Elastic Recoil Detection Technique Research Articles

Hydrogen in diamond-like carbon films

Properties of physical vapor deposited diamond-like carbon films and the migration of hydrogen in co-deposited samples were studied. Measurements utilizing Rutherford backscattering spectrometry and Doppler-shift-attenuation techniques were used to obtain the average mass density of the films. Distributions of co-deposited hydrogen and deuterium were measured by the nuclear resonance reaction 1H ( 15N,αγ) 12C, and the elastic recoil detection technique, respectively. Secondary ion mass spectrometry was also used in combination with these two methods. It was observed that in H and CH 4 co-deposited DLC films the temperature of H release varied between 950 and 1070°C depending on the H concentration.

Dynamic behavior of hydrogen isotopes in tungsten–carbon composite materials

The thermal re-emission of hydrogen isotopes from WC layers on graphite, implanted with 5 keV H + 2 and D + 2 ion beams up to saturation at room temperature, has been studied by means of the elastic recoil detection (ERD) technique. It is found on isochronal annealing for 10 min that the re-emission takes place in three stages: the first stage occurs for retained fraction of 1.0–0.6, the second stage for retained fractions of 0.6–0.2 and the third stage below the retained fraction of 0.2, which is ascribed to re-emission from carbon segregated in the grain boundaries of the WC layers. It is also found on isothermal annealing that the concentration of retained hydrogen decreases rapidly in the beginning and hereafter very gradually with increasing the annealing time. The isothermal re-emission curves have been analyzed by taking into account the two trapping sites and the mass balance equations with two kinds of thermal detrapping ( Σ d 1 , Σ d 2 ), retrapping (Σ t) and local molecular recombination ( K 1) between free hydrogen atoms. The isotope difference of the rate constants for elementary processes determined by best fitting of the solution to the experimental re-emission profiles is discussed with relevance to the nature of two trapping sites.

Thermal behavior of deuterium implanted into SrCe 0.95Yb 0.05O 3−δ

The concentration change of D and H retained in SrCe 0.95Yb 0.05O 3−δ by 5 keV D 2 + and H 2 + irradiation and subsequent thermal annealing has been studied by means of the elastic recoil detection (ERD) and Rutherford backscattering (RBS) techniques. It has been found that the saturation concentration of D implants is D/SrCe 0.95Yb 0.05O 3−δ=1.1. Decay curves of D concentration on isothermal annealing show that the retained numbers of D decrease rapidly and hereafter gradually, and finally reach a constant level at each temperature. The decay curves have been analyzed using the mass balance equations for free and trapped species of D, which include the rate constants of the thermal detrapping, retrapping and local molecular recombination between free species leading to the release of D. The analysis indicates that the activation energy for thermal detrapping is 0.56 eV and that for effective molecular recombination is 1.7 eV. These data are compared with some data obtained from the other measurement.

Retention and re-emission of deuterium implanted into tungsten monocarbide

The retention of deuterium in tungsten monocarbide on graphite, implanted with 5 keV D + 2 ion beams up to saturation at room temperature and the re-emission of deuterium from tungsten monocarbide by post thermal annealings have been studied by means of the elastic recoil detection (ERD) technique. It is found that the steady state concentration of retained deuterium is 1.7×10 22 cm −3 at room temperature, which decreases to 1.4×10 22 cm −3 due to spontaneous re-emission in 5 h of terminating the implantation. It is also found on isothermal annealing at temperatures of 70°C, 100°C, 150°C, 200°C and 250°C that the concentration of retained deuterium decreases rapidly in the beginning and hereafter very gradually with increasing annealing time. The re-emission profiles have been analysed taking into account thermal detrapping ( Σ d), retrapping ( Σ T), local molecular recombination ( K 1) between movable deuterium atoms. It is determined that the activation energy of the effective molecular recombination rate constant ( K 1/ C 0)( Σ d/ Σ T) 2 is 0.47 eV, where C 0 is the trap density and that the activation energy of the thermal detrapping rate constant Σ d is 0.20 eV.

Anomalous exchange of deuterium implanted into an oxide ceramic for protium in air vapor

This paper describes an anomalous exchange of deuterium in an oxide ceramic, SrCe 0.95Yb 0.05O 3− δ by protium in air-vapor. The ceramic specimen was implanted with 5 keV D 2 + ion beam up to saturation at room temperature and exposed to normal air introduced into the vacuum chamber. It was eventually found by means of the elastic recoil detection technique that deuterium implanted was almost completely exchanged for protium which was included in the air-vapor. On the other hand, it was found in the vice versa case that no exchange of protium implanted into the ceramic for deuterium in D 2O vapor took place. The mechanism for such an anomalous isotope replacement is discussed.

Low-energy random and channeled H ion ranges in Si: Measurements, simulation, and interpretation

We present measurements of the range profiles of 0.5 and 1 keV H and D ions implanted in amorphous Si (a-Si) and crystalline Si (c-Si) in random, 〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉 directions. The profiles were obtained by the E × B filtered Elastic Recoil Detection (ERD) technique with a resolution of ∼10 nm. This is the first such complete set of low-energy data to our knowledge. The whole set of profiles could not be simulated self-consistently with standard versions of existing codes. After critically reviewing the codes, we conclude this is due to the neglect of the anisotropy of the valence electron density in covalent solids. The localization of these electrons in the walls of the channels causes a reduction in screening and prompter dechanneling in the narrower channels 〈1 0 0〉 and 〈1 1 1〉. Moreover, it reduces the inelastic losses near the channel axes. We implemented an appropriate adjustment in the binary collision code MARLOWE (M.T. Robinson, Phys. Rev. B 40 (1989) 10717). We then successfully fitted all the data using only three parameters. The first of these is essentially determined by the random profiles and indicates that the inelastic energy loss is ∼1.5 × larger than the well-known Lindhard–Scharff–Schiott (LSS) value; this agrees with high energy data. An Oen–Robinson (OR) type local energy loss is also required. The second parameter, introduced by us, serves to adjust the screening function in the interatomic potential to account for the anisotropy of the electron density around the Si atoms. The third parameter is connected with simultaneous interactions of the ion with several atoms due to the crystal symmetry; in particular, focussing of the ion by trios of atoms in the 〈1 1 0〉 channel is evidenced.

Influence of the condensed phase state on the energy loss determination in Na-faujasite

In porous crystals such as zeolites, there is more than one kind of cavity or channel to which small guest molecules may have access. This property may provide a variety of natural environments in which one can evaluate the dispersion energy contribution to the physical bond between different molecules. This work is aimed to determine the contribution of physical state and condensed sorbed water molecules to the stopping power measurements in zeolite material. Electronic stopping power for helium projectiles have been measured with a combined backscattering and transmission methods in different states of Y-faujasite, in the range of energy 953–2734 keV. The physical state of the zeolite has been changed by irradiating the faujasite samples with helium ions at 3 MeV up to doses 4 × 10 12–2 × 10 14 He/cm 2. The variation in the chemical structure of the Y-faujasite has been studied by means of IR absorption spectra and the Elastic Recoil Detection technique analysis (ERDA) has been used to determine the amount of hydrogen desorbed after each irradiation. The main results of these experiments are that the response to irradiation is completely different according to the irradiation fluence considered, in which case a correlation between changes in d E/d x and the nature of the modifications created by the irradiation in the material can be made.

Characterization of nucleation and growth of MW-CVD diamond films by spectroscopic ellipsometry and ion beam analysis methods

The time evolution of diamond film nucleation and growth have been investigated by spectroscopic ellipsometry (SE). Rutherford backscattering spectrometry (RBS) combined with elastic recoil detection (ERD) techniques. Diamond films were prepared using the microwave plasma CVD (MW-CVD) method on Si. In the plasma chamber, bias voltage of −200 V DC was applied to the Si substrate for 4–12 min in H2-CH4 (10%) to nucleate diamond. The substrate modification by H2 plasma cleaning and the DC bias nucleation of carbon layer followed by diamond film growth in H2-CH4 (0.5%) gas were studied. After H2 plasma cleaning the native 2.7 nm thick SiO2 is partly removed and the bias nucleation resulted in a mixture of SiO2 and SiC. With longer time, a very slow increase in film thickness up to 4.6 nm and a fast enrichment of the SiC contents have been observed. Thicker diamond films were found to consist of a 2–40 nm thick porous SiC-H layer, a bulk microcrystalline diamond layer and an amorphous capping layer 2–6 nm thick. The refractive index and the density of the bulk layers were identical to those of the single crystal diamond mixed with about 2% graphite and hydrogen. Porous layered structures were found in films reaching up to 2–40% porosities.

Retention of hydrogen isotopes in beryllium by simultaneous H + and D + irradiation

The concentration profiles of H and D retained in beryllium by simultaneous dual H + and D + ion irradiation at room temperature and on post isochronal annealing have been measured by means of the elastic recoil detection (ERD) and Rutherford backscattering (RBS) techniques. It has been found that as the irradiation time increases, the concentrations of H and D retained increase linearly in the beginning of the irradiation and hereafter that of H saturates faster than that of D. The ratio of the concentration of D to H at steady state was determined to be 1.2 ± 0.1. The isotope ratio is in good agreement with the theoretical one (1.25) calculated from the kinetic equations for free and trapped hydrogen species at steady state and local equilibrium, in which the diffusion-limited rate constants for the trapping, local molecular recombination and the ion-induced detrapping cross-section are taken into account. It has also been found from the isochronal annealing curve that there are two stages at 363 K and 573 ± 100 K and the re-emission rate of H is the same as that of D at the lower stage and is faster at the higher stage, which is so-called isotope effect.

Retention and re-emission processes of hydrogen isotopes in graphite and beryllium

The mass balance equations and the rate constants of elementary processes related to retention and re-emission of hydrogen isotopes have been described for evaluation of their transient recycling fluxes from targets irradiated simultaneously with H + and D +. The D/H ratios of the concentrations of H and D retained at steady state calculated under three different conditions are compared with the experimental values for graphite and beryllium measured by means of the elastic recoil detection technique. The retention and re-emission processes of hydrogen isotopes in graphite and beryllium are discussed.

The reduction of sample memory effects in the Chalk River AMS ion source

The mechanism underlying Cl and I sample-to-sample interference in the new Chalk River AMS ion source has been studied and compared with the interference observed in an earlier ion source of different internal geometry. The distribution of sputtered material and its degree of migration was measured with the radioactive tracer, 82Br. The temperature dependence of the surface constitutent was measured with the elastic recoil detection (ERD) technique and the effect of sample geometry and ion source cleaning was studied with elevated (5 × 10−10) 36ClCl and 129II samples. These measurements indicate that a hot (>350°C) aperture plate ahead of the sample can prevent the sputtering of contaminated regions near the sample. The plate itself remains relatively free of Cl or I itself since these elements or their Cs-gettered compounds are desorbed at this temperature. A small, fixed quantity of Cl or I on this surface is observed, which if sputtered by Cs+ ions, may contribute to ion source memory. Relative sample-to-sample interference for both Cl and I is about 10−3 after 20 min or 10−4 after 60 min.

Isotope effects in hydrogen retention of graphite and beryllium irradiated simultaneously with dual H + and D + beams

The concentration profiles of H and D retained in graphite at temperatures from room temperature to 900 K and beryllium at room temperature by simultaneous dual H + and D + ion implantation have been measured by means of an elastic recoil detection (ERD) technique. It has been found that as the fluence increases, the concentrations of H and D retained in graphite and beryllium increase at the same rate in the beginning of the implantation and hereafter that of H saturates faster than that of D. The concentration ratios of D to H retained in graphite and beryllium n T D n T H , at steady state were determined to be 1.8±0.2 and 1.25±0.2, respectively. The steady state values of n T D n T H for graphite at room and high temperatures and beryllium at room temperature have been also calculated to be 1.5±0.2, 1.5±0.2 and 1.3±0.2, respectively, by solving a set of mass balance equations for H and D under simultaneous H + and D + ion implantation. The experimental and theoretical values are compared and discussed.

Mechanical and Tribological Properties of a-GeCx Films Deposited by DC-Magnetron Sputtering

ABSTRACTAmorphous carbon-germanium films were grown by dc-magnetron sputtering at different argon plasma pressures ranging from 0.17 and 1.4 Pa. The water-cooled sample holder was grounded. The film thickness were typically 0.5 μm. The ratio between germanium and carbon atomic concentration ranges up to 2.8, as measured by Rutherford backscattering spectrometry (RBS). Elastic recoil detection technique was used to measure hydrogen contamination. The film hardness was measured by nanoindentation techniques and the internal stress was determined by the bending of the substrate. The incorporation of Ge reduces both the film hardness and the internal stress. Hardness and internal stress increases when the films are deposited in lower pressures. Atomic Force Microscopy (AFM) was used to measure the surface roughness, which was found to be insensitive to the pressure and to the Ge content. A possible influence of the thickness on the morphology of pure carbon films is discussed. The friction coefficient measured by AFM is independent on the film composition within experimental errors.

Hydrogen and deuterium mass transfer and separation during hydriding-dehydriding of palladium studied by the NERD method

The neutron induced elastic recoil detection (NERD) technique with monochromatic 14 MeV neutrons was applied to a hydrogen and deuterium concentration depth profile study during the hydriding—dehydriding process in palladium placed as a membrane or a membrane electrode within a gas or an electrolytic cell, respectively. It was found that hydrogen diffusion may be accompanied by a distinct α-β interphase boundary movement to the membrane exit whereupon a sharp growth of permeation gas flux takes place. An anomalous behaviour of gas flux was also revealed at the point of opposite β-α phase transition of the Pd-D system induced by the membrane heating. Dehydriding of the Pd-membrane as well as both hydriding and dehydriding of a membrane made from a Pd-Ag alloy do not reveal any concentration gradients in the membrane bulk. A much higher H/D isotope separation factor was found in the case of Pd membrane loading with an isotope mixture, when using electrochemical hydriding compared with that observed from gas surroundings.

Retention and re-emission of hydrogen in beryllium studied by the ERD technique

Isochronal and isothermal re-emissions of D atoms retained in Be by room temperature implantation with 3 keV D 2 − ions up to saturation have been studied by combined use of elastic recoil detection (ERD) and Rutherford backscattering (RBS) techniques. In the isochronal re-emission curves, two re-emission stages are observed, a stage at 90°C and a broad stage at 300 ± 100°C. It is found from the change in the ERD spectra that the former stage corresponds to re-emission of D retained around the projected range in the bulk and the latter broad stage is composed of two stages, a lower temperature one corresponds to re-emission from the oxidized surface layers and a higher temperature one from the bulk. From the analysis of the isothermal re-emission curves measured at various temperatures, the activation energies at the three re-emission stages are determined and the trapping states for the three stages are discussed.

Isotope difference between hydrogen inventories in graphite under simultaneous H + and D + irradiation

The concentration of H and D atoms retained in graphite by simultaneous dual implantation at room temperature with H + and D + ions, of which the peak depths in the target coincide with each other, have been measured as a function of time by means of an elastic recoil detection (ERD) technique. It has been observed that the relative concentrations of H and D increase in the same way in the beginning of the implantation, while thereafter separate from each other; and the relative concentration of H saturates to a lower level faster than that of D does to a higher level. The ratio of the saturation concentrations of D to H has been found to be 1.8 which is the so-called isotope effect in hydrogen retention by simultaneous dual irradiation. The experimental result on dual irradiation is shown to be very consistent with the theoretical value, 1.6 ± 0.2, calculated by solving a set of the mass balance equations for H and D, which has been developed from a model for formation of mixed molecule HD and the mass balance equations successfully describing the retention and re-emission of hydrogen isotopes on single ion implantation.

Elastic recoil detection (ERD) with extremely heavy ions

Extremely heavy-ion beams such as 209Bi in elastic recoil detection (ERD) make ERD a uniquely valuable technique for thin-film analysis of elements with mass ≤ 100. We report ERD measurements of compositional analysis of dinosaur eggshells and bones. We also show the capability of the ERD technique on studies of thin-film, high-temperature superconductors.

Retention of H and D in graphite by simultaneous H + and D + ion implantation

The concentrations of H and D atoms retained in graphite by simultaneous dual implantation at room temperature with H + and D + ions, of which the peak depths in the target coincide with each other, have been measured as a function of time by means of the elastic recoil detection (ERD) technique. It has been shown that the retained numbers of H and D increase in the same way in the beginning of the implantation and hereafter separately from each other and the retained number of H saturates to a lower level faster than that of D does to a higher level. The ratio of the saturation concentrations of D to H has been found to be 1.7, which is so-called the isotope effect in the hydrogen retention by simultaneous dual irradiation. The experimental value is shown to be very consistent with the theoretical value, 1.6, calculated by solving a set of the mass balance equations for H and D, which is developed from a model for formation of mixed molecule HD and the mass balance equations successfully describing the hydrogen retention on single ion implantation.

ERD: hydrogen profiling and application to the lattice expansion study

H 2 + ion implantations were performed at 80 KeV and different doses on pure aluminium samples with a 4 MV VDG accelerator. An exact determination of the hydrogen amount implanted is allowed by the use of the elastic recoil detection technique with 2.5 MeV 4He + beam, prior to which the optimization of the ERDA experimental parameters is discussed. Typical application for hydrogen profiling in a-Si:H is presented. The lattice strain variation in implanted AI samples upon the hydrogen concentration is determined using transmission electron microscopy together with the ERDA technique.

Re-emission of H and D implants from graphite by D+ and H+ ion bombardments

The re-emission of H and D, which are implanted into graphite up to saturation at room temperature, by 2.0 keV D+ and 2.5 keV H+ ion bombardments has been studied by means of an elastic recoil detection (ERD) technique. It is found that the decay rate of H implants by the D+ ion bombardment is larger at the low ion fluences than that of D implants by the H+ ion bombardment and hereafter the former becomes almost the same as the latter. The experimental decay curves have been analyzed by best fitting the analytical solution of the mass balance equations, in which retrapping, ion-induced detrapping and molecular recombination are taken into account. The detrapping cross sections of H and D implants by the D+ and H+ ion bombardments have been determined to be 3.3 × 10−18 and 2.5 × 10−18 cm2, respectively. The isotope effect observed in the detrapping cross sections is discussed on the basis of the two possible collision processes.