MeV Ion Beam Research Articles

Mev Ion Beam Induced Index of Refraction Changes in Layered GaAs/AlGaAs Waveguides

AbstractPreviously, we showed that localized optical modifications could be produced without subsequent post thermal annealing in selectively masked planar GaAs/Al 4Ga6As waveguide structures using 10 MeV oxygen ions. In our present investigation, irradiation experiments were performed on masked GaAs/Al 4Ga6As waveguide samples at 298 K using 10 MeV oxygen and 8 MeV carbon ions. The two ion incident energies were chosen to yield the maximum electronic stopping power near the interface septing the top cladding layer and the guiding layer. This localized modification process emphasizes the crucial role that the electronic energy transfer plays on the degree to which the refractive index of the guiding layer is altered. Propagation loss measurements on the fabricated channel waveguides were performed by end fire coupling a laser diode source at a wavelength of 1.3 μm. Observation of the extracted propagation loss values reveal that further optimization of the ion beam pmeters are required before practical applications can be achieved. The relative efficiency of the various ions to induce optically altered regions which serve as lateral confinement barriers of laser light shows that this fabrication process is sensitive to the ion beam current.

Quantitative analysis of films by ion microbeam methods. I: RBS, NRA, and channeling

The aim of this review paper is to illustrate the application of the so-called nuclear techniques, i.e. MeV ion beam techniques, to the analysis of thin solid films. First a brief description of the basic interaction processes between an energetic ion and solid matter is given in order to clarify the fundamental basis of the different techniques. Then the main features and an application overview of Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and channeling are presented.

Persistent room-temperature relaxation of InP amorphized and compacted by MeV ion beams

Ion beam induced deformation and compaction has been observed in InP, amorphized by MeV Se ion implantation. The initial density of amorphous InP is 0.55%±0.05% larger than that of crystalline InP. During a period of two months, most of the excess density is lost in a spontaneous, room-temperature relaxation. This relaxation can be described by two time constants: τ1≊8±2 h and τ2≊14±1 days.

Modification of the carbon and beryllium walls in JET by erosion, redeposition and deuterium trapping after the 1991 discharge period

After plasma operation in 1991 samples were cut from C and Be tiles of the JET vessel walls, limiters, and X-point tiles along a poloidal cross section in octant 4W, and the surface layers were analysed by the MeV ion beam methods NRA, PIXE, and RBS to determine the D and metal impurity distributions. The amount of trapped deuterium ranges from 5 × 10 15 to 5 × 10 17 D/cm 2, metal impurities such as Ni, Cr, and Fe are in the range of 10 15 to 3 × 10 16/cm 2, Cl in the range of 10 16 to 10 18/cm 2, K and Ca in the range of 10 15 to 10 16/cm 2 and Ti about 10 15/cm 2. Except for Cl, all measured concentrations are a factor of up to about ten lower than those observed on JET walls tiles before Be evaporation and Be wall components were used. This observation is in agreement with the reduced impurity concentrations measured in the JET plasma. The D and impurity distributions along the X-point tiles were analysed in some detail. Generally, the deuterium trapping and impurity deposition show minima in areas where erosion dominates and amounts a factor of about ten larger in between.

Chemical modification of PMMA by MeV and GeV, light and heavy, ion irradiations

Chemical modification of the polymers polymethylmethacrylate (PMMA) and polyimide (PI) irradiated with MeV and GeV ion beams has been studied using infrared absorption spectroscopy. Whilst at GeV energies heavy ion irradiation results in a greatly enhanced production of aromatic compounds, at lower energies destructive chemical mechanisms dominate. There are indications of an energy threshold value corresponding to the required energy density transferred, above which molecular construction surpasses destruction processes. The formation of ring structures in organic solids at high transferred electronic energy densities may be an early step in a growth chain reaction similar to that which gives rise to fullerene creation along high energy ion tracks in materials very rich in carbon.

MeV ion processing applications for industry

Ions beams with MeV energies produce a variety of interactions with matter, broadly classified as either electronic or nuclear. These interactions in turn lead to changes in the properties of the matter which may be beneficial or detrimental. In high technology industry, use is increasingly made of ion beam technologies to process novel materials. Typical applications include high energy implantation, in which the deposition of a specific element at depth within the structure of material is the required objective, and irradiation modification, in which the balance between the beneficial and the detrimental effects of the fast ion interactions is exploited. The basic principles behind MeV ion processing are described. Broad areas of application in industrial materials include effects in ion beam analysis, Thin Layer Activation for wear and corrosion measurement, carrier lifetime control in electronic devices, and the simulation of radiation damage effects in, for example, solar cells for spacecraft. New development areas are described in which subtle but potentially significant changes in the chemistry of surfaces and interfaces may be generated by exposure to MeV ion beams.

Ion beam induced luminescence from diamond and other crystals from a nuclear microbeam

Analysis of the luminescence induced by a MeV ion beam offers the potential to provide useful information about the chemical properties of atoms in crystals to complement the information provided by more traditional Ion Beam Analysis (IBA) such as Rutherford Backscattering Spectrometry (RBS), ion channeling and Particle Induced X-ray Emission (PIXE). Furthermore, the large penetration depth of the MeV ion beam offers several advantages over the relatively shallow penetration of keV electrons typically employed in cathodoluminescence. We have developed an Ion Beam Induced Luminescence (IBIL) detection system for the Melbourne microprobe that allows the spatial mapping of the luminescence signal along with the signals from RBS and PIXE. Homoepitaxial diamond growth has been studied and remarkable shifts in the characteristic blue luminescence of diamond towards the green were observed in the overgrowth. This has been tentatively identified as being due to transition metal inclusions in the epitaxial layers. We have also found IBIL to be useful in the study of damage produced by the analysis beam, since the intensity of the luminescence signal is very sensitive to the ion beam dose in diamond and other crystals.

Acceleration of high current heavy ions using a variable energy radio-frequency quadrupole linac and measurement of the input beam emittance

A high current ion beam injection system and a variable energy radio-frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four-rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time-averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time-averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high-dose implantation and high throughput production of semiconductor devices and material surface modifications.

MeV metal ion implantations for buried layer fabrication in silicon

A review is given of MeV ion beam synthesis of deep-buried compound layers in silicon with special emphasis on the formation of buried metal silicide layers. The formation of buried NiSi 2 layers by 6 MeV Ni high dose implantation and annealing is described in detail. The evolution of Ni concentration profiles, the dose-dependent interaction of implanted metal atoms and radiation damage, and the formation of the silicide phase are treated up to overstoichiometric doses. Layer formation during the anneal is described for both pure Ni implanted (111)Si wafers and for Ni irradiated Si/Si 3N 4/(100)Si silicon-on-insulator structures, leading to heteroepitaxial Si/NiSi 2/Si systems and to Si/Si 3N 4/Si/NiSi 2/Si multilayer sequences, respectively. The latter experiments possibly imply a new application of MeV implantations for the formation of buried layers.

Controlled Formation of Buried Layers of Carbon

ABSTRACTPartially cured and cured PF-resin samples were prepared at 150°C, 170°C and at 200°C in an inert environment and then bombarded by MeV ion beams using protons, alphas and nitrogen. Using low ion beam current density, 100 to 500 pA/mm2 for the nitrogen ions, 10 to 20 nA/mm2 for the alpha ions, and 50 to 500 nA/mm2 for protons, we have produced buried carbon layers without breakdown i.e., crack formation. The thicknesses of the carbon layers produced were of the order of a few tens of nanometers at a depth of a few nanometers to several micrometers depending on the energy, the type of bombarding ions and the curing temperature of the precursor. The electrical resistivity of these layers was measured in situ and was reduced from 109 Ω-cm to 10 Ω-cm. The lowest resistivity, 10 Ω-cm, was measured in the alpha bombarded, 150°C heat-treated resin. The carbonized volumes were analyzed by Raman microprobe spectroscopy which showed that the strongest graphitic (G-line) and distorted (D-line) Raman signals observed were from the nitrogen and alpha irradiated samples.

Fabrication of Optical Channel Waveguides in the GaAs/AlGaAs System by Mev Ion Beam Bombardment

AbstractWe have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3x1013 and 3x1014 ions/cm2. Although disordering of GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors' knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 μm.

Applying MeV Ion Beam Techniques to Geochemical Issues: Cross-Fertilizing Nuclear Physics and Geosciences

Applying MeV Ion Beam Techniques to Geochemical Issues: Cross-Fertilizing Nuclear Physics and Geosciences

Spinning-wire dosimetry for ion-beam analysis of materials

A novel spinning-wire dosimetry system has been developed for the MeV ion beams normally used in ion-beam analyses of materials. The system consists of a spinning wire that crosses the beam axis before the specimen, a surface barrier detector with externally selectable collimating apertures, and a retractable Faraday cup located behind the retractable specimen holder. The surface barrier detector provides energy spectroscopy of the ions backscattered from the spinning wire as it passes through the ion-beam axis. A high-energy segment of the backscattered spectrum is counted in a single-channel analyzer and calibrated against a simultaneous measurement of the integrated beam current using the Faraday cup. For MeV He + ions with currents of 2–200 nA, the present system has been shown to provide counts that are proportional to the integrated currents with a precision of 1%.

On the effect of beam spatial broadening in ion microtomography (IMT) image quality

Ion microtomography (IMT) is a quantitative MeV ion beam technique capable of mapping spatial variations in specimen density. IMT images are obtained from ion energy loss measurements using computed tomography methods. Multiple scattering of individual ions results in cumulative small directional changes that can ultimately lead to significant spatial broadening of the focussed microbeam. Quantitative studies on the effect of beam spatial broadening on IMT image quality have not previously been performed and current reconstruction methods ignore this effect when computing cross-sectional density images. In this work, the effect of beam spatial broadening on IMT image quality is examined and an algorithm that partially corrects for it is described for specimens with suitable composition. The algorithm is initially tested by considering a single slice of a simulated test object in which spatial broadening out of the plane of the slice is neglected. This approximation has a negligible effect on the corrected image quality in this case since the test object geometry is taken to be identical over neighbouring slices. The correction algorithm is then applied to measured data collected from a single slice of a specimen having similar properties as the test object. Comparisons between the measured and simulated data show qualitative agreement. Results with spatial broadening corrections are presented for contiguous multi-slice data of other samples. It is shown that beam spatial broadening can have an appreciable effect on IMT image quality.

The 6 MV Pelletron at Stuttgart - an Accelerator for Ions, Positrons and Electrons

A 6 MV Pelletron accelerator has been installed at the Max-Planck-Institut fur Metallforschung in Stuttgart/Busnau during the last few years. It is used for the production of MeV ion beams and-as a novelty-also of a positron beam for solid state investigations. An upgrading of the accelerator with an electron beam for low temperature (1.8 K) electron irradiations is in progress. After a short introduction and a description of the accelerator facility the paper surveys the experiments which were performed with the ion and positron beams of this accelerator since its installation in Stuttgart. Selected examples are presented for either characteristic or novel applications in more detail

Study of nuclear microprobe beam halo using IBIC

There are many factors which can give rise to a halo around a focused MeV ion beam, and a method of detecting the distribution and determining the amount of beam current in the halo will help to assess its effect on spatial resolution. This paper describes how the technique IBIC (ion beam induced charge) can be used as an extremely sensitive method of imaging and quantifying the beam halo around focused 3 MeV proton beam current of 200 pA and 0.3 fA. It is also shown how the momentum of the beam fraction in the halo can be calculated from its spatial extent in the IBIC images.

MeV ion beam lithography of PMMA

X-ray lithography mask contrast is limited by the thickness of the patterned absorber layer. This is limited by the need to use thin resist layers to maintain the high spatial resolution when fabricated using electron beam lithography (EBL) because electron scattering severely limits the minimum achievable linewidth in thick samples. A MeV proton beam suffers much less lateral scattering than a keV electron beam so higher resolutions should be possible in thick resist layers. This paper presents experimental results showing a 2.0 μm wide channel etched through ∼ 10 μm of PMMA (polymethyl methacrylate) using a focused 3 MeV proton beam. Simulations demonstrating that the minimum attainable linewidths for 3 MeV protons are ∼ 120 nm through 10 μm of PMMA are also presented.

A comparison between the use of MeV ion beams and synchrotron radiation for element analysis

In this contribution, a comparison is made between the use of ion beams of several MeV and synchrotron radiation of tens of keV for the analysis and characterization of a variety of samples. Included in the comparison are the use of beams in the total reflection mode. Also mentioned are additional techniques with both kinds of incoming beams to extract more information from the samples. Such techniques include nuclear reactions of various kinds, elastic and inelastic scattering with ion beams and the study of near edge structures such as XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) with synchrotron radiation. These latter methods aim at obtaining chemical information from the elements present in the samples.

Radiation damage and flux pinning in high temperature superconductors

Radiation damage and flux pinning of high temperature superconducting (HTS) materials were studied with MeV ion beams and internal MeV ion irradiation by thermal neutron triggered reaction products. The materials used included epitaxial thin film of YBCO, melt-textured YBCO and single crystal YBCO. The flux pinning was measured by a vibrating sample magnetometer (VSM). The pinning mechanism in each material was radiation-induced weak pinning centers, resulting in an enhancement of critical surrent density ( J c ) by a factor of 6 and 18 in single crystal and melt-textured YBCO, respectively. Details of neutron-triggered internal irradiation and its possible application to bulk materials are discussed. The defect structure was observed with transmission electron microscopy (TEM) and compared with TRIM simulations.

Ion Beam Induced Graphitization of Phenolformaldehyde

ABSTRACTWe have studied MeV ion beam induced phase transformation in phenolformaldehyde cured at 170°C by both Raman Microprobe spectroscopy and in situ resistance measurement of the irradiated area. Samples were irradiated using various doses of protons, alphas and nitrogen beams. Irradiated volumes in each sample were tested in situ for enhanced electrical conductivity and later on by Raman Microprobe spectroscopy. The results have shown changes in the resistance as much as seven orders of magnitude by alpha particles, six orders by nitrogen bombardment and three orders by hydrogen. Raman Microprobe spectroscopy of the darkened phase shows development of the D- and G-lines which are characteristic of the production of a carbonized resin. These spectra indicate that maximum carbonization was caused by the nitrogen beam.