Interaction Of Multiply Charged Ions Research Articles

Interaction of multiply charged ions with large free silver nanoparticles: Multielectron capture, fragmentation, and sputtering phenomena

We report on the interaction of multiply charged ions at keV energies with free Ag nanoparticles with diameters of $\ensuremath{\sim}6$ nm (containing about 6600 Ag atoms). As the ionization energy increases only very slowly with the degree of ionization, multielectron capture processes are very likely to occur in peripheral collisions with large cluster sizes. However, due to the large particle size, the produced highly charged Ag nanoparticles are mostly stable. For projectile charge states below $q=8$ the geometrical cross section overcomes the cross section for peripheral electron transfer, and penetrating collisions become dominant. Therefore, these collisions can be described as ion collision with a nanosurface, where the distribution of small-size fragments with $nl20$ is due to sputtering events from the nanoparticle surface. This is in contrast to nanoparticles with a smaller diameter ($l2$ nm), where small fragments are produced by fission of multiply charged clusters.

Interaction of multiply charged ions with single layer graphene Part II: electron emission

SynopsisA new setup is used to measure the number statistics of electrons emitted during the transmission of slow multiply charged ions through single layers of graphene and 1 nm thick carbon nanomembranes.

Interaction of multiply charged ions with single layer graphene Part I: charge exchange and energy loss

SynopsisThe exit charge state distribution and the energy loss of slow multiply charged ions transmitted through single layers of graphene and 1 nm thick carbon nanomembranes is analyzed.

Interaction of multiply charged ions with isolated polycyclic aromatic hydrocarbon molecules

The interaction of multiply charged ions (He2+, O3+, and Xe20+, v ≤ 0.6 a.u.) with gas phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules (pyrene and coronene) was studied. Positively charged ionic products were analyzed with a linear time-of-flight mass spectrometer.

Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions

The interaction of multiply charged ions (He${}^{2+}$, ${\mathrm{O}}^{3+}$, and Xe${}^{20+}$) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C${}_{24}$H${}_{12}$) and pyrene (C${}_{16}$H${}_{10}$) is studied for low-velocity collisions ($v\ensuremath{\leqslant}0.6$ a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, $n$, in the intensity distributions of the ${\mathrm{C}}_{n}$H${}_{x}^{+}$ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C${}_{60}$ collisions. The latter oscillations are known to be due to dissociation energy differences between even- and odd-$n$ ${\mathrm{C}}_{n}$-chain molecules. For PAH molecules, the average numbers of H atoms attached to the ${\mathrm{C}}_{n}$H${}_{x}$ chains are larger for even-$n$ reflecting acetylenic bond systems.

Formation and decay of the Rydberg states of multiply charged ions interacting with solid surfaces

Processes of formation and decay of the Rydberg states of multiply charged ions escaping solid surfaces with intermediate velocities (v ≈ 1 a.u.) represent complex quantum events that require a detailed quantum description. We have developed a two-state vector model for the population process, with the functions Ψ1 and Ψ2 for definition of the state of a single active electron. The electron exchange between the solid and the moving ion is described by a mixed flux through a plane positioned between them. For the low values of the angular momentum quantum numbers l the radial electronic coordinate ρ can be neglected, whereas for the large-l values a wide space region around the projectile trajectory was taken into account. The reionization of the previously populated states is considered as a decay of the wave function Ψ2. The corresponding decay rates are obtained by an appropriate etalon equation method: in the large-l case the radial electronic coordinate ρ is treated as a variational parameter. The theoretical predictions based on that population-reionization mechanism are compared with the available beam-foil experimental data, as well as the experimental data obtained in the interaction of multiply charged ions with micro-capillary foil. Generally, the model reproduces the experimentally observed non-linear trend of the l distributions from l = 0 to lmax = n − 1.

Coherent x-ray pulse generation in the sub-Ångström regime

A mechanism is proposed to generate femtosecond coherent light pulses with a wavelength shorter than the dimension of a single atom. X rays of such short wavelength and high energy are shown to arise from the relativistic interaction of multiply charged ions with short and intense near-optical laser pulses. The generated x-ray pulses have thus potential to be useful in investigating the dynamics of chemical and biological systems with a subatomic resolution.

HCI-Induced Ionization and Fragmentation of Fullerenes and Organic Molecules

The interaction of multiply charged ions with fullerenes is governed by electron capture as well as nuclear and electronic stopping. The fullerene excitation due to electronic stopping leads mainly to direct ionization and multifragmentation. Our experiments show that the according patterns in the fragmentation spectra can serve as fingerprints for the electronic stopping. A quantitative analysis of the cross sections for ionization and multifragmentation reveals the characteristic linearity in the projectile velocity v as well as an oscillatory dependence on the projectile atomic number Z. The π-electron dominated electronic structure of fullerenes has some similarities to that of biomolecular species. Qualitatively similar dynamics are therefore expected to occur in HCI collisions with biomolecules. First experimental results indeed indicate a strong dependence of the fragmentation pattern on projectile charge state and velocity.

Formation of hollow atoms at metal- and insulator surfaces

The interaction of multiply charged ions with various surfaces gives rise to the formation of so-called hollow atoms via multiple electron capture into excited orbitals. The potential energy of the ions is partly converted into photons and kinetic energy of emitted electrons during subsequent decay of these hollow atoms. Also it might give rise to localized surface structure modifications. We have used Auger electron spectroscopy to investigate the various electronic processes which take place at metal- and LiF insulator surfaces as well as a LiF-covered Au(111) surface. The surface sensitivity of these processes is demonstrated by the fact that after a monolayer coverage, the spectra closely resemble those of a pure LiF target.

Charge state effects in the interaction of multiply charged ions with surfaces

The interaction of multiply charged ions (MCI) with clean solid surfaces is discussed, with main emphasis on the ion-induced electron emission. At projectile impact energies close to the lower limit set by the projectile's image charge attraction, multiply excited “hollow atoms” are transiently formed and mainly decay under potential emission which strongly dependes on the projectile's charge state. At sufficiently higher energies the electron emission is dominated by the projectile's kinetic energy. Charge state effects in kinetic electron emission are considerably weaker and therefore not so well understood as for PE, and respective experimental results show that they are much more pronounced for insulator than for metal targets. To achieve a still better understanding of potential and kinetic emission processes a new experimental setup has been designed, which permits coincidence measurements between emitted electrons and charge state analysed scattered projectiles. This setup will be described together with some preliminary results.

Interaction of multiply charged ions with metals

We present a theoretical study of the energy deposition by slow multiply charged ions interacting with an electron gas and its dependence on the electronic configuration (excitation state) of the particle. Applications of the results to explain experimental findings of projectile induced electron emission and energy loss as a function of charge state are also discussed.

Interaction of Highly Charged Ions with Surfaces

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.

Above-surface neutralization of highly charged ions: The formation of hollow atoms

We investigate the interaction of multiply charged ions with metallic surfaces. Simulations are presented displaying the formation of hollow atoms when slow highly charged ions approach the surface. It is shown that above surface neutralization 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. Recent experimental data on K Auger emission and image acceleration confirm this scenario.

Interaction of multiply charged ions with solid surfaces

Abstract The observation of the decay of inner-shell vacancies can serve as an excellent probe of the neutralization of multicharged ions during their approach to a metal surface. Several recent experiments that have measured electrons emitted during this neutralization are discussed. Measurements of the total electron yield for incident ions with inner-shell vacancies first showed marked differences from the yield observed for lower charge states and indicated the need for further investigations. Measurements of the emitted electron energy distributions have led to a qualitative understanding of the timescales of the neutralization process. For incident ions with high enough energies, projectile inner-shell vacancies have been observed to survive the neutralization process above the surface and then to be transferred to target atoms in close collisions. The inner-shell reactions occuring in such close collisions are analogous to those that have been observed in ion-atom and ion-foil collisions. Recent me...

Electron emission from the interaction of multiply charged ions with a Au(110) surface

We measured electron energy distributions from the interaction of N+q and O+q (q = 5–7) at grazing incidence with a clean Au(110) surface. The acceleration voltage of 10 kV results in velocity components perpendicular to the surface which correspond to impact energies of a few hundred eV. The main source for the electronic particle-surface interaction is therefore the potential energy of the incoming projectile. For the experiment the Oak Ridge National Laboratory ECR source was used, the electron energy spectra were measured using a standard four-grid LEED Auger system. The same system served to control the surface structure and cleanliness. The results show evidence of kinetic electron emission and strong peaks at 250 eV for both N+6 and O+7 projectiles and peaks at 380 eV for N+6 and at 480 eV for O+7. With the lower charge states N5+ and O+6 no peaks are found. The results clearly indicate the important role of the K-shell hole in the interaction. We identify the higher-energy peaks as projectile KLL-like Auger decay from poorly defined upper states. The 250 eV peak is interpreted as Au NVV-like Auger emission, where the hole in the Au N shell is created by an interaction with the projectile K-shell hole.

Electron emission from the interaction of multiply charged ions with a Au(110) surface

Abstract We measured electron energy distributions from the interaction of N+q and O+q (q = 5–7) at grazing incidence with a clean Au(110) surface. The acceleration voltage of 10 kV results in velocity components perpendicular to the surface which correspond to impact energies of a few hundred eV. The main source for the electronic particle-surface interaction is therefore the potential energy of the incoming projectile. For the experiment the Oak Ridge National Laboratory ECR source was used, the electron energy spectra were measured using a standard four-grid LEED Auger system. The same system served to control the surface structure and cleanliness. The results show evidence of kinetic electron emission and strong peaks at 250 eV for both N+6 and O+7 projectiles and peaks at 380 eV for N+6 and at 480 eV for O+7. With the lower charge states N5+ and O+6 no peaks are found. The results clearly indicate the important role of the K-shell hole in the interaction. We identify the higher-energy peaks as projectile KLL-like Auger decay from poorly defined upper states. The 250 eV peak is interpreted as Au NVV-like Auger emission, where the hole in the Au N shell is created by an interaction with the projectile K-shell hole.

Interaction of Multiply-Charged Ions with Electrons and Photons

The current status of ion beam excitation and ionization by high energy electrons and photons is discussed. Recent advances in multiply-charged ion source development are mentioned, and plans for electron-ion and synchrotron-ion crossed beam experiments at Brookhaven National Laboratory are described.