[en] Tunnel junctions with AlN (AlNxOy) barriers and CoFe and FeTaN electrodes were studied. The AlN barrier was formed by nitridizing a 10 Aa thick Al layer using radio frequency N₂ plasma. The nitrogen and oxygen content in the barriers was determined by Rutherford backscattering spectroscopy (RBS) on specially prepared barriers deposited on DLC coated substrates. RBS results indicate less than 10% O₂ incorporation in the barrier. Top-pinned junctions formed by nitridizing a 10 Aa thick Al layer (CoFe electrodes) show resistance x area products from 73Ωμm² to 8.5kΩμm² for increasing nitridation x from 30 to 200 s, with corresponding tunneling magnetoresistance (TMR) values from 13% to 33%. Bottom-pinned junctions with FeTaN electrodes were also fabricated. Maximum TMR signal is 17% after anneal at 225 degreeC for 30 min. In both cases (CoFe or FeTaN electrodes), TMR degrades for anneals above 250 degreeC. [copyright] 2001 American Institute of Physics

[en] The γ-γ Perturbed Angular Correlation technique was used to study the hyperfine interaction of ¹⁸¹Ta at the Hf site(s) in UFe₄Al₈ at room temperature and 12 K. The data at room temperature are well described by two electric field gradients, while at low temperature two combined hyperfine interactions have to be considered, one with the magnetic hyperfine field collinear with the c-axis and another with the magnetic hyperfine field in the basal plane. The results are compared with previous Moessbauer and neutron diffraction experiments and the lattice site of Hf is discussed.

[en] The 'IBA DataFurnace v2.1' code based on a simulated annealing algorithm was released in April 1998. It is capable of handling multiple RBS, EBS and ERD spectra simultaneously and self-consistently. The DataFurnace automatically solves the general inverse RBS problem: Given the spectrum what is the structure? All practical methods published up to now have depended on an analyst guessing what the spectrum means, with the help of more or less sophisticated tools of various types. There is a large class of relatively simple samples for which this approach works well; however, many samples are not conveniently simple and are either very time consuming to analyze by manual methods or even inaccessible to them in a reasonable time. We give examples of current problems which have generated large numbers of complex spectra which our new code has solved readily. The algorithm is general, readily extensible to other techniques such as NRA or PIXE, and can easily accommodate stopping power or multiple/plural scattering corrections. We can also take advantage of the Bayesian structure of the formalism to calculate confidence intervals of the solution obtained. We give examples of all of these

[en] A dual cathode magnetron sputtering system was used for synthesising carbon-nitride (CN) and boron-carbon-nitride (BCN) films at a nitrogen gas pressure of 2.0 Pa onto Si and NaCl substrates. The stoichiometry and thickness of the films were measured with Rutherford backscattering. The results were analyzed with the Simulated Annealing algorithm, which allowed the determination of the B content in samples with as little as 15 at. % B, with a detection limit of 7 at. %. The deposition rate of the CN films increased linearly with graphite target dc power. The deposition rate of the BCN films grown with 100 W rf power to the boron target and between 0 and 100 W dc power to the graphite target was higher than that of the CN films deposited with the same dc power. The absorption bands corresponding to hexagonal-BN (800 and 1350 cm^-1), cubic-BN (1050 cm^-1), graphite-like carbon bonded with nitrogen (1500 cm^-1), nitrile and isocyanate groups (2200 cm^-1), and -NH or -OH (3300 cm^-1) were detected in Fourier transform infrared (FTIR) spectra. These results show that the B is effectively introduced into the structure of the BCN films

[en] The accuracy of ion beam analysis experiments depends critically on the stopping power values available. While for H and He ions accuracies normally better than 5% are achieved by usual interpolative schemes such as SRIM, for heavier ions the accuracy is worse. One of the main reasons is that the experimental data bases are very sparse, even for important materials such as Si. New measurements are therefore needed. Measurement of stopping power is often made with transmission in thin films, with the usual problems of film thickness homogeneity. We have previously developed an alternative method based on measuring bulk spectra, and fitting the yield by treating the stopping power as a fit parameter in a Bayesian inference Markov chain Monte Carlo procedure included in the standard IBA code NDF. We report on improvements of the method and on its application to the determination of the stopping power of ⁷Li in Si. To validate the method, we also apply it to the stopping of ⁴He in Si, which is known with 2% accuracy.

[en] Group III nitrides such as InN, GaN, and their alloys are increasingly important in a host of optoelectronic and electronic devices. The presence of unintentional impurities is one of the factors that can strongly affect the electronic properties of these materials, and thus ion beam analysis techniques can play a fundamental role, in particular heavy ion elastic recoil detection analysis tracing and quantifying these contaminations. However, stopping powers in InN and GaN have not yet been measured, and data analysis relies on using the Bragg rule, which is often inaccurate. We have used a bulk method, previously developed by us and applied successfully to other systems, to determine experimentally the stopping power of several ions in InN. The results of our measurements and bulk method analysis are presented.

[en] Nanocomposites consisting of a dielectric matrix, such as TiO₂, with embedded noble metal nanoparticles (NPs) possess specific optical properties due to the surface plasmon resonance (SPR) effect, interesting for several applications. The aim of this work is to demonstrate that these properties are sensitive to the nanostructure of magnetron-sputtered TiO₂/Au thin films, which can be tuned by annealing. We study the role of the shape and size distribution of the NPs, as well as the influence of the crystallinity and phase composition of the host matrix on the optical response of the films. All these characteristics can be modified by vacuum annealing treatments of the deposited films. A theoretical interpretation and modeling of the experimental results obtained is presented. The model involves a modified Maxwell-Garnett approach for the effective dielectric function of the composite (describing the SPR effect) and the transfer matrix formalism for multilayer optics. Input data are based on the experimental information obtained from the detailed structural characterization of the films. It is shown that the annealing treatments can be used for controlling the optical properties of the composite films, making them attractive for decorative coatings.

[en] Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N₂:O₂ during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 deg. C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.

[en] GaN was implanted with 300 keV Eu ions over a wide fluence range from 1 x 10¹³ to 1 x 10¹⁶ Eu cm^-2 at room temperature (RT) or 500 ⁰C. Detailed structural and optical characterizations of the samples were performed using Rutherford backscattering spectrometry and channelling, transmission and scanning electron microscopy, wavelength dispersive x-ray emission and RT cathodoluminescence (CL) spectroscopy. RT implantation results in a sigmoidal-shaped damage build-up curve with four regimes that were correlated with the formation of specific kinds of defects. After annealing at 1000 ⁰C only samples implanted to fluences below 0.8 x 10¹⁵ Eu cm^-2 showed near complete recovery of the crystal. Implantation at elevated temperature significantly decreases the implantation damage and increases the fraction of Eu incorporated on substitutional Ga-sites. The improved structural properties of samples implanted at elevated temperature are reflected in a higher intensity of Eu-related red light emission after annealing at 1000 ⁰C. The RT CL intensity is correlated with the number of Eu ions on substitutional Ga-sites after annealing. Furthermore, a detailed study of optical activation shows that the optimum annealing temperature depends on the implantation fluence due to the sensitive balance of defects removed and created during high temperature annealing.

[en] IBA techniques such as RBS, ERDA, NRA, or PIXE are highly complementary, and are often combined to maximize the extracted information. In particular, they have different sensitivities to various elements and probe different depth scales. The same is true for secondary ion mass spectrometry (SIMS), that can have much better detection limits for many species. Quantification of SIMS data normally requires careful calibration of the exact system being studied, and often the results are only semi-quantitative. Nevertheless, when SIMS is used together with other IBA techniques, it would be highly desirable to integrate the data analysis. We developed a routine to analyse SIMS data, and implemented it in NDF, a standard IBA data analysis code, that already supported RBS, ERDA, resonant and non-resonant NRA, and PIXE. Details of this new routine are presented in this work.