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  • 1. Burgdörefer, J
    et al.
    Reinhold, c O
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Meyer, F
    Interaction of highly charged ions with surfaces1996In: Australian Journal of Physics, ISSN 0004-9506, Vol. 49, no 2, p. 527-541Article in journal (Refereed)
    Abstract [en]

    An overview is given of recent advances in the theoretical description of the interaction of multiply charged ions with surfaces. Simulations are presented displaying the formation of hollow atoms when slow highly charged ions approach the surface. It is shown that above-surface neutralisation proceeds via hollow-atom formation. Relaxation of the multiply excited states to the ground state occurs only subsequent to the close encounter with the topmost atomic layer.

  • 2. Goscinski, O
    et al.
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Dimensional Scaling of Local Pseudopotentials1993In: Journal of Molecular Structure - THEOCHEM, ISSN 0166-1280, Vol. 287, p. 17-21Article in journal (Refereed)
    Abstract [en]

    The integral equations of Gelfand and Levitan were previously used by Abraham and Moses (Phys. Rev. A, 22 (1980) 1333) to construct a modified local potential Vpert(r), which in this work is added to a coulombic potential in order to remove the lowest s state from the spectrum. The total modified potential Vnew(r), for excited states is used in conjunction with the shifted 1/D expansions of dimensional scaling. It is verified that it is feasible to find the lowest energies and the mean radius for Vnew, treating it now as a ground state problem. This indicates that a potential for excited states can be generated by the procedure, with the possibility of using it in the study of excited states and valence states. The potentials applied can be considered as local pseudopotentials.

  • 3. Goscinski, O
    et al.
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    The maximum entropy method and relaxation for multiple collisions involving highly charged ions1996In: International Journal of Quantum Chemistry, ISSN 0020-7608, Vol. 58, no 6, p. 689-698Article in journal (Refereed)
    Abstract [en]

    Advantages and disadvantages of the maximum entropy method (MEM) in application to the theory of relaxation are studied. The time evolution of distributions and of associated moments must obey stringent conditions for both finite and infinite intervals. The theoretical considerations are illustrated with examples from charge-state distributions arising in beam-foil spectroscopy. The examples indicate that the possibility to include more than two moments (extension to non-Gaussian case) is severely limited (though feasible) in the static case due to nonpositive definiteness as well as stiffness of the Hessian matrices appearing in the computations. This takes place already for the finite charge-state distribution intervals. For infinite intervals, this is a severe problem as required by the Marcinkiewicz theorem, affecting characteristic functions and, hence, the description of the time evolution of distributions.

  • 4. Hayderer, G.
    et al.
    Schmid, M.
    Varga, P.
    Winter, H. P.
    Aumayr, F.
    Wirtz, L.
    Lemell, C.
    Burgdörfer, J.
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Threshold for Potential Sputtering of LiF1999In: Physical Review Letters, ISSN 0031-9007, Vol. 83, no 19, p. 3948-3951Article in journal (Refereed)
    Abstract

  • 5.
    Hägg, Lotten
    Uppsala universitet.
    Studies of distributions in physics using maximum entropy and scaling methods1993Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The maximum entropy method (MEM) is applied in the analysis of equilibrium systems. Some general properties of the MEM and how to choose constraints as well as moments are discussed. A numerically stable algorithm is developed and implemented. Distributions arising from physical processes are studied. In particular, charge-state distributions arising in beam-foil spectroscopy have been studied in detail. The main emphasis lies on finding regularities and systematic behaviour through the MEM. It is shown that in the studied system there is a general Gaussian behaviour and the implications of using only Gaussians are discussed. Extending the MEM to an analysis of non-equilibrium systems requires care when choosing the number of moments. How to use the MEM to examine time-dependent problems is discussed. Time evolution of a distribution can be described on a microscopic level by master equations and on a macroscopic level by Fokker-Planck equations. These approaches can be connected through a scaling method: the large-Omega scaling. The procedure and its applications are thoroughly described . Scaling methods in general have a wide applicability in many fields. The method of dimensional scaling is applied in the calculation of multipole polarizabilities. The result is compared to what is obtained from an exact calculation. Also, a procedure to calculate energies of excited states in atoms or molecules by using dimensional scaling on local pseudopotentials is developed.

  • 6.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Bárány, A
    Cederquist, H
    Thumm, U
    Angular Differential Cross Sections for Slow Highly Charged Ions Interacting with C601999In: Physica Scripta. Topical Issues, ISSN 0281-1847, Vol. 80, p. 205-206Article in journal (Refereed)
    Abstract [en]

    Angular differential cross sections are presented for collisions between 26.4 keV Ar8+ ions and C60 molecules. Using a classical overbarrier simulation the deflection function is calculated for large impact parameters. To compare with experimental data the theoretical cross section values are convoluted with an instrumental function. Both the theoretical and experimental cross sections are absolute in magnitude and position. The experimental cross section for retaining one electron on the projectile is qualitatively well described by the theoretical cross section for initially capturing one to four electrons from the target.

  • 7.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Goscinski, O
    Dimensional scaling and spectral properties1993In: Dimensional scaling in chemical physics, Dordrecht: Klüwer , 1993, p. 510-Chapter in book (Other scientific)
    Abstract [en]

    A review is made of the calculation of multipole polarizabilities in three dimensions, for hydrogen-like ions with nuclear charge Z, in which the solutions of the inhomogeneous equations in perturbation theory are used. The procedure is extended to arbitrary dimension D, and an explicit expression for exact multipole polarizabilities is obtained. A calculation of an approximate ground state energy using 1/D expansions is made, leading to a classic harmonic oscillator problem. The possibility to estimate the dipole polarizability in the large D limit from the obtained expressions is used. A comparison with the exact result yields quantitative agreement in the coefficient as well as in the D dependence, when using a physically motivated form of the perturbation. Inequalities for oscillator strengths, previously used for estimating dipole polarizabilities in three dimensions, are generalized to D dimensions, and expressions for the dipole polarizability in the large D limit are obtained. The exact results, the dimensional scaling calculations, and the expressions obtained from inequalities are compared and evaluated. It is shown that the exact first order correction to the unperturbed wave function reduces to one term in the sum over states expression. The asymptotic result for the dipole polarizabilities is, in atomic units, alpha2 = (64Z4)-1 D6. in Dimensional

  • 8.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Goscinski, O
    Gaussian Approximations to Equilibrium Charge State Distributions with the Maximum Entropy Method1994In: Journal of Physics B, ISSN 0953-4075, Vol. 27, no 1, p. 81-95Article in journal (Refereed)
    Abstract [en]

    Charge-state distributions for ions in beam-foil experiments are discussed in detail and analysed using the maximum entropy method (MEM). The symmetric distributions can be well described by one Gaussian in the whole charge-state interval. It is found that asymmetric distributions, exhibiting the shell effect, can be treated using two disjoint Gaussians, in two separate intervals. The relative weights of these Gaussians are interpreted by using Fermi-Dirac statistics. Physically this corresponds the varying occupancy of some of the shells in the ions. The fact that no more than two moments, in one interval or two, is sufficient is of significant importance in the analysis of charge-state distributions in general. An interpolation procedure to obtain the charge-state distribution for an energy is developed and tested. The procedure, which is made possible by the Gaussian character, uses MEM and experimental information. It is only possible to predict distributions in energy regions where experimentally measured values for other energies exist. The method is tested on asymmetric distributions of copper ions in the energy range 0.902-1.505 MeV u-1 and symmetric distributions for calcium, titanium, yttrium, rhodium, holmium and bismuth ions for energies from 0.191 to 3.184 MeV u-1.

  • 9.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Goscinski, O
    Maximum Entropy and Equilibrium Charge State Distributions1993In: Journal of Physics B, ISSN 0953-4075, Vol. 26, no 15, p. 2345-2358Article in journal (Refereed)
    Abstract [en]

    The maximum entropy method is implemented in order to describe equilibrium distributions arising in beam-foil spectroscopy. Since there are very few charge states involved, the usual moment conditions, based on simple powers xi, give rise to severe numerical difficulties already for three moments and cannot be applied in these systems. Earlier devised methods, based on Lagrange interpolation polynomials Qi(x) with abscissae chosen as zeros of Chebyshev polynomials in the interval being studied, are adapted and implemented for the present problems of charge state distributions. A reduced variable x= (q-)/, where q is the charge and the mean charge, is chosen. Using the method described above calculations of equilibrium charge state distributions for copper ions (exit energy range 0.599-2.304 MeV u-1) colliding with carbon foils are carried out in order to exhibit the usability of the method. The new moment conditions associated to the Qi(x) provide a framework for a systematic analysis of equilibrium distributions. In future work the algorithm will be applied for systematic studies of charge state distributions, of approach to equilibrium, of deviations from Gaussian behaviour, of the shell effect etc. Applications to related problems like fragmentation will also be possible.

  • 10.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Reinhold, C. O.
    Burgdörfer, J.
    Interaction of multicharged Ions with insulator surfaces1998In: Photonic, electronic and atomic collisions : invited papers of the Twentieth International Conference on the Physics of Electronic and Atomic Collisions, Vienna, Austria, 23 - 29 July 1997, Singapore: World Scientific , 1998, p. 683-Conference paper (Refereed)
    Abstract [en]

    We present a summary of recent theoretical progress on the neutralization of multiply charged ions near insulators, in particular LiF. Capture and loss processes are investigated using a classical trajectory Monte Carlo approach. Estimates from this simulation of the onset of charge transfer are compared with predictions from the classical over-the-barrier model. It is found that capture effectively begins a few atomic units closer to the surface than predicted by the latter model. Calculations of the energy the ion gains on the way to the surface are compared with recent measurements.

  • 11.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Reinhold, Carlos O.
    Burgdörfer, Joachim
    Above Surface Neutralization of Slow Highly Charged Ions in Front of Ionic Crystals1997In: Physical Review A, ISSN 1050-2947, Vol. 55, no 3, p. 2097-2108Article in journal (Refereed)
    Abstract [en]

    We present a theoretical analysis of the above-surface neutralization of highly charged ions in front of LiF. The study is based on the assumption that the dominant electron transfer occurs in the classically allowed region. Estimates of critical distances and corresponding quantum numbers for capture from an ionic crystal within the classical over-barrier (COB) model are presented, which differ considerably from corresponding results for metals. The role of the dielectric response of LiF is investigated. In addition, classical trajectory simulations are performed for the first time for a slow highly charged ion approaching an insulator. It is shown that capture effectively begins about 3 a.u. closer to the surface than estimated from the COB model. This correction can be incorporated into a modified COB model. The energy gain for grazing incidence ions is obtained using a staircase model which includes the deceleration due to charge-up of the surface.

  • 12.
    Hägg, Lotten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Reinhold, Carlos O.
    Burgdörfer, Joachim
    Energy gain of highly charged ions in front of LiF1997In: Nuclear Instruments & Methods in Physics Research, Section B, ISSN 0168-583X, Vol. 125, no 1-4, p. 133-137Article in journal (Refereed)
    Abstract [en]

    We present estimates of the energy gain of highly charged ions approaching a LiF surface, based on a modified classical-over-barrier model for insulators. The analysis includes the energy gain by image acceleration as well as the deceleration due to charge-up of the surface in a staircase sequence. The resulting velocity dependent total energy gain is studied in detail and the results are compared with experimental data.

  • 13.
    Högberg, Björn
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Helmersson, Jing
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Boo, Jörgen
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Glans, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Programmable self-assembly:: Theoretical aspects and DNA-linked nanoparticles2008In: Systems Self-Assembly: Multidisciplinary Snapshots, Amsterdam: Elsevier, 2008, p. 245-258Chapter in book (Other academic)
    Abstract [en]

    We briefly present a method for the parameterization of assembly systems derived from their ability to form unique structures. The concept of bond uniqueness is introduced and we show how it influences the number of unique structures that a programmable, or algorithmic, self-assembly system can create. Further, we argue that programmable self-assembly systems create embedded, additional computation that is reflected in the complexity of the generated structures and show how this complexity is related to the bond uniqueness of the building blocks. A brief introduction to sticky graphs, a mathematical tool for modeling self-assembly systems, is given. From the theoretical discussions it becomes clear that building blocks for programmable self-assembly need to have at least four distinct, geometrically separated bonds. A scheme for the production of building blocks with well-directed bonds for programmable self-assembly using DNA-nanoparticles is presented. The introduced procedure is a completely bottom–up approach and can be used to produce quite advanced PSA building blocks like nanoparticle eight-mers with eight bonds. Initial experiments are presented.

  • 14.
    Olin, Håkan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Högberg, Björn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Glans, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Method and computer program for the self-assembly of a nanostructure2005Patent (Other (popular scientific, debate etc.))
    Abstract [en]

    Programmable self-assembly

  • 15. Thumm, U
    et al.
    Bárány, A
    Cederquist, H
    Hägg, Lotten
    Mid Sweden University, Faculty of Educational Sciences, Department of Education.
    Setterlind, C. J.
    Energy gain in collisions of highly charged ions with C601997In: Physical Review A, ISSN 1050-2947, Vol. 56, no 6, p. 4799-4086Article in journal (Refereed)
    Abstract [en]

    We have extended the recently developed dynamical classical over--barrier model for charge transfer in soft ion--cluster collisions in order to simulate the projectile kinetic energy gain of 3.3q keV Arq+ ions in large impact parameter collisions with neutral C60 targets. Our semi-classical theory allows for the direct calculation of the energy defect Q and of the projectile kinetic energy gain in two different ways, either as difference of electronic binding energies before and after the collision or by integration of the dynamically varying force between the collision partners along the trajectory. A comparison between the two ways provides an intrinsic test of the model calculations. Comparison with recent experimental data shows good agreement in the main features of the projectile energy gain spectra and facilitates their interpretation in terms of the number of transferred electrons and projectile shells into which electrons are captured.

  • 16. Wirtz, L.
    et al.
    Hayderer, G.
    Lemell, C.
    Burgdörfer, J.
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Reinhold, C. O.
    Varga, P.
    Winter, H. P.
    Aumayr, F.
    Curve-Crossing Analysis for Potential Sputtering of Insulators2000In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 451, no 1-3, p. 197-202Article in journal (Refereed)
    Abstract [en]

    We develop a theoretical model for the recently observed threshold for potential sputtering of LiF by slow singly and doubly charged ions. The threshold coincides with the potential energy to create a cold hole in the valence band of LiF by resonant neutralization. We calculate the level shift of the incident ion and the deformation of the valence band under the influence of the projectile. Resonant neutralization becomes possible for ions with recombination energies larger than 10 eV in agreement with the experimental findings.

  • 17.
    Wirtz, L.
    et al.
    Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8-10/136, 1040 Wien.
    Lemell, C.
    Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8-10/136, 1040 Wien.
    Reinhold, C. O.
    Oak Ridge National Laboratory, Oak Ridge, TN 37831-6377, United States.
    Hägg, Lotten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Burgdörfer, J.
    Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstraße 8-10/136, 1040 Wien.
    Vertical incidence of slow Ne10+ ions on an LiF surface: Suppression of the trampoline effect2001In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 182, no 1-4, p. 36-40Article in journal (Refereed)
    Abstract [en]

    We present a Monte Carlo simulation of the neutralization of a slow Ne10+ ion in vertical incidence on an LiF(100) surface. The rates for resonant electron transfer between surface F- ions and the projectile are calculated using a classical trajectory Monte Carlo simulation. We investigate the influence of the hole mobility on the neutralization sequence. It is shown that backscattering above the surface due to the local positive charge up of the surface ("trampoline effect") does not take place.

1 - 17 of 17
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