R. Szymanski

The new CSIRO-GEMOC nuclear microprobe: First results, performance and recent applications

Abstract A new nuclear microprobe (NMP) has been designed and built at the CSIRO featuring: (1) a quadrupole quintuplet lens system with a demagnification of 67 and 80 mm working distance; (2) a close detection geometry for Ge X-ray, 30% Ge γ-ray and particle detectors; (3) a high-quality normal-viewing microscope, coaxial with the beam; (4) computer-controlled beam-shaping and 5-axis sample stage; (5) scanning for imaging to > 5×2 mm 2 ; and (6) a vibration isolated mounting. Most design goals have been successfully achieved. On the first day of operation, a spot size of 1.3 μm was obtained at a beam current of 0.5 nA, suitable for fluid inclusion analysis and imaging. The spot size grows to just 1.8 μm at 8 nA (3 MeV protons) and 2 μm at 10 nA, despite the low brightness of our tandem accelerator ( 1.2 pA μm −2 mrad −2 MeV −1 ). This beam current is ideal for geological samples with PIXE detection limits down to 0.2 ppm (Br) achieved in silicates (39 ppb (Ge) in diamond at 22–25 nA) in quantitative, high resolution, trace element images.

Ion source brightness and nuclear microprobe applications

Abstract The ion source used to provide beams for nuclear microprobe systems must ideally satisfy several demands. Of primary importance is the beam brightness. It is clearly desirable to employ the brightest possible source in order to focus the smallest possible probe size on the specimen, with the highest possible beam current. Also important is the need for minimal maintenance, particularly for ion sources used inside single ended accelerators. We report here on measurements conducted on the beam from the RF ion source in our 5U Pelletron accelerator. We have found that the beam brightness is highly heterogenous, with the paraxial rays about an order of magnitude brighter than the surrounding rays. This is desirable for nuclear microprobe operation because probe forming lens systems optimised for large demagnification magnitude can exploit the high brightness of the paraxial region. We find several other accelerators around the world also exhibit this characteristic.

The Leipzig high-energy ion nanoprobe: A report on first results

Abstract The high-energy ion nanoprobe LIPSION at the University of Leipzig has been operational since October 1998. Its magnetic quadrupole lens system, arranged as a separated Russian quadruplet, has been developed by the Microanalytical Research Centre (MARC), Melbourne. The ultrastable single-ended 3.5 MV SINGLETRON™ accelerator (High Voltage Engineering Europa) supplies H+ and He+ ion beams with a beam brightness in the range of 10–20 A rad −2 m −2 eV −1 [D.J.W. Mous, R.G. Haitsma, T. Butz, R.-H. Flagmeyer, D. Lehmann, J. Vogt, Nucl. Instr. and Meth. B 130 (1997) 31]. Due to this high brightness, the excellent optical properties of the focusing system of the nanoprobe and the suppression of mechanical vibrations, lateral resolutions of 100 nm for the low current mode (STIM) and 340 nm at a current of 10 pA (PIXE, RBS, SEI modes) were achieved. Further improvements are expected.

The new Melbourne nuclear microprobe system

Abstract The spatial resolution in a nuclear microprobe system has been stalled at around 1 μm for many years. In Melbourne we are presently constructing a new facility which aims to break this barrier. The key ingredients of the new facility are: (i) a novel magnetic quadrupole lens quintuplet probe forming system that is a further optimised version of the CSIRO/MARC system presently in operation in Sydney, (ii) high solid angle detectors for particles, X-rays and secondary electrons and (iii) a fast data acquisition system able to cope with greater than 20 kHz count rates from up to four detectors with full deadtime correction. This paper describes the optimised probe forming lens system which is comprised of four thin lenses and one thick lens to produce an orthomorphic probe forming lens system with a demagnification of 150.

Filiform corrosion imaged beneath protection layers on Al alloys

Aluminium alloys used extensively in aircraft, ships and land transport vehicles are typically protected by a thin conversion coating based on chromium compounds followed by a surface protection layer of polymer paint. Breeching of the protection layer and exposure to a salt spray induces the growth of filiforms from the breech across the aluminium surface under the protective layers. The growth of the filiform is promoted by the formation of a galvanic cell based on chlorine chemistry. In this paper we study the elemental composition of the filiforms using a nuclear microprobe with 3 MeV proton beams. The deep penetration of this beam allows the composition of the intact filiform to be probed in situ through the surface layers. We present elemental maps of the intact filiforms that clearly highlight the presence of Cl in the growing end of the filiform, where the Cl concentration exceeds 20 wt.%, and the peculiar role of potassium in the trail of oxide left behind the growing filiform head.

The Amsterdam quintuplet nuclear microprobe

Abstract A new nuclear microprobe comprising of a quintuplet lens system is being constructed at the Ion Beam Facility of the “Vrije Universiteit” Amsterdam in collaboration with the Microanalytical Research Centre of the University of Melbourne. An overview of the Amsterdam set-up will be presented. Detailed characterisation of the individual lenses was performed with the grid shadow method using a 2000 mesh Cu grid mounted at a relative angle of 0.5° to the vertical lens line focus. The lenses were found to have very low parasitic aberrations equal or below the minimum detectable limit for the method, which was approximately 0.1% for the sextupole component and 0.2% for the octupole component. We present experimental and theoretical grid shadow patterns, showing results for all five lenses.

PIXE cluster analysis of ancient ceramics from North Syria

Abstract Tell Ahmar is a place situated on the east bank of the Euphrates river, near the Turkish border. The site was well known as a major trade centre in the Iron Age. From the many potsherds excavated from the site, it is necessary to distinguish pottery imported from outside from that made locally. Therefore a sample of the Iron Age potsherds that were excavated from this site was analyzed with particle induced X-ray emission to identify the characteristic composition of the different sherds. Potsherds from four other places near Tell Ahmar were also analyzed. The samples were irradiated with a scanned 3 MeV proton beam in the Melbourne nuclear microprobe. The composition of all sherds measured by this method was similar. However, cluster analysis of the 12 most abundant elements, ranging from Mn to Ba, revealed that the samples known to be from Tell Ahmar could be distinguished from those known to be from elsewhere.

Nuclear microprobe analysis of U-doped (Bi,Pb)2Sr2Ca2Cu3Oy/Ag superconducting tapes

Superconducting (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tapes are doped with uranium compounds to introduce flux pinning defects from neutron-induced fission. The composition and distribution of elements in cross sections of the tapes were probed with a scanned 3 MeV proton microbeam using proton induced X-ray emission (PIXE). Distributions of the constituent elements were found to be heterogeneous on a scale of 10 μm. By combining the PIXE analysis with Rutherford backscattering spectrometry, the stoichiometry of the superconductor within the tape was measured, including oxygen from elastic scattering, revealing a departure from the desired 2223 composition. In one of the tapes, PIXE elemental maps of the Ag distribution showed diffusion of Ag into the superconductor from the enclosing jacket. Crystals of the same material, not fabricated into tapes, did not contain the contaminants and had a more ideal stoichiometry. Correlation maps between the constituent elements, deduced from the elemental maps, indicate the presence of secondary or unreacted phases.

Few-layered graphene growth by carbon implantation into polycrystalline nickel substrate

Carbon ions were implanted into nickel films to facilitate growth of few-layered graphene. After vacuum annealing at 950 °C, G and 2D peaks were seen in micro-Raman measurements of the nickel film. No D peak, which is associated with sp3 adsorbates and vacancies/defects in graphene, was observed.

Crack Nucleation in ion Beam Irradiated Magnesium Oxide and Sapphire Crystals

Monocrystals of magnesium oxide and sapphire have been subjected to ion implantation with 86 keV Si − ions to a dose of 5×10 16 cm −2 and with 3 MeV H + ions with a dose of 4.8×10 17 cm −2 prior to thermal stress testing in a pulsed plasma. Fracture and deformation characteristics of the surface layer were measured in ion implanted and unimplanted samples using optical and scanning electron microscopy. Ion implantation is shown to modify the near-surface structure of samples by introducing damage, which makes crack nucleation easier under the applied stress. The effect of ion dose on the thermal stress resistance is investigated and the critical doses which produce a noticeable change in the stress resistance is determined for sapphire crystals implanted with 86 keV Si − . In comparison with 86 keV Si − ions the high energy implantation of sapphire and magnesium oxide crystals with 3 MeV H + ions results in the formation of large-scale defects, which produce a low density crack system and cause a considerable reduction in the resistance to damage. Fracture mechanics principles are applied to evaluate the size of the implantation-induced microcracks which are shown to be comparable with the ion range and the damage range in the crystals tested. Possible mechanisms of crack nucleation for a low and high energy ion implantation are discussed.