We used scanning tunneling microscopy and spectroscopy (STM/S) techniques to analyze the relationships between the edge shapes and the electronic structures in as-grown chemical vapor deposition ...(CVD) graphene nanoribbons (GNRs). A rich variety of single-layered graphene nanoribbons exhibiting a width of several to 100 nm and up to 1 μm long were studied. High-resolution STM images highlight highly crystalline nanoribbon structures with well-defined and clean edges. Theoretical calculations indicate clear spin-split edge states induced by electron–electron Coulomb repulsion. The edge defects can significantly modify these edge states, and different edge structures for both sides of a single ribbon produce asymmetric electronic edge states, which reflect the more realistic features of CVD grown GNRs. Three structural models are proposed and analyzed to explain the observations. By comparing the models with an atomic resolution image at the edge, a pristine (2,1) structure was ruled out in favor of a reconstructed edge structure composed of 5–7 member rings, showing a better match with experimental results, and thereby suggesting the possibility of a defective morphology at the edge of CVD grown nanoribbons.
A three-dimensional elemental carbon kagome lattice, made of only fourfold-coordinated carbon atoms, is proposed based on first-principles calculations. Despite the existence of 60° bond angles in ...the triangle rings, widely perceived to be energetically unfavorable, the carbon kagome lattice is found to display exceptional stability comparable to that of C(60). The system allows us to study the effects of triangular frustration on the electronic properties of realistic solids, and it demonstrates a metal-insulator transition from that of graphene to a direct gap semiconductor in the visible blue region. By minimizing s-p orbital hybridization, which is an intrinsic property of carbon, not only the band edge states become nearly purely frustrated p states, but also the band structure is qualitatively different from any known bulk elemental semiconductors. For example, the optical properties are similar to those of direct-gap semiconductors GaN and ZnO, whereas the effective masses are comparable to or smaller than those of Si.
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·This novel approach can simulate particle sintering coupled to moisture transfer.·Strong viscosity gradients can exist as a result of the moisture transfer.·FEM simulations predict a ...slower sintering compared to simplified analytical models.·The particle size affects strongly both the sintering and moisture transfer dynamics.·Particles can be considered homogeneous when sufficiently small.
In many applications, amorphous particles bond together through a phenomenon known as sintering to minimize their surface energy. Water is a plasticizer for many food and pharmaceutical powders and the strong reduction in viscosity induced by moisture absorption can accelerate strongly particle sintering 1. Numerical simulations of particle sintering usually neglect the coupling with moisture transfer, considering a uniform viscosity throughout the particle.
In this study, a novel approach based on solving Navier-Stokes equation using an Arbitrary Lagrangian-Eulerian (ALE) approach is proposed to model the dynamics of particle sintering coupled with moisture transfer. Maltodextrin DE21 is considered as an industrially relevant example of amorphous particles. Due to moisture uptake, strong gradients of viscosity can exist in the particles undergoing sintering.
FEM simulations consider accurately the forces acting on the contact area between the particles, leading to slower dynamics than commonly used approximate analytical models. This study highlights that FEM simulations considering a homogeneous moisture and viscosity within the particles are in many cases sufficiently accurate and identifies the limits of validity of this assumption. In the conditions considered in this study, the intraparticle gradients were found to condition significantly the sintering dynamics only when particle diameter is above 1.5 mm. The particle size affects strongly both the dynamics of sintering and of moisture transfer. Moreover, higher external relative humidity leads to a lower viscosity and a faster sintering kinetics. The initial water content was found to have a lower impact in the conditions studied.
This coupled simulation approach can be used to identify conditions reducing the risk of caking during the storage of amorphous powders or to master sintering during powder structuration processes. Furthermore this study helps identifying when simpler simulation approaches considering homogeneous particles can be safely used and shows the limitations of simplified analytical models.
One of the great challenges in surface chemistry is to assemble aromatic building blocks into ordered structures that are mechanically robust and electronically interlinked—i.e., are held together by ...covalent bonds. We demonstrate the surface-confined growth of ordered arrays of poly(3,4-ethylenedioxythiophene) (PEDOT) chains, by using the substrate (the 110 facet of copper) simultaneously as template and catalyst for polymerization. Copper acts as promoter for the Ullmann coupling reaction, whereas the inherent anisotropy of the fcc 110 facet confines growth to a single dimension. High resolution scanning tunneling microscopy performed under ultrahigh vacuum conditions allows us to simultaneously image PEDOT oligomers and the copper lattice with atomic resolution. Density functional theory calculations confirm an unexpected adsorption geometry of the PEDOT oligomers, which stand on the sulfur atom of the thiophene ring rather than lying flat. This polymerization approach can be extended to many other halogen-terminated molecules to produce epitaxially aligned conjugated polymers. Such systems might be of central importance to develop future electronic and optoelectronic devices with high quality active materials, besides representing model systems for basic science investigations.
Substitutional phosphorus doping in single-wall carbon nanotubes (SWNTs) is investigated by density functional theory and resonance Raman spectroscopy. Electronic structure calculations predict ...charge localization on the phosphorus atom, generating nondispersive valence and conduction bands close to the Fermi level. Besides confirming sustitutional doping, accurate analysis of electron and phonon renormalization effects in the double-resonance Raman process elucidates the different nature of the phosphorus donor doping (localized) when compared to nitrogen substitutional doping (nonlocalized) in SWNTs.
Distal upper limb surgery is performed under WALANT (Wide Awake Local Anesthesia No Tourniquet) in many outpatient centers because the benefits are numerous: simple, low-cost technique, with fast ...turnover and short length of stay. In view of a paucity of data concerning patient satisfaction, this non-randomized cohort study was designed to compare EVAN-LR anesthesia satisfaction questionnaire results (information, pain, expectation, attention, discomfort: 0-100 points) between patients receiving WALANT or axillary nerve block (AxB). After IRB approval, patients (>18 years, stable ASA 1-3) scheduled for outpatient distal upper limb surgery were prospectively enrolled in the two groups. At discharge, patients in both groups received standard information on postoperative recovery and care, with a multimodal analgesic regime (acetaminophen and ketoprofen for 5 days). The primary endpoint was EVAN-LR score before discharge. Secondary endpoints were pain relief and side-effects over a 7-day period. Results were recorded as median and 25-75% interquartile range. Propensity-score-matched analysis was performed. Over the study period, from October 2019 to November 2020, 183 patients were included; 48 WALANT patients were propensity-score matched to 48 AxB patients. Pre-procedural APAIS anxiety score was lower in the WALANT than the AxB group: 9 (IQR, 6-12) vs 12 (IQR, 8-14) (p = 0.01). EVAN-LR scores were similar between the WALANT (78 72-82) and the AxB group (73 67-80). Incidences of paresthesia and of pain (NRS pain score, opioid rescue) were similar. WALANT patients had shorter length of stay: 135 (110-175) min vs 170 (110-250) min (p = 0.01). The present study demonstrated that WALANT was associated with a high level of patient satisfaction. For clinical relevance and quality of care, WALANT should be proposed in first line for distal limb surgery.
We show extensive theoretical studies related to the generation and characterization of 2D and 3D ordered networks using 1D units that are connected covalently. We experimentally created ...multi-terminal junctions containing 1D carbon blocks in order to study the most common morphologies and branched structures that could be used in the theoretical design of network models. We found that the mechanical and electronic characteristics of ordered networks based on carbon nanotubes (ON-CNTs) are dominated by their specific super-architecture (hexagonal, cubic, square, and diamond-type). We show that charges follow specific paths through the nodes of the multi-terminal systems, which could result in complex integrated nanoelectronic circuits. The 3D architectures reveal their ability to support extremely high unidirectional stress when their mechanical properties are studied. In addition, these networks are shown to perform better than standard carbon aerogels because of their low mass densities, continuous porosities, and high surface areas.
We investigate the phonon normal modes in hydrogen-terminated graphene nanoribbons GNRs using the second-generation reactive empirical bond order REBOII potential and density-functional theory ...calculations. We show that specific modes, absent in pristine graphene and localized at the GNR edges, are intrinsic signatures of the vibrational density of states of the GNRs. Three particular modes are described in details: a transverse phonon mode related to armchair GNRs, a hydrogen out-of-plane mode present in both armchair and zigzag GNRs, and the Raman radial-breathing-like mode. The good agreement between the frequencies of selected edge modes obtained using REBOII and first-principles methods shows the reliability of this empirical potential for the calculation and the assignment of phonon modes in carbon nanostructures where carbon atoms present a sp2 hybridization.
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