3D hydrogen profiling by elastic recoil detection analysis in transmission geometry

An analytical procedure and a simulation-optimization algorithm are described for hydrogen determination based on elastic recoil detection induced by low-energy ⁴He ions ( 3 MeV) using transmission geometry. Hydrogen concentration depth profiles can be derived from the experimental recoil spectra for a depth range of up to 6 μm with a resolution better than 40 nm at the surface. The method is applied to thin polyimide films irradiated by high-energy heavy ions. The 3D hydrogen distribution is determined with a ⁴He⁺ mubeam. A high-hydrogen-concentration zone below the surface is shown. The hydrogen distribution is seen to evolve during the ⁴He⁺ irradiation.     

Hydrogen profiling of Nb-Hf-Nb layers by the N method

Investigations of the behavior of hydrogen in thin Nb-Hf-Nb layers were performed by the nuclear reaction ¹H(¹⁵N, γ)¹²C. The preparation of the samples as well as first studies of the surfaces and interfaces of this system by Auger electron spectroscopy and low-energy electron diffraction are described. The influence of lattice distortions at the metal-metal interfaces on the depth profile of the hydrogen concentration is discussed.     

Electron microscopy and Rutherford backscattering spectrometry characterisation of 6H SiC samples implanted with He

6H SiC single crystals were implanted at room temperature with 1 MeV He⁺ up to a fluence of 2 × 10¹⁷ at./cm². RBS-channeling analysis with a 2 MeV He⁺ beam indicated the formation of extended defects or the generation of point defects at a constant concentration over a depth of about 1 μm. Electron microscopy characterisation revealed the presence of two amorphous buried layers at depths of about 1.75 and 4.8 μm. They are due to the implantation and to the analysing RBS beam, respectively. No extended planar or linear faults were found in the region between the surface and the first amorphous layer. However, at the surface, a 50 nm thick amorphous layer was observed in which crystalline inclusions were embedded. Electron diffraction and HREM data of the inclusions were typical for diamond. These inclusions were even found in the crystalline SiC material below this layer, however at a reduced density.     

Hydrogen dynamics in electrochromic multilayer systems investigated by the N technique

The resonant reaction ¹H(¹⁵N, γ)¹²C was used to determine the depth distribution of hydrogen in two electrochromic multilayer systems. The systems can be bleached and colored by applying an external voltage. To test models explaining this effect by a change of H content (c_H) in electrochromic layers, H profiles of the systems were measured as a function of the applied voltage. For NiO_x, c_H was found to vary as predicted, whereas for WO₃, c_H changes were smaller than expected. Additionally, H uptake into the ITO electrode was observed.     

Hydrogen analysis of mineral samples at University of Tsukuba

This study reports the present status of our work on the hydrogen analysis of mineral and rock samples. The preparation of a standard material by means of ion implantation, a method of its calibration and the application of the method are described. The number of hydrogen atoms per unit volume in the standard material can be determined from the simultaneous observation of -particles, γ rays and –γ coincidence events for the ¹H(¹⁹F,γ) reaction at the 16.44 MeV resonance energy. The hydrogen content in a natural obsidian determined with the method mentioned above is in agreement with that obtained by FTIR. A heavy-ion microbeam system under construction, which consists of a Russian-type quadrupole magnet for beam focusing, a beam defining slit system and a γ-ray detector, is also described.     

The Stuttgart positron beam, its performance and recent experiments

A monoenergetic MeV positron (e⁺) beam, with a flux at present of 6 × 10⁴ e⁺/s in the energy range of 0.5 to 6.5 MeV, has been installed at the Stuttgart Pelletron accelerator. The stabilization and the absolute calibration of the energy E is monitored by a Ge detector with real-time feedback; a relative energy stability of ΔE/E 10⁻⁴ is obtained. So far, e⁺e⁻ scattering and annihilation-in-flight experiments for investigating the low-energy e⁺e⁻ interaction as well as β⁺ γ positron lifetime measurements in condensed matter have been performed. The advantages of the β⁺ γ method compared to the conventional γγ coincidence technique have been demonstrated. Recently, triple-coincidence positron “age-momentum correlation” measurements have been carried out on fused quartz. A brief account is given on the development of a “positron clock” aiming at a substantial improvement of the time resolution of the β⁺ γ positron lifetime measurements.     

The aging of zirconium tritides: A transmission electron microscopy study

Young Zr tritides were investigated for aging times up to about 6 months' using analytical transmission electron microscopy. No isotopic differences between hydrides and tritides were seen as far as precipitation morphology and structures are concerned. Also, no low-temperature phase transitions were observed in the tritides γ and δ. ³He generated by tritium decay was found to precipitate in very small bubbles (1–2 nm in diameter and densities of about 5×10²³ m⁻³) which were first clearly visible after approximately 24 days of aging. In addition to the ³He bubbles, interstitial loop damage was observed. Acoustic emission techniques applied to 5 and 6 months old Zr-T samples did not reveal any above background acoustic activity.     

PECVD Si nitride and Si oxide layers — Hydrogen analysis and etching after ion implantation

lon-implantation-induced selective etching of dielectric materials is considerably diminished with increasing hydrogen content. Making use of the ¹H(¹⁵N,γ)¹²C resonance reaction, low-temperature PECVD Si oxide and Si nitride layers were observed to contain 12 and 23 at.% H, respectively. For different reagents etch rates were measured regarding the virgin and ion—implanted-He⁺ Ne⁺ at 60, 100 keV — PECVD films.     

Investigations of lattice location and mobility of carbon in GaAs using the channeling technique

In order to get information about the lattice location and the mobility of ¹²C in GaAs wafers, the channeling technique in combination with nuclear reaction analysis (NRA) is a powerful method. The targets were implanted with ¹²C ions (2.6 × 10¹³−2.6 × 10¹⁵cm⁻²) at energies between 60 and 3000 keV. This corresponds to implantation depths of about 0.1 to 3 μm. Using the nuclear reaction ¹²C(d, p)¹³C a depth distribution of the implanted carbon is obtained. The relationship between the concentration of ¹⁴C in random and along the 100 and 110 axial directions gives information about the substitutional lattice location of carbon within the GaAs crystal. In addition, we measured lattice defect depth distributions with a 1.5 MeV ⁴He⁺ beam before and after thermal annealing at temperatures up to 600°C.     

Influence of Pt, Fe/Ni/Cr-containing intermetallics and deuterium on the oxidation of Zr-based materials

An in situ gas phase analysis technique and the ¹⁸O-SIMS technique are used to evaluate the transport of oxygen and hydrogen in oxidation of Zr-based materials. At 400 °C, it is found that oxygen dissociation efficiency decreases in the order: Pt > Zr₂Fe > Zr₂Ni > ZrCr₂  Zircaloy-2. Two Zr-plates partly coated with 200 Å porous Pt, with and respectively without D in the substrate, were oxidized in two stages at 400 °C. SIMS depth profiles in the Pt area show that an enhanced oxidation takes place mainly by inward oxygen transport. A minimum in the oxide thickness was found near the Pt area on both Zr plates. Two Ar-filled Zircaloy-2 tubes with ZrSn liner were exposed at 370 °C to 22 mbar water, filled in from one side. Our experimental results suggest that a proper choice of the SPP composition and size distribution can lead to reduced hydrogen uptake during oxidation of Zr-based materials in water.     

Determination of sulphur and copper depth distribution in patina layers using nuclear reaction techniques

A method for Cu and S profiling in patina layers was developed by applying a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). The copper profiling was performed by using the 1327 keV γ-ray deexciting the third excited state to the ground state of ⁶³Cu produced by the reaction ⁶³Cu(p,p^′γ)⁶³Cu. For the determination of sulphur the 2230 keV γ-ray was used deexciting the first excited state to the ground state of ³²S formed through the reaction ³²S(p,p^′γ)³²S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. The technique was tested using artificially produced and natural copper patina layers. Supporting information on the depth distribution of the constituent elements of the patina samples was obtained by p-RBS (E_p: 1.5 MeV, θ: 160°).     

Effect of Si implantation on the microstructure of silicon nanocrystals and surrounding SiO2 layer

Si nanocrystals (Si-nc) embedded in a SiO₂ layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess  8 × 10²¹ Si⁺/cm³, the size of the Si-nc was found to be 3 nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of 2.4 × 10²² Si⁺/cm³, the Si-nc diameter ranges from 2 to 12 nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first 25 nm in this sample (also visible on TEM image) and most of the SiO₂ bonds have been replaced by Si–O bonds. Experimental and simulation results suggest that a local Si concentration in excess of 3 × 10²¹ Si/cm³ is required for the production of Si-nc.     

Measurement of the cross sections for the reactions Cr(n,2n)Cr, Zn(n,2n)Zn, Y(n,2n)Y and Zr(n,2n)Zr from 13.5 to 14.8 MeV

Cross section measurements for the reactions ⁵²Cr(n,2n)⁵¹Cr, ⁶⁶Zn(n,2n)⁶⁵Zn, ⁸⁹Y(n,2n)⁸⁸Y and ⁹⁶Zr(n,2n)⁹⁵Zr were carried out in the neutron energy range 13.47–14.79 MeV applying the activation technique. Neutrons were produced via the T(d,n)⁴He reaction, making use of the variation of neutron energy with the emission angle. The neutron fluences incident on the samples were determined relative to the well-evaluated cross section for the reaction ⁹³Nb(n,2n)^92mNb.

The induced γ-ray activities of the irradiated Zn, Zr and Y₂O₃ samples and their monitor foils were measured by means of a calibrated Ge(Li) γ-ray detector at the KFI, Debrecen. At the IRK, Vienna, relative γ-ray measurements using a high-purity Ge detector were combined with integral γ-ray counting by means of a NaI(TI) well-type detector on the Cr, Zn and Zr foils of highest activity and on some Nb monitor foils; integral γ-ray counting only was applied in the case of the Y₂O₃ samples. All necessary corrections were taken into account.

The results are compared to the corresponding results of cross section measurements published in the literature. The uncertainties obtained in this work are considerably smaller in most cases than the uncertainties given by other authors.     

Depth profiling study on the migration of tritium in titanium induced by deuterium-ion bombardment

A thin titanium layer with uniformly absorbed tritium (T/Ti ˜1.0) was bombarded by 390 keV D₃⁺ ions (130 keV per deuteron). Bombardment was performed at low (111 K) and room temperatures up to fluences of 5.9 × 10¹⁸ D/cm² and 3.0 × 10¹⁸ D/cm², respectively. Depth profiles of tritium up to a depth of 0.8 mg/cm² (˜1.8 μm) were measured and the change of the profile with fluence was investigated by means of the T(d, )n nuclear reaction. At both of the temperatures, a dip was formed on the depth profile of tritium at the depth around the projected range, indicating that the deuteron bombardment induced the migration of tritium against the concentration gradient. At the low temperature, the dip showed a gradual growth with fluence and saturation of the growth at the higher fluences, which could not be described by the existing model for isotope mixing. The spectrum of protons from the D(d, p)T reaction obtained in the same measurement suggested that the release of deuterium suddenly started at the final stage of the present bombardment. The dip formed at room temperature was larger than that at the low temperature. The migration of tritium induced by the bombardment is discussed on the basis of the experimental results obtained.     

Contribution of uranium diffusion on creep behavior of uranium dicarbide

Compressive creep tests of uranium dicarbide (UC₂) have been conducted. The general equation best describing the creep rate over the temperature range 1200–1400°C and over the stress range 2000–15000 psi is represented by the sum of two exponential terms ge =A(σ/E)^0.9 exp(−39.6 ± 1.0/RT) + B(σ/E)^4.5 exp(−120.6 ± 1.7/RT), where pre-exponential factors are A(σ/E)^0.9 = 12.3/h at low stress region (3000 psi) and B(σ/E)^4.5 = 3.17 × 10¹³/h at high stress region (9000 psi), and the activation energy is given in kcal/mol. Each term of this experimental equation indicates that important processes occurring during the steady state creep are grain-boundary diffusion of the Coble model at low stress region and the Weertman dislocation climb model at high stress region. Both mechanisms are related to migration of uranium vacancies.     

Ion beam induced damage in InP during heavy-ion elastic recoil detection analysis

Heavy-Ion Elastic Recoil Detection Analysis (HIERDA) is an analytical technique which has undergone rapid development in the past few years with the availability of high-energy Tandem accelerators for materials science applications. HIERDA has found application in the study of various semiconductor systems, particularly III–V compounds. The technique employs a high-energy heavy-ion analysing beam to knock constituent nuclei from the target material and a time of flight and energy (ToF-E) detector system to extract mass and depth of origin information from these recoiling nuclei. Present work examines the sample damage produced in InP under typical analysis conditions. The depth distribution of damage induced by an ¹²⁷I analysing beam of varying energy (54–98 MeV) and dose (10¹³−2 × 10¹⁴ ions/cm²) in InP has been examined using RBS channelling, and cross-sectional TEM.     

Carbon clustering in Si1−xCx formed by ion implantation

Silicon-carbon alloys were formed by multiple energy implantation of C⁺ ions in silicon and in Silicon on Sapphire (SOS). The ion fluence ranged between 5 × 10¹⁶ − 3 × 10¹⁷ ions/cm² and the energy between 10–30 keV in order to obtain constant carbon concentration into a depth of 100 nm. The carbon atomic fraction (x) was in the range 0.22–0.59 as tested by Rutherford backscattering spectrometry (RBS). Thermal annealing of the implanted films induced a transition from amorphous to a polycrystalline structure at temperatures above 850°C as detected by Infrared spectrometry (IR) in the wavenumber range 600–900 cm⁻¹. The optical energy gap and the intensity of the infrared signal after annealing at 1000°C depended on the film composition: they both increased linearly with carbon concentration reaching a maximum at the stoichiometric composition (x = 0.5). At higher carbon concentration the IR intensity saturated and the optical energy gap decreased from the maximum value of 2.2 to 1.8 eV. The behaviour at the high carbon content has been related to the formation of graphitic clusters as detected by Raman spectroscopy.     

2 MeV Si ion implantation damage in relaxed Si1−xGex

The damage produced by implanting, at room temperature, 3 μm thick relaxed Si_1−xGe_x layers with 2 MeV Si⁺ ions has been measured as a function of Ge content (x = 0.04, 0.13, 0.24 or 0.36) and Si dose in the dose range 10¹⁰–10¹⁵ cm⁻². The accumulation of damage with increasing dose has been studied as a function of Ge content by Rutherford Backscattering Spectrometry, Optical Reflectivity Depth Profiling and Transmission Electron Microscopy and an increased damage efficiency in Si_1−xGe_x with increasing x is observed. The characteristics of implantation-induced defects have been investigated by Electron Paramagnetic Resonance. The results are discussed in the context of a model of the damage process in SiGe.     

Formation of uranium mononitride by the reaction of uranium dioxide with carbon in ammonia and a mixture of hydrogen and nitrogen: II. Reaction rates

Kinetics of the carbothermic synthesis of UN from UO₂ in an NH₃ stream and a mixed 75% H₂ + 25% N₂ stream were studied in the temperature range of 1400–1600°C by X-ray analysis and weight change measurement of the sample. The weight change was divided into two parts; i.e. weight loss due to carbothermic reduction of UO₂ and weight loss due to removal of carbon by hydrogen. The former followed the first-order rate equation −1n(1 − ₀) = k₀t, and the latter the rate equation of phase boundary reaction 1 − (1 − _c)^1/3 = k_ct. The apparent activation energy of the former was in the range of 320–380 kJ/mol. The value of the latter in an NH₃ stream was 175–185 kJ/mol, which was smaller than that in a mixed 75% H₂ + 25% N₂stream (285 kJ/mol). In this method, the rate of the removal of carbon by hydrogen determines that of the formation of high purity UN.     

Isomer separation of Cu and Cu with a resonance ionization laser ion source

Radioactive copper isotopes were ionized with the resonance ionization laser ion source (RILIS) at the on-line isotope separator ISOLDE (CERN). Using the different hyperfine structure in the 3d¹⁰ 4s  ²S_1/2 – 3d¹⁰ 4p  ²P⁰_1/2 transition the low- and high-spin isomers of ⁷⁰Cu were selectively enhanced by tuning the laser wavelength. The light was provided by a narrow-bandwidth dye laser pumped by copper vapor lasers (CVL) and frequency doubled in a BBO crystal. The ground state to isomeric state intensity ratio could be varied by a factor of 30, allowing to assign gamma transitions unambiguously to the decay of the individual isomers. It is shown that the method can also be used to determine magnetic moments. In a first experiment for the 1⁺ ground state of ⁷⁰Cu a magnetic moment of (+)1.8(3) μ_N and for the high-spin isomer of ⁷⁰Cu a magnetic moment of (±)1.2(3) μ_N could be deduced.