MeV 127I Ions Research Articles

Si‐nanoparticle synthesis using ion implantation and MeV ion irradiation

AbstractA dielectric matrix with embedded Si‐nanoparticles may show strong luminescence depending on nanoparticles size, surface properties, Si‐excess concentration and matrix type. Ion implantation of Si ions with energies of a few tens to hundreds of keV in a SiO2 matrix followed by thermal annealing was identified as a powerful method to form such nanoparticles. The aim of the present work is to optimize the synthesis of Si‐nanoparticles produced by ion implantation in SiO2 by employing MeV ion irradiation as an additional annealing process. The luminescence properties are measured by spectrally resolved photoluminescence including PL lifetime measurement, while X‐ray reflectometry, atomic force microscopy and ion beam analysis are used to characterize the nanoparticle formation process. The results show that the samples implanted at 20%‐Si excess atomic concentration display the highest luminescence and that irradiation of 36 MeV 127I ions affects the luminosity in terms of wavelength and intensity. It is also demonstrated that the nanoparticle luminescence lifetime decreases as a function of irradiation fluence. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of heavy ion irradiation on DC and gate-lag performance of AlGaN/GaN HEMTs**Project supported by the National Natural Science Foundation of China (Grant No. 61204112).

AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated by 256 MeV 127I ions with a fluence up to 1×1010 ions/cm2 at the HI-13 heavy ion accelerator of the China Institute of Atomic Energy. Both the drain current Id and the gate current Ig increased in off-state during irradiation. Post-irradiation measurement results show that the device output, transfer, and gate characteristics changed significantly. The saturation drain current, reverse gate leakage current, and the gate-lag all increased dramatically. By photo emission microscopy, electroluminescence hot spots were found in the gate area. All of the parameters were retested after one day and after one week, and no obvious annealing effect was observed under a temperature of 300 K. Further analysis demonstrates that swift heavy ions produced latent tracks along the ion trajectories through the hetero-junction. Radiation-induced defects in the latent tracks decreased the charges in the two-dimensional electron gas and reduced the carrier mobility, degrading device performance.

Physical properties of monolithic U8 wt.%–Mo

As a possible high density fuel for research reactors, monolithic U8 wt.%–Mo (“U8Mo”) was examined with regard to its structural, thermal and electric properties. X-ray diffraction by the Bragg-Brentano method was used to reveal the tetragonal lattice structure of rolled U8Mo. The specific heat capacity of cast U8Mo was determined by differential scanning calorimetry, its thermal diffusivity was measured by the laser flash method and its mass density by Archimedes’ principle. From these results, the thermal conductivity of U8Mo in the temperature range from 40 °C to 250 °C was calculated; in the measured temperature range, it is in good accordance with literature data for UMo with 8 and 9 wt.% Mo, is higher than for 10 wt.% Mo and lower than for 5 wt.% Mo. The electric conductivity of rolled and cast U8Mo was measured by a four-wire method and the electron based part of the thermal conductivity calculated by the Wiedemann-Frantz law. Rolled and cast U8Mo was irradiated at about 150 °C with 80 MeV 127I ions to receive the same iodine ion density in the damage peak region as the fission product density in the fuel of a typical high flux reactor after the targeted nuclear burn-up. XRD analysis of irradiated U8Mo showed a change of the lattice parameters as well as the creation of UO 2 in the superficial sample regions; however, a phase change by irradiation was not observed. The determination of the electron based part of the thermal conductivity of the irradiated samples failed due to high measurement errors which are caused by the low thickness of the damage region in the ion irradiated samples.

Modification of magnetic anisotropy in ferromagnetic metallic glasses using high energy ion beam irradiation

The modification in the magnetic anisotropy introduced by swift heavy ion irradiation has been investigated. Ferromagnetic metallic glasses Fe 78B 13Si 9 and Fe 40Ni 38Mo 4B 18 have been irradiated with 100 MeV 127I ions at different doses from 5×10 12 to 7.5×10 13 ions/cm 2. Magnetic anisotropy has been studied by measuring the relative intensity ratio D 23 of Mossbauer sextet. As received samples display orientation of the magnetic moments nearly parallel to the surface of the ribbon, which upon irradiation to a dose of 5×10 12 ions/cm 2 rotates to a nearly random orientation. At the dose of 7.5×10 13 ions/cm 2, the magnetic moments display completely random orientation.

Deformation yield of Co nanoparticles in SiO 2 irradiated with 200 MeV 127I ions

Cobalt ions of 160 keV have been implanted into SiO 2 layers at a fluence of 10 17 at cm −2 at 873 K. The resulting spherical metallic Co nanoparticles have been in their turn irradiated by 200 MeV 127I ions at between 10 11 and 10 14 ions cm −2 at 300 K. The latter procedure induces an increase of the particle size for lower fluences and a deformation for higher fluences. The modification of particle size and shape has been followed by transmission electron microscopy. An incubation fluence for Co nanoparticle deformation of a few 10 12 ions cm −2 and deformation yields of 1.7 × 10 −14 and 3.3 × 10 −14 cm 2 have been measured for Co nanoparticles of 7.2 and 15.6 mean diameters, respectively. The results are compared with existing models.

Elongated Co nanoparticles induced by swift heavy ion irradiations

Spherical nanoparticles have been formed in SiO 2 layers by 160 keV Co + ion implantation. Different particle sizes have been obtained depending on implantation fluence (2 × 10 16, 5 × 10 16 and 1 × 10 17 Co + cm −2) and substrate temperature (77, 295 and 873 K). These spherical particles have been subsequently irradiated with 200 MeV 127I ions at fluences from 10 11 to 10 14 cm −2 at 300 K. Modifications of magnetic properties of the irradiated samples, studied by a SQUID magnetometer at 5 and 295 K in a magnetic field applied perpendicular or parallel to the incident beams, have been related to the modifications of the particle size and shape observed by transmission electron microscopy (TEM). The results are in good agreement with calculations based on a model describing two different regimes: a spherical growth at low irradiation fluences and a prolate deformation along the beam direction for the high fluences.

Modification of ALE-grown SrS thin films by ion implantation of Cu and codopants

Atomic Layer Epitaxy (ALE) grown Al 2O 3/SrS/Al x Ti y O z /glass films were ion-implanted and annealed to study photoluminescence (PL) characteristics of potential blue color phosphors. 63Cu + and 37Cl + or 18O + ions with partially overlapping spots were implanted with three doses (0.2, 0.6 and 1.7×10 16 at./cm 2) using ion energies 60, 80 and 120 keV for 18O +, 37Cl + and 63Cu +, respectively. Cu acts in SrS as an activator, while O and Cl are possible codopants. Samples were annealed in N 2 atmosphere at 600 ∘C and 800 ∘C for 2 h. Time-of-flight elastic recoil detection analysis (TOF-ERDA) using 34 MeV 127I ions as projectiles was utilized to study diffusion of implanted ions and impurity concentrations. All samples showed green PL. Those codoped with 18O and annealed at 600 ∘C showed enhanced PL intensity compared to only Cu implanted samples. 37Cl codoping shifted the peak maximum from 520 nm towards blue by 20 nm without decreasing intensity when annealed at 600 ∘C. In TOF-ERDA analysis, 18O was found to diffuse through the SrS/ATO interface, 37Cl evaporated mainly out and 63Cu remained inside the SrS film. The oxygen impurity concentration increased when samples were annealed at higher temperatures.

Fast-ion-induced surface tracks in bioorganic films

Surface tracks, induced by single grazing incidence 55 MeV 127I ions, incident on various bioorganic films, were studied by intermittent contact (tapping-mode) scanning force microscopy (SFM). Targets composed of biomolecules with different masses (10 2 − 10 5u) were employed. Surface tracks appeared as craters with raised rims and tails. In SFM, probe-tip-induced deformation of surface features under study is a possible complication, since it can lead to false imaging. In tapping-mode-SFM, larger amounts of tip oscillation attenuation with respect to the free amplitude imply greater tip-surface contact force. We found that reproducible track size results were obtained with a low attenuation (< 4%), and track dimensions on the various surfaces could be compared quantitatively. The crater lateral dimensions decreased with increased target molecular mass. For surfaces composed of large protein molecules the craters are smaller than the molecules, which implies an upper mass limit for the detection of intact proteins by PDMS. The measurements were compared with various sputtering model predictions. A pressure-pulse model calculation assuming extensive cluster ejection showed fair agreement with observed crater widths and lengths.

Simulation of surface roughness effects in ERDA

The program SURF has been developed to simulate surface roughness effects in elastic recoil detection analysis (ERDA). The Program calculates the recoil energy spectrum from a sample with a rough surface from a superposition of spectra, each corresponding to a subdivision of the beam spot. All parameters which influence the depth resolution are taken into account. The algorithm was tested successfully on well defined periodic structures which were produced by ion etching of Si. Recoil energy spectra measured with 200 MeV 127I ions of samples with random roughness exhibit two characteristic features: large broadening and lower yield in the high energy region. Both features are well reproduced in the simulated spectra, from which the variance of the statistical roughness can be deduced. The program can assist in the understanding of surface roughness effects, and enable such effects to be identified in concentration depth profiles.

Interdiffusion phenomena in SrBi2Ta2O9 films

Mass and Energy Dispersive Heavy Ion Recoil Spectrometry (RS) employing 75.6 MeV 127I ions has been used to analyse thin films of strontium bismuth tantalate (SBT) at the heavy ion recoil facility at ANSTO, Lucas Heights. The new ferroelectric material ‘Y1’, SrBi2Ta2O9 or SBT, has been developed for application in memory chips due to its excellent fatigue resistance. In other ferroelectric films developed for similar applications, e.g. BaxSr1−xTiO3 or BST1, there has been evidence of interdiffusion during the annealing process of the films. This study uses RS to determine the amount of interdiffusion in a standard treatment of SBT deposited on a Pt electrode on a Si substrate with a Ti adhesion layer. Depth profiles for all major elements and carbon have been obtained. Analysis reveals no depletion of oxygen in the SBT layer closest to the platinum electrode.

Surface defect formation on gypsum surfaces due to grazing incidence 78.2 MeV 127I ions: A comparative study employing tapping-mode scanning force microscopy and shadow-replica electron microscopy

We have performed, for the first time, comparative studies of surface tracks employing both tapping-mode scanning force microscopy (TM-SFM) and shadow-replica electron microscopy (SR-EM). The surface tracks, with dimensions of the order of 10 to 100 nm, were induced on gypsum by 78.2 MeV 127I ions impacting at surface-grazing angles of incidence. Using TM-SFM, finite probe-tip radius of curvature limited the available spatial resolution, and under some conditions, apparent deformation of the surface defects was observed, indicating that TM-SFM can be sensitive to surface properties besides topography. Rim-to-rim crater widths (perpendicular to the ion incidence azimuth) and overall lengths (parallel to the ion incidence azimuth) were measured equivalently by TM-SFM and SR-EM. However, the defect heights were somewhat overestimated by TM-SFM relative to SR-EM. Each surface track caused by an incident swift, heavy atomic ion is considered to represent the material response to an explosive vaporization process which cracks open the surface.

Limits in elastic recoil detection analysis with heavy ions

Severe alterations of the sample by the ion beam limits the detectable concentrations in elastic recoil detection analyses (ERDA). Therefore, sputtering and effusion yields were determined and an enhancement was found in comparison to collisional theory. The sputter yield ranges from 650 carbon atoms per incident 120 MeV 197Au ion to about 2500 for hydrogen of a hydrogenated polycrystalline c-BN layer for 60 MeV 58Ni ions, and up to several millions of CH x for organic materials using 60 MeV 127I ions. In addition plural scattering and secondary reactions limit sensitivity, especially when probing materials which mainly contain light elements. The actual limits in ERD with respect to depth resolution and sensitivity are discussed in terms of these principle effects and those induced by the used detection systems.

Composition analysis of Nd xFe yB thin films by RBS and heavy ion ERDA

Thin sputter deposited layers with a nominal composition of Nd 2Fe 14B (thickness 120 to 400 nm) on Si SiO 2 were analysed by the combined application of RBS and heavy ion ERDA. These methods, based on elastic Coulomb scattering, are advantageous for composition analysis of thin compound layers due to their known cross sections. For high accuracy it is necessary that the spectral contributions of each element can be separated from each other and from the substrate background. This is difficult for light elements with RBS. The light element concentration however can be measured by ERDA with heavy incident ions. With 200 MeV 127I ions from the Munich MP tandem the light elements as well as the Fe recoils were detected using a gas telescope. The Fe peak was used as cross reference to the RBS measurements. With 36 MeV 35Cl ions at the 5 MV Rossendorf tandem too little energy is transferred to the Fe recoils to be identified with the Bragg ionisation chamber (BIC) detector. Therefore a thin aluminium layer was evaporated onto the Nd 2Fe 14B layer. The aluminium peak is well separated both in the RBS and in the ERDA spectra and is used as cross reference here.

Latent (sub-surface) tracks in mica studied by tapping mode scanning force microscopy

This short communication presents information on the structure of latent (i.e subsurface) tracks in muscovite mica due to single 78.2 MeV 127I ions incident at an angle of 67° with respect to the surface normal. The latent tracks have been studied for the first time using tapping mode scanning force microscopy. Images of an underlying mica surface, exposed by cleaving after ion bombardment, displayed hillocks accompanied by raised tails. These features were significantly lower in height compared to similar features observed on the originally outermost mica surface. The inner back surface of the mica sheet cleaved away also displayed shallow hillocks with raised tails, but on that surface, the tails stretched in the opposite direction to those observed on the originally outermost mica surface. On both surfaces exposed by cleaving, the tail is located in close proximity to the latent ion track, showing a symmetry of expansion along the track. The present results provide more evidence for a permanent expansion occurring around each ion track, as described qualitatively by theoretical models.

Radiation damage features on mica and L-valine probed by scanning force microscopy

The radiation damage tracks on the surface of muscovite mica due to single 78.2 MeV 127I ions from the Uppsala EN tandem accelerator have been studied using tapping mode scanning force microscopy (TM-SFM). Conically-shaped hillocks having nearly circular bases were observed on a sample irradiated at normal incidence. Samples irradiated at grazing angles of incidence displayed wider and taller hillocks, and each hillock was accompanied by a raised tail over the bulk ion track. First SFM results are also presented from a study of radiation damage features on mica and single crystals of L-valine induced by single 23 MeV C 60 ions from the Orsay tandem accelerator. Brief comments are made on the scaling laws that could link results obtained with atomic and cluster ions.

Measurement of carbon contamination in barium strontium titanate films

Ferroelectric films are being developed for use in DRAMs. The films are often manufactured using spin-on techniques making contamination with residual carbon inevitable. The concentration of carbon is rarely known and its effect not understood. This paper describes the analysis of barium strontium titanate (BST) films for carbon content using both Mass and Energy Dispersive Recoil Spectrometry (RS) with 77 MeV 127I ions and Nuclear Reaction Analysis (NRA) using the 12( 3He,p 0) 14N reaction.

Stoichiometric analysis of a barium strontium titanate film by heavy ion recoil spectrometry

Abstract Heavy ion recoil spectrometry employing 77 and 98 MeV 127I ions has been used to analyse thin films of barium strontium titanate (BST) at the new heavy ion recoil facility at ANSTO, Lucas Heights. Depth profiles for all major elements and carbon have been obtained. Analysis reveals depletion of oxygen in the BST layer next to the platinum electrode and interdiffusion of strontium and oxygen through the layers.

Heavy ion recoil spectrometry of barium strontium titanate films

Thin films of barium strontium titanate have been analysed using heavy ion recoil spectrometry with 77 and 98 MeV 127I ions at the new heavy ion recoil facility at ANSTO, Lucas Heights. New calibration procedures have been developed for quantitative analysis. Energy spectra for each of the elements present reveal interdiffusion that was not previously known.

Mass and energy dispersive recoil spectrometry of SixGe1−x grown by electron beam evaporation

Mass and energy dispersive recoil spectrometry employing 77 MeV 127I ions from the recently commissioned ANTARES (FN Tandem) accelerator facility at Lucas Heights have been used to examine the isotopic composition of samples of SixGe1−x grown by Electron Beam Evaporation (EBE) at the Australian National University. Analysis of RBS spectra using yield simulations indicated the presence of an unobserved element. Oxygen was considered a likely contaminant for incorporation into the SixGe1−x layer by a reaction between Ge and residual oxygen in the EBE system. Determination of oxygen concentration and distribution is not normally possible with RBS but may be inferred from yield simulations using the code RUMP. Recoil spectrometry has shown the presence of oxygen in the SixGe1−x layer at lower concentrations than inferred from RBS and has enabled the determination of energy spectra for individual elements.

Electronic sputtering of fullerenes and the influence of primary ion charge state

Even-numbered positive ion carbon clusters, fullerenes ( C 2 n , n = 20, 21, …), are formed and ejected as a result of the interaction of swift atomic ions with a solid film of organic polymer — poly(vinylidene difluoride), PVDF. Studies of that phenomenon including the dependence of fullerene yield on the incident MeV ion's stopping power and initial radial velocity distributions of ejected ions, have been reported earlier [G. Brinkmalm et al., Chem. Phys. Lett. 191 (1992) 345; Phys. Rev. B 47 (1993) 7560]. In this paper, the dependence of the yield of the ejected cluster ions from PVDF as a function of the charge state of the incident MeV ion is reported. Swift 72.3 MeV 127I ions in charge states ranging from + 13 to + 25 from the Uppsala EN-tandem accelerator are used in the experiments, and the secondary ion yield is measured in a time-of-flight mass spectrometer, equipped with an electrostatic ion mirror. The results are compared to data for secondary ions, ejected by the same primary ions, from samples of synthetic fullerenes (C 60 and C 70). No dependence of the yield on the charge state of the incoming ion is observed for the high mass even-numbered carbon clusters from PVDF, while yields of C 60 and C 70 ions from synthetic fullerene targets show a weak charge state dependence. This finding indicates that excited polymer material from layers deeper than the MeV ion charge equilibration length in the solid contributes to the formation of ejected carbon cluster ions ejected from PVDF.