[en] A crucial step in the development of mechanically strong microstructures is the conversion of structures made from resist material of low hardness and strength, to harder and more durable metallic microstructures. The implementation of a post lithographic process step such as electroplating offers the possibility of producing metallic structures. In proton beam micromachining (PBM) a focused MeV beam is scanned in a predetermined pattern over a resist (e.g. PMMA or SU-8), which is subsequently chemically developed. The proton beam in resist follows an almost straight path, enabling the production of microstructures with well-defined rectangular side walls. If the resist layer is laid down with a thickness of typically 50% of the proton range on a conductive substrate, then the end of range straggling and resultant end of range beam broadening does not occur in the resist, but in the substrate. The conducting substrate acts as a seed layer for plating. In this current work, smooth well-defined metallic microstructures with a height of 10 μm are produced using electrolytic Ni plating. One spin-off application is that the plated Ni structures, which have excellent side wall definition, exhibit properties that are far superior to the current 2000 lines per inch gold grid resolution standard used by many nuclear microscopy groups worldwide

[en] Ionoluminescence (IL) performed with a nuclear microprobe is potentially a highly sensitive method for measuring optically active impurities and defects in diamonds. In this study, a Sumitomo synthetic diamond sample grown in the presence of a Ni catalyst is imaged with IL and particle induced X-ray emission (PIXE). Ni impurities incorporated during the growth are identified with IL spectroscopy, and shown to segregate into <1 1 1> growth sectors with IL imaging. This finding is consistent with previously published luminescence results. PIXE analysis performed on the same regions of the sample confirm the presence of Ni. PIXE and IL analyses are compared and used to show that the improved sensitivity of IL over PIXE is ideal for imaging such optically active impurities in diamonds

[en] The recent development of blue and green light emitting diodes (LED) based on single quantum well structures made from GaN and related materials (AlGaN, InGaN) has created large efforts to optimise the growth methods used in their production. Rutherford Backscattering (RBS), in combination with channeling analysis, is a powerful tool for the quantitative characterization of the depth profile and the crystallinity of such structures. New growth modes, e.g. lateral overgrowth processes, are being rapidly developed. Channeling contrast microscopy (CCM), which employs a focused ion beam in order to obtain laterally resolved channeling yield data, is ideally suited to determine micro structural characteristics, (e.g. defect densities, tilts in lattice planes, strain) of such samples. Here we report results from proton channeling contrast measurements of laterally overgrown GaN thin films. Such measurements require a sub-micron ion beam focus size as well as an highly stable accelerator system, both of which are available at the Research Centre for Nuclear Microscopy at the National University of Singapore, where an ultrastable Singletron accelerator was recently installed

[en] The effect of ion implantation on the nucleation of CVD diamond on silicon and diamond substrates has been investigated. The strategy employed is to create laterally confined regions of strain in the substrates by focused MeV implantation of light ions. Raman Microscopy has been employed to obtain spatially resolved maps of the strain in these implanted regions. On diamond substrates a homo-epitaxial CVD diamond film was grown on top of both the implanted and unimplanted regions of the substrate. Raman analysis of the film grown on top of the implanted region revealed it to be under slightly tensile strain as compared to that grown on the unimplanted diamond substrate. The film deposited on the implanted portion of the diamond showed a lower fluorescence background; indicating a lower concentration of incorporated defects. These results suggest that the strain and defects in the diamond substrate material have an important influence on the quality of the homo-epitaxially grown diamond films. 6 refs., 5 figs

[en] In this work, we introduce the use of ionoluminescence (IL) with ion beam induced secondary electron (IBISE) imaging to correlate the surface topography and crystal faces with luminescence properties. Since both IL and IBISE require low beam currents of <1 pA, simultaneous analysis can be performed. The newly installed system for light and electron detection in the NUS micro-beam facility is described. The performance of the present setup is demonstrated with high-resolution IL and IBISE images collected on Al-doped (1 1 1) c-BN and undoped (1 0 0) c-BN under 2 MeV proton irradiation. Results show that blue luminescence of Al-doped c-BN appears as triangular patterns and they tend to be associated with triangular voids on the surface. This work demonstrates the importance of combined IL and IBISE for characterizing wide band gap semiconductors

[en] The characterisation of the band structure properties of materials and devices by ion microprobe techniques has been made possible at the Melbourne MeV ion microprobe facility with the development of Ion Beam Induced Luminescence (IBIL). A number of diamond films grown by Microwave Plasma Chemical Vapour Deposition (MPCVD) on silicon substrates are analysed. A preliminary study of the luminescence properties of these samples has revealed information not previously obtainable via traditional microprobe techniques. The optical effects of incorporating dopants during the deposition process is determined using IBIL. The presence of trace element impurities introduced during growth is examined by Particle Induced X-ray Emission (PIXE), and a measurement of the film thickness is made using Rutherford Backscattering Spectrometry (RBS). 7 refs., 2 figs

[en] Proton beam micro-machining (PBM) is a direct write lithographic technique that utilizes a high energy (MeV) sub-micron focused proton beam to machine or modify a material, usually a polymer. The technique has been developed in recent years at the Research Centre for Nuclear Microscopy, National University of Singapore where structures with feature sizes of well below 1 μm have recently been demonstrated. The PBM technique has several desirable features that make it suitable for rapid prototyping of micro-optical components. Structures made using PBM have very smooth side walls, high aspect ratio, and a scale that can be easily matched to existing optical fiber technology (0.1-1000 μm). Furthermore, PBM can also be used to modify the optical properties of polymers, particularly if the end of range is used. In this paper we demonstrate the use of proton beam micro-machining and modification for manufacturing micro-optical components in positive and negative resist. The structures that are fabricated can be used for both rapid prototyping and for large scale replication

[en] The quest for smaller spot sizes has long been the goal of many nuclear microprobe groups worldwide, and consequently there is a need for good quality resolution standards. Such standards have to be consistent with the accurate measurement of state-of-the-art nuclear microbeam spot sizes, i.e. 400 nm for high current applications such as Rutherford backscattering spectrometry and proton-induced X-ray emission, and 100 nm for low current applications such as scanning transmission ion microscopy or ion beam-induced charge. The criteria for constructing a good quality nuclear microprobe resolution standard is therefore demanding: the standard has to be three dimensional with a smooth surface, have an edge definition better than the state-of-the-art beam spot resolutions, and exhibit vertical side walls. Proton beam micromachining (PBM) is a new technique of high potential for the manufacture of precise 3D microstructures. Recent developments have shown that metallic microstructures (nickel and copper) can be formed from these microshapes. Prototype nickel PBM resolution standards have been manufactured at the Research Centre for Nuclear Microscopy, NUS and these new standards are far superior to the 2000 mesh gold grids currently in use by many groups in terms of surface smoothness, vertical walls and edge definition. Results of beam resolution tests using the new PBM standards with the OM2000 microprobe end station/HVEE Singletron system have yielded spot sizes of 290 nmx450 nm for a 50 pA beam of 2 MeV protons

[en] Ionoluminescence (IL) combined with particle induced X-ray emission (PIXE) imaging has been employed to identify intrinsic growth bands in the spire region, and extrinsic bands at the growth edge of Australian Black-lip abalone shell (Haliotis rubra). Previous studies using optical flood cathodoluminescence, scanning electron microscope cathodoluminescence (SEM-CL) and Raman spectroscopy on samples from the same population suggest that the visible luminescence is due to Mn²⁺ activated calcium carbonate. In this study we confirm Mn²⁺ as the activator in both the spire and growth edge regions of the shell. The sensitivity of ionoluminescence to the co-ordination environment of the Mn²⁺ activators in the shell allows for the spatial identification of the calcium carbonate polymorph responsible for the growth lines observed optically. Furthermore the detection and mapping of trace elements such as Mn and Sr with the PIXE technique enables comparisons to be made between calcite and aragonite biomineralized in the wild and under laboratory conditions

[en] High resolution (<1 μm) channeling contrast microscopy (CCM) is employed to map variations of crystallographic orientation across micron-sized regions of lateral epitaxial overgrown (LEO) GaN thin film structures. The sample consists of 6 μm thick GaN stripes, aligned along the [1 1-bar 0 0]_GaN direction, grown by LEO from 3 μm wide Si₃N₄ windows spaced 13 μm apart. Axial CCM using 2 MeV He⁺ is employed to investigate the crystalline structure of the LEO GaN layer. A low χ_min of ∼2.8% and a critical angle ψ_1/2 of ∼0.85 deg. is found, comparable with data obtained from broad beam channeling [J. Portmann, C. Huag, R. Benn, T. Frey, B. Schottker, D.J. As, Nucl. Instr. and Meth. B 155 (1999) 489]. 5 μm wide bands of high and low yield at a periodicity of 13 μm are observed in the CCM maps. This contrast is due to the opposing tilts of the [0 0 0 1] axis in the overgrown regions (the so-called wings) on either side of the window regions. From angular scan curves this tilt is found to be ±0.45 deg. in the direction perpendicular to the GaN stripes and no measurable wing tilt is found along the stripe direction