A proposed nuclear nanoprobe with Angstrom resolution

An idea is presented for an entirely new point-projection nuclear microscope that theoretically would have sub-nanometer resolution, approaching one Angstrom. The concept involves using a Kalbitzer super tip as a source of low energy (～100 eV) He or H ions that would be transmitted through a molecular sample (e.g. buckyball, carbon nanotube, graphene sheet, DNA molecule, etc.) placed very near the tip (～1–100 nm), and then projected onto a microchannel plate (MCP) screen placed ～1 m from the tip. Small angle scattering of the incident ions with atoms in the sample result in the development of shadow cones with an increase in scattered ion intensity at the critical cone angle. The enhanced intensity patterns formed at multiple intersections of cone perimeters are called “threads”. The shadow cones and threads are projected onto a suitable low-energy ion position sensitive detector to create a “shadow or thread image” of the sample. Such point-projection microscopes have no aberrations that affect the image, and the magnification would be of the order 1 m/10 nm, or 1.E8! The feasibility of this scheme is currently being studied theoretically using a deterministic atomic scattering model and a Monte Carlo molecular dynamics code. The results of these calculations indicate that only very low energy (60–120 eV) incident hydrogen ions can be used to avoid displacing atoms in the sample. At these energies, the critical cone angles are quite large and it would be necessary to position the molecular samples very close to the tip (down to only 1 nm) so that the projected ion maps are interpretable as distinct threads. Projecting distinct shadows is not supported by the scattering physics.     

Evaluation of soft error rates using nuclear probes in bulk and SOI SRAMs with a technology node of 90 nm

The difference of soft error rates (SERs) in conventional bulk Si and silicon-on-insulator (SOI) static random access memories (SRAMs) with a technology node of 90 nm has been investigated by helium ion probes with energies ranging from 0.8 to 6.0 MeV and a dose of 75 ions/μm². The SERs in the SOI SRAM were also investigated by oxygen ion probes with energies ranging from 9.0 to 18.0 MeV and doses of 0.14–0.76 ions/μm². The soft error in the bulk and SOI SRAMs occurred by helium ion irradiation with energies at and above 1.95 and 2.10 MeV, respectively. The SER in the bulk SRAM saturated with ion energies at and above 2.5 MeV. The SER in the SOI SRAM became the highest by helium ion irradiation at 2.5 MeV and drastically decreased with increasing the ion energies above 2.5 MeV, in which helium ions at this energy range generated the maximum amount of excess charge carriers in a SOI body. The soft errors occurred by helium ions were induced by a floating body effect due to generated excess charge carriers in the channel regions. The soft error occurred by oxygen ion irradiation with energies at and above 10.5 MeV in the SOI SRAM. The SER in the SOI SRAM gradually increased with energies from 10.5 to 13.5 MeV and saturated at 18 MeV, in which the amount of charge carriers induced by oxygen ions in this energy range gradually increased. The computer calculation indicated that the oxygen ions with energies above 13.0 MeV generated more excess charge carriers than the critical charge of the 90 nm node SOI SRAM with the designed over-layer thickness. The soft errors, occurred by oxygen ions with energies at and below 12.5 MeV, were induced by a floating body effect due to the generated excess charge carriers in the channel regions and those with energies at and above 13.0 MeV were induced by both the floating body effect and generated excess carriers. The difference of the threshold energy of the oxygen ions between the experiment and the computer calculation might be due to the difference between the designed and real structures.     

Photoluminescence properties of ZnO thin film on sapphire substrates fabricated by ion implantation at elevated temperature and thermal oxidation

ZnO thin films on sapphire substrate were fabricated by ion implantation combined with thermal oxidation. A sapphire substrate was implanted with 50 keV zinc ions at 350 °C with a fluence of 1.5 × 10¹⁷ ions cm^?2, then annealed in a tube furnace in oxygen ambient in 2 h at 650 °C. Photoluminescence spectra were collected at temperatures from 80 to 300 K to understand the optical properties of this film. The photoluminescence spectrum at 300 K included a UV peak at 377 nm and a broad peak from deep level emission at 500 nm. The fine spectra structure at 80 K consisted of the free exciton at 3.373 eV and the donor bound exciton at 3.357 eV. The first and second phonon replicas of free excitons were also observed and the origin of the deep level emission peak was clarified.     

Development of a TOF-ERDA measurement system for analysis of light elements using a He beam

A time-of-flight ERDA (TOF-ERDA) measurement system has been developed for the analysis of light elements. He ions are used for the incident beam, and recoil light ions are detected with the system. The system consists of a time detector and a silicon detector, and energy and velocity of recoil ion are measured simultaneously. The depth resolution of 21.6 ± 2.2 nm (FWHM) has been obtained by an ERDA measurement of a thin carbon layer onto a silicon wafer using a 5.7 MeV He beam. The mass resolution is better than 1 for elements up to oxygen. Maximum detectable depth of carbon in a PET film is about 650 nm. An ERDA measurement of implanted carbon in a silicon wafer has been demonstrated.     

Angular and lateral spreading of ion beams in biomedical nuclear microscopy

Nuclear scattering from target atoms gives rise to a spatial broadening of energetic ion beams penetrating matter. The spatial broadening of the ion beam presents an ultimate limit to the resolving power that can be achieved in nuclear microscopy methods. The pressing of the attainable resolution limit in biomedical nuclear microscopy to dimensions approaching 10 nm, or so, implies the fundamental limitation from ion-target scattering will become increasingly significant. This effect has been investigated by a combined analytical and numerical computational approach to determine the extent and how single and multiple scattering processes limit the resolution for analysis with 2 MeV ⁴He and ¹H ions of realistic biomedical samples. The cases studied were direct-Scanning Transmission Ion Microscopy (direct-STIM), Particle Induced X-ray Emission (PIXE) studies of 20 μm tissue sections and in vivo single-ion irradiation of cells.     

Optical measurements of nanoporous anodic alumina formed on Si using novel X-ray spectroscopy set up CLASSIX

We present X-ray spectroscopy measurements to investigate the chemistry and structure of nanoporous alumina using novel instrument CLASSIX [N.R.J. Poolton, B.M. Towlson, B. Hamilton, D.A. Evans, Nuclear Instruments and Methods in Physics Research B246 (2006) 445] (chemistry luminescence and structure of surfaces by micro-imaging X-ray absorption). X-ray excited optical luminescence (XEOL) measurements show that the porous anodic alumina (PAA) films obtained have blue emission band with a peak position at 2.63 eV (470 nm) which can be attributed to mixed emission from F and F⁺ centres. The L_Ш absorption edge of aluminium in porous anodic alumina has been observed at 76.64 eV that shows a chemical shift from pure aluminium.     

Swift heavy ion induced modifications of optical and microstructural properties of silver–fullerene C60 nanocomposite

In this paper, we study the optical and microstructural properties of silver–fullerene C₆₀ nanocomposite and their modifications induced by swift heavy ion irradiation. Silver nanoparticles embedded in fullerene C₆₀ matrix were synthesized by co-deposition of silver and fullerene C₆₀ by thermal evaporation. The nanocomposite thin films were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 10¹² to 3 × 10¹³ ions/cm². Optical absorption studies revealed that the surface plasmon resonance of Ag nanoparticles showed a blue shift of ～49 nm with increasing ion fluence up to 3 × 10¹³ ions/cm². Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction in the nanocomposite film. Growth of Ag nanoparticles was observed with increasing ion fluence. Raman spectroscopy was used to understand the effect of heavy ion irradiation on fullerene matrix. The blue shift in plasmonic wavelength is explained by the transformation of fullerene C₆₀ matrix into amorphous carbon.     

Radiation-induced luminescence of PET and PEN films under MeV ion and pulsed UV laser irradiation

Ion- and photo-induced luminescence of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) films was investigated during irradiation by MeV H and He ions and an ultraviolet pulsed laser. At the beginning of ion irradiation, the PEN film emitted blue luminescence, whose intensity was an order of magnitude higher than that emitted by the PET film. Successive ion irradiation effectively reduced the luminescence centers, and the rate of decease in luminescence intensity depended on the energy deposited along the trajectory of the ions. Optical absorption measurements in the infrared region revealed an irradiation-sensitive feature of the PEN film. Moreover, a photo-induced band grew remarkably at 470 nm in the PET film under 266 nm pulsed laser irradiation, while the PEN film showed a moderate decrease in luminescence intensity at 440 nm.     

Low temperature formation of luminescent Si nanocrystals with combined process of excimer UV-light irradiation and RTA

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to achieve low temperature (below 1000 °C) formation of luminescent Si nanocrystals in SiO₂ have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluences of 7.5 × 10¹⁶ and 1.5 × 10¹⁷ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp for 2 h. After the process, the samples were rapidly thermal annealed at 1050 °C for 5 min before furnace annealing (FA) at 900 °C. Photoluminescence spectra were measured at various stages at the process. Effective visible photoluminescence is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA, prior to a low temperature FA process. Based on our experimental results, we discuss the mechanism for the initial formation process of the luminescent Si nanocrystals in SiO₂, together with the effects with excimer lamp irradiation and RTA process on the luminescence.     

Point defects induced in ion irradiated 4H–SiC probed by exciton lines

The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H⁺ ion beam in the fluence range 6.5 × 10¹¹–1.8 × 10¹³ ions/cm² are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P₁ lines (e, f, g) and the P₂ lines (a, b, c, d) that exhibit different trends with the ion fluence. The P₁ group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 10¹² ions/cm² and then decreases. The P₂ group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 10¹² ions/cm² and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P₁ and P₂ lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.     

Damage accumulation in gallium nitride irradiated with various energetic heavy ions

In this work a study of damage production in gallium nitride via elastic collision process (nuclear energy deposition) and inelastic collision process (electronic energy deposition) using various heavy ions is presented. Ordinary low-energy heavy ions (Fe⁺ and Mo⁺ ions of 110 keV), swift heavy ions (²⁰⁸Pb²⁷⁺ ions of 1.1 MeV/u) and slow highly-charged heavy ions (Xeⁿ⁺ ions of 180 keV) were employed in the irradiation. Damage accumulation in the GaN crystal films as a function of ion fluence and temperature was studied with RBS-channeling technique, Raman scattering technique, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).For ordinary low-energy heavy ion irradiation, the temperature dependence of damage production is moderate up to about 413 K resulting in amorphization of the damaged layer. Enhanced dynamic annealing of defects dominates at higher temperatures. Correlation of amorphization with material decomposition and nitrogen bubble formation was found. In the irradiation of swift heavy ions, rapid damage accumulation and efficient erosion of the irradiated layer occur at a rather low value of electronic energy deposition (about 1.3 keV/nm³), which also varies with irradiation temperature. In the irradiation of slow highly-charged heavy ions (SHCI), enhanced amorphization and surface erosion due to potential energy deposition of SHCI was found. It is indicated that damage production in GaN is remarkably more sensitive to electronic energy loss via excitation and ionization than to nuclear energy loss via elastic collisions.     

Imaging of single cells and tissue using MeV ions

With the attainment of sub-100 nm high energy (MeV) ion beams, comes the opportunity to image cells and tissue at nano-dimensions. The advantage of MeV ion imaging is that the ions will penetrate whole cells, or relatively thick tissue sections, without any significant loss of resolution. In this paper, we demonstrate that whole cells (cultured N2A neuroblastoma cells ATCC) and tissue sections (rabbit pancreas tissue) can be imaged at sub-100 nm resolutions using scanning transmission ion microscopy (STIM), and that sub-cellular structural details can be identified. In addition to STIM imaging we have also demonstrated for the first time, that sub-cellular proton induced fluorescence imaging (on cultured N2A neuroblastoma cells ATCC) can also be carried out at resolutions of 200 nm, compared with 300–400 nm resolutions achieved by conventional optical fluorescence imaging. The combination of both techniques offers a potentially powerful tool in the quest for elucidating cell function, particularly when it should be possible in the near future to image down to sub-50 nm.     

Study of modifications in Lexan polycarbonate induced by swift O6+ ion irradiation

Swift Heavy Ion (SHI) irradiation of the polymeric materials modifies their physico-chemical properties. Lexan polycarbonate films were irradiated with 95 MeV oxygen ions to the fluences of 10¹⁰, 10¹¹, 10¹², 10¹³ and 2 × 10¹³ ions/cm². Characterization of optical, chemical, electrical and structural modifications were carried out by UV–Vis spectroscopy, FTIR spectroscopy, Dielectric measurements and X-ray Diffraction. A shift in the optical absorption edge towards the red end of the spectrum was observed with the increase in ion fluence. The optical band gap (E_g), calculated from the absorption edge of the UV–Vis spectra of these films in 200–800 nm region varied from 4.12 eV to 2.34 eV for virgin and irradiated samples. The cluster size varied in a range of 69–215 carbon atoms per cluster. In FTIR spectra, appreciable modification in terms of breaking of the cleavaged C–O bond of carbonate and formation of phenolic O–H bond was observed on irradiation. A rapidly decreasing trend in dielectric constant is observed at lower frequencies. The dielectric constant increases with fluence. It is observed that the loss factor increases moderately with fluence and it may be due to scissoring of polymer chains, resulting in an increase in free radicals. A sharp increase in A.C. conductivity in pristine as well as in irradiated samples is observed with frequency and is attributed to scissoring of polymer chains. XRD analyses show significant change in crystallinity with fluence. A decrease of ～9.02% in crystallite size of irradiated sample at the fluence of 2 × 10¹³ ions/cm² is observed.     

Ion beam mixing in uranium nitride thin films studied by Rutherford Backscattering Spectroscopy

Thickness, composition, concentration depth profile and ion irradiation effects on uranium nitride thin films deposited on fused silica have been investigated by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The films were prepared by reactive DC sputtering at the temperatures of ?200 °C, +25 °C and +300 °C. A perfect 1U:1N stoichiometry with a layer thickness of 660 nm was found for the film deposited at ?200 °C. An increase of the deposition temperature led to an enhancement of surface oxidation and an increase of the thickness of the mixed U–N–Si–O layers at the interface. The sample irradiation by 1 MeV Ar⁺ ion beam with ion fluence of about 1.2–1.7 × 10¹⁶ ions/cm² caused a large change in the layer composition and a large increase of the total film thickness for the films deposited at ?200 °C and at +25 °C, but almost no change in the film thickness was detected for the film deposited at +300 °C. An enhanced mixing effect for this film was obtained after further irradiation with ion fluence of 2.3 × 10¹⁶ ions/cm².     

Deuterium trapping by irradiation damage in tungsten induced by different displacement processes

The deuterium trapping behaviors in tungsten damaged by light ions with lower energy (10 keV C⁺ and 3 keV He⁺) or a heavy ion with higher energy (2.8 MeV Fe²⁺) were compared by means of TDS to understand the effects of cascade collisions on deuterium retention in tungsten. By light ion irradiation, most of deuterium was trapped by vacancies, whose retention was almost saturated at the damage level of 0.2 dpa. For the heavy ion irradiation, the deuterium trapping by voids was found, indicating that cascade collisions by the heavy ion irradiation would create the voids in tungsten. Most of deuterium trapped by the voids was desorbed in higher temperature region compared to that trapped by vacancies. It was also found that deuterium could accumulate in the voids, resulting in the formation of blisters in tungsten.     

Stopping force and straggling of 0.6–4.7 MeV H,He and Li ions in the polyhydroxybutyrate foil

Stopping force and straggling of 0.6–3.5 MeV ¹H ions, 2.0–4.7 MeV ⁴He ions and 1.4–4.4 MeV ⁷Li ions in the polyhydroxybutyrate (PHB) foil were measured by means of a transmission technique. The measured stopping forces are in well agreement with the SRIM 2008 calculation and the ICRU Report tables, except for the lower energy region. The obtained energy loss straggling deviates from the Bohr’s value by as much as 23.6% for the energies under study. The validity of the Bragg’s rule has also been demonstrated in the stopping force and straggling for ¹H, ⁴He and ⁷Li ions in the PHB foil.     

High energy Si ions bombardment effects on the properties of nano-layers of SiO2/SiO2 + Ag

We grew 50 periodic SiO₂/SiO₂ + Ag multi-layers by electron beam deposition technique. The co-deposited SiO₂ + Ag layers are 7.26 nm, SiO₂ buffer layers are 4 nm, and total thickness of film was determined as 563 nm. We measured the thickness of the layers using in situ thickness monitoring during deposition, and optical interferometry afterwards. The concentration and distribution of Ag in SiO₂ were determined using Rutherford backscattering spectrometry (RBS). In order to calculate the dimensionless figure of merit, ZT, the electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment with 5 MeV Si ions. The energy of the Si ions was chosen such that the ions are stopped deep inside the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. Optical absorption (OA) spectra were taken in the range 200–900 nm to monitor the Ag nanocluster formation in the thin layers.     

The effect of displacement damage on deuterium retention in ITER-grade tungsten exposed to low-energy,high-flux pure and helium-seeded deuterium plasmas

Samples prepared from polycrystalline ITER-grade tungsten were damaged by irradiation with 20 MeV W ions at room temperature to a fluence of 1.4 × 10¹⁸ W/m². Due to the irradiation, displacement damage peaked near the end-of-range, 1.35 μm beneath the surface, at 0.89 displacements per atom. The damaged as well as undamaged W samples were then exposed to low-energy, high-flux (10²² D/m² s) pure D and helium-seeded D plasmas to an ion fluence of 3 × 10²⁶ D/m² at various temperatures. Trapping of deuterium was examined by the D(³He,p)⁴He nuclear reaction at ³He energies varied from 0.69 to 4.0 MeV allowing determination of the D concentration at depths up to 6 μm. It has been found that (i) addition of 10% helium ions into the D plasma at exposure temperatures of 440–650 K significantly reduces the D concentration at depths of 0.5–6 μm compared to that for the pure plasma exposure; (ii) generation of the W-ion-induced displacement damage significantly increases the D concentration at depths up to 2 μm (i.e., in the damage zone) under subsequent exposures to both pure D and D–He plasmas.     

Ion bombardment induced surface electrical degradation monitoring by means of luminescence in aluminas

Oxide ceramics for use as electrical insulators in future fusion devices, will be exposed to ionization and displacement damage (neutrons, gammas, ion bombardment). Enhanced oxygen loss due to ion bombardment increases surface electrical conductivity, and at the same time the surface emits light due to ion beam induced luminescence (IBIL). Results for 3 types of α-alumina and sapphire measuring electrical surface conductivity and IBIL as a function of dose at different temperatures between 20 and 200 °C, show a clear correlation between luminescence and surface electrical degradation. This indicates the potential to remotely monitor insulating material degradation not only in ITER and beyond, but also in the more immediate in-reactor experiments required for materials testing. Partial reduction of degradation by heating in air suggests the possibility for in situ recovery of the insulating properties.     

Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon

The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0 × 10¹³–5.0 × 10¹⁶ cm^?2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.