Y. Le Beyec

Impact of slow gold clusters on various solids: nonlinear effects in secondary ion emission

Abstract A liquid metal ion source (LMIS) has been installed on a pulsed ion gun built at the IPN. The time of flight (TOF) spectra of the pulsed beam were recorded. With the gold source several cluster ions (up to 10 atoms in the cluster) and doubly charged ions were identified in the ion beam TOF spectra. With a second pulsation, single cluster ions can be selected as projectiles for secondary ion TOF mass spectrometry. We have studied the secondary ion emission (SIE) induced by cluster impact from a variety of targets: organic, CsI, metallic. A large enhancement of yield is observed by comparison to single atomic ion impact (e.g. factor of 30 between Au 3 + and Au + ). The secondary ion yields increase strongly with the number of constituents in the cluster. This effect is not linear. A comparison with other types of clusters and also fission fragments of 252 Cf has been performed. The rate of secondary emission stimulated by cluster is similar to SI yield induced by fission fragments.

Energy loss by MeV carbon clusters and fullerene ions in solids

Abstract Energy losses by carbon clusters C p ( p ≤ 8) and fullerene ions C 60 in thin carbon foils have been measured in the energy range from 0.3 to 5.65 MeV/atom. A small enhancement in energy loss is obtained for carbon atoms in the clusters relative to single carbon ions at the same velocity. Very large pulse height defects have been observed in the energy response of a silicon detector bombarded by C 60 ions with energies ranging from 6 to 30 MeV.

Acceleration of Cn+60 molecules to high energy

Abstract For the first time fullerene ions have been accelerated to high energy (4–36 MeV). Negative ions of C − 60 were produced in an ion source with a Cs gun and injected into a tandem accelerator. The change of charge from negative to positive was achieved by collisions with N 2 molecules in a gas cell at the high voltage terminal before the second acceleration step. To identify the accelerated molecular ions, the injected beam was pulsed, and time-of-flight measurements combined with energy measurements allowed mass and charge assignments.

Radiation damage features on mica and L-valine probed by scanning force microscopy

The radiation damage tracks on the surface of muscovite mica due to single 78.2 MeV 127I ions from the Uppsala EN tandem accelerator have been studied using tapping mode scanning force microscopy (TM-SFM). Conically-shaped hillocks having nearly circular bases were observed on a sample irradiated at normal incidence. Samples irradiated at grazing angles of incidence displayed wider and taller hillocks, and each hillock was accompanied by a raised tail over the bulk ion track. First SFM results are also presented from a study of radiation damage features on mica and single crystals of L-valine induced by single 23 MeV C60 ions from the Orsay tandem accelerator. Brief comments are made on the scaling laws that could link results obtained with atomic and cluster ions.

Multiparameter coincidence experiments to investigate desorptionmechanisms with heavy ions of Kr, Ag, U in the energy range of 0.1 MeV/u TO 5 MeV/u

Abstract Experiments with heavy ion beams from accelerators have been performed to study the desorption of atomic and secondary ions. The shapes of the yield curves have been measured for energies of projectiles ranging from O.1 to about 5 MeV/u. Secondary electron yields have been measured in coincidence with projectiles and secondary ions. A Different primary ion velocity dependence is found for electron and secondary ion yields.

Q β Measurements and mass excess values for neutron deficient isotopes nearN∼Z∼40

The decay characteristics of neutron deficient isotopes of Sr, Y and Zr have been studied. Mass excess values have been deduced fromQβ measurements and the results compared with mass tables. Deviations from theoretical predictions are observed for the lightest isotopes.

Secondary ion emission under cluster impact at low energies (5–60 keV); influence of the number of atoms in the projectile

Abstract The impact of gold clusters on solid organic surfaces has been compared to the impact of fullerenes and organic clusters. Langmuir-Blodgett (LB) films and vacuum evaporated organic films were used as targets. A nonlinear effect in the secondary ion emission from these targets is observed with gold cluster projectiles. It is shown that this effect vanishes when the projectiles contain a large number of atoms. It is also shown that the emission yield is larger for projectiles with light atoms. In the case of LB films emission was found to come mainly from the first 50 angstroms.

Emission of hydrogen ions under multiply charged ion bombardment

Abstract The emission yield of hydrogen ions emitted from a solid surface under multiply charged ion bombardment increases rapidly with the incident charge state. This trend has been observed with slow (keV energy range) and fast (MeV energy range) projectiles. A model of Coulomb explosion of a surface charged small domain is proposed to explain the H + emission yield. A comparison with the experimental results is given and energy distributions are calculated. Further experiments are proposed to confirm the model.

COLLISIONS OF FAST CLUSTERS WITH SOLIDS AND RELATED PHENOMENA

Abstract Fast ions, impinging on solid targets at a few MeV per atom, deposit energy in the material through electronic excitation processes. The relaxation of this energy induces emissions of photons, electrons, ions and neutral species from the target. The detailed study of these ejecta can give insight on the energy deposition and relaxation steps of the ion-solid interaction. Fast polyatomic projectiles allow to deposit very high energy densities (at the surface and in the bulk) well beyond that being possible with any single ion impact. As a result, new and unexpected phenomena are oberved which will be discussed: large non linear emission of ions and cluster ions, very high sputtering yields, production of giant tracks and craters in various irradiated materials including metals. When entering the solid, the atomic constituents of the projectile remain in a close proximity for a certain distance, and the energy density deposited in the overlapping trajectories region is high enough to induce collective effects. Secondary ion emission experiments, performed with various carbon cluster beams delivered by the Tandem accelerator in Orsay, aim to determine this depth of spatial correlation by probing these collective effects inside the solid. The influence of the proximity of the cluster constituents on some of their properties such as their charge state distributions inside the solid has been studied and it has been shown that the mean charge state of the constituents is significantly smaller than when the atoms penetrate the target independently.

Surface secondary electron and secondary ion emission induced by large molecular ion impacts

This paper presents results on secondary ion and secondary electron yields under impact of large ions at 18 keV and with 100 < m/z < 70 000 on a CsI-coated surface. Ratios of secondary electron emission to secondary ion emission have been measured and it is shown that the negative secondary ion yield is much larger than the electron yield. Electrons are still emitted below an energy of impact per mass unit of 1 eV Da−1 (106 cm s−1). Effects of grids in the acceleration of secondary ions and secondary electrons are important.