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International audience; Nanoporous graphene displays salt-dependent ion permeation. In this work, we investigate the differences in Donnan potentials arising between reservoirs, separated by a perforated graphene membrane, containing different cations. We compare the case of monovalent cations interacting with nanoporous graphene with the case of bivalent cations. This is accomplished through both measurements of membrane potential arising between two salt reservoirs at different concentrations involving a single cation (ionic potential) and between two reservoirs containing different cations at the same concentration (bi-ionic potential). In our present study, Donnan dialysis experiments involve bivalent MgCl 2 , CaCl 2 , and CuCl 2 as well as monovalent KCl and NH 4 Cl salts. For all salts, except CuCl 2 , clear Donnan and diffusion potential plateaus were observed at low and high salt concentrations, respectively. Our observations show that the membrane potential scaled to the Nernst potential for bivalent cations has a lower value (≈50%) than for monovalent cations (≈72%) in the Donnan exclusion regime. This is likely due to the adsorption of these bivalent cations on monolayer graphene. For bivalent cations, the diffusion regime is reached at a lower ionic strength compared to the monovalent cations. For Mg 2+ and Ca 2+ , the membrane potential does not seem to depend upon the type of ions in the entire ionic strength range. A similar behavior is observed for the KCl and NH 4 Cl membrane potential curves. For CuCl 2 , the membrane potential curve is shifted toward lower ionic strength compared to the other two bivalent salts and the Donnan plateau is not observed at the lowest ionic strength. Bi-ionic potential measurements give further insight into the strength of specific interactions, allowing for the estimation of the relative ionic selectivities of different cations based on comparing their bi-ionic potentials. This effect of possible ion adsorption on graphene can be removed through ion exchange with monovalent salts.

Sensitivity of the anatase and rutile phases of titanium dioxide to Swift Heavy Ion (SHI) irradiation was experimentally probed and compared with the predictions of the Coulomb explosion, analytical and inelastic thermal spike models of ion-matter interaction. Conforming to the predictions of all these models, our study indicated higher sensitivity of anatase to these ions than the rutile phase. A detailed examination however revealed that Coulomb explosion model cannot explain either the nature of variation of the interaction cross section of SHI with the energy deposited by these ions, Se to the target electrons, or the relative values of the threshold electronic energy loss, Seth of anatase and rutile. The analytical thermal spike (a-TS) model, using the available physicochemical data for this oxide, predicted that tracks cannot form either in anatase or in rutile by 297 MeV and 511 MeV Ni ions, while inelastic thermal spike (i-TS) model predicted formation of ion tracks by 297 MeV Ni ions and their absence with 511 MeV Ni ions in both anatase and rutile. Our observation agreed with the predictions of i-TS model albeit with a difference in the radius of the tracks. In addition, we observed halo of defect ridden crystalline region of much larger radius around the ion track. Interestingly, the radius of the halo scales with the velocity of the ions, which is opposite to the conventionally observed velocity effect.

Pronounced swelling is observed when single crystals of yttrium iron garnet Y3Fe5O12 (YIG) are irradiated in the electronic energy loss regime with various swift heavy ions. The out-of-plane swelling was measured by scanning across the border line between an irradiated and a virgin area of the sample surface with the tip of a profilometer. The step height varied between 20 and 600 nm depending on fluence, electronic energy loss and total range of the ions. The step height divided by the ion range as a function of the ion fluence exhibits a linear increase in the initial phase and saturates at high fluences leading to a density decrease of around 1.7%. With complementary channeling-Rutherford-backscattering experiments (c-RBS), the damage fraction and the corresponding damage cross section were extracted and compared to the cross section deduced from swelling measurements. Irradiation effects were also characterized by scanning force microscopy (SFM). A threshold for damage creation as deduced from all the present physical characterizations is 5.5 ± 1.0 keV/nm. The value is in full agreement with previous measurements confirming that swelling and SFM characterizations can provide information concerning the electronic energy loss threshold for track formation. In contrast, track radii deduced from swelling measurements are smaller and radii from SFM are larger than deduced from c-RBS analysis. The results of Y3Fe5O12 of this work are compared with data obtained for other crystalline oxides and for ionic crystals.

This paper discusses recent results on the recrystallization effect induced by swift heavy ions (SHI) in pre-damaged silicon carbide. The recrystallization kinetics was followed by using increasing SHI fluences and by starting from different levels of initial damage within the SiC samples. The quantitative analysis of the data shows that the recrystallization rate depends drastically on the local amount of crystalline material: it is nil in fully amorphous regions and becomes more significant with increasing amount of crystalline material. For instance, in samples initially nearly half-disordered, the recrystallization rate per incident ion is found to be 3 orders of magnitude higher than what it is observed with the well-known IBIEC process using low energy ions. This high rate can therefore not be accounted for by the existing IBIEC models. Moreover, decreasing the electronic energy loss leads to a drastic reduction of the recrystallization rate. A comprehensive quantitative analysis of all the experimental results shows that the SHI induced high recrystallization rate can only be explained by a mechanism based on the melting of the amorphous zones through a thermal spike process followed by an epitaxial recrystallization initiated from the neighboring crystalline regions if the size of the latter exceeds a certain critical value. This quantitative analysis also reveals that recent molecular dynamics calculations supposed to reproduce this phenomenon are wrong since they overestimated the recrystallization rate by a factor ∼40.

Investigations of the structural modifications induced in amorphous silica by ion irradiations in a wide energy range from ∼1 MeV to ∼1 GeV are reviewed. Several characterization methods such as infrared spectroscopy, chemical etching, dimensional measurements, and small-angle x-ray scattering have been used to measure the damage induced by individual ions and to analyze its evolution as a function of the energy released by the irradiating species. The comparison of the obtained results shows that high-energy ions lead to the formation along the ion trajectories of damaged zones (called ion tracks) above an electronic energy loss threshold depending on the ion specific energy. This threshold can be as low as ∼1.4 keV/nm for ion beams of 0.2 MeV/u and increases to ∼2.4 keV/nm at ∼5 MeV/u, in agreement with the velocity effect which predicts a narrower radial distribution of the deposited electronic energy with low-velocity ions than with high-velocity ions. Above these threshold values, track radii increase approximately with the square root of the electronic energy loss. In addition, for Au beams between 0.3 and 27 MeV, the generated damage exhibits a U-shaped dependence on the incident ion energy, suggesting a combined effect of the nuclear and electronic energy loss in this energy range. A unified thermal spike model taking into account the contributions of both energy losses allows to reproduce the whole experimental data.

High resolution AFM imaging of swift heavy ion irradiated muscovite mica under grazing incidence provides detailed insight into the created nanostructure features. Swift heavy ions under grazing incidence form a complex track structure along the surface, which consists of a double track of nanohillocks at the impact site accompanied by a single, several 100 nm long protrusion. Detailed track studies by varying the irradiation parameters, i.e. the angle of incidence (0.2 degrees-2 degrees) and the kinetic energy of the impinging ions (23, 55, 75, 95 MeV) are presented. Moreover, the track formation in dependence of the sample temperature (between room temperature and 600 degrees C) and of the chemical composition (muscovite mica and fluorphlogopite mica) is studied.

Tetragonally structured barium titanate (BaTiO 3 ) single crystals were irradiated using 635 MeV 238 U + ions to fluences of 1 × 10 7 , 5 × 10 10 and 1.4 × 10 12 ions cm −2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ∼10 nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ∼22 keV nm −1 . Molecular dynamics simulations show an amorphous track of ∼1.2 nm in radius under thermal energy deposition at 5 keV nm −1 ; the radius increases to ∼4.5 nm at 20 keV nm −1 . A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ∼8.4 nm due to thermal recrystallization if electron–phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates.

TiO2 films prepared by sol–gel were irradiated with 25.8 MeV Cu and 90 MeV Xe ions at room temperature under normal incidence. The irradiation with Cu and Xe ions were performed respectively at iThemba labs, South Africa and GANIL, Caen, France. The properties of radiation defects induced in TiO2 nanostructures were investigated using grazing angle X-ray diffraction (GAXRD), atomic force microscopy (AFM) and UV–visible spectrophotometry. From GAXRD analysis, it is found that anatase (1 0 1) peak intensity decrease with increasing the fluence and disappear completely above a threshold ion fluence of 5 × 1012 ion/cm2. This indicates that the crystallinity of the TiO2 film is destroyed upon irradiation due to the amorphous track formation. The track radius estimated from the Poisson’s law is about 2 and 4 nm after irradiation with 25.8 MeV Cu and 90 MeV Xe ions, respectively. According to the AFM analysis, the elaborated TiO2 films are composed of particles with a triangular shape of a size in the range of 200–500 nm. It is found that the particle size increases after irradiation with both Cu and Xe ions. In addition, the root-mean-square (RMS) surface roughness for 780 nm × 780 nm area scans decreases exponentially with increasing fluence up to 1013 ions/cm2 in the case of Xe irradiation, but increases drastically above 2.68 × 1011 ions/cm2 in the case of Cu ion irradiation and reaches a mean value of ∼3 nm. The absorption measurements reveal that the optical band gap is not affected by both Xe and Cu ions irradiation.

Zirconia and hafnia are known to exhibit similar phase transitions under temperature, pressure or swift heavy (i.e., GeV) ion irradiation. In the present study, both monoclinic zirconia and hafnia were irradiated with 5-MeV I ions in order to comprehend the underlying mechanism governing phase transition by low-energy ion irradiation. Surprisingly, it was found that, although monoclinic zirconia can easily transform to the tetragonal phase, monoclinic hafnia does not show any transition to the tetragonal structure even after irradiation with ∼19 displacements per atom. The absence of this phase transition in hafnia and its presence in zirconia clearly break the parallel between these two oxides in their response to intense excitation. Furthermore, this comparative study allowed severe constraints to be imposed on the possible mechanisms aimed at explaining phase transformation by low-energy ion irradiation. It is found that the monoclinic-to-tetragonal phase transition in these oxides is very likely driven by oxygen vacancies and occurs once their concentration reaches a certain value. The absence of phase transition in hafnia can thus be explained by the lower concentration level attained by these defects, owing to their higher diffusivity in this material. A similar mechanism can also be invoked to explain the remarkable phase stability of tetragonal zirconia under prolonged low-energy ion irradiation.

It is now well established that the irradiation of pure zirconia (ZrO 2 ) with swift heavy ions can lead to a transformation from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold ∼12 keV nm −1 . Previous swift heavy ion irradiations carried out with electronic energy losses less than ∼30 keV nm −1 evidenced that this phase transition is characterized by two constant features: (i) it is driven by a double ion impact process, and (ii) it is never complete even at extremely high fluences. It is then quite interesting to check whether this phase transformation does not depart from this behaviour at very high electronic energy losses. For this purpose, zirconia was irradiated with 0.6-GeV Pb ions giving rise to an electronic energy loss ∼42 keV nm −1 at the sample surface. Despite this huge value, the experimental data revealed that the phase change is here again still characterized by a double ion impact process. However, contrary to previous cases, it was found that this phase transformation not only occurs very rapidly but achieves full completion at rather low fluences.

Silicon carbide (SiC) single crystals were irradiated at room temperature with different ion species of several hundreds MeV in order to explore a wide range of the deposited electronic and nuclear energy losses. The samples were characterized by optical absorption spectroscopy. The comparison of the transmittance data obtained after irradiation with different ion species in combination with the use of energy degraders of different thicknesses allowed to demonstrate that the optical defects created by swift heavy ions are essentially produced by elastic collisions and occur mainly at the end of the ion range region.

International audience; In this study, we performed irradiation experiments on nanostructured 3C–SiC samples, with 95 MeV Xe ions at room temperature. This energy permits the observation of the combined electronic and nuclear interactions with matter. The grazing incidence X-ray diffraction results do not reveal a complete amorphization, despite value of displacement per atom overcoming the total amorphization threshold. This may be attributed to competing effects between nuclear and electronic energy loss in this material since a total amorphization induced by nuclear interactions was found after low energy ion irradiation (4 MeV Au). Moreover, electronic interactions created by high energy ion irradiations induce no disorder in single crystalline 6H–SiC. But in samples previously disordered by low energy ion implantation (700 keV I), the electronic interactions generate a strong defects recovery.

International audience; A novel form of ion-tracks, namely nanogrooves and hillocks, are observed on CaF2 after irradiation with xenon and lead ions of about 100 MeV kinetic energy. The irradiation is performed under grazing incidence (0.3°–3°) which forces the track to a region in close vicinity to the surface. Atomic force microscopy imaging of the impact sites with high spatial resolution reveals that the surface track consists in fact of three distinct parts: each swift heavy ion impacting on the CaF2 surface first opens a several 100 nm long groove bordered by a series of nanohillocks on both sides. The end of the groove is marked by a huge single hillock and the further penetration of the swift projectile into deeper layers of the target is accompanied by a single protrusion of several 100 nm in length slowly fading until the track vanishes.By comparing experimental data for various impact angles with results of a simulation, based on a three-dimensional version of the two-temperature-model (TTM), we are able to link the crater and hillock formation to sublimation and melting processes of CaF2 due to the local energy deposition by swift heavy ions.

Thermally grown amorphous SiO2 samples were implanted at room temperature (RT) with 120 keV C-ions to a dose ranging from 1.0 × 1016 to 8.6 × 1017C ions/cm2, then irradiated at RT with 950 MeV Pb, 345 or 1754 MeV Xe ions to a fluence in the region from 1.0 × 1011 to 3.8 × 1012 ions/cm2, respectively. The irradiated samples were investigated using micro-FTIR and micro-Raman spectroscopes. It was found that new chemical bonds such as Si–C, C C(O), C C and Si(C)–O–C bonds formed significantly in the C-doped SiO2 films after heavy ion irradiations. The evolution of Si–O–C bonds and possible mechanism of structural modification in C-doped SiO2 induced by swift heavy ion irradiations were discussed.

It is now well established that the high electronic energy loss released by swift heavy ions in solid materials can lead to different final manifestations like modification of defect concentration, atomic transport, phase transformation and track formation. The subject is quite vast and this contribution therefore concentrates on phase transformations in oxides. After a brief overview of the most significant findings obtained in this research field, a special attention is paid to zirconia and hafnia which both transform from the monoclinic to the tetragonal phase. In fact, the likeness of these materials offers the unique opportunity to impose drastic constraints on the possible models proposed to explain the creation of atomic movements in the wake of swift heavy ions. The comparison of the experimental results with the models’ predictions clearly suggests that the thermal spike is the right process which governs the transition from the monoclinic to the tetragonal phase in zirconia and hafnia.

Samples of monosilicated sintered fluorapatite (Ca 9 Nd(PO 4 ) 5 (SiO 4 )F 2 , britholite) and full-phosphated Durango fluorapatite were irradiated using different heavy ions with incident energies in the range of several hundred MeV, corresponding to the electronic stopping power regime. The induced damage was characterized by means of X-ray diffraction for the monosilicated fluorapatites and Rutherford backscattering spectrometry associated with channeling technique (CRBS) for the Durango fluorapatites. Characterizing the amorphization of the monosilicated fluorapatites revealed two main features. First, the evolution of the damaged fraction with the ion fluence and the ion species shows that amorphization is mainly dependent on the electronic energy loss ( S e ) value. Second, we suggest that a percolation of defects only occurs when S e is above a threshold near 5 keV nm −1 . This can be related to the limit of a fragmentation zone defined from microscopic observations. We have quantified damage in monosilicated fluorapatites by calculating amorphization effective radii ( R e ). By plotting these results versus S e , we found that they are in good agreement with those obtained from the irradiated single crystals of Durango fluorapatite.

Single crystals of LiF were irradiated at 10 different temperatures from room temperature to 780 K with Pb ions of 4.1 MeV/u. The irradiated surfaces were analyzed with scanning force microscopy, which revealed ion-induced hillocks with diameters of ∼20 nm and with heights of a few nm. Above 450 K, the number of hillocks strongly decreased with irradiation temperature. No hillocks were created under irradiation at 780 K. In addition, LiF samples irradiated at room temperature with Ni (2.5 MeV/u) and U ions (11.1 MeV/u) were bleached with UV-light on part of the crystal surface. In the bleached area, the characteristic F- and F2-centers disappeared, whereas the mean diameter and height of the hillocks did not show any significant change.

Samples of monoclinic hafnia were irradiated with increasing fluences of 800 and 300 MeV Kr ions giving rise to a slowing down essentially caused by high electronic excitations. Their structural evolution was monitored in situ by the X-ray diffraction technique. The results indicate, for the first time to our knowledge, the occurrence in monoclinic hafnia of an ion-beam induced crystalline-to-crystalline phase transition. The new formed phase is very likely tetragonal and appears with an effective threshold in the deposited electronic energy loss which is around 20 keV nm-1. In addition, the evolution of the amount of the produced phase with the ion fluence exhibits a sigmoidal shape suggesting a mechanism for phase transformation which needs two ion impacts. Some features of this phase transition are compared with those obtained in the case of zirconia, a well-known isomorphic material with hafnia.

It is generally admitted that the irradiation of crystalline oxides with high energy heavy ions, where the slowing down is mainly due to electronic excitations or ionizations, often leads to the formation of highly defective or amorphous tracks. In the latter case, the amorphization process follows a single ion impact mechanism. However, recent results demonstrate that in certain circumstances crystalline to crystalline phase transitions can also occur. This is the case of pure zirconia which transforms from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold near 13 keV nm−1. Moreover, recent experiments exploring a wide range of the deposited electronic energy loss demonstrate that the kinetics of phase transformation is always sigmoidal and is consistently characterized by a double ion impacts mechanism. Therefore, it seems that this process is a constant feature of this ion-beam induced crystalline to crystalline phase transition. The origin of this behaviour will be discussed and confronted with the existing models.

In this contribution we present new experimental results for swift heavy ion irradiation under grazing incidence. This particular collision geometry forces the track formation to a region close to the surface, sometimes visible as a chain of individual nanodots, whose length can be controlled by the angle of incidence. For irradiation of mica surfaces a new track form is observed.

In many different insulators, the irradiation with heavy ions in the MeV to GeV energy regime induces pronounced volume expansion. This swelling increases with fluence, projected range and electronic stopping power of the ions. From the relative volume change per single ion as a function of the mean energy loss, a critical swelling threshold can be deduced. In amorphizable materials such as quartz and garnets (e.g. Y3Fe5O12 and Gd3Ga5O12), swelling is directly linked to the crystalline–amorphous phase change in each ion track, whereas for non-amorphizable ionic crystals (e.g. LiF and CaF2), the correlation to known defects is not yet clear.

Pure single crystals of CaF2 were irradiated with different heavy ion species having energies of several hundred MeV. The induced damage was characterised by means of optical absorption spectroscopy, Rutherford backscattering spectrometry in channeling geometry (RBS-C), and out-of-plane swelling measurements using surface profilometry. For all ion species and energies, the optical spectra of the irradiated CaF2 samples exhibit a wide absorption band with a maximum around 550 nm, typical for small calcium aggregates. The absolute absorbance depends on the fluence and on the electronic energy loss (Se) of the ions, but there is no indication for a new band or a specific defect at high Se values. In contrast to this, profilometry clearly indicates that swelling occurs only above a critical electronic energy loss of about 5 keV nm−1. Furthermore, structural damage as measured by RBS-C starts to become significant above the same threshold. Therefore, swelling is obviously not directly related to the defects detected by optical absorption but is most likely linked to the structural disorder evidenced by the channeling technique.

Glass slices with a low roughness (∼0.2 nm) irradiated with swift heavy ions were studied by atomic force microscopy (AFM). Ion impacts are materialized by the formation of hollow structures having a maximal depth of ∼3 nm. In order to investigate the role played by such modifications on the surface properties, thin gold films of ∼2 nm thickness were deposited on both virgin and pre-irradiated samples. After annealing at 150 °C, a red shift is observed in the optical absorption of virgin samples indicating a gold cluster formation, whereas no significant modifications were observed in samples pre-irradiated with energetic Kr ions. By combining AFM observations with optical absorption spectroscopy we discuss in this paper the role played by topographic modifications on both the surface diffusion and the film wetting phenomena.

To investigate possible beam guiding and current density enhancement properties for conical glass capillaries for MeV ions transmission measurements with well collimated ion beams of 1 MeV He+ and 71 MeV Xe 19+ were done. No guiding effect was observed and only decent enhancement factors e between 1 and 2 were measured and attributed to scattered particles. A 3D Monte Carlo simulation which is based on SRIM code was developed. The simulation reproduces the experimental results very well. This shows that the transmission properties of capillaries for MeV ion beams are governed by simple elastic scattering of the ions in the glass of the capillary. © 2014 Elsevier B.V. All rights reserved.

Single crystals of lithium fluoride were irradiated with 790 MeV Pb ions in the temperature range between 300 and 700 K. The creation of defects along the ion trajectory was studied using optical absorption spectroscopy and small-angle X-ray scattering (SAXS). Surprisingly, the track radius is not significantly influenced by the increase of irradiation temperature, but the ion-induced change of the electron density in the track decreases substantially.

Samples of monoclinic zirconia were irradiated with heavy ions having incident energies in the range of a few hundred MeV giving then rise to a slowing down essentially caused by high electronic excitations. The characterizations of the samples by X-ray diffraction and complementary Raman spectroscopy analyses revealed two main features. First, in the electronic stopping power regime, it is only when the electronic energy loss is above a threshold near 13 keV nm−1 that monoclinic zirconia undergoes a transformation to the tetragonal phase. Second, the evolution of the amount of the tetragonal phase with the ion fluence exhibits a sigmoidal shape suggesting a mechanism for phase transformation which very likely needs two ion impacts.

Compressed pellets of 40 nm sized CaF2 powder were exposed to Pb ions of about 4 MeV/u. The structural change of the irradiated crystals was monitored by in situ X-ray diffraction experiments. The evolution of the diffraction spectra as a function of the ion fluence gives evidence for two different phenomena: (1) the area of the diffraction peaks slowly decreases due to the loss of the crystalline phase of CaF2, and (2) the width of the peaks broadens at a much faster rate. We assume that this latter observation can be ascribed to a grain breaking process.

As a model material of fluorite type structure, single crystals of CaF 2 were irradiated with various heavy ions (from 32 S to 209 Bi) of specific energies between 1 and 12 MeV u -1 . Using a profilometer, out-of-plane swelling was measured by scanning over the border line between irradiated and virgin areas of the sample surface. The step height as a function of the ion fluence exhibits a linear increase in the initial phase and saturates at high fluences. Track radii contributing to the swelling effect are deduced. Above a critical energy loss of about 5 keV nm -1 , the initial swelling rate per incident ion shows two separated regimes. Finally, the response of CaF 2 submitted to high electronic energy loss is discussed in combination with earlier track observations by transmission electron microscopy.

Samples of 100Cr6 steel were treated by different ion beams in order to study the evolution of their tribological properties. A strong correlation was found between the amount of surface carbon, whatever its origin (contamination, direct C implantation or ion-beam mixing of a deposited carbon layer), and the reduction of the friction coefficient as well as the improvement of the wear resistance. These results are discussed in the framework of a recent statistical model founded on the asperity concept and describing the tribological behaviour of bilayer systems.

Samples of 100Cr6-bearing steel were treated by different ion beams in order to study the evolution of their tribological properties. Complementary physico-chemical characterisation techniques give evidence for a strong correlation between the amount of surface carbon, whatever its origin (contamination, direct C implantation or ion beam mixing of a deposited carbon layer), and the reduction of the friction coefficient as well as the increase of the wear resistance. It is found that the friction coefficient is improved by a factor 5 and the wear volume by two orders of magnitude when the amount of surface carbon exceeds 1017 C cm−2.

International audience; Carbon implantation into titanium is known to enhance some of its surface properties like wear behavior, mechanical hardness or the friction coefficient. Therefore the method is a candidate to be applied as a powerful surface engineering tool for titanium alloys. Recently, a new implantation technique has been developed, which is based on a compact particle accelerator device that is easy to handle. The device allows simultaneous multi-charged ion-implantation (from C+ up to C4+) in order to get a plateau like implantation profile based on the energetic distribution. The aim of this study is to investigate microstructural modifications of the near surface region of Ti–6Al–4V due to this processing technology and to enhance the surface performance. Nanoindentation and tribological measurements revealed a threshold of critical C contents where friction coefficient and wear are significantly reduced. Furthermore, these enhancements have been correlated to the presence of additional graphitic carbon.

Comparison of the transmission of 27 keV Ar9+ ions through insulating funnel and conical shaped glass capillaries of outlet diameters of ~22 µm is reported. Beam intensities of 1 5 and 10 pA were injected into both capillaries. Transmission at the untilted angle of 0 was measured as well as at a tilt angle of ~0.5 for the funnel capillary and a tilt angle of ~1.1 for the conical capillary. For the funnel capillary blocking of transmission was observed whereas the transmission was continuous for the conical capillary. These measurements suggest that conical shaped capillaries have transport properties that are different than funnel shaped capillaries for slow highly charged ions. © 2013 American Physical Society.

A Monte-Carlo simulation of MeV ion transmission through glass micro-capillaries had successfully reproduced experimental energy and angular distributions obtained for 71 MeV Xe19+ ions on the IRRSUD beam line of GANIL as well as for MeV protons at ETH facility. The transmitted beam is composed of two parts: a core beam, due to direct transmission through the capillary, and a diffuse halo around, experiencing a large energy loss. The present calculation shows that the halo part is due to elastic scattering by the capillary wall.

Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single‐crystal alumina (α‐Al2O3) substrates heated at 675 °C. The ion beam mixing of these α‐Fe2O3/α‐Al2O3 couples was carried out using 300 keV Kr3+ ions at a fluence of 2×1016 ions/cm2. The mixing effect was followed by Rutherford backscattering spectrometry (RBS), conversion electron Mossbauer spectroscopy, and grazing incidence x‐ray diffraction method. RBS spectra do not show any evidence of mixing at the interface, whereas the data obtained with the two other techniques display phases like oxygen deficient Fe3O4, Fe3−yAlyO4, and Fe1+xAl2−xO4. For this last phase, x is determined as being equal to about 0.5. It is shown that ion beam mixing is more efficient for the thinner Fe2O3 layer, in accordance with the projected range of the Kr3+ ions.

The atomic transport induced by ion electronic energy loss in amorphous systems is studied on metallic sandwiches irradiated at liquid nitrogen temperature with 500 MeV iodide ions delivered by the VICKSI accelerator of the Hahn-Meitner-Institut (Berlin). The sandwiches are composed of two amorphous Ni3B layers of 1 or 1.5 μm thickness embedding a crystalline Au or W layer of thickness varying from 20 to 900 nm. Rutherford backscattering experiments using a 3.6 MeV He2+ beam delivered by the ARAMIS accelerator of the CSNSM (Orsay) were performed in order to determine the modifications of the geometry of the sandwiches after swift heavy ion irradiation. The results show a huge creep of the crystalline part of the sandwiches. The magnitude of this creep depends on the nature of the crystalline layer (Au or W) and increases steadily with the irradiating ion fluence with a strain-rate decreasing with increasing layer thickness. This creep phenomenon is due to the plastic deformation process occurring in the surrounding amorphous layers and is induced by ion electronic energy loss. A simple rheological model is developed to reproduce the observed effects.

Experimental data presented in our earlier paper [Toulemonde et al., Phys. Rev. B 85, 054112 (2012)] indicate that there are two thresholds for damage creation by swift heavy ions in CaF${}_{2}$. Moreover, the comparison of the track sizes observed by transmission electron microscopy and generated by different cluster and monoatomic ion beams supports the occurrence of a velocity effect in this material.

CaF${}_{2}$ crystals as representatives of the class of ionic nonamorphizable insulators were irradiated with many different swift heavy ions of energy above 0.5 MeV/u providing a broad range of electronic energy losses (${S}_{e}$). Beam-induced modifications were characterized by Channeling Rutherford Backscattering Spectrometry (C-RBS) and x-ray diffraction (XRD), complemented by transmission electron microscopy (TEM). Results from C-RBS give evidence of significant damage appearing above a ${S}_{e}$ threshold of 5 $\ifmmode\pm\else\textpm\fi{}$ 2 keV/nm. A second critical ${S}_{e}$ appears around 18 $\ifmmode\pm\else\textpm\fi{}$ 3 keV/nm; below this value the damage as function of ion fluence saturates at 20$%$, while above this the damage saturation level increases with ${S}_{e}$, reaching $\ensuremath{\sim}$60$%$ for ions of ${S}_{e}$ $=$ 30 keV/nm. XRD measurements also show effects indicating two threshold values. Above 5 keV/nm, the widths of the XRD reflection peaks increase due to the formation of nanograins, as seen by TEM, while a significant decrease of the peak areas only occurs above 18 keV/nm. The track radii deduced from C-RBS measurements are in agreement with those extracted from the fluence evolution of the widths of the XRD peaks. Moreover, track radii deduced from the peak area analysis are slightly smaller but in agreement with previous track observations by high resolution electron microscopy. Calculations based on the inelastic thermal spike model suggest that the lower threshold at 5 keV/nm is linked to the quenching of the molten phase, whereas the threshold at 18 keV/nm can be interpreted as quenching of the boiling phase. The results of CaF${}_{2}$ are compared with other nonamorphizable materials such as LiF and UO${}_{2}$.

Expérience GANIL/ARIBE; We have measured the transmission of 230-keV (10-keV/q) Xe23+ ions through insulating tapered glass capillaries of microscopic dimensions. The dynamics of charging and discharging processes have been investigated, evidencing an unexpected slow alignment of the beam along the capillary axis. Oscillations of the exiting beam position have been observed during the charging process associated to the formation of charge patches on the capillary inner walls. The emerging ions are guided with a characteristic guiding angle falling on a universal curve proposed for PET polymer nanocapillaries. This result, very similar to the channeling process, is somewhat surprising in view of the significant differences between the straight nanocapillary polymer foils and the tapered microscopic single glass capillary used here. The transmitted ions show no evidence of energy loss or charge changing except for the production of a small neutral fraction that was determined to be due to ions that had become neutralized to form atoms rather than due to photon emission. These results thus test and confirm the validity of transmission and guiding and provide insight into the dynamics of higher-energy ions than have been previously studied in this regard, allowing a determination of the maximum energy for which the guiding process might occur.

Single crystals of Al2O3 samples were irradiated at GANIL with 4.32 MeV/amu 208Pb ions to fluences of 4 × 1011 and 8 × 1011 ions cm−2 and with 2.78 MeV/amu 238U ions to fluences of 1.2 × 1012 and 2.1 × 1012 ions cm−2 at a temperature of 77 K. Before irradiation the samples were implanted with 101657Fe ions cm−2 at 110 keV and annealed at 1673 K for 1 hour in order to introduce a local probe in very low concentration in the substitutional alumina sites. A conversion electron Mossbauer spectroscopy study (CEMS) was carried out so as to measure the effects of the high electronic energy losses. These results are discussed in comparison with those obtained by Rutherford backscattering spectrometry in channeling position. It should be pointed out that two specific iron sites appear after irradiation.

The macroscopic atomic transport induced in amorphous systems by ion electronic energy loss is studied by means of RBS experiments on a marker either implanted (Bi) or evaporated (Au) in the target. Irradiation of amorphous Ni3B with 500 MeV I ions leads to (i) a huge shift of the marker profile towards the sample surface, (ii) a surprising decrease of its distribution width. The results are totally accounted for by the plastic deformation phenomenon induced by electronic excitation in amorphous materials.

Single crystals of Al 2 O 3 have been irradiated at GANIL with 3.5 MeV/amu Pb ions, at a temperature of ≌ 8 K. The fluence range extended from 4×10 11 to 1.2×10 12 ions cm −2 . The effects of high electronic excitation induced in the samples have been characterized by Rutherford backscattering on channeling (RBS) in conjunction with optical absorption measurements. Moreover, some samples preliminary implanted with 10 16 57 Fe + ions cm −2 at 110 keV and annealed at 1673 K during one hour were studied using conversion electron Mossbauer specroscopy (CEMS) in order to obtain complementary informations. Preliminary RBS results (77 K irradiations) indicate a damage cross section of ∼ 10 −13 cm 2 , consistent with a track radius of about 1.8 nm. The defect efficiency has been also investigated as a function of the electronic stropping power (d E /D x ) c .

Monoclinic zirconia samples were irradiated with 300 MeV Ge and Ni ions at increasing ion fluences. Their structural evolution was monitored in situ by x-ray diffraction and ex situ by Raman spectroscopy. No amorphization of zirconia was observed in both cases. However, a transition from the monoclinic to the tetragonal phase was found in the case of Ge ion irradiation. On the contrary, no such effect was detected upon Ni ion irradiation. A comparison of these experiments indicates that the electronic energy loss released by swift heavy ion irradiation needs to be quite in excess of ∼12 keV nm−1 in order to induce a monoclinic to a tetragonal phase transition in pure (i.e., unstabilized) zirconia.

International audience; Although silicon carbide has attracted extensive investigations of ion irradiation effects at low energy owing to its potential use in harsh environments, very few works were carried out in the field of ion irradiation at high energy. A recent preliminary study exploring the combination of low and high energy ion irradiation effects in silicon carbide revealed that the damaged layer formed by low energy ion irradiation can undergo an epitaxial recrystallization under subsequent swift heavy ion irradiation. The present paper is devoted to the investigation of the mechanisms at the origin of this phenomenon by performing additional experiments. A detailed analysis of the kinetics of this recrystallization effect demonstrates that the latter cannot be explained by the models proposed for the well-known ion-beam-induced epitaxial crystallization process. Furthermore, it is found that this effect can be accounted for by a mechanism combining the melting within the ion tracks of the amorphous zones through a thermal spike process and their subsequent epitaxial recrystallization initiated from the neighboring crystalline regions wherever the size of the latter surpasses a certain critical value.

Amorphous solids exhibit at temperatures far below the glass transition plastic flow when bombarded with fast heavy ions (kinetic energy {similar to}1 MeV/u). The dimensions perpendicular to the ion beam grow whereas the sample dimension parallel to the ion beam shrinks. The strain tensor describing phenomenologically these dimensional changes is derived from symmetry considerations and compared with experiment. Particular attention is devoted to angular changes, which have not been discussed in this context so far.

International audience; Silicon carbide exhibits different behaviours in response to ion beam irradiation depending on the ion energy. At room temperature, this material is well known to be easily amorphized by low energy (i.e. a few hundred keV) ions. On the other hand, recent studies revealed that high energy (i.e. several hundred MeV) ions do not produce damage in crystalline silicon carbide. More interestingly, they instead induce at room temperature an epitaxial recrystallization in pre-damaged material by low energy ion irradiation. These swift heavy ion induced effects can both be interpreted in term of the thermal spike model where it is demonstrated that the amorphous phase does effectively attain the liquid state in contrast to the case of the crystalline structure.

Ni-P alloys were formed by P ion implantation into pure Ni single crystals at low (15 K) and high (300 K) temperature up to a metalloid ion concentration (≈0.12) such that the fractions of amorphous volume obtained at the maximum disorder depth were ≈0.5 for both temperatures. The samples were then heated up or cooled down to the reverse temperature (300 and 15K) and implanted up to total amorphization. The disordering kinetics was followed by RBS and channeling at the different stages of the experiments. The results demonstrate that the implantation temperature entirely governs the amorphization kinetics and the final state of the sample: the amorphous phase formed before the temperature change is transformed by the subsequent implantation into a new amorphous phase with a mean metalloid concentration characteristics of the final implantation temperature.

Expérience GANIL; As potential actinide-bearing phase for geological deposit of nuclear wastes, the $\beta$-Thorium Phosphate Diphosphate ceramic ($\beta$-TPD), Th$_4$(PO$_4$)$_4$P$_2$O$_7$, must be resistant against radiation. A high-energy ion beam (840-MeV Kr) was used to check this property by simulating the electronic effects of radiation. The amorphization of the material was followed in situ by using the on line XRD analysis setup (CHEXPIR) of the GANIL accelerator. XRD measurements show a complete amorphization of the material with a kinetics which fits to a direct impact model. Thermal annealing of amorphized samples leads to a complete recrystallization of the structure at 1023 K.

X-ray diffraction (XRD) was used to investigate the damage and the correlated stress induced by the slowing-down of swift heavy ions in cubic zirconia polycrystals doped with 10 mol% Y2O3. Samples were irradiated at room temperature with 944 MeV Pb ions at the GANIL accelerator in Caen and 2.6 GeV U ions at the UNILAC accelerator in Darmstadt at fluences ranging from 5 × 1011 to 4 × 1013 cm−2. Changes of XRD profiles with increasing fluences were then examined using the X-ray diffractometer of the LEMHE/ICMMO in Orsay. Residual macroscopic stresses induced by irradiation were determined by the sin2ψ method. The lattice strain, obtained by a Williamson-Hall analysis of the XRD profiles, obeys a single impact model and the measured diameter of the Pb-ion track is 4.7 nm.

Silicon carbide single crystals were irradiated at room temperature with low energy I ions and high energy Pb ions. It is found that the damaged layer formed by the elastic collisions generated during low energy I ion irradiation can readily be removed by the electronic excitations induced by swift Pb ions. This effect occurs at a temperature quite below that at which the conventional ion-beam induced crystallization process is generally achieved by nuclear energy loss. This finding is interesting both from a fundamental point of view for the understanding of the interaction of swift heavy ions with solids and for a large number of technological applications.