Resonant Nuclear Reaction Analysis Research Articles

Investigation of deep implanted fluorine channeling profiles in silicon using resonant NRA

Si(1 0 0) and (1 1 1) crystals were irradiated in the random as well as in the channeling direction, using 5 MeV 19F + ions, to a maximum fluence of approximately 1×10 17 particles/cm 2. The occurring deep implanted profiles were subsequently investigated using the Resonant Nuclear Reaction Analysis technique in the energy range E p=950–1200 keV. The reaction 19F(p,αγ) 16O reaction exhibits a strong resonant behavior in the above mentioned energy range, thus providing an excellent tool for the depth profiling of fluorine, yielding minimum detection limits of the order of a few ppm. The occurring profiles are analyzed with SRIM and c-TRIM codes and an attempt is made to explain the characteristics of the experimental spectra, as well as to compare with results already existing in literature.

Mobility and retention of implanted hydrogen in Ti225 titanium alloy

The behaviours of implanted hydrogen in Ti225 alloy was investigated in this work. Hydrogen ion beam implantation was used to load hydrogen into the sample. Resonant nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA) were applied to obtain the depth profiles of hydrogen versus implantation dose. Two kinds of hydrogen have been found in the samples, one is as quasi-mobile and another is chemically bonded hydrogen. Three hydrogen precipitation stages, which relate to the different chemical states of hydrogen, are determined. Using X-ray diffraction (XRD), the hydride phase transformation from solid solution in titanium to titanium hydride (TiH 1) and then titanium dihydride (TiH 2) tetragonal structure has been observed. The change is dose dependent in the implantation dose range between 2×10 16 and 6×10 17 H/cm 2. The phase transformation from TiH 1 to TiH 2 occurs at an implantation dose greater than 1×10 17 H/cm 2 but finishes at a dose of 6×10 17H/cm 2 with the saturation of hydrogen concentration at approximately 23 at.%. The inhomogeneous planar distribution of the hydrogen was also observed using both scanning micro-probe ERDA and scanning electron microscopy (SEM).

Mass transport mechanisms during excimer laser nitriding of aluminum

Surface layers of aluminum nitride were formed by irradiating pure aluminum substrates in nitrogen atmosphere with a pulsed excimer laser. The beam was focused on the sample placed inside a chamber filled with nitrogen gas. The irradiation was carried out at various laser fluences, nitrogen gas pressures, and numbers of pulses in order to investigate the influence of each parameter on the nitrogen incorporation and the mass transport mechanisms. X-ray diffraction showed the formation of polycrystalline AlN phase with the wurtzite structure, and the analysis of the nitrogen depth profiles by means of resonant nuclear reaction Analysis revealed a monotonic increase of the nitrogen concentration with the ambient gas pressure and the number of laser shots. It has been found that the laser fluence directly determines the temperature of the substrate and strongly changes the transport mechanism. The thermal simulations and the experimental evidence show that for fluences higher than 3 J/cm 2 the temperature of the substrate exceeds 2900 K. This value is higher than the dissociation temperature (∼2400 K) and close to the melting point (∼3070 K) of AlN, which can therefore dissociate or melt. The atomic nitrogen can rapidly diffuse to greater depths in the liquid Al matrix or it can degas (outgas) through the surface of the sample, leading to the formation of rather homogeneous concentration profiles. For fluences lower than 3 J/cm 2 the temperature of the substrate is not sufficient to destroy the nitride phase and the AIN grains can move inside the molten Al. In this case, the material transport can be attributed to Brownian motion and thermophoretic drift, which in turn are correlated with the chemical and thermal gradient, respectively.

Hydrogen depth resolution in multilayer metal structures, comparison of elastic recoil detection and resonant nuclear reaction method

Four different metals: Al, Cu, Ag and Au have been used to produce four special multilayer samples to study the depth resolution of hydrogen. The layer structure of each sample was analysed using 2 MeV He Rutherford backscattering spectrometry, 4.5 MeV He elastic recoil detection (ERD) and 30 MeV F 6+ HIERD. Moreover the hydrogen distribution was analysed in all samples using H( 15 N, αγ) 12C nuclear reaction analysis (NRA) with resonance at 6.385 MeV. The results show that the best depth resolution and sensitivity for hydrogen detection are offered by resonance NRA. The He ERD shows good depth resolution only for the near surface hydrogen. In this technique the depth resolution is rapidly reduced with depth due to multiple scattering effects. The 30 MeV F 6+ HIERD demonstrated similar hydrogen depth resolution to He ERD for low mass metals and HIERD resolution is substantially better for heavy metals and deep layers.

Complementary investigations using charged particles and muons in the study of hydrogen in diamond

The defect that has almost exclusively occupied attention has been that associated with nitrogen. With the advent of quantitative nuclear analytical techniques it has become evident that, in natural diamond, hydrogen and oxygen are also major impurities. In recent years increasing attention has been paid to the role of hydrogen in the growth, particularly, of CVD diamond, but also its influence on the properties of all types of diamond. Traditional nuclear resonant reaction analysis and nuclear scattering, time differential perturbed angular distribution and correlation measurements, ion implantation and ion channeling have been deployed. Recently the atom ‘muonium’ has been appreciated as behaving as a light isotope of hydrogen, and hence presents a powerful instrument for hydrogen studies. In diamond muonium has revealed the lattice location and temperature stability of the preferred sites that it occupies, and has shown a new and unexpected defect of rhombic symmetry which is interpreted as a hydrogen (muonium)—nitrogen structure.

Nuclear-reaction analysis of H at the Pb/Si(111) interface: Monolayer depth distinction and interface structure

Hydrogen atoms buried at the interface between Pb layers and the Si(111) surface were investigated by resonant nuclear reaction analysis (NRA) using ${}^{1}\mathrm{H}{(}^{15}\mathrm{N},\ensuremath{\alpha}\ensuremath{\gamma}{)}^{12}\mathrm{C}$ in grazing incidence geometry. Pb atoms were deposited on the H-terminated Si(111) surface at 110 K, and the H depth was clearly distinguished with a depth scale of one monolayer. The NRA spectrum revealed a monotonous shift to higher energy with increasing Pb coverage indicating H remains at the interface between Pb and the Si substrate. The dependence of the spectral shift on the Pb coverage was found to have an offset corresponding to a depth of about 0.1 nm. This offset suggests a model for the Pb/H/Si(111) interface structure implying that the initial Pb layer resides in the preadsorbed H layer.

Investigation of Fluorine Distribution on the Surface of Acid-Treated Apatite Single Crystals using Nuclear Resonant Reaction Analysis

The surface of natural fluorine-containing apatite (fluoroapatite) single crystals treated with acidic solutions of pH between 0.05 and 2.5 was investigated by nuclear resonant reaction analysis (NRRA) techniques using the 19F(p,αγ)16O nuclear reaction. The experimental results showed that partial defluoridation takes place due to acid attack characteristically depending on the pH of the solutions. Powder-XRD data indicated that the crystallinity of the apatite surface was etained despite of the etchpits observed by SEM-EDS. Relevant investigations of the surface of acid-treated apophyllite crystals, a typical fluorine-containing mineral, indicated a complete amorphization and besides a total absence of fluorine.

Height control of silicon nano-whiskers embedded in ultra thin silicon nitride layers by rapid thermal annealing

Two steps are necessary to produce nanometre sized silicon whiskers rising out of ultra thin silicon nitride layers: (i) production of under-stoichiometric silicon nitride surface layers by ion implanting of silicon wafer material, (ii) growth of silicon whiskers by the formation of silicon nitride bonds in the surface region through rapid thermal electron beam annealing. Depending on the implantation and annealing conditions, whiskers of different height and width can be produced. As an example, 25 nm high whiskers were formed by implanting 10 keV 15 N 2 + ions into silicon (fluence 5×10 16 cm −2 ) followed by rapid thermal electron beam annealing at 900°C for 15 s . In atomic force microscope studies, it was observed that the structures became more pronounced with increased temperature. Resonant nuclear reaction analysis revealed the absence of nitrogen in the whiskers and the stoichiometry of the silicon nitride layer formed by implantation.

Simulation and deconvolution program WinRNRA for depth profiling of light elements via nuclear resonance reactions

In this paper, a Windows PC-program is described that performs the transformation of measurement spectra obtained by resonant nuclear reaction analysis (RNRA) into concentration depth profiles. For the shape of the resonance a simple Breit–Wigner form is implemented. For the calculation of the straggling both the Bohr and the Lindhard–Scharff models can be used. The program can be used to evaluate depth profiles of an element in an otherwise homogeneous target. A nanometer depth scale is obtained by considering the concentration-dependent densities of the phases. This is exploited for the investigation of nitrogen profiles via the resonance reaction 15 N( p, αγ) 12 C . For demonstration purposes the program is used to determine nitrogen depth profiles of laser nitrided iron.

Ion beam analysis of porous silicon layers

The composition of porous silicon layers prepared by anodising silicon in HF–methanol medium has been studied using a combination of nuclear resonance reaction analysis (NRRA) and non-Rutherford backscattering spectrometry. The 1 H( 15 N, αγ) 12 C resonance reaction has been used for determining depth distribution of hydrogen in the films. The distribution of other low Z elements like C, O and Si has been probed and the ratio of their atomic concentrations determined using 12 C( α, α) 12 C and 16 O( α, α) 16 O scattering. Anodisation resulted in the formation of Si 1C x H y layers. The composition and thickness of the layers depend on the conditions of preparation.

Heavy ion irradiation induced effects in Ni 3N/Al bilayers

The article reports on the Xe ion beam irradiation studies of Ni 3N/Al bilayers at 80 K. The ion-induced modifications were monitored by Rutherford backscattering (RBS), resonant nuclear reaction analysis (RNRA), X-ray diffraction (XRD) and atomic force microscopy (AFM). We found preferential loss of nitrogen from the surface region of the Ni 3N top layers. The surface roughness Δσ S and the interface broadening variance Δσ int 2 increase linearly with the Xe ion fluence Φ. The experimental mixing rate of Δσ 2/Φ=1.8 nm 4 is explained by considering an enhancement of ballistic mixing due to chemical reactions at the interface.

Thermal stability of laser-produced iron nitrides

Laser nitriding is a very efficient method to improve the mechanical properties, surface hardness, corrosion, and wear resistance of iron and steel, with the advantages of a high nitrogen concentration, fast treatment, and accurate position control, and without any undesired heating effect on the substrate. However, the stability of laser-produced iron nitrides is still under investigation. This article reports investigations of the thermal stability of these iron nitrides upon annealing treatments, which were conducted both in vacuum and air. The phase and elemental composition of the nitride layers were deduced from conversion electron Mössbauer spectroscopy, resonant nuclear reaction analysis, and grazing incidence x-ray diffraction. The surface hardness was measured by the nanoindentation method. In laser-nitrided iron, two critical temperatures are found: at 523 K the predominant iron-nitride phase changes from the γ/ε to the γ′ phase. When the temperature exceeds 773 K, all of the nitrogen has escaped from the surface layer. For annealing in air the nitrogen escapes completely already at 673 K, where a thick oxide layer has formed. Stainless steel proved to be more stable than iron, and even up to 973 K no new phases or oxides were produced, here, also, only at 973 K the nitrogen content decreased significantly. Therefore, laser-nitrided stainless steel is well suited for applications.

Xenon irradiation ofNi3N/Sibilayers: Surface roughening and interface mixing and reactions

The irradiation effects in ${\mathrm{Ni}}_{3}\mathrm{N}/\mathrm{Si}$ bilayers induced by 100--700 keV Xe ions at fluences up to $4\ifmmode\times\else\texttimes\fi{}{10}^{16}$ $\mathrm{ions}/{\mathrm{cm}}^{2}$ were investigated at 80 K and room temperature. The element depth profiles were measured via Rutherford backscattering (Ni,Si) and resonant nuclear reaction (N) analysis, the phase formation at the interface via x-ray diffraction, and the surface roughness by atomic force microscopy. The observed dissociation and preferential sputtering of ${\mathrm{Ni}}_{3}\mathrm{N}$ followed by nitrogen out-diffusion were related to the small binding energy of this compound. Mixing at the ${\mathrm{Ni}}_{3}\mathrm{N}/\mathrm{Si}$ interface occurs via a combination of diffusion and reaction controlled transport processes and the interface broadening varies in second order with the ion fluence. At higher ion fluences, the formation of ${\mathrm{NiSi}}_{2}$ and ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ phases at the interface was found.

Characterization of the induction period in tricalcium silicate hydration by nuclear resonance reaction analysis

Nuclear resonance reaction analysis has been applied for the first time to measure the development of the hydrogen depth profile in the early stages of hydration of tricalcium silicate using the 1H(15N,αγ)12C reaction. The surface layer had an H concentration and thickness consistent with a few unit cells (1.1 nm) of tobermorite-like material. The inner regions exhibited diffusion-controlled growth with time until the hydrogen concentration approaches that of the surface layer at 4.25 ± 0.07 h. This event marked the end of the induction period and the onset of the rapid hydration reaction period.

Hydrogen and disorder in diamond-like carbon

Diamond-like carbon is a system of rather high disorder as it has a wide optical absorption tail and a high density of paramagnetic defects. The defect density remains high even in DLCs containing 30-60% hydrogen, so hydrogen does not appear to passivate defects well unlike in a-Si:H. To investigate the role of hydrogen on the disorder in DLCs we have investigated the effect of low concentrations of hydrogen on the disorder in ta-C, by introducing 10(-6)-10(-3) mbar hydrogen into the deposition of ta-C by filtered cathodic vacuum are (FCVA), which corresponds to 0.1-15 at.% hydrogen in the films. Higher pressures of hydrogen reduces the ionisation leading to sp(2) bonding, and ultimately the thermalisation of the plasma leads to nanotubes and fullerenes. The deposited ta-C:H films were investigated by electron energy loss spectroscopy (EELS), Raman spectroscopy, optical measurements, electronic transport and N-15 resonant nuclear reaction analysis. Plasma characterisation with a retarding field analyser showed that the ion current density remains nearly unchanged in the pressure range used to deposit the films. Raman measurements indicate the onset of clustering of sp(2) sites when the hydrogen pressure exceeds 2 x 10(-4) mbar. We find that small amounts of hydrogen increase the optical gap up to 2X10(-6) mbar hydrogen pressure, and then the band gap decreases continuously. The absorption tail sharpens by the addition of hydrogen, as measured by photothermal deflection spectroscopy (PDS) and thus confirms the Raman measurements that suggest that the order in the material increases with increasing hydrogen content.

Laser-produced iron nitrides seen by Mössbauer spectroscopy

Mossbauer spectroscopy is a very powerful tool to investigate technological processes performed mainly at the surface of materials. Nitriding of metals and steel is well established in surface engineering, and gas nitriding is used most frequently. Laser nitriding, i.e. the nitrogen take-up from the ambient gas upon irradiation of a steel surface with short laser pulses, is presented in its application to iron, stainless steel and plain carbon steels. It will be demonstrated how Mossbauer spectroscopy in combination with complementary methods (Rutherford backscattering spectroscopy, Resonant nuclear reaction analysis, Nanoindentation) can help to reveal basic mechanisms in these processes.

Characterization of Crystallinity of SiC Surface Layers Produced by Ion Implantation

Carbon implantations into silicon were carried out in order to form thin surface layers of SiC. Single crystalline 〈100〉 silicon samples were implanted with 40 keV 13C ions with a fluence of 3.8 × 1017 ions/cm2 and subsequently thermally treated under high vacuum conditions at different temperatures using a 20 keV electron beam. The isotope 13C offers the advantage to measure the carbon redistribution caused by the thermal treatment process with the nuclear resonance reaction analysis. The crystallinity of SiC surface layers is studied by X-ray diffraction and transmission electron microscopy measurements. A polycrystalline 3C-SiC surface layer with a low content of 6H-SiC grains is formed with a thickness of about 70 nm. The analysis of high resolution TEM micrographs from the interface region obviously shows that the 6H-SiC phase coexists with the 3C-SiC modification in the SiC layer.

Investigation of laser nitriding of iron using ion beam analysis

Most metals can be nitrided by irradiation with short pulses of an excimer laser in nitrogen containing atmospheres. By the laser nitriding process with a XeCl excimer laser beam (wavelength λ=308 nm, average energy density H=4 J/cm 2, pulse width τ=55 ns) in pure nitrogen, iron nitride coatings of 1–2 μm thickness at a level of up to 15 at.% nitrogen were produced. The results of the complicated laser-plasma-material interaction can be resolved by combining Resonant nuclear reaction analysis (RNRA) and Rutherford backscattering spectrometry (RBS). Utilizing the exclusive sensitivity of RNRA to the isotope 15N, RNRA via the 15N(p,αγ) 12C resonance reaction and alternate irradiations in a N 2 atmosphere of natural or enriched 15N abundance are employed to study the take-up of new nitrogen into the surface and the transport mechanisms upon irradiation with subsequent pulses. Together with RBS investigations of convective transport of the molten base material using thin Au marker layers, information on basic mechanisms of the nitriding process (convection, diffusion) was gained enabling a simulation of the nitrogen depth profiles.

Diffusion of hydrogen implanted in α-quartz during air annealing

α-quartz samples were implanted with 20 keV H 2 +-ions to fluences of 5×10 16 H/cm 2 at a target temperature of 77 K. Rutherford Backscattering in channeling geometry (RBS-C) revealed that an amorphous surface layer of 1.54×10 18 atoms/cm 2 forms under these conditions. Resonant nuclear reaction analysis (RNRA) utilizing the 1H( 15N, αγ)-resonance at 6.385 MeV beam energy was used to measure the implanted hydrogen profile. The samples were then annealed in air for 1 h at temperatures between 300°C and 950°C. After annealing, RBS-C and RNRA were again employed to study the alterations of the hydrogen profile and the amorphous layer induced by the heat treatment. In contrast to the observation with alkali ions no epitaxial regrowth could be detected even after the 950°C annealing. Below about 450°C also no changes of the hydrogen profile were observed, while at about 600°C almost all hydrogen has left the sample. This behavior fits nicely to the results obtained for other alkali implantations. Hydrogen as the lightest (and smallest) group-I atom becomes mobile at the lowest temperature and also the observed trend that the quality of the regrown layer decreases with decreasing atomic number of the implanted species has been confirmed, since no epitaxial recrystallization has taken place.

Nucleation study of titanium nitride onto steel using 15N(p,αγ) 12C resonant nuclear reaction

In this research, titanium nitride is deposited by reactive DC magnetron sputtering with two original constraints due to the expected industrial application as roll to roll decorative coating of steel: the samples should be grounded and could not be heated during deposition. The growth of titanium nitride on low-carbon steel has been studied using the 15N(p,αγ) 12C resonant nuclear reaction analysis for 429 keV protons. Using gas flow of isotope 15N enriched nitrogen during deposition, it is possible to detect nitride layer of about 0.3 ML (MonoLayer) calculated thickness with the help of the above very sharp nuclear reaction. Films from 0.3 ML to bulk-like thicknesses deposited on low-carbon steel have been analysed. The spectra obtained were deconvoluted to obtain the straggled energy width and the height proportional to the depth of nitride layer and to the 15N coverage, respectively. It is then possible to observe the nitride growth onto steel substrates: an island nucleation is followed by coalescence and finally by a continuous growth. These three nucleation steps suggest an island growth mode, the basis of the well-known columnar structure for sputtered titanium nitride on steel.