15N Nuclear Reaction Research Articles

Analysis of a plasma nitrided Ti-6Al-4V spur gear surface

The unworn and worn surface of a cold forged and plasma nitrided Ti-6Al-4V gear was analyzed for the distribution of elements. Titanium, aluminum and vanadium distributions were mapped using the micro-PIXE technique, while nitrogen concentration and depth profiles were carried out in the surface region by NRA resonance profiling, and also micro-NRA techniques using the nuclear reaction 15N(p,αγ) 12C. The nitrogen layer thickness was determined as about 17 μm below the surface, and the concentration at the surface reached the value of up to 16 mass%. Due to plasma nitriding process aluminum and vanadium were found depleted in the first few micrometers from the surface. It was evident that local agglomeration occurred for both elements in the surface layer. This was probably caused by the residual stresses developed during the forging process.

Nuclear microprobe study of stress-oxidation of nickel

In order ot study the stress oxidation, a specific device has been designed to perform mechanical loadings under controlled temperature and oxygen pressure. Time-dependent strain-stress curves may be recorded according to the usual modes: creep, fatigue and fatigue-creep. A set of two sorption pumps allows to alternate oxygen-16 and oxygen-18. Oxygen-18 diffusion profiles have been measured by SIMS (Secondary Ion Mass Spectroscopy) and by nuclear microprobe, by means of the 18O(p, α) 15N nuclear reaction to characterize selected areas. For the purpose of further investigations on nickel-based alloys, initial experiments have been performed on pure nickel to obtain knowledge of the fundamental properties of nickel. Because of complex relationships between mechanical behaviour, microstructure modifications and oxygen diffusion, both polycrystalline and monocrystalline samples have been investigated.

Hydrogen accumulation in titanium, zirconium and hafnium caused by nitrogen implantation

The influence of nitrogen implantation on the hydrogen accumulation in Ti, Zr and Hf was investigated depending on nitrogen ion fluence. The samples were implanted with 15N ions in the fluence range from 3 × 10 17 to 9 × 10 17 ions/cm 2. The 15N ion energy, varied between 150 and 220 keV, was chosen to obtain nearly the same projected range in each metal. The concentration depth distributions of the implanted nitrogen and the accumulated hydrogen were quantitatively analysed with the resonant nuclear reaction 15N( 1H,αγ) 12C at 429 keV and by the reverse reaction at 6396 keV, respectively. The hydrogen content is markedly increased in the implanted layer (up to 8 at.%), according to the nitrogen distribution profile. This is attributed to the lattice distortion in titanium, zirconium and hafnium. At a nitrogen concentration above 20 at.%, however, the hydrogen content continuously decreases in the implanted layer due to precipitates of nitrides and thus the hydrogen depth distribution alters its appearance to a saddle-shaped profile. With further increasing nitrogen concentration the two maxima are separated by a plateau with a hydrogen content less than 1 at.%.

In-situ ion-beam annealing of damage in GaAs during O implantation and O-site determination by 18O(p,α) 15N nuclear reaction

Damage introduced by 40 keV 16,18O implantation in the crystalline GaAs substrate is investigated by the Rutherford backscattering spectroscopy (RBS) channeling method and cross-sectional transmission electron microscopy (X-TEM). Anomalously little damage was formed at room temperature (< 43°C), in spite of the large energy density being deposited in the nuclear scattering process. In-situ ion-beam annealing during irradiation effectively occurred below 43°C. For the 5 × 10 15/cm 2 dose sample, the RBS channeling yield increases with the annealing temperature, due to the formation of stacking faults, confirmed by X-TEM observation. Yield increase with the temperature was not observed for lower 1 × 10 15/cm 2 and higher 1 × 10 16/cm 2 doses. A possible site occupied by 18O atoms after annealing is determined by 18O(p,α) 15N nuclear reaction. The ratios of channeling-yields to the corresponding random-yields for α-particles emitted from 18O atoms were compared with simulated results.

Thickness of the [formula omitted] interface and composition of silicon oxide thin films: effect of wafer cleaning procedures

We determined the areal density of Si atoms constituting the oxide-silicon interface and the stoichiometry of ultra-thin silicon oxide films, thermally grown on Si(001) in dry 18O 2 atmospheres, using the channeling of α-particles along the 〈001〉 axis of the Si substrates associated with grazing angle detection of the scattered particles. The amount of 18O atoms in the films was determined independently using the 18O(p,α) 15N nuclear reaction at 730 keV. The Si wafers were submitted to different cleaning procedures before oxidation in 18O 2, namely: standard RCA cleaning, HF etching followed by a rinse in ethanol and rapid thermal cleaning (RTC) under high vacuum. The stoichiometry of all oxide films having thicknesses between 2 and 13 nm could be fitted assuming a ratio O Si = 2 , that is, the films were constituted by silicon dioxide. By comparing the results for samples cleaned in different ways, however, we noticed a pronounced change in the number of atoms in the non-registered Si layers at the SiO 2 Si interface and so in the thickness of these interfaces.

Conventional depth profiling using narrow nuclear resonances

A simple energy scanning and data acquisition system for nuclear resonance analyses with a narrow resonance is presented. Ion beam energy was scanned by directly supplying a bias in the range −30 to +30 kV to a target holder. Details of the energy scanning and the data acquisition are described. Some examples for the depth profiling of nitrogen implanted into metals using the system with the nuclear reaction 15N(p, αγ) 12C at 429 keV are shown in comparison with the calculated results by a Monte Carlo simulation. The data analysis program used to obtain depth profiles from excitation curves is also shown. The target is divided into layers of uniform concentration and the reaction probability in a layer is calculated from a starting depth profile obtained from raw data, using the normalized error function with Gaussian approximation for the overall energy spread. This leads to a very simple computer program, fast to operate with a small computer.

Nuclear reaction analysis of hydrogen in Li-containing material

For clarifying the nature of the γ-ray background observed in H profiling measurements of a LiAl-silicate glass with the 15N nuclear reaction technique, a γ-ray spectroscopy study was carried out using a Ge(Li) detector and 6,7LiF targets. The energies of a great number of γ-ray transitions arising from 6,7Li + 15N reactions were determined and the γ-ray emitting product nuclei 20,21Ne, 18,19,20,21F, 16,17,18O and 13C were identified. The excitation functions of γ-transitions, measured in the 15N energy range 6.0 MeV to 13.4 MeV, were found to vary smoothly with energy and to rise by about three orders of magnitude in this range. Based on these data, a procedure for background correction in spectra taken with a NaI(Tl) scintillation detector could be set up and was used for H profiling of glass samples containing up to 7 at.% lithium.

Diffusion phenomena of implanted nitrogen in chromium

The properties of thin chromium films (ca. 800 nm) evaporated on glassy carbon substrate and modified by nitrogen ion implantation were studied. Nuclear analysis methods were used to characterize these films. 15N ions with an energy of 30 keV were implanted up to a maximally attainable dose of 3.2 × 10 17 15N/cm 2. After annealing the samples at 650°C under vacuum conditions with different annealing times as parameter the 15N-depth distributions were measured using the resonant nuclear reaction 15N(p, αγ) 12C. A drastic change in the nitrogen distribution was observed already after five minutes of annealing resulting in a decrease of the maximum nitrogen concentration from 44 at.% to 25 at.%. The nitrogen distribution shows a second peak separated from the first with about 30% of the implanted dose in a depth of 400 nm which might indicate anomalous diffusion. During further annealing that peak moves towards the sample surface. This effect will be discussed.

Depth profile analysis and study of the electronic properties of silicon nitride layers produced by ion implantation

Thin surface-near nitride layers (SiN x ) were formed by implanting 15N + ions with an energy of 30 keV in 〈100〉 silicon under high vacuum conditions at RT. The stoichiometric N Si ratio of the Si 3N 4 compound of 1.33 in the maximum of the 15N depth distributions was adjusted using the fluence of 6 × 10 17 at./cm 2. The 15N depth distributions of the implanted specimens were measured by the resonant nuclear reaction 15N(p, αγ) 12C ( E res = 429 keV) by varying the energy of the incident proton ion beam. The implanted specimens were subsequently annealed by EB-RTA (electron beam rapid thermal annealing) at 1100°C for 15 s and 30 min to investigate the high thermal stabílity of the SiN x layers. Furthermore, the etch resistance of the SiN x layers was tested by applying the HF:HNO 3 etch solution on the specimens. The electrical characteristics of the as-implanted and annealed SiN x layers were analysed with I-V measurements. It was observed that the prevailing current conduction mechanism is the Poole-Frenkel emission, as it is found also for silicon nitrides prepared by other technologies.

Low-energy 15N implantation in carbon for the synthesis of carbon nitride layers

15N 2 + molecular ions with an energy of 12 keV were implanted in glassy carbon and 40 keV 15N + ions were implanted into different carbon forms (glassy carbon, graphite and polycrystalline diamond) at room temperature in order to form thin carbon nitride layers. The nitrogen depth profiles were measured using the resonant nuclear reaction 15N(p, αγ) 12C ( E res = 429 keV, Γ = 120 eV) by varying the projectile energy during the analysis. In the case of the 6 keV implantation the saturation dose was 8 × 10 16 at./cm 2 whereas for the 40 keV implantation the saturation dose was found to be 3.9 × 10 17 at./cm 2. A maximum nitrogen concentration of 25 at.% was measured at both implantation energies. The saturation dose, the maximal attainable nitrogen concentration and the form of the 15N depth distribution are not dependent on the used carbon form. Sputtering yield measurements showed that the sputter process (measured sputtering yield < 0.2) is not responsible for the saturation dose (4 × 10 17 at./cm 2) and the maximal attainable nitrogen concentration (25 at.%). For the formation of carbon-nitrogen bonds, samples with an implanted fluence of 6 × 10 17 ions/cm 2 were rapidly heated for 120 s using an electron beam. A reduction of the dose from 4 × 10 17 at./cm 2 to 1.3 × 10 17 at./cm 2 was observed indicating the formation of a carbon nitride phase stable to temperatures up to 1000°C.

Layer and interface analysis of ultra thin ion beam produced silicon nitride layers by NRA and TEM

Ultra thin silicon nitride layers with stoichiometric N Si ratios in the maximum of the depth distributions were produced by implanting 10 keV 15N 2 + ions into single-crystal silicon at RT under high vacuum conditions. The 15N depth distributions were measured by the resonant nuclear reaction 15N(p,αγ) 12C (NRA). The depth resolution at the surfaces of the specimens is 3 nm, if the tilt angle is 55°. The layer structure of the implanted region and the relevant real geometry was characterized by high resolution TEM. High-temperature stability of the 15N depth distribution in the implanted specimens was proved by electron beam rapid thermal annealing (EB-RTA) at 1100°C. The results obtained by NRA and TEM are in agreement.

Stoichiometry of a-C:H(Ta) films determined by means of RBS and the 15N technique

The stoichiometry of a-C:H(Ta) films on Si wafer produced by a combined physical- and chemical-vapor-deposition process was determined by means of the 15N nuclear resonance reaction technique and Rutherford backscattering spectrometry (RBS). RBS as well as the 15N technique need for quantification of the original measurement data the element information from the other technique. Therefore, the data evaluation was performed in an iterative procedure. Teh carbon content was deduced indirectly from the hydrogen and tantalum contents. It was found that an increase of the tantalum concentration leads to a decrease of the hydrogen and carbon concentration. Only two values for the hydrogen-to-carbon ratio were observed depending on the tantalum concentration. They are correlated with different film structures.

Novel results on compensation processes in ZnSe:N

Compensation in ZnSe:N was investigated. The total nitrogen concentration in the samples was determined by two different techniques: secondary ion mass spectroscopy and nuclear reaction 15N(p, αγ)12C analysis. The net free hole concentration NA − ND was correlated with these results. A ratio of (NA − ND)[N] up to 50% was observed. Furthermore, we studied the excitonic region of the photoluminescence of ZnSe:N. Two different transitions correlated with nitrogen complexes could be observed. In lightly doped ZnSe:N a donor like complex was observed, while in highly doped an acceptor like complex dominates. The origin of these complexes is discussed.

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.

Hydrogen-charging of Nb/Fe multilayers

Nb/Fe multilayers with a Pd top layer were prepared by electron beam evaporation on Si substrates. The multilayer stacks were charged with hydrogen from the gas phase at 200°C and at a gas pressure of 0.1 mbar. The resulting hydrogen concentration profiles were measured by the 15N nuclear reaction method. We find that the multilayers take up hydrogen under these conditions, that hydrogen also reaches the low lying layers and that hydrogen is accumulated in Nb, leaving the Fe layers essentially hydrogen-free. The present work was undertaken as a preparatory study for the investigation of the magnetic coupling of the Fe layers through the Nb spacers as a function of the hydrogen content.

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.

Chemical bonding and interface analysis of ultrathin silicon-nitride layers produced by ion implantation and Electron Beam Rapid Thermal Annealing (EB-RTA)

15N2+ions were implanted into c-Si with an energy of 5 keV/atom and fluences ranging from 5×1016 to 2×1017 atoms/cm2 at RT to form ultrathin silicon-nitride layers (SiNx) with different N/Si ratios depending on the fluences (up to an overstoichiometric N/Si ratio of 1.65). The 15N depth distributions were analysed by the resonant nuclear reaction 15N(p, αγ)12C(Eres=429 keV). The implanted samples were processed by Electron Beam Rapid Thermal Annealing (EB-RTA) at 1150° C for 15 s (ramping up and down 5° C/s). The chemical structure of the 15N implantation into Si was investigated by EXAFS and NEXAFS. Channeling-RBS (4He+, E0=1.5 MeV) measurements were performed to observe the transition region (disordered-Si layer, d-Si) being underneath of the SiNx layer (typical values of layer thicknesses:SiNx 24 nm, d-Si 6 nm).

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.

Radiolytic effects in organic compounds induced and analyzed by a 15N beam

Cd-arachidat in the form of Langmuir-Blodgett films and thick photoresist layers of AZ5412H have been exposed to 15N-ion beams. The physico-chemical state of these targets as a function of the 15N fluence has been monitored by the 15N nuclear reaction with the respective H component. In this way, radiolytic changes in H distribution and bonding have been measured. In particular, diffusion and desorption processes have quantitatively been followed up to fluences of about 1 × 1016 N/cm2 at temperatures as low as 40 K. The correlated changes in H bonding, obtained by analyzing the concomitant Doppler widths as a function of the 15N fluence, consist of both decomposition and restoration of C-H and H-H molecular groups.

Nitrogen implantation in iron: Influence of the beam current density and of the chamber residual pressure

Abstract Iron samples were implanted at a fluence of 1017 N+ ions.cm−2 with an energy of 50 keV. The beam current density was varied in the range 6–60 μA.cm−2 as well as the quality of the vacuum in the implantation chamber. Implantations were performed at 150°C to favour the carburization process. Carbon and oxygen contaminations were controlled using nuclear backscattering spectrometry (NBS) with α particles of 5.7 MeV and 7.5 MeV respectively or by using Auger electron spectroscopy (AES). The depth profiles of implanted nitrogen were determined by the 15N(p,αγ) nuclear reaction or by AES when 15N or 14N ions were implanted respectively. Implantation induced chemical phases were characterized using Mossbauer spectroscopy and electron diffraction. It is shown that at 150°C the beam current density which has an influence on the implantation time as well as the contamination carbon content at the surface play an important role in the migration process of nitrogen. Consequently, the nitrogen depth distribut...