C.V.Barros Leite

Methodology and application of the nuclear resonance reaction 16O(α, α)16O for the profiling of titanium oxide

Abstract A method is presented for the application of the 16 O(α,α) 16 O resonance at 3.045 MeV to the depth profiling of oxide films. The resonance yield is translated into oxygen to metal stoichiometry as a function of the depth probed. The method is applied to anodic titanium oxide films grown in the absence and presence of tungsten anions. The oxygen depth profile is then utilized to obtain the profile of the dopants (W) incorporated in the oxide. A depth resolution of 6 μg/cm is achieved. The incorporation of tungsten anions of the order of 2 at.%, evaluated from the RBS yields, precludes the establishment of a constant oxygen to metal stoichiometry in the doped film. The tungsten atomic fractions have an estimated error of 5%.

Simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions

Abstract (CsI) n I − ( n =0−3), low mass organic negative clusters, and H − , in the 20–46 keV energy range, have been used in time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments to study the relationships between secondary ion and photon emission from a surface. We report on the simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions. Our results indicate that, for a CsI target, secondary ions and photons are produced independently of each other through different mechanisms. Secondary ion emission is strongly dependent upon the complexity of the primary ion, i.e. monoatomic or polyatomic. However, photon emission appears to be independent of the primary ions complexity and depends primarily upon the velocity of the primary ion. Unlike the secondary ion yields, no yield enhancements for the photons were observed due to polyatomic primary ions. Only broad band light emission from the bulk of the target was observed; no line emissions from sputtered species were detected. We compare the yields of both secondary ions and photons that were collected simultaneously, and present a simple model that describes the observed photon yields as a function of both the electronic and nuclear stopping powers of the primary ion.

Study of oxygen self-diffusion in oxides by ion beam techniques: comparison between nuclear reaction analysis and SIMS

Abstract Oxygen self-diffusion in Fe1−xO single crystals has been studied by means of the isotope exchange method in H2/H218O atmospheres. The 18O concentration profiles were determined by using two different techniques based on ion beams: secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA); the latter by means of the narrow nuclear resonance reaction 18 O(p , α) 15 N at 629 keV, Γ = 2.1 keV. The diffusion coefficients obtained from the analysis of the measured profiles are in good agreement with those found in the literature. To compare the depth resolution and sensitivity of both techniques, the 18O profiles of implanted Cr2O3 single crystals (E18O=50 keV, fluence=1.6 × 1016 ions/cm2 were also measured.

STUDIES IN HEAVY ION ACTIVATION ANALYSIS I. ON THE SELECTION OF ACTIVATION REACTIONS

Among the numerous heavy ion reactions, those of potential interest for chemical analysis can be identified based on their Q values, Coulomb barriers, and threshold energies. A simple computer code has been written for these calculations. The use of the calculated data is illustrated with a survey of the possibilities of HIAA with N+, Li+, B+, Be+ and C+ beams yielding radioisotopes with half-lives of 10 to 104 sec.

Analysis of tin films using alpha resonant scattering

Abstract The 3.576 MeV 14 N(α, α) nuclear resonant scattering is used to determine the nitrogen depth profile in TiN films deposited by reactive sputtering or hollow cathode discharge ion plating. The depth resolution is of the order of 100 A. This resonant scattering combined with Rutherford backscattering is used to determine the atomic ratio Ti: N. The broad resonance at 3.71 MeV is used to confirm this atomic ratio in the case of thick films produced by ion plating.

Rutherford Backscattering with Heavy Ions

The mass resolution capabilities of heavy ion Rutherford backscattering spectrometry (HIRBS) have been explored. A generalized prediction has been made of the maximum mass resolution that can be obtained in HIRBS. The experimental mass analysis capabilities of three heavy ion beams, 24 MeV 16O, 23 MeV 20Ne, and 38 MeV 40Ar was investigated in detail. Using these beams, a mass difference of 1 amu can be determined at a target mass of 25 amu; a mass difference of 2 amu can be determined at a target mass of 65 amu. For each beam, the energy differences necessary for qualitative and quantitative analysis were determined. For the 16O beam the corresponding experimental values are 250 and 350 keV, respectively, for qualitative and quantitative determination. For the 20Ne beam the values are 275 and 425 keV, for the 40Ar beam the values are 700 and 1200 keV. From these experimental ¿E values the mass resolution achievable with each beam is estimated. HIRBS is potentially capable of resolving neighboring masses for 50 < M < 100 and appears well suited for detecting such species on the surface of low Z substrates.

Coincidence counting analysis of secondary ions emitted from a phenylalanine target under multicharged MeV carbon bombardment

Abstract Coincidence counting techniques for time-of-flight mass spectrometry have been applied to the study of secondary ion correlations. Phenylalanine samples were exposed to 2.5 MeV carbon ions with charge states ranging from +1 to +6. The influences of the projectile charge state on secondary ion yields and correlations are reported. The degree of secondary ion correlation was observed to decrease as the charge state of the primary ion increases. For the cases studied, the data indicate that more inefficient projectiles are better suited for monitoring secondary ion correlations.

Surface analysis with keV polyatomic projectiles

Abstract Bombardment of solids with polyatomic projectiles (e.g., Cs 2 I + ) results in high secondary ion (SI) yields. For projectiles of 5–30 keV, SI yields as high as 10% have been observed; they are up to 50 times higher than those obtained with equal velocity monoatomic ions. Our data show that the SI yields increase with the mass of the projectile and its velocity. The SIs are identified by TOF-MS in an event-by-event counting mode, allowing the study of sputtering phenomena in the limit of a single projectile-target interaction. Moreover, the SIs emitted from a single primary ion impact can be acquired in a coincidence mode, i.e., the masses which are desorbed together from a primary impact site can be identified.

Interaction of atomic and molecular MeV ions with surface

Abstract Secondary ion emission was studied using atomic and molecular ions bombarding organic and metallic targets. The energy of the projectile ions varied from 200 keV to 3 MeV. Relative yields of positive and negative secondary ions desorbed from phenylalanine and aluminum targets were identified by time-of-flight mass spectrometry. C q + , O q + , N q + , CO + and CO 2 + (0 ≤ q ≤ 7) were the beams used in this study. The yield obtained for [M−H] − , [M + H] + and H − and H + secondary ions indicate the existence of two mechanisms for the desorption process: the kinetic and the surface mechanism.

Time-of-flight mass spectrometry using mega-electronvolt neutral beams

Abstract Neutral carbon, nitrogen and oxygen beams with an energy range of 300 keV–2 MeV (velocity range of 0.2–0.6 cm ns−1) have been used to induce secondary ion emission from solid samples. In this work, results for the ion desorption yield for hydrogen and some organic species emitted by bombardment of neutral and low charge state carbon beams on a phenylalanin target are reported. The positive and the negative ion mass spectra obtained for neutral projectiles show very similar features as those obtained for 1+ −6+ charge state projectiles, However, the ion emission yields corresponding to neutral beams are observed to be slightly smaller than those produced by positive ion beams. The secondary ion desorption yield dependence on the projectile velocity is also analyzed. It is found that the hydrogen desorption yield slowly decreases with the projectile velocity, whereas the yields of the other desorbed ions show a second to third power dependence of the projectile stopping power in the target.