings for Optimizing Condensate Transfer Ability.

Systematic regulation of hydrophilic regions plays a key role in optimizing the heterogeneous hydrophilic-hydrophobic surface for promoting condensate transfer ability (CTA) under subcooling or high-humidity conditions. In this work, we develop an operable method to fabricate wettability-controllable coatings by regulating the mass ratio of superamphiphobic and superamphiphilic powder (MRP). By investigating the synergic relationship between CTA and MRP, we display an interesting competition between condensation and detachment of condensates. The initial dewing rate associated with reflecting phase change heat transfer capacity could be continuously strengthened by promoting MRP, while the detachment capacity with respect to improving the long-term condensing rate can be limited by the excessive superamphiphilic microregions. Based on this, we have optimized the threshold of MRP for promoting the condensation heat transfer ability and the water harvesting efficiency with the values of 10:0-8:2 and 10:0-4:6, respectively. This work provides important guidance in designing and optimizing heterogeneous hydrophilic-hydrophobic surfaces for multiple industrial applications including heat management, water harvesting, and desalination.

Design of Continuous Transport of the Droplet by the Contact-Boiling Regime.

Joule-heat-driven directional transport of liquid droplets has comprehensive engineering applications in various water and thermal management, cooling systems, and self-cleaning. Generally, the driving force for the transport of liquid droplets was always observed at an extremely high Leidenfrost temperature, which limits the potential application between liquid boiling and Leidenfrost points. In this work, we design a new strategy to directionally drive the transport of droplets by blockading the vapor cushion at a temperature much lower than the Leidenfrost point. On the surface of the microhole arrays, we observed the continuous rebound behavior of ethanol droplets at Ts = 110 °C. Employing the thermal multiphase lattice Boltzmann model, the continuous rebound behavior was reproduced, verifying that the driving force was provided by the blockaded vapor pressure in microholes. By cooperating with the Laplace pressure difference, we directionally transport ethanol and water droplets on the horizontal asymmetrical concentric microridge surface. The horizontal velocity of water is 11.25 cm/s at Ts = 180 °C, similar to the traditional ratchets at the Leidenfrost point. The design of microtextures enriches the fundamental understanding of how to drive droplets at far below the Leidenfrost point and pushes the application in nongravity-driven self-cleaning and cooling systems.

Pressure-induced order-disorder transitions in ß-In2S3: an experimental and theoretical study of structural and vibrational properties.

This joint experimental and theoretical study of the structural and vibrational properties of ß-In2S3 upon compression shows that this tetragonal defect spinel undergoes two reversible pressure-induced order-disorder transitions up to 20 GPa. We propose that the first high-pressure phase above 5.0 GPa has the cubic defect spinel structure of α-In2S3 and the second high-pressure phase (ϕ-In2S3) above 10.5 GPa has a defect α-NaFeO2-type (R3̄m) structure. This phase, related to the NaCl structure, has not been previously observed in spinels under compression and is related to both the tetradymite structure of topological insulators and to the defect LiTiO2 phase observed at high pressure in other thiospinels. Structural characterization of the three phases shows that α-In2S3 is softer than ß-In2S3 while ϕ-In2S3 is harder than ß-In2S3. Vibrational characterization of the three phases is also provided, and their Raman-active modes are tentatively assigned. Our work shows that the metastable α phase of In2S3 can be accessed not only by high temperature or varying composition, but also by high pressure. On top of that, the pressure-induced ß-α-ϕ sequence of phase transitions evidences that ß-In2S3, a BIII2XV3 compound with an intriguing structure typical of AIIBIII2XVI4 compounds (intermediate between thiospinels and ordered-vacancy compounds) undergoes: (i) a first phase transition at ambient pressure to a disordered spinel-type structure (α-In2S3), isostructural with those found at high pressure and high temperature in other BIII2XV3 compounds; and (ii) a second phase transition to the defect α-NaFeO2-type structure (ϕ-In2S3), a distorted NaCl-type structure that is related to the defect NaCl phase found at high pressure in AIIBIII2XVI4 ordered-vacancy compounds and to the defect LiTiO2-type phase found at high pressure in AIIBIII2XVI4 thiospinels. This result shows that In2S3 (with its intrinsic vacancies) has a similar pressure behaviour to thiospinels and ordered-vacancy compounds of the AIIBIII2XVI4 family, making ß-In2S3 the union link between such families of compounds and showing that group-13 thiospinels have more in common with ordered-vacancy compounds than with oxospinels and thiospinels with transition metals.

Understanding carbon dioxide capture on metal-organic frameworks from first-principles theory: The case of MIL-53(X), with X = Fe3+, Al3+, and Cu2.

Metal-organic frameworks (MOFs) constitute a class of three-dimensional porous materials that have shown applicability for carbon dioxide capture at low pressures, which is particularly advantageous in dealing with the well-known environmental problem related to the carbon dioxide emissions into the atmosphere. In this work, the effect of changing the metallic center in the inorganic counterpart of MIL-53 (X), where X = Fe3+, Al3+, and Cu2+, has been assessed over the ability of the porous material to adsorb carbon dioxide by means of first-principles theory. In general, the non-spin polarized computational method has led to adsorption energies in fair agreement with the experimental outcomes, where the carbon dioxide stabilizes at the pore center through long-range interactions via oxygen atoms with the axial hydroxyl groups in the inorganic counterpart. However, spin-polarization effects in connection with the Hubbard corrections, on Fe 3d and Cu 3d states, were needed to properly describe the metal orbital occupancy in the open-shell systems (Fe- and Cu-based MOFs). This methodology gave rise to a coherent high-spin configuration, with five unpaired electrons, for Fe atoms leading to a better agreement with the experimental results. Within the GGA+U level of theory, the binding energy for the Cu-based MOF is found to be Eb = -35.85 kJ/mol, which is within the desirable values for gas capture applications. Moreover, it has been verified that the adsorption energetics is dominated by the gas-framework and internal weak interactions.

Molecules versus Nanoparticles: Identifying a Reactive Molecular Intermediate in the Synthesis of Ternary Coinage Metal Chalcogenides.

The identification of reactive intermediates during molecule-to-nanoparticle (NP) transformation has great significance in comprehending the mechanism of NP formation and, therefore, optimizing the synthetic conditions and properties of the formed products. We report here the room temperature (RT) synthesis of AgCuSe NPs from the reaction of di-tert-butyl selenide with trifluoroacetates (TFA) of silver(I) and copper(II). The isolation and characterization of a molecular species during the course of this reaction, [Ag2Cu(TFA)4(tBu2Se)4] (1), which shows extraordinary reactivity and interesting thermochromic behavior (blue at 0 °C and green at RT), confirmed that ternary metal selenide NPs are formed via this intermediate species. Similar reactions with related dialkyl chalcogenide R2E resulted in the isolation of molecular species of similar composition, [Ag2Cu(TFA)4(R2E)4] [R = tBu, E = S (2); R = Me, E = Se (3); R = Me, E = S (4)], which are stable at RT but can be converted to ternary metal chalcogenides at elevated temperature. Density functional theory calculations confirm the kinetic instability of 1 and throw light on its thermochromic properties.

Capacity enhancement of polylithiated functionalized boron nitride nanotubes: an efficient hydrogen storage medium.

By using first principles density functional theory simulations, we report detailed geometries, electronic structures and hydrogen (H2) storage properties of boron nitride nanotubes (BNNTs) doped with selective polylithiated molecules (CLi2). We find that unsaturated bonding of Li-1s states with BNNT significantly enhances the system stability and hinders the Li-Li clustering effect, which can be detrimental for reversible H2 storage. The H2 adsorption mechanism is explained on the basis of polarization caused by the cationic Li+ of CLi2 molecules bonded with BNNT. The incident H2 molecules are adsorbed with BNNT-nCLi2 through electrostatic and van der Waals interactions. We find that with a maximum of 5.0% of CLi2 coverage on BNNT, an H2 gravimetric density of up to 4.41 wt% can be achieved with adsorption energies in the range of -0.33 eV per H2, which is suitable for ambient condition H2 storage applications.

Van der Waals induced molecular recognition of canonical DNA nucleobases on a 2D GaS monolayer.

In the present study, we systematically investigated the adsorption mechanism of canonical DNA nucleobases and their two nucleobase pairs on a single-layer gallium sulfide (GaS) substrate using DFT+D3 methods. The GaS substrate has chemical interactions with molecules 0.02 |e| 0.11 |e| from molecules to the monolayer GaS surface. Due to the chemical interactions of adenine, cytosine, guanine, and thymine on the monolayer GaS surface, the work function is decreased by 0.69, 0.60, 0.97, and 0.20 eV, respectively. It is displayed that the bandgap of the monolayer GaS sheet can be significantly affected as induced molecular electronic states tend to appear near the Fermi level region due to chemical and physisorption mechanism. We have also investigated the transport properties of DNA nucleobases, namely, AT and GC pair molecules on the GaS surface, which shows significant reduction in the zero-bias transmission spectra. Moreover, with and without DNA nucleobases, namely, AT and GC pair molecules' absorptions on the GaS surface, clearly expressed in terms of distinct current signals, can be observed as ON and OFF states for this device. The distinctive nucleobase adsorption energies and different I-V responses may serve as potential probes for the selective detection of nucleobase molecules in imminent DNA sequencing applications based on a monolayer GaS surface.

Stability of Ar(H2)2 to 358 GPa.

"Chemical precompression" through introducing impurity atoms into hydrogen has been proposed as a method to facilitate metallization of hydrogen under external pressure. Here we selected Ar(H2)2, a hydrogen-rich compound with molecular hydrogen, to explore the effect of "doping" on the intermolecular interaction of H2 molecules and metallization at ultrahigh pressure. Ar(H2)2 was studied experimentally by synchrotron X-ray diffraction to 265 GPa, by Raman and optical absorption spectroscopy to 358 GPa, and theoretically using the density-functional theory. Our measurements of the optical bandgap and the vibron frequency show that Ar(H2)2 retains 2-eV bandgap and H2 molecular units up to 358 GPa. This is attributed to reduced intermolecular interactions between H2 molecules in Ar(H2)2 compared with that in solid H2 A splitting of the molecular vibron mode above 216 GPa suggests an orientational ordering transition, which is not accompanied by a change in lattice symmetry. The experimental and theoretical equations of state of Ar(H2)2 provide direct insight into the structure and bonding of this hydrogen-rich system, suggesting a negative chemical pressure on H2 molecules brought about by doping of Ar.

TiS2 Monolayer as an Emerging Ultrathin Bifunctional Catalyst: Influence of Defects and Functionalization.

We have envisaged the hydrogen evolution and oxygen evolution reactions (HER and OER) on a two-dimensional (2D) noble-metal-free titanium disulfide (TiS2 ) monolayer, which belongs to the exciting family of transition metal dichalcogenides (TMDCs). Our theoretical investigation to probe the HER and OER on both the H and T phases of 2D TiS2 is based on electronic-structure calculations witihin the framework of density functional theory (DFT). Since TiS2 is the lightest compound among the group-IV TMDCs, it is worth exploring the catalytic activity of a TiS2 monolayer through the functionalization at the anion (S) site, substituting with P, N, and C dopants as well as by incorporating single sulfur vacancy defects. We have investigated the effect of functionalization and vacancy defects on the structural, electronic, and optical response of a TiS2 monolayer by determining the density of states, work-function, and optical absorption spectra. We have determined the HER and OER activities for the functionalized and defective TiS2 monolayers based on the reaction coordinate, which can be constructed from the adsorption free energies of the intermediates (H*, O*, OH* and OOH*, where * denotes the adosrbed state) in the HER and OER mechanisms. Finally, we have shown that TiS2 monolayers are emerging as a promising material for the HER and OER mechanisms under the influence of functionalization and defects.

Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI3.

Metal halide compounds with photovoltaic properties prepared from solution have received increased attention for utilization in solar cells. In this work, low-toxicity cesium bismuth iodides are synthesized from solution, and their photovoltaic and optical properties as well as electronic and crystal structures are investigated. The X-ray diffraction patterns reveal that a CsI/BiI3 precursor ratio of 1.5:1 can convert pure rhombohedral BiI3 to pure hexagonal Cs3Bi2I9, but any ratio intermediate of this stoichiometry and pure BiI3 yields a mixture containing the two crystalline phases Cs3Bi2I9 and BiI3, with their relative fraction depending on the CsI/BiI3 ratio. Solar cells from the series of compounds are characterized, showing the highest efficiency for the compounds with a mixture of the two structures. The energies of the valence band edge were estimated using hard and soft X-ray photoelectron spectroscopy for more bulk and surface electronic properties, respectively. On the basis of these measurements, together with UV-vis-near-IR spectrophotometry, measuring the band gap, and Kelvin probe measurements for estimating the work function, an approximate energy diagram has been compiled clarifying the relationship between the positions of the valence and conduction band edges and the Fermi level.

Ab initio study of a 2D h-BAs monolayer: a promising anode material for alkali-metal ion batteries.

The selection of a suitable two dimensional anode material is one of the key steps in the development of alkali metal ion batteries to achieve superior performance with an ultrahigh rate of charging/discharging capability. Here, we have used state of the art density functional theory (DFT) to explore the feasibility of two dimensional (2D) honeycomb boron arsenide (h-BAs) as a potential anode for alkali-metal (Li/Na/K)-ion batteries. The structural and dynamic stability has been confirmed from the formation energy and the non-negative phonon frequency. The h-BAs monolayer exhibits negative adsorption-energy values of -0.422, -0.321 and -0.814 eV, for the Li, Na, and K-ions, respectively. Subsequently, during the charging process the adsorption-energy increases considerably without an energy-barrier when any of the A-atoms achieve a crucial distance (∼8 Å). In addition, it has been observed that insertion of the mono alkali metal atom into the h-BAs surface results in the semi-conducting nature of the monolayer being transformed into a metallic-state. The low energy barriers for Li (0.522 eV), Na (0.248), and K (0.204 eV) active ion migration imply high diffusion over the h-BAs surface, hence suggesting it has a high charge/discharge capability. Moreover, we have obtained low average operating voltages of 0.49 V (Li), 0.35 V (Na) and 0.26 V (K) and high theoretical capacities of 522.08 mA h g-1 (for Li and Na) and 209.46 mA h g-1 (for K) in this study. The aforementioned findings indicate that a h-BAs monolayer could be a promising anode material in the search for low cost and high performance alkali metal ion batteries.