Stability of Near-Surface Nitrogen Vacancy Centers Using Dielectric Surface Passivation

We study the photophysical stability of ensemble near-surface nitrogen vacancy (NV) centers in diamond under vacuum and air. The optically detected magnetic resonance contrast of the NV centers was measured following exposure to laser illumination, showing opposing trends in air compared to vacuum (increasing by up to 9% and dropping by up to 25%, respectively). Characterization using X-ray photoelectron spectroscopy (XPS) suggests a surface reconstruction: In air, atmospheric oxygen adsorption on a surface leads to an increase in NV- fraction, whereas in vacuum, net oxygen desorption increases the NV0 fraction. NV charge state switching is confirmed by photoluminescence spectroscopy. Deposition of ∼2 nm alumina (Al2O3) over the diamond surface was shown to stabilize the NV charge state under illumination in either environment, attributed to a more stable surface electronegativity. The use of an alumina coating on diamond is therefore a promising approach to improve the resilience of NV sensors.

Investigating the mechanism of phosphorene nanoribbon synthesis by discharging black phosphorus intercalation compounds

Phosphorene nanoribbons (PNRs) can be synthesised in intrinsically scalable methods from intercalation of black phosphorus (BP), however, the mechanism of ribbonisation remains unclear. Herein, to investigate the point at which nanoribbons form, we decouple the two key synthesis steps: first, the formation of the BP intercalation compound, and second, the dissolution into a polar aprotic solvent. We find that both the lithium intercalant and the negative charge on the phosphorus host framework can be effectively removed by addition of phenyl cyanide to return BP and investigate whether fracturing to ribbons occurred after the first step. Further efforts to exfoliate mechanically with or without solvent reveal that the intercalation step does not form ribbons, indicating that an interaction between the amidic solvent and the intercalated phosphorus compound plays an important role in the formation of nanoribbons.

The local ordering of polar solvents around crystalline carbon nitride nanosheets in solution

The crystalline graphitic carbon nitride, poly-triazine imide (PTI) is highly unusual among layered materials since it is spontaneously soluble in aprotic, polar solvents including dimethylformamide (DMF). The PTI material consists of layers of carbon nitride intercalated with LiBr. When dissolved, the resulting solutions consist of dissolved, luminescent single to multilayer nanosheets of around 60-125 nm in diameter and Li+ and Br- ions originating from the intercalating salt. To understand this unique solubility, the structure of these solutions has been investigated by high-energy X-ray and neutron diffraction. Although the diffraction patterns are dominated by inter-solvent correlations there are clear differences between the X-ray diffraction data of the PTI solution and the solvent in the 4-6 Å-1 range, with real space differences persisting to at least 10 Å. Structural modelling using both neutron and X-ray datasets as a constraint reveal the formation of distinct, dense solvation shells surrounding the nanoparticles with a layer of Br-close to the PTI-solvent interface. This solvent ordering provides a configuration that is energetically favourable underpinning thermodynamically driven PTI dissolution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Amphoteric dissolution of two-dimensional polytriazine imide carbon nitrides in water

Crystalline two-dimensional carbon nitrides with polytriazine imide (PTI) structure are shown to act amphoterically, buffering both HCl and NaOH aqueous solutions, resulting in charged PTI layers that dissolve spontaneously in their aqueous media, particularly for the alkaline solutions. This provides a low energy, green route to their scalable solution processing. Protonation in acid is shown to occur at pyridinic nitrogens, stabilized by adjacent triazines, whereas deprotonation in base occurs primarily at basal plane NH bridges, although NH2 edge deprotonation is competitive. We conclude that mildly acidic or basic pHs are necessary to provide sufficient net charge on the nanosheets to promote dissolution, while avoiding high ion concentrations which screen the repulsion of like-charged PTI sheets in solution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Exploring the length scales, timescales and chemistry of challenging materials (Part 2)

This themed issue explores the different length and timescales that determine the physics and chemistry of a variety of key of materials, explored from the perspective of a wide range of disciplines, including physics, chemistry materials science, Earth science and biochemistry. The topics discussed include catalysis, chemistry under extreme conditions, energy materials, amorphous and liquid structure, hybrid organic materials and biological materials. The issue is in two parts, with this second set of contributions exploring hybrid organic materials, catalysis low-dimensional and graphitic materials, biological materials and naturally occurring, super-hard material as well as dynamic high pressure and new developments in imaging techniques pressure. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Exploring the length scales, timescales and chemistry of challenging materials (Part 1)

This themed issue explores the different length scales and timescales that determine the physics and chemistry of a variety of key materials, explored from the perspective of a wide range of disciplines, including physics, chemistry, materials science, Earth science and biochemistry. The topics discussed include catalysis, chemistry under extreme conditions, energy materials, amorphous and liquid structure, hybrid organic materials and biological materials. The issue is in two parts, with the present part exploring glassy and amorphous systems and materials at high pressure. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Synthesis of Black Phosphorene Quantum Dots from Red Phosphorus

Black phosphorene quantum dots (BPQDs) are most commonly derived from high-cost black phosphorus, while previous syntheses from the low-cost red phosphorus (Pred ) allotrope are highly oxidised. Herein, we present an intrinsically scalable method to produce high quality BPQDs, by first ball-milling Pred to create nanocrystalline Pblack and subsequent reductive etching using lithium electride solvated in liquid ammonia. The resultant ~25 nm BPQDs are crystalline with low oxygen content, and spontaneously soluble as individualized monolayers in tertiary amide solvents, as directly imaged by liquid-phase transmission electron microscopy. This new method presents a scalable route to producing quantities of high quality BPQDs for academic and industrial applications.

Production of Magnetic Arsenic-Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities

Quasi-1D nanoribbons provide a unique route to diversifying the properties of their parent 2D nanomaterial, introducing lateral quantum confinement and an abundance of edge sites. Here, a new family of nanomaterials is opened with the creation of arsenic-phosphorus alloy nanoribbons (AsPNRs). By ionically etching the layered crystal black arsenic-phosphorus using lithium electride followed by dissolution in amidic solvents, solutions of AsPNRs are formed. The ribbons are typically few-layered, several micrometers long with widths tens of nanometers across, and both highly flexible and crystalline. The AsPNRs are highly electrically conducting above 130 K due to their small band gap (ca. 0.035 eV), paramagnetic in nature, and have high hole mobilities, as measured with the first generation of AsP devices, directly highlighting their properties and utility in electronic devices such as near-infrared detectors, quantum computing, and charge carrier layers in solar cells.

Understanding and Optimizing Capacitance Performance in Reduced Graphene-Oxide Based Supercapacitors

Reduced graphene-oxide (RGO)-based electrodes in supercapacitors deliver high energy/power capacities compared to typical nanoporous carbon materials. However, extensive critical analysis of literature reveals enormous discrepancies (up to 250 F g^-1 ) in the reported capacitance (variation of 100-350 F g^-1 ) of RGO materials synthesized under seemingly similar methods, inhibiting an understanding of capacitance variation. Here, the key factors that control the capacitance performance of RGO electrodes are demonstrated by analyzing and optimizing various types of commonly applied electrode fabrication methods. Beyond usual data acquisition parameters and oxidation/reduction properties of RGO, a substantial difference of more than 100% in capacitance values (with change from 190 ± 20 to 340 ± 10 F g^-1 ) is found depending on the electrode preparation method. For this demonstration, ≈40 RGO-based electrodes are fabricated from numerous distinctly different RGO materials via typically applied methods of solution (aqueous and organic) casting and compressed powders. The influence of data acquisition conditions and capacitance estimation practices are also discussed. Furthermore, by optimizing electrode processing method, a direct surface area governed capacitance relationship for RGO structures is revealed.

Black Phosphorus Degradation during Intercalation and Alloying in Batteries

Numerous layered materials are being recognized as promising candidates for high-performance alkali-ion battery anodes, but black phosphorus (BP) has received particular attention. This is due to its high specific capacity, due to a mixed alkali-ion storage mechanism (intercalation-alloying), and fast alkali-ion transport within its layers. Unfortunately, BP based batteries are also commonly associated with serious irreversible losses and poor cycling stability. This is known to be linked to alloying, but there is little experimental evidence of the morphological, mechanical, or chemical changes that BP undergoes in operational cells and thus little understanding of the factors that must be mitigated to optimize performance. Here the degradation mechanisms of BP alkali-ion battery anodes are revealed through operando electrochemical atomic force microscopy (EC-AFM) and ex situ spectroscopy. Among other phenomena, BP is observed to wrinkle and deform during intercalation but suffers from complete structural breakdown upon alloying. The solid electrolyte interphase (SEI) is also found to be unstable, nucleating at defects before spreading across the basal planes but then disintegrating upon desodiation, even above alloying potentials. By directly linking these localized phenomena with the whole-cell performance, we can now engineer stabilizing protocols for next-generation high-capacity alkali-ion batteries.

Ex Situ Characterization of 1T/2H MoS2 and Their Carbon Composites for Energy Applications, a Review

The growing interest in the development of next-generation net zero energy systems has led to the expansion of molybdenum disulfide (MoS₂) research in this area. This activity has resulted in a wide range of manufacturing/synthesis methods, controllable morphologies, diverse carbonaceous composite structures, a multitude of applicable characterization techniques, and multiple energy applications for MoS₂. To assess the literature trends, 37,347 MoS₂ research articles from Web of Science were text scanned to classify articles according to energy application research and characterization techniques employed. Within the review, characterization techniques are grouped under the following categories: morphology, crystal structure, composition, and chemistry. The most common characterization techniques identified through text scanning are recommended as the base fingerprint for MoS₂ samples. These include: scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Similarly, XPS and Raman spectroscopy are suggested for 2H or 1T MoS₂ phase confirmation. We provide guidance on the collection and presentation of MoS₂ characterization data. This includes how to effectively combine multiple characterization techniques, considering the sample area probed by each technique and their statistical significance, and the benefit of using reference samples. For ease of access for future experimental comparison, key numeric MoS₂ characterization values are tabulated and major literature discrepancies or currently debated characterization disputes are highlighted.

Weak Interactions in Dimethyl Sulfoxide (DMSO)-Tertiary Amide Solutions: The Versatility of DMSO as a Solvent

The structures of equimolar mixtures of the commonly used polar aprotic solvents dimethylformamide (DMF) and dimethylacetamide (DMAc) in dimethyl sulfoxide (DMSO) have been investigated via neutron diffraction augmented by extensive hydrogen/deuterium isotopic substitution. Detailed 3-dimensional structural models of these solutions have been derived from the neutron data via Empirical Potential Structure Refinement (EPSR). The intermolecular center-of-mass (CoM) distributions show that the first coordination shell of the amides comprises ∼13-14 neighbors, of which approximately half are DMSO. In spite of this near ideal coordination shell mixing, the changes to the amide-amide structure are found to be relatively subtle when compared to the pure liquids. Analysis of specific intermolecular atom-atom correlations allows quantitative interpretation of the competition between weak interactions in the solution. We find a hierarchy of formic and methyl C-H···O hydrogen bonds forms the dominant local motifs, with peak positions in the range of 2.5-3.0 Å. We also observe a rich variety of steric and dispersion interactions, including those involving the O═C-N amide π-backbones. This detailed insight into the structural landscape of these important liquids demonstrates the versatility of DMSO as a solvent and the remarkable sensitivity of neutron diffraction, which is critical for understanding weak intermolecular interactions at the nanoscale and thereby tailoring solvent properties to specific applications.

Platinum deposition on functionalised graphene for corrosion resistant oxygen reduction electrodes

Graphene-related materials are promising supports for electrocatalysts due to their stability and high surface area. Their innate surface chemistries can be controlled and tuned via functionalisation to improve the stability of both the carbon support and the metal catalyst. Functionalised graphenes were prepared using either aryl diazonium functionalisation or non-destructive chemical reduction, to provide groups adapted for platinum deposition. XPS and TGA-MS measurements confirmed the presence of polyethyleneglycol and sulfur-containing functional groups, and provided consistent values for the extent of the reactions. The deposited platinum nanoparticles obtained were consistently around 2 nm via reductive chemistry and around 4 nm via the diazonium route. Although these graphene-supported electrocatalysts provided a lower electrochemical surface area (ECSA), functionalised samples showed enhanced specific activity compared to a commercial platinum/carbon black system. Accelerated stress testing (AST) showed improved durability for the functionalised graphenes compared to the non-functionalised materials, attributed to edge passivation and catalyst particle anchoring.

TOF-SIMS analysis of curcuminoids and curcumin crystals crystallized from their pure and impure solutions

Impurities are frequently encountered during the crystallisation of active pharmaceutical compounds. Impurities can either adsorb onto active sites or replace atoms of the crystal lattice. Locating the impurities, especially structurally-similar...

Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction

Phosphorene nanoribbons (PNRs) have been widely predicted to exhibit a range of superlative functional properties; however, because they have only recently been isolated, these properties are yet to be shown to translate to improved performance in any application. PNRs show particular promise for optoelectronics, given their predicted high exciton binding energies, tunable bandgaps, and ultrahigh hole mobilities. Here, we verify the theorized enhanced hole mobility in both solar cells and space-charge-limited-current devices, demonstrating the potential for PNRs improving hole extraction in universal optoelectronic applications. Specifically, PNRs are demonstrated to act as an effective charge-selective interlayer by enhancing hole extraction from polycrystalline methylammonium lead iodide (MAPbI₃) perovskite to the poly(triarylamine) semiconductor. Introducing PNRs at the hole-transport/MAPbI₃ interface achieves fill factors above 0.83 and efficiencies exceeding 21% for planar p-i-n (inverted) perovskite solar cells (PSCs). Such efficiencies are typically only reported for single-crystalline MAPbI₃-based inverted PSCs. Methylammonium-free PSCs also benefit from a PNR interlayer, verifying applicability to architectures incorporating mixed perovskite absorber layers. Device photoluminescence and transient absorption spectroscopy are used to demonstrate that the presence of the PNRs drives more effective carrier extraction. Isolation of the PNRs in space-charge-limited-current hole-only devices improves both hole mobility and conductivity, demonstrating applicability beyond PSCs. This work provides primary experimental evidence that the predicted superlative functional properties of PNRs indeed translate to improved optoelectronic performance.

Intermediate Range Order in Metal-Ammonia Solutions: Pure and Na-Doped Ca-NH3

The local and intermediate range ordering in Ca-NH₃ solutions in their metallic phase is determined through H/D isotopically differenced neutron diffraction in combination with empirical potential structure refinements. For both low and high relative Ca concentrations, the Ca ions are found to be octahedrally coordinated by the NH₃ solvent, and these hexammine units are spatially correlated out to lengthscales of ∼7.4-10.3 Å depending on the concentration, leading to pronounced ordering in the bulk liquid. We further demonstrate that this liquid order can be progressively disrupted by the substitution of Ca for Na, whereby a distortion of the average ion primary solvation occurs and the intermediate range ion-ion correlations are disrupted.

Charge Density Waves in Electron-Doped Molybdenum Disulfide

We present the discovery of a charge density wave (CDW) ground state in heavily electron-doped molybdenum disulfide (MoS₂). This is the first observation of a CDW in any d² (column 6) transition metal dichalcogenide (TMD). The band structure of MoS₂ is distinct from the d⁰ and d¹ TMDs in which CDWs have been previously observed, facilitating new insight into CDW formation. We demonstrate a metal-insulator transition at 85 K, a 25 meV gap at the Fermi level, and two distinct CDW modulations, (2√3 × 2√3) R30° and 2 × 2, attributable to Fermi surface nesting (FSN) and electron-phonon coupling (EPC), respectively. This simultaneous exhibition of FSN and EPC CDW modulations is unique among observations of CDW ground states, and we discuss this in the context of band folding. Our observations provide a route toward the resolution of controversies surrounding the origin of CDW modulations in TMDs.

A novel fuel cell design foroperandoenergy-dispersive x-ray absorption measurements

A polymer electrolyte fuel cell has been designed to allowoperandox-ray absorption spectroscopy (XAS) measurements of catalysts. The cell has been developed to operate under standard fuel cell conditions, with elevated temperatures and humidification of the gas-phase reactants, both of which greatly impact the catalyst utilisation. X-ray windows in the endplates of the cell facilitate collection of XAS spectra during fuel cell operation while maintaining good compression in the area of measurement. Results of polarisation curves and cyclic voltammograms showed that theoperandocell performs well as a fuel cell, while also providing XAS data of suitable quality for robust XANES analysis. The cell has produced comparable XAS results when performing a cyclic voltammogram to an establishedin situcell when measuring the Pt LIII edge. Similar trends of Pt oxidation, and reduction of the formed Pt oxide, have been presented with a time resolution of 5 s for each spectrum, paving the way for time-resolved spectral measurements of fuel cell catalysts in a fully-operating fuel cell.

Aquaporin-like water transport in nanoporous crystalline layered carbon nitride

Designing next-generation fuel cell and filtration devices requires the development of nanoporous materials that allow rapid and reversible uptake and directed transport of water molecules. Here, we combine neutron spectroscopy and first-principles calculations to demonstrate rapid transport of molecular H2O through nanometer-sized voids ordered within the layers of crystalline carbon nitride with a polytriazine imide structure. The transport mechanism involves a sequence of molecular orientation reversals directed by hydrogen-bonding interactions as the neutral molecules traverse the interlayer gap and pass through the intralayer voids that show similarities with the transport of water through transmembrane aquaporin channels in biological systems. The results suggest that nanoporous layered carbon nitrides can be useful for developing high-performance membranes.

Realising the electrochemical stability of graphene: scalable synthesis of an ultra-durable platinum catalyst for the oxygen reduction reaction

Creating effective and stable catalyst nanoparticle-coated electrodes that can withstand extensive cycling is a current roadblock in realising the potential of polymer electrolyte membrane fuel cells. Graphene has been proposed as an ideal electrode support material due to its corrosion resistance, high surface area and high conductivity. However, to date, graphene-based electrodes suffer from high defect concentrations and non-uniform nanoparticle coverage that negatively affects performance; moreover, production methods are difficult to scale. Herein we describe a scalable synthesis for Pt nanoparticle-coated graphene whereby PtCl₂ is reduced directly by negatively charged single layer graphene sheets in solution. The resultant nanoparticles are of optimal dimensions and can be uniformly dispersed, yielding high catalytic activity, remarkable stability, and showing a much smaller decrease in electrochemical surface area compared with an optimised commercial catalyst over 30 000 cycles. The stability is rationalised by identical location TEM which shows minimal nanoparticle agglomeration and no nanoparticle detachment.

Solvation of Na? in the Sodide Solution, LiNa?10MeNH2

Alkalides, the alkali metals in their ?1 oxidation state, represent some of the largest and most polarizable atomic species in condensed phases. This study determines the solvation environment around the sodide anion, Na^?, in a system of co-solvated Li⁺. We present isotopically varied total neutron scattering experiments alongside empirical potential structure refinement and ab initio molecular dynamics simulations for the alkali?alkalide system, LiNa?10MeNH₂. Both local coordination modes and the intermediate range liquid structure are determined, which demonstrate that distinct structural correlations between cation and anion in the liquid phase extend beyond 8.6 ?. Indeed, the local solvation around Na^? is surprisingly well defined with strong solvent orientational order, in contrast to the classical description of alkalide anions not interacting with their environment. The ion-paired Li(MeNH₂)₄⁺?Na^? species appears to be the dominant alkali?alkalide environment in these liquids, whereby Li⁺ and Na^? share a MeNH₂ molecule through the amine group in their primary solvation spheres.

Formation of an ion-free crystalline carbon nitride and its reversible intercalation with ionic species and molecular water

Crystalline layered carbon nitrides can be inter-converted by simple ion exchange process allowing their properties to be tuned.

The development of processes to tune the properties of materials is essential for the progression of next-generation technologies for catalysis, optoelectronics and sustainability including energy harvesting and conversion. Layered carbon nitrides have also been identified as of significant interest within these fields of application. However, most carbon nitride materials studied to date have poor crystallinity and therefore their properties cannot be readily controlled or easily related to their molecular level or nanoscale structures. Here we report a process for forming a range of crystalline layered carbon nitrides with polytriazine imide (PTI) structures that can be interconverted by simple ion exchange processes, permitting the tunability of their optoelectronic and chemical properties. Notable outcomes of our work are (a) the creation of a crystalline, guest-ion-free PTI compound that (b) can be re-intercalated with ions or molecules using “soft chemistry” approaches. This includes the intercalation of HCl, demonstrating a new ambient pressure route to the layered PTI·xHCl material that was previously only available by a high-pressure-high-temperature route (c). Our work also shows (d) that the intercalant-free (IF-) PTI material spontaneously absorbs up to 10 weight% H₂O from the ambient atmosphere and that this process is reversible, leading to potential applications for membranes and water capture in dry environments.

Single Crystal, Luminescent Carbon Nitride Nanosheets Formed by Spontaneous Dissolution

A primary method for the production of 2D nanosheets is liquid-phase delamination from their 3D layered bulk analogues. Most strategies currently achieve this objective by significant mechanical energy input or chemical modification but these processes are detrimental to the structure and properties of the resulting 2D nanomaterials. Bulk poly(triazine imide) (PTI)-based carbon nitrides are layered materials with a high degree of crystalline order. Here, we demonstrate that these semiconductors are spontaneously soluble in select polar aprotic solvents, that is, without any chemical or physical intervention. In contrast to more aggressive exfoliation strategies, this thermodynamically driven dissolution process perfectly maintains the crystallographic form of the starting material, yielding solutions of defect-free, hexagonal 2D nanosheets with a well-defined size distribution. This pristine nanosheet structure results in narrow, excitation-wavelength-independent photoluminescence emission spectra. Furthermore, by controlling the aggregation state of the nanosheets, we demonstrate that the emission wavelengths can be tuned from narrow UV to broad-band white. This has potential applicability to a range of optoelectronic devices.

Chemical routes to discharging graphenides

Chemical and electrochemical reduction methods allow the dispersion, processing, and/or functionalization of discrete sp²-hybridised nanocarbons, including fullerenes, nanotubes and graphenes. Electron transfer to the nanocarbon raises the Fermi energy, creating nanocarbon anions and thereby activating an array of possible covalent reactions. The Fermi level may then be partially or fully lowered by intended functionalization reactions, but in general, techniques are required to remove excess charge without inadvertent covalent reactions that potentially degrade the nanocarbon properties of interest. Here, simple and effective chemical discharging routes are demonstrated for graphenide polyelectrolytes and are expected to apply to other systems, particularly nanotubides. The discharging process is inherently linked to the reduction potentials of such chemical discharging agents and the unusual fundamental chemistry of charged nanocarbons.

Electron Solvation and the Unique Liquid Structure of a Mixed-Amine Expanded Metal: The Saturated Li-NH3 -MeNH2 System

Metal-amine solutions provide a unique arena in which to study electrons in solution, and to tune the electron density from the extremes of electrolytic through to true metallic behavior. The existence and structure of a new class of concentrated metal-amine liquid, Li-NH₃ -MeNH₂ , is presented in which the mixed solvent produces a novel type of electron solvation and delocalization that is fundamentally different from either of the constituent systems. NMR, ESR, and neutron diffraction allow the environment of the solvated electron and liquid structure to be precisely interrogated. Unexpectedly it was found that the solution is truly homogeneous and metallic. Equally surprising was the observation of strong longer-range order in this mixed solvent system. This is despite the heterogeneity of the cation solvation, and it is concluded that the solvated electron itself acts as a structural template. This is a quite remarkable observation, given that the liquid is metallic.

Questioning Antiferromagnetic Ordering in the Expanded Metal, Li(NH3)4: A Lack of Evidence from μSR

We present the results of a muon spin relaxation study of the solid phases of the expanded metal, Li(NH3)4. No discernible change in muon depolarization dynamics is witnessed in the lowest temperature phase (≤25 K) of Li(NH3)4, thus suggesting that the prevailing view of antiferromagnetic ordering is incorrect. This is consistent with the most recent neutron diffraction data. Discernible differences in muon behavior are reported for the highest temperature phase of Li(NH3)4 (82-89 K), attributed to the onset of structural dynamics prior to melting.

Probing the charging mechanisms of carbon nanomaterial polyelectrolytes

Chemical charging of single-walled carbon nanotubes (SWCNTs) and graphenes to generate soluble salts shows great promise as a processing route for electronic applications, but raises fundamental questions. The reduction potentials of highly-charged nanocarbon polyelectrolyte ions were investigated by considering their chemical reactivity towards metal salts/complexes in forming metal nanoparticles. The redox activity, degree of functionalisation and charge utilisation were quantified via the relative metal nanoparticle content, established using thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The fundamental relationship between the intrinsic nanocarbon electronic density of states and Coulombic effects during charging is highlighted as an important area for future research.

Electrochemical processing of discrete single-walled carbon nanotube anions

The dissolution of single-walled carbon nanotubes (SWCNTs) remains a fundamental challenge, reliant on aggressive chemistry or ultrasonication and lengthy ultracentrifugation. In contrast, simple nonaqueous electrochemical reduction leads to spontaneous dissolution of individualized SWCNTs from raw, unprocessed powders. The intrinsic electrochemical stability and conductivity of these nanomaterials allow their electrochemical dissolution from a pure SWCNT cathode to form solutions of individually separate and distinct (i.e., discrete) nanotube anions with varying charge density. The integrity of the SWCNT sp² framework during the charge/discharge process is demonstrated by optical spectroscopy data. Other than a reversible change in redox/solvation state, there is no obvious chemical functionalization of the structure, suggesting an analogy to conventional atomic electrochemical dissolution. The heterogeneity of as-synthesized SWCNT samples leads to the sequential dissolution of distinct fractions over time, with fine control over the electrochemical potential. Initial preferential dissolution of defective nanotubes and carbonaceous debris provides a simple, nondestructive means to purify raw materials without recourse to the usual, damaging, competitive oxidation reactions. Neutral SWCNTs can be recovered either by electroplating at an anode or by reaction with a suitable electrophile.

Scalable method for the reductive dissolution, purification, and separation of single-walled carbon nanotubes

As synthesized, bulk single-walled carbon nanotube (SWNT) samples are typically highly agglomerated and heterogeneous. However, their most promising applications require the isolation of individualized, purified nanotubes, often with specific optoelectronic characteristics. A wide range of dispersion and separation techniques have been developed, but the use of sonication or ultracentrifugation imposes severe limits on scalability and may introduce damage. Here, we demonstrate a new, intrinsically scalable method for SWNT dispersion and separation, using reductive treatment in sodium metal-ammonia solutions, optionally followed by selective dissolution in a polar aprotic organic solvent. In situ small-angle neutron scattering demonstrates the presence of dissolved, unbundled SWNTs in solution, at concentrations reaching at least 2 mg/mL; the ability to isolate individual nanotubes is confirmed by atomic force microscopy. Spectroscopy data suggest that the soluble fraction contains predominately large metallic nanotubes; a potential new mechanism for nanotube separation is proposed. In addition, the G/D ratios observed during the dissolution sequence, as a function of metal:carbon ratio, demonstrate a new purification method for removing carbonaceous impurities from pristine SWNTs, which avoids traditional, damaging, competitive oxidation reactions.

Electronic structure of superconducting KC8 and nonsuperconducting LiC6 graphite intercalation compounds: evidence for a graphene-sheet-driven superconducting state

We have performed photoemission studies of the electronic structure in LiC(6) and KC(8), a nonsuperconducting and a superconducting graphite intercalation compound, respectively. We have found that the charge transfer from the intercalant layers to graphene layers is larger in KC(8) than in LiC(6), opposite of what might be expected from their chemical composition. We have also measured the strength of the electron-phonon interaction on the graphene-derived Fermi surface to carbon derived phonons in both materials and found that it follows a universal trend where the coupling strength and superconductivity monotonically increase with the filling of graphene π(*) states. This correlation suggests that both graphene-derived electrons and graphene-derived phonons are crucial for superconductivity in graphite intercalation compounds.

Anisotropic electron-phonon coupling and dynamical nesting on the graphene sheets in superconducting CaC6 using angle-resolved photoemission spectroscopy

We present the first angle-resolved photoemission studies of electronic structure in CaC6, a superconducting graphite intercalation compound with T_{c}=11.6 K. We find that, contrary to theoretical models, the electron-phonon coupling on the graphene-derived Fermi sheets with high-frequency graphene-derived phonons is surprisingly strong and anisotropic. The shape of the Fermi surface is found to favor a dynamical intervalley nesting via exchange of high-frequency phonons. Our results suggest that graphene sheets play a crucial role in superconductivity in graphite intercalation compounds.

Formation of giant solvation shells around fulleride anions in liquid ammonia

Here, we measure the solvation structure of fulleride C605- anions in potassium ammonia solution using neutron diffraction. We find a very strong solvation structure consisting of two shells of ammonia densely packed around the anion. The system's structure is driven by the propensity of ammonia molecules to direct one of their hydrogen bonds to the center of the anion while retaining axial hydrogen bonding within the shells. This permits high concentrations of solvent separated fulleride anions.

The ethical dimensions of cultural competence in border health care settings

Through thematic stories of patient and provider interactions on the U.S.-Mexico border, this article challenges the commonly understood definition of culture. It explores areas of concern related to cultural competency and medical ethics. Stories outline issues related to communication and comprehension, use of interpreters, gender and sexual orientation, traditional health care practices, socioeconomic status, age, health care settings, and involvement of community representatives. Policy recommendations address language, continuity of care, and health care professions education.

Industrial Genotoxicology Group collaborative trial to investigate cell cycle parameters in human lymphocyte cytogenetics studies

Human lymphocyte cultures have been used for many years for assessing the in vitro clastogenic potential of test substances. In these assays the harvest time should be based on the cell cycle time in order to ensure that cells are sampled at an appropriate time for the detection of clastogenic effects. The sources of variation in the cell cycle time in routine cytogenetic assays have not been well studied. Consequently 13 laboratories, all members of the Industrial Genotoxicology Group, participated in a collaborative study to measure the variation in cell cycle time in cultured human peripheral blood lymphocytes under various conditions. The study was performed in two phases, spaced 6 months apart. The average generation time (AGT) was measured by the incorporation of bromodeoxyuridine. Very similar AGTs were found in the presence and absence of S9 mix. The mean AGT (mean of four donors) in each laboratory varied from 11.2 to 17.1 h, indicating there is significant variability in cell cycle times of human peripheral blood lymphocytes between laboratories. There was greater variation between laboratories than within laboratories. A comparison of AGT values at 72 h performed in experiments at least 6 months apart indicated good reproducibility in most laboratories. The study indicates that a 24 h post-treatment harvest may result in the analysis of very few first division cells unless very significant cell cycle delay is induced by the test substance. It was also found that a post-harvest time equivalent to 1.5 cell cycles will result in an approximately equal mixture of first and second division cells and therefore should by suitable for assessing both the induction of chromosome aberrations and polyploidy.

A simple splenic reticuloendothelial function test: counting erythrocytes with argyrophilic inclusions

The presently accepted methods for evaluation of splenic reticuloendothelial (RE) function include 99mTc sulfur colloid spleen scan, antibody-coated autologous erythrocyte clearance, and pocked erythrocyte count. All methods involve special equipment and/or risk and inconvenience to patients. A simple method of assessing splenic RE function was developed by counting erythrocytes with argyrophilic inclusions using a simple silver stain and an ordinary microscope. To test the validity of this method, blood samples were collected from patients suspected of having hyposplenia or asplenia, including patients with history of splenectomy, sickle cell disease or trait, and newborns. Blood samples were also collected from normal adults and from patients without hyposplenia or asplenia as controls. The samples were tested by this method and compared to the pocked erythrocyte count that served as a gold standard. The results obtained by the two methods were found to be very comparable with little overlap between those from controls and patients with definite hyposplenia or asplenia. With the pocked erythrocyte count as the gold standard, this method has a sensitivity of 88.9% and a specificity of 97.1%. However, this method requires no special equipment. Staining can be applied to fresh blood smears as well as to Wright-stained smears, and the silver-stained smears are permanent.

Extended harvest times are not necessary for the detection of in vitro clastogens in regulatory cytogenetics studies

The choice of harvest time in in vitro cytogenetics assays is a critical factor in determining the sensitivity of the assay for detecting clastogenic potential. As yet there is no harmonization of regulatory requirements in this aspect. It has been suggested that the use of extended harvest times can improve the sensitivity of detecting some chemicals which either induce cell cycle delay or produce lesions which induce chromosome aberrations at divisions subsequent to the first post-treatment mitosis. The incidence of such chemicals encountered in the routine testing of chemicals for regulatory submissions is not known. Therefore a large database of 550 chemicals tested in nine laboratories using standard regulatory protocols, including a late harvest time, was assessed for the incidence of chemicals uniquely positive only at a delayed harvest time. The number of such chemicals was very low ( < 0.2%) and the chromosome damage induced by these chemicals may not result from direct genotoxic mechanisms. Based on these data it is recommended that there is no need to include an extended harvest time in in vitro cytogenetics assays except where it might help to resolve an equivocal result.

Trichloroacetic acid: investigation into the mechanism of chromosomal damage in the in vitro human lymphocyte cytogenetic assay and the mouse bone marrow micronucleus test

Trichloroacetic acid (TCA) was tested for its ability to induce chromosomal damage in cultured human peripheral blood lymphocytes and in bone marrow cells of male and female C57BL/6JfBL10/Alpk mice. Two in vitro cytogenetic assays were conducted with TCA. In the first TCA, as free acid, was added to whole blood cultures at final concentrations of 500, 2000 and 3500 micrograms/ml in the presence and absence of an auxiliary metabolic activation system (rat liver S9-mix). Statistically significant increases in the percentage of aberrant cells compared with solvent control values were observed in cultures treated with TCA at 2000 and 5000 mu/ml. Investigation into the effects of TCA on the pH of the culture medium revealed significant reductions in pH at both these TCA concentrations. Neutralized TCA was then tested at concentrations of 500, 2,000 and 5000 micrograms/ml, also in the presence and absence of S9-mix. No statistically or biologically significant increases in the percentage of aberrant cells were observed in any of these cultures. In the mouse micronucleus test, neutralized TCA was administered in two equal intraperitoneal doses 24 h apart to C57BL/6JfBL10/Alpk mice (337, 675 and 1080 mg/kg in males; 405, 810 and 1300mg/kg in females). These dose levels represent 25%, 50% and 80% of the median lethal dose (MLD) in this strain of mouse. Bone marrow samples were taken 6 and 24 h after the second dose and the chromosomal damage assessed by analysis of the bone marrow for micronuclei. No statistically or biologically significant increases in the incidence of micronucleated polychromatic erythrocytes compared with the solvent control dosed animals were observed in either sex at the 6 h sampling time or in the females at the 24 h sampling time. A small but statistically significant increase in micronucleated polychromatic erythrocytes was observed in male mice 24 h after a dose of 675 mg/kg (50% MLD). Since no increases were noted at the 25 or 80% MLD, and the levels recorded are within the range of the concurrent solvent control values, the small increase observed in the males at the 50% MLD is considered not to be biologically significant. Flow cytometric studies on suspensions of isolated liver cell nuclei revealed that changes in FITC binding (indicating altered chromatin conformation) were induced by pH changes alone and were not caused by neutralized TCA.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin-binding protein expression in benign and malignant melanocytic proliferations

Studies on melanoma cell lines indicate the expression of actin-binding protein (ABP), a peripheral cytoplasmic protein that crosslinks actin, is important for melanoma cell motility. We used an ABP-specific monoclonal antibody to characterize ABP expression in 18 benign nevi and 28 primary and metastatic malignant melanomas. Heterogeneous expression of ABP staining was observed in metastatic melanoma. No clear differences in ABP staining were identified among compound nevi, dysplastic nevi, and superficial spreading melanoma; however, the lentiginous intraepidermal component of the benign and malignant lesions and the pagetoid cells of superficial spreading malignant melanoma were negative for ABP. In contrast, the nested intraepidermal and dermal components of both benign nevi and primary malignant melanoma were positive. The differential expression of ABP of the lentiginous component as opposed to the intraepidermal nests and pagetoid cells of benign nevi or melanoma may represent a capacity of the nested melanocytes to migrate from the epidermis to the dermis during maturation or invasion. Taken together, the findings support that ABP may be important for cell-cell adhesion during tumorigenesis and may play a role in tumor cell ameboid motility during tissue invasion.

Acculturation, education, and income as determinants of cigarette smoking in New Mexico Hispanics

Surveys of cigarette smoking among Hispanics in the Southwest have shown a pattern of smoking distinct from that of non-Hispanic whites, but determinants of smoking by Hispanics remain inadequately characterized. We have assessed household income, education, and language preference as predictors of cigarette smoking in 1072 Hispanic adults residing in a community in New Mexico. Cigarette smoking status (never, former, or current smoker) varied strongly with educational attainment, showing the anticipated gradient of increasing smoking as level of education declined. In contrast, cigarette smoking status did not vary in a consistent pattern with reported language preference. A composite measure of socioeconomic status, combining education and household income, predicted continued smoking among ever smokers, whereas language preference had no effect. In males, the age at which subjects started to smoke increased significantly with increasing education; a similar trend in females did not reach statistical significance. Determinants of numbers of cigarettes smoked daily were not identified. The findings suggest that, as in other U.S. populations, Hispanics in the Southwest with lower education and less income should be targeted for smoking prevention and cessation.

Heritability of ventilatory function in smoking and nonsmoking New Mexico Hispanics

Familial aggregation of ventilatory function has been described in several populations, but the effects of age and cigarette smoking on the extent of aggregation have not been well characterized. We used data from a survey of a Hispanic population in New Mexico to obtain estimates of heritability for FVC and FEV1 as percentages of predicted value. Product-moment correlations for FVC of spouse pairs were 0.18 (n = 90 pairs) if neither smoked, 0.013 (n = 45 pairs) if only the wife smoked, 0.18 (n = 118 pairs) if only the husband smoked, and -0.04 (n = 83 pairs) if both smoked. Correlations for FEV1 of spouse pairs were similar. Because parent-child correlations did not vary with sex, we calculated product-moment correlations from the pooled data. The parent-child correlations for nonsmoking parents with nonsmoking children 6 to 17 yr of age and living in the same house were 0.16 (n = 335 pairs) and 0.17 for FVC and FEV1, respectively. For parents whose children were 25 yr of age or older, the parent-child correlations for those living in different houses were 0.37 (n = 63 pairs) for FVC and 0.40 for FEV1 if neither smoked, and 0.24 (n = 27 pairs) for FVC and 0.14 for FEV1 if both smoked. Heritability estimates, estimated by path analysis, were 0.43 for FVC and 0.42 for FEV1 if neither family member smoked and 0.65 for FVC and 0.44 for FEV1 if both family members smoked. We conclude that there is a moderate degree of heritability of FVC and FEV1 with no substantial change based on age or smoking status.

Several testis-expressed genes in the mouse t-complex have expression differences between wild-type and t-mutant mice

The t-complex of the mouse occupies the proximal half of chromosome 17 and contains genes which have profound effects on spermatogenesis. Mutations of several loci in the t-complex appear to interact to cause male sterility or transmission ratio distortion (TRD). By cDNA screening or chromosomal walking we have identified seven genes, which are expressed in the germ cells of testis and map to various regions of the t-complex. These genes were named t-complex testis-expressed (Tctex) genes. An analysis of their expression patterns in testes from +/+, +/t, and t/t mice was done by in situ hybridization and by northern blotting. Six genes begin to be expressed at the pachytene stage: Three of them are more abundant at pachytene stage, while three others are more abundant at postmeiotic stages. One gene is expressed at all the stages of spermatogenesis. Interestingly, four Tctex genes show differences in the amount of transcript between wild-type and t-mutant testes. The chromosomal location and expression pattern imply that Tctex genes might be candidate genes for sterility or TRD.