SIMS depth profiling of multilayer metal-oxide thin films — improved accuracy using a xenon primary ion

Multilayer thin films containing silver and copper, sandwiched in a metal oxide, have been depth profiled by secondary ion mass spectrometry (SIMS) using primary ions of differing mass, energy and chemical reactivity. These results were compared for accuracy with those obtained by Rutherford backscattering spectrometry (RBS). The use of O₂⁺ or O^? as primary ions resulted in severe distortion of the silver ion intensity distribution in the SIMS profile of a ZnO/Ag/ZnO thin film on glass; O₂⁺ bombardment at energies from 3–10 keV resulted in the detection of silver at the glass interface, while the use of O^? caused the silver to be detected closer to the outer surface than expected from RBS results. Primary beams of Ar⁺ and Xe⁺ gave progressively more accurate results for the Zn/Ag/Zn distribution; Xe⁺ at 5.0 keV energy produced profiles that agreed within 10% of RBS-derived values. The same beam conditions, used to profile a double silver layer in ZnO, resulted in some discrepancy in the position of the inner layer, compared to RBS results, and this was attributed to an enhanced sputter rate in the oxide under the outside metal film. Depth profiling of TiO₂/Cu/TiO₂ films with oxygen also resulted in significant distortion of the perceived position of the metal layer, and this was again significantly improved using Xe⁺ primary ions of 6–9 keV energy. The distorting effects of oxygen bombardment can be understood in terms of a migration of metal ions in an electrostatic field created by a charged surface. Ionization of the metallic layer is enhanced by the use of oxygen. By contrast, the use of rare gases reduces the production of ions from the metallic layer which can migrate prior to the onset of sputtering.     

Emission of large molecules from methane by ion bombardment

Condensed layers ot methane at 20 K have been bombarded by 6–8 keV Ar⁺, He⁺ and H₂⁺ ions. Mass spectra and Kinetic energy distributions of neutral species sputtered from these layers have been measured. We have found sputtered species with masses up to 72 amu and thus with at least 5 carbon atoms. In addition to this an involatile residue was formed. Analysis by pyrolysis mass spectrometry showed this residue to contain species with masses up to at least 170 amu which therefore contain at least 12 carbon atoms. The kinetic energy distributions of sputtered methane molecules lie between those of a Maxwell-Boltzmann distribution and a collision cascade. Higher values are reached for Ar⁺ than for the light ions. From these observations we conclude: for both light and heavy ions radicals are formed, which combine to new molecules. These exothermic reactions produce heat which causes desorption. The high energy tail for bombardment with argon ions shows that part of the sputtering is caused by momentum transfer.     

Effect of H+ and O+ implantation on electrical properties of SrBi2Ta2O9 ferroelectric thin films

The effect on the crystalline structure and ferroelectric properties of ion implantation in SrBi₂Ta₂O₉(SBT) ferroelectric thin films has been investigated. 25 keV H⁺, 140 keV O⁺ with doses from 1 × 10¹⁴/cm² to 3 × 10¹⁵/cm² were implanted into the Sol–Gel prepared SBT ferroelectric thin films. The X-ray diffraction patterns of SBT films show that no difference appears in the crystalline structure of as-H⁺-implanted SBT films compared with as-grown films, H⁺ and O⁺ co-implanted SBT films show an obvious degradation of crystalline structure. Ferroelectric properties measurements indicate that both remnant polarization and coercive electric field of H⁺ implanted SBT films decrease with increasing the implantation dose. The disappearance of ferroelectricity was found in the H⁺, O⁺ co-implanted SBT films at room temperature. The great recovery of hydrogen-induced degradation in SBT films was obtained with O⁺ implantation using a heat-target-implantation technique.     

Mass Spectrometric Study of Ions Formed from Cesium Metaborate Vapor under Electron Impact

An ionization behavior of cesium metaborate vapor under electron impact has been studied by a mass spectrometric method. Formations of Cs²⁺, CsB⁺, CsO⁺, Cs⁺ ₂, Cs₂O⁺, B⁺ and BO^? ₂ ions have been identified in addition to the well known ions of Cs⁺, CsBO⁺, CsBO⁺ ₂ and Cs₂BO⁺ ₂. Ionization processes and vapor precursors for these ions have been given from ionization efficiency curves, appearance energies, temperature dependence of ion intensities and energetics of the ionization processes as follows: the process for the formations of Cs⁺ with AE(Cs⁺)=3.9± 1.0 eV and BO^? ₂ ions is the ion pair formation from CsBO₂(g), that for CsBO⁺ ₂ ion is the simple ionization of CsBO₂(g), that for Cs⁺ with AE (Cs⁺) =9.1±0.5 eV, Cs²⁺, CsBO⁺, CsB⁺, CsO⁺ and B⁺ ions is the dissociative ionization from CsBO₂(g) and that for Cs⁺ ₂, Cs₂O⁺ and Cs₂BO⁺ ₂ ions is the dissociative ionization from Cs₂(BO₂)₂(g). The knowledge of the ionization behavior of cesium metaborate vapor under electron impact is very useful in the mass spectrometric study of vaporization behaviors of CsBO₂(s) and simulated radioactive waste borosilicate glasses.     

Depth distribution of rare earth ions implanted into KTiOPO4 determined by the Rutherford backscattering technique

Potassium titanyl phosphates (KTiOPO₄ or KTP) samples were implanted with rare earth ions such as Tm⁺, Er⁺, and Yb⁺. The ion energy implanted was varied from 100 keV up to 400 keV. The fluence was 1–2 × 10¹⁵ ions/cm². The depth distributions of the implanted rare earth ions were determined using the Rutherford backscattering technique. The experimental data were compared with TRIM (transport of ions in matter) code. It is found that for Tm⁺ and Er⁺ the experimental mean projected ranges are in relatively good agreement with values calculated by the TRIM code after taking into account inelastic effects in the energy transfer. But that in the case of Yb⁺ the ranges are overestimated by theory, anyway the deviation of experimental values from calculated one is less than 9% for all cases. The deconvoluted experimental range stragglings are in all cases higher than the calculated values.     

Energy distributions of secondary ions from GaAs

Energy distributions have been measured for Ga⁻, As⁻, Ga⁺ and As⁺ secondary ions emitted from a GaAs crystal using Cs ⁺, O₂⁺, Ar⁺ and O⁻ primary ion bombardment. Dramatic differences among these distributions have been observed and provide new chemical information for the understanding of the ion formation mechanism.     

The ion-induced electron yield as a function of the target material

The total (backward) electron yield from 27 elemental, noncrystalline solids under bombardment by H⁺, H₂⁺ and H₃⁺ ions at 100 keV/proton was measured. It is observed that the yield exhibits an oscillatory dependence on the atomic number Z₂ of the target material which is correlated with the periods of the periodic system.     

Ion guiding through capillaries in uncoated Al2O3 membranes

We made an experimental study on ion guiding through capillaries in uncoated Al₂O₃ membranes using a variety of ions such as O¹⁺, O³⁺, and O⁶⁺. The incident energy was varied within the range of 30-150 keV. The results were compared with others using coated PET and Al₂O₃ capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q_∞ seems to exist in our experiment.     

Temperature-dependent surface modification of InSb(0 0 1) crystal by low-energy ion bombardment

Structural and compositional modification of InSb(0 0 1) single crystal surfaces induced by oblique incidence 2-5 keV Ar and Xe ion irradiation have been investigated by means of scanning tunneling and atomic force microscopies, and time-of-flight mass spectroscopy of secondary ion emission. In general, ion-induced patterns (networks of nanowires, or ripples) are angle of incidence- and fluence-dependent. Temperature dependences (from 300 to 600 K) of the RMS roughness and of the ripple wavelength have been determined for the samples bombarded with various fluences. Secondary ion emission from an InSb(0 0 1) surface exposed to 4.5 keV Ar⁺ ions has been investigated with a linear TOF spectrometer working in a static mode. Mass spectra of the sputtered In⁺, Sb⁺ and In₂⁺ secondary ions have been measured both for the non-bombarded (0 0 1) surface and for the surface previously exposed to a fluence of 10¹⁶ ions/cm². In⁺ and In₂⁺ intensities for the irradiated sample are much higher in comparison to the non-bombarded one, whereas Sb⁺ ions show a reversed tendency. This behavior suggests a significant In-enrichment at the InSb(0 0 1) surface caused by the ion bombardment.     

Thermal desorption of D2 and CD4 from bulk-boronized graphites

Thermal desorption spectra of D₂ and CD₄ from bulk-boronized graphites containing 3 to 38 wt% B as well as from pure graphite and stoichiometric B₄C were measured. The samples were implanted with 3 keV D⁺₃ ions at temperatures between 130 and 700°C to fluences between 2.3 × 10¹⁶ and 2.3 × 10¹⁹ D/cm² prior to the desorption. An enhancement of D₂ release is observed with increasing boron content, while the CD₄ release decreases correspondingly. The desorption peak maximum of D₂ is shifted towards lower temperatures with increasing boron concentrations. Apparently, it is the boron in solid solution which mainly influences the trapping and release behaviour of deuterium. The formation of CD₄ is suggested to proceed via a precursor state. The formation of the complete CD₄ molecule takes place only close to the desorption temperature. The reduction of binding energy for D has only a minor influence on ion-beam-induced detrapping.     

Application of a Chemical ion Exchange Model to Transport Cask Surface Decontamination

Abstract

Radionuclide contamination of stainless steel surfaces occurs during submersion in a spent fuel storage pool. Subsequent release or desorption of these contaminants from a nuclear fuel transportation cask surface under varying environmental conditions occasionally results in the phenomenon known as contamination ‘weeping’. Experiments have been conducted to determine the applicability of a chemical ion exchange model to characterise the problem of cask contamination and release. Surface charge characteristics of Cr₂O₃ and stainless steel (304) powders have been measured to determine the potential for ion exchange at metal oxide-aqueous interfaces. The solubility of Co and Cs electrolytes at varying pH and the adsorption characteristics of these ions on Cr₂O₃ and stainless steel powders in aqueous slurries have been studied. Experiments show that Co ions do reversibly adsorb on these powder surfaces and, more specifically, that adsorption occurs in the nominal pH range (pH=4–6) of a boric acid moderated spent fuel pool. Desorption has been demonstrated to occur at pH≤3. Cs⁺ ions also have been shown to have an affinity for these surfaces although the reversibility of Cs⁺ bonding by H⁺ ion exchange has not been fully demonstrated. These results have significant implications for effective decontamination and coating processes used on nuclear fuel transportation casks.     

Defects creation in sapphire by swift heavy ions: A fluence depending process

Single crystals of sapphire (α-Al₂O₃) were irradiated at GANIL with 0.7 MeV/amu xenon ions corresponding to an electronic stopping power of 21 keV/nm. Several fluences were applied between 5 × 10¹¹ and 2 × 10¹⁴ ions/cm². Irradiated samples were characterized using optical absorption spectroscopy. This technique exhibited the characteristic bands associated with F and F⁺ centers defects. The F centers density was found to increase with the fluence following two different kinetics: a rapid increase for fluences less than 10¹³ ions/cm² and then, a slow increase for higher fluences. For fluences less than 10¹³ ions/cm², results are in good agreement with those obtained by Canut et al. [B. Canut, A. Benyagoub, G. Marest, A. Meftah, N. Moncoffre, S.M.M. Ramos, F. Studer, P. Thévenard, M. Toulemonde, Phys. Rev. B 51 (1995) 12194]. In the fluences range: 10¹³-10¹⁴ ions/cm², the F centers defects creation process is found to be different from the one evidenced for fluences less than 10¹³ ions/cm².     

Surface analytical studies of ion-implanted uni-directionally aligned silicon nitride for tribological applications

Uni-directionally aligned silicon nitride, which exhibits both high strength and high toughness, was implanted with B⁺, N⁺, Si⁺ and Ti⁺ ions at a fluence of 2 × 10¹⁷ ions/cm² and an energy of 200 keV. The effect of ion implantation on the surface structure of the uni-directionally aligned silicon nitride has been studied, in terms of surface analyses such as atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray absorption near edge structure (XANES). It was clarified that the ion-implanted layer was amorphized and the implantation profile showed good agreement with that estimated from a TRIM simulation. It was found that BN and TiN were formed in B⁺- and Ti⁺-implanted Si₃N₄, respectively. There was a slight difference in ion implantation depth among different structures of Si₃N₄, considered to be due to differences in ion channeling.     

Sputtering yields of 1 to 20 kev light ions on stainless steel

Sputtering yields for 1 to 20 keV H⁺, D⁺, He⁺, Ne⁺ and Ar⁺ ions on 304 stainless steel films have been measured. The films with a thickness of 0.1 to 1 μm were sputter deposited onto polycrystalline Be substrates. Rutherford backscattering of 2 MeV He⁺ ions was used for in situ measurement of the thickness of the stainless steel film. The sputtering yields were obtained from the slope of the decrease in film thickness with increasing sputtering ion dose. The measured yields agree well with yields obtained by weight loss in this laboratory, they are however lower than those published earlier.     

Influence of surface condition on deuterium release from Li2TiO3 pebble

Lithium titanate (Li₂TiO₃) pebbles were irradiated with D₃⁺ ions with energy of 5.0 keV, and the amounts of retained deuterium in the pebbles were measured by thermal desorption spectroscopy. In this research the irradiation/heating cycles were carried out repeatedly in order to investigate the influence of surface condition on deuterium release from Li₂TiO₃. The composition ratio of Li decreased with the increase of the number of the irradiation/heating cycle. Then, the desorption peaks of the gases contained deuterium atoms were shifted to higher temperature region, and the amount of desorbed gases in forms of water tended to increase. In addition, we carried out other experiments for the comparison. Comparing these results, we considered that the increase of the defects created by the irradiation was more responsible for the change in the desorption behavior by the irradiation/heating cycles than the lithium depletion. These results suggest that the tritium recovery efficiency would decrease with the increase of the defects and the damages especially at the low temperature region during the operation.     

Radiation blistering of Nb Implanted sequentially with helium ions of different energies (3–500 keV)

Cold rolled, polycrystalline niobium samples were irradiated at room temperature with ⁴He⁺ ions sequentially at 14 different energies over an energy range from 3–500 keV. The dose for each energy was chosen to give an approximately uniform concentration of helium between the implant depths corresponding to 3 keV and 500 keV. In one set of experiments the irradiations were started at the Kurchatov Institute with 3-keV ⁴He⁺ ions and extended up to 80 keV in several steps. Subsequently, the same target area was irradiated with ⁴ He⁺ ions at Argonne National Laboratory (ANL) starting at 100 keV and increased to 500 keV in steps of 50 keV. Another set of irradiations was started at ANL with 500-keV ⁴ He⁺ ions and continued with ion energies decreasing to 100 keV. Subsequently, the same area was irradiated at the Kurchatov Institut starting at 80 keV and continued with ion energies decreasing to 3 keV. Both sets of irradiations were completed for two different total doses, 0.5 C cm^?2 and 1.0 C cm^?2.     

The chemical interaction of hydrogen discharges with non metals

The impurity ions in an r.f. discharge have been directly extracted and then both energy and mass analysed. A variety of surfaces have been exposed to the plasma including borosilicate glass, alumina and carbon. In each case a large variety of species were produced initially, due to desorption of impurities from the surface. After some hours exposure to the plasma many of these species decayed away and relatively simple ion mass spectra were observed. The principal species with oxide surfaces were OH⁺, OH⁺₂ and OH⁺₃ and the corresponding OD⁺, OD⁺₂, OD⁺₃ in a deuterium plasma. Two other major impurities were mass 28 and 29. These are attributed to CO⁺ and COH⁺. When the carbon sample was exposed to the plasma the main species observed were CH⁺₃, CH⁺₄ and the series C₂H⁺₂ to C₂H⁺₆.     

Ion bombardment of insulators

Some of the effects which were observed when some stable inorganic insulators were subjected to ion bombardment are described. Most of the results were for bombardment at room temperature with the light ions H⁺, D⁺, He⁺, having energies in the neighborhood of 100 keV. Phenomena associated with destruction of the surface: stress, deformation, fracture, and blistering, are emphasized.     

Range distributions of 50–400 keV Hg+in amorphous silicon and Si-Ar binary targets

Range distributions of 50–400 keV Hg⁺ in amorphous Si and Si-Ar binary targets have been investigated by Rutherford backscattering spectrometry. The Si(100) wafers were amorphized by means of 150 keV Ar⁺ irradiation to a dose of 2 × 10¹⁵ ions/cm². To produce Si-Ar binary targets, the Si(100) wafers were implanted with 150 keV Ar⁺ to a dose of 3 × 10¹⁷ ions/cm². 50–400 keV Hg⁺ were introduced into amorphous Si and Si-Ar binary targets in increments of 50 keV. Parallel scanning of the Hg⁺ beams was used. The measured ranges and range stragglings have been compared to the Biersack theory. The results show that good agreements are found between the experimental and theoretical projected ranges for both Si and Si-Ar, but the predicted range straggling for both Si and Si-Ar are systematically lower than the experimental results in the case of a first order treatment. After correcting for second order energy loss terms, a better agreement for the range straggling is obtained.