Resonant Nuclear Reaction Analysis Research Articles

Mössbauer investigation of laser nitrided stainless steel and annealing treatments of laser nitrided iron

Laser nitriding is used for the fast and easy production of nitride coatings on iron and alloys. Here, first results of the laser nitriding process applied to stainless steel are reported. The laser treatment led to the appearance of additional lines in the Mossbauer spectra, which are attributed to γ-Fe(N) produced by the laser nitriding process. The Mossbauer results are discussed in connection with the results obtained from X-ray diffraction and resonant nuclear reaction analysis. Furthermore, the results of isochronical annealing treatments of laser nitrided iron are reported.

Dissociative water vapour absorption in BaZr0.85Y0.15O2.925/H2O: pressure–composition isotherms in terms of Fermi–Dirac statistics

Thin films of proton-conducting BaZr0.85Y0.15O2.925 perovskite-type ceramics, prepared in a sol–gel process by multiple dip-coating on silicon single crystal wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressures and temperatures. The absolute content of the absorbed hydrogen was determined ex situ at room temperature using the 15N nuclear resonance reaction analysis. From the resulting water vapour pressure–hydrogen composition isotherms the absorption enthalpies and entropy were calculated, using our two site model, based on Fermi–Dirac statistics.

Analysis of laser-nitrided stainless steel via nuclear methods

Laser nitriding of iron and other metals is governed by the complicated interplay of the laser–plasma–liquid surface interactions which lead to a superposition of several mechanisms. This article reports on the influence of the nitrogen gas pressure on the nitriding process for stainless steel. The effects of the nitrogen gas pressure on the nitrogen depth profiles and the phase formation are revealed by resonant nuclear reaction analysis, Mossbauer spectroscopy, and X-ray diffraction. We found that the surface nitrogen concentration reaches 10 at. % with a mean value of about 7.5 at. % in the first 150 nm. There seems to be a pressure window between 0.1 and 0.7 MPa for the most efficient treatment. In the surface layer, an additional γ-Fe(N) phase can be distinguished from the original γ-phase of the stainless steel.

Comparative study of thin film physical properties for TiNx deposited by DC magnetron sputtering under temperatures less than 100°C on monocrystalline silicon and polycrystalline iron substrates

In this research, titanium nitride thin films were deposited by reactive DC magnetron sputtering with two original constraints imposed by the expected industrial application as roll to roll decorative coating of steel: the samples should be connected to earth and should not be heated during deposition. Previous work has shown that low N2 atmospheres should be maintained during sputtering processes in order to obtain a colour range from grey to gold. In this study, the nitrogen content measured by Resonant Nuclear Reaction Analysis and the crystal structure revealed by glancing angle X-ray diffraction, were used to determine the coating composition. The appearance presented in CIE L*a*b* colour coordinates and the micro-hardness obtained with a Berkovitch nano-indenter were also evaluated for all the films. Results obtained with the TiNx layers deposited on monocrystalline polished silicon were then compared to coating physical properties measured on polycrystalline iron (α-Fe) substrates. Only the coating produced under the lowest N2 gas flow exhibits a different nitrogen content on both substrates resulting in an hexagonal phase on iron. Colour differences appear and are probably due to different substrate roughness. Hardnesses between 12 and 22 GPa are obtained on both substrates. Such results tend to qualify this process for possible industrial application as a protective coating with a pleasant appearance.

Proton conducting Ba3Ca1.18Nb1.82O8.73–H2O: pressure–compositions isotherms in terms of Fermi-Dirac statistics, concentration and fuel-cell measurements, and impedance spectroscopy

Thin films of Ba3Ca1.18Nb1.82O8.73, prepared in a sol-gel process by multiple dip-coating on silicon wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressure and temperature. The hydrogen content was determined ex situ at room temperature using nuclear resonance reaction analysis. From the resulting water vapour pressure–composition isotherms the absorption enthalpies Δ∅HO, Δ∅Ht and the absorption entropy Δ∅S were calculated, using a two-site model, based on Fermi-Dirac statistics. On Ba3Ca1.18Nb1.82O8.73 bulk material also impedance spectroscopy, concentration and fuel-cell measurements as well as neutron diffraction were performed. From these data, taken together, the proton diffusion coefficient DH could be evaluated and compared to quasielastic neutron scattering results.

Hydrogen in undoped and heavily in situ phosphorus doped silicon films deposited using disilane and phosphine

The kinetics of hydrogen incorporation in amorphous silicon films were studied. The layers were deposited by low pressure chemical vapor deposition using disilane (Si2H6) and phosphine (PH3). The hydrogen concentration, determined by nuclear resonant reaction analysis, increased with decreasing substrate temperature. In accordance with the reported reduction of hydrogen adsorption in the presence of surface phosphorus, the addition of phosphine to disilane was observed to reduce the hydrogen film concentration. The results are discussed in terms of hydrogen adsorption/ desorption kinetics. The activation energy for hydrogen desorption in an undoped film was 1.8±0.2 eV, in good agreement with previously reported values obtained by surface analysis and desorption studies. When phosphine was added, an increase in activation energy was observed.

Influence of the spatial laser intensity distribution on laser nitriding of iron

Laser nitriding of iron and other metals is governed by the complicated interplay of the laser–plasma–solid interactions which lead to a superposition of several mechanisms. This work reports on the drastic influence of the spatial laser intensity distribution on the nitriding process. The effects of the lateral laser intensity on the nitrogen lateral and depth profiles, the phase formation, the surface topology, and the microhardness are revealed by resonant nuclear reaction analysis, Mössbauer spectroscopy, surface profilometry, and nanoindentation. Homogeneous laser beams lead to a strong reduction or almost the absence of the piston mechanism, thus confining the nitriding and the transport processes to the laser spot and avoiding the fallout. The details are discussed in relation to the results obtained for the raw-beam irradiations. Much higher nitrogen saturation concentrations can be achieved with a homogenized beam, but the surface hardness and the hardening depth are lower than in the case of irradiation with the raw beam. The ε nitride is only found for raw-beam irradiation.

Origin of nitrogen depth profiles after laser nitriding of iron

In spite of its technological importance, the basic mechanisms of laser nitriding of metals and alloys are hardly understood. The nitrogen depth profiles achieved by laser nitriding of pure iron were measured with high accuracy by resonant nuclear reaction analysis and described by two superimposed diffusion profiles. Using simple estimates, together with the results of marker experiments and laser treatments in N15-isotopically enriched atmospheres, the development of these profiles with the number of pulses can be simulated in excellent agreement with the experimental results.

Nitride layers formed by nitrogen implantation into metals

Abstract For nitrogen implantation into several kinds of metals (Al, Ti, V, Fe, Co, Ni, Zr, Nb, Mo, Ta, Hf, W) with a dose up to 2×10 18 ions cm −2 , dose dependence of the nitrogen depth profile, retained nitrogen dose and sputtering yield were calculated by Monte Carlo simulation using the dynamic SASAMAL code for the energy rage of 1 keV to 1 MeV. The calculated results were compared with the experimental results obtained by a resonant nuclear reaction analysis using 15 N(p, αγ ) 12 C reaction. In the simulation, it was assumed that the nitrogen concentration could not exceed that of saturated nitride phase and that the excess nitrogen migrated towards the surface depending on the radiation damage. The depth dependence of the chemical state measured by XPS and the crystalline structure of the surface layer obtained by a glancing angle XRD are also presented for Zr implanted with 50 keV nitrogen at room temperature and at high temperature or with post implantation annealing. The depth dependence of microhardness was also measured by an ultra-micro indentation tester. In order to find the method to overcome the limited thickness and the severe radiation damage problem at high dose implantation necessary for the saturation, the nitrogen depth profiles for an energy scanning implantation with a uniform and a non-uniform energy distribution were calculated and compared with those of monoenergetic implantation.

Backside aluminisation effects on solar cell performance

In this work the effect of the back surface field (BSF) formation by high temperature treatment of backside aluminisation was analysed in silicon solar cells. Systematic I−V and spectral response (SR) characterisation shows an obviously superior performance of Al-diffused cells especially in the red near infrared region compared to those with conventional boron BSF. These findings along with the result of the performed XTEM, NRA (Resonance Nuclear Reaction Analysis), SIMS, and ECV (Electrochemical CV) analyses on the backside layer structure lead to the conclusion that the main contribution to the improvement, relative to the conventional reference sample, is the minority carrier lifetime enhancement by gettering effect in the Al-diffusion tail and the improved light trapping by backside roughening.

Proton conducting Ba 3Ca 1.18Nb 1.82O 8.73/H 2O: Sol–gel preparation and pressure/composition isotherms

Thin films of Ba 3Ca 1.18Nb 1.82O 8.73, prepared in a sol–gel process by multiple dip-coating on silicon wafers, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressures and temperatures. The hydrogen content was determined using nuclear resonance reaction analysis. From the resulting water vapour pressure/hydrogen composition isotherms the absorption enthalpies and the absorption entropy were calculated in the framework of a two site model, based on Fermi–Dirac statistics. On Ba 3Ca 1.18Nb 1.82O 8.73 also impedance spectroscopy was performed yielding the bulk conductivity. From these data in combination with proton transport numbers and the thermodynamic results as noted above the proton diffusion coefficient could be evaluated.

Depth profiles in nitrogen implanted Si xAl y coatings post-implanted with oxygen

“Sialons” are phases in the Si–Al–O–N and related systems based on the (Si, Al)(O, N) 4 tetrahedral structure. They have several interesting mechanical, thermal and chemical properties to make them candidates for high temperature applications. Thin Si–Al–O–N layers (200 nm) were synthesized using nitrogen and oxygen implantation into Si 33Al 67, Si 45Al 55 and Si 63Al 37 thin films deposited by d.c. magnetron sputtering on glassy carbon substrates. Nitrogen has been first implanted at 50 and 20 keV, then oxygen was post-implanted at 50 keV with doses ranging from 1 to 10×10 17 ions cm −2. High depth resolution profiles and stoichiometry have been obtained using Rutherford backscattering spectrometry and resonant nuclear reaction analysis. The chemical bonds have also been investigated using low energy electron induced X-ray spectrometry. Analysis of the results shows that the nitrogen concentration decrease when oxygen is post-implanted. Chemical bond analysis indicates the presence of a solid solution containing Si, SiO 2, Si 3N 4, Al, Al 2O 3 and AlN. The percentage of these compounds are correlated with the heat of formation.

Ion beam induced amorphization in α quartz

The amorphization of α quartz induced by light and medium mass ion bombardment has been investigated by means of Rutherford backscattering spectrometry in channeling geometry, resonant nuclear reaction analysis and mechanical surface profiling. The single crystalline samples were irradiated at 77 K with H+, N+, Ne+ and Na+ ions at energies of 10–100 keV and fluences up to 5×1016 ions/cm2. Disordering of α quartz by ion bombardment was found to occur by three-dimensional nucleation and growth of defect agglomerates and, possibly, small, spatially separated amorphous zones in the still crystalline surrounding. The nucleation rate scales with the energy density FD in elastic collisions. Above a critical energy density EC=1.92(7)eV/at deposited by nuclear collisions (corresponding to a displacement rate of 0.04 dpa) a coherent amorphous layer forms at the depth of maximum energy deposition, which then grows towards the surface and into larger depths during continued ion bombardment. Mechanical surface profiling reveals large compressive stresses (∼1.5 GPa), built up at low fluences, which are released at higher fluences after the amorphous layer extends to the surface. The stress release is accompanied by a significant reduction of the atomic density by about 19%.

Material transport during excimer-laser nitriding of iron

The surface topology and nitrogen concentration profiles of iron irradiated with pulses of an excimer laser in a nitrogen atmosphere were studied by means of optical and scanning electron microscopy, surface profilometry, energy-dispersive x-ray spectroscopy, and resonant nuclear reaction analysis. The observations are combined to distinguish several mechanisms contributing to the material transport: ablation, redeposition of nitride from the plasma and pressure-induced lateral flow of the molten iron towards the edges of the laser spot (piston mechanism). Numerical estimates of the time and spatial evolution of temperature and pressure at the surface led to average rates of the material transport in good agreement with the experiment.

Correlation of the microhardness with the nitrogen profiles and the phase composition in the surface of laser-nitrided steel

The effect of the nitrogen take-up upon irradiation of iron or steel with excimer laser pulses in air or nitrogen atmosphere is well established. The resulting nitrogen depth profiles and phase compositions were measured by a combination of Rutherford backscattering spectrometry, resonant nuclear reaction analysis and conversion electron Mössbauer spectroscopy for various laser parameters. The accuracy of the nitrogen profiling via the 15N(p, xy) 12C reaction allowed the detection of very low nitrogen concentrations and also the resolving of them laterally across the laser spot. The laser-induced changes in surface topography were observed with optical microscopy and surface profilometry. The microhardness across the laser spot and as a function of the depth is compared with the nitrogen depth and lateral profiles and the phase composition. Thus the mechanical properties can be related to the microstructure and phase composition in the laser modified surfaces of iron and steel. A comparison is made between the effects for irradiation of pure iron and the carbon steel C80.

Iron nitrides and laser nitriding of steel

Nitriding of iron and steels is well known to improve hardness, wear and corrosion resistance of surfaces. Recently, it has been found that a simple irradiation of iron and steel with pulses of an excimer laser in air or nitrogen leads to a significant nitrogen take-up into the surface and to improvements in the surface properties. The mechanisms of the laser-nitriding process are not yet understood but the nitrification will be proved by several methods. Among these, Mossbauer spectroscopy is very powerful, especially when Conversion Electron and Conversion X-ray Mossbauer Spectroscopy (CEMS and CXMS) are applied simultaneously. Nevertheless, only a combination of methods gives a satisfying overview of the laser induced nitriding processes: Rutherford Backscattering Spectrometry (RBS) and Resonant Nuclear Reaction Analysis (RNRA) were also used to characterize the treated surfaces. First measurements show an increase of the hardness and the wear resistance with the number of pulses. From the results of the CEMS analyses this should be correlated with the increase in the fraction of the e-phase. This may be important for industrial applications.

Laser nitriding investigated with Mössbauer spectroscopy

The effect of the nitrogen take‐up upon irradiation of iron or steel with excimer laser pulses in air or in nitrogen atmosphere is well established. The resulting phase compositions and nitrogen depth profiles were measured by a combination of simultaneous Conversion Electron Mossbauer Spectroscopy (CEMS), Conversion X‐ray Mossbauer Spectroscopy (CXMS), and Resonant Nuclear Reaction Analysis (RNRA) as a function of the nitrogen gas pressure during irradiation. A maximum nitrogen content and a maximum fraction of the ɛ-nitride was found at 0.1 MPa. This result is in accordance with hardness measurements performed by the nanoindentation technique.

Characterization of magnetron-sputtered chromium and iron nitride films

Chromium and iron nitride layers (with thicknesses of 100–1000 nm) were deposited onto silicon substrates via reactive rf magnetron sputtering. Stoichiometry, phase formation and surface morphology were analyzed by a combination of different methods: Rutherford Backscattering Spectrometry, Resonant Nuclear Reaction Analysis, Conversion Electron Mössbauer Spectroscopy, Scanning Tunneling Microscopy and X-Ray Diffraction.

Pressure/composition isotherms of proton conducting SrYb0.05Zr0.95O2.975/H2O by means of nuclear resonance reaction analysis

AbstractFilms of SrYb0.05Zr0.095O2.975 were prepared by sol‐gel processing. Water vapour pressure/hydrogen composition isotherms were recorded ex‐situ comprising pressures between 0 and 84.5 kPa and temperatures between 873 and 1073 K. Nuclear Resonance Reaction Analysis (NRRA) was used to determine the hydrogen concentration and, in addition, depth profiles of hydrogen concentration. The chemical potential of interstitial hydrogen in oxides could be determined; from its temperature dependence thermodynamical constants were calculated. We observe two hydrogen fractions with a site energy difference of 20 kJ/mol. A size effect of the thermodynamic properties is observed below a thickness of 350 nm: nanofilms exhibit higher solubility than bulk material.

High fluence nitrogen implantation into Zr with energy scanning mode

In order to study effects of the ion implantation with a distributed energy and its energy scanning mode on the surface structure and the depth profile, dynamic Monte Carlo simulations were carried out for nitrogen implantations to Zr with uniform energy distribution from 15 to 85 keV, with three energy scanning modes. The modes were: (a) the energy increasing mode from the lowest energy to the highest energy in steps of 1 keV; (b) the energy decreasing mode from the highest to the lowest energy; and (c) the energy sweeping mode of 100 times between the lowest and the highest energies. The calculated results were compared with the experimental results obtained for the implantation with the energy distribution and the energy scanning modes. The depth profiles and the retained fluences of the implanted nitrogen agree well with the experimental results obtained by resonant nuclear reaction analysis. The displacement per atom in the outermost surface layer was in the order of (a), (c), and (b). The displacement of (a) was lower than that of the mono-energetic implantation at 50 keV. The results were consistent with the experimental surface topography observed by scanning electron microscope.