Depth Profile Concentration Research Articles

Study of the Elastic Scattering in the d + 11B system for EBS purposes

The implementation of boron in several fields, such as in the creation of p-type semiconductors in electronics, has created the need for the accurate quantitative determination of its depth profile concentrations in near surface layers of various matrices. In the framework of IBA techniques a combination of Elastic Backscattering Spectroscopy, along with Nuclear Reaction Analysis, has been proposed in order to address the current needs for boron depth profiling, focusing on the use of proton beams. Deuteron beams however offer superior mass resolution with similar stopping power values and simultaneous excitation of most light elements. Unfortunately, the lack of experimental datasets concerning the deuteron elastic scattering on boron impedes their use. Thus, in the present work, the first set of measurements for the 11B(d,d0) differential cross section covering the Ed,lab=1300-1860 keV energy range for the backscattering angles of 150ο, 160ο and 170ο were carried out. The study was conducted at the 5.5 MV Tandem Accelerator of the Institute of Nuclear and Particle Physics, in the National Center of Scientific Research “Demokritos”, Athens, Greece. The target was a thin, self-supporting aluminum foil, upon which a thin natB (isotopic ratio: 11B 80.1%, 10B 19.9%) layer was deposited using the sputtering technique at RBI, Zagreb, Croatia, followed by the evaporation of an ultra-thin layer of 197Au on top for normalization and wear protection purposes. The outgoing particles were detected using silicon surface barrier (S.S.B.) detectors and the differential cross sections for elastic scattering were determined from the resulting spectra via the relative technique

Differential Cross-section Measurements for Deuteron Elastic Scattering on 11B

The implementation of boron in several fields, such as in the creation of p-type semiconductors in electronics, has created the need for the accurate quantitative determination of its depth profile concentrations in near surface layers of various matrices. In the framework of IBA techniques, a combination of Elastic Backscattering Spectroscopy (EBS), along with Nuclear Reaction Analysis (NRA), has been proposed in order to address the current needs for boron depth profiling, based on the use of a proton beam. Deuterons offer superior mass resolution with respect to protons, having similar stopping power values, but, unfortunately, the lack of experimental datasets concerning the deuteron elastic scattering on boron impedes their use. Thus, in the present work, the first set of measurements for the 11B(d,d0) differential cross sections covering the Ed,lab=1300-1860 keV energy range for the backscattering angles of 150°, 160° and 170° was carried out. The study was conducted at the 5.5 MV Tandem Accelerator of the Institute of Nuclear and Particle Physics, in the National Center of Scientific Research “Demokritos”, Athens, Greece. The target was a thin, self-supporting aluminum foil, upon which a thin natB (isotopic ratio: 11B 80.1%, 10B 19.9%) layer was deposited using the sputtering technique at RBI, Zagreb, Croatia, followed by the evaporation of an ultra-thin layer of 197Au on top for wear protection and normalization purposes. The outgoing particles were detected using 6 Silicon Surface Barrier (S.S.B.) detectors and the differential cross sections for the elastic scattering were determined from the resulting spectra via the relative measurement technique.

Comparative study on low energy ion beam modification of thermoplastic polymers

ABSTRACTPolycarbonate (PC) and polyethylene terephthalate (PET) thermoplastic polymer films were irradiated by low energy ion beams such as 100 keV Hydrogen (H+) ions and 350 keV Nitrogen (N+) ions at varied fluence from 1 × 1013 ions/cm2 to 5 × 1014 ions/cm2. The depth profile concentration of ions was calculated using Stopping and Range of Ions in Matter (SRIM) software code. Fourier Transform Infrared (FTIR) technique shows decrement in the intensity of peaks and disappearance of peaks mainly related to carbonyl stretching at 1770 cm−1 and C–C stretching at 1500 cm−1. Scanning electron microscopy (SEM) of irradiated polymers showed the formation of pores. X-ray diffraction (XRD) analysis has showed decrease in the intensity indicating the decrease in crystallinity after irradiation. Mechanical studies revealed that the molecular weight and microhardness decrease with increase in ion fluence due to increase in chain scission. The contact angle increased with increase in ion fluence indicating the hydrophobic nature of polymer after irradiation. Antibiofilm activity test of irradiated films shows resistance to Salmonella typhi (S. typhi) pathogen responsible for typhoid. The study shows that Nitrogen ion induces more damage compared to Hydrogen ions and PC films get more modified than PET films.

14C High Concentration Measurements with Relevance for Decommissioning of Nuclear Reactors

ABSTRACTDecommissioning of nuclear reactors requires determination of all remnant long-lived isotopes that were produced during their long functioning time of the respective facilities. Radiocarbon (14C) is such an isotope (T1/2 = 5730 yr), widely produced by neutron reactions in a thermal column of a nuclear reactor. Accelerator mass spectrometry (AMS) uses 14C for precise dating of up to 50,000 years old archaeological artifacts. This study presents a premier AMS measurement of high concentrated 14C samples that are strictly forbidden in laboratories dedicated to perform 14C dating. The determined 14C activities range from the natural level (isotopic ratio 14C/12C = 1.2 × 10–12) up to values of 10,000 times higher. 14C bulk and depth profile concentrations were measured in the thermal column disks of a decommissioned nuclear reactor. Results have shown that the 14C concentration in the thermal column, close the reactor core is about 75 kBq/g and decreases to 0.7 Bq/g and the end of the column. Such AMS measurements are applicable for decommissioning and waste management of nuclear reactors.

Plasmonic properties of implanted Ag nanoparticles in SiO2 thin layer by spectroscopic ellipsometry

We report an uncommon study of the insertion of distributions of both volume fraction and depolarization factors in the modeling of the plasmonic properties of implanted Ag nanoparticles (Ag-NPs) in a SiO2 layer when using spectroscopic ellipsometry (SE) characterization. The Ag-NPs were embedded in the SiO2 matrix by Ag+ ion implantation at various doses of 0.5 × 1016, 1 × 1016, 2 × 1016, and 5 × 1016 ions cm−2. The formation of the Ag-NPs in a host matrix of SiO2 was controlled by transmission electron microscopy (TEM). The Ag-NPs are self-organized in the layer, and their mean radius ranges between 2 and 20 nm. The optical properties of layers were extracted by modeling the SE parameters by taking into account the depth profile concentration of Ag-NPs. The mixture of SiO2 and Ag-NP inclusions was modeled as an effective medium according to the shape distributed effective medium theory (SDEMT). In addition to the optical responses, it is shown that this model enables the explanation of the impact of NP shape distribution on the plasmon band and provides precious information about the NP shape characteristics. A good agreement was obtained between ellipsometry and TEM results. The distribution of the volume fraction in the film was found to lead to a gradient of effective dielectric function which was determined by the SDEMT model. The effective dielectric function reveals distinct Ag plasmon resonance varying as the Ag+ ions dose is varied. The real part of the dielectric function shows a significant variation around the plasmon resonance in accordance with the Kramers-Kronig equations. All determined optical parameters by SDEMT are provided and discussed. We highlight that SE combined with SDEMT calculations can be considered as a reliable tool for the determination of the NP shape and volume fraction distributions without the need of TEM.

Influence of pH on the optical, structural and compositional properties of nanocrystalline CdSe thin films prepared by chemical bath deposition

Cadmium selenide (CdSe) thin films have been prepared by chemical bath deposition on glass substrates in chemical solution and the pH controlling agent has been altered. The band gap energy of CdSe thin films was determined by using UV–visible spectra. The structural and surface morphological properties were studied by X-ray diffraction and scanning electron microscopy. Furthermore, Rutherford backscattering spectroscopy, as a powerful technique in surface science, was used to investigate the stoichiometry and the variation of the depth profile concentration of Cd and Se elements along the thickness of the prepared samples. The result indicated that the pH has a crucial role in physical properties of prepared CdSe thin film and can control the procedure of deposition to achieve the desired value of band gap energy, quality of crystallity and homogeneity of the prepared thin films.

Interpreting scattered in-situ produced cosmogenic nuclide depth-profile data

Modelling the evolution of the concentration of in-situ produced cosmogenic nuclides as a function of depth (depth-profile) has been developed to allow determining both the exposure duration and the denudation rate affecting geomorphic features. However, material sampled through surficial deposits may exhibit an inherited component resulting from exposure to cosmic rays before deposition. In case of homogeneous inheritance, this inherited component may be estimated through sampling at increasing depths and subsequently subtracted. In case of variable inheritance, the measured concentrations are scattered and the random distribution of the depth-profile concentrations prevents modelling confidently a depth-profile and precludes constraining an exposure duration. Often observed in desert and endorheic regions, this greatly restricts the possibilities to determine an accurate abandonment age of alluvial surfaces in such environments. Provided the denudation is demonstrated negligible, a method for determining a more accurate range of minimum inheritance, hence a more accurate maximum abandonment age for a given alluvial surface, is proposed. This method, based on the rejuvenation of depth-profile samples, relies on the simple hypothesis that at least one of the depth-profile samples would be emplaced with no or negligible inherited component and on the obvious principle that none of analysed sample has been emplaced with a negative cosmogenic nuclide concentration. The method consists then in determining which of the measured depth-profile sample may have been emplaced with a null CRE concentration; i.e., with a zero inheritance value. This requires to calculate the in-situ duration of exposure needed to reach the concentration measured for each depth-profile sample and to retain the one that provides the smallest in-situ exposure duration. Several examples from alluvial surfaces of central Iran illustrate the profile rejuvenation method and highlight a variable inheritance ranging between 1.5×105 and 16.1×105at/g (SiO2) for terraces whose abandonment ages range from ten to several hundreds of ka.

Assessment of natural radioactivity levels and their relationship with soil characteristics in undisturbed soils of the northeast of Buenos Aires province, Argentina

Surface and depth profile concentrations (down to 50 cm) of 232Th chain, 226Ra, and 40K radionuclides were determined in undisturbed coastal and inland soils of La Plata city region, Argentina, through their gamma-ray activity using a high-purity Ge detector spectrometer. These results were compared with superficial activities determined in soils from the surroundings of the Centro Atómico Ezeiza (Ezeiza Atomic Center) located in Ezeiza, Buenos Aires Province, Argentina. The hyperfine and magnetic Fe phase’s properties of soil profiles were characterized by Mössbauer spectroscopy, magnetic hysteresis loops and AC magnetic susceptibility. No dependence of the activity of the 232Th natural chain on depth was found, whereas variations for 226Ra and 40K activities were observed. Positive correlations, determined by the Pearson correlation coefficients, were established between 40K, 226Ra and 232Th activity concentrations for the whole set of soil samples. The annual external equivalent dose for adults was similar for La Plata and Ezeiza regions, with average values of 0.08 ± 0.01 mSv and 0.06 ± 0.02 mSv, respectively. The thermal dependence of the AC magnetic susceptibility revealed the existence of magnetite and hematite. The Mössbauer spectra of all soils were made up of signals associated with α-Fe 2O 3, a paramagnetic relaxation component, and Fe 3+ and Fe 2+ doublets. In addition, the spectra of inland soils revealed the presence of Fe 3O 4. A negative correlation was found between the activity concentrations and the α-Fe 2O 3 and Fe 3O 4 relative fractions, whereas a positive correlation was found between the Fe 3+ relative fraction and the 40K activity.

Hyperfine and radiological characterization of soils of the province of Buenos Aires, Argentina

The depth profile concentration of both natural and anthropogenic gamma-ray-emitter nuclides were determined in soil samples collected in an area located at 34° 54.452′ S, 58° 8.365′ W, down to 50 cm in depth, using an hyper-pure Ge spectrometer. The soil samples were also characterized by means of Mössbauer spectrometry and X-ray diffraction. The activities of 238U and 232Th natural chains remain constant in depth at 41 Bq/kg and 46 Bq/kg, respectively, while the 40K activity increases from 531 Bq/kg to 618 Bq/kg between 2.5 cm y 25.5 cm of depth. The only anthropogenic detected nuclide is 137Cs, whose activity changes form 1.4 Bq/kg to values lower than the detection limit (LD) for depths below 25 cm, exhibiting a maximum at 10 cm beneath the surface. The Mössbauer spectra show two magnetic sextets associated with α-Fe2O3 and Fe3O4, as well as two Fe+3 Fe+2 doublets, probably originated in octahedral and tetrahedral sites of paramagnetic phases. The Fe3+ paramagnetic signal relative fraction increases up to 82% at the expense of the α-Fe2O3 one when de depth increases. No correlation between Fe3O4 and the 137Cs was identificated.

X‐ray photoelectron spectroscopy and the pattern recognition method—their application to surface studies in CoPd alloys

AbstractIn the present work, polycrystalline CoPd alloys in varying range of bulk atomic percent composition (Co30Pd70, Co50Pd50 and Co70Pd30) are investigated by means of X‐ray photoelectron spectroscopy (XPS). The results of conventional XPS quantitative multiline (ML) approach are compared to the results obtained on the basis of XPS lines shape analysis, where the selected XPS or X‐ray induced Auger electron (XAES) transitions, are processed using the pattern recognition method known as the fuzzy k‐nearest neighbour (fkNN) rule. The fkNN rule is applied to the following spectra line shapes: Pd MNV, Co 2p, Co LMM, Pd 3d and valence band, analysing electrons in a varying range of selected kinetic energies.Both methods showed the surface segregation of Pd in Co30Pd70 and Co50Pd50 alloys. The results of the ML, the binding energy shift (ΔBE) analysis and the fkNN rule remained in agreement. Discrepancies in quantitative results obtained using different approaches are discussed within the accuracy of the applied methods, differences due to mean escape depth (MED) of electrons in considered transitions, their depth distribution function, the sensitivity of electron transition line shape on the environmental change (weaker effect for the inner shell transitions, and stronger effect for the outer shell transitions and Auger electron spectroscopy (AES) electrons transitions) and the non‐uniform depth profile concentrations. Copyright © 2005 John Wiley & Sons, Ltd.

Modelling of grazing incidence X-ray diffraction spectra from Mo-implanted stainless steel: Comparison with experimental data

Mo ion implantation at 150 keV in an austenitic stainless steel leads to a pseudo-Gaussian concentration depth profile as predicted by calculation using TRIM code and confirmed by RBS analyses. The structural modification of the implanted layer was investigated using grazing incidence X-ray diffraction (GIXD) for different incidence angles. The X-ray austenite peak depends strongly on fluence and incidence angle, and presents one or two peaks as a function of incidence angle. Using the concentration depth profile of implanted element, the information depth profile of diffracted intensity, and a linear relationship between Mo concentration and lattice parameter, we predicted the γ diffracted X-ray peaks. The experimental X-ray diffraction peaks are comparable to the predicted ones. Mo implantation induces a continuous expansion of austenite lattice, which follows the depth profile concentration in the implanted layer even if the signature of this expansion is the apparition of a new austenite peak.

Study of tasin diffusion barrier

Due to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced high-density memory devices. In this study we report on the properties and the resistance to oxidation of TaSiN thin films deposited by reactive magnetron sputtering and processed by rapid thermal annealing (RTA) in 18O2 at 650°C. In order to determine the composition, RBS (Rutherford Backscattering Spectroscopy) and NRA (Nuclear Reaction Analysis) techniques have been used. 18O depth profile concentrations were measured after RTA using the narrow (fwhm=100eV) resonance at 151 keV of the nuclear reaction 18O(p,α)15N.

Oxidation Resistance of TaSiN Diffusion Barriers for Stacked Capacitors

AbstractDue to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this study we report on the properties and the resistance to oxidation of TaSiN thin films deposited by reactive magnetron sputtering and processed by rapid thermal annealing (RTA) in 18O2 at 650°C. In order to determine the composition, RBS (Rutherford Backscattering Spectroscopy) and NRA (Nuclear Reaction Analysis) techniques have been used. 18O depth profile concentrations were measured after RTA using the narrow (fwhm=100eV) resonance at 151 keV in the nuclear reaction 18O(p,α)15N.

Bulk diffusion and solubility of silver and nickel in lead, lead-silver and lead-nickel solid solutions

The results of a study of solubility and bulk diffusion of 110Ag and 63Ni in lead, lead-silver and lead-nickel solid solutions in the temperature range 220 to 88°C are reported. Owing to the low solubility of silver and nickel in lead, Pick's solution corresponding to the boundary condition of a constant concentration of solute at the surface has been used. Depth-profile concentration analysis of 110Ag and 63Ni suggests a fundamental difference between the diffusion mechanisms of silver and nickel. Since silver penetration profiles in pure lead give diffusion coefficients independent of the penetration depth and silver concentration, it is suggested that slight decrease of silver diffusivity in lead-silver solid solutions (which remain within experimental error) have no significance. This implies that the interstitial silver atoms do not associate significantly with each other to form Ag-Ag dimers. In contrast, different behaviors of 63Ni depth profile concentration in pure lead and saturated PbNi solid solutions agree with a strong Ni-Ni interaction leading to the formation of less mobile dimers near the surface in pure lead. The model proposed by Decker to describe the diminution of gold diffusivity in PbAu solid solutions yields H = 9500 cal/mol and S = 0.9 k for the binding enthalpy and entropy of Ni-Ni substitutional dimers.

X-ray photoelectron spectroscopy studies of copper diffusion behaviour and related degradation phenomena in thin film CdS:Cu 2S solar cells

Quantitative growth of thin Cu 2S layers in chemiplated thin film CdS:Cu 2S solar cells was observed by studying the depth profile concentrations of copper and sulphur by the X-ray photoelectron spectroscopy technique. Scanning electron microscopy examination of the junction revealed a complex and corrugated structure at the interface. From a study of the spatial distributions of cadmium, copper and sulphur and measurements of the saturated [Cd]/[S] ratios it is inferred that in deep layers the copper originates from grain boundaries. Similarly, by isolating the copper profile in the Cu 2S layers, the CdS grain-grain boundary region and the CdS grain boundaries and by applying suitable diffusion equations with appropriate boundary conditions, the diffusion coefficients in the midgrain and grain boundary regions were evaluated. In the chemiplating process copper diffusion is 5 × 10 2 times faster in the grain boundary than in midgrain. A short heat treatment of the cells causes the redistribution of cadmium and copper in the junction, making the interface sharper. Analysis yields diffusion coefficients of 5.8 × 10 −11 exp(−0.229/kT) in midgrain and 1.06 exp(−0.964/kT) in the grain boundary. In order to gain knowledge of the degradation effects arising from copper migration, the evaluated diffusion coefficients were used to compute the time in which loss of Cu 2S stoichiometry and widening of the copper-compensated layer will lead to significant reduction in cell performance. This study shows that copper diffusion is not a severe life-limiting factor for CdS solar cells.