HYDROGEN IONS EMISSION UNDER FAST CHARGED PARTICLES : THE BEGINNING OF THE DESORPTION PROCESS

L'émission des ions H-, H+ et H+2 par des surfaces exposées au bombardment de fragments de fission du 252Cf a été analysée. Des taux de desorption relatifs on été mesurés, ainsi que la distribution de leur energie cinetique initiale. Il a été observé que le taux de desorption des ions H- est à peu près le même que celui des ions H+ mais que leur énergie cinetique initiale moyenne est clairement inferieur à celles des ions H+ et H+2. Il est proposé que le mécanisme de la desorption est un processus d'ionisation ou d'excitation electronique, suivi d'une dissociation du système. Un modèle de desorption genre dissociation d'une molecule H2 est presenté. Des résultats obtenus par l'impact d'electrons sont également considerés dans la discussion.The emission of H-, H+ and H+2 ions by solid samples exposed to the bombardment of 252Cf fission fragments has been analyzed. Relative desorption yields have been measured, as well as the initial kinetic energy. It was found that the H- desorption yield is close to the H+ yield but its average initial kinetic energy is clearly smaller than that of the H+ and H+2. It is proposed that the basic desorption mechanism is an ionization/electronic excitation process followed by dissociation of the system. A H2 - dissociation desorption model is presented. Processes such Auger efect and ionization induced by secondary electrons may also participate. Results are compared with with electron impact data

CLUSTERS AS PROJECTILES FOR SIMS

Des agrégats polyatomiques et ions moléculaires ont été produits par désorption induite par des fragments de fission. Après accélération à des énergies de quelques keV, ces agrégats ont été utilisés à leur tour comme projectiles pour induire des émissions d'ions secondaires. Des spectres de masse en temps de vol indiquent pour des ions secondaires positifs émis à partir de LiF, une possibilité d'effets chimiques dans le processus de désorption. Les possibilités d'utilisation de la source d'agrégats décrite sont évidentes. Des rendements réhaussés en ions secondaires peuvent être escomptés, les rendements expérimentaux restent cependant à déterminer.Atomic and molecular cluster ions have been generated by fission fragment induced desorption and then accelerated to keV energies for use as projectiles inducing secondary ion emission. Time of flight mass spectra of positive secondary ions emitted from LiF are presented which show possible chemical effects in the desorption process. Although experimental verification of enhanced secondary ion yields remain to be completed, the potential benefits of using this type of cluster ion source are apparent

Massive Clusters : Secondary emission from qkeV to qMeV. New emission processes? New SIMS Probe?

International audienc

Electron Emission from Hypervelocity C60 Impacts

Secondary ion mass spectrometry (SIMS) performed in the event-by-event bombardment detection mode when coupled to an electron emission microscope allows one to investigate individual nano-objects. Two groups of Au and Al oxide nano-objects were compared with their bulk counterparts based on their secondary ion and electron emission from individual C60 impacts at 15 and 30 keV total impact energy. Our results show that electron yields depend on the size and surroundings of the nano-object, and at higher impact energies, these differences in electron emission are more pronounced. A second key observation for systems of similar chemical makeup but different surface topography and size is that the emission of secondary ions and electrons is independent of each other

Ion-induced desorption in insulators by hydrogen cluster impact up to 600 KeV

BIA

Desorption mass spectrometry using cluster ions

This article synthesizes our published works as far as articles circulation of a documents supplier is concerned. It explains the mathematical model and recall the main results obtained. New ones complete previous ones and show a wider prospect of our model fixing it to former results which refer to bibliometric works about mathematical models of circulation

Emission of molecular fragments synthesized in hypervelocity nanoparticle impacts

We report on experiments with Aun nanoparticles (100 ≤ n ≤ 400) at velocities of 10–60 km/s. They are implanted virtually intact via hydrodynamic penetration. The products of the extreme pressure transient are observed by mass analyzing the ionized ejecta. Targets of labeled molecules (13C-, 15N-glycine) reveal fragmentation–recombination processes, producing CN− and OCN− with high efficiency (45%). This value is over two orders of magnitude larger than that obtained with atomic and small cluster projectiles. The experiments could simulate collisions of nanosized dust particles in interstellar space

Prompt in situ emission of gold adducts from single impacts of large gold clusters on organics solids

We report the first observation of single impacts of 136 keV Aun4+ (100 ≤ n ≤ 400) on organic solids, generating prolific emission of Au and Au2 - containing fragments and molecular ions. We show that the individual impacting cluster is both the source of energy stimulating the emission, and the donor of atoms for adducts synthesis. The emission of Au and Au2 was observed when n ≥ 100. The most abundant species is Au(CN)2−. The adduct yields behave as follows when the projectile size varies from n = 100 to 400: (a) they increase with n; (b) the dependence with n for the formation of Au(CN)2− differs from those for more complex species suggesting different pathways of synthesis; (c) the combined yields of the Au or the Au2 - adducts are the same for different targets. There is evidence that the projectiles were implanted virtually intact in the organic targets, thus, the adduct synthesis involves a small number of Au atoms ablated from the projectile, which implies extensive ionization of the detached atoms. The abundance of three-body assemblies, e.g. Au(CN)2−, Au(CN) (M–H)−, suggests that the adduct formation occurs likely in a dense phase