Fullerene Ions Research Articles

Formation of coatings from accelerated ions of fluorinated fullerene C<sub>60</sub>(CF<sub>3</sub>)<sub>12</sub>

The first results of the deposition of coatings from accelerated ions of fluorinated fullerene C60(CF3)12 are presented. The coatings were formed at room temperature on Si substrates from a beam of singly charged C60(CF3)+12 ions with an energy of 5 keV, as well as from an ion beam, which also contained doubly charged C60(CF3)122+ ions and a certain amount of ionized fragments of molecules. The properties and structure of coatings obtained from accelerated ions of fluorinated fullerene are compared with the properties and structure of coatings obtained from accelerated C60 fullerene ions under the same conditions. According to X-ray photoelectron spectroscopy, fluorinated fullerene coatings contain about 4% fluorine. Investigations of the coatings structure and chemical bonds by X-ray photoelectron spectroscopy and Raman scattering showed that the presence of fluorine leads to decrease in the content of sp3 bonds and the formation of graphite-like sp2 structures. Coating hardness (H) and Young's modulus (E) compared to C60 ion coatings decrease from 36 to 18 GPa and from 245 to 133 GPa, respectively. The H/E ratio remained the same (~0.14). Tribological tests have shown for all coatings a friction coefficient close to 0.1. Also, all coatings are characterized by very low wear, less than 10–7 mm3/N∙m for coatings obtained from C60(CF3)12 ions, the contact angle is ~76°–78°. In the absence of fluorine, for the coating obtained from C60 ions, it is ~90°.

Latent ion tracks were finally observed in diamond

Injecting high-energy heavy ions in the electronic stopping regime into solids can create cylindrical damage zones called latent ion tracks. Although these tracks form in many materials, none have ever been observed in diamond, even when irradiated with high-energy GeV uranium ions. Here we report the first observation of ion track formation in diamond irradiated with 2–9 MeV C60 fullerene ions. Depending on the ion energy, the mean track length (diameter) changed from 17 (3.2) nm to 52 (7.1) nm. High resolution scanning transmission electron microscopy (HR-STEM) indicated the amorphization in the tracks, in which π-bonding signal from graphite was detected by the electron energy loss spectroscopy (EELS). Since the melting transition is not induced in diamond at atmospheric pressure, conventional inelastic thermal spike calculations cannot be applied. Two-temperature molecular dynamics simulations succeeded in the reproduction of both the track formation under MeV C60 irradiations and the no-track formation under GeV monoatomic ion irradiations.

Iron Complexes as Potential Carriers of Diffuse Interstellar Bands: The Photodissociation Spectrum of Fe+(H2O) at Optical Wavelengths.

The fullerene ion C60+ is the only carrier of diffuse interstellar bands (DIBs) identified so far. Transition-metal compounds feature electronic transitions in the visible and near-infrared regions, making them potential DIB carriers. Since iron is the most abundant transition metal in the cosmos, we here test this idea with Fe+(H2O). Laboratory spectra were obtained by photodissociation spectroscopy at 80 K. Spectra were modeled with the reflection principle. A high-resolution spectrum of the DIB standard star HD 183143 served as an observational reference. Two broad bands were observed from 4120 to 6800 Å. The 4120-4800 Å band has sharp features emerging from the background, which have the width of DIBs but do not match the band positions of the reference spectrum. Calculations show that the spectrum arises from a d-d transition at the iron center. While no match was found for Fe+(H2O) with known DIBs, the observation of structured bands with line widths typical for DIBs shows that small molecules or molecular ions containing iron are promising candidates for DIB carriers.

Effect of intermolecular interaction of the charge-transfer complex between molecular "tweezers" and C60/C70 on second-order nonlinear optical properties.

To enhance understanding of the correlation between the intermolecular interaction and second-order nonlinear optical (NLO) properties, we studied a "molecular tweezer" with two corannulene substituents linked by a tetrahydro[5]helicene imide, which enabled highly sensitive and selective complexation of C60/C70 through convex-concave π-π interactions. The geometric structure, molecular orbitals, intermolecular interactions, electron absorption spectra and second-order NLO properties of the charge-transfer (CT) complexes formed by molecular tweezers and C60/C70 were studied by density functional theory. Larger fullerenes helped to increase the intermolecular interaction and CT, thereby increasing the first hyperpolarizabilities of CT complexes. Embedding of lithium ions helped to enhance the electron-absorption ability of fullerenes, thereby increasing the intermolecular interaction and intermolecular CT and, thus, enhancing their first hyperpolarizability significantly. Our data indicated that, through structure adjustment (including increasing the volume of fullerene and embedding alkali metal ions), we could enhance intermolecular interactions and improve intermolecular CT significantly. These actions could improve the second-order NLO properties of CT complexes.

Development of a mass spectrometer for high-precision mass measurements of superheavy elements at JINR

A multiple-reflection time-of-flight (MR TOF) mass spectrometer for mass measurements of superheavy elements is currently being developed for an experimental cave of the Superheavy Element Factory at the Joint Institute for Nuclear Research in Dubna. Its conceptual and ion-optical designs are described in the present paper. The spectrometer is designed to achieve a mass measurement accuracy of 10^-7 at low measurement statistics (~5 events) for nuclides with half-lives down to 50 ms. To reach this goal, a new generation MR TOF analyzer with an ultra-high mass resolving power and highly-stable power supplies has been designed. An advanced set of ion-optical solutions for preparation and mass separation of the sample and calibrant ion beams is proposed for the spectrometer: a radiofrequency multiplexer trap separator of charge states, high vacuum quadrupole filters with two-stage differential pumping, operated in the “beat node coincidence” mode, a focused beam transport through the gate valve gaps, as well as a fullerene soot electron ionization calibrant ion source.

Incident Angle Dependent Formation of Ion Tracks in Quartz Crystal with C60+ Ions: Big Ions in Small Channels

Quartz (SiO2) crystals possess intrinsic columnar pores perpendicular to (0001) surfaces, consisting of three- and six-membered ring (3MR and 6MR) structures of Si and O atoms. The diameters of the larger pores, i.e., 6 MRs, are ~0.49 nm, while the diameters of fullerene (C60) ions are 0.7 nm, i.e., larger than either type of the pores. Transmission electron microscopy observation evidenced approximately two times longer ion tracks in the channeling condition, i.e., 0° incidence to (0001) surface, than an off-channeling condition, i.e., 7° incidence in this case, under 6 MeV C60 ion injection. The track length at the 0° incidence decreases more steeply than that at the 7° incidence with decreasing the energy from 6 MeV to 1 MeV. Finally, the track lengths at the 0° and 7° incidences become comparable, i.e., the channeling-like effect disappears at 1 MeV irradiation. This study experimentally indicates that the channeling-like effect of C60 ions is induced in quartz crystals, while the sizes of the channels are smaller than the C60 ions.

Velocity correlated emission of secondary clusters by a single surface impact of a polyatomic ion: a new mechanism of cluster emission and subpicosecond probing of extreme spike conditions.

Emission of secondary clusters off clean solid surfaces following the impact of a projectile ion at kiloelectronvolt (keV) kinetic energies is important from both practical and fundamental points of view. Understanding the underlying emission mechanisms using different types and sizes of projectile ions is therefore of high interest. In this perspective article we provide an up-to-date review of our recently observed new mechanism of velocity correlated cluster emission (VCCE) describing the emission of large clusters off different targets following the impact of a large polyatomic ion (C60-). Due to its large collision cross section and large number of light constituent atoms, the incoming C60- disintegrates completely upon an impact resulting in a rather broad and shallow energy deposition, high subsurface energy density and ultrafast evolution of an extreme nonlinear collision cascade dynamics. It is shown that kinetic energy distributions (KEDs) of the emitted clusters behave very differently from the KEDs of cluster ions emitted following the impact of a heavy monoatomic ion. All the large clusters emitted from a given target (following the keV C60- impact) move with nearly the same velocity and their KEDs could be fairly well described by a shifted Maxwellian. Namely, a thermal distribution superimposed on a center-of-mass velocity of a moving precursor which is the source of the emitted clusters. So far we have measured and analyzed KEDs for NbnCn+, TanCn+,Agn+, Cun+, Aun+ and Aln+ clusters emitted from their respective metallic targets, thus demonstrating the general validity of the VCCE effect as a new sputtering mechanism. We have also proposed a simple model for the initial, subpicosecond emission step of the precursor (and the resulting emitted clusters) and supported it by molecular dynamics (MD) simulations of the thermal behavior of the impact induced spike on the subpicosecond timescale. It is shown that each complete family of measured cluster KEDs (for a given target) can serve as a unique diagnostic tool, probing the extreme temperature and pressure evolving in the impact induced spike. We will discuss our accumulated findings from new perspectives and report new observations and additional analysis aspects.

Producing Iron Endohedral Fullerene on Electron Cyclotron Resonance Ion Source

An electron cyclotron resonance (ECR) ion source (ECRIS) can generate an available amount of multicharged ions, thus it is not limited for use in the field of accelerator science, but also in medical/biological fields, such as for heavy ion beam cancer treatment and ion engines. The processes of generating multicharged ions are mainly sequential collisions of a direct ionization process by electrons, and have good ion confinement characteristics. By utilizing this confinement property, we have synthesized iron-encapsulated fullerenes, which are supramolecular and can be expected to have various high functions. Fullerenes and iron ions are vaporized from pure solid materials and introduced into the ECRIS together with the support gas. We investigated conditions under which fullerene ions do not dissociate and iron ions are generated so that both can coexist. Generated ions are extracted from the ECRIS and separated by mass/charge with a dipole magnet, and detected with a Faraday cup. This measurement system is characterized by a wide dynamic range. The charge-state distribution (CSD) of ion currents was measured to investigate the optimum conditions for supramolecular synthesis. As a result, a significant spectrum suggesting the possibility of iron-encapsulated fullerenes was obtained. This paper describes the details of these experimental results.

Theoretical Study of Electronic Structure of Charged Fullerenes

The properties of excited short-living electron quantum levels of positively charged C 60 + Z fullerenes are numerically investigated with the help of the density functional theory (DFT) packages Quantum Espresso, ORCA, and VASP. Earlier, the existence of the volume-localized electron states for neutral and charged fullerenes was demonstrated analytically by making use of the model potential approach based on the unique quasispherical geometrical shape of C60. Here, we revisit this issue by verifying numerically the existence of volume-localized states and by calculating physical parameters of all electronic states with a special focus on highly charged fullerene ions. The ionization potentials of C 60 + Z are calculated and compared with available experimental data. The photoionization cross-sections for neutral fullerene using wave functions are obtained by making use of DFT codes. We demonstrate that lifetimes of excited states vary in the range 10 − 11 ÷ 10 − 4 s, and for the volume-localized levels, lifetimes are longer than those for the surface-localized states.

Experimental studies on photoabsorption by endohedral fullerene ions with a focus on Xe@C60 + confinement resonances

A brief overview on the status of experimental investigations into photoionization and fragmentation of fullerenes and endohedral fullerenes by absorption of a single short-wavelength photon is presented. The focus of this paper is on the endohedral Xe@C60 + molecular ion in which a xenon atom is centrally encapsulated inside a fullerene cage. Confinement resonances that result from the interference of Xe photoelectron matter waves emerging from the cavity were studied by exposing Xe@C60 + ions to synchrotron radiation of 60 to 150 eV energy which is the region of the well-known giant atomic Xe excitation resonance. Photoions Xe@C n q+ (with final charge states of the product ions and numbers of carbon atoms left in the cage) were recorded as a function of photon energy and cross sections for the individual reaction channels were determined. In addition to previous work, new final channels ( and ) were observed, and thus, about 70% of the oscillator strength expected for the encapsulated Xe atom in the investigated energy range could be recovered. The present results establish the first and, so far, only conclusive experimental observation of confinement resonances in an endohedral fullerene. The data are in remarkable agreement with relativistic R-matrix calculations that accompanied the previous experimental work.

Theoretical elucidation of the energy conversion rate in organic photovoltaic cells of the fullerene nanostructure derivatives. A density functional theory study

A comparative theoretical study of the kinetics of the Diels–Alder (DA) reaction between empty fullerene (C[Formula: see text]) and lithium ion encapsulated fullerene ([Formula: see text]) with 1,3 cyclohexadiene (C[Formula: see text]H[Formula: see text]) was carried out. This reaction takes place in a photovoltaic cell. The effect of the encapsulated [Formula: see text] ion on the conversion rate of solar energy into electricity has been highlighted through calculations based on the density functional theory (DFT). In addition, a static study using the global conceptual DFT indices, as part of the demonstration of the significant electrophilic power of the fullerene nanostructure, was carried out to show the effect of encapsulating the [Formula: see text] ion in this nanoparticle on the electrophilic power of Li[Formula: see text]@C[Formula: see text] and therefore on the acceleration of the reaction. The relationship between the HOMOdonor–LUMOacceptor energy difference and the DA reaction acceleration, and therefore the acceleration of light conversion (a rapid conversion implies a small gap), has been thoroughly examined. Moreover, a mechanistic study of the kinetics of the DA reaction of the fullerene involved in an organic photovoltaic cell has been carried out. In this section, a concerted synchronous mechanism with no effect of [Formula: see text] encapsulation on the synchronicity of the reaction was observed. Finally, it was revealed that Li[Formula: see text]@C[Formula: see text] reacted approximately 2466 times faster than C[Formula: see text]. Moreover, the experimental results were found in good agreement with the computer calculations.

Photoionization and photofragmentation of singly charged positive and negative Sc3N@C80 endohedral fullerene ions

SynopsisPhotoprocesses of the endohedral fullerene ions and in the gas phase have been experimentally investigated with emphasis on the specific effects of the encapsulated trimetallic nitride cluster Sc3N on the observed reaction yields. Clear evidence of photoexcitation near the Sc L edge is obtained with the dominating contributions visible in the one- and two-electron-removal channels. The experiments are accompanied by model calculations employing density functional theory (DFT).

C60 ions of 1\u2009MeV are slow but elongate nanoparticles like swift heavy ions of hundreds MeV

This study reports that high fluence fullerene ion (C60+) irradiation of 1–6 MeV, which was made possible by a new-type of high-flux ion source, elongates metal nanoparticles (NPs) in amorphous SiO2 as efficiently as swift heavy ions (SHIs) of 200 MeV Xe14+, i.e., two orders of the magnitude higher energy ions. Comparing the irradiation effects induced by both the beams, the stopping processes of C60 ions in SiO2 are discussed in this paper. Despite of having almost the same elongation efficiency, the C60+ irradiation induced ~10 times more efficient sputtering due to the clustering enhancement and/or the synergy effect. Ion tracks of ~10.4 nm in diameter and 60–80 nm in length were observed in crystalline SiO2 under 4 MeV C60 irradiation. While the track diameter was comparable to those by SHIs of the same electronic stopping, much shorter track lengths than those predicted by a rigid C60 molecule model indicates that the fragmentation occurred due to nuclear collisions. The elongation of the metal NPs was induced only down to the depth where the tracks were observed but not beyond.

X-Ray Photoelectron Study of the Binder/Electrode Interface on Silicon Anodes for Lithium Ion Batteries

Polymeric binders are a critical component of all composite electrodes used in today's lithium ion batteries (LIB). Binders keep active material and conductive additive mixture together, while also adhering this mixture to the current collector. At the particle level the binder forms bridges between particles of active material. Failure of these bridges contributes to electrical isolation of active material and thus poor cyclic life. the mechanical strength of these binder bridges is of key interest to understand the failure mechanisms of LIBs. Failure of binder bridges is highlighted in LIBs that incorporate Li-alloy forming anode materials such as Si which are known to degrade due to expansion and contraction during cycling. Meanwhile, the formation of solid electrolyte interphase (SEI) can also exacerbate capacity loss in novel anode materials, however the contribution of the binder to SEI formation and stability of alloying anodes has not been emphasized. Favorable interface properties between binder and active material resulting in good adhesion is desirable for anodes which encounter larger stresses during cycling. The objective of this study is to understand the effect different polymer binders have on the nature, formation, and location of the SEI layer of silicon based anodes. In this study crystalline Si wafers coated with thin films of CMC and PVDF binders were utilized. No conductive additives were used. Half cells containing either bare crystal Si or a wafer with a thin film of CMC or PVDF were cycled in a standard lithium-ion electrolyte (1 molar LiPF6 in 1:1:1 vol. ratio of EC:DC:DMC) to form a stable SEI. After cycling, the cells were opened in an inert atmosphere and x-ray photoelectron spectroscopy (XPS) was carried out to analyze and compare the surface chemistries. Depth profiling was then conducted utilizing C-60 fullerene ions opposed to the conventional Ar ion milling probe due to the known issue of chemical degradation caused by the Ar ion milling. In addition, the morphology of the substrates and binder films were characterized by SEM. Preliminary results indicate that binder layers on the order of hundreds of nm thick do not impede the lithiation and delithiation of Si (Figure 1A) but do play a role in the SEI composition (Figure B-D). These results can help inform the optimization of current and advanced composite electrodes for commercial LIB. Figure 1

Comparing Empty and Filled Fullerene Cages with High-Resolution Trapped Ion Mobility Spectrometry.

We have used trapped ion mobility spectrometry (TIMS) to obtain highly accurate experimental collision cross sections (CCS) for the fullerene C80- and the endohedral metallofullerenes La2@C80-, Sc3N@C80-, and Er3N@C80- in molecular nitrogen. The CCS values of the endohedral fullerenes are 0.2% larger than that of the empty cage. Using a combination of density functional theory and trajectory calculations, we were able to reproduce these experimental findings theoretically. Two effects are discussed that contribute to the CCS differences: (i) a small increase in fullerene cage size upon endohedral doping and (ii) charge transfer from the encapsulated moieties to the cage thus increasing the attractive charge-induced dipole interaction between the (endohedral) fullerene ion and the nitrogen bath gas molecules.

Photoionization and photofragmentation of singly charged positive and negative Sc3N@C80 endohedral fullerene ions

Author(s): Muller, A; Martins, M; Kilcoyne, ALD; Phaneuf, RA; Hellhund, J; Borovik, A; Holste, K; Bari, S; Buhr, T; Klumpp, S; Perry-Sassmannshausen, A; Reinwardt, S; Ricz, S; Schubert, K; Schippers, S | Abstract: Photoprocesses of the endohedral fullerene ions Sc3N@C80+ and Sc3N@C80- in the gas phase have been investigated in the photon energy ranges 30-50 eV and 280-420 eV. Single and double ionization as well as single ionization accompanied by the release of a C2 dimer were observed as a function of the photon energy for the positive parent ion and double detachment was measured for the negative parent ion. The emphasis of the experiments was on the specific effects of the encapsulated trimetallic nitride cluster Sc3N on the observed reactions. Clear evidence of photoexcitation near the Sc L edge is obtained with the dominating contributions visible in the one- and two-electron-removal channels. K-vacancy production in the encapsulated central nitrogen atom is seen in the single ionization of Sc3N@C80+ but is much less pronounced in the photoionization-with-fragmentation channel. Comparison of the cross sections near the carbon K edge with the corresponding channels measured previously in the photoionization of Lu3N@C80+ reveal strong similarities. Previously predicted sharp resonance features in the ionization of Sc3N@C80+ ions below the Sc M edge are not confirmed. The experiments are accompanied by quantum-chemistry calculations in the Hartree-Fock approximation and by model calculations employing density functional theory (DFT).

The photon‐ion merged‐beams experiment PIPE at PETRA III—The first five years

The Photon‐Ion Spectrometer at PETRA III—in short, PIPE—is a permanently installed user facility at the "Variable Polarization XUV Beamline" P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. The careful design of the PIPE ion‐optics in combination with the record‐high photon flux at P04 has lead to a breakthrough in experimental studies of photon interactions with ionized small quantum systems. This short review provides an overview over the published scientific results from photon‐ion merged‐beams experiments at PIPE that were obtained since the start of P04 operations in 2013. The topics covered comprise photoionization of ions of astrophysical relevance, quantitative studies of multi‐electron processes upon inner‐shell photoexcitation and photoionization of negative and positive atomic ions, precision spectroscopy of photoionization resonances, photoionization and photofragmentation of molecular ions, and of endohedral fullerene ions.

Characteristics of Ion–Ion Thruster Generating Continuously Positive and Negative Ion Beams

The neutralizers in ion thruster systems do not generate thrust force. Hence, the power consumption of a neutralizer limits the thrust efficiency of the ion thruster system. Therefore, an ion thruster system is proposed that uses a negative ion source that generates thrust force as well as neutralizes the positive ion beam. In this study, in order to verify the feasibility of this ion thruster system by ground experiments, a negative fullerene ion source was developed and three experiments were conducted. First, in order to demonstrate that the satellite can accelerate ions without becoming charged, the positive and negative ion beams were accelerated in the floating condition using a feedback circuit. Second, in order to verify whether the formation of the virtual anode could be suppressed, the space potential and the beam profile in the downstream region of the ion beam were measured. Third, in order to demonstrate that the thruster system generates thrust force, the thrust with a beam target was measured. From the aforementioned results, it was concluded that the experimental verification of the feasibility of the ion thruster with combined positive and negative ions without a neutralizer was successful.

Desorption of Fullerene Dimers upon Heating Non-IPR Fullerene Films on HOPG

Low energy ion beam deposition of mass-selected fullerene ions was used to generate thin films of non-IPR fullerenes, C2n (2n = 48–58 and 52–68) on graphite under UHV. These were probed by mass-resolved thermal desorption spectroscopy. We observe the emission of dimers in addition to dominant monomer desorption for 2n = 58–68, while for 2n = 48–56 no dimer desorption was detected. Dimer signals were typically at <1% level compared to the monomers. The desorption temperature ranges of these dimer species were higher and much narrower than for the corresponding monomers. Building also on theoretical considerations, we came to the conclusion that coalescence reactions between the fullerenes must take place below 1000 K and that fullerenes with more than three pairs of adjacent pentagons cross-link too strongly to allow the desorption of dimers.

Tagging fullerene ions with helium in a cryogenic quadrupole trap

Helium tagging of charged C60q+ ions (q = 1–3) has been used for measuring electronic and infrared gas phase spectra, allowing astronomers to improve the identification of fullerenes in space. Here, we present a detailed study of the attachment of He to cold mass selected fullerene ions. Experiments were performed in the temperature variable radio frequency (rf) ion trap ISORI at high He densities and a few K. For all three charge states, the ternary rate coefficients for forming He-C60q+ are below 10−31 cm6s–1 and all three show temperature dependences, proportional to exp(-T/T0) with T0.< 1.5 K. While most of our knowledge on the interaction of C60+ with He atoms comes from ab initio calculations, from gas phase ion mobility experiments, and from fullerene ions ejected from He-droplets, the sequential addition of He to C60q+ in ter- or maybe bimolecular collisions provides complementary information. Our experimental results are tentatively explained with difficulties to form and stabilize the short-lived He-fullerene complexes while relaxation of hot fullerenes in collisions with cold He seems to be rather efficient. Severe restrictions are due to the fact that thermalized C60q+ ions behave like fast rotating rigid spheres. Despite the low efficiency in attaching the first He, measurements reveal a fast subsequent growth as soon as a few He atoms stick to the fullerene. In the case of triply charged ions, almost all primaries can be quickly converted into the particular structure He32-C603+. IR excitation of this thermalized complex with one 1329 cm-1 photon provides interesting insight into the decay kinetics.