Christopher P Ewels

• Materials Science
• Research Director at French National Centre for Scientific Research

We present an efficient strategy for on-surface engineering of organic metal-free supramolecular complexes with long-term spin protection. By vacuum deposition of azafullerene (C59N•) monomers on a pre-deposited template layer of [10]cycloparaphenylene ([10]CPP) nanohoops on Au(111) surface we exploit the molecular shape matching between the C59N•...

We present an efficient strategy for on-surface engineering of organic metal-free supramolecular complexes with long-term spin protection. By vacuum deposition of azafullerene (C59N•) monomers on a pre-deposited template layer of [10]cycloparaphenylene ([10]CPP) nanohoops on Au(111) surface we exploit the molecular shape matching between the C59N•...

We use molecular dynamics calculations to investigate the behavior of metal cations (Li, Na and Zn) within ionic liquids (ILs), specifically EMIM-TFSI, and their impact on key properties, particularly focusing...

AlF3 and MgF2 are important catalysts for fluorination processes. In this study we characterise structures consisting of either AlF3, or MgF2 supported over AlF3, using Fourier Transform Infrared Spectroscopy of...

We deposit azafullerene C59N• radicals in a vacuum on the Au(111) surface for layer thicknesses between 0.35 and 2.1 monolayers (ML). The layers are characterized using X-ray photoemission (XPS) and X-ray absorption fine structure (NEXAFS) spectroscopy, low-temperature scanning tunneling microscopy (STM), and by density functional calculations (DFT...

We investigate the contribution of pseudocapacitance to the overall capacitance of MnO2 electrodes in pure and alkaline-doped ionic liquids via two spectroscopic methods: step potential electrochemical spectroscopy (SPECS) and in situ Raman spectroscopy. For both characterization methods, thin-film electrodes of birnessite-like amorphous MnO2 were...

Folded regions are commonly encountered in a number of hexagonal boron nitride (h-BN) based bulk and nanostructured materials. Two types of structural modifications occur in folded h-BN layers: local curvature at the folded edges and interlayer shear of the layers which changes the stacking of the overlapping flat regions. In this work we discuss,...

Explosive percolation is an experimentally-elusive phenomenon where network connectivity coincides with onset of an additional modification of the system; materials with correlated localisation of percolating particles and emergent conductive paths can realise sharp transitions and high conductivities characteristic of the explosively-grown network...

Folded regions are commonly encountered in a number of hexagonal boron nitride (h-BN)-based bulk and nanostructured materials. Two types of structural modifications occur in folded h-BN layers: local curvature at the folded edges and interlayer shear of the layers which changes the stacking of the overlapping flat regions. In this work, we discuss,...

Using laser-induced vaporisation to evaporate and ionise a source of curved polyaromatic hydrocarbons (carbon nanobelts), we show collision impacts between species cause mass loss and the resultant ions are catalogued via mass-spectrometry. These data are interpreted via a series of “in-silico”-simulated systematic hydrogen-loss studies using densi...

We explore the importance of curvature in carbonaceaous species transformation and stability, using laser-induced vaporisation to evaporate and ionise a source of curved polyaromatic hydrocarbons: carbon nanobelts. Collision impacts between species cause mass loss and the resultant ions are catalogued via mass-spectrometry. To interpret the mass sp...

We report the intercalation of iodine chains in highly crystalline arc-discharge multiwalled carbon nanotubes (MWCNTs), not in the central cavity but instead between the concentric graphene shells. High-resolution transmission electron microscopy demonstrated that the intercalation was asymmetric with respect to the longitudinal axis of the nanotub...

Dislocations are a central concept in materials science, which dictate the plastic deformation and damage evolution in materials. Layered materials such as graphite admit two general types of interlayer dislocations: basal and prismatic dislocations, of which prismatic dislocations have been relatively less studied. Using density functional theory...

Molecular entities with robust spin-1/2 are natural two-level quantum systems for realizing qubits and are key ingredients of emerging quantum technologies such as quantum computing. Here we show that robust and abundant spin-1/2 species can be created in situ in the solid state from spin-active azafullerene C59N cages supramolecularly hosted in cr...

Hydrogenated small fullerenes (Cn, n < 60) are of interest as potential astrochemical species, and as intermediates in hydrogen-catalysed fullerene growth. However, the computational identification of key stable species is difficult due to the vast configurationally space of structures. In this study, we explored routes to predict stable hydrogenat...

Dislocations are a central concept in materials science, which dictate the plastic deformation and damage evolution in materials. Layered materials such as graphite admit two general types of interlayer dislocations: basal and prismatic dislocations, of which prismatic dislocations have been relatively less studied. Using density functional theory...

Hydrogenated small fullerenes (Cn, n<60) are of interest as potential astrochemical species, and as intermediates in hydrogen catalysed fullerene growth. However computational identification of key stable species is difficult due to the vast combinatorial space of structures. In this study we explore routes to predict stable hydrogenated small full...

We present a comprehensive theoretical and experimental Raman spectroscopic comparative study of bulk Phosphorus allotropes (white, black, Hittorf's, fibrous) and their monolayer equivalents, demonstrating that the application of the Placzek approximation to density functional theory calculated frequencies allows reliable and accurate reproduction...

Vertically aligned multiwalled carbon nanotubes synthetized by catalytic chemical vapor deposition are irradiated with low kinetic energy oxygen ions to graft oxygen functional groups at their surface. Subsequently, the thermal stability of these functional groups is investigated by heating the sample progressively to 200, 300, 400 and 500 °C. X-Ra...

We report the effect of −(CH2)n−COOH (n=0,1,3) functional groups on pyrene adsorption and associated electropolymerization mechanisms on carbon nanotube model electrodes, as well as resulting electrochemical charge‐storage properties in a Li metal supercapacitor configuration. The impact of pyrene functional groups is tested by varying the alkyl ch...

Ionogels represent a route to biphasic materials, for the use of ionic liquids (ILs) for all solid devices. Confining ILs within host networks enhances their averaged dynamics, resulting in improved charge transport. Fragility, short relaxation times, low viscosity, and good ionic conductivity, all them appear to be related to the IL / host network...

Two efficient excited state intramolecular proton transfer (ESIPT) dyes based on the hydroxyphenyl-oxazole core and containing one or two triphenylamine donor groups are explored with theoretical tools. These compounds are known to show clear experimental dual emission behaviour, leading to nearly pure white-light emission for one derivative. To pr...

Pyrene carrying an 1,2-dithiolane linker was employed to functionalize exfoliated WS2 and the resulting material was used in a proof-of-concept application as a photoresistor type sensor. The WS2–pyrene hybrid material was comprehensively characterized by spectroscopic, thermal and microscopy techniques, coupled to density functional theory modelli...

Laser-deposited carbon aerogel is a low-density porous network of carbon clusters synthesized using a laser process. A one-step synthesis, involving deposition and annealing, results in the formation of a thin porous conductive film which can be applied as a chemiresistor. This material is sensitive to NO2 compared to ammonia and other volatile org...

The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)–type bond rotation. In this stud...

Density functional studies of the edges of single‐layer 1H‐MoS2 are presented. This phase presents a rich variability of edges that can influence the morphology and properties of MoS2 nano‐objects, play an important role in industrial chemical processes, and find future applications in energy storage, electronics and spintronics. The so‐called Mo‐1...

Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical...

Above a critical diameter, single- or few-walled carbon nanotubes spontaneously collapse as flattened carbon nanotubes. Raman spectra of isolated flattened and cylindrical carbon nanotubes have been recorded. The collapse provokes an intense and narrow D band, despite the absence of any lattice disorder. The curvature change near the edge cavities...

Alkylamine-strapped chromophores based on a dithienylpyrrole core, and in which the Excited State Intramolecular Proton Transfer (ESIPT) process yields a zwitterionic structure rather than a keto tautomer have been reported recently (Suzuki et al., Angew. Chem. Int. Ed. 2014, 53, 8231), and are known to exhibit large Stokes shifts. Using Time-Depen...

Vertically aligned multiwalled carbon nanotubes (v-CNTs) were functionalized with oxygen groups using low kinetic energy oxygen ion irradiation. X-ray photoelectron spectroscopy (XPS) analysis indicates that oxygen ion irradiation produces three different types of oxygen functional groups at the CNTs surface: epoxide, carbonyl and carboxyl groups....

A major handicap towards the exploitation of radicals is their inherent instability. In the paramagnetic azafullerenyl radical C59N., the unpaired electron is strongly localized next to the nitrogen atom, which induces dimerization to diamagnetic bis(azafullerene), (C59N)2. Conventional stabilization by introducing steric hindrance around the radic...

Using density functional theory with van der Waals (vdW) corrections, we study the collapse of free-standing single-walled carbon nanotubes (also called “dogbone” nanotubes). Their thermodynamic stability is strongly influenced by the initial stacking sequence, with lateral shear allowing registry change with turbostratic stacking predominant. The...

Durch supramolekulare Komplexierung mit einem [10]Cycloparaphenylen([10]CPP)‐Nanogürtel kann das C59N.‐Radikal effektiv stabilisiert werden. Das charakteristische Triplett‐EPR‐Signal von C59N.⊂[10]CPP wurde auch mehrere Wochen nach seiner Generierung noch detektiert. Abstract A major handicap towards the exploitation of radicals is their inherent...

Double-layer capacitors (EDLC) [1-2] show superior power density, excellent shelf life, high coulombic efficiency, which make them ideal candidates for high-power applications. However, their use remains hindered because of their relatively low energy density in comparison to batteries. Molecular redox grafting[3,4] is one of the two main strategie...

Despite decades of study the precise behavior of bromine in graphitic carbons remains unclear. In this report, using Raman spectroscopy , we reveal two types of bromine structure in graphitic carbon materials. Between fluorinated graphene layers with a composition close to C2F, Br2 molecules are intercalated in a form similar to liquid bromine. Bro...

Aqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability and low-cost materials. Herein, a novel di-block oligomer (DNVBr), serving as the negative e...

Aqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability, and low‐cost materials. Herein, a novel di‐block oligomer, serving as the negative electrod...

In this chapter we explore the possibilities of using MoS2 for chemical gas sensing. We first introduce monolayer MoS2 and discuss the different reconstructed phases that can be produced in terms of their atomic and electronic structure. We show how these properties can vary drastically from their bulk counterparts, and how MoS2 can be taken as a u...

div>Herein, we report a improved method for the physical grafting of 1-nitropyrene (Pyr-NO2) onto highly graphitized carbon onion. This is achieved through a lowering of the onset potential of the pyrene polymerization via in situ reduction of the NO2 group. The additional redox activity pertaining to the reduced NO2 enables exceeding the faradaic...

This book presents a blueprint for researchers in the area of nanotechnology for chemical defense, especially with regard to future research on detection and protection. It addresses the synthesis of complex nanomaterials with potential applications in a broad range of sensing systems. Above all, it discusses novel experimental and theoretical tool...

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss...

Using density functional calculations, we explore π-π and π-H stacking interactions in conjugated polymer-carbon nanomaterial composites, through a detailed surface energy mapping procedure. Taking the triphenyl vinylene oligomer as a structural model for poly para-phenylene vinylene (PPV), we map intermolecular stacking configurations between PPV...

Our trifluoromethyl functionalization method enables the dissolution and isolation of missing metallofullerenes of Gd@C74(CF3) n . After multi-stage high-performance liquid chromatography purification, Gd@C74(CF3)3 and two regioisomers of Gd@C74(CF3) are isolated. X-ray crystallographic analysis reveals that all of the isolated metallofullerenes r...

Using density functional theory approaches, we follow the sequential addition of CF3 functional groups to the surface of the metallic endofullerene species [email protected]60. The presence of gadolinium in the interior of the cage strongly influences the addition sequence. The calculations are able to successfully identify end points in the additi...

Endohedral metallofullerenes have been extensively studied since the first experimental observation of La@C60 in a laser-vaporized supersonic beam in 1985. However, most of these studies have focused on metallofullerenes larger than C60 such as (metal)@C82, and there are no reported purified C60-based monomeric metallofullerenes, except for [Li@C60...

Hybrid systems based on graphene and semiconductor quantum dots are prospective materials for optoelectronics and photonics. In this work, electronic structure and dielectric properties of small particles of cadmium sulfide on the surface of graphene were studied using the density functional theory. The optical spectrum of this hybrid structure dep...

The complex of [10]cycloparaphenylene ([10]CPP) with bisazafullerene (C59N)2 is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59N)2⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the com‐ponents especially with the second [10]CPP bound...

The complex of [10]cycloparaphenylene ([10]CPP) with bisazafullerene (C59N)2 is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP⊃(C59N)2⊂[10]CPP. Photophysical and redox properties support an electronic interaction between the com‐ponents especially with the second [10]CPP bound...

In article number 1701988, Joël Gaubicher, Philippe Poizot, Fabrice Odobel and co-workers report the first ever battery material that works with simultaneous uptake and release of both cations and anions. This represents one of a new family of organic electrode materials that shows great promise, thereby promoting the design of cutting-edge, low-co...

Endohedral metallofullerenes have been extensively studied, since the first experimental observation of La@C60 in a laser-vaporized supersonic beam in 1985. However, all of these studies have been carried out on metallofullerenes larger than C60 such as (metal)@C82, and there are no reported purified C60-based metallofullerenes except for [Li@C60]+...

Aqueous batteries are an emerging candidate for low-cost and environmentally friendly grid storage systems. Designing such batteries from inexpensive, abundant, recyclable, and nontoxic organic active materials provides a logical step toward improving both the environmental and economic impact of these systems. Herein the first ever battery materia...

The covalent functionalization of exfoliated semiconducting MoS2 by 1,2-dithiolanes bearing an ethylene glycol alkyl chain terminated to a butoxycarbonyl-protected amine and a photoactive pyrene moiety is accomplished. The MoS2-based nanohybrids were fully characterized by complementary spectroscopic, thermal, and microscopy techniques. Markedly, d...

N-methyl-2-pyrrolidone (NMP) has been shown to be the most effective solvent for liquid phase exfoliation and dispersion of a range of 2D materials including graphene, molybdenum disulphide (MoS2) and black phosphorus. However, NMP is also known to be susceptible to sonochemical degradation during exfoliation. We report that this degradation gives...

Plasma fluorination of graphene is studied using a combination of spectroscopy and microscopy techniques, giving insight into the yield and fluorination mechanism for functionalization of supported graphene with both CF4 and SF6 gas precursors. Ion acceleration during fluorination is used to probe the effect on grafting functionalities. Adatom clus...

As potential donor materials for organic photovoltaic (OPV) devices, six conjugated small molecules with donor-acceptor configuration based on 3-hexylthiophene monomer (3HT) were designed and studied by means of density functional theory (DFT) and time-dependent DFT. Their geometric structure, electronic and optical properties were investigated at...

Double-walled carbon nanotubes (DWCNTs) are fluorinated using (1) fluorine F2 at 200 °C, (2) gaseous BrF3 at room temperature, and (3) CF4 radio-frequency plasma functionalization. These have been comparatively studied using transmission electron microscopy and infrared, Raman, X-ray photoelectron, and near-edge X-ray absorption fine structure (NEX...

Additional experimental data.

AA-stacked graphite and closely related structures, where carbon atoms are located in registry in adjacent graphene layers, are a feature of graphitic systems including twisted and folded bilayer graphene, and turbostratic graphite. We present the results of ab initio density functional theory calculations performed to investigate the complexes tha...

We use a density functional theory approach under the local density approximation (DFT/LDA) to describe the formation of polybromide chain structures, their stretching frequency modes and charge transfer induced by the interaction of these molecules with a graphene sheet. In many cases, we find polybromides to be more thermodynamically stable than...

C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density fu...

We calculate the infrared (IR) absorption spectra using DFT B3LYP(6–311G) for a range of small closed-cage fullerenes, C n , n =20, 24, 26, 28, 30 and 60, in both neutral and multiple positive and negative charge states. The results are of use, notably, for direct comparison with observed IR absorption in the interstellar medium. Frequencies fall t...

Since its creation at the end of the 1990's, the EELS and X‐ray Absorption Spectroscopy (XAS) database has gathered more than 220 spectra covering 37 elements of the periodic table, becoming the largest open‐access electronic repository of spectra from EELS and XAS experiments. The EELS database is now a common tool used by spectroscopists, theoret...

Density functional calculations are used to study the role of edge-functionalization on the structure and electronic properties of cycloparaphenylene (CPPs) containing from six to twenty benzenoid rings. We substitute hydrogen by the halogens fluorine, chlorine and bromine. The resultant Cyclotetrahalo-p-phenylenes are compared with their hydrogena...

The filling of single-walled carbon nanotube films with 1-adamantanemethanol and 1-bromoadamantane molecules was carried out by a gas-phase procedure. Optical absorption and Raman spectroscopies revealed the effects of charge transfer for samples treated with 1-bromoadamantane. Using density functional simulations we show that the charge transfer t...

A facile approach to individualize spherically aggregated pristine carbon nanohorns (pr-CNHs) was established. Specifically, we found that treatment of pr-CNHs with chlorosulfonic acid generates positively charged polarized species, which disintegrate toward individualized carbon nanohorns (in-CNHs). Interestingly, the isolated in-CNHs were reveale...

A facile approach to individualize spherically aggregated pristine carbon nanohorns (pr-CNHs) was established. Specifically, we found that treatment of pr-CNHs with chlorosulfonic acid generates positively charged polarized species, which disintegrate toward individualized carbon nanohorns (in-CNHs). Interestingly, the isolated in-CNHs were reveale...

An original and practical procedure for preparing graphene-modified gold electrodes has been developed by careful control of the electrochemical exfoliation process of natural graphite. Pre-exfoliated (intercalated) graphite is first mechanically deposited onto a gold electrode. A cathodic treatment is then performed in N,N-dimethylformamide contai...

Carbon nanohorns (sometimes also known as nanocones) are conical carbon nanostructures constructed from an sp(2) carbon sheet. Nanohorns require no metal catalyst in their synthesis, and can be produced in industrial quantities. They provide a realistic and useful alternative to carbon nanotubes, and possibly graphene, in a wide range of applicatio...

The electron energy-loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) database has been completely rewritten, with an improved design, user interface, and a number of new tools. The database is accessible at https://eelsdb.eu/ and can now be used without registration. The submission process has been streamlined to encourage spectrum...