Improved high energy microbeam techniques

The University at Albany ion scanning microprobe has been used for many industrial applications in thin films. Of prime importance for rapid analysis, the beam should be set-up and in-use very shortly after the beam is turned on. Rapid optical and electronic tune-up methods are discussed. Standard 1–2 micron, 2 MeV helium or proton beams are generally used with RBS (Rutherford Backscattering) and PIXE (Particle Induced X-ray Emission) to obtain composition analysis in one- or two-dimensions. We demonstrate the use of 3-dimensional analysis in thin films, wherein film thickness is the third dimension.     

High energy resolution PIXE with high efficiency using the heavy ion microbeam

An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E < 6 MeV) with reasonable detection efficiency. The design of the spectrometer, such as detection geometry, detectable energy range and energy resolution, are described. This system was applied to high energy resolution PIXE analysis of Ti, SUS and Si with 2 MeV proton and 5 MeV Si³⁺ focused or collimated beams. The best energy resolution was 2 eV for the Si K line.     

Fabrication of nanowires by varying energy microbeam lithography using heavy ions at the TIARA

In TIARA facility of Japan Atomic Energy Agency (JAEA) Takasaki, we have produced three-dimensional micro/nano-structures with high aspect ratio using cross linking process based on negative resist such as SU-8 by a technique of mask less ion beam lithography. By bombarding high energy heavy ions such as 450 MeV Xe²³⁺ to SU-8, on the other hand, it appeared that a nanowire could be produced just with a single ion hitting. Then we tried to produce nanowires, of which both ends were fixed in the three-dimensional structure. This paper shows a preliminary experiment for this purpose using a combination of 15 MeV Ni⁴⁺ ion microbeam patterning and the 450 MeV ¹²⁹Xe²³⁺ hitting on SU-8.     

Detectors for microbeam applications at medium ion energy

Nuclear microprobes with excellent lateral resolution can be realized using a liquid metal ion source and electrostatic einzel lens system in a few hundred keV energy range. In case of ion beam analysis it is better to provide a special detector for Rutherford Backscattering (RBS) analysis or elastic recoil detection. Good mass and depth resolutions should be attained while keeping the damage caused by the beam at tolerable level. Two solutions are considered in the present work: (1) toroidal electrostatic analyzer combined with simultaneous Time-of-Flight (TOF) measurement for mass identification; (2) TOF measurement only, using a large area microchannel plate. Both solutions can be combined with 2D position sensitive anode plates for excellent performance. In case of the first solution, it is possible to distinguish the different mass atoms by the scattering angle where their peak in the angular distribution appears. Similarly to the energy distribution at a fixed scattering angle the angular distribution at a fixed energy represents mass and depth distribution. In case of the second solution the huge acceptance angle will make it possible to analyze submicron spot size without serious beam effects and both heavy and light elements can be investigated.     

3D mapping of individual cells using a proton microbeam

Various imaging techniques carried out with a nuclear microprobe make it possible to reveal by 2D mapping, the internal structure of isolated cells. An improvement of those techniques allows today 3D mapping of cells. STIM- and PIXE-Tomography have been recently implemented on the CENBG microbeam line. The performance offered by these methods, which are capable of resolving objects having diameters less then 100 μm, has been validated on reference specimens and on human cells from cultures. In addition to the fineness of the resolution, these techniques offer the advantage of performing volume analyses without prior cutting of the samples. The ultimate aim of this program of research is to perform 3D elemental chemical analysis of individual cells in the field of biomedicine.     

Development of a real-time beam current monitoring system for microbeam scanning-PIXE analysis using a ceramic channel electron multiplier

Microbeam scanning-PIXE (micro-PIXE) analysis is a useful method for obtaining information of multi-elemental distribution in samples by two-dimensional images of sample surfaces such as mammalian cells, tissues, and other environmental monitoring species. In addition to elemental distribution information, quantitative analysis is in demand for further investigations of environmental and biomedical studies concerning heavy metals accumulated in terms of cells and sub-cellular organelles. To make quantitative analysis possible, a real-time beam monitoring system that gives a precise number of ions, and an output independent from a sample that enables one to keep a beam resolution of micrometer size is required. In this paper, we report on the development of beam current monitoring. The beam current was monitored using a ceramic channel electron multiplier (CEM) to detect secondary electrons induced from a 50 nm thick carbon film (10 μg/cm²). This carbon film was attached to a sample holder, which was set at the targeted sample position. The output value of the CEM was proportional to the Faraday cup installed just after the sample position. The beam resolution was measured using off-axis STIM by scanning a copper grid, and was estimated at 1.79 and 1.72 μm for the horizontal and vertical directions, respectively, sufficient for routine micro-PIXE analysis.     

A heavy-ion acceleration system using a low energy Van de Graaff

A system has been developed for heavy-ion irradiation using a 4.75 MV single-ended horizontal Van de Graaff. The present paper describes the development of two PIG ion sources, a beam energy analyzing and a transport system. The facility has been utilized for H(¹⁵N, αγ)¹²C hydrogen depth profiling and Ne surface bombardment studies. Examples of experimental results are discussed.     

Scanning RBS-PIXE study of ancient artifacts from South America using a microbeam

Pre-Hispanic goldsmiths developed original techniques to manufacture and to gild ornaments and artifacts. Gold metallurgy in ancient America was mainly a surface technology. Surface studies of artifacts from various regions of pre-Hispanic South America were carried out using a 2 MeV proton microbeam (10 μm diameter). Several regions of the artifacts were scanned: RBS and PIXE were used simultaneously to determine the elemental composition and to characterize the homogeneity in depth and at the surface. Complementary information is provided from previous analyses using a macrobeam. Outstanding aspects about the metallurgical processes involved in the gilding of the artifacts have been established.     

Photon production using a low energy electron expansion of the EGS4 code system

An expansion of the EGS4 code system has been developed in which electron-atom inelastic collisions are modelled taking into account atomic bound effects. Additional models have been developed to deal with the ionisation of the K-shell and improved angular sampling of newly created bremsstrahlung photons. The incorporation of these features in EGS4 is described and the updated code is used to simulate photon generation in X-ray tubes. The accuracy of the new code and some of its possible applications are discussed.     

Synthesis of carbon-nitride films using a fast-switched dual-source low energy ion beam deposition system

Thin C_xN_y films were deposited in UHV using alternating low energy ion beams of C⁺ and N⁺ or N₂⁺ in the energy range of 5 to 100 eV. The ion beam deposition system is equipped with two Freeman ion sources, mass analysis and fast automated beam switching, allowing perpendicular bombardment of the target with a single ion beam at a time. The composition and density of the films were studied by ARS (in situ), XPS and RBS. The dependence of the film properties and growth mechanisms on ion energy, beam switching rate, and C-to-N arrival ratio have been investigated. The influence of the deposition parameters on the film stoichiometry is discussed. Exposure of the film to atmosphere leads to oxygen incorporation, resulting in a lowered surface concentration of nitrogen. The XPS N 1s and C Is binding energies vary in a relatively broad range indicating that several bond states may be present. The influence of the substrate material on film growth has also been studied. On Si{100}, film growth commences with the formation of an interfacial silicon nitride. No film growth was observed on gold, however deposition was possible on tantalum and molybdenum.     

Depth resolution calculations for heavy-ion microbeam RBS analysis

A detailed study has been made on the use of MeV heavy ions (Z₁ = 6–8) for microbeam Rutherford backscattering (RBS) analysis, to improve the depth resolution of this technique. The algorithm for determination of the depth resolution was created and applied to the Zagreb microbeam facility. Theoretical estimates of depth resolution for C and O ion RBS analysis of thin oxide films and semiconductors, using annular silicon surface barrier detector (SSBD), are compared to those for proton backscattering analysis. Depth resolution in certain cases may be improved by increasing the heavy-ion energy. Therefore, by the proper choice of the heavy ion and the heavy-ion energy, the depth resolution may be improved, maintaining the efficiency of the RBS method.     

Optimization of aluminum thickness for absorption of undesired Ti K X-rays in the measurement of low energy brachytherapy source strength

The contribution of Ti K X-rays to total air kerma strength for low energy brachytherapy sources (¹²⁵I and ¹⁰³Pd) are calculated for different source-to-aperture distances of an indigenously designed free air ionization chamber. For 30 cm source-to-aperture distance, calculated contribution of Ti K X-rays is 4%. The Ti K X-rays can be eliminated by a relatively thin aluminum filter, but the primary photons emitted by the source will also be attenuated. This effect should be compensated by applying a suitable correction factor. The uncertainty in the attenuation correction factor has been also calculated for different thicknesses of aluminum by a Monte Carlo uncertainty analysis algorithm programmed in FORTRAN. The results show that the optimum thickness of the aluminum absorber is 100 μm, for which the contribution of Ti K X-rays in air kerma strength is reduced to less than one hundredth of the uncertainty in the correction factor, ensuring that the uncertainty in the air kerma strength will be mainly due to the uncertainty in the correction factor. The calculated uncertainties are 1.7 × 10^?3, and 3.4 × 10^?3 for ¹²⁵I and ¹⁰³Pd sources, respectively.     

Design of a low energy positron beam

A low energy positron beam apparatus has been designed and constructed. Experimental details are presented and the performance characteristics are described.     

Slit scattering in a microbeam set-up

Slit scattering of beam particles in a microbeam set-up becomes significant for low current applications and thus limits its lateral resolution and application potential. In this work, the angular and energy distributions of beam particles interacting with cylindrically shaped slit-jaws of different radii, surface roughnesses, and materials are calculated numerically, employing the computer code SRIM. To quantitatively investigate their effect on the beam spot quality of a microbeam set-up, a quality factor is proposed as an index to evaluate the effect of slit-scattered particles on the beam spot. The results of the investigation reveal a high sensitivity of slit scattering in relation to the slit-jaw surface roughness.     

Time Resolved Ion Beam Induced Current measurements on MOS capacitors using a cyclotron microbeam

As overlayers on electronic devices become progressively thicker, radiation effects microscopy using traditional microbeams (with ion energies up to a few tens of MeVs) is becoming less and less viable. To penetrate to the sensitive regions of these devices, much higher energies, several hundreds of MeVs are necessary. These high energies are available only from cyclotrons. A nuclear microprobe has been developed on the AVF cyclotron of the Takasaki Ion Accelerators for Advanced Radiation Applications (TIARA) facility. In this paper we will present the first results using 260 MeV Ne and 520 MeV Ar microbeams to perform Time Resolved Ion Beam Induced Current (TRIBIC) measurements on Metal-Oxide-Semiconductor (MOS) capacitors. The results will be compared to data taken with a traditional 15 MeV O microbeam.     

Simulation of a low energy beam transport line

A 2.45 GHz electron cyclotron resonance intense proton source and a low energy beam transport line with dual-Glaser lens were designed and fabricated by Institute of Modern Physics for a compact pulsed hadron source at Tsinghua. The intense proton beams extracted from the ion source are transported through the transport line to match the downstream radio frequency quadrupole accelerator. Particle-in-cell code BEAMPATH was used to carry out the beam transport simulations and optimize the magnetic field structures of the transport line. Emittance growth due to space charge and spherical aberrations of the Glaser lens were studied in both theory and simulation. The results show that narrow beam has smaller aberrations and better beam quality through the transport line. To better match the radio frequency quadrupole accelerator, a shorter transport line is desired with sufficient space charge neutralization.     

Advances in elemental imaging of rocks using the AGLAE external microbeam

Rocks are widely represented in cultural heritage materials. They constitute the major part of archaeological artefacts like stone carvings, tools and weapons, and are present in art works in various forms, such as precious stone inlays or paint pigments. The study of such geomaterials, which are usually constituted of a complex aggregate of mineral phases, aims at determining their exact nature, their provenance and at understanding their possible alteration. Since minerals are often composed of light elements, IBA techniques such as PIXE and PIGE, thanks to their ability to measure with high sensitivity elements down to lithium, should be well adapted to their analysis. However, the bulk composition classically obtained using macro-IBA on pelletized samples or using a broad beam hides the multi-phased nature of the rocks and considerably blurs the searched chemical fingerprint. In contrast, the small size of a nuclear microprobe allows imaging the chemical composition at a finer scale and, when implemented in air, appears ideally suited to analyse without sampling these often precious items. This paper illustrates chemical micro-imaging of rocks with examples performed with the AGLAE external nuclear microprobe: characterisation of microscopic inclusions in gems and detailed chemical mapping of rocks with special emphasis to lapis lazuli. Lapis lazuli is of particular interest in both archaeology and art history: after being employed in Asia since the 7th millennium BC to make carvings and beads, it was used in Medieval Europe as a precious blue painting pigment known as ultramarine. The chemical imaging of major and trace elements in lapis lazuli using external μ-PIXE has permitted to identify its mineral phases, to assign their trace elements and to evidence undetected elements. In combination with μ-XRD and μ-Raman spectrometry, this approach provides a clear mineralogical fingerprint useful to determine rock provenance and to authenticate artefacts of unknown origin. These encouraging results call for the generalization of this non-destructive approach to the study of other heterogeneous materials in art and archaeology.     

Thin film analysis by low energy proton induced X-ray emission

A 100 keV proton beam has been used for measuring the thickness of thin films from the proton energy loss determined by using the energy dependence of the yield of X-rays emitted from a gold backing.Comparison between the proposed method and Rutherford backscattering is shown for erosion, thermal interdiffusion or ion beam mixing experiments with carbon and aluminum-gold films.     

Mass thickness measurements for dual-component samples utilizing equivalent energy of X-rays

In this paper,equivalent energy method is introduced for measuring mass thickness of dual-component samples using dual-energy X-rays.Approximately,the method adopts equivalent mass attenuation coefficients of the two components in mass thickness measurements for dual-component samples,in a certain range of thicknesses.Feasibility of the method is proven by numerical calculations and Monte Carlo simulations（EGSnrc package）.The results of absorption experiments using an X-ray machine at tube voltages of 30 and 45 kV,the relative errors are less than 5%between the nominal and detected values.Also,optical low energy is discussed at given high voltages.