MeV Heavy Ions Research Articles

Secondary ion mass spectrometry measurements under ambient and humid conditions using MeV ions

Secondary ion emission with MeV heavy ions provides a unique opportunity for insight into ion collisions and material analysis. MeV-energy ion beams excite electrons near the surface and enhance the ionization of high-mass molecules, enabling the acquisition of secondary ion mass spectrometry (SIMS) spectra of ionized molecules with suppressed fragments. The SIMS technique with MeV-energy heavy ions (MeV-SIMS) has opened new possibilities for investigating the chemical composition and structure of organic and biological materials, as well as for their imaging. The ambient analysis system is essential for analyzing solid–liquid interfaces, because liquid materials evaporate easily in a vacuum. It is difficult to measure volatile liquid (wet) samples using conventional SIMS. The mean free path of ions with energy in the keV range is very short in low vacuum, and these ions cannot penetrate the surface. By contrast, evaporation of liquid materials in He at atmospheric pressure is suppressed and samples containing liquid can be measured using the MeV-SIMS technique without the need for preparing dry samples. Recently, the authors developed a humidity-controlled ambient MeV-SIMS system because the water evaporation rate strongly depends on humidity. To obtain imaging mass spectra of wet samples, the wet sample surface needs to be maintained under ambient and humid conditions for a prolonged time. At 0.04 MPa, under 100% humidity, a sample of aqueous solution of benzoic acid produced water droplets that remained in the target chamber for more than 30 min, and clusters and compounds of benzoic acid with water were detected with high sensitivity by the humidity-controlled ambient MeV-SIMS system.

Development of MeV TOF-SIMS capillary microprobe at the Ruđer Bošković Institute in Zagreb

New Time-of-flight Secondary Ion Mass Spectrometry (TOF SIMS) setup using MeV heavy ions for the excitation is developed at the Ruđer Bošković Institute accelerator facility. To focus heavy MeV ions to micron dimensions, conical glass capillary is used instead of quadrupole magnetic lenses. The setup uses a continuous primary beam where START signal for TOF is obtained from the PIN diode placed behind the thin transmission sample. Measured energy spectra for several primary heavy ions are presented and compared with theoretical simulations. The first mass spectra obtained with the new setup using reflectron-type TOF analyser are given together with the mass and spatial resolution values of the new setup.

Mechanical properties of 6H-SiC irradiated by neutron and MeV heavy ions: A nanoindentation and finite element method study

Understanding the mechanical properties of structural materials under an irradiation environment stands as a major challenge for developing advanced nuclear systems. In this paper, the mechanical properties, including the Young's modulus, yield stress, and hardness, of SiC samples irradiated by neutron and heavy ions (3 MeV C and Si ions) have been investigated by nanoindentation measurement. When the load-depth curves were analyzed by the widely used Oliver-Pharr method, for the samples irradiated at the same displacement damage level (0.1 and 0.2 dpa), both the elastic modulus and hardness of the ion irradiated SiC are significantly higher compared with those of neutron irradiated samples. The discrepancy is mainly attributed to the irradiation induced surface lateral stress in ion irradiated samples, which cannot be taken into account for the Oliver-Pharr method. After carefully considering this effect by the finite element method in simulating the load-depth curves, both the Young's modulus and yield stress of ion irradiated samples agree well with those of neutron irradiated samples. This study reveals that by the combined method of nanoindentation and finite element, the mechanical properties, including the Young's modulus, yield stress and hardness, for neutron irradiated SiC can be reasonably evaluated by MeV heavy ion irradiation.

Sputtering of bismuth thin films under MeV Cu heavy ion irradiation: Experimental data and inelastic thermal spike model interpretation.

The sputtering of bismuth (Bi/Si) thin films deposited onto silicon substrates and irradiated by swift Cuq+ heavy ions (q = +4 to +7) was investigated by varying both the ion energy over the 10 to 26‐MeV range and the ion fluence ϕ from 5.1 × 1013 cm−2 to 3.4 × 1015 cm−2. The sputtering yields were determined experimentally via the Rutherford backscattering spectrometry technique using a 2‐MeV He+ ion beam. The measured sputtering yields versus Cu7+ ion fluence for a fixed incident energy of 26 MeV exhibit a significant depression at very low ϕ‐values flowed by a steady‐state regime above ~1.6 × 1014 cm−2, similarly to those previously pointed out for Bi thin films irradiated by MeV heavy ions. By fixing the incident ion fluence to a mean value of ~2.6 × 1015 cm−2 in the upper part of the yield saturation regime, the measured sputtering yield data versus ion energy were found to increase with increasing the electronic stopping power in the Bi target material. Their comparison to theoretical predicted models is discussed. A good agreement is observed between the measured sputtering yields and the predicted ones when considering the contribution of 2 competitive processes of nuclear and electronic energy losses via, respectively, the SRIM simulation code and the inelastic thermal spike model using refined parameters of the ion slowing down with reduced thermophysical proprieties of the Bi thin films.

MeV ion irradiation effects on the luminescence properties of Si‐implanted SiO2‐thin films

AbstractThe effects of MeV heavy ion irradiation at varying fluence and flux on excess Si, introduced in SiO2 by keV ion implantation, are investigated by photoluminescence (PL). From the PL peak wavelength (λ) and decay lifetime (τ), two PL sources are distinguished: i) quasi‐direct recombination of excitons of Si‐nanoparticles (SiNPs), appearing after thermal annealing (λ > 720 nm, τ ∼ μs), and ii) fast‐decay PL, possibly due to oxide‐related defects (λ ∼ 575‐690 nm, τ ∼ ns). The fast‐decay PL (ii) observed before and after ion irradiation is induced by ion implantation. It is found that this fast‐decay luminescence decreases for higher irradiation fluence of MeV heavy ions. After thermal annealing (forming SiNPs), the SiNP PL is reduced for samples irradiated by MeV heavy ions but found to stabilize at higher level for higher irradiation flux; the (ii) band vanishes as a result of annealing. The results are discussed in terms of the influence of electronic and nuclear stopping powers. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modification of semiconductor or metal nanoparticle lattices in amorphous alumina by MeV heavy ions

In the present work we investigate effects of MeV heavy ions (from 0.4 MeV Xe to 15 MeV Si) on regularly ordered nanoparticle (NP) lattices embedded in amorphous alumina matrix. These nanostructures were produced by self-assembling growth using magnetron-sputtering deposition. From grazing incidence small-angle x-ray scattering measurements we have found that the used MeV heavy ions do not change the NP sizes, shapes or distances among them. However, ions cause a tilt of the entire NP lattice in the direction parallel to the surface. The tilt angle depends on the incident ion energy, type and the applied fluence and a nearly linear increase of the tilt angle with the ion fluence and irradiation angle was found. This way, MeV heavy ion irradiation can be used to design custom-made NP lattices. In addition, grazing incidence small-angle x-ray scattering can be effectively used as a method for the determination of material redistribution/shift caused by the ion hammering effect. For the first time, the deformation yield in amorphous alumina was determined for irradiation performed at the room temperature.

Pattern dependence in synergistic effects of total dose on single-event upset hardness**Project supported by the National Natural Science Foundation of China (Grant No. U1532261).

The pattern dependence in synergistic effects was studied in a 0.18 μm static random access memory (SRAM) circuit. Experiments were performed under two SEU test environments: 3 MeV protons and heavy ions. Measured results show different trends. In heavy ion SEU test, the degradation in the peripheral circuitry also existed because the measured SEU cross section decreased regardless of the patterns written to the SRAM array. TCAD simulation was performed. TID-induced degradation in nMOSFETs mainly induced the imprint effect in the SRAM cell, which is consistent with the measured results under the proton environment, but cannot explain the phenomena observed under heavy ion environment. A possible explanation could be the contribution from the radiation-induced GIDL in pMOSFETs.

Radiation chemical yields for the losses of typical functional groups in PADC films for high energy protons registered as unetchable tracks

A series of FT-IR spectrometric studies has been performed to understand the latent track structure in poly(allyl diglycol carbonate), PADC, which were exposed to proton beams with energies of 20, 30 and 70 MeV. These energies are too high to register etchable tracks in PADC. Chemical damage parameters, such as damage density, effective track core radius and radiation chemical yields, for losses of ether bond, carbonate ester bond and CH groups in PADC are evaluated as a function of the stopping power, which were compared to the previous results for 5.7 MeV proton and heavy ions, between He and Xe. Graphs of the chemical damage parameters are given at the wide stopping powers ranging from 1 to 12,000 keV/μm. The decreasing behaviors of the ether and carbonate ester bonds are on the almost identical trends with those of the heavy ions. On the contrary to this, the reducing behavior of CH groups is similar to that of the gamma rays. Different dependence of the chemical damage parameters for the loss of CH groups is found on the stopping powers between the both sides of the detection threshold as an etched track detector.

Fragmentation of multiply ionized biomolecules induced by MeV heavy ions

SynopsisCollision-induced ionization and fragmentation of gas-phase adenine molecules (C5N5H5) have been investigated for single electron capture collisions of 1.2 MeV C2+ ions. Coincidence measurements between the number of ejected electrons and the time-of-flight of fragment ions allows us to determine charge states of intermediate parent ions r. Highly charged parent ions are observed up to r ∼ 6 and the production of lighter fragment ions becomes predominant with increasing r. We found that kinetic energies of H+ are significantly larger than those of other fragment ions and become nearly equivalent irrespective of r for r > 1.

The long-range effect in 6H-SiC under irradiation with Xe ions

Results of an electrical study of the “long-range effect” in 6H-SiC crystals under irradiation with 167 MeV heavy Xe ions at fluences of 4 × 109 to 7 × 1011 cm−2 are reported for the first time. Structures with Schottky barriers formed on the C face of the crystals have been studied. The structures were irradiated in the same modes on the barrier and base (Si face) sides. Electrical procedures revealed for the first time the effect of a deep penetration of radiation defects to a depth several tens of times the range of Xe ions. It was found that radiation defects of the acceptor type are formed at the beginning of the range of Xe ions, whereas radiation defects of the donor type appear at the end of this range.

Confinement effects of ion tracks in ultrathin polymer films.

We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40 nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model.

Simulation of neutron-induced damage in tungsten by irradiation with energetic self-ions

A direct comparison of the deuterium (D) decoration of radiation-induced damage in polycrystalline tungsten irradiated with self-ions [present work] and neutrons in the high-flux isotope reactor (HFIR) (Hatano et al., 2013) shows a reasonably good agreement at least up to 0.3 displacement per atom indicating that MeV heavy ions can be a good proxy to simulate neutron-produced damage at room temperature and low dpa. The coefficient of similarity between two kinds of irradiation was obtained experimentally to be Kexp∼0.65±0.1 in the case of the deuterium decoration of both kinds of radiation-induced defects with low and high de-trapping energies for deuterium. We introduced the theoretical estimation for coefficient of similarity between neutron- and self-ion-irradiations, which is a fraction of common area under the curves of two overlapping damage energy spectra of primary knock-on atom (PKA) produced in tungsten by these two types of irradiation. In other words, Ksim is a part of displaced atoms produced in the similar conditions under two different types of irradiation. The theoretical values of Ksim=0.34 and Ksim=0.29 were obtained for tungsten target irradiated with 20MeV self-ions in comparison to irradiation with neutrons in HFIR reactor (>0.1MeV) and 14MeV neutrons, respectively. The theoretical value of Ksim=0.34 is about two times less than the experimental value of Kexp=0.65. It means that high energy PKAs can play more important role in the production of similar damage structure by irradiation with self-ions and neutrons which is responsible for deuterium retention. The model assuming that all cascades with an energy higher than Tc=150keV split into identical sub-cascades gives the value of Ksim=0.64±0.01 for the coefficient of similarity between HFIR-neutron and 20MeV self-ion irradiations that is in an agreement with experimental value of Kexp=0.65±0.1. Consequently, splitting of high-energy part of cascades might take place in W that results in a reduction of the effective PKA spectrum and a change of types and density of post-radiation defects.

Direct measurements of irradiation-induced creep in micropillars of amorphous Cu56Ti38Ag6, Zr52Ni48, Si, and SiO2

We report in situ measurements of irradiation-induced creep on amorphous (a-) Cu56Ti38Ag6, Zr52Ni48, Si, and SiO2. Micropillars 1 μm in diameter and 2 μm in height were irradiated with ∼2 MeV heavy ions during uniaxial compression at room temperature. The creep measurements were performed using a custom mechanical testing apparatus utilizing a nanopositioner, a silicon beam transducer, and an interferometric laser displacement sensor. We observed Newtonian flow in all tested materials. For a-Cu56Ti38Ag6, a-Zr52Ni48, a-Si, and Kr+ irradiated a-SiO2 irradiation-induced fluidities were found to be nearly the same, ≈3 GPa−1 dpa−1, whereas for Ne+ irradiated a-SiO2 the fluidity was much higher, 83 GPa−1 dpa−1. A fluidity of 3 GPa−1 dpa−1 can be explained by point-defect mediated plastic flow induced by nuclear collisions. The fluidity of a-SiO2 can also be explained by this model when nuclear stopping dominates the energy loss, but when the electronic stopping exceeds 1 keV/nm, stress relaxation in thermal spikes also contributes to the fluidity.

Fragmentation of molecules under charge-changing collisions of a few MeV heavy ions

We investigated molecular fragmentation of CO and C2H2 molecules by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions and kinetic energy release (KER) in various charge-changing collisions. It was found that the KER spectra show strong dependence on the type of charge-changing collisions. This may be caused by the difference of impact parameters associated with individual charge-changing collisions. Moreover we revealed the different fragmentation pathway between ion impacts and photoionization.

An electrostatic quadrupole doublet focusing system for MeV heavy ions in MeV-SIMS

The importance of imaging mass spectrometry (MS) for visualizing the spatial distribution of molecular species in biological tissues and cells is growing. In conventional SIMS with keV-energy ion beams, elastic collisions occur between projectiles and atoms in constituent molecules. The collisions produce fragments, making acquisition of molecular information difficult. In contrast, MeV-energy ion beams excite electrons near the surface and enhance the ionization of high-mass molecules, hence, fragment suppressed SIMS spectrum of ionized molecules can be obtained. This work is a further step on our previous report on the successful development of a MeV secondary ion mass spectrometry (MeV-SIMS) for biological samples. We have developed an electrostatic quadrupole doublet (EQ doublet) focusing system, made of two separate lenses, Q1 and Q2, to focus the MeV heavy ion beam and reduce measurement time. A primary beam of 6MeV Cu4+ was focused with this EQ doublet. We applied 1120V to the Q1 lens and 1430V to the Q2 lens, and the current density increased by a factor of about 60. Using this arrangement, we obtained an MeV-SIMS image of 100×100pixels of cholesterol-OH+ of cerebellum (m/z=369.3) over a 4mm×4mm field of view, with a pixel size of 40μm within 5min, showing that our EQ doublet reduces the measurement time of current imaging by a factor of about 30.

Damage production in carbide single crystals irradiated with MeV heavy ions

Carbide (SiC, TiC, and ZrC) single crystals were irradiated at room temperature with MeV Au ions. The damage created by irradiation was evaluated by RBS-C, XRD, and Raman experiments. The results indicate a different radiation behavior of TiC and ZrC as compared with SiC. The accumulation of defects created by nuclear collisions leads to amorphization of SiC at the lowest Au fluence used (2.8×1014cm−2), whereas TiC and ZrC do not amorphize at the highest Au fluence used (3.3×1015cm−2). The different properties of TiC and ZrC carbides versus SiC could be related to differences in the nature of the chemical bonds in TiC and ZrC versus SiC.

Angular distribution of MeV heavy ions through tapered glass capillary: experiment and simulation

The two dimension angular distribution for 71 MeV Xe19+ and 26.5 MeV Kr10+ through individual tapered glass capillary was measured on IRRSUD beam line at GANIL facility. Funnel and conical shape capillaries have been tested and both show that the transmitted beam is composed of contributions: a collimated fraction and a fraction scattered at small angles by the capillary walls. By imaging the beam cross section using a PSD detector, doughnut shape beams have been observed. A Rutherford scattering-based simulation has been used to analyze the experimental data.

Sputtering and surface topography modification of bismuth thin films under swift 84Kr15+ ion irradiation

The sputtering and surface topography modification of bismuth thin films deposited onto Si substrates and irradiated by 27.5MeV 84Kr15+ ions over the fluence range 1012–1014cm−2 have been studied using three complementary techniques: Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The RBS analysis reveals a linear reduction of the initial thickness of the irradiated bismuth samples by ∼4% up to 7% with increasing ion fluence corresponding to a mean sputtering yield of ∼2.9×102at/ion. Besides, significant sample surface topography changes occur upon ion irradiation consisting in grain growth and surface roughening clearly pointed out by performed AFM and XRD analyses. Moreover, a close correlation is observed between the variations versus ion fluence of the measured sputtering yield and the determined Bi surface grain size and compressive strain. These moderate Bi surface effects are similar to those pointed out previously for thin films irradiated by MeV heavy ions. They can be mainly caused by inelastic electronic collision mechanisms taking place within the Bi material electronic stopping power regime below the threshold for latent track formation.

The large-scale energetic ion layer in the high latitude Jovian magnetosphere as revealed by ULYSSES/HI-SCALE cross-field intensity-gradient measurements

ULYSSES investigated the high latitude Jovian magnetosphere for a second time, after Pioneer 11 mission, and gave us the opportunity to search the structure and the dynamics of this giant magnetosphere above the magnetodisc. Kivelson and Williams (1976) and Kennel and Coroniti (1979) reported that Pioneer 11 observed energetic particle intensities at high latitudes at the same level with those measured in the plasma sheet and inferred that they were not consistent with the magnetodisc model. ULYSSES observations supported the idea about a large-scale layer of energetic ions and electrons in the outer high latitude Jovian magnetosphere (Cowley et al., 1996; Anagnostopoulos et al., 2001a). This study performs a number of further tests for the existence of the large scale layer of energetic ions in the outer high latitude Jovian magnetosphere by studying appropriate cross-B field anisotropies in order to monitor the ion northward/southward intensity gradients. In particular, we examined ULYSSES/HI-SCALE observations of energetic ions with large gyro-radius (0.5–1.6MeV protons and>2.5MeV heavy (Z>5) ions) in order to compare instant intensity changes with remote sensing intensity gradients. Our analysis confirms the existence of an energetic particle layer in the north hemisphere, during the inbound trajectory of ULYSSES traveling at moderate latitudes, and in the south high-latitude duskside magnetosphere, during the outbound segment of the spacecraft trajectory. Our ULYSSES/HI-SCALE data analysis also provides evidence for the detection of an energetic proton magnetopause boundary layer during the outbound trajectory of the spacecraft. During ULYSSES flyby of Jupiter the almost permanent appearance of alternative northward and southward intensity gradients suggests that the high latitude layer appeared to be a third major area of energetic particles, which coexisted with the radiation belts and the magnetodisc.

Quenching of impact ionization in heavy-ion induced electron-hole pair plasma tracks in wide bandwidth avalanche photodetectors

Optoelectronics such as Si avalanche photodiodes (APDs) used in space are subjected to background cosmic radiation including highly energetic heavy ions. As these swift ions pass through a device, they lose energy by promoting free electron-hole pairs. The resultant ionization track is an extremely dense two-component free carrier plasma with submicron radial diameters. Within the track, injected space charge is high enough to severely distort the local electric field, which perturbs the current transient or impulse response induced on the device electrodes. In this paper, the time-resolved ion beam induced current response of a low breakdown bias, high-frequency Si APD has been observed for a sequence of front side irradiations with MeV heavy ions species with different track geometries. These results are compared with focused picosecond laser experiments, where injection levels are controlled from low to high. Ion induced tracks are found to effectively quench the avalanche process. Simulations using Synopsis technology computer aided design are performed to clarify the role of screening in quenching avalanche mechanisms under the conditions prevalent here.