Interaction Of Low-energy Ions Research Articles

MATHEMATICAL MODEL OF THE INTERACTION OF LOW-ENERGY INERT GAS IONS WITH POLYPROPYLENE IN RADIO-FREQUENCY PLASMA OF LOW PRESSURE

Results of the molecular dynamic simulation of the interaction of low-energy ions (from 10 to 100 eV) with the surface of polypropylene fibrous materials in low pressure radio-frequency (RF) argon plasma is presented. A full-atomic model using the LAMMPS classical molecular dynamics code was made. As a result of numerical calculations, it was found that argon ion bombardment initiates the breaking both of an intermolecular and intramolecular bond of polypropylene with sputtered particles being the hydrocarbon radicals and single atoms. The depth of implantation of the ion is determined, the change in the kinetic energy of the argon atom and the temperature of the simulated cell is obtained.

Study on the interaction of low-energy ions with organisms

The discovery of bio-effects by implantation of low-energy ions into biological organisms has opened a new branch in the field of ion beam application in life sciences. The groundwork of this area is based on the hypothesis of a combination of energy absorption, mass deposition, and charge transfer of energetic ions in the organisms, resulting in damage and inducing mutation effects. Although mechanism studies of the interaction between low-energy ions and organisms have made progress, ion beam applications in biotechnology have attained more achievements than the study of the interaction mechanisms.

Interaction of Low-Energy Ions and Atoms of Light Elements with a Fluorinated Carbon Molecular Lattice

The mechanism of interaction of low-energy atoms and ions of light elements (H, H+, He, Li, the kinetic energy of the particles 2-40 eV) with C6H6, C6F12, C60, and C60F48 molecules was studied by ab initio MD simulations and quantum-chemical calculations. It was shown that starting from 6 A from the carbon skeleton for the "C6H6 + proton" and "C60 + proton" systems, the electronic charge transfer from the aromatic molecule to H+ occurs with a probability close to 1. The process transforms the H+ to a hydrogen atom and the neutral C6H6 and C60 molecules to cation radicals. The mechanism of interaction of low-energy protons with C6F12 and C60F48 molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the uncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized on the proton and on the C6F12 and C60F48 molecules and makes the electronic charge transfer energetically unfavorable. On the different levels of theory, the barriers of the proton penetration for the C6F12 and C60F48 molecules are from two to four times lower than those for the corresponding parent systems (C6H6 and C60). The penetration barriers of the He atom and Li+ ion depend mainly on the effective radii of the bombarding particles. The theoretical penetration and escaped barriers for the "Li+ + C60" process qualitatively explain the experimental conditions of synthesis of the Li@C60 complex.

Chemical sputtering of carbon materials due to combined bombardment by ions and atomic hydrogen

Simultaneous interaction of low-energy ions and atomic hydrogen—a process named chemical sputtering—causes erosion of C:H surfaces which is significantly higher than the sum of the individual processes—chemical erosion due to atomic hydrogen alone and physical sputtering due to ions. Above that, this process occurs also at energies below the threshold for physical sputtering. A microscopic reaction mechanism for chemical sputtering was recently suggested. A mathematical model based on this reaction mechanism is able to quantitatively reproduce the energy dependence of chemical sputtering by atomic hydrogen and argon using just one free parameter. The model is briefly reviewed and the underlying physical processes are discussed. We present new predictions for the chemical sputtering of carbon by atomic hydrogen and different ions relevant to plasma–wall interaction in nuclear fusion devices (He+, H+, D+, T+ and Ne+) and new experimental data for the chemical sputtering due to hydrogen and Ne+ ions.

Simulation of the interaction of low-energy ions with copper clusters on a graphite surface

The sputtering of a lone cluster consisting of 27 copper atoms from a (0001) graphite surface bombarded by normally incident 100-and 200-eV Xe+ ions was simulated by the molecular dynamics method. The angular distributions of sputtered copper atoms and scattered xenon ions are discussed.

Influence of primary beam profile on LEIS spectra

The importance of low energy ion scattering (LEIS) as a technique for surface characterization is in its low information depth. Serious problems concerning the quantitative analysis of the surface composition by means of LEIS are mainly associated with the neutralization phenomena during the interaction of low energy ions with surface atoms. It is known that intensities of quasi-single (QS) peaks in LEIS spectra depend on the experimental setup such as a detection system or an acceptance region of an energy analyzer. If the acceptance region of the analyzer is smaller than the spot size of the primary ion beam, QS peak intensities will depend on the primary ion beam profile. Therefore, a significant error can be made in quantitative characterization by means of relative sensitivity factors. In this paper, we study the influence of the beam profile on QS peak intensities obtained in LEIS experiments with a polycrystalline copper target. For this purpose, our LEIS experiment is modified in order to provide fast and simple determination of the primary ion beam profile during the measurement of the energy distributions of scattered ions. On the other hand, the acceptance region of the 127° cylindrical energy analyzer used in these experiments is calculated according to results of numerical simulations. The correlation between the experimental results and the calculated magnitudes of the acceptance region will be discussed.

Computer simulation of the defect structure formation in crystal lattices by low-energy ion irradiation

The present paper is aimed at studying nonlinear effects induced by the interaction of low-energy ions with the surface of crystal lattices. We showed by a computer simulation that nonlinear oscillations were excited in the system of coupled atomic oscillators of solids, which resulted in the formation of new collective stable structural states in crystal lattices. The formation of atomic clusters with irregular atomic rearrangements, running autosolitons, long-lived undamped oscillations in local ranges of lattices and nanometrical structures of crystal lattices can occur. The specific kind of these new heterogeneous structures depends on the properties of the potential characterizing bonds between atomic oscillators and the magnitude of the external influence. These effects cannot be neglected in studying the structure and surface topography of thin crystal films by scanning microscopy.

A multipurpose apparatus for studying the interaction of low energy ions with solid state surface

A new concept of a multipurpose device for the investigation of a low energy in beam interactions with solid state surfaces is realized in an apparatus for surface analysis by means of low energy ion scattering (LEIS), direct recoil spectrometry (DRS), mass spectrometry of recoil ions (MRSI), and secondary-ion mass spectrometry (SIMS). This device provides broad alkali ion beams, homogeneous and much more intense than in standard commercial realizations available, as well as various high quality intense gas ion beams. A long tube with a magnetic quadrupole triplet is introduced. This construction disjoins the high vacuum from the ultrahigh vacuum (UHV) parts of the system and makes possible low cost differential pumping. The use of an UHV broad alkali ion beam in SIMS experiments should importantly decrease crater effect problems without use of rastering and electrical gating systems. In order to demonstrate the possibilities and the advantages of the proposed concept, we present the results of experimental analysis of primary ion beam characteristics, as well as LEIS and DRS experimental results obtained by use of gas ion beams scattered from silver polycrystalline surfaces. This design concept results in a simple and low cost device with operating characteristics comparable to those of high quality devices of similar type.

Effect of multiple scattering in the interaction of low-energy ions with the magnetite surfaces covered by xenon

The energy spectra of 5.5 keV Ne + and Ar + ions scattered from a cleavage surface of a single-crystal magnetite covered by condensed xenon layers as a function of target temperature and of xenon density were investigated. Under the small-angle geometry, the energy spectra contain one broad peak (the substrate peak) in case of the “clean” surface (i.e. without xenon cover) while two broad peaks were observed for the xenon covered surfaces. The substrate peak was located at lower energy whereas the xenon peak was at higher energy, but both the peaks were distinctly shifted relative to the single scattering energy. A large increase of the intensity of the xenon peak with increasing xenon layer thickness was observed. The substrate peak, however, was found to be almost independent on the xenon pressure for both bombarding ions. Relatively large energy losses, which were found, can be well explained in the framework of the zigzag collision model including the last re-ionizing collision. A very large change in the scattered ion yields at temperature of 120 K, i.e. the Verwey phase transition temperature of magnetite, was observed for the clean target. Some reduction of such a phase transition effect by the xenon layers was found, but the anomaly at the phase transition temperature still occurred. The presence of the separated xenon peak and its energy position suggests that some arrangement of the first xenon layer on the target surface exists.

Ion beam application in genetic modification

People pay little attention to the interaction between low-energy ions and matter compared to that of high-energy ions. It is even more unusual to find studies of the interaction of low-energy ions and complicated organisms. The discovery of bioeffects induced by ion implantation has, however, opened a new branch in the field of ion beam applications in the life sciences. This paper reports recent advances in research on the role of low-energy ions in genetic modification.

Multiple scattering in the interaction of low energy ions with a cold Zn(0001) surface covered by condensed carbon dioxide

Energy spectra of ions emitted from a cold Zn(0001) surface covered by a thin film of condensed carbon dioxide as a function of detection angle and density of the film were investigated. It has been shown elsewhere that some fine structure of the substrate quasi-single-scattering peak is observed due to multiple scattering which directs the ions to the detector after single scattering from the substrate atoms over the angles larger or smaller than the detection angle. It can be predicted that some fine structure should occur also in the energy spectra of recoils. The occurrence of the structure of the recoil energy spectra has been tested in the case when the cold zinc target is covered by a thin film of the condensed carbon dioxide.

Multiple scattering in the interaction of low energy ions with a cold Au surface covered by a film of condensed argon

Energy spectra of ions emitted from a cold (< 40 K) Au surface covered by a thin film of condensed argon at small scattering angles (including the case of specular reflection) were examined. Depending on the density of the film new effects such as a splitting or shifting of the gold quasi-single-scattering peak are observed. It is postulated that these effects are connected with multiple scattering of projectiles inside the adsorbed film. Multiple scattering directs the ions to the detector after single scattering from the substrate atoms over the angles larger or smaller than the detection angle. At a certain density of adsorbed film only large-angle substrate scattering occurs. This phenomenon is manifested experimentally by a shift of the gold quasi-single-scattering peak.

A role of multiple scattering in the interaction of low energy ions with a cold Au surface covered by a film of condensed xenon

Energy spectra of ions emitted from a cold Au surface covered by a thin film of condensed xenon in the range of small scattering angles (including the case of specular reflection) were measured. If the concentration of particles in adsorbed film and its thickness are relatively small, new scattering effects such as a splitting and shifting of ‘single scattering peaks’, are observed. These effects are connected with multiple scattering of ions inside the adsorbed film of condensed xenon.

Interaction of low-energy ions (< 10 eV) with polymethylmethacrylate during plasma treatment

Using in-situ X-ray photoelectron spectroscopy (XPS) we investigated the chemical modification of the polymethyl-methacrylate (PMMA) surfaces after plasma and low-energy ion beam treatment. A comparison between plasma and ion beam treatment has shown, that for noble gases both treatments produce absolutely the same modifications of the chemical composition on the PMMA surface. In reactive gases (O 2, N 2) molecular ions were found to decompose polar bonds at the polymer surface, but they do not contribute to the incorporation of reactive gas atoms. Reactive atomic ions and radicals are responsible for this incorporation. We found that in the case of PMMA less than three ions are needed to decompose the ester group (OCO) completely. Therefore, we conclude that the decomposition of the ester group by ions is a chemical and not a physical effect due to the kinetic energy of the ions.

Accommodation coefficients for low-energy ions on metal surfaces

Abstract The interaction of low-energy ions (E = 3 to 100 eV) with the surface of a solid cannot be treated in terms of gas dynamics. The scattering of particles at an energy of E o > 20 eV may be explained in terms of binary collisions with the atoms of the target. The validity of the single collision model with free surface atoms for medium energies from 10 to 100 eV and even down to 1 eV was confirmed on the basis of both experimental and computational data. This paper describes experimental studies of the secondary ion emission from the (100) and (110) faces of a Mo single crystal and both experimental and theoretical studies of alkaline ion accommodation coefficient on polycrystalline Mo within the energy range E = 3 to 50 eV with a varying direction of the primary ion beam from normal to the glancing angle of incidence (ρ = 0 to 75°). On the basis of the retarding potential method using a spherical condenser whose central electrode was the target, we measured the energy distribution of secondary ion...