Elastic Recoil Detection Technique Research Articles

Microbeam recoil detection for the study of hydration of minerals

The elastic recoil detection technique in the glancing angle geometry is ideally suited for hydrogen content determination of thick geological samples, obviating the need for elaborate sample preparation such as that required for the transmission mode. With an appropriate scheme for locating the sample, the technique can be applied generally with a microbeam. Combined with simultaneous PIXE measurements, problems arising from uncertainties in beam charge collection are eliminated. The method is applied to the investigation of the hydration characteristics of silicates, in experimental petrological samples produced at high pressure and temperature, simulating lower crust and upper mantle conditions. Preliminary results show that the technique can be applied readily on a microscopic ( < 100 μm) scale for determination of H at a fraction of atomic percent level, at beam current levels that avoid radiation and thermal damage to the specimen.

Fraction of hydrocarbon emission in thermal re-emission of hydrogen implanted into graphite

Isothermal re-emission of hydrogen, implanted into graphite with 3 keV H 2 + ions up to different fluences at room temperature has been measured at 450, 500 and 600°C by means of the elastic recoil detection (ERD) technique. It is found that as the time of the post-isothermal annealing increases the concentration of hydrogen retained at each implantation fluence decreases rapidly in the beginning and hereafter very gradually. The decay curves due to hydrocarbon molecule emission are obtained as the differences between the experimental decay curves and the decay curves due to hydrogen molecule emission, calculated by fitting the solution of the mass balance equations to the experimental ones at large annealing times, where thermal detrapping, retrapping and local molecular recombination are taken into account without hydrocarbon molecule formation. The ratios of the rate constants of hydrocarbon molecule formation to trapping are determined by best fitting of the calculated decay curves due to hydrocarbon molecule emission to the experimental ones obtained in the above procedure. The ratios determined and the process of hydrocarbon molecule formation are discussed on the basis of the diffusion-limited reaction model.

MeV He ion impact desorption of hydrogen isotopes from an InP(001)-p(1 × 1) surface

MeV He + ion impact desorption of hydrogen isotopes adsorbed on the InP(001)-p(1 × 1) surface has been studied by continuous measurements of decrease of their surface coverage by means of the elastic recoil detection (ERD) technique using a He + ion beam at different energies. It is found that the surface coverage of hydrogen decreases exponentially as the He + ion fluence increases, while no change of the p(1 × 1) spots by LEED and the In surface composition by AES has been observed even when the surface coverage decreases from 2 ML down to 0.3 ML. The desorption cross sections of MeV He + ions for hydrogen isotopes, determined from the exponential decay curves, are (8−10) × 10 −17 cm 2 in the range from 0.7 to 1.9 MeV. Their energy dependence corresponds well to that of the electronic stopping cross section for MeV He + ions of In atoms, to which the hydrogen atoms are directly bound. The desorption process of hydrogen by MeV ion impact is discussed on the basis of the experimental data.

Thermal reemission of hydrogen isotopes from graphite in the high temperature regime above 1000 K

The isothermal reemission of hydrogen isotopes, implanted into graphite up to saturation at room temperature, has been measured by means of an elastic recoil detection (ERD) technique in the high temperature regime above 1000 K. As the annealing time increases, the surface concentration of retained hydrogen becomes gradually lower and the concentration gradient into the bulk also becomes gradually steeper. This result is a clear indication of hydrogen diffusion and ejection at the surface. The experimental data have been analyzed using the mass balance equations and the rate constant of thermal ejection of the hydrogen atom and the effective diffusion constant have been determined. It is shown that the activation energies of the thermal ejection rate and the effective diffusion constant are 3.8 ± 0.6 and 3.1 ± 0.6 eV, respectively. The high activation energies are compared with the previous data obtained at temperatures below 1000 K and the mechanism of the thermal reemission is discussed.

Hydrogen-helium scattering cross-sections for transmission elastic recoil detection analysis

1H(α,p) 4He scattering cross-sections were determined for the 6.5–13 MeV (incident α energy) range, thereby extending the energy range for such data beyond that available in the literature. These values are essential for the further development of hydrogen concentration profiling by the transmission elastic recoil detection technique, of particular interest in the design of surface-engineered hydrogen contamination barriers for steels.

Forward elastic recoil measurements using heavy ions

The application of the elastic recoil detection technique utilizing heavy ions for the analysis of semiconductor samples is demonstrated. With this technique the depth profiles of the primary constituents as well as profiles of all impurities can be measured in one spectrum. Depending on the target material, a depth resolution down to 20 nm can be achieved. All elements except hydrogen can be detected with almost the same sensitivity, namely ∼1×1015 at/cm2 with 136 MeV I in a 30° recoil geometry. For hydrogen, the sensitivity is about four times better.

Energy dependence of depth profiles and peak concentrations of hydrogen retained by implantation into graphite

The depth profiles of hydrogen retained in graphite by implantation with H 2 + ion beams at energies from 0.2 to 4.9 keV at room temperature have been studied by means of the elastic recoil detection technique. It is found that the peak concentration, the peak depth and the peak width of the steady state depth distribution increase as the implantation energy increases. It is also found that the concentrations extended from the peak toward deeper layers are approximated to be A exp(− b( z-R)), where A is the peak concentration, R is the peak depth and b is the characteristic parameter and the value of b is proportional to the sputtering yield divided by the target density. The experimental parameters characterizing the depth profiles are compared with the theoretical ones obtained from a steady state solution of the mass balance equations. The experimental depth profiles are shown to be in reasonable agreement with the theoretical prediction.

Forward elastic recoil measurements using heavy ions

The potential of the elastic recoil detection technique using heavy ions for the analysis of low Z-elements such as C, N, and O is shown. Heavy ions at high energies, such as 136 MeV 127I, allow the separation of neighbouring elements up to Si. Heavier elements can also be separated as long as they are not too close together in atomic number.

Investigation of hydrogen isotope behaviour in palladium membrane cathodes in the process of water electrolysis by the NERD method

The elastic recoil detection technique with monochromatic 14-MeV neutrons (NERD) was applied for a hydrogen and deuterium concentration depth profile study in an electrolytic cell with a palladium membrane electrode. It was found that at ambient temperature the maximum H-content in a Pd membrane with its surfaces activated by Pd black depends on the current density, but does not exceed the value of 0.7 at% H/at% Pd while in a membrane without surface activation it is ∼ 0.82 at% H/at% Pd and does not change within the current density interval of 40–400 mA/sm2. In the case of isotope mixture water solution electrolysis, a higher H/D ratio was found at the electrolyte/membrane interface in comparison with that at zero current and a rather large isotope separation factor of (H/D)Pd/(H/D)sol ∼8 was measured.

Depth microscopy at interfaces

High resolution depth microscopy with swift heavy ions is performed at the Munich tandem accelerator and its Q3D magnetic spectrograph using the elastic recoil detection technique. The method gives the possibility to analyze elemental and isotopic concentration profiles of light and medium heavy atoms in thin films and at interfaces. A monitor detector has been installed in the scattering chamber of the Q3D in order to get the relative elemental content for the high resolution depth profiles without absolute knowledge of beam current and charge yields. It is a detector telescope which consists of an ionisation chamber for energy loss and a silicon detector for a residual energy measurement in order to obtain the nuclear charge of the detected target atoms. Depth microscopy was applied for quantitative analysis of concentration profiles at the interfaces between a-Si : H and a-SiC : H layers. Hydrogen profiles can directly be compared to carbon and oxygen profiles showing an excess hydrogen content at the interface between the two layers.

Simultaneous measurement of the hydrogen isotopes H, D, T and 3He with HIERD

The most straightforward method to measure simultaneously the amount and the depth distribution of different light atoms trapped in the surface layers of a solid, such as needed in investigations of the plasma-wall interaction in controlled thermonuclear fusion research, is the heavy ion elastic recoil detection (HIERD) technique. This technique has been applied using 30 MeV 35Cl ions to measure the light ions collected in a Ti target and in C targets. The recoiled atoms have been identified and detected by a ΔE − E telescope consisting of a 14 μm transmission detector and a SSB detector with a 12 μm Al foil at the entrance to stop all heavy ions. The hydrogen and helium isotopes are clearly identified. The sensitivity of this technique is the largest for H and decreases proportional to Mr3 i.e. proportional to 8 and 27 for the two heavier hydrogen isotopes, while the depth resolution is the best for tritium. Recoils heavier than He up to sodium are simultaneously detected by a Bragg ionization chamber.

Deuterium concentration profiles in electrochemically deuterated titanium and their evolution after electrolysis

Deuterium concentration profiles in electrochemically deuterated titanium plates have been obtained by using elastic recoil detection and Rutherford backscattering spectrometry techniques. Measurements were done several months after finishing electrolysis. Experimental results are analyzed in the light of the Wagner model. Conclusions from this analysis are compared with those obtained by other authors in Ti and similar metals like Zr. Finally, the relevance of these data in relation to some recently accomplished electrolytic “cold fusion” experiments is also discussed.

ERD technique with monochromatic neutrons as an effective tool for hydrogen-material systems study

Neutron elastic recoil detection (NERD) technique for hydrogen isotope concentration depth profiling is considered in comparison with IBA techniques. The use of 14 MeV neutrons instead of the usually applied accelerated ions provides a number of essential advantages which allow us to analyze the deep regions of the sample and to perform the investigations of some processes in H-M systems inaccessible for the ion methods. Examples of both analytical and scientific applications of the NERD technique are presented.

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite.

The energy dependence of MeV He+ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ d and the rate constants of the retrapping Σ T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ d and K/Σ T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ d and K/Σ T for H are twice as large as those for D, which is the so-called isotope effect. It has been shown that the experimental values of σ d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Tho...

Optical constants of ion-irradiated hydrogenated amorphous carbon films

Optical constants in the range 1–6 eV of ion-irradiated hydrogenated amorphous carbon have been obtained in order to gain information on the atomic and electronic structure of this material. The film composition was checked by the elastic recoil detection technique and Rutherford backscattering. Ion irradiation leads to a decrease of hydrogen concentration (up to 10%) and an increase of trigonal carbon fraction (up to 60%). A comparison with several atomic models is reported.

Depth microscopy for thin film analysis

Depth microscopy with swift heavy ions has recently been developed. It is an elastic recoil detection technique with high depth resolution performed at the Munich tandem accelerator and its Q3D magnetic spectrograph. The method provides the possibility of analyzing elemental and isotopic concentration profiles in thin films and foils with high accuracy up to single layer depth resolution near the surface. This technique was applied to examine surface and bulk concentrations of hydrogen in thin carbon foils and carbon films deposited with different deposition techniques. In addition, mixing zones were investigated between silicon substrates and carbon films deposited by ablation of carbon with a Nd:YAG laser at different light intensities. The width of the mixing zone strongly depends on the light intensity for the laser ablation and varies from 0.6 μg/cm 2 for a power density of 2 GW/cm 2 to 2.5 μg/cm 2 for 20 GW/cm 2.

Profiling of semiconductor surface layers by heavy ion TOF-E-ERD

We have adapted the elastic recoil detection (ERD) technique to analyse passivation layers of Si x N y O 1− x− y grown on Si substrates in low pressure CVD process. Sample targets were bombarded by 9.87 MeV 35Cl ions to recoil Si, O, N and C atoms incorporated in the sample film. The atomic species of recoils have been identified through eventwise registration of flight time (TOF) and kinetic energy ( E). Using an unfolding program developed by Bachmann the depth profile for each element has been calculated from the TOF energy spectrum. The unfolding program is based on an iterative algorithm that takes into account the interplay between the stopping of projectiles as well as recoils and the stoichiometry of the sample. The chemical composition as a function of depth is discussed in the context of sample preparation conditions.

Characterization of SiN thin films with spectroscopic ellipsometry

In this work we present spectroscopic ellipsometry (SE) measurements on a variety of SiN thin films grown with different techniques. In conjunction with the tetrahedron model for amorphous semiconductors and dielectrics and Rutherford backscattering spectroscopy results we propose that the dielectric function can be indicative of the nitrogen content in the material. In addition, we estimate major optical parameters characterizing the materials, such as the fundamental and Penn gaps and the thickness. Furthermore, we analyze and discuss the effect of annealing under vacuum conditions and in N 2 atmosphere on the thin-film stoichiometry and the modification of the bonds by both SE and elastic recoil detection techniques.

Surface hydrogen profiling in metallic materials by the elastic recoil detection technique

Results are presented for a study of hydrogen concentration profiles obtained by the elastic recoil detection technique for samples of a stainless steel contaminated by hydrogen during service, comparing the data with those obtained for samples of the same material after cathodic hydrogen-charging in the laboratory. Through-thickness hydrogen concentration profiles were calculated from the proton energy spectra obtained, identifying potentially dangerous maximum hydrogen concentrations from 2 to 14 ppm (by weight).

Isotopic effect in thermal re-emission of hydrogen from graphite at elevated temperatures

The thermal re-emission of protium and deuterium from graphite, implanted with 3 keV H2+ or D2+ ion beams up to saturation at room temperature, due to isothermal annealing at temperatures of 450, 500, 550 and 600°C has been studied by means of the elastic recoil detection technique. It is found that the concentrations of retained protium and deuterium decrease rapidly in the beginning and hereafter very gradually with the increase of the annealing time and that the former decay is faster than the latter. The re-emission profiles have been analysed taking into account thermal detrapping (Σd), retrapping (ΣT), local molecular recombination (K1) and hydrocarbon emission. It is determined that the activation energies of Σd for H and D are both equal to 0.60 eV and the isotopic ratio of their pre-exponential factors is 1.4, and that the activation energies of the effective recombination rate constants (K1/C0) (Σd/ΣT)2 for H and D are also 1.2 eV (C0 is the trap density) and the isotopic ratio of their pre-exponential factors is about 2.5 on average. The isotopic effects are discussed in terms of elementary processes.