Main significant results

In 1966 the origin of the X ray satellites was not well understood. In a review paper Edwards listed ten different possible processes suspected to be responsible of the emission of these lines. A likely assumption was that these lines might be emitted by atoms doubly ionized in their innershells, by contrast to the (regular) 'diagram' lines which come from singly ionized atoms.

The existence of these doubly ionized states, which can be formed during photoionisation or electron bombardment processes, has however only been demonstrated in 1967 by Carlson and Krause. We carried out in 1970 a coincidence experiment between Auger electrons which sign the creation of double ionization states and the X rays emitted during the filling of these states, and gave the direct demonstration that the X ray satellites are emitted by doubly ionized atoms; we also observed in these experiments, for the first time, a new kind of X ray lines, characteristic of atoms twice ionized in the same shell (K or L), which we named hypersatellites, and which provide interesting probes of the atomic electron correlations.

Few years later we experimentally directly demonstrated with B.Crasemann that the atomic double ionization processes in photoionisation or electron bombardment come from, in first approximation, a shake off process due to the rearrangement of the atomic cloud during the removal of one electron as assumed by Carlson and Satchenko. We then compared the X ray spectra emitted during a photoionisation event and an ionization process induced by nuclear electron capture (NEC). We observed, by contrast to what happens in photoionisation, that the satellite lines vanish in the spectra emitted during a NEC ionization. This findings may be explained by the different behavior of the ejected electron in the two considered processes. In photo-ionization an e.g. K electron leaving the atom causes a sudden change of the inner charges which shakes the atomic cloud and may induce a process of double ionization, while in NEC ionization the K electron, which moves from the K shell into the nucleus, does not shake the atomic cloud, hindering any 'extra' ionization.

The alpha particles emitted by radioactive nuclei are known to be monoenergetic. During the radioactive decay the atomic cloud surrounding the nucleus has to adjust to be that of the final atom, and must then plays a cooperative role during the nuclear decay. We have experimentally demonstrated this role, in coincidence experiments, by observing, for the first time, weak continuous alpha spectra showing that the available decay energy is shared between the alpha particles and the atomic cloud.

The Raman-Compton effect has been first observed in the X ray regime on final states of collective levels in solids by Sparks. We observed for the first time in 1980 the (distinct) Raman and Compton effects on an atomic discrete level. In this experiment we irradiated at the LURE synchrotron radiation facility Mn atoms with X rays of continuously varying energies close to the 1s threshold. We observed resonant Raman discrete lines as well as Compton continua in the vicinity of this level and studied their separate different resonance behavior with the energy of the photons. These results provide interesting theoretical insights on the continua (Raman + Compton) extensively studied in valence bands of solids.

The main processes of interaction between electrons and ions: radiative electron capture, dielectronic recombinaison and excitation, are usually observed in hot plasmas were both partners of the collision are simultaneously present. In these media the electrons have continuous energy spectra and all ion species are simultaneously present in all charge states; one can then only get integrated information about all the considered interactions. We developed in 1983 a new technique to study separately each of these interactions and their evolutions with the collision energy, based on the use of an EBIS source. In an EBIS ion source one prepares highly charged ions by trapping singly charged ions during quite a long time inside a narrow electron beam where they can be re- ionized as many time as needed to get quasi fully stripped. We looked at the X rays emitted by the trapped ions during their interaction with the considered, monoenergetic, electrons of the beam and, by tuning the energy of the electrons, observed, for the first time, the resonance of a dielectronic process. This method allows, in a more general way, to excite very selectively any ion present in the source, in any given level, by properly choosing the energy of the electrons.The same year, by using cross beam technique three other groups also observed the same effect. The EBIT technique, which is orders of magnitude more luminous than the cross beam technique, is now routinely used for studying all the cross sections for all electron- ion interactions.

In 1972 M.Gavrila predicted the existence of an infra red divergence of the Raman - Compton scattering. This divergence would give rise to characteristic low energy X ray continua which we observed for the first time in 1988 at the LURE synchrotron radiation facility

Until 1978 the relativistic quantum mechanics and the QED theory(e.g. the Lamb shift), have been checked, with an extraordinary precision, on hydrogen atoms. The relativistic and QED corrections to the classical quantum mechanics are known to scale as Z4 up to Z10. We started in 1979 with R. Marrus a systematic study of hydrogenlike and heliumlike heavy ions all over the periodic table. These ions were produced by ultimately stripping the most energetic ion beams delivered by the most powerful accelerators of nuclear physics (Ar, Z = 18 , @ the Orsay Cyclotron ALICE in 1978, Fe, Z = 26,@ the HILAC at Berkeley in 1982, Kr, Z = 36, @ GSI Darmstadt in 1994, Xe, Z = 54, @GANIL in 1996, and U, Z = 92, @ the BEVALAC in Berkeley in 1990).We measured for the first time the 1s Lamb shift for all these elements (check of QED in strong fields), observed for the first time, for the heaviest elements for which the relativistic perturbative approximations are not any longer valid, the full relativistic energy depression of the atomic levels predicted by Dirac, by measuring the spin orbit coupling for all these elements the non equivalence of the action - reaction in relativity, and got for the heliumlike ions first information on the magnetic three body correlation and QED effects

The above quoted experiments have been carried out with extremely energetic ions, the highly ionized ions being only produced at that time with the beam foil technique at the highest energies (up to hundreds of GeV). In the eighties R.Geller and S.Donets discovered how to prepare very highly charged ions at low energies. Ion beams up to fully ionized uranium are now available at very low energies, opening the way to a completely different kind of Physics. In 1988 with R.Geller we sent, by curiosity, the intense Ar 17+ ion beam delivered by the Minimafios ECR source of Grenoble on solid targets, and discovered that these ions capture an huge number of electrons of the solid in excited states of the projectile (M and N shells), while the innermost K and L shells remain empty, exotic species which we named Hollow Atoms. Sometimes later we demonstrated that there are two different kinds of hollow atoms : those formed above the surface before any contact (only observed with fully decelerated ions at typical energies of eV/q ) which we named Rydberg Hollow Atoms because the electrons are captured in very excited Rydberg states, and those which are formed below the surface in which the electrons are captured in lower but still very excited states: the Surface Hollow Atoms. We then studied the atomic properties of these new exotic species. We demonstrated that the innermost shells are sequentially filled and that their decay cascade constitutes some kind of atomic clock of period of the order of few tenths of a femtosecond. We studied the atomic properties of these exotic species for elements from Ne up to U, in various situations where we separated the many electron capture processes from the many step decay processes. We studied for instance the interactions of these ions on very small surfaces like C 60 and demonstrated that the Rydberg Hollow Atoms formed nearby the surface of the buckyballs by capturing many electrons, lose all them but one, while escaping the capture area. By contrast we studied the case of surface hollow atoms in which the electrons are captured in lower excited states and may decay outside extremely thin ( few atomic layers) foils.

We demonstrated in 1996 with fully decelerated ions that the kinematics of the ions is fully different above metal and insulator or semiconductor surfaces. Above metal and dielectrics, as demonstrated by H.Winter, the ions are accelerated by their own electric image and must touch the surface. It seems then mandatory that the ion must, in any case, touch the surface, hindering any pure observation of the above the surface interaction We demonstrated that above dielectrics the ions experience, in addition to their attraction toward the surface by the image, some repellent forces induced by the holes created by the removal of the electrons and may be backscattered, a process which we named the Trampoline Effect .

In 1996 we started studying the nano and micro surface modifications induced on semiconductors and insulators by the impact of highly charged ions. The first observation of dots printed on surfaces following the impact of highly charged ion has been done by D.Schneider at Livermore on lamellar compounds. Later on we irradiated with various ions Si 111 Si wafers passivated by a monolayer of hydrogen and studied, in collaboration with C.Sebenne, G.Guichard, S.Bouffard and M.Edrieff the STM images on the impact of single ions. Nanometer dots have been observed which were interpreted as coming from the local removal on small area of the surface of the H coverage followed by a subsequent oxidation of the dot, printing insulator dots on conductive highly doped silicon. On request of our funding agency (CNRS) we did not publish these results, and under the recommendation and control of the University P.& M. Curie we founded a corporate firm (X-Ion) to develop on a long term basis all the industrial applications of the interaction of highly charged ions. Our tentative got soon famous and lot of funding were easily found attracting speculators. As soon as the instrumentation of X-ion was completed by our laboratory we were firmly fired from the company which concentrated on short term basis on financial objectives, with incompetent businessmen and inexperienced and ambitious engineers. The company is in bankruptcy since 2003 with a debt of 8 M$, and his CEO under judicial action. In spite of the pernicious image given by X-ion on this new and not well known technology, we have in 2005 restarted R&D with corporate companies on the industrial applications of the interaction of highly charged ions on surfaces to valorize the patents .

After studying these hollow atoms from the point of view of Atomic Physics we further used the atomic clock property of the hollow atoms (ACPHA) to study the interaction itself. The stepwise decay of the hollow atoms with a period quasi constant of few tenths of a femtosecond may be used to study the interaction above and below the surface at a precision of a fraction of an Angstrom up to few Angstroms according to the velocity of the ion (milestones along the ion trajectory above and below the surface).We used this property to study the evolution of the ion above the surfaces and found that, by contrast to what was expected, the electron capture proceeds through a series of distinct capture and decay processes for the most highly charged ions (the hollow atoms are fully re ionized before restarting any capture process). We further demonstrated, by studying the quantum number of the excited levels in which all the electrons are quasi resonantly captured in the hollow atoms formed below the surfaces, and which continuously increases with the charge of the ion, that the main process of formation of hollow atoms below a surface was an Auger neutralization process. We later on demonstrated that the X ray spectra of the hollow atoms formed below clean metal or insulator surfaces were dramatically different, a property which we now currently use to diagnose the surfaces and their ‘on line’ structural changes under the irradiation with highly charged ions. This property is easily explained by considering that the capture process is much faster on metal surfaces where the electrons come from the conduction band than on dielectrics in which the come from valence bands of the solid. It is now then possible for instance to clean a dirty metal surface with highly charged ions and diagnose on line the removal of the last top layer of the metal surface contaminants. We are currently studying the influence of the last conductive or insulating top layer of insulator and metal surfaces namely on diamond and graphite surfaces.

Highly charged ions approaching or touching a surface extract an extremely large number of electrons. Above metal these charges are quickly neutralized, but above dielectrics they provoke an extremely intense stress which may sputter the surface or even change their structural properties e.g. prints on crystaline silicon dots of porous silicon character. We concentrated in the last few years on the study of carbon surfaces which own extremely different structural properties such as diamond or graphite.

By using the Atomic Clock Property of the Hollow Atoms (ACPHA) technique, which allows to determine when highly charged ions approach a surface if the exposed surfaces are conductive or isolative we demonstrated that gem (monocrystaline) or CVD (polycristaline) diamonds are always originally covered by a graphitic layer. This property has also been demonstrated by other authors for diamondlike carbon (DLC), but while such ions print on crystalline diamond graphitic dots, as we demonstrated, this is not the case for DLC. Still using the same technique we demonstrated in parallel to Meguro that HCI print on graphite diamond dots. We filed patents on these findings and are exploring their industrial applications.

We have measured the absolute value of the mean decay times of Ar hollow atoms formed inside metal and dielectric materials,determining the mean emission depths below the surface of the x-ray or the series of x-rays emitted either during the filling of the unique hole of Ar9+or the stepwise filling of the 4 or 8 holes of Ar12+ and Ar16+. It has been found that the decay times of these hollow atoms are much longer in dielectrics than in metals,and at keV/q kinetic energies at depths of the order of 10-20 nm,well deeper any expected value.These findings have been explained by the different responses of metals and dielectrics to the slow penetration of a highly charged ions and the re-ionization of the ions after each filling of a L hole, which resets to zero the internal clock of the hollow atom . These findings may then also lead to reconsider some of the conclusions drawn from previous experiments in Auger spectroscopy, a technique which can only detect what happens below the very first atomic layers of surfaces.