Ion Microbeam Research Articles

Status of ion microbeam facility at the Institute of Physics, Bhubaneswar, India

An ion microbeam facility has been set up at one of the beam lines of the 3 MV tandem Pelletron accelerator facility at IOP, Bhubaneswar. This is the first facility of its kind in India, having potential applications in the growing fields involving semiconductors, materials science, biology, archeology and environmental science, from both scientific and industrial points of view. So far we have achieved a spatial resolution of ∼3 μm with a beam current of about 80 pA using a 3 MeV He + beam. A brief description of various components along with the experimental setup is given. As first applications of this microprobe, elemental maps, obtained by RBS measurements on epitaxial gold silicide islands grown on Si(1 1 0) surfaces, and results of mass transport in ion beam interaction with a Ag(1 1 1) epitaxial layer are presented.

Development of an automated single cell irradiation system combined with a high-energy heavy ion microbeam system

An automated single cell recognition and irradiation system has been developed at a high-energy heavy ion microbeam. The system has been installed on a vertical beam line of the JAERI Takasaki AVF-cyclotron accelerator to irradiate individual biological cells in an air environment with energies of more than 10 MeV/u by single ions. The system consists of high-precision stages, optical microscopes with CCD camera, a computer network and software packages to obtain positional data from a cluster of individual samples randomly placed on a holder before irradiation and to irradiate them with individual ions according to the obtained data. This paper will describe the new systems, and show results from irradiation experiments for CR-39.

ERDA with an external helium ion micro-beam: Advantages and potential applications

Preliminary ERDA experiments at atmospheric pressure have been performed with our external microprobe set-up currently used for the analysis of museum objects by PIXE, RBS and NRA. The objective was to check the feasibility of hydrogen (and deuterium) profiling with an external beam of 3-MeV helium ions. The standard scattering geometry (incident beam at 15° with respect to sample surface and emerging protons or deuterons at 15° in the forward direction) was kept, but the thin foil absorber was replaced by helium gas filling the space between the beam spot and the detector over a distance of about 84 mm. Several standards prepared by ion implantation, with well known H or D depth profiles, were first analysed, which indicated that the analytical capability was as good as under vacuum. A striking feature is the much lower surface peak than under vacuum, a fact that enhances the sensitivity for H analysis near the surface. The same type of measurement was then performed on different materials to show the usefulness of the technique. As a first example, we have checked that the incorporation of H or D into sapphire crystals during mechanical polishing is below the detection limit. Another example is the measurement of the H content in emeralds which can be used as an additional compositional criterion for determining the provenance of emeralds set in museum jewels. The advantages and limitations of our set-up are discussed and several possible applications in the field of cultural heritage are described.

Light detection with spectral analysis at the Legnaro nuclear microprobe: Applications in material and earth sciences

Among the numerous ion beam analytical (IBA) techniques available for material characterisation, ionoluminescence (IL) has not attracted the interest that it should deserve. Although the importance of IL technique, particularly if combined with other IBA techniques, has been widely proven, very few apparatuses to analyse light emission spectra have been installed at the microbeam facilities. In this paper we present the new IL apparatus installed at the Legnaro (LNL) Ion Microbeam Facility. The system is a modification of the OXFORD MONOCL2 apparatus for cathodoluminescence. Light collection is performed by using a retractable parabolic mirror located at a very short distance from the sample, with a small aperture to allow the ion beam to hit the sample. Accurate positioning of the retractable mirror directly coupled to a chamber mounted high-resolution monochromator allows for high light collection efficiency. This design assures that IL can be used with low beam currents (<1 pA) with the consequent reduction of the radiation damage, which often occurs during ionoluminescence measurements. A summary of some meaningful results obtained with such an apparatus is presented. The combination of IL/PIXE was used to characterise natural silica glass, known as Libyan Desert Glass, and cubic BN grains; polycristalline CVD diamond has been studied by a synergetic combination of IBICC/IL technique.

The Investigation of Charge Transport Properties of SOI Semiconductor Devices Using a Heavy Ion Microbeam

The Investigation of Charge Transport Properties of SOI Semiconductor Devices Using a Heavy Ion Microbeam

Investigation of the electronic properties of cadmium zinc telluride (CZT) detectors using a nuclear microprobe

The electronic transport properties of Cadmium Zinc Telluride (CZT) determine the charge collection efficiency (i.e. the signal quality) of CZT detectors. These properties vary on both macroscopic and microscopic scales and depend on the presence of impurities and defects introduced during the crystal growth. Ion Beam Induced Charge Collection (IBICC) is a proven albeit relatively new method to measure the charge collection efficiency. Using an ion microbeam, the charge collection efficiency can be mapped with submicron resolution, and the map of electronic properties (such as drift length) can be calculated from the measurement. A more sophisticated version of IBICC, the Time Resolved IBICC (TRIBICC) allows us to determine the mobility and the lifetime of the charge carriers by recording and analyzing the transient waveform of the detector signal. Furthermore, lateral IBICC and TRIBICC can provide information about how the charge collection efficiency depends on the depth where the charge carriers are generated. This allows one to deduce information on the distribution of the electric field and transport properties of the charge carriers along the detector axis. IBICC and TRIBICC were used at the Sandia microbeam facility to image electronic properties of several CZT detectors. From the lateral TRIBICC measurement the electron and hole drift length profiles were calculated.

Study of proton irradiation induced CVD diamond priming by lateral micro-ion beam induced charge technique

Lateral micro-ion beam induced charge (IBIC) is a powerful method to characterize the electrical behavior of chemical vapor deposition (CVD) diamond thin film and further to evaluate its quality. In the process of IBIC data handling, a new model that the product of mobility and lifetime linearly increases from substrate side to growth side was proposed in order to separately analyze the carriers’ contributions to charge collection efficiency. IBIC results shows that CVD diamond was primed by irradiation of 46 Gy proton dose with a 82.4% increase of average collection distance due to the space charge elimination inside the CVD diamond after irradiation.

Profiling of collimated swift ion microbeam using 16 M bit DRAM

High-energy heavy-ion microbeams are useful for studying single-event phenomena(SEP) in semiconductor devices. However, current SEP research is concentrating on higher energies provided by cyclotrons. Focusing such high-energy beams is extremely difficult so we have taken the approach of using microcollimator to form a highly collimated beam which can then be positioned accurately on the device under test. In order to measure the beam profiles produced by such a system, we have employed a 16 Mbit DRAM (dynamic random access memory) to measure both the occurrence of a single-event upset and its spatial location. Using the DRAM method, 150 MeV 40Ar 8+ beams collimated to 100 μm have been characterized. The results indicate that high integrated memory devices can replace a position-sensitive detector (PSD) and provide an even higher spatial resolution.

Studies of single-event transient current induced in GaAs and Si diodes by energetic heavy ions

To investigate the tolerance of single-event upset (SEU) for GaAs devices, we have measured the transient currents induced in GaAs diodes by energetic heavy particles such as 15 MeV oxygen ions. The measurements were made by combining a focused ion microbeam and a wide-bandwidth current-pulse measurement system. The resulting transients were found to be markedly different to those measured in Si diodes. This result can be mostly attributed to a difference in the carrier drift velocities between GaAs and Si. The amount of collected charge in GaAs diodes was also found to be less than that in Si diodes with similar device properties. This fact strongly suggests that GaAs devices have a higher SEU tolerance than Si devices.

Single-event upset and snapback in silicon-on-insulator devices and integrated circuits

The characteristics of ion-induced charge collection and single-event upset are studied in silicon-on-insulator (SOI) transistors and circuits with various body tie structures. Impact ionization effects, including single-event snapback, are shown to be very important. Focused ion microbeam experiments are used to find single-event snapback drain voltage thresholds in n-channel SOI transistors as a function of device width. Three-dimensional device simulations are used to determine single-event upset and snapback thresholds in SOI SRAMs, and to study design tradeoffs for various body-tie structures. A window of vulnerability to single-event snapback is shown to exist below the single-event upset threshold. The presence of single-event snapback in commercial SOI SRAMs is confirmed through broadbeam ion testing, and implications for hardness assurance testing of SOI integrated circuits are discussed.

Microanalysis of Light Elements by Means of a Nuclear Microprobe: Application to Boron Compounds

The nuclear microanalysis is an elemental analysis technique based on the use of the atomic and nuclear interactions of a light ion microbeam with the sample to be analyzed. Both light particles and photons (X, γ) are detected. The determination of the local stoichiometry of boron-based compounds is possible with the use of nuclear reactions. Boron and carbon mapping of YPd-based borocarbides is presented. Additional possibilities of in-depth carbon profiling are also reported.

Self-assembled gold silicide wires on bromine-passivated Si(110) surfaces

Thin Au films (∼45 nm) deposited by thermal evaporation under high vacuum on bromine-passivated Si(110) substrates, upon annealing showed the formation of long gold silicide wire-like islands on top of a thin uniform layer of gold silicide in a self-assembled Stranski–Krastanov growth process. Optical micrographs showed long, straight and narrow islands with aspect ratios as large as 200:1. Scanning electron microscopy images revealed the presence of facets. The islands are aligned along the [1̄10] direction on the Si(110) surface. Rutherford backscattering spectrometry measurements with an ion microbeam identified the islands to possess varying thickness across a single island as one would expect for islands having facets and also showed the uniform silicide layer over the Si substrate to be very thin (∼1.5 nm). The observed alignment of the gold silicide islands on the Si(110) surface has been explained in terms of the lattice mismatch between gold–silicide and silicon and invoking the theory of shape transition in heteroepitaxial growth. We have observed islands as long as 200 μm and as narrow as 100 nm in this nonultrahigh vacuum growth on chemically passivated Si(110) surfaces. The method, with properly optimized parameters, may provide a way to grow quantum wires.

A Novel Micro-Structured Reference Material for Ion and X-Ray Microbeam Analysis

In order to determine the beam spot size and the linear or raster scanning properties of microprobe analytical systems, a novel reference material has been developed by IRMM, consisting of permalloy (81% Ni, 19% Fe) strip patterns of different widths on a silicon substrate. The general layout of this micro-structured reference material with pattern sizes ranging from 2 to 100 μm, fabricated with production schemes of microelectronics circuitry on silicon wafers, is discussed. The large size range of the individual pattern structures makes the material equally applicable to very fine and less focused microbeams. Due to the choice of substrate and pattern materials, these samples exhibit a high elemental contrast suitable for analysis with X-ray and electron detection and with ion scattering techniques. First chips of this material were investigated with both X-ray tube based as well as synchrotron radiation based X-ray microprobes with capillary optics. Due to the very good definition of the metal lines and their edge profiles (0.5 μm high, shape irregularities and undulations < 0.1 μm) line scan results of for example XRF can be directly converted to spot size and microbeam profile.

Sputtering and thermal effect during ion microbeam patterning of polymeric films

The purpose of this article is to investigate the machinability of polymers and the main parameters involved during ion microbeam processing of polymers. Investigations were made for the case of ion microbeam patterning of polyethyleneterephthalate and nylon-6 using a focused ion beam system with a needle type ion source. The extracted beam diameter was 0.2 μm, the current density on the target was 1.0 A/cm2, and the beam energy was 30 keV. The removal rate, which shows the number of atoms removed when an ion impinges on the surface, was obtained experimentally. By comparing the removal rate and the theoretical sputtering yield, it became clear that effects other than sputtering have a great influence on the machinability of polymers. Two-dimensional unsteady heat conduction equations were computed using the finite difference method in order to estimate the temperature increment within and around the beam irradiated area. The results show that localized heating and a change of chemical bonding state during ion microbeam processing strongly influence the patterning of polymers.

DEVELOPMENT OF IN-AIR MICRO-PIXE ANALYSIS AND DATA SHARING SYSTEMS IN JAERI TAKASAKI

An external scanning ion microbeam system has been developed for in-air micro-PIXE analysis at JAERI Takasaki. The analysis system is widely used for various researches in recent years. The system consists of the external scanning ion microbeam system, a multi-parameter data acquisition system, a file transfer protocol (FTP) server and analysis software. The software of the system provides a graphical user interface for interaction between users and an experimental setup. The server is connected to the Internet and allows remote users to access the experimental data.

An external ion microbeam for studies of biological samples.

A new external ion-beam system was developed and combined with a light ion-microbeam system in JAERI Takasaki. The system is designed for micro-particle-induced X-ray emission analysis of biological samples in air environment with 1 micron spatial resolution. One of the most serious problems in keeping such a high spatial resolution is multiple scattering in a beam exit window. Thin Kapton film (7.5 microns thick) was adopted as the exit window as well as a sample backing foil to minimize the distance between the film and samples. The lifetime of the foil under ion irradiation and spatial resolution of the external microbeam were investigated. The results shows that the film can endure sufficient long-time irradiation to take elemental maps and the resolution can be kept nearly 1 micron.

High-energy resolution PIXE study of heat induced changes in cadmium compounds using ion microbeam

The intensity changes of the satellite X-ray line spectra can be related to the changes in the chemical environment of atoms in the sample. High-energy resolution PIXE analysis of chemical effects in X-ray spectra of Cd L lines was applied in studies of heat-treated CdS and CdTe cadmium compounds. The applicability of the method for monitoring crystal phases and chemical states in these and other materials using ion microbeam with high energy resolution PIXE spectrometer is discussed.

Single ion hitting to living samples

Single ion hit system for living biological samples has been designed. An external scanning microbeam system with about 1 μm spatial resolution, a fast beam chopping system with less than 5 ns and a thin plastic scintillator based transmission-type detection system are combined together at the JAERI light ion microbeam system. The first step to develop a single ion facility was completed in this work. The next steps to verify the reliability of the total system have been started.

Ion microbeam studies of cadmium zinc telluride radiation detectors by IBICC

Ion beam induced charge collection (IBICC) and time resolved IBICC (TRIBICC) techniques were used for imaging electronic properties of cadmium zinc telluride (CZT) room temperature radiation detectors. The detectors were bombarded with a scanned 5.4 MeV He microbeam and the detector response was analyzed at each point. The electron mobility (μe) and lifetime (τe), and charge collection efficiency maps were calculated from the data. In order to determine the radiation damage to the detectors, the signal deterioration was measured as the function of dose.

Application of an ion microbeam to the study of multiphase borocarbides

The multiphase YPd5B3C0.35 borocarbide shows the highest superconducting transition temperature (Tc∼23 K) ever observed for an intermetallic compound. Micrographs of as cast sample reveal the presence of 6 phases of various shapes (thin needles, small spherical inclusions,...) whose dimensions range from a few microns to a few tens of microns. The determination of the phase compositions, especially the boron and carbon concentrations, poses difficulties for most analytical techniques. This paper presents results from the use of 3He and 2H microbeams for the stoichiometric characterization of YPd5B3C0.35. Combination of RBS and NRA allows complete determination of the composition of the different phases, however with some limitations on the probed depth. Comparison is presented with similar measurements by means of an electron microprobe. Another example is shown in the Ho–Ni–B–C system, whose physical properties are known to be sensitive to the carbon content.