MeV 4He Ions Research Articles

Energy loss straggling of energetic 3He and 6Li ions into polymer foils

Energy loss straggling of 1.1–4.5MeV 3He ions and 1.2–4.8MeV 6Li ions into three widely-used polymer foils (polycarbonate, polyethylene terephthalate and polypropylene) was measured by means of a transmission technique. An improved self-supporting method using a surface barrier detector was used to determine the corresponding energy straggling. The experimental results are in satisfactory agreement with those yielded with Bohr theoretical calculations as well as an empirical formula except at lower energies. The measured data also confirm the validity of Bragg’s rule when applied to lighter ions bombarded into polymer foils.

Products of the Triplet Excited State Produced in the Radiolysis of Liquid Benzene

The radiation chemical yields of the products derived from the triplet excited state produced in the radiolysis of liquid benzene with gamma-rays, 10 MeV 4He ions, and 10 MeV 12C ions have been determined. Iodine scavenging techniques have been used to examine the formation and role of radicals, especially the H atom and phenyl radical. For all irradiation types examined here, the increase in hydrogen iodide yields with increasing iodine concentration matches the increase in iodobenzene yields. This agreement suggests that the benzene triplet excited state is the common precursor for the H atom and the phenyl radical. Pulse radiolysis studies in liquid benzene have determined the rate coefficients for the reactions of phenyl radicals with iodine and with the solvent benzene to be 9.3 x 10(9) M(-1) s(-1) and 3.1 x 10(5) M(-1) s(-1), respectively. Direct measurements of polymer formation, which refers to trimers (C18) and higher order compounds (>C18), in liquid benzene radiolysis using gamma-rays, 4He ions, and 12C ions at relatively high doses have been performed using gel permeation chromatography. The yields of trimers increase from gamma-rays to 12C ions due to the increased importance of intratrack radical-radical reactions that can be scavenged by the radical scavenging reactions of iodine. On the other hand, the >C18 product yields decrease from gamma-rays to 12C ions. The structure of the polymer consists of a partly saturated ring as determined by infrared and gas chromatography/mass spectrometry studies. A schematic representation for the radiolytic decomposition of the benzene triplet excited state is presented.

Vacancy defects induced in sintered polished UO 2 disks by helium implantation

Vacancy defects have been investigated in sintered polished and annealed uranium oxide disks. Slow positron beam coupled with Doppler broadening spectrometer was used to probe the track region of 1 MeV 3He ions implanted in uranium dioxide (UO 2) disks. The low and high momentum annihilation fractions, S and W, respectively, were measured in the first micrometer near surface region of the disks as a function of positron energy. The S and W values indicate that the 1 MeV He ions induce vacancy defects in the track region of their range. The vacancy defect depth distribution is heterogeneous. The positron trapping at these vacancy defects increases with the depth and with the implantation fluence indicating an increase of the vacancy defect concentration. The nature of the induced vacancy defects does not change with the fluence.

ERDA with 15 MeV 4He ions under atmospheric pressure

ERDA measurements in reflection geometry have been performed on titanium deuteride (TiDx) set in air of 1atm and titanium hydride (TiHx) set in a mixture of hydrogen gas of 0.5atm and deuterium gas of 0.5atm. A 4He beam with an energy of 15MeV is extracted through a molybdenum foil with a thickness of 5μm into the gases. Spectra from deuterium and hydrogen in these samples are obtained by subtraction of spectra of titanium from spectra of the TiDx and TiHx, respectively. Depth profiles of the deuterium and hydrogen atoms are calculated from the obtained spectra. The atomic ratios of deuterium and hydrogen to titanium in the samples are 0.83 and 0.79 up to a depth of 8μm, respectively.

Effects of ion-beam irradiation on the L10 phase transformation and their magnetic properties of FePt and PtMn films (Invited)

ABSTRACTIon-beam irradiation shows enhancement or degradation of magnetic properties on L10 phase of FePt and PtMn films. A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The in-plane coercivity greater than 5700 Oe can be obtained after disordered FePt films were irradiated at the beam current of several μA/cm2 with the ion does of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230°C. The comparison has been made on the [Fe/Pt]10/C films by RTA and high current-density He irradiation. Although RTA and ion irradiation both reach high coercivity, ion irradiation seems to suppress the (001) texture, leading to isotropic Hc. Ion-beam irradiation can also be applied to the transformation of PtMn. An ordered PtMn phase, a large exchange field and a high GMR ratio (11%) were obtained in PtMn-based spin valves by using 1.25 μA/cm2 He-ions. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and GMR of PtMn-based spin valves, respectively. We propose a novel approach to achieve magnetic patterning by using ion irradiation, which can be applied for patterned media and magnetic sensors.

Electrical characterization of ion bombarded AlGaN Schottky photodetectors

We detected electron traps in AlGaN photodetectors with carrier densities (5–9) × 1017 cm−3 using DLTS and thermal admittance spectroscopy (TAS). The electron traps P2 and P1, as detected by DLTS in AlGaN with an Aluminium (Al) content of 41% are located at 0.57 eV and at 0.27 eV respectively, below the conduction band minima. The same pair of traps is detected in samples with 12% Al content; these levels are situated at 0.54 eV and 0.16 eV below the conduction band, respectively. TAS in the sample set with Al mole fraction of 12%, yielded a level at EC − 0.15 eV. In all our samples, independent of the Al mole fraction, we find P1 always has a concentration higher than P2's. We believe the trap P2 is the same as the defect, E1, detected by Wang et al. [1] in as grown GaN; and, P1 is the 0.61 eV level reported by Gotz et al. [2]. 1.8 MeV He-ion irradiation, up to a dose of 5.5 × 1012 cm−2, results in the uniform removal of free carriers at a rate of 24000 cm−1. We were unable to detect any significant defect(s) responsible for this compensation, however, we believe the culprits are acceptor-type defects. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

He migration in implanted UO 2 sintered disks

The behaviour of helium implanted in sintered uranium dioxide disks has been investigated as a function of annealing temperature. UO 2 disks have been implanted with 1 MeV 3He ions at a fluence of 1 × 10 16 3He cm −2 using a Van der Graaff accelerator. These implantation conditions lead to a local helium concentration of 0.2 at.% at a depth of 1.9 μm in UO 2. The 3He(d,α) 1H Nuclear Reaction Analysis method was used to determine the helium depth profile after the various annealing stages. The experimental results measured after 1100 °C anneal were analysed using a simple model which satisfactorily reproduces the observed helium depth profile changes. The intragranular helium diffusion coefficient is estimated and the result is assessed against other data published in the open literature.

Compositional analysis of thin SiO xN y:H films by heavy-ion ERDA, standard RBS, EDX and AES: a comparison

The composition of silicon oxynitride (SiO x N y :H) films deposited by electron cyclotron resonance chemical vapour deposition (ECR-CVD) was analysed by ion beam techniques, heavy-ion elastic recoil detection analysis (HI-ERDA) with 150 MeV 86Kr ions and Rutherford backscattering spectroscopy (RBS) with 1.4 MeV 4He ions. The results were compared with energy dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES). Since HI-ERDA provides absolute atomic concentrations of all film components including hydrogen with a sensitivity of at least 0.005 at% the data from this method were used as a quantitative reference to assess the applicability of RBS, EDX and AES to the analysis of silicon oxynitrides. For each of these techniques the comparison with HI-ERDA allowed a discussion of the different sources of error, especially of those causing systematic deviations of the measured concentration values. A novel approach to determine from RBS spectra also the hydrogen concentrations appeared to be applicable for hydrogen levels exceeding 2 at%. Furthermore, it is shown that the film density can be determined from the HI-ERDA results alone or in combination with single-wavelength ellipsometry.

Ion-irradiation-induced direct ordering of L1 FePt phase

A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The coercivity greater than 5700 Oe can be obtained after disordered FePt was irradiated at the beam current of several μA/cm2 with the ion doses of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230 °C. Due to the feasibilities of the fast temperature rise and the focused beam size, this ion-irradiation heating treatment can be potentially used as an alternative technique for the rapid thermal annealing and for the magnetic patterning.

The evolution of cavities in Si co-implanted with Si and He ions 1

Different levels of damage were first introduced into CZ p-type Si (100) by the implantation of 80 keV Si ions to different doses ranging from 10 14 to 5×10 15 cm −2. All the Si implanted samples together with virgin Si were then subjected to 1 MeV 3He ion implantation to the same dose of 5×10 16 cm −2. Cross-sectional transmission electron microscopy (XTEM) and nuclear reaction analysis (NRA) measurements were used to quantify the evolution of He-cavities and He desorption from the cavities after subsequent annealing, respectively. Our results show that the presence of high level of damage induced by Si implants tends to inhibit the growth of He-cavities and increase the rate of He desorption. The results are tentatively interpreted on the basis of the evolution of Si induced damage upon annealing and its interaction with He-cavities.

Trapping of Hydrogen in Tantalum Bombarded with Helium-3 Ions

Hydrogen trapping in tantalum was experimentally studied using an in-situ observation technique. One side of a tantalum membrane was continuously exposed to a deuterium plasma and was bombarded with 0.8 MeV 3He ions to introduce traps. After the bombardment, the deuterium depth profiles near the surface were observed by nuclear reaction analysis with the reaction of D(3He, p)4He. The result indicated that many deuterium atoms were present in traps which were associated with radiation damages. The temperature dependence of the deuterium concentration showed that there were two kind of traps, called trap 1 and trap 2 here. The difference in the peak shape of the depth profiles and the difference in the trapping energy suggested that traps 1 and 2 were caused by vacancy clusters and monovacancy sites, respectively. The concentration of the trapped deuterium was found to be of the same order of magnitude as those in molybdenum and nickel under the same experimental conditions.

Response of radiochromic dye films to low energy heavy charged particles

We have studied the possible use of radiochromic dye films (RCF) as heavy charged particle dosemeters. We present the results of irradiating two commercial RCF (GafChromic HD-810 and MD-55-1) with 1.5, 2.9 and 4.4 MeV protons, 1.4, 2.8, 4.7, 5.9, 6.8 MeV 4He ions and 8.5 and 12.4 MeV 12C ions, at proton doses from about 1 Gy up to 3 kGy, helium ions doses from 3 Gy to 5 kGy and carbon ion doses from 30 Gy to 20 kGy. The films were scanned and digitized using commercial equipment. For a given particle, the response per unit dose at different energies indicates an energy dependence of the sensitivity, which is discussed. Comparison was made for the use of a standard spectrophotometer to obtain optical density readings versus a white light scanner.

The TL fluence response to heavy charged particles using the track interaction model and track structure information.

The extended track interaction model, ETIM, has recently being proposed to explain the TLD-100 fluence response of peak 5 to heavy ions. This model includes the track structure information through the use of the luminescent centre occupation probability obtained from radial dose distributions produced by the ions as they travel through the dosemeter. In this work an implementation of ETIM using Monte Carlo techniques is presented. The simulation was applied to calculate the response of peak 5 of both sensitised and normal TLD-100 crystals to 2.6 and 6.8 MeV 4He ions. The simulation shows that the TL-fluence response has a strong dependence on ion energy, in disagreement with experimental observations. In spite of this, good agreement between the simulated TL-fluence response calculated for the 6.8 MeV 4He radial distributions and the experimental data for the two energies was achieved.

Evolution of nucleation sites and bubble precursors in silicon as a function of helium implanted dose

Abstract(111) oriented silicon samples were implanted at room temperature with 1.55 MeV 3He ions in the dose range of 5×1015 to 5×1016/cm2. Cross-sectional transmission electron microscopy (XTEM) was used to study the evolution of bubbles and extended defects during subsequent thermal annealing at 800°C and 900°C for 30min. The He desorption from bubbles and bubble precursors was measured by means of nuclear reaction analysis (NRA). TEM observations show that no bubbles were observed in Si implanted at doses lower than 1×1016/cm2, while a well-defined cavity band was formed after implantation at 5×1016/cm2 and subsequent thermal annealing. At the intermediary dose of 2×1016/cm2, however, the evolution of bubbles and extended defects is quite different. The bubbles prefer to nucleate in large planar clusters surrounded by a high density of dislocation loops emerging from them. The clusters of bubbles act as the sources of the dislocation loops. NRA measurements indicate that the He desorption behavior is also dose-dependent. The He desorption is achieved much faster in low dose implanted Si. The results are qualitatively discussed.

Radiolysis of Aqueous Solutions with Pulsed Ion Beams. 4. Product Yields for Proton Beams in Solutions of Thiocyanate and Methyl Viologen/Formate

The yields of radicals from water decomposition produced in the radiolysis of two types of aqueous solutions, thiocyanate and methyl viologen (MV2+), were determined using proton pulses of 5.2 MeV energy. Aerated thiocyanate solutions in the concentration range of 0.001−0.75 M gave yields of (SCN)2•-, formed from scavenging OH radicals, that were lower than those for high-energy electrons and higher than those for 4He ions of 21 MeV energy. The (SCN)2•- yield increased with increasing thiocyanate concentration, but the decay of thiocyanate radicals through intratrack reactions appears to be substantial in proton radiolysis. Methyl viologen radical cations (MV•+) formed by scavenging eaq-, H atoms, and OH radicals were measured in deaerated 0.5 mM MV2+ solutions containing formate. The MV•+ yields agreed with the results of steady-state proton beam radiolysis, which confirms earlier results that this system is a suitable chemical dosimeter for ion beam pulse radiolysis. The yields of MV•+ in deaerated MV2+ solutions containing formate and formate/tertiary butanol were used to determine the yields of OH radicals and the sum of the eaq- and H atom yields. Both sets of yields for proton beams were lower than the corresponding ones for high-energy electrons and higher than those for 21 MeV 4He ions. The predicted hydroxyl radical yields for proton beams increase with increasing scavenging capacity and approach the value found for high-energy electron radiolysis. The sum of the eaq- and H atom yields is about 1.8 molecules/100 eV and nearly independent of the scavenging capacity for OH radical. Intratrack reactions were simulated using a deterministic diffusion kinetic model, and the results qualitatively predict the observed yields in the thiocyanate and the MV2+ solutions.

Lattice location of implanted tellurium in GaN heteroepitaxial films

The lattice site of implanted tellurium in gallium nitrideheteroepitaxial films grown on sapphire substrates has been studied. GaNsamples were implanted with 400 keV 130Te ions at 300 °C. Theion dose was 1.5×1015 cm-2. The samples were analysedwith Rutherford backscattering spectrometry channelling using 2.0 MeV4He ions. The maximum Te concentration was 0.2 at.%. Based onmeasured channelling angular scans for Ga and Te along the ⟨0001⟩ and ⟨101̅1⟩ axial directions,analysed by comparison with Monte Carlo simulations, it was concluded thatin the as-implanted sample about 70% of Te atoms were on the Ga atomlattice sites, slightly displaced. The measured ⟨101̅1⟩ scan showed no evidence of substitutional Te on Nlattice site. The post-implantation annealing at 900 °C was foundto decrease the substitutional fraction of Te while little recovery of thehost lattice was observed. This indicates an interaction process betweenTe atoms and implantation-induced lattice defects. No migration of Teduring annealing at 900 °C was observed. In addition, the effect ofmisfit dislocations in the host lattice on the channelling yield wasvisible in the ⟨101̅1⟩ angular scan measured at a47° tilt angle.}\\fnm{3}{Present address: Vaisala Oyj, FIN-00421 Helsinki, Finland.

Comparative concentration analysis of Cr and Co in FeSi 2 films performed by ERDA and RBS

Thin films of β-FeSi 2 doped by Co or Cr were grown on Si substrates by molecular beam epitaxy (MBE) using three separately controlled evaporation sources. The dopant concentration was measured concurrently by heavy-ion ERDA with 129Xe ions of 140–250 MeV, by heavy-ion RBS with 15 MeV 14N and by standard RBS with 1.4 MeV 4He ions. Among these techniques, the TOF–ERDA was most powerful in providing a high mass resolution and a low detection limit for Co and Cr (≈0.1 at.%) . Because of the complete overlap of the dopant signals with the Fe signal the standard RBS spectra were evaluated by relying on the differences between the scattering cross-sections from the dopant atoms and Fe. This approach proved to be applicable as far as the dopants had a constant depth profile with sufficiently high concentration. For Cr concentrations exceeding the miscibility limit the RBS results deviate significantly from those of ERDA due to increasing dopant depth inhomogeneities.

High accuracy, high energy He-ERD analysis of H, D and T

A new analysis technique using high-energy helium ions for the simultaneous elastic recoil detection of all three hydrogen isotopes in metal hydride systems extending to depths of several μm's is presented. Analysis shows that it is possible to separate each hydrogen isotope in a heavy matrix such as erbium to depths of 5 μm using incident 11.48 MeV 4He ions with a detection system composed of a range foil and Δ E − E telescope detector. Newly measured cross-sections for the elastic recoil scattering of 4He ions from protons and deuterons are presented in the energy range 10–11.75 MeV for the laboratory recoil angle of 30°.

Electronic and transformation properties of a metastable defect introduced in epitaxially grown sulfur doped n-GaAs by particle irradiation

We report on the electronic and metastable properties of a new defect, EαIR10 positioned 0.262 eV below the conduction band, and introduced after particle irradiation of sulfur doped epitaxial n-GaAs. Using deep level transient spectroscopy (DLTS), we detected EαIR10 after 5.4 MeV He-ion, 10 and 12 MeV electron, and 1 MeV proton irradiations. However, we could not detect EαIR10 after irradiation by electrons with energy 0.2–2.4 MeV. DLTS measurements coupled with bias-on/bias-off cooling cycles were used to study the removal and introduction kinetics of EαIR10. After removing EαIR10 (ΔEremoval=0.76±0.08 eV) by zero bias annealing at room temperature, it can be re-introduced by reverse bias annealing (ΔEintroduction=0.58±0.08 eV), in the 230–260 K temperature region under predominantly first order kinetics. Annealing studies revealed that EαIR10 completely anneals out at 420 K.

Behavior of cesium implanted in zirconia based inert matrix fuel

Retention of cesium in yttria stabilized zirconia (YSZ) was studied experimentally and discussed on the basis of its solubility estimated on a thermodynamic basis. The retention was investigated experimentally by determination of the temperature dependence of diffusion and the cesium release. Cesium was introduced using 1 MeV ions or by chemical reaction in yttria stabilized zirconia. The distribution of the implanted cesium was evaluated by using TRIM computer calculation and measured by Rutherford backscattering spectroscopy (RBS) using 5 MeV 4He ions. The cesium profile was quantified after successive annealing up to 1373 K. Cesium release was rather weak up to 1173 K. The retention of Cs chemically introduced by Cs 2ZrO 3 was also experimentally investigated for different calcination temperatures. The chemically introduced cesium followed similar release behavior as the implanted one. Thermodynamic modelling of the system cesium, zirconium and oxygen was performed in a comprehensive way and as a function of temperature.