Microbeam line with 1.5 MeV helium ions and protons at Osaka

A microprobe for Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE) measurements has been realized by focusing 1.5 MeV helium-ion or proton beams with a demagnification system consisting of piezo-driven objective slits and a magnetic quadrupole doublet. Minimum beam spot sizes of 1.3 × 2.2 μm² for helium ions and 2.2 × 4.0 μm² for protons have been achieved. The factors which may limit the minimum spot size are discussed using a Monte Carlo simulation procedure. Rutherford backscattering image mapping of 3-dimensional structures is demonstrated.     

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl₂, K₂Cr₂O₇, and NaAsO₂. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.     

Study of basic mechanisms of semiconductor devices using ion beam induced charge (IBIC) collection

A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 μm width and 10 μm length as a function of the ion incident position. Three pn junctions were made on a 3 μm thick Si epilayer (1 × 10¹⁶/cm³) grown on Si substrate and were in a line along an aluminum electrode with 10 μm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a 1 μm diameter 15 MeV C⁺ heavy ion microbeam spacing steps by 3 μm. At a bias voltage of − 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 μm and 4 μm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He⁺ ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.     

Research of Si and GaAs diode structures by Ion Beam Induced Charge (IBIC) collection

A Si pn junction diode and a GaAs Schottky diode were prepared for studying the basic mechanism of charge collection followed by high energy charged particle incidence in order to improve the resistance against single event upset. A 2 μm wide and 20 μm long rectangular Al electrode attached to a circular Al electrode with a 50 μm diameter was made on a 2.5 μm thick epilayer (minority carrier density 2 × 10¹⁵ /cm³). Both a Schottky electrode of Al (5 μm × 110 μm) and two ohmic electrodes of AuGe/Ni (110 μm × 110 μm) were made on a 2 μm thick epilayer (7.3 × 10¹⁵ /cm³) grown on a semi insulator GaAs substrate (1 × 10⁷ Ω cm). The internal device structure was examined by the IBIC (Ion Beam Induced Charge) method using a 2 MeV He⁺ ion microbeam. IBIC images clearly show an Al electrode, the SiO₂, and an epilayer. These results were then used to improve the qualities of the test diodes.     

The nuclear microprobe at the University of Arizona

A nuclear microprobe has been operational at the University of Arizona since early 1994. It utilizes a magnetic quadrupole doublet (model QL-300 from Microscope Associates, Inc.) with an 11 mm diameter aperture and lens lengths of 6 cm each. The magnetic pole tips are electrically insulated to enable electric rotational alignment and beam rastering by application of varying voltages to the pole tips. Ion beams are obtained from a 5.5 MV model CN, High Voltage Engineering Corp. Van de Graaff accelerator with a Penning type ion source. Present mininum beam spot size is about 2 μm obtained with a 4 MeV H₂⁺ beam with a current of about 40 pA. To date, the instrument has been successfully used to map concentrations of Hg, Cr, and As in rabbit renal slices using PIXE.     

A scanning positron microscope for defect analysis in materials science

The realisation of a scanning positron microscope will be presented and discussed. A positron beam with a variable energy from 0.5 to 30 keV, with a spot diameter of 1 μm or below, can be scanned over an area of 0.6 × 0.6 mm². This beam is formed after a double stage stochastic cooling (moderation) of positrons emitted from a radioactive isotope. In addition the positron beam will be pulsed in order to have a well-defined time base for positron lifetime measurements. In the system included is a conventional scanning electron microprobe for surface analysis. The design of the scanning positron microscope is dominated by the special demands of positron physics.     

Nuclear mubeams: Realization and use as scientific tool

A nuclear mubeam is an ion beam focussed down to a spot of only a few μm in diameter. If such a beam is surrounded by equipment for elemental analysis we have the nuclear muprobe (NMP) suited for elemental analysis with μm spatial resolution and detection limits of a few ppm. The beam focus is achieved by collimation to some 10 μm and further demagnification with the help of an appropriate lens system. The need to fabricate the mechanical parts to a very high precision and to avoid slit scattering at the collimators will be demonstrated and a guide to the optimal design will be given. The different ways of realization are illustrated. Applications in different fields of science are given and the availability of NMPs throughout the world illustrated.     

Microbeam RBS on flat panel displays

We have demonstrated the utility of microbeam-Rutherford BackScattering (μ-RBS) in spatially resolved studies of operational plasma effects on the interior surfaces of plasma flat panel displays manufactured by Photonics Imaging. The experiments were performed at the Sandia Nuclear microprobe using a 2.8 MeV He beam with an average beam spot size of less than 8 μm. The interior surface of the top panes of the flat panels is composed of approximately 800 nm of MgO on top of a 2000 nm thick PbO layer. μ-RBS of sample panels operated under varying conditions measured changes in the surface MgO film thickness due to plasma erosion and redeposition as accurately as ± 1.5 nm. The high accuracy in the MgO thickness measurement was achieved by inferring the MgO thickness from the shift of the Pb front edge in the RBS spectrum. An estimate for the thickness accuracy as a function of the acquired statistics is presented. The surface of the flat panels' bottom panes is also comprised of MgO on top of PbO. However, troughs 100 μm wide by 10 μm deep were partially filled with phosphor and cover the entire width of the surface. This leaves only 100 μm long sections of MgO within the trough exposed. Using μ-RBS, we were able to analyze the surface composition of these regions.     

The performance of the Ljubljana ion microprobe

In August 2000 the setup of the Ljubljana ion microprobe, based on OM 150 triplet, has been completed. The beam line is installed at the 10° exit port of the 2 MeV Tandetron accelerator. It is equipped with motor driven slits, a precise five-axis goniometer and a spherically shaped measuring chamber with detectors for PIXE, PIGE, PESA, SE and RBS. In order to understand the beam optics along the complete system, consisting of the tandem accelerator and the beam line optical elements, an interactive computer code, based on a linear approximation, has been developed. The program is used both to determine the optimal parameters of the tandem focusing system in its daily use and to develop new beam line configurations. Test measurements performed on a copper grid yielded a spatial resolution of 1.0×1.5 μm² in the high current mode (30–100 pA) and 0.5×0.9 μm² in low current mode (10⁴ counts/s). First analytical results confirmed excellent performance of the new Ljubljana ion microprobe.     

Annealing effects of helium implanted single crystals and polycrystalline magnesium aluminate spinel

The effects of transmutation produced -particles and the thermal behaviour of the incorporated helium is simulated by 900 keV ³He ion implantations at 2 μm depth in (100) surface oriented single crystals and in polycrystalline samples. Thermal Helium Desorption Spectrometry (THDS) and Neutron Depth Profiling (NDP) have been applied to study the release rate of helium and changes in the depth profile, respectively, during isothermal annealing. Release of the helium took place in at least two stages in a wide temperature interval ranging from 600 to 1600 K. For polycrystalline spinel an additional high temperature release stage at T> 1300 K was ascribed to trapping in pores. For the high dose implanted single crystals mainly helium release in bursts was observed due to thermally induced flaking.     

Electron microscopy and Rutherford backscattering spectrometry characterisation of 6H SiC samples implanted with He

6H SiC single crystals were implanted at room temperature with 1 MeV He⁺ up to a fluence of 2 × 10¹⁷ at./cm². RBS-channeling analysis with a 2 MeV He⁺ beam indicated the formation of extended defects or the generation of point defects at a constant concentration over a depth of about 1 μm. Electron microscopy characterisation revealed the presence of two amorphous buried layers at depths of about 1.75 and 4.8 μm. They are due to the implantation and to the analysing RBS beam, respectively. No extended planar or linear faults were found in the region between the surface and the first amorphous layer. However, at the surface, a 50 nm thick amorphous layer was observed in which crystalline inclusions were embedded. Electron diffraction and HREM data of the inclusions were typical for diamond. These inclusions were even found in the crystalline SiC material below this layer, however at a reduced density.     

Micro-PIXE analyses of trace elements in black shales from the Lower Zechstein copper deposits, Poland

Micro-PIXE analyses made, using the Heidelberg proton microprobe, of thucholite-like organic matter and noble metals bearing shale matrices from the Lower Zechstein copper deposits of the Fore-Sudetic Monocline (Poland) are reported. The experimental conditions included a proton microbeam with a beam spot of ˜ 3 × 3 μm, 3 MeV proton energy and a 195 μm thick external Al absorber. Quantitative results and the detection limits for various elements are reported.     

The interaction of iron with molten uranium

The rate of penetration of Armco iron by molten uranium, U-34 at % Fe eutectic and U-77 at % Fe eutectic was investigated in the range of 740 to 1300° C. This was done in an effort to understand the mode of penetration of uranium-base fuels through iron-base claddings. The phenomenon of particular interest was a penetration rate reversal, i.e. decreasing rate with increasing temperature, between 1150 and 1244° C.

Penetration rates at 1150° C were found to be 760 μm/sec in uranium, 690 μm/sec in U-34 at % Fe and 5.5 μm/sec in U-77 at % Fe. At 1244° C these rates changed to 150 μm/sec in uranium, 130 μm/sec in U-34 at % Fe and 5.7 μm/sec in U-77 at % Fe. The study showed that the penetration rate is related to the rate and mode of formation of UFe₂. The rate changes correlate well with the phases of the U-Fe equilibrium diagram.     

Suitable test structures for submicron ion beam analysis

For the precise determination of the sizes of submicron beam spots test structures with an excellent edge definition are required. For this purpose a semiconductor heterostructure consisting of an 1.62 μm GaInP epi-layer grown on (0 0 1) GaAs has been made, which provides atomically sharp edges for beam spot size measurements. Since the sample has been thinned down by standard transmission electron microscope (TEM) preparation techniques, it can be used for both PIXE and STIM. The sample has been investigated with a TEM and the ion nanoprobe LIPSION. A one-dimensional beam profile in the low current mode was determined by a STIM measurement using 2 MeV protons and yielded a FWHM of (41±4) nm, which is the smallest value reported so far for high energy nuclear micro- and nanoprobes. Furthermore we present nickel nanowhiskers produced at the GSI Darmstadt by electrochemical preparation of etched ion track membranes that have been used to obtain two-dimensional images of the shapes of submicron beam spots. For these measurements a scan over a single nickel nanowhisker having a diameter of 220 nm and a height of about 6 μm was performed.     

Helium retention of vanadium alloy after energetic helium ion irradiation

Helium irradiation experiments of V–4Ti alloy were conducted in an ECR ion irradiation apparatus by using helium ions with energy of 5 keV. The ion fluence was in the range from 1 × 10¹⁷ He/cm² to 8 × 10¹⁷ He/cm². After the helium ion irradiation, the helium retention was examined by using a technique of thermal desorption spectroscopy (TDS). After the irradiation, the blisters with a size of about 0.1 μm were observed at the surface, and the blister density increased with the ion fluence. Two desorption peaks were observed at approximately 500 and 1200 K in the thermal desorption spectrum. When the ion fluence was low, the retained helium desorbed mainly at the higher temperature regime. As increase of the ion fluence, the desorption at the lower temperature peak increased and the retained amount of helium saturated. The saturated amount was approximately 2.5 × 10¹⁷ He/cm². This value was comparable with those of the other plasma facing materials such as graphite.     

Measurement of the H2-D mass difference with a nuclear microprobe

A 1.24 MeV deuteron (D) beam mixed with a H₂ molecular beam was separated with a microslit system of a nuclear microprobe consisting of a 100 μm diameter object and a 1 mm diameter aperture diaphragm. D was distinguished from H₂ by Rutherford backscattering (RBS) on a thin Au film. By slightly changing the magnetic field strength of the beam steerer installed in front of the object diaphragm, the maximum and the minimum RBS D/H₂ ratios were found to be 50.3 and 1.5, respectively. M/ΔM = 3.9 × 10³ was obtained as the mass resolution of the nuclear microprobe. The transmission of this system was 2 × 10⁻³.     

Corrosion of steels with surface treatment and Al-alloying by GESA exposed in lead–bismuth

Corrosion tests were performed for T91, E911 and ODS (oxide dispersion strengthened) with surface treatment and Al-alloying by pulsed electron beam (GESA—GepulsteElektronenStrahlAnlage) in flowing lead bismuth eutectic (LBE) with an oxygen content of 10⁻⁶ wt% at 550 °C for 2000 h. The result was that the surface treatment by GESA led to a faster growing multiphase oxide layer which was very homogenous in thickness. After exposure of specimens to LBE, the average oxide layer at the surface was 14–15 μm thick for ODS, 19–20 μm for E911 and 8–22 μm for T91. No dissolution attack occurred. On the surface of the Al-alloyed specimens, thin protective alumina layers were observed at the places where FeAl was formed by the GESA process, otherwise multiphase oxide layers or corrosion attack were observed.     

Analysis of metallic pigments by ion microbeam

Metallic paints consist of metallic flakes dispersed in a resinous binder, i.e. a light-element polymer matrix. The spatial distribution and orientation of metallic flakes inside the matrix determines the covering efficiency of the paint, glossiness, and its angular-dependent properties such as lightness flop or color flop (two-tone). Such coatings are extensively used for a functional (i.e. security) as well as decorative purpose. The ion microbeam analysis of two types of silver paint with imbedded metallic flakes has been performed to determine the spatial distribution of the aluminum flakes in paint layer. The average sizes of the aluminum flakes were 23 μm (size distribution 10–37) and 49 μm (size distribution 34–75), respectively. The proton beam with the size of 2×2 μm² at Ljubljana ion microprobe has been used to scan the surface of the pigments. PIXE mapping of Al K map shows lateral distribution of the aluminum flakes, whereas the RBS slicing method reveals tomograms of the flakes in uppermost 7 μm of the pigment layer. The series of point analysis aligned over the single flake reveal the flake angle in respect to the polymer matrix surface. The angular sensitivity is well below 1 angular degree.     

Aerosol composition and source apportionment in Santiago de Chile

Santiago de Chile, São Paulo and Mexico City are Latin American urban areas that suffer from heavy air pollution. In order to study air pollution in Santiago area, an aerosol source apportionment study was designed to measure ambient aerosol composition and size distribution for two downtown sampling sites in Santiago. The aerosol monitoring stations were operated in Gotuzo and Las Condes during July and August 1996. The study employed stacked filter units (SFU) for aerosol sampling, collecting fine mode aerosol (dp<2 μm) and coarse mode aerosol (210 mass of particles smaller than 10 μm) and black carbon concentration were also measured. Particle-Induced X-ray Emission (PIXE) was used to measure the concentration of 22 trace elements at levels below 0.5 ng m⁻³. Quantitative aerosol source apportionment was performed using Absolute Principal Factor Analysis (APFA). Very high aerosol concentrations were observed (up to 400 μg/m³ PM₁₀). The main aerosol particle sources in Santiago are resuspended soil dust and traffic emissions. Coarse particles account for 63% of PM₁₀ aerosol in Gotuzo and 53% in Las Condes. A major part of this component is resuspended soil dust. In the fine fraction, resuspended soil dust accounts for 15% of fine mass, and the aerosols associated with transportation activities account for a high 64% of the fine particle mass. Sulfate particle is an important component of the aerosol in Santiago, mainly originating from gas-to-particle conversion from SO₂. In the Gotuzo site, sulfates are the highest aerosol component, accounting for 64.5% of fine mass. Direct traffic emissions are generally mixed with resuspended soil dust. It is difficult to separate the two components, because the soil dust in downtown Santiago is contaminated with Pb, Br, Cl, and other heavy metals that are also tracers for traffic emissions. Residual oil combustion is observed, with the presence of V, S and Ni. An aerosol components from industrial emissions is also present, with the presence of several heavy metals such as Zn, Cu and others. A factor with molybdenum, arsenic, copper and sulfur was observed frequently, and it results from emissions of copper smelters.