C60 Ions Research Articles

Femtosecond X-ray-induced explosion of C60 at extreme intensity.

Understanding molecular femtosecond dynamics under intense X-ray exposure is critical to progress in biomolecular imaging and matter under extreme conditions. Imaging viruses and proteins at an atomic spatial scale and on the time scale of atomic motion requires rigorous, quantitative understanding of dynamical effects of intense X-ray exposure. Here we present an experimental and theoretical study of C60 molecules interacting with intense X-ray pulses from a free-electron laser, revealing the influence of processes not previously reported. Our work illustrates the successful use of classical mechanics to describe all moving particles in C60, an approach that scales well to larger systems, for example, biomolecules. Comparisons of the model with experimental data on C60 ion fragmentation show excellent agreement under a variety of laser conditions. The results indicate that this modelling is applicable for X-ray interactions with any extended system, even at higher X-ray dose rates expected with future light sources.

Self-Healing Phenomenon and Dynamic Hardness of C60-Based Nanocomposite Coatings

The phenomenon of surface self-healing in C60-based polymer coatings deposited by ion-beam assisted physical vapor deposition was investigated. Nanoindentation of the coatings led to the formation of a protrusion rather than an indent. This protrusion was accompanied by an abnormal shape of the force-distance curve, where the unloading curve lies above the loading curve due to an additional force applied in pulling the indenter out of the media. The coatings exhibited a nanocomposite structure that was strongly affected by the ratio of C60 ion and C60 molecular beam intensities during deposition. The coatings also demonstrated the dynamic hardness effect, where the effective value of the hardness depends significantly on the indentation speed.

Transmission secondary ion mass spectrometry using 5 MeV C60+ ions

In the secondary ion mass spectrometry (SIMS), use of cluster ions has an advantage of producing a high sensitivity of intact large molecular ions over monatomic ions. This paper presents further yield enhancement of the intact biomolecular ions by measuring the secondary ions emitted in the forward direction. Phenylalanine amino acid films deposited on self-supporting thin Si3N4 films were bombarded with 5 MeV C60 ions. Secondary ions emitted in the forward and backward directions were measured. The yield of intact phenylalanine molecular ions emitted in the forward direction is significantly enhanced compared to the backward direction while fragment ions are suppressed. This suggests a large potential of using transmission cluster ion SIMS for the analysis of biological materials.

Sputtering of SiN films by 540 keV [formula omitted] ions observed using high-resolution Rutherford backscattering spectroscopy

Amorphous silicon nitride films deposited on Si(001) were irradiated with 540keV C60 ions to fluences ranging from 2.5×1011 to 1×1014ions/cm2. The composition depth profiles of the irradiated samples were measured using high-resolution Rutherford backscattering spectroscopy. Both silicon and nitrogen in the film decrease rapidly with fluence. From the observed result the sputtering yields are obtained as 3900±500N atoms/ion and 1500±1000 Si atoms/ion. Such large sputtering yield cannot be explained by either the elastic sputtering or the electronic sputtering, indicating that the synergy effect between the elastic sputtering and the electronic sputtering plays an important role.

Electronic properties and structure of carbon nanocomposite films deposited from accelerated C60 ion beam

By methods of scanning tunnelling microscopy and tunnelling spectroscopy the surface structure and electronic properties of carbon films deposited from the mass-separated beam of accelerated C60 ions are studied. The main feature of the surface relief is the presence of quasi-periodic globular structures with characteristic sizes of 2–4 nm and a height of about 1 nm. They are lined up in straight rows and curved chains on the entire surface of the film with a typical scale of 3–4 nm. Tunnelling spectra show that the film consists of nanoscale regions with a wide band gap (4–4.6 eV, p-type conductivity) and regions of narrow band gap (1.3–1.8 eV, n-type conductivity). The electronic properties of the surface layers are close to the diamond to a greater extent than the properties of the underlying layers. Transmission electron microscopy allowed attributing the wide band gap regions to amorphous diamond, and the narrow-gap regions to nanocrystals of graphite.

Production of fullerene ions by combining of plasma sputtering with laser ablation

We have produced C60 ion beams by combining plasma sputtering and laser ablation. A C60 sample was placed in an electron cyclotron resonance type ion source, negatively biased and sputtered by argon plasma. The beam current of C60 (+) decreased rapidly, but it was transiently recovered by a single laser shot that ablates the thin sample surface on the sputtered area. Temporal variations in beam current are reported in response to laser shots repeated at intervals of a few minutes.

Cluster secondary ion mass spectrometry microscope mode mass spectrometry imaging

Microscope mode imaging for secondary ion mass spectrometry is a technique with the promise of simultaneous high spatial resolution and high-speed imaging of biomolecules from complex surfaces. Technological developments such as new position-sensitive detectors, in combination with polyatomic primary ion sources, are required to exploit the full potential of microscope mode mass spectrometry imaging, i.e. to efficiently push the limits of ultra-high spatial resolution, sample throughput and sensitivity. In this work, a C60 primary source was combined with a commercial mass microscope for microscope mode secondary ion mass spectrometry imaging. The detector setup is a pixelated detector from the Medipix/Timepix family with high-voltage post-acceleration capabilities. The system's mass spectral and imaging performance is tested with various benchmark samples and thin tissue sections. The high secondary ion yield (with respect to 'traditional' monatomic primary ion sources) of the C60 primary ion source and the increased sensitivity of the high voltage detector setup improve microscope mode secondary ion mass spectrometry imaging. The analysis time and the signal-to-noise ratio are improved compared with other microscope mode imaging systems, all at high spatial resolution. We have demonstrated the unique capabilities of a C60 ion microscope with a Timepix detector for high spatial resolution microscope mode secondary ion mass spectrometry imaging.

Nanocomposite-carbon coated at low-temperature: A new coating material for metallic bipolar plates of polymer electrolyte membrane fuel cells

A nanocomposite-carbon layer is coated onto the surface of 316L stainless steel (SS316) using a beam of accelerated C60 ions at low temperature. The coating is composed of textured graphite nanocrystals ranging in size from 1 to 2 nm, with the graphene plane normal to the coating plane; the nanocrystals are separated by amorphous carbon. This orientation of the graphene layer provides low film resistivity in the direction of the substrate normal. Corrosion resistance tests performed in aggressive anodic and cathodic environments of a polymer electrolyte membrane fuel cell (PEMFC) show that the nanocomposite-carbon coated SS316L exhibits better anticorrosion properties than does bare SS316L. The interfacial contact resistance (ICR) of the nanocomposite-carbon coated SS316L is 12 mΩ cm2, which is similar to that of graphite at a compaction force of 150 N cm−2 and lower than a target of ∼20 mΩ cm2. A low value of ICR is maintained even after corrosion tests in aggressive anodic and cathodic environments. The fabricated nanocomposite-carbon coated SS316L exhibits excellent corrosion resistance and low interfacial contact resistance under simulated PEMFC bipolar plate conditions.

Formation of Indium Carbide Cluster Ions: Experimental and Computational Study

We report the observation and structural analysis of novel indium carbide gas phase cluster ions generated by bombardment of a clean indium surface by keV C60(–) ions. Positive In(m)C(n)(+) (m = 1–21, 1 ≤ n ≤ 9) ions were ejected off the surface and analyzed mass spectrometrically. C60(–) ion beam irradiation is shown to be an efficient way of producing new kinds of gas phase carbide ions with relatively balanced stoichiometries. The rise kinetics of the ion signal (immediate jump within the beam opening time to a plateau value) indicates that the formation/ejection of the carbide ions constitute a single impact event. In3C2(+) was found to be the most abundant carbide cluster ion. Optimal geometries of the different clusters were derived via density functional theory calculations. The acetylenic/cumulenic nature of the impact emitted cluster ions is manifested by the high abundance of In2C2(+), In3C2(+), and the calculated structures for In(m)C(n)(+) (m = 3–4, n = 2–8). Odd/even intensity alternations in the In3C(n)(+) (n = 1–8) and In4C(n)(+) (n = 1–9) abundances are observed and rationalized by the calculations.

Peptide structural analysis using continuous Ar cluster and C60 ion beams

A novel application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) with continuous Ar cluster beams to peptide analysis was investigated. In order to evaluate peptide structures, it is necessary to detect fragment ions related to multiple neighbouring amino acid residues. It is, however, difficult to detect these using conventional ToF-SIMS primary ion beams such as Bi cluster beams. Recently, C60 and Ar cluster ion beams have been introduced to ToF-SIMS as primary ion beams and are expected to generate larger secondary ions than conventional ones. In this study, two sets of model peptides have been studied: (des-Tyr)-Leu-enkephalin and (des-Tyr)-Met-enkephalin (molecular weights are approximately 400Da), and [Asn(1) Val(5)]-angiotensin II and [Val(5)]-angiotensin I (molecular weights are approximately 1,000Da) in order to evaluate the usefulness of the large cluster ion beams for peptide structural analysis. As a result, by using the Ar cluster beams, peptide molecular ions and large fragment ions, which are not easily detected using conventional ToF-SIMS primary ion beams such as Bi3 (+), are clearly detected. Since the large fragment ions indicating amino acid sequences of the peptides are detected by the large cluster beams, it is suggested that the Ar cluster and C60 ion beams are useful for peptide structural analysis.

Transmission properties of C60 ions through micro- and nano-capillaries

We apply the capillary beam-focusing method for the C60 fullerene projectiles in the velocity range between 0.14 and 0.2a.u. We study the C60 transmission properties through two different types of capillaries: (1) borosilicate glass microcapillary with an outlet diameter of 5.5μm, and (2) Al2O3 multi-capillary foil with a pore size of about 70nm and a high aspect ratio of about 750. We measured the transmitted particle composition by using the electrostatic deflection method combined with the microchannel plate imaging technique. For the experiments with the single microcapillary, the main transmission component is found to be primary C60 beams that are focused in the area equal to the capillary outlet diameter. Minor components are charge-exchanged C60 ions and charged or neutral fragments (fullerene-like C60-2m and small Cn particles), and their fractions decrease with decreasing the projectile velocity. It is concluded that the C60 transmission fraction is considerably high for both types of the capillaries in the present velocity range.

Improving Secondary Ion Mass Spectrometry C60n+ Sputter Depth Profiling of Challenging Polymers with Nitric Oxide Gas Dosing

Organic depth profiling using secondary ion mass spectrometry (SIMS) provides valuable information about the three-dimensional distribution of organic molecules. However, for a range of materials, commonly used cluster ion beams such as C60(n+) do not yield useful depth profiles. A promising solution to this problem is offered by the use of nitric oxide (NO) gas dosing during sputtering to reduce molecular cross-linking. In this study a C60(2+) ion beam is used to depth profile a polystyrene film. By systematically varying NO pressure and sample temperature, we evaluate their combined effect on organic depth profiling. Profiles are also acquired from a multilayered polystyrene and polyvinylpyrrolidone film and from a polystyrene/polymethylmethacrylate bilayer, in the former case by using an optimized set of conditions for C60(2+) and, for comparison, an Ar2000(+) ion beam. Our results show a dramatic improvement for depth profiling with C60(2+) using NO at pressures above 10(-6) mbar and sample temperatures below -75 °C. For the multilayered polymer film, the depth profile acquired using C60(2+) exhibits high signal stability with the exception of an initial signal loss transient and thus allows for successful chemical identification of each of the six layers. The results demonstrate that NO dosing can significantly improve SIMS depth profiling analysis for certain organic materials that are difficult to analyze with C60(n+) sputtering using conventional approaches/conditions. While the analytical capability is not as good as large gas cluster ion beams, NO dosing comprises a useful low-cost alternative for instruments equipped with C60(n+) sputtering.

Enhancing the Sensitivity of Molecular Secondary Ion Mass Spectrometry with C60+-O2+ Cosputtering

In the past decade, the C60-based ion gun has been widely utilized in the secondary ion mass spectrometry (SIMS) analysis of organic and biological materials because molecular secondary-ions of high masses could be generated by cluster-ion bombardment. This technique furthers the development of SIMS in bioanalysis by eliminating the need for either heteroatom or isotope labeling. However, the intensity of high-mass parent ions was usually low and limited the sensitivity of the analysis, thus requiring an enhancement in the intensity of these molecular ions to widen the application of SIMS. In this work, the aim was to preserve samples in their original state while using a low kinetic energy O2(+) beam cosputtered with high-energy C60(+) to enhance the ion intensity through the depth-profile. Although O2(+) is generally used to enhance ion intensities in positive SIMS, it is known to alter the chemical structure and primarily provide elemental information; hence, it is not suitable for profiling organic and biological specimens. Nevertheless, owing to its high sputtering yield, cluster C60(+) ion removes and masks the structural damage, hence O2(+) may be used to enhance the ion intensity. The characteristic molecular ions of polyethylene terephthalate (PET), trehalose, and a peptide (papain inhibitor) are enhanced by 35×, 12×, and 3.5× with the use of the auxiliary O2(+) beam, respectively. This significant enhancement in ionization yield is attributed to the oxidation of molecules and formation of a hydroxyl group that serves as a proton donator. In addition to enhancing molecular SIMS signals, C60(+)-O2(+) cosputtering could also alleviate several problems, including sputtering rate decay, carbon deposition, and surface roughening, that are associated with C60(+) bombardment and produced better depth profiles.

Tribological properties of nanostructured DLC coatings deposited by C60 ion beam

The frictional and wear characteristics of nanostructured DLC films were investigated. The coatings were deposited on silicon substrates by irradiation of a mass-separated C60 ion beam with 5keV of energy and a deposition temperature ranging from 100 to 450°C. The effects of deposition temperature on the surface morphology, nano-structure, mechanical properties and tribological characteristics of the coatings were assessed. Results showed that deposition temperature strongly affects the nanostructure and surface morphology of the coatings. Coatings deposited at temperatures exceeding 350–400°C exhibited an increase in surface roughness as well as compressive stress due to the formation of graphite, which led to a significant increase in the friction coefficient and wear rate. Coatings deposited at 300°C showed the best tribological properties.

Growth of nanocomposite films from accelerated C60 ions

A beam of accelerated C60 ions is used to deposit superhard (∼50 GPa) carbon films that exhibit high index plasticity (∼0.13–0.14) and high conductivity (up to 3000 S m−1). Transmission electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy are subsequently used to study the microstructure and bond character of the deposited films. The films consist of textured graphite nanocrystals and diamond-like amorphous carbon (DLC). The graphene plane of the nanocrystals is aligned perpendicular to the film surface. It is shown that sp2 bonds dominate in the films. The percentage of sp3 bonds depends on the ion energy and the substrate temperature, and does not exceed 40%. The obtained results suggest that a new nanocomposite material consisting of oriented graphite nanocrystals reinforced by a DLC matrix is synthesized. A simple model is proposed to correlate the excellent mechanical properties with the observed structure.

Dual beam depth profiling of polymer materials: comparison of C60 and Ar cluster ion beams for sputtering

Dual beam depth profiling was applied in order to investigate the possibilities and limitations of C60 and Ar cluster ion sputtering for depth profiling of polymer materials. Stability and intensity of characteristic high mass molecular ion signals as well as sputter yields will be compared. For this purpose, different beam energies resulting in 2–10 eV/atom for Arn and 167–667 eV/atom for C60 sputtering were applied to various polymer samples. From our experiments, we can conclude that most of the limitations C60 sputtering suffers from could be successfully overcome and that the Ar gas cluster ion beam seems to be a more universal tool for sputtering of organic materials. Copyright © 2012 John Wiley & Sons, Ltd.

Time‐of‐flight SIMS depth profiling of Na in SiO2 glass using C60 sputter ion beam

A depth profile analysis of SiO2 glass ion implanted with 23Na+ was carried out on a time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) with OX, Cs and buckminsterfullerene (C60) ion sputtering. The Na migration in SiO2 glass during both analysis process and sputter process was investigated under the various operating conditions. During the analysis process, 23Na+ intensity stayed constant on the dose density of the Bi primary ion regardless of the conditions and went up using higher primary ion current. The Na profile in SiO2 glass similar to that of the Lindard–Scharff–Schiott theory was successfully acquired by the use of C60 ion sputtering regardless of the operating conditions. It is considered that Na does not migrate during the sputter process with C60 sputter ion beam. In addition, the detection limit of Na depth profile with C60 ion sputtering was almost the same with existing dynamic SIMS analysis with Cs primary ion. Thus, the ToF‐SIMS with C60 ion sputtering is shown to be more versatile than the existing method by avoiding the necessity to optimize the operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Cooperative Jahn-Teller effect in a 2D mesoscopic C 60 n− system with D5d symmetry adsorbed on buffer layers using Ising EFT model

Fullerene molecules adsorbed on surfaces often show macroscopic average distortions. As charged ions C 60 are known to be Jahn-Teller (JT) active, it is suggested that these distortions could be a manifestation of cooperative JT effects (CJTE) due to interactions between neighbouring fullerene ions. In order to understand the distortion properties it is necessary to take correlations between different distortions into account. However, this can’t easily be done in the mean field approximation usually used to describe the CJTE. We therefore propose an alternative procedure to describe 2D mesoscopic islands of C60 ions in which a pseudo vector spin $$\vec S$$ is evoked to represent degenerate JT-distorted states when the quadratic JT coupling is considered. This approach is analogous to methods used for 2D magnetic systems. We then use the differential operator technique in effective field theory within the Ising approach. We include the effects of weak surface interactions and dynamic motion between equivalent distortions via terms equivalent to anisotropy and a transverse field in magnetism respectively. For distortions to D 5d symmetry, we determine single site correlations as a function of temperature, the macroscopic average distortion describing a structural phase transition, and the isothermal response function. Phase diagrams are presented for relevant cases of the system parameters.

Modification of Fullerene Nanocolumn Structure by Accelerated C60 Ions

Crystalline C60 and amorphous graphite-like films of nanocolumn arrays fabricated by glancing angle deposition of C60 fullerene at substrate temperatures of -425 K were studied by transmission electron microscopy (TEM) and atomic-force microscopy (AFM). Characteristic dimension of columns is 200-400 nm. We used co-deposition of C60 molecules and accelerated C60 ions to modify the structure and properties of nanocolumn arrays. Influence of incidence angle for C60 ions on formation of film morphology was revealed. Raman spectrum analysis showed that amorphous carbon nanocolumns consist of nanographite areas with average size of -1.5 nm. The films have high conductivity (close to graphite) and have no mechanical stresses. The carbon films were applied in all-solid-state rechargeable thin-film battery as an anode layer. The nanocolumn amorphous carbon film as anode electrode showed the discharge capacity of about 50 microAh cm(-2)microm(-1) and good cycling ability over 100 times in full cell system.

Comparison of C60 and GCIB primary ion beams for the analysis of cancer cells and tumour sections

We have implemented a gas cluster ion beam (GCIB) system developed by Ionoptika Ltd (Southampton, UK) with sufficient control to allow us to exploit the unique capabilities of our J105 instrument for imaging and depth profiling. The J105 allows us to use the GCIB as continuous primary ion beam, thereby overcoming the issues associated with pulsing these slow moving, mixed species beams. We have performed a direct comparison with C60 ions on the same samples in the same instrument. The GCIB beams are more difficult to focus than the C60+ ion beam, making single‐cell imaging difficult, although spot sizes of 15–20 µm are readily obtainable for Ar1000 and Ar2000, providing good resolution for larger area imaging on tissue section/biopsy samples. In this paper, we present results from the assessment of these new beams as primary ions for the analysis of ‘real’, complex biological systems. Initial spectra and those following increased primary ion bombardment were compared for in vitro cultured cells deposited on silicon and cryo‐sectioned tumour samples originating in vivo. Ar1000+ and Ar2000+ showed increased persistence of the signals from intact molecular ions of phospholipids and a reduction in the accumulation of chemical background noise compared with C60+ analysis. Copyright © 2012 John Wiley & Sons, Ltd.