G.G. Ross

Depth-profiling of hydrogen and helium isotopes by means of the ERD E × B technique

The ion beam analysis technique of elastic recoil detection, with an E × B filter, has been upgraded to depth profile all isotopes of hydrogen and helium in light materials (Z < 25). The adjustment of the E × B filter as well as a discussion of the depth-resolution and the sensitivity are presented for every isotope detected. Typically, when a 350 keV He beam is used, the depth resolution (which depends significantly on the material) is ≈ 4 nm at the surface decreasing to 15 nm at a depth of 100 nm, while the depth probed is ≈ 100 nm and the sensitivity is ≈ 1 at %. The possibility of using a 1 MeV He beam is also discussed. Examples of measured isotope profiles are presented.

H−, H0, H+ He0, He+ and He2+ fractions of projectiles scattered from 14 different materials at 30 to 340 keV

Abstract Some ion-beam methods require the knowledge of the charge fractions of light atoms emerging from solids. We have measured these fractions in the energy range from 30 to 340 keV under a vacuum of ~1 × 10−7 mbar. For hydrogen we used samples of Be, C, SiC, Si, Al, Ti, stainless steel (S.S.), Ni, NiOx, Cu, CuOx, Ge, Zr and Nb; for helium: Be, C, Al, Ti, Cu and CuOx. We compare to other results. We also find that the following equations fit the data: for H−, H0 and He0, f = exp(−(E + E0)/E1), for He2+, f = ( E E 1 ) 2 , where f = fraction, E = energy, E0, E1 and E1= fit parameters. All materials give very similar results, except Be and C for f (H0).

Ranges and variances of 0.2–1.0 keV hydrogen and deuterium ions implanted into Be, C and Si

Abstract The ion beam analysis technique of elastic recoil detection with an electromagnetic filter has been used to measure the mean ranges and variances of 0.2–1.0 keV H and D ions implanted in Be, C and Si. Two corresponding Monte Carlo (BABOUM and TRIM) code calculations have also been performed and compared. Other theoretical and experimental results are included. Power law fits as a function of energy, R p = R 0 E n , have been adjusted to the ranges and a general function is deduced which allows a rapid estimation of the mean ranges.

Ranges of 0.7–2.1 keV hydrogen ions in Be, C and Si

Abstract We have used the convenient new ion-beam analysis technique of elastic recoil detection, with an E × B filter to measure the ranges of H ions of 720 to 2080 eV/amu in Be, C and Si. We have also performed the corresponding Monte Carlo computations. The results are compared to other experimental and theoretical ones. Power law fits give for the mean ranges a universal energy dependence R0En with n=0.87 ± 0.10, but the values of R0 differ substantially between theories and between theory and experiment.

Nuclear microanalysis by means of 350 keV Van de Graaf accelerator

Abstract An inexpensive and quantitative method to depth profile hydrogen and helium isotopes in low- Z materials ( Z ≤ 25) by ERD E × B and, simultaneously, elements heavier than the substrate by RBS, has been developed. It uses a 350 keV He + beam, low-noise ion-implanted detectors and a filter built out of crossed magnetic and electric fields. Typically, with this setup, the depth resolution (which depends significantly on the materials) is ∽ 4 nm at the surface degrading to ∽ 15 nm at a depth of 100 nm, while the depth probed is ∽ 100 nm for H and He and ∽ 500 nm for heavier elements. The sensitivity is ∽ 1 at.% for H and He, ≈ 0.1 at.% for other light elements (e.g.: C, N, O, etc.) and 1 ppm for heavier elements such as gold. It is also possible to use a 350 keV 1 H + beam to simultaneously depth profile heavier elements by RBS and identify them by PIXE. These combined techniques are especially useful to detect elements with neighbouring Z , such as stainless steel components.

Charge fractions of deuterium scattered from 17 different materials at 50 to 340 keV

Abstract We have measured and compiled charge fractions of deuterium in the energy range from 50 to 340 keV ((2–6) × 106 m s ) scattered on Be, C, Mg, Al, Si, TiC, Ti, V, Ni, Cu, brass, Ge, Mo, Pd, Ta, W and Au. We have compared these to other results and to previous measurements of H and He. We have also found that the following equations fit the data: for H0, D−, D0 and He0, f = A exp(− V2/ViV0), where f = fraction, V = velocity, V i = “mBohr velocity” for the most weakly bound electron of projectiles, A and V0 = fitting parameters, and for He+, f = B exp[−(V2/3Vii V0)2] − A exp(−V2/ViV0) where Vi and Vii are the “Bohr velocity” for the first and the second electron respectively and B a fitting parameter.

Influence of the ion beam induced desorption on the quantitative depth profiling of hydrogen in a variety of materials

Abstract Ion induced depletion of hydrogen implanted or included in different materials was observed during analysis by means of the ERD E × B technique. This technique uses a 4He+ beam of 350 keV and has an excellent depth resolution. H depletion by the beam with a fluence from 1.2 × 1014 to 1 × 10174He+/cm2 was observed to different degrees in almost all materials although it was practically negligible in Sc, Si and SiC. The depletion rate depended on the implanted H concentration. Modification of depth profiles was observed showing a displacement of implanted H to the surface before desorption. The total quantity of implanted H was deduced and plotted as a function of the total 4He analyzing fluence. A two-term inverse exponential curve was fitted to these plots allowing extrapolation to zero fluence. The ion induced desorption was particularly large in C where a large H or D depletion was observed at the very beginning of the analysis. So, special care must be taken for H and D depth profiling and a systematic use of fitted equations is highly recommended to extrapolate to zero fluence.

Measured stopping powers of hydrogen and helium in polystyrene near their maximum values

Abstract Rutherford backscattering at two different angles on multilayer targets is used to measure the stopping powers of hydrogen and helium ions in polystyrene in the energy range near their maximum values. In the energy range from 40 to 300 keV/amu, the hydrogen stopping power reaches a maximum value of 9.8 eV/(10 15 atoms/cm 2 ) at 81 keV/amu. As the energy increases from 25 to 90 keV/amu, the helium stopping power increases from 15.7 to 26.0 eV/(10 15 atoms/cm 2 ). Identical results (in keV/amu energy units) were obtained for 2 H and 1 H, as well as for 4 He and 3 He. The hydrogen and helium measured stopping power values are compared to the results calculated from two empirical models (Braggs rule and the cores-and-bonds model). A function has been fit to the experimental data, including those previously published, which permits rapid calculation of the stopping powers.

ERD measurement of the mean ranges and variances of 0.75–2.0 keV deuterium ions in Be, C and Si

Abstract The ion beam analysis technique of elastic recoil detection, with E × B filter, has been used to measure the mean ranges and variances of 0.75–2.0 keV D ions in Be, C and Si. Two corresponding Monte Carlo computations (BABOUM and TRIM) have also been performed. Power-law fits as a function of energy, RP = AEn have been adjusted to the experimental and theoretical results. Values of the electronic energy loss parameter (K in d E d x = KE 0.5 ) have been deduced. Possible sources of the significant differences between these and other measurements and computations are discussed.

Experiments and simulations on the effect of channeling on the ranges of 1 keV deuterons in silicon

Abstract Simple extrapolation of the Lindhard analytic theory of channeling predicts very wide channeling angles (∼ 10°) at low keV energies; however, the effect is highly sensitive to the exact atomic interaction potential chosen, as shown by computer simulations. Amorphous, polycrystalline, and single-crystalline 〈110〉, 〈111〉 and 〈100〉 silicon samples have been implanted with 1 keV deuterons in channeled and random directions. The ranges are measured by the ERD biE × biB (elastic recoil detection) ion beam technique and compared to simulations with the codes MARLOWE, TRIM and BABOUM. Some significant conclusions are that the channeling angle is approximately 10° in the 〈110〉 direction, and that polycrystalline material gives significant “accidental” channeling.