Nuclear Reaction Analysis Method Research Articles

Deuterium trapping in sintered polished UO2 disks

In this work we present deuterium analysis performed using the 2H(3He,α)1H Nuclear Reaction Analysis method. Different sets of sintered polished uranium oxide disks have been investigated before and after annealing at 400°C in ArD2 atmosphere. Heterogeneous lateral deuterium distributions have been found for all the ArD2 annealed UO2 disks. The average deuterium amount increases after annealing at 400°C in ArD2 and decreases after a second annealing at 400°C in vacuum whatever is the set of sintered polished uranium oxide disks.

Determination of inverse electric field strength of Ta 218O 5 film produced in biological electrolytes using 18O(p, α) 15N nuclear reaction analysis

A 18O(p, α) 15N nuclear reaction analysis (NRA) method was developed for the determination of inverse electric field strengths (also referred to as anodic constants) of Ta 2O 5 oxide films prepared in biological solutions (urine, blood plasma and serum). The results show that fresh biological electrolytes have inverse electric field strengths equal to 17.5 ± 1.2, 17.3 ± 1.2, 17.3 ± 0.8 Å/V for plasma, serum and urine, respectively compared to 16.2 ± 0.2 and 15.7 Å/V, for 3% ammonium citrate water and distilled water, respectively. The inverse electric field strength is shown to depend on the pH variation, the metal substrate and the electrolytic ionic concentration. Freezing or aging of the biological sample results in greater variation and reduction of solution pH. Particle-induced X-ray emission (PIXE) and energy dispersive X-ray (EDS) analyses show no incorporation of ions of Z > 11.

Measurement of deuterium and tritium retentions on the surface of JT-60 divertor tiles by means of nuclear reaction analysis

It is important to measure retentions and depth profiles of deuterium and tritium on plasma facing materials to understand plasma-wall interactions. The nuclear reaction analysis (NRA) has been established using a deuteron beam with an adjustable energy. By means of the NRA, depth profiles of deuterium and tritium on the surface of JT-60 divertor graphite tiles irradiated with DD burning were obtained. The NRA method showed that the average concentrations of the deuterium retained in the surface of two different were 1.3 × 10 16 and 0.3 × 10 16 cm −2. α-particles from the T(d, α)n reaction were measured from a dome unit tile of JT-60U W-shaped divertor and the measured activity of tritium was about 18 kBq/cm 2. The peak energy of the α spectrum obtained with the NRA was about 1.2 MeV. This result implies that energetic tritons were implanted in the divertor graphite tile.

He migration in implanted UO 2 sintered disks

The behaviour of helium implanted in sintered uranium dioxide disks has been investigated as a function of annealing temperature. UO 2 disks have been implanted with 1 MeV 3He ions at a fluence of 1 × 10 16 3He cm −2 using a Van der Graaff accelerator. These implantation conditions lead to a local helium concentration of 0.2 at.% at a depth of 1.9 μm in UO 2. The 3He(d,α) 1H Nuclear Reaction Analysis method was used to determine the helium depth profile after the various annealing stages. The experimental results measured after 1100 °C anneal were analysed using a simple model which satisfactorily reproduces the observed helium depth profile changes. The intragranular helium diffusion coefficient is estimated and the result is assessed against other data published in the open literature.

Application of nuclear reaction analysis for aging investigations of detectors

The article presents a thorough discussion of the applications of the Nuclear Reaction Analysis (NRA) method for investigating aging effects in gas-filled detectors. This technique is particularly efficient in a quantitative evaluation of the presence of light elements (oxygen, carbon, nitrogen, etc.) in the gold coating of the anode wire. The NRA method is also adequate for determining light element distribution with a depth measurement over a range of more than 1 μm. Such data are especially important in studies of gas-discharge avalanche plasmas because they are a starting point for most aging processes. The sensitivity of NRA to these elements is very high—about 5×10 −2%. Application of NRA in our aging investigations gave us a reliable confirmation of the key role of oxygen in the wire-swelling mechanism and demonstrated the kinetics of oxygen transport into the depth of the gold coating.

Helium behavior in UO 2 polycrystalline disks

The behavior of helium implanted in sintered uranium dioxide disks has been investigated as a function of annealing temperature. UO 2 disks have been implanted with 1 MeV 3He at a nominal fluence of 5 × 10 16 3He cm −2 using a Van de Graaff accelerator. The 3He(d,α) 1H nuclear reaction analysis method was used to determine the helium depth profile in the UO 2 disks. Partial flaking was observed after annealing at 500 °C for local He concentration of 1 at.%. After annealing at 600 °C flaking has affected the whole surface. The formation of helium bubbles is discussed.

Determination of the helium diffusion coefficient in nuclear waste storage ceramics by a nuclear reaction analysis method

Host matrices for actinide immobilisation will undergo the formation of large helium quantities due to alpha decay. Helium diffusion rate has to be known in order to predict the long-term behaviour of the material, and particularly, the influence of helium accumulation on mechanical properties. A nuclear reaction analysis method, namely the 3He(d, p) 4He reaction, has been used to analyse the evolution of 3He profiles after ion implantations at 1 and 3 MeV in two materials, monoclinic ZrO 2 (as a test material) and Ca 9Nd(PO 4) 5(SiO 4)F 1.5(OH) 0.5 britholite (envisaged for Am and Pu long-term storage). Two data processing methods are used: the classical excitation curve (proton yields versus deuteron energy) and second, the proton energy spectrum for a given deuteron energy. The characteristics of the 3He profiles (depth, width) obtained by both methods are compared to SRIM estimations. Their evolution during subsequent annealings allows an estimation of the helium diffusion rate in the britholite: D ( cm 2/ s)=(2.5±1.5)×10 −4 exp(−(1.07±0.03 eV)/ kT) in the temperature range 200–400 °C, in agreement with previous results on similar materials. Moreover, the shape of the proton energy spectra suggests channeling effects in britholite.

Below-surface behavior of hydrogen studied by nuclear reaction analysis

The behavior of hydrogen in the near-surface region can be investigated by a nuclear reaction analysis (NRA) technique. The H atom adsorbed on a surface might penetrate the surface and in-diffuse toward the bulk. During metal–semiconductor interface formation, H might be trapped at the interface or out-diffuse toward the surface of the overlayer. The NRA method combined with surface science techniques provides insight into the ‘below-surface’ behavior of H on a nanometer scale.

Analysis of deuterium and lithium on titanium surface by NRA method

Concentrations of deuterium (D) and lithium (Li) in titanium (Ti) were measured with nuclear reaction analysis (NRA) method. With ΔE& E-counter-telescope, proton peaks by the D(d,p)T and 6Li(d,p) 7Li reactions were well resolved from continuous spectrum of α-particles by the 7Li(d,α + n)α reaction. The yields of these protons were obtained and densities of deuterium and lithium isotopes on the Ti surfaces were obtained. Isotopic ratio of lithium was determined by comparing the yield of 6Li(p,3He)α, 6Li(p,α) 3He and 7Li(p,α)α reactions with proton beam bombardment. Deviation among the experimental values was about 9%.

Hydrogen concentration in chalcopyrite thin-film solar cells

A survey of the hydrogen concentration distribution in the various layers of chalcopyrite solar cells is presented. Depth profiles were measured by the nuclear reaction analysis method for the glass substrate, Mo back contact, Cu(In,Ga)S2 or Cu(In,Ga)Se2 absorber, CdS buffer, and ZnO window layer. We find that hydrogen is present in all layers in concentrations exceeding the solubility of hydrogen in the corresponding crystalline bulk materials. This indicates that the deposition process and the polycrystallinity of the layers favor the uptake of hydrogen. The measured concentrations range from some 1018 H/cm3 in the absorber up to some 1021 H/cm3 in the CdS buffer layer. Effects of annealing at elevated temperatures are reported.

Nuclear reaction analysis of hydrogen migration in silicon dioxide films on silicon under 15N ion irradiation

Hydrogen concentration profiles in wet, thermally grown SiO 2/Si layer structures were measured using the 15N nuclear reaction analysis (NRA) method: the measured hydrogen concentration in the SiO 2 layer is initially about 2.2×10 20 cm −3 and almost constant throughout the SiO 2. For the NRA measurement of the initial H-profile a low dose of 15N ions has been taken in order to minimize a change in the profile by the NRA measurement itself. After high dose 15N ion irradiation an accumulation of hydrogen in the SiO 2/Si transition region (called interface) is observed together with a loss of hydrogen through the surface. SiO 2/Si structures with a SiO 2 film thickness of 32, 92 and 173 nm were investigated. A rapid initial increase of the H concentration in the transition region with increasing irradiation fluence is observed for all three samples. In the 32 and 92 nm samples prolonged irradiation leads to a subsequent reduction of the H concentration at the interface.

Thickness measurement of light elemental films

A non-destructive method for measuring the thickness of films composed of light elements has been developed. The method utilizes a conventional electron microscope equipped with a windowless energy-dispersive X-ray spectrometer. The film thickness is determined from the intensity of a characteristic X-ray line from one element in the film after comparison with the intensity of the same X-ray line from a bulk standard. This means that only one standard is needed. The method includes the necessary corrections to obtain the film thickness as a function of the X-ray intensity. The accuracy of this method was checked experimentally by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). Hydrogen-containing amorphous carbon films (60 nm to 2.0 μm thick) deposited on Si(100) wafers from a CH 2I 2+Ar reaction gas mixture served as test samples. The atomic concentration of hydrogen was 10%±5%. The error in the thickness using measurements based on the X-ray signal was found to be less than 5% which was comparable with the accuracy of the TEM, SEM, NRA and RBS methods. By optimization of the method a thickness range of 15 nm to 5.6 μm could be covered.

Ion beam analysis of diamond-like carbon films

Diamond-like carbon films are deposited with a number of different methods. This results in a wide variety of different microstructures and even compositions of the films, which challenges characterization capabilities. Ion beam analysis can be used in many ways to probe the properties of the films. A classic application is the determination of hydrogen concentrations in hydrogenated amorphous carbon films, a-H : C. This is performed by using either a resonance of the nuclear reaction 1H( 15N, αγ) 12C or a forward recoiling technique. Diamond-like films have been doped with metals, Si, F, etc. in order to modify mechanical, tribological, or optical properties. Dopand concentrations can be qualitatively measured using either a backscattering or nuclear reaction analysis (NRA) method. A fairly trivial application is the utilization of either Rutherford or non-Rutherford backscattering to obtain the number of carbon atoms per square centimetre. Combined with other information on the chemical composition of the film and with the thickness obtained with a profilometer, for example, the density of the very thin films can be calculated. The density is an interesting parameter of the films and may vary considerably, depending on the hydrogen concentration and the structure of chemical bonding. If the thickness of the films is not constant or if a diamond-like material is just a deposition with an irregular shape, the above method cannot be utilized. The ion beam technique may still be useful and the Doppler shift attenuation of the resonance can be used. Resonance techniques are useful in analysing some other carbon related films, for example in analysing nitrogen in CN x films. In this paper, the most useful ion beam techniques for analysing diamond-like materials are given with examples.

Hydrogen in thin films of CuInS2 solar cell material

The production of thin films of CuInS2 by the reactive annealing process in H2S atmosphere leads to the incorporation of hydrogen. Hydrogen concentrations of up to 5×1020 cm−3 were measured by means of a nuclear reaction analysis method. No negative influence on the electrical properties of the films containing hydrogen was observed. Instead, hydrogen, when incorporated in situ, seems to help to passivate electrically active lattice defects.

Measurement and analysis of hydrogen depth profiles in MOS-structures by using the 15N nuclear reaction method

The application of the 1H( 15N, αγ) 12C nuclear reaction analysis method promises to become the preferred measurement tool for hydrogen depth profiling in solids. A depth resolution of approximately 5 nm in the near surface region and a sensitivity < 50 ppma makes it the best choice for the analysis of thin films such as the metal-oxide-silicon system in semiconductor research. The experimental setup for depth profiling at the authors' laboratory, which was recently improved, is presented and its main features are highlighted. The recorded measurement data need to undergo a deconvolution procedure which is solved by the use of a computer program. Hydrogen depth profiles of aluminum and poly-Si gate metal-oxide-silicon capacitors are presented to show the usefulness of this deconvolution. Applying physically justifiable parameters, a deeper insight at the important interface region is possible.

Ion beam analysis of ultrathin dielectric films

Nuclear reaction analysis and nuclear resonance profiling methods are currently used to study silicon-based ultrathin (thickness < 10 nm) dielectric films, like silicon oxide, silicon nitride and silicon oxinitrides. The nuclear reactions are used to measure the total amounts of hydrogen, nitrogen and oxygen isotopes that take part in the films, with sensitivities as low as 10 12 atoms cm −2. Nuclear resonance profiling and also step-by-step chemical etching associated with nuclear reaction analyses are used to measure the concentration versus depth profiles of hydrogen, nitrogen, oxygen and silicon isotopes with depth resolutions of about 1 nm. Furthermore, channeling of alpha-particles combined with detection at very grazing angles is used to measure the average stoichiometry of the ultrathin films.

Development of Na+-sensitive membranes based on sputtered Na-Al-Si glasses

Na+-sensitive microdevices are of increasing interest for integration in microanalytical systems e.g. for biomedical applications or for industrial process control. In order to produce ultra thin Na+-sensitive layers with fixed and reproducible composition and, in particular, defined Na concentration by means of RF sputtering, an off-axis geometry of a magnetron with cylindrical target was chosen for minimizing back-sputtering effects from the already deposited material. With this inverted cylindrical magnetron (ICM) it was possible to obtain reproducible and controllable sodium aluminosilicate glass layers on semiconductor substrates. Several surface and thin layer analytical techniques were applied for characterization of the membranes and for stoichiometry control. Especially by the non-destructive nuclear reaction analysis method a constant Na profile throughout the glass layer and — together with AES depth profiles — the diffusion barrier effect of an Si3N4 interface layer could be verified. Electrochemical measurements proved Nernstian sensitivity down to 10−4 M Na+ in solutions of pH 7, supporting sufficient stability and reproducibility of the sputtered Na+-sensitive layers.

Hot-electron-induced hydrogen redistribution and defect generation in metal-oxide-semiconductor capacitors

Redistribution of hydrogen caused by hot-electron injection has been studied by hydrogen depth profiling with 15N nuclear reaction analysis and electrical methods. Internal photoemission and Fowler–Nordheim injection were used for electron injection into large Al-gate and polysilicon-gate capacitors, respectively. A hydrogen-rich layer (∼1015 atoms/cm2) observed at the Al/SiO2 interface was found to serve as the source of hydrogen during the hot-electron stress. A small fraction of the hydrogen released from this layer was found to be retrapped near the Si/SiO2 interface for large electron fluences in the Al-gate samples. Within the limit of detectability, ∼1014 cm−2, no hydrogen was measured using nuclear reaction analysis in the polysilicon-gate samples. The buildup of hydrogen at the Si/SiO2 interface exhibits a threshold at ∼1 MV/cm, consistent with the threshold for electron heating in SiO2. In the ‘‘wet’’ SiO2 films with purposely introduced excess hydrogen, the rate of hydrogen buildup at the Si/SiO2 interface is found to be significantly greater than that found in the ‘‘dry’’ films. During electron injection, hydrogen redistribution was also confirmed via the deactivation of boron dopant in the silicon substrate. The generation rates of interface states, neutral electron traps, and anomalous positive charge are found to increase with increasing hydrogen buildup in the substrate and the initial hydrogen concentration in the film. It is concluded that the generation of defects is preceded by the hot-electron-induced release and transport of atomic hydrogen and it is the chemical reaction of this species within the metal-oxide-semiconductor structure that generates the electrically active defects.

Study of hydrogen incorporation in MOS-structures after various process steps using nuclear reaction analysis (NRA)

We present hydrogen depth profiles in thin multilayer films determined by the use of the 1H( 15N,αγ) 12C nuclear reaction analysis method. Samples of aluminum gate MOS capacitors with a different annealing history show significant differences in hydrogen content in the bulk SiO 2 as well as at the interfaces of the MOS system. The measured profiles are brought into correlation with the radiation induced increase of oxide charge density N ot and interface state density N it. Along with this study we describe the use of a computer program to simulate the folding of certain model hydrogen profiles with the excitation function of the NRA method to get the true hydrogen distribution out of the measured gamma ray yield.

Analysis for hydrogen by nuclear reaction and energy recoil detection

The use of MeV ion beams to measure hydrogen concentration profiles is reviewed. Both nuclear reaction analysis (NRA) and energy recoil detection (ERD) methods are discussed. Details of experimental approaches used and the effects of these different approaches on the analytic characteristics obtained are considered. The use of Doppler spectroscopy in both NRA and ERD to study the bonding of hydrogen in solids is briefly reviewed. The different methods are compared in terms of their advantages and disadvantages for certain analytic characteristics including accuracy, beam damage effects, sensitivity, and depth resolution.