15N Nuclear Reaction Analysis Research Articles

Accurate measurement of hydrogen concentration in transition metal hydrides utilizing electronic excitations by MeV ions

This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of 15N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for 15N-ions at 6.5 MeV measured (64.55±3.38) eV cm2/1015 atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using 15N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.

Nuclear reaction analysis for H, Li, Be, B, C, N, O and F with an RBS check

15N nuclear reaction analysis (NRA) for H is combined with 1.2MeV deuteron (D) NRA which provides a simultaneous analysis for Li, Be, B, C, N, O and F. The energy dependence of the D NRA has been measured and used to correct for the D energy loss in film being analyzed. A 2MeV He RBS measurement is made. Film composition is determined by a self-consistent analysis of the light element NRA data combined with an RBS analysis for heavy elements. This composition is used to simulate, with no adjustable parameters, the complete RBS spectrum. Comparison of this simulated RBS spectrum with the measured spectrum provides a powerful check of the analysis.

Novel insight into the hydrogen absorption mechanism at the Pd(110) surface

The microscopic mechanism of low-temperature (80 K < T < 160 K) hydrogen (H) ingress into the H2 (<2.66 × 10(-3) Pa) exposed Pd(110) surface is explored by H depth profiling with (15)N nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS) with isotope (H, D) labeled surface hydrogen. NRA and TDS reveal two types of absorbed hydrogen states of distinctly different depth distributions. Between 80 K and ∼145 K a near-surface hydride phase evolving as the TDS α1 feature at 160 K forms, which initially extends only several nanometers into depth. On the other hand, a bulk-absorbed hydrogen state develops between 80 K and ∼160 K which gives rise to a characteristic α3 TDS feature above 190 K. These two absorbed states are populated at spatially separated surface entrance channels. The near-surface hydride is populated through rapid penetration at minority sites (presumably defects) while the bulk-absorbed state forms at regular terraces with much lower probability per site. In both cases, absorption of gas phase hydrogen transfers pre-adsorbed hydrogen atoms below the surface and replaces them at the chemisorption sites by post-dosed hydrogen in a process that requires much less activation energy (<100 meV) than monatomic diffusion of chemisorbed H atoms into subsurface sites. This small energy barrier suggests that the rate-determining step of the absorption process is either H2 dissociation on the H-saturated Pd surface or a concerted penetration mechanism, where excess H atoms weakly bound to energetically less favorable adsorption sites stabilize themselves in the chemisorption wells while pre-chemisorbed H atoms simultaneously transit into the subsurface. The peculiarity of absorption at regular Pd(110) terraces in comparison to Pd(111) and Pd(100) is discussed.

Depth profiling of oxygen in oxide films by 18O(p,α)15N nuclear reaction analysis

The paper describes the determination and depth profiling of oxygen in thin oxide films using 18O(p,α)15N nuclear reaction. The excitation function of 18O(p,α)15N nuclear reaction exhibits a resonance at 629 keV and a plateau at 730 keV with uniform cross-section. The resonance is used to determine the depth profile of oxygen in films while the plateau, to estimate its overall concentration. The resonance, characterized by a width of 2.1 keV enables high-depth resolution (~20 nm) measurements and has a probing depth of more than a micron. The paper presents depth profile measurements of oxygen in several metal oxide films (SiO2, TiO2 and HfO2) using this resonance. Possible interferences arising from 15N(p,α)12C, 19F(p,α)16O and 11B(p,α)2α nuclear reactions are also discussed. It has been shown that it can serve as a suitable alternative to 3.05 MeV 16O(α,α)16O resonant scattering which is generally used for depth profiling oxygen. It is, in fact, more reliable and precise in materials that witness significant large angle multiple scattering. It can also be advantageously used to monitor 18O, when used as a tracer.

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.

Hydroxide in olivine: A quantitative determination of the absolute amount and calibration of the IR spectrum

Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by 15N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H2O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750–3100 cm−1 region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle‐derived olivine analyzed to date contains 240 ppm wt. H2O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra.

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.

Determination of hydrogen in 6H–SiC epitaxial layers by the 15N nuclear reaction analysis technique

By using the 15N nuclear reaction analysis (NRA) technique the hydrogen concentrations in 6H–SiC epilayers were determined and compared with the results of infrared (IR) absorption measurements. Both methods found similar hydrogen concentration. The hydrogen depth profile measured by the NRA technique is shown. The NRA spectra show hydrogen concentrations that remain constant for depths larger than 150 nm. The measured bulk concentrations for the two SiC epilayers are 1.4 × 10 20 and 2.5 × 10 20 hydrogen atoms/cm 3.

Depth resolution and dynamic range of 18O(p,α) 15N depth profiling

This paper discusses an approach to get better depth resolution and the 2–3 μm dynamic range needed for diffusion studies of oxygen, using 18O(p,α) 15N nuclear reaction analysis (NRA). This was achieved by optimizing the experimental parameters, and using fast electronics without the absorber in front of the detector. By energy analysis of the α-particles, a depth resolution of 170 to 300 Å was obtained with the dynamic range varying from the surface to a depth of 3 μm. Problems in data analysis, i.e., the cross sections and energy straggling will be discussed. Examples in depth profiling of 18O-implanted SrTiO 3 single crystals and Yttrium stabilized zirconia (YSZ) single crystals annealed in 18O at high temperature are presented.

Analysis of hydrogen in technical layers

The experimental set-up for hydrogen analysis with the 15N nuclear reaction analysis technique at the 2.1 MV tandem accelerator at BAM is described. Hydrogen concentrations in diamond-like carbon coatings produced by laser-induced vacuum arc deposition have been determined. Hydrogen contents of 0.15–3 at.% were measured. Some coatings show remarkable variations of the hydrogen concentration with depth. Variations up to a factor of 3 within 50 nm were found. Silicon oxynitride SiN x O y films deposited by DC-magnetron reactive sputtering on silicon substrates were also investigated. For pure Si 3N 4, a H-content of 1.6 at.% was found whereas in the films containing oxygen H-concentrations from 4 to 9 at.% were measured. Finally, H-contents of hydrated glass samples have been measured in order to calibrate infrared spectrometric measurements on the same samples.

Surface Oxygen Exchange Kinetics and Oxygen Diffusion Rates in Ysz Single Crystals

ABSTRACTIsotope exchange with C18O2 followed by depth profiling analysis was used to study surface exchange and bulk diffusion of oxygen in single crystal ((100) surface orientation) yttria-stabilized zirconia (YSZ) in the temperature range 250°C - 350°C. The depth profiles, which were obtained using 18O(ρ,α)15N nuclear reaction analysis (NRA) and secondary ion mass spectrometry (SIMS), reveal both the bulk oxygen diffusion coefficients (D) and surface exchange coefficients (k). Bulk oxygen diffusion coefficients are consistent with an extrapolation to lower temperature of previously published results with an activation energy of 114 kJ/mol (1.2 eV). The surface exchange rates, however, depend strongly on the gas exchange species. Much higher exchange rates are observed with C18O2 than with 18O2 (over four orders of magnitude when compared to an extrapolation to lower temperatures of previously published results) with a measured activation energy of 152 kJ/mol (1.6 eV). This faster surface exchange rate enabled measurable 18O tracer profiles to be generated at lower temperatures than previously reported, further contributing to the understanding of YSZ material properties and bringing to light a possible order/disorder transition similar to that previously observed at 650°C.

Analysis of hydrogen in Nb/Cu multilayers using ion beams

The dependence of the H concentration on the layer thickness in H-charged Nb/Cu multilayer samples has been studied using 15N nuclear reaction analysis and high-energy elastic recoil detection. This system shows a smooth increase in H concentration in the Nb layers with increasing layer thickness. The H concentration shows a tendency towards saturation as the thickness increases. The relative concentrations are independent of the total amount of incorporated H in the measured range up to about 40 at.%. These results are also independent of the stacking order of the 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.

XPS study of the passive films formed on nitrogen-implanted austenitic stainless steels

Austenitic stainless steels (304-type) have been implanted with nitrogen ions in order to investigate the effects of implanted nitrogen on their electrochemical behaviour and on the nature of the passive film formed on the steels in acid (0.5M H 2SO 4). Alloys with two nitrogen doses have been prepared (2.5×10 16 and 2×10 17 N atoms/cm 2). The implanted alloys have been characterized by 15NNRA (nuclear reaction analysis) and XPS (X-ray photoelectron spectroscopy). Alloy surfaces with well-defined N concentrations were prepared, prior to the electrochemical measurements, by argon-ion sputtering of the implanted material for a fixed time in order to reach a well-defined point on the nitrogen depth profile. The samples were then transferred without exposure to air to an electrochemical cell mounted in an inert gas glove box. The implanted nitrogen modifies the electrochemical behaviour of the alloy. The anodic dissolution in the active state is enhanced, and the current density in the passive state is increased. Surface analysis of the alloys by XPS after passivation shows that implanted nitrogen is enriched on the surface during dissolution and passivation of the alloys. The process by which N is enriched on the surface is anodic segregation, which was first observed and characterized for S on Ni and NiFe alloys [J. Oudar and P. Marcus, Appl. Surf. Sci. 3 (1979) 48: P. Marcus, A. Teissier and J. Oudar, Corros. Sci. 24 (1984) 259]. The passive films formed on both the unimplanted and implanted alloys have a bilayer structure with an inner oxide layer and an outer hydroxide layer, but on the nitrogen-implanted alloy, a chromium nitride phase is formed at the expense of the chromium oxide. After passivation of the implanted alloys, three chemical states of nitrogen are detected in the N 1s spectrum. The high binding energy (399.4 eV) peak corresponds to a nitrogen species located on the surface of the passive film, which is produced by reaction of the implanted nitrogen with the solution. The peak at low binding energy (396.3 eV) is assigned to nitrogen bonded essentially to chromium, under the form of a nitride, which is incorporated in the passive film. The peak at intermediate binding energy (397.0 eV) corresponds to implanted nitrogen in the alloy, and is detected because the passive film is very thin. The XPS measurements and the sputter depth profiles indicate that during the anodic segregation of N, the chromium-rich nitride which is formed is incorporated as islands in the passive film.

Analysis of hydrogen in low pressure diamond layers

The hydrogen concentration of diamond layers produced by a low pressure chemical vapour deposition method on SiAlON substrates has been determined by means of the 15N nuclear reaction analysis technique. The results show distinct differences in the hydrogen content which depend on the gas pressure and on the acetone-hydrogen gas mixture used in the deposition. The resulting diamond morphology is found to be related to the hydrogen content, well-faceted layers containing about 0.2–0.9 at % H, and balas-type layers with about 1.4 at.%H. Contrary to expection, no relation between the crystal size in the well-faceted layers and the average hydrogen content was found. Additional Rutherford backscattering measurements revealed a high purity of the films with respect to elements heavier than carbon.

Intrinsic stress and mechanical properties of hydrogenated silicon carbide produced by plasma-enhanced chemical vapor deposition

Hydrogenated SiC films were deposited by radio frequency plasma chemical vapor deposition in a silane–ethylene gas mixture. In the as-deposited condition the films are in compression with absolute values as high as 2×1010 dyn/cm2 (2 GPa). The origin of the stress is attributed to hydrogen incorporation, as evidenced by C–H and Si–H bands observed in infrared transmission measurements of as-deposited films. The hydrogen content was measured directly by 15N nuclear reaction analysis. Values as high as 40% (at.) were observed. Annealing the films in vacuum above 400 °C eliminated the hydrogen-related bands, accompanied by a simultaneous stress reversal from compressive to tensile. It is shown that the stress magnitude and sign can be modulated, depending on the annealing conditions. The ultimate tensile strength and elastic modulus were measured using the bulge test on free-standing membranes. Their values are close to bulk values. Raman spectroscopy and x-ray diffraction show that the films are amorphous. SiC membranes 3 μm thick and 50 mm in diameter were produced with 75% transmission at 632.8 nm, uncorrected for reflection losses.

Intrinsic stress in diamond films prepared by microwave plasma CVD

The stress in diamond films prepared by microwave plasma CVD was investigated as a function of methane concentration (0.2%–3.0%) and deposition temperature (600–900 °C). Tensile and compressive total (thermal and intrinsic) stress were observed, depending on the deposition conditions. The thermal stress is compressive and relatively constant (0.215–0.275 GPa) over the temperature range investigated. The intrinsic stress is tensile and its origin is interpreted in terms of the grain boundary relaxation model. Calculations indicate a value of 0.84 GPa, using the grain boundary model, which is in fair agreement with the measured value. For the methane series, the tensile intrinsic stress decreases with increasing the methane fraction. The increasing compressive stress is ascribed to increased impurity (hydrogen and nondiamond phase carbon) incorporation with increasing methane fraction. 15N nuclear reaction analysis shows a linear correlation between hydrogen in the film and methane in the supply gas while spectroscopic ellipsometry shows a direct correlation between optically absorbing nondiamond (sp2) carbon incorporation and methane. For the temperature series, the intrinsic tensile stress increases with deposition temperature. The increase is ascribed to decreasing sp2 C incorporation with temperature, as confirmed by spectroscopic ellipsometry measurements.

Properties of diamond membranes for x-ray lithography

Microwave plasma chemical vapor deposition was used to deposit diamond films on polished silicon and then the substrate was back-etched to form taut free-standing membranes up to 75 mm diam. Raman spectroscopy and x-ray diffraction verify that the films are diamond. Transmission electron microscopy and x-ray diffraction reveal that the films are fine-grained polycrystalline diamond with an average grain size between 15 and 110 nm. The films contain microcrystalline graphite and nondiamond carbon as indicated by the broad Raman bands at 1355 and 1560 cm−1, respectively. The measured x-ray transmission of a 3.25-μm-thick membrane at the Cu Kα line is 99.2% while the optical transmission at the He-Ne laser line is 58% for a 1-μm membrane, uncorrected for reflection losses from both surfaces, absorption, and scatter. The transmission in the ir is at the theoretical limit, 71%. The surface roughness of a typical 3-μm-thick membrane is about 30 nm on the side away from the silicon substrate and 20 nm on the side adjacent to the substrate. The surface roughness scales inversely with methane fraction in the supply gas due to decreasing grain size. The typical membrane stress is 0.03–0.15 GPa. The films contain between 0.8% and 7.0% hydrogen, as determined by 15N nuclear reaction analysis. No correlation was observed between hydrogen content in the film and deposition temperature; however, a direct correlation was observed with methane fraction. The average in-plane distortion is 70 nm for a 1.5-μm-thick diamond mask with 0.2-μm-thick tungsten absorber. No measurable out-of-plane distortion was observed for evaporated gold absorber metallization while tungsten produced 0.8 μm distortion.

Depth Profiling of Tritium in Materials for Fusion Technology

The paper outlines recent progress in depth profiling of tritium distribution near the surface of materials by two ion beam techniques; elastic recoil detection (ERD) and T(d,/alpha/)n nuclear reaction analysis (NRA). The sensitivity and depth-resolution of both methods are examined for a series of tritiated titanium films. Calculated depth profiles and ranges of implanted tritium ions in selected candidate materials for thermonuclear fusion devices are also given. Depth profiles of tritium implanted into specimens of graphite and lithium oxides as a function of temperature are discussed as the examples of applications.

Chemisorption and implantation of hydrogen isotopes in lithium-based fusion blanket ceramics and their thermal release: A study by nuclear reaction analysis

A brief summary is presented on tritium implantation techniques and depth profiling analysis by elastic recoil detection (ERD) and T(d, α)n nuclear reaction analysis (NRA), as applied to the studies of lithium ceramic materials to be used as tritium-breeding blankets in fusion reactors. New data about thermal behaviour of hydrogen and tritium near the surface of both poly- and monocrystalline Li 2O, and ceramic γ-LiAlO 2, are discussed. Ion beam techniques are especially suitable for studying near-surface diffusion and chemisorption of tritium, as well as for modelling the influence of irradiation damage on tritium transport phenomena.