Mass-separated Ion Beam Research Articles

A review of material processing by low energy ion beams at the ion beam engineering laboratory of Kyoto University

This paper reviews some of the applications of ion beams for material processing in Kyoto University. Ionized cluster beams and low energy ion beams of several eV to a few hundreds of eV are utilized for film formation. The ionized cluster beam method is a unique technique that produces a low energy and high flux ion beam without the problem of space charge limitation. Mass-separated ion beams of hundreds of keV are applied for the formation of a buried layer and the study of the fundamental effects of ion-surface interaction. The results have shown that the formation of unique materials, which would not have been formed by conventional thermal equilibrium methods, is possible.

Ion-assisted deposition and metastable structures

Ion-assisted deposition (IAD) has become an established method for the synthesis of thin films and the modification of their structure, composition, hardness and electrical and optical properties. A variety of techniques are used to achieve the desired ion bombardment during film growth and to produce ionized species from which the film is condensed. The optimum kinetic energy of ions or condensing ionized species is between a few electronvolts and about 1 keV. IAD techniques provide non-equilibrium growth conditions which are exploited to produce unusual materials with metastable structures or phases and possessing exceptional properties. The most common IAD techniques are reviewed, including those based on plasmas and ion beams and those based on the condensation of ionized-cluster beams and mass-separated ion beams. Recent results on the preparation and properties of metastable materials are also reviewed including diamond-like carbon, hard boron nitride, superconducting cubic MoN and higher nitrides of transition metals.

Molecular beam epitaxy of InP using low-energy P + ion beam

InP was grown on Fe-doped semi-insulating InP(100) substrates by a new technique in which phosporus was supplied as a mass-separated low-energy ion beam and indium as molecular beam. The electrical and optical properties of the films grown under various conditions are discussed. The epitaxial growth of InP occured at growth temperatures above 200°C, and high quality InP films were obtained with a P + ion energy of 100 eV. The unintentionaly doped epilayers were n-type. The room temperature carrier concentration and Hall mobility of an InP film growth at 480°C and with a P + ion energy of 100 eV were 1.3×10 16 cm -3 and 3100 cm 2⧸V · s, respectively. The as-grown surfaces was smooth without any oval type defects.

Negative ion source (NIABNIS) and preparation of transparent carbon films by negative carbon ion beam deposition

A high current heavy negative ion source of the neutral and ionized alkaline metal bombardment type (NIABNIS) has been newly developed for negative ion beam applications such as deposition and implantation. This source is a sputter type, and the sputtering target is placed on the extractor of a cesium plasma ion source in order to obtain a large current of cesium ions bombarding the target simultaneously with a controlled amount of neutral cesium atoms. The work function of the sputtering target surface in operation is kept as low as possible so that a high efficiency of the negative ion production is realized. Mass-separated ion beams of 0.74 mA for C −, 200 μA for C 2 −, 320 μA for Cu −, and 170 μA for Si − were obtained. A negative ion beam deposition system with the NIABNIS, in which divergent effects of the ion beam were effectively suppressed, has also been developed. A decelerated C − ion current of several tens of μA in the range of a final energy of 25–100 eV, and about 100 μA in the range higher than 100 eV was obtained. By using C − and C 2 − ion beams with an energy of 10–1000 eV, transparent carbon films of several thousands of Å in thickness were deposited.

Neutral and ionized alkaline metal bombardment type heavy negative ion source (NIABNIS)

A high current NIABNIS has been developed for negative ion beam applications such as negative ion beam deposition and negative ion implantation. In the NIABNIS, a sputter cone for negative ion production is placed on a cesium ion extractor of a cesium plasma ion source in order that a large amount of cesium ions together with controlled neutral cesium particles are simulteneously bombarded on the sputter cone surface. The temperature of the sputter cone can be controlled. Thus, the optimal surface for the negative ion production with the minimum work function can be obtained. Ion beams of 0.74 mA for C −, 320 μA for Cu −, and 170 μA for Si − were produced, and are adequate for negative ion beam applications. A mass-separated negative ion beam deposition system with the NIABNIS was developed and a transparent carbon film of several thousands of Å in thickness was deposited by using a C − ion beam with an energy of 10–1000 eV. A negative ion implanter with the NIABNIS in which an ion beam was accelerated to an energy of 5–60 keV was also developed and experiments such as destructive cross-section of negative ion beams with gases and SiC formation by C − ion implantation into Si substrates were performed.

Density measurements of diamond-like coatings using a low energy accelerator

With the aid of nuclear physical methods based on the use of a low energy accelerator it is shown that the density of even a small, uneven and rough diamond-like coating prepared by mass-separated ion beam deposition can be determined reliably. The density of the coating corresponds to that of diamond. Outlines of the used methods, i.e. Rutherford backscattering and/or nuclear resonance shift combined with the use of a profilometer and Doppler shift attenuation, are presented.

Pn-values of 94Rb and 95Rb measured by a β−γ spectroscopic method

The delayed-neutron emission probabilities ( P n-values) of 94Rb and 95Rb have been measured as 9.73 ± 0.62 and 8.60 ± 0.57%, respectively, by a β−γ spectroscopic method utilizing the on-line isotope separator KUR-ISOL. This method can be usefully applied if a pure isotopic and mass-separated ion beam is available and the absolute emission probabilities per decay of main γ-rays emitted from relevant nuclides are well-established.

Wear and hardness of diamondlike coatings prepared by ion beam deposition

The wear rate of 10-μm-thick 12C coatings prepared by mass separated ion beam deposition has been measured to be 60 times lower than WC+Co hard metal and 10 times lower than the conventional hard coating material TiN. The hardness of the 12C coatings was measured to be at least the same as that of the natural diamonds.

Germanium and silicon ion beam deposition

Epitaxial growth of germanium and silicon on Si(100) substrates by low energy mass-separated ion beam deposition is demonstrated. Heteroepitaxial germanium films are obtained by irradiating Ge + ions with a kinetic energy of 100 eV onto a silicon substrate at a substrate temperature of 300 °C. Homoepitaxial growth of silicon is possible at an ion energy of 200 eV and a substrate temperature of 740 °C. The crystalline structure of these films is discussed in detail.

The 49K beta decay

The decay of 49K has been studied using a mass-separated ion beam by neutron and gamma-ray singles and multiparameter spectroscopic measurements. The 49K activity was produced by 600 MeV proton fragmentation reactions in a uranium target. The observed beta-strength function displays two resonances centered at about 6.5 MeV and 9.5 MeV in 49Ca. This structure is discussed in simple shell-model terms.

Comparative yields of alkali elements and thallium from uranium irradiated with GeV protons,3He and12C

Mass-separated ion beams of the alkali elements Na, K, and Fr, and of the element Tl, were produced by bombarding a uranium target with 600 MeV protons, 890 MeV3He2 +, and 936 MeV12C4 +. Isotopic production yields are reported. In the case of the12C beam, these are thick target yields. Absolute cross-sections for the proton beam data were deduced by normalizing the delay-time corrected yield curves to measured cross-sections. For products farthest away from stability, the3He2 + beam generally gives the highest yields.

The PS on-line mass spectrometer dedicated to the study of the exotic light nuclei

Abstract The experiments performed with the PS on-line mass spectrometer: atomic hyperfine structure determinations and nuclear spectroscopy of Li, Na and K isotopes require high efficiency and as low as possible radioactive background in the area of the detectors. A view of the lay-out will be given concerning in particular the very thick iron and concrete shielding and the mass separated ion beam line going through the shielding from the mass spectrometer to the detector room. This device is an L-shaped pipe with electrostatic focusing elements. The background correlated with the proton beam pulse is lower than the sensitivity of the γ detector and the neutron flux is less than 1 n/cm2s. Slow rate events, corresponding to nuclei far from the stability, such as 34Na, are recorded with a good signal-to-noise ratio.

Low-energy mass-separated ion beam deposition of materials

A low energy mass-separated ion beam deposition system was developed. Ge + ions of 100 μA were obtained at an acceleration energy of 100 eV with a beam spot size of 5 mm ø at 5 × 10 −8 Torr. Material buildup has been observed at the range of ion energy where the self-sputtering yield is below unity. The incident ion energy dependence of the reactions of the F + and CF x + ions with a silicon substrate has been measured, as well as the physical phenomena conventionally observed between impinging ions and a substrate material. Epitaxial growth of Ge films on Ge and Si single crystal substrates has been observed at 300°C with a Ge + ion energy of 100 eV. Deposited Ge crystal properties were evaluated.

Nuclear spins and magnetic moments of some cesium isotopes

Using an atomic-beam magnetic resonance apparatus connected on-line with the ISOLDE isotope separator, CERN, hyperfine structure measurements have been performed in the 2S 1 2 electronic ground state of some cesium isotopes. An on-line oven system which efficiently converts a mass separated ion beam of alkali isotopes to an atomic beam is described in some detail. Experimentally determined nuclear spins of 120, 121, 121m, 122, 122m, 123, 124, 126, 128, 130m, 135mCs, the isomer of 121Cs being discovered in this work, and magnetic moments of 121, 122, 123, 124, 126, 128, 130, 130mCs are reported and discussed in terms of different nuclear models. The experimental data indicate deformed nuclear shapes of the lightest cesium isotopes.

High-resolution spectroscopy on a fast beam of metastable xenon ions

For the case of xenon we show that metastable ions are very suitable for optical experiments on fast ion beams (FIB experiments). It is possible to study the hyperfine structure of spectral lines in absorption from a mass separated ion beam which is exposed to a monomode laser beam. The absorption is detected by observing the fluorescence radiation. As expected, the width of the absorption signals is strongly reduced if laser- and ion-beam are parallel to each other.

Modification of the lunar surface by the solar-wind bombardment

Long-duration, solar-wind sputtering conditions were simulated at a much accelerated scale with mass-separated hydrogen ion beams or in low-pressure, noble gas or hydrogen plasmas. Experiments with metal targets and metal-, oxide-, and rock-powder samples demonstrate the leveling and smoothing of macroscopic surface features, and cementing together of loose particles into a porous, brittle, fibrous crust. Certain oxide surfaces become enriched with metal atoms under the bombardment and sputtering action. It is concluded that many of the unusual properties of the lunar surface can be explained by the action of solar-wind bombardment.