J.C. Soares

• Professor Catedrático
• University of Lisbon

In this work we report on the lattice site location of rare earths in single-crystalline ZnO by means of the emission channeling (EC) technique. Following low dose (3x10E13at/cm2) 60 keV ion implantation of the precursor isotope 169Yb, a position-sensitive electron detector was used to monitor the angular distribution of the conversion electrons em...

YBa2Cu3O6+x (YBCO) superconducting thin films implanted with low doses of radioactive 197mHg and 199mHg isotopes were studied with a combination of nuclear and non-nuclear characterization techniques. We show that after implantation Hg lies on an unique site in the YBCO lattice and the critical temperature increases slightly with the increase of th...

High quality YBa2Cu3O6+x (YBCO) superconducting thin films were implanted with the radioactive 197m Hg (T1/2 = 24 h) isotope to low fluences of 10^13 atoms/cm^2 and 60 keV energy. The lattice location and stability of the implanted Hg were studied combining the Perturbed Angular Correlation (PAC) and Emission Channeling (EC) techniques. We show tha...

Electric field gradients (EFG) on mercury sites of the Hg1201 high-TC superconductors were measured with the perturbed angular correlation (PAC) technique. In Hg1201 samples where PAC detects higher oxygen content the EFGs have decreased to lower values indicating an elongation of the Hg-apical oxygen dumbbell. On the same samples the asymmetry par...

Combined high precision RBS/channeling, NRA/channeling and perturbed angular correlation studies were used to characterize near-stoichiometric and congruent LiNbO3 crystals. In congruent LiNbO3 two non-equivalent Li sites are distinguished whereas in near-stoichiometric LiNbO3 only one of them exists. A comparison of the experimental results with M...

Multilayers of different Co and Re thickness were studied using RBS/ Channeling combined with hyperfine interaction techniques. We observe interface sharpness for film thickness down to a few monolayers. The magnetic hyperfine field corresponds to the well–known bulk hcp value but slightly depends on the layer thickness. Preferential c–axis orienta...

Single crystalline lithium niobate samples cut perpendicular to the $\langle0{\bar 1}10 \rangle$-direction (Y-cut) have been implanted with 1 × 10¹⁶cm⁻²He⁺ ions of 20 KeV energy. He-implanted and virgin samples were implanted with Au⁺ ions at energies of 50 KeV or 800 KeV to the fluences of 5 × 10¹⁵cm⁻² or 1 × 10¹⁶cm⁻², respectively. In the first c...

Spin dependent tunnel junctions are of technological interest for applications in magnetic non-volatile random access memories due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical structures are Si/Al2O3600Å/Ta70Å/NiFe70Å/CoFe30Å/AlxNyOzt/CoFe40Å/MnIr200Å/Ta30Å, with t = 6-30 Å, annealed to tempera...

Single crystalline colorless α-Al2O3 samples were implanted with several fluences of Fe+ ions in the range of 1×1016 to 5×1017 Fe+ cm-2 at room temperature. Optical absorption and luminescence measurements were carried out before and after annealing in reducing and oxidizing atmospheres. The structural changes were studied with RBS/channeling and x...

We investigated the formation of a buried HfSi2 layer by high fluence ion implantation of isotopically mass separated 179–180 Hf+ on heated silicon (100) substrates. It is shown that for the substrate temperature of 600°C a buried HfSi 2 layer is formed. By subsequent annealing at 1000 °C a continuous 12 nm HfSi2 layer on the Si surface is formed f...

The dependence of the properties of hydrogenated amorphous silicon-carbon alloys deposited with a 1:10 silane (SiH4) to methane (CH4) or ethylene (C2H4) gas flow ratios with the hydrogen dilution, deposition pressure and power is studied. In methane-based films the carbon content shows a decrease (from ≈0.75 to 0.55) with increasing hydrogen diluti...

The behaviour of 300 keV Ba ions implanted at room temperature with doses between 1015 and 1017 cm−2 in Mg single crystal and foils was investigated. The results show that the Ba ions do not occupy substitutions sites in Mg, either after the implantation or the annealing treatments. However, pronounced migration of Ba to the surface is observed abo...

Low and high dose hafnium imolanted beryllium samoles have been prepared at room temperature by ion implantation of beryllium commercial foils and single crystals. These samples have been studied before and after annealing with the time differential perturbed angular correlation method (TDPAC) and with Rutherford backscattering and channeling techn...

LiNbO3 is a relevant material to prepare a number of electrooptic (bulk and waveguide) devices. Moreover, its photorefractive (PR) behavior is also potentially useful for optoelectronic applications such as holographic storage and coherent optical amplification. For a full understanding and optimization of the PR effect, the lattice location and va...

Iridium silicides formation by rapid thermal annealing (RTA) under vacuum at several temperatures in the range of 350 to 650°C has been investigated. The substrates and the silicide films were analyzed by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). At 350°C, no distinguishable phase was detected for 240 secon...

Erbium was implanted with 160 keV at doses between 5×1014 and 5×1015 at/cm2 into (0001) epitaxial GaN on sapphire and annealed at various temperatures between 600° and 1000° C. The RBS/Channeling technique was used to analyze the damage recovery during different annealing steps and to determine the lattice location of the implanted Er. For a sample...

The results of parallel RBS and photoluminescence studies of erbium implanted GaAs are presented. Low dose implantations do not produce any significant PL signals, and the dose must be in the range le14 to le15 /cm2 in order that Er related emission dominates in the PL spectrum. A comprehensive analysis of the effects of coimplantation with oxygen...

The thermal stability of ion irradiated 1.7 μm thick AZ-1350J photoresist films was investigated using the RBS and ERDA techniques to measure the composition of the irradiated and annealed films. The films have been irradiated with He, N and Ar ions at energies from 380 to 760 keV and fluences between 2 × 1015 and 1016 ions cm−2. A considerable inc...

In this work the perturbed angular correlation technique is used to locally monitor the epitaxy and thermal stability of the hafnium layer in a Zr/Hf/Zr multilayer. The studies reveal that the system is highly homogeneous and presents high epitaxy. Measurements at high temperatures show that no HfO x formation occurs up to 562 K but at this tempera...

The hyperfine field at metal lattice sites in a nanostructured HfO2 thin film was studied by the Perturbed Angular Correlation (PAC) technique using 181Ta as probe nuclei. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The resulting film thickness was about 25 nm. The 181Ta isotopes are formed in Hf...

The Zr/Hf system is highly interesting due its various applications, e.g. formation of amorphous ternary alloys, superconductive properties and production of gate oxide layers with high dielectric coefficients by oxidation of Zr/Hf multilayers. In this work Zr/Hf/Zr trilayers with an individual layer thickness of approximately 50nm were deposited b...

The hyperfine field at 181Ta lattice sites in nanostructured HfO2 thin films was studied by the Perturbed Angular Correlation (PAC) technique. Thin oxide films were deposited by Electron Beam Evaporation on a silicon substrate. The thickness of the films was ~100 nm and ~250 nm. Radioactive 181Hf nuclei were produced by neutron activation of the fi...

We developed a two dimensional transient numerical model that solves the first step of heat transfer of an active magnetic regenerative refrigerator (AMR) using the heat conduction equation for an adiabatic system. For micro-refrigeration, an AMR device is constituted by a magnetic material, placed on a silicon wafer containing micro-channels where...

In this work, we report the fabrication process of nanostrutured powder using a Sol-Gel method and HfO2 nanofilms obtained via Pulsed-Laser-Ablation and Electron-Beam Evaporation. The results of the investigation of structural properties and defects of HfO2 nanoparticles and thin films are discussed in terms of the electric quadrupole interactions...

We developed a two-dimensional transient numerical model that solves the first step of heat transfer of an active magnetic regenerative refrigerator (AMR). The magnetic materials considered are Gd5Si2Ge2 (GSG), La(Fe0.88Si0.12)13 (LFS) and La0.66Sr0.33MnO3 (LSMO), pointed as promising materials to be used in magneto-refrigeration near room temperat...

The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source and further precise 180Hf isotope implantation, in a high current implanter is described. The spectrometry system uses two signals (x–y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potent...

Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO2 layers with different thickness were deposited by Low Pressure Chemical Vapor Deposition and annealed to crystallize the SiGe nanoparticles. The use of grazing incidence RBS was necessary to obtain sufficient depth resolution to separate the signals arising from the indivi...

Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO2 layers with different thickness were deposited by Low Pressure Chemical Vapor Deposition and annealed to crystallize the SiGe nanoparticles. The use of grazing incidence RBS was necessary to obtain sufficient depth resolution to separate the signals arising from the indivi...

The development of a low-cost, accurate, non-intercepting continuous method for measuring the beam current in a high-current ion implanter is described. The method, named a differential current monitor, is based on the electric charge conservation principle, applied to the currents that flow in the implanter electrical system, due to the accelerati...

The hyperfine field at 181 Ta lattice sites in a nanostructured HfO 2 thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive 181 Hf ions were produced by neutron activation of the very...

Recovery of point defects and local phase transitions were studied in the neighbourhood of implanted 111mCd (low fluence of 1.5×1012at/cm2) into undoped and 2%Nb-doped SrTiO3 single crystals by means of the perturbed angular correlation technique. Measurements in the as implanted state and after subsequent 720°C and 1000°C 20min air annealings have...

The lattice location of Fe in LiNbO3 single crystals has been investigated by PIXE-channelling techniques. For the first time, it has unambiguously shown that Fe (mostly as Fe3+) lies at or near the Li-site, although a small fraction sitting at the Nb or intrinsic vacant sites cannot be ruled out.

Radioactive 73As ions were implanted into a ZnO single crystal at room temperature with 60 keV up to a fluence of 2×1013 cm−2. Subsequently, the angular emission channeling patterns of emitted conversion electrons were recorded by means of a position-sensitive detector in the as-implanted state and following annealing up to 900 ∘C, and were compare...

The authors have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive 73As. They give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fa...

Technical progress on silicon pad electron detectors, currently used in emission channelling experiments to study lattice location of radioactive dopants and impurities in single crystals, is reported. Noise and trigger efficiency improvements are achieved by using 500μm and 1mm thick detectors coupled to a cooled readout system. The static propert...

Modifying the properties of ZnO and GaN by means of incorporating arsenic impurities is of interest in both of these semiconductors, although for different reasons. In the case of ZnO, the group V element As has been reported in the literature as one of the few p-type dopants in this technologically promising II-VI compound. However, there is an on...

We have used the emission channeling technique in order to study the lattice sites of radioactive 59Fe and 67Cu following 60 keV ion implantation into Si single crystals at fluences around 1012–1014 cm−2. We find that in the room temperature as-implanted state in high-resistivity Si both Fe and Cu occupy mainly lattice sites displaced around 0.05 n...

Nanomemories, containing Ge-nanoparticles in a SiO2 matrix, can be produced by dry thermal oxidation of a SiGe layer deposited onto a Si-wafer with a barrier SiO2 layer on its top. Rutherford backscattering spectrometry has been used to characterize the kinetics of the oxidation process, the composition profile of the growing oxide, the Ge-segregat...

Grazing incidence RBS has been tested as a technique to detect and characterize SiGe nanoparticles embedded in a SiO2 matrix. Suitable structures were deposited by low pressure chemical vapour deposition and characterized by TEM and RBS. The layers containing nanoparticles have been modelled by stacks of sublayers consisting of SiGeO layers with co...

Lattice site location and local environment characterization of implanted 111Ag in SrTiO3 by means of the emission channeling (EC) and γ–γ perturbed angular correlation (PAC) techniques are reported. The angular distribution of β− particles emitted from the 111Ag decay was monitored with a position-sensitive detector as a function of annealing temp...

The effects of high-energy silicon (5MeV, 7.5MeV and 30MeV) irradiations have been optically investigated by the dark-mode m-lines technique. In all cases, an optically isotropic homogeneous layer is created after a certain critical fluence that depends on ion and energy. The structure of the layer has been investigated by micro-Raman spectroscopy...

Silicon capped by thermal oxide has been implanted with 1 x 10(17) H/cm(2) and the implant profile peaking at the interface. Samples were subjected to thermal annealing and characterized by ERD, FTIR, RBS/channeling, UV/VIS reflectance and cathodoluminescence regarding H-content, crystalline quality and light emission. The results show that the lum...

Grazing incidence RBS has been tested as a technique to detect and characterize SiGe nanoparticles embedded in a SiO 2 matrix. Suitable structures were deposited by low pressure chemical vapour deposition and characterized by TEM and RBS. The layers containing nanoparticles have been modelled by stacks of sublayers consisting of SiGeO layers with c...

Arsenic has been reported in the literature as one of the few p-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the p-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined...

The refractive-index profiles induced by high- energy (5 MeV, 7.5 MeV) silicon irradiation in LiNbO3 have been systematically determined as a function of ion fluence in the range 10 13 -10 15 cm −2 . At variance with irradiations at lower energies, an optically isotropic ('amorphous') homo- geneous surface layer is generated whose thickness increas...

Lattice sites and collective ordering of fluorine atoms in oxygen-reduced samples of HgBa2CuO4 were investigated with the perturbed angular correlation technique by measuring the electric field gradients induced at Hg199m nuclei. The experimental data were interpreted with the help of ab initio calculations of charge distributions for different flu...

Nanoparticles of Ge embedded in a formed dielectric matrix appear as very promising systems for electronic and photonic applications. We present here an exhaustive characterization of the oxidation process of polycrystalline SiGe layers from the starting of its oxidation process to the total oxidation of it. We have characterized the process by RBS...

The angular distribution of β − particles emitted by the radioactive isotope 59 Fe was monitored following implantation into Si single crystals at fluences from 1.4×10 12 cm −2 to 1×10 14 cm −2 . We identified Fe on three distinct sites: ideal substitutional, displaced substitutional and displaced tetrahedral interstitial. Whereas displaced substit...

The results reported in this work show the relevance of the lithium deficiency for the Li lattice site occupation of dopants in congruent lithium niobate crystals co-doped with 0.1 mol% Cr2O3 and different concentrations of HfO2, up to 3 mol%. The same behavior is observed in a crystal doped with 1 mol% of HfO2 and co-doped with 4 mol% MgO where af...

The local environment of implanted 111Ag (t 1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 1013 cm−2) 111Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperat...

The emission channeling technique was applied to evaluate the lattice location of implanted ⁵⁹ Fe in single-crystalline ZnO. The angular distribution of β^- particles emitted by ⁵⁹ Fe was monitored with a position-sensitive electron detector, following 60 keV low dose (2.0×10¹³ cm ^-2) room-tempe...

The local environment of implanted 111Ag (t 1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 1013 cm−2) 111Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperat...

The results reported in this work show the relevance of the lithium deficiency for the Li lattice site occupation of dopants in congruent lithium niobate crystals co-doped with 0.1 mol% Cr2O3 and different concentrations of HfO2, up to 3 mol%. The same behavior is observed in a crystal doped with 1 mol% of HfO2 and co-doped with 4 mol% MgO where af...

Low resistance spin-dependent tunnel junctions are investigated for read-head applications due to their large tunnelling magnetoresistance effect and low junction resistance-area product. Typical full junction structures can be Ta 70 Å/NiFe 70 Å/MnIr 80 Å/CoFe 35 Å/HfxAlyOz 10 Å/CoFe 35 Å/NiFe 40 Å/Ta 30 Å, annealed to temperatures up to 250 °C. We...

Low resistance spin-dependent tunnel junctions are investigated for read-head applications due to their large tunnelling magnetoresistance effect and tow junction resistance-area product. Typical full junction structures can be Ta 70 Angstrom/NiFe 70 Angstrom/MnIr 80 Angstrom/CoFe 35 Angstrom/HfxAlyOz 10 Angstrom/CoFe 35 Angstrom/NiFe 40 Angstrom/T...

Position-sensitive detector systems, initially developed for the detection of X-rays, have been adapted for their use in electron emission channeling experiments. Each detection system consists of a 30.8×30.8 mm2 22×22-pad Si detector, either of 0.3, 0.5 or 1 mm thickness, four 128-channel preamplifier chips, a backplane trigger circuit, a sampling...

We present results of recent emission channeling experiments on the lattice location of implanted Fe and rare earths in wurtzite GaN and ZnO. In both cases the majority of implanted atoms are found on substitutional cation sites. The root mean square displacements from the ideal substitutional Ga and Zn sites are given and the stability of the Fe a...

We report on emission channeling experiments using the radioactive isotope 67Cu implanted into single crystalline i-Ge at a dose of 2.4x10E12 cm-2. The lattice location of 67Cu was determined from the angular-dependent beta- emission yield, which was measured by means of a position-sensitive detector around the <111>, <100> and <110> directions. We...

SiC composite reinforced fibres are still considered to be an important material to be used in nuclear fusion reactors due to their high temperature and low neutron activation properties. Two different kinds of SiC/SiCf composite were manufactured, one of them presenting an extra SiC coating obtained by chemical vapour deposition technique. Several...

AlO(x)N(y) ultrathin films are used as insulating layers in advanced microelectronic devices. Structural characterization of these films is often done by the Rutherford backscattering (RBS) analysis. The RBS analysis of these oxinitrides is a difficult task since the relevant signals of the spectrum are washed out by the large substrate background...

Single crystals of alpha-Al2O3 with different orientations were implanted with several fluences of Ti and Co ions. For low fluences both Ti and Co ions are fully incorporated in Al lattice sites and remain stable up to annealing temperatures of 1000 degreesC. For fluences of 5 x 10(16) cm(-2) the implanted region becomes completely disordered (amor...

Single crystalline samples of bismuth tellurite were implanted with 800 keV Au+and 450 keV Ag+ions to fluences between 5×1015 and 2.5×1016 cm−2 at room temperature. The samples were annealed at temperatures of 600 °C for Au, 450 °C for Ag and 500 °C for Au/Ag implanted crystals. Strong optical absorption maxima at about 630 nm yielding Au-implanted...

In this work we present the results to develop standards of reduced activation ferritic-martensitic (RAFM) alloys for the quantitative determination of uranium in these materials. The results show that a very low efficiency can be obtained during alloying of uranium due to the segregation to the slags. The solubility of U can be increased by adding...

The temperature dependence of the electrical resistivity of a 1 mm single-size pebble bed is presented as a function of different applied pressures. The pebble bed was maintained in a He+0.1 vol.% H 2 flowing atmosphere. In agreement with previous studies, the resistivity displays two distinct regimes under the applied load. The first one is charac...

In this paper, a remote O₂ ion source is used for the formation of nano-oxide layers. The oxidation efficiency was measured in CoFe-oxide films, and a decrease of the oxide layer with the pan angle and the oxidation pressure is observed. For the same oxidation pressure, the oxidation efficiency depends on the O₂ content in the...

Spin dependent tunnel junctions with AlOx barrier were fabricated by in situ natural oxidation of a 7 Å (or 8 Å) thick Al film. Junctions were deposited on top of preannealed, ion-beam smoothed, 600 Å thick Al bottom electrodes. By changing the oxidation time from 10 min to 10 h with the oxygen pressure of 10 and 100 Torr, the top-pinned junctions...

We measured the (p,p) elastic scattering cross-sections of natural samples of carbon, nitrogen, oxygen, aluminium and silicon at energies ranging between 500 and 2500 keV and at laboratory scattering angles of 178° and 140°. Results are compared with previous literature data and simulations and are presented in graphical form. The measured cross-se...

Gallium nitride (GaN) is a direct wide-band-gap semiconductor material, which can be used to produce blue-light-emitting diodes and lasers, high-temperature and high-power devices. While manganese (Mn) represents a potential acceptor in GaN, Mn-doped GaN may form an interesting diluted magnetic semiconductor. In this study, GaN was implanted at roo...

Single crystalline GaN samples were implanted with several fluences of Ca ions at room temperature (RT) and 550 °C. The implantation at high temperature reduces significantly the damage. The measured minimum yield along the 〈0 0 0 1〉 axis in the implanted region increases from 15% to 40% when the substrate temperature during the implantation was ch...

The behaviour of Ir implanted into Si during subsequent thermal processing has been studied using ion beam analysis and transmission electron microscopy. Si(100) samples preamorphized by Si implantation and subsequently implanted with Ir were used. After regrowth of the amorphized substrate region at 550 °C, the samples were further annealed in vac...

The incorporation of W in lithium niobate (LiNbO3) by diffusion was studied using RBS/charineling. Tungsten was deposited onto LiNbO3 single crystals at 1000 degreesC under vacuum, resulting in a W rich layer with a peak concentration of 7 at.%. To decrease the damage introduced by the deposition process the samples were annealed at 1000 degreesC i...

Gold nanoclusters were formed by implantation of 1×1016 cm−2 Au+ ions with an energy of 800 keV into Y-cut LiNbO3 and subsequent annealing at 600 and 800 °C in flowing wet oxygen atmosphere. Rutherford backscattering/channeling and electron diffraction studies in plan-view transmission electron microscopy (TEM) samples revealed a highly coherent gr...

Bismuth tellurite single crystals, undoped and doped with 0.1% of Er atoms per mol of host during growth, have been investigated by ion beam methods. Despite the complex structure of the material axial directions with a strong channeling effect have been located and characterized. In addition the lattice location of Er was investigated using PIXE/c...

Spin dependent tunnel junctions (Si/Al2O3/Ta/CoFe/AlNx/CoFe/Ta) were studied with grazing angle of incidence Rutherford backscattering spectrometry experiments using a 1.6 MeV He+ beam. While the sensitivity to light elements is too small to detect the N directly, the thickness and composition of the AlNx insulating barrier can be obtained by caref...

The structure of N-implanted sapphire (single crystal α-Al2O3) has been studied using Rutherford backscattering-ion channeling spectroscopy (RBS-C), transmission electron microscopy (TEM) and optical absorption. Specimens having the c-axis normal to the optically polished surface were implanted with 3×1016 N/cm2 (150 keV) at room temperature and 10...

Airborne particulate matter plays an important role in the Earth's energy balance. One of the main reasons is that the real size of a significant number of the particles, mainly those of anthropogenic origin, is similar to the wavelength of visible light. Knowledge of the composition of such particles, as well as their dynamics and trajectories in...

The ability to define, or recognise particular regions of interest or surface features is vital to the analysis and interpretation of spatially-resolved images collected with a nuclear microprobe. However, good topographic image contrast is difficult to accomplish using PIXE or RBS images due to their inherent insensitivity to topography, lack of e...

Improvement of the high temperature oxidation behavior of conventional EN-1.4301 (AISI type 304) stainless steel was achieved by implanting cerium ions. Implantation was performed in samples with two different surface treatments: commercial 2B mill finishing and preoxidation in synthetic air. One set of samples was annealed after implantation in or...

Summary form only given. The oxidation of CoFe layers in specular spin-valves or thin Al layers (<10 Å) in low resistance tunnel junctions is currently done either by natural oxidation (where no plasma is used) or by plasma oxidation. In this work, the spin valve and tunnel junctions were prepared by ion beam deposition, and the oxidation was done...

In this work the (p,p) non-Rutherford scattering cross-sections for nitrogen and aluminium at energies ranging between 500 and 2500 KeV and at laboratory angles of 178° and 140° have been measured. The target sample consisted of a layer of AlN (1.35×10 18 at cm -2 thickness) deposited on vitreous graphite and covered with an Au film (5.5×10 16 at/c...

In this work the (p,p) non-Rutherford scattering cross-sections for nitrogen and aluminium at energies ranging between 500 and 2500 KeV and at laboratory angles of 178° and 140° have been measured. The target sample consisted of a layer of AIN (1.35×1018 at cm-2 thickness) deposited on vitreous graphite and covered with an Au film (5.5×1016 at/cm2...

In this work the (p,p) non-Rutherford scattering cross-sections for nitrogen and aluminium at energies ranging between 500 and 2500 KeV and at laboratory angles of 178degrees and 140degrees have been measured. The target sample consisted of a layer of AlN (1.35x10(18) at cm(-2) thickness) deposited on vitreous graphite and covered with an Au film (...

Spin-dependent tunnel junctions with crystalline ZrOx barriers were fabricated, with tunnel magnetoresistance (TMR) reaching 20% and a resistance×area product of 24 k Ω μm2, after annealing at 260 °C. Effective barrier height and thickness are 1.6 eV and 10.6 Å, respectively. The ZrOx barriers were fabricated by rf plasma oxidation of a 5 Å thick Z...

GaN epilayers grown on sapphire were implanted with several fluences of In, Er and Hf ions to study the damage behavior and lattice site location of the implanted species. The damage in the Ga sublattice develops a double peak structure with one peak at the surface and the other near the end of the range of the implanted ions. For fluences above 5...

The gamma gamma 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 magn...

The doping of lithium niobate (LiNbO3) with uranium is of high interest due to the possible infrared laser action of U3+. On the other hand LiNbO3:U crystals grown from melt contain uranium only as U6+. It has been recently shown that by thermal reduction the valence state can be altered to U3+/U4+. Studies on the lattice site of uranium show that...

Conversion electron - gamma PAC measurements of the 49 keV - 37 keV cascade in 80Br through the intermediate 2- state with T1/2 = 7.4 ns were performed with a system of two magnetic lens spectrometers and two BaF2 scintillation detectors. The parent 80mBr activity with halflife of 4.4 hrs was implanted into Ni, Zn and graphite at the ISOLDE separat...

Spin-dependent tunnel junctions with AlOx barriers were fabricated by in situ natural oxidation of a 7 Å thick Al film. Oxygen pressure was varied from 0.5 to 100 Torr, and oxidation time ranged from 5 min to 2 h. Junction resistances as low as 10 to 12 Ω μm2 were obtained with corresponding tunnelling magnetoresistance values (TMR) ranging from 14...

In this article we report the damage and annealing behavior as well as lattice site location of Fe atoms in GaN. The Fe ions were homogeneously implanted in GaN films with an energy of 150 keV at room temperature. A two-step annealing (650 °C 15 min and then 1000 °C 2 min) was performed to remove the implantation-induced damage and to drive the dop...

A study of the oxide layer formed on the surface of high silicon (0.8%) EN-1.4301 (AISI-304) stainless steel after 125 h oxidation in air at 1273 K has been performed by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), RBS and proton microprobe. Oxidation experiments in synthetic air were performed in a thermobalance and the ki...

Among the advanced materials with potential interest for applications in fusion technology the SiC/SiCf composites are considered to be one of the most promising. We used microbeam RBS and PIXE techniques to follow the structural changes of several SiC/SiCf samples in contact with lithium orthosilicate and lithium titanate breeders at 800°C for dif...

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 N{sub 2} plasma. The nitrogen and oxygen content in the barriers was determined by Rutherford backscattering spectroscopy (RBS) on specially prepared barriers deposited on DLC...

The thermal stability of magnetic tunnel junctions with ultrathin (<8 Å) Al2O3 barriers was studied and compared with 15 Å barriers. The tunnel magnetoresistance (TMR) decay cannot be explained only by Mn diffusion into the pinned CoFe layer since this diffusion starts above 300 °C independently of the barrier thickness, while the TMR degradation a...

Spin tunnel junctions fabricated with one interposed Fe–FeOx layer between the Al2O3 barrier and the top CoFe pinned electrode show large tunneling magnetoresistance (TMR) (40%) for anneals up to 380 °C. The annealing temperature TTMR∗, where maximum TMR occurs, increases with the inserted Fe–FeOx layer thickness. For samples with thicker inserted...

Spin tunnel junctions with one interposed Fe oxide layer between the Al2O3 barrier (tAl = 8–9Å) and the top CoFe pinned layer show large tunneling magnetoresistance (TMR) values (39%) after 40 min anneal at 380 °C. The as-deposited TMR is low and does not increase until 350 °C (<10%), but then increases sharply, peaking at 380°C. Further anneals at...

High dose ion implantation was used to form cobalt silicide on porous Si containing different concentrations of light impurities (C and O). Samples were implanted with 100 keV Co+ ions to fluences of at room temperature, 350°C and 450°C, and then annealed (600°C for 60 min + 1000°C for 30 min). The formed silicide compounds were studied by Rutherfo...

The ion-beam-induced amorphization of GaN was studied by using 180 keV Ar+ and Ca+ implantation at −150°C and room temperature, respectively. The structure of the GaN films before and after implantation was characterized by Rutherford backscattering/channeling and X-ray diffraction. Lattice expansion due to ion implantation was found, and excessive...

Different Ge/Si superlattices were irradiated with 150 keV Ar ions at room temperature with fluences in the range 1012 to 5×1015cm−2. Defect production was studied with Rutherford backscattering/channeling spectrometry and X-ray diffraction (XRD). The evolution of the damage with ion fluence reveals the existence of three distinct regimes. During t...