Highly Charged Ions Research Articles

High-precision X-ray spectroscopy of highly-charged ions at the experimental storage ring using silicon microcalorimeters

X-ray spectroscopy on highly charged heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. One limitation of the current accuracy of such experiments is the energy resolution of available X-ray detectors for energies up to 100keV. To improve this accuracy, a novel detector concept, namely the concept of microcalorimeters, is exploited for this kind of measurements. The microcalorimeters used in the present experiments consist of silicon thermometers, ensuring a high dynamic range, and of absorbers made of high-Z material to provide high X-ray absorption efficiency. Recently, besides an earlier used detector, a new compact detector design, housed in a new dry cryostat equipped with a pulse tube cooler, was applied at a test beamtime at the experimental storage ring (ESR) of the GSI facility in Darmstadt. A U89+ beam at 75MeV/u and a 124Xe54+ beam at various beam energies, both interacting with an internal gas-jet target, were used in different cycles. This test was an important benchmark for designing a larger array with an improved lateral sensitivity and statistical accuracy.

Detailed analysis of self-absorption profiles of highly-charged tin ions in the EUV region

Plasma dynamics simulation is a very effective method for the spectral diagnosis and analysis of plasmas, which has been widely used in the interpretation of spectral structure and evolution analysis of the laser-produced plasmas. In this paper, a simplified radiation hydrodynamic model based on the fluid dynamic equations and the radiative transfer equation, and combined with a steady-state collisional-radiative model was presented and used to analyze the origin of extreme ultraviolet (EUV) spectrum of middle- and high-Z highly charged ions from laser-produced plasma, and has been successfully applied to analyze and simulate the spectrum of laser-produced tin plasma in the EUV spectral region. The results show that there is a good agreement between theoretical simulation and experimental spectrum at a laser power density of 1.90×1011 W/cm2. By comparison of the emission profiles and self-absorption profiles of 4d-4f, 4p-4d and 4d-5p, 5f transition arrays from Sn7+ to Sn11+ ions, the influence of opacity effect to the emission profile was identified. We are succeeded in explaining the origin of self-absorbed band and self-absorbed dips around 13.5 nm in tin spectrum. Our results are expected to provide a reference for the applications of extreme ultraviolet radiation in the fields of lithography, metrology and biological imaging.

Supercharging Proteins: How Many Charges Can a Protein Carry?

Very highly charged proteins, so-called "supercharged" ions, can lose (excess) protons to background gases like N2 . It is remarkable that such extremely acidic species can be generated in electrospray ionization, in the presence of not just N2 but also much higher-basicity solvents. What mechanism(s) can explain such high charging, and what is the ultimate limit?

Simple Synthesis and Supercapacitive Performances of NiMoS4 Particles

A simple method was used to prepare amorphous NiMoS4 particles that were subsequently characterized with X-ray diffraction, X-ray fluorescence spectrum, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectrum. The supercapacitive properties of NiMoS4 were measured for the first time. It exhibits high capacitance and low charge ion transfer resistance owing to its accessible multiple valences, amorphous structure and high conductivity of sulfides.

X-ray Pump–Probe Investigation of Charge and Dissociation Dynamics in Methyl Iodine Molecule

Molecular dynamics is of fundamental interest in natural science research. The capability of investigating molecular dynamics is one of the various motivations for ultrafast optics. We present our investigation of photoionization and nuclear dynamics in methyl iodine (CH3I) molecule with an X-ray pump X-ray probe scheme. The pump–probe experiment was realized with a two-mirror X-ray split and delay apparatus. Time-of-flight mass spectra at various pump–probe delay times were recorded to obtain the time profile for the creation of high charge states via sequential ionization and for molecular dissociation. We observed high charge states of atomic iodine up to 29+, and visualized the evolution of creating these high atomic ion charge states, including their population suppression and enhancement as the arrival time of the second X-ray pulse was varied. We also show the evolution of the kinetics of the high charge states upon the timing of their creation during the ionization-dissociation coupled dynamics. We demonstrate the implementation of X-ray pump–probe methodology for investigating X-ray induced molecular dynamics with femtosecond temporal resolution. The results indicate the footprints of ionization that lead to high charge states, probing the long-range potential curves of the high charge states.

Pair production in low-energy collisions of uranium nuclei beyond the monopole approximation

A method for calculation of electron-positron pair production in low-energy heavy-ion collisions beyond the monopole approximation is presented. The method is based on the numerical solving of the time-dependent Dirac equation with the full two-center potential. The one-electron wave functions are expanded in the finite basis set constructed on the two-dimensional spatial grid. Employing the developed approach the probabilities of bound-free pair production are calculated for collisions of bare uranium nuclei at the energy near the Coulomb barrier. The obtained results are compared with the corresponding values calculated in the monopole approximation.

Towards precision measurements on highly charged ions using a high harmonic generation frequency comb

Highly charged ions (HCI) offer many advantages over neutral and singly charged ions for probing fundamental physics. Recently they have been proposed as candidates for novel frequency standards. The project presented here aims at studying HCI with high precision in the extreme ultraviolet (XUV) region, where many of their transitions are located. To this end, an XUV light source is being developed, using a stabilized frequency comb to generate high-order harmonics inside the focus of an enhancement cavity. This optical resonator resides in an ultra-high vacuum (UHV) chamber and is designed to have a very tight focus. The generated XUV light will be guided to a cryogenic linear Paul trap, where trapped HCI are sympathetically cooled by Be+ ions. Individual comb lines can then be used to drive narrow transitions in HCI, enabling XUV spectroscopy with unprecedented accuracy.

Analysis of magnetic-dipole transitions in tungsten plasmas using detailed and configuration-average descriptions

This paper is devoted to the analysis of transition arrays of magnetic-dipole (M1) type in highly charged ions. Such transitions play a significant role in highly ionized plasmas, for instance in the tungsten plasma present in tokamak devices. Using formulas recently published and their implementation in the Flexible Atomic Code for M1-transition array shifts and widths, absorption and emission spectra arising from transitions inside the 3*n complex of highly-charged tungsten ions are analyzed. A comparison of magnetic-dipole transitions with electric-dipole (E1) transitions shows that, while the latter are better described by transition array formulas, M1 absorption and emission structures reveal some insufficiency of these formulas. It is demonstrated that the detailed spectra account for significantly richer structures than those predicted by the transition array formalism. This is due to the fact that M1 transitions may occur between levels inside the same relativistic configuration, while such inner configuration transitions are not accounted for by the currently available averaging expression. In addition, because of configuration interaction, transition processes involving more than one electron jump, such as 3p1/23d5/2 → 3p3/23d3/2, are possible but not accounted for in the transition array formulas. These missing transitions are collected in pseudo-arrays using a post-processing method described in this paper. The relative influence of inner- and inter-configuration transitions is carefully analyzed in cases of tungsten ions with net charge around 50. The need for an additional theoretical development is emphasized.

Modification of gold and titanium nanolayers using slow highly charged Xeq+ ions

Nanostructures created by irradiation of gold and titanium nanolayers with slow highly charged xenon ions are studied in this work. The gold and titanium nanolayers were prepared by sputtering deposition of the metals on polished quartz SiO2(100) or crystalline silicon Si(100) substrates. The irradiations were performed at room temperature using q×3.4keVXeq+ions from EBIT ion source, with charge state q=35 for gold and q=15–35 for titanium. The fluence of the ions on the irradiated samples was in the range of 7–12×109ions/cm2. Topographic atomic force microscopy (AFM) images of unmodified and ion-irradiated surfaces were measured. The AFM images of ion-irradiated surfaces clearly demonstrate the nanostructures in a form of hillocks created on the gold and titanium conducting surfaces as the result of an highly charged ion (HCI) impact. The ion charge state dependent measurements performed for titanium nanolayers suggest that the hillock formation is the due to kinetic energy deposition of HCI, while the role of potential energy seems to be less important. The hillock height and volume distributions are statistically analyzed. Additionally, for titanium the volume dependence on the charge state of the ions is presented. Possible influence of the nanolayer substrate on the hillock formation is discussed.

Hyperfine induced effects on the angular distribution of the dielectronic hypersatellite line

We investigate the dielectronic recombination (DR) of an electron and a highly-charged ion with non-zero nuclear spin. We assume that the incident electron is captured into doubly-excited 1s2κκ′J=0,1,2 levels of Be-like ions just above of its autoionization threshold. The angular distribution of the subsequent radiative emission is investigated especially for its dependence upon the nuclear spin and the nuclear magnetic moment. While the hyperfine and even the fine-structure of the ions cannot be resolved in typical DR experiments, we found the photon angular distribution, following the decay of the 1s22p3/2nsJ=1,2 DR resonance very sensitive to the nuclear parameters.

Infrared and visible laser spectroscopy for highly-charged Ni-like ions

Application of visible or infrared (IR) lasers for spectroscopy of highly-charged ions (HCI) has not been particularly extensive so far due to a mismatch in typical energies. We show here that the energy difference between the two lowest levels within the first excited configuration 3d94s in Ni-like ions of heavy elements from ZN=60 to ZN=92 is within the range of visible or near-IR lasers. The wavelengths of these transitions are calculated within the relativistic model potential formalism and compared with other theoretical and limited experimental data. Detailed collisional-radiative simulations of non-Maxwellian and thermal plasmas are performed showing that photopumping between these levels using relatively moderate lasers is sufficient to provide a two-order of magnitude increase of the pumped level population. This accordingly results in a similar rise of the X-ray line intensity thereby allowing control of X-ray emission with visible/IR lasers.

Multiphoton ionization of many-electron atoms and highly-charged ions in intense laser fields: a relativistic time-dependent density functional theory approach

We develop an efficient numerical implementation of the relativistic time-dependent density functional theory (RTDDFT) to study multielectron highly-charged ions subject to intense linearly-polarized laser fields. The interaction with the electromagnetic field is described within the electric dipole approximation. The resulting time-dependent relativistic Kohn–Sham (RKS) equations possess an axial symmetry and are solved accurately and efficiently with the help of the time-dependent generalized pseudospectral method. As a case study, we calculate multiphoton ionization probabilities of the neutral argon atom and argon-like xenon ion. Relativistic effects are assessed by comparison of our present results with existing non-relativistic data.

Additivity of kinetic and potential energy contributions in modification of graphene supported on [formula omitted

The damage production induced by MeV highly charged ions (HCI) irradiations in graphene supported on a SiO2 substrate is investigated using molecular dynamics method. We get results in agreement with our recent experiments. We find that the electronic energy loss and potential energy deposition have similar effects on the defects creation in SiO2 substrate-supported graphene and both mechanisms of energy deposition seem to contribute in an additive way. The influences of the energy deposition depth and radius are studied. Only the energy deposited below the surface within 2.5nm will induce the damage in graphene. Hence, the HCI can be a powerful tool to induce defects in graphene without causing deep damage of the substrate. When charge of incident Xeq+ is above 30, a nanopore is formed and the size of nanopore in graphene can be controlled by changing the incident charge state.

The role of Stern layer in the interplay of dielectric saturation and ion steric effects for the capacitance of graphene in aqueous electrolytes

Nano-scale devices continue to challenge our theoretical understanding of microscopic systems. Of particular interest is the characterization of the interface electrochemistry of graphene-based sensors. Typically operated in a regime of high ion concentration and high surface charge density, dielectric saturation and ion crowding become non-negligible at the interface, complicating continuum treatments based upon the Poisson-Boltzmann equation. Using the Poisson-Boltzmann equation, modified with the Bikerman-Freise model to account for non-zero ion size and the Booth model to account for dielectric saturation at the interface, we characterize the diffuse layer capacitance of both metallic and graphene electrodes immersed in an aqueous electrolyte. We find that the diffuse layer capacitance exhibits two peaks when the surface charge density of the electrode is increased, in contrast with experimental results. We propose a self-consistent (and parameter-free) method to include the Stern layer which eliminates the spurious secondary peak in the capacitance and restores the correspondence of the model with experimental observations. This study sheds light on the interplay between the ion steric effects and the dielectric saturation in solvent, exposes the importance of quantum capacitance when graphene is used as an electrode, and demonstrates the importance of a self-consistent treatment of the Stern layer in continuum models of the electrode-electrolyte interface. Furthermore, the theoretical foundation provides a base upon which more detailed models of graphene-based sensors can be built.

Electromagnetic instability in plasmas heated by a laser field.

Electromagnetic instability is investigated in homogeneous plasmas heated by a laser wave in the range α=v_{0}^{2}/v_{t}^{2}≤2, where v_{0} is the electron quiver velocity and v_{t} is the thermal velocity. The anisotropic electron distribution function that drives unstable quasistatic electromagnetic modes is calculated numerically with the Vlasov-Landau equation in the high ion charge number approximation. A dispersion relation of electromagnetic waves which accounts for further nonlinear terms on v_{0}^{2} from previous results is derived. In typical simulation with ion charge number Z=13, a temperature T=5keV, a density n=9.8×10^{20}cm^{-3}, and a laser wavelength λ_{laser}=1.06μm, growth rates larger than 10^{12}s^{-1} in the quasicollisionless wave-number range were found for α≥1. In the same physical conditions and in the mildly collisional range a growth rate about 10^{11}s^{-1} was also obtained. The extent of the growth wave-number region increases significantly with increasing α.

An attempt to apply the inelastic thermal spike model to surface modifications of CaF2 induced by highly charged ions: comparison to swift heavy ions effects and extension to some others material

Surface damage appears on materials irradiated by highly charged ions (HCI). Since a direct link has been found between surface damage created by HCI with the one created by swift heavy ions (SHI), the inelastic thermal spike model (i-TS model) developed to explain track creation resulting from the electron excitation induced by SHI can also be applied to describe the response of materials under HCI which transfers its potential energy to electrons of the target. An experimental description of the appearance of the hillock-like nanoscale protrusions induced by SHI at the surface of CaF2 is presented in comparison with track formation in bulk which shows that the only parameter on which we can be confident is the electronic energy loss threshold. Track size and electronic energy loss threshold resulting from SHI irradiation of CaF2 is described by the i-TS model in a 2D geometry. Based on this description the i-TS model is extended to three dimensions to describe the potential threshold of appearance of protrusions by HCI in CaF2 and to other crystalline materials (LiF, crystalline SiO2, mica, LiNbO3, SrTiO3, ZnO, TiO2, HOPG). The strength of the electron–phonon coupling and the depth in which the potential energy is deposited near the surface combined with the energy necessary to melt the material defines the classification of the material sensitivity. As done for SHI, the band gap of the material may play an important role in the determination of the depth in which the potential energy is deposited. Moreover larger is the initial potential energy and larger is the depth in which it is deposited.

Damage effects of proton beam irradiation on single layer graphene

Graphene was first discovered in 2004 (Novoselov K S, et al. 2004 Science 306 666), it is a single atomic layer of sp2-bonded carbon atoms arranged in a honeycomb-like lattice. According to its extraordinary electronic, mechanical, thermal and optical properties, one can expect it to have a variety of applications in nanoscale electronics, composite materials, energy storage, and biomedicine fields. Although many experimental and theoretical studies on graphene have been carried, there still exist many obstacles to its applications. A representative example is nanoscale electronics (e.g., field-effect transistors and optoelectronic devices) that requires non-zero band-gap. Therefore, introducing defects into graphene and leading to band-gap opening are key steps for its technique applications.Recently, ion beam irradiation as a defects introducing technique was performed by Lee et al. (2015 Appl. Surf. Sci. 344 52) and Zeng et al. (2016 Carbon 100 16) through 5, 10, and 15 MeV protons and highly charged ions (HCIs) irradiating the graphene separately. Considering the advantages of simplity for preparing samples and feasibility in atmospheric condition of Raman spectroscopy compared with common characterization techniques (high resolution transmission electron microscopy, scanning electron microscopy, atomic force microscopy) for nano-materials, in both studies, Raman spectroscopy is used to obtain the evolution of ID/IG (ID is the peak intensity excited by defects, IG is the peak intensity origining from lateral vibration of carbon atoms) with different energies and fluences, respectively. In this work, considered are the following points:1) the absence of quantitive characterization for defects in the above two studies; 2) the low displacement energy of 25 eV required for a carbon atom to be knocked out (Zhao S J, et al. 2012 Nanotechnology 23 285703); 3) the complex interaction between HCIs and material. The irradiation effects of single layer graphene on silicon substrate are investigated by 750 keV and 1 MeV proton bombarding. This introduces the defects into graphene and thus leads to band-gap opening. By comparing Raman spectra of the samples before and after irradiation, a quantitive characterization about defects in graphene is achieved. Detailed analysis shows that 1) the value of ID/IG increases with the energy loss of incident proton, which is consistent with the result of SRIM simulation; 2) the average distance of defects LD increases with the incident proton energy; 3) the defect density nD decreases with the incident proton energy. These indicate that the damage effect for MeV protons in single layer graphene with substrate is similar to those in three-dimensional materials. The method presented here may facilitate the understanding of the physical mechanism of MeV proton interaction with two-dimensional materials, and provide a potential way of controlling the electronic structure and band-gap.

Corrosion behavior of Al film on uranium in salt spray test

The corrosion behavior of Al film coated uranium and bare uranium under neutral salt spray conditions are evaluated.

Physics book: CRYRING@ESR

The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum fur Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).

NiCoO2 flowers grown on the aligned-flakes coated Ni foam for application in hybrid energy storage

Abstract Many NiCoO2 flowers with an average diameter of about 4 μm were grown on the NiCoO2 flakes coated Ni foam (denoted as NiCoO2/Ni foam) through a simple hydrothermal method and confirmed by scanning and transmission electron microscopies, X-ray diffraction and X-ray photoelectron spectrum measurements. The NiCoO2/Ni foam with high specific area and porosity was directly used as the working electrode without any binders. The measured specific capacitance of NiCoO2 grown on Ni foam is 756 F/g at 0.75 A/g using a three-electrode setup in 1 M KOH. Considering the high capacity of NiCoO2 and the good stability of rGO, the NiCoO2/Ni foam//rGO hybrid supercapacitor combining NiCoO2/Ni foam and rGO shows very good properties, such as high specific capacitance (82 F/g at 2 A/g based on the total mass of active materials), high energy density (25.7 Wh/kg at 1500 W/kg based on the total mass of active materials), good stability (about 90% capacitance retention after 2000-cycle at 100 mV/s), and low charge ion transfer resistance.