B. Rout

Ion-beam-induced-charge characterisation of particle detectors

Abstract Ion-beam-induced-charge collection (IBIC) in a nuclear microprobe has been used to characterise detectors for the measurement of particles over a median energy range (100 keV–1 MeV). Three standard detector devices have been studied: a PIPS detector with a buried (ion-implanted) junction structure, a Schottky barrier junction device and a PN-junction photodiode. A 2.0 MeV focussed helium ion beam was used to probe the active area of each device with a spatial resolution ∼1–2 μm, to quantify the thickness of the dead layer, the charge collection response and the reduction in charge collection efficiency induced by ion-beam damage.

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.

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.

An investigation of the native oxide of aluminum alloy 7475-T7651 using XPS, AES, TEM, EELS, GDOES and RBS

The native oxide on the rolled aerospace aluminum alloy 7475-T7651 was characterized using a variety of different techniques, including X-ray Photoelectron Spectrometry (XPS), Auger Electron Spectrometry (AES), Transmission Electron Microscopy (TEM), Electron Energy Loss Spectrometry (EELS), Glow Discharge Optical Emission Spectrometry (GDOES), and Rutherford Backscattered Spectrometry (RBS). All techniques revealed that the native oxide layer is magnesium-rich and is probably a mixture of magnesium and aluminum–magnesium oxides.1 The oxide layer was found to be of nonuniform thickness due to the rolling process involved during the manufacture of this sheet alloy; this complicates analysis using techniques which have poor spatial resolution. Direct thickness measurement from cross-sectional TEM reveals an oxide thickness which varies between 125 and 500 nm. This large variation in thickness was also evident from GDOES and AES depth profiles as well asthe RBS data. Both XPS and RBS also show evidence for the presence of heavy metals in the oxide.

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.

Nanoscale fabrication using single-ion impacts

We describe a novel technique for the fabrication of nanoscale structures, based on the development of localized chemical modification caused in a polymethylmethacrylate (PMMA) resist by the implantation of single ions. The implantation of 4 MeV He ions through a thin layer of PMMA into an underlying silicon substrate causes latent damage in the resist. On development of the resist we demonstrate the formation within the PMMA layer of clearly defined etched holes, of typical diameter 30 nm, observed using an atomic force microscope employing a carbon nanotube SPM probe in intermittent-contact mode. This technique has significant potential applications. Used purely to register the passage of an ion, it may be a useful verification of the impact sites in an ion-beam modification process operating at the single-ion level. Furthermore, making use of the hole in the PMMA layer to perform subsequent fabrication steps, it may be applied to the fabrication of self-aligned structures in which surface features are fabricated directly above regions of an underlying substrate that are locally doped by the implanted ion. Our primary interest in single-ion resists relates to the development of a solid-state quantum computer based on an array of31P atoms (which act as qubits) embedded with nanoscale precision in a silicon matrix (Kane B E 1998 Nature 393 133?7). One proposal for the fabrication of such an array is by phosphorus-ion implantation. A single-ion resist would permit an accurate verification of31P implantation sites. Subsequent metallization of the latent damage may allow the fabrication of self-aligned metal gates above buried phosphorus atoms.

Thin film resists for registration of single-ion impacts

We demonstrate registration of the location of the impact site of single ions using a thin film polymethyl methacrylate resist on a SiO2/Si substrate. Carbon nanotube-based atomic force microscopy is used to reveal craters in the surface of chemically developed films, consistent with the development of latent damage induced by single-ion impacts. The responses of thin PMMA films to the implantation of He+ and Ga+ ions indicate the role of electronic and nuclear energy loss mechanisms at the single-ion level.

Phase correlations of elemental maps using nuclear microscopy

In complex multi-elemental samples it is often necessary to determine the presence of various chemical phases. More complexity arises if it is also necessary to determine the spatial distribution of these phases. Here we present a new technique, based on the elemental maps, for the study of the phase distribution of multi-elemental samples. This technique uses the elemental maps obtained with nuclear microscopy to extract the spatially distributed phase information. We will explain the basic technique of phase correlation mapping, and then provide simulated and experimental results to demonstrate its capability in materials analysis. The simulations show the effect of the beam spatial resolution on the correlation maps and the experimental results show the phase correlation maps of elements in an array of phosphors from a video tube.

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.

Ion beam implantation for fabrication of periodic structures in optical fibres

Ion beam implantation using 2.4 MeV H+ ions was used to fabricate long period gratings in multimode optical fibres. The Bragg peak from the ion beam was located in the centre of the core of the fiber. The ion beam was implanted through a mask on the fibre with a period of 1.1 mm to produce a periodic a refractive index modulation, of up to 1%, along the axis of the core of the fibre. The mode scrambling, from the established fundamental mode, was monitored in situ as the implantation was done by observation of the light transmitted through the fibre. This paper describes the experimental method used to achieve this and describes the results. Significant mode scrambling was observed to occur when 3 grating periods were written into the fibre.